Sometimes the grass isn’t always greener


High content screening methods or automated microscopy based assays, are a more recent development in drug discovery. This technology is rapidly becoming a mainstream tool in profiling compound activities. One clear harbinger of this uptake in high content screening is the numerous different vendors which have brought their platforms to market enabling this work to proceed.

There are many advantages of using automated microscopy assays, compared to conventional assays. One generally assumed advantage is removal of compounds that cause optical interference due to the type of data obtained by a high content readout and the methods used in the assay (wash steps for example)

This assumption was tested in the following publication:

http://journals.sagepub.com/doi/full/10.1177/2472555217707725

In this article the authors screened 315,000 compounds with a high content assay using the IN cell Analyser 3000 platform, where they were looking for modulators of micro RNA biogenesis pathway using HeLa S3 expressing green fluorescent protein. Active compounds would lead to an increase in expression of the fluorescence signal.

Using a hit threshold of 20% signal increase for the screen, they were able to obtain a hit rate of 0.36% (1130 compounds). The authors were able to retest 836 of these primary screen hits, in both single concentration and concentration response curves with both the original cell line and the parental cell line which did not express the green fluorescent protein. This is where the project hit some trouble.

Gareth 1

Around 22% of hit compounds reconfirmed with the GFP cell line in both the single concentration and concentration response curves, which is not unreasonable. Disappointingly, roughly the same numbers repeated in the cell line which did not contain the GFP expression system. Effectivity all the active compounds were not specific and would suggest that they are all false positives.

These identified false positive compounds were grouped together by structure into four main classes and were listed in the publication by the authors. This could be a useful tool if you want to compare other compounds which you might be working against this list. It should be remembered that (currently) these compounds are only false positives in this assay, with its specific fluorescent wavelengths used. Just because the key compound in your project is a member of one of these classes, it does not mean you need to stop working on them, but it would suggest further investigation would be warranted.

If possible, it would have been interesting to see if the results were repeated with a standard conventional fluorescence assay compared to the automated microscopy method whether the team would have achieved the same results?

So in summary, automated microscopy assay can suffer from optical interference caused by compounds, they are not immune.

However, overall the authors should be commended for releasing this publication; it highlights that all assay formats (including automated microscopy assays) will have a degree of false positive compounds and that you have to use all available methods to ensure your data output is as confident as possible.

Blog written by Gareth Williams

 

Bacterial immunotherapy: Can Salmonella be used to kill cancer?


I was recently at dinner with a family friend, who has survived stomach cancer, but lost his wife to liver cancer two and a half years ago. He is an interesting man, who worked for a large oil company for many years, travelling Saudi Arabia and other areas of the Middle East before retiring about 20 years ago. He has an incredible wealth of knowledge in almost all matters, and there are very few conversations to which he cannot contribute. So, with this in mind and his own past suffering with cancer, it is safe to say that when he starts talking about a novel cancer therapeutic, he probably has done his research and knows a little about the subject matter. I was told that the Telegraph had printed an article on Salmonella and its ability to flag tumours to the immune system. Stories about novel cancer therapeutics often appear in newspapers and social media, and I rarely give them much thought, but this left me somewhat intrigued so I thought it would be interesting to look into it further.

The use of bacterial preparations to stimulate the immune system in cancer patients has been a contested subject for over a hundred years, since William Coley began routinely injecting streptococcal organisms into bone cancer and sarcoma patients. Prior to this, Coley lost one of his first patients due to widespread metastases, despite a forearm amputation in response to a malignant tumour. This deeply moved him and, having trawled through the literature, he found a correlation between concurrent bacterial infection and tumour regression. Results from his bacterial treatment of cancer patients suggested that treatment with “Coley’s toxin” lead to the regression of tumours. However since the advent of chemotherapy and radiotherapy, the use of Coley’s toxin gradually disappeared (McCarthy, E.F., 2006).

Immunology has progressed quite a lot since Coley carried out this work; the mechanisms involved are now better understood and it is for this reason that interest in this area of research has been reignited.

One of the main drawbacks of chemotherapy is its inability to target tumours specifically; this leads to high off-target toxicity in non-cancerous cells and low tumour penetration with the chemotherapeutic. However, the use of bacteria provides unique mechanisms by which site-specific treatment of tumours may be possible.

The natural ability of bacteria to sense their environment through chemoattractants, and then actively follow chemical gradients whilst crossing biological barriers means they are able to penetrate tumour tissue. Metabolically-active, genetically-modified bacteria are also able to perform specific tasks once at the tumour site, such as the production of immunomodulatory molecules (cytokines) or enzymatic conversion of a pro-drug into an active therapeutic (St Jean, A.T., 2008). Bacterial vectors are also inherently immunostimualtory, as Toll-like receptors (TLRs) expressed by innate immune cells recognise bacterial-expressed virulence factors such as peptidoglycan and LPS. This leads to downstream activation of DCs, which travel from the local tumour environment to draining lymph nodes and activate adaptive immune responses through presenting tumour antigens to T-cells (Chorobik, P., 2013).

So, why is Salmonella a favourable candidate for potential bacterial therapy? Salmonella Typhimurium have been shown to have a high affinity for tumour cells and their facultative anaerobic nature means they can happily infiltrate the hypoxic areas of tumours, but they have also been shown to target non-hypoxic regions and metastases. Salmonella spp. are highly motile and can therefore penetrate into therapeutically-resistant regions of tumours, and have been shown to be preferentially attracted to such areas. Salmonella also displays direct tumour-killing activity, as they compete for nutrients and also stimulate primary and secondary immune responses. Toxins produced by the bacteria may have apoptotic effects on tumour cells, and intracellular infection with Salmonella can lead to cell death through autophagy. The combination of all these attributes can lead to reduction in tumour size (Chang, W.W., 2014).

In order to develop new, Salmonella-based vector strains for the administration of therapies, they must be attenuated/altered to stimulate an appropriate immune response. Both S. Typhimurium and S. Typhi are responsive to attenuation, and roughly 50 genes can be inactivated to produce a specific profile of virulence factors, which lends them to being used as appropriate vectors for therapeutics.

The successful use of Salmonella in reducing tumour size in murine models of cancer has been well documented in the literature. Attenuated Salmonella has been shown to work in combination with cisplatin to demonstrate an additive effect on the reduction of tumour size in mice (Lee, C.H., 2005). These results show the impact of untransformed attenuated bacteria as a result of its inherent ability to augment immune responses. Multiple studies using S. Typhimurium, genetically engineered to express pro-inflammatory mediators (e.g. TNF, IL-18) or chemokines (CCL21) also demonstrate similar success in treating tumours in murine models of cancer (Chorobik, P., 2013).

However, the story is not quite so successful when it comes to looking at similar studies in humans. An attenuated strain of S. Typhimurium (VNP20009) has been tested in a phase I study in which metastatic cancer patients were dosed intravenously with the bacteria. None of the 25 patients experienced cancer regression, significant levels of circulating TNF were measured in the peripheral blood and tumour colonisation with Salmonella was only observed in biopsies from three of the 25 patients (Toso et al., 2002). These results are in contrast with all of the animal models and could be a result of limited tumour-specific targeting by the bacteria.

The more recent developments in this field of research, which prompted the news media to publish articles suggesting that Salmonella can cure cancer, uses a much less virulent strain of bacteria, with a much higher lethal dose. This means that larger concentrations of the bacteria can be used without the side effects observed in the original phase I study by Toso et al. The bacteria are also engineered to overexpress and inducibly secrete Vibrio vulinficus flagellin B (flaB), which stimulates innate immune responses through the TLR 5 pathway and in this way acts as an excellent adjuvant for immunotherapy. Three days post infection, levels of intratumoural bacteria were 10000 fold higher than other organs, and it was at this time point that the FlaB payload was delivered through induction with L-arabinose. As a result of this, the off-target toxic effects are massively reduced and targeted therapy is achieved (Zheng, J.H., et al., 2017). So far, this research utilising Salmonella’s innate ability to target tumours, as well as inducibly secrete the therapeutic looks promising in mice, but we will have to wait and see if this is developed for human trials.

In summary, bacteria have been used as immunomodulators for cancer therapy for a long time, but the more recent advances in immunology and molecular biology mean that we are now able to further tailor microbes to create potentially viable therapeutics. The more recent studies look promising in mice, and perhaps the use of genetically engineered bacteria to deliver therapeutics to tumour sites will be used routinely in the future. However, the only recent study in humans shows that the mouse models are not always indicative of how these therapies will fare in man. The unique ability of bacteria to specifically colonise tumour sites and then deliver their payload means they are ideal candidates for tumour-specific therapy, so advances in this area of research will hopefully lead to novel and viable therapies for cancer in the near future.

Blog written by Will Pearce

References

Chang, W.W. and Lee, H.C., (2014), Salmonella as an Innovative Therapeutic Antitumor Agent, nt. J. Mol. Sci. 15(8), 14546-14554

Chorobik, P. et al., (2013); Salmonella and cancer: from pathogens to therapeutics, Acta Biochim Pol.  60 (3):285-97

Lee, C.H.; Wu, C.L.; Tai, Y.S.; Shiau, A.L (2005) Systemic administration of attenuated Salmonella choleraesuis in combination with cisplatin for tumor therapy. Mol. Ther.  11, 707–716

McCarthy, E.F., (2006); The Toxins of William B. Coley and the Treatment of Bone and Soft-Tissue Sarcomas, Iowa Orthop J, 26: 154-158

St Jean, A.T., (2008); Bacterial therapies: completing the cancer treatment toolbox, Curr Opin Biotechnol, 19: 511-517

Toso JF1Gill VJHwu PMarincola FMRestifo NPSchwartzentruber DJSherry RMTopalian SLYang JCStock FFreezer LJMorton KESeipp CHaworth LMavroukakis SWhite DMacDonald SMao JSznol MRosenberg SA (2002), Phase I study of the intravenous administration of attenuated Salmonella typhimurium to patients with metastatic melanoma. J Clin Oncol. 2002 Jan 1;20(1):142-52

Zheung, J.H., Nguyen, V.H, Jian., S.N., Park, S.H., Tan, W., Hong, S.H., Shin, M.G., Chung, I.J., Hong, Y., Bom, H.S., Choy, H.E., Lee, S.E., Rhee, J.H., Min, J.J., (2017), Two-step enhanced cancer immunotherapy with engineered Salmonella typhimurium secreting heterologous flagellin, Science Translational Medicine  Vol. 9, Issue 376,

 

 

 

 

 

 

 

Vaccines: a great human conquest


It was 1796 when Edward Jenner opened a new page in human history by laying the foundations of modern immunisation and successfully developing a vaccine against smallpox. This disfiguring infectious disease with high mortality (>30%, higher in children), left survivors marked for life with terrible scars. The development of the first vaccine was followed by several others (tetanus, whooping cough, tuberculosis, polio, to cite a few), leading to a remarkable decrease of reported cases of common diseases in children and so saving the lives of millions. In 1956, the WHO started a global vaccination campaign to eradicate smallpox from the world; it took 24 years (until 1980) to succeed. Vaccines are now considered one of the greatest medical achievements in modern civilization.

Marco

Fig. 1: Comparison of 20th Century Annual Morbidity and 2010 Morbidity for Vaccine-Preventable Diseases in the United States: 20th century (JAMA 2007, 298(18): 2155-2163) – 2010 (CDC. MMWR January 7, 2011; 59(52);1704-1716)

Despite these tremendous results, there has also been quite a lot of controversy around vaccinations, mainly regarding efficacy and safety. These days, driven by widespread use of the internet and the advent of social media, several anti-vaccination campaigns have been launched and are becoming more and more popular. Surfing the web, it is possible to find all sort of contradicting and confusing information about vaccines and how harmful they can be. Once news has spread, it is very difficult to retract and requires quite a lot of work to establish what is real and what is not. Everyone has the right to gather information and have their own opinion with regards to vaccination, but as the real efficacy and safety of vaccines can be questioned, the opposite should also be taken into consideration and should be evaluated very cautiously (see “Six common misconceptions about immunization”).

One of the most controversial of these campaigns was the publication of a research paper in 1998 in which a link was reported between measles-mumps-rubella (MMR) vaccine and the development of autism in children. Following the publication of the paper, multiple large epidemiological studies were undertaken establishing that there was no link between MMR-vaccine and autism. The original paper was subsequently retracted by the publishing journal. Despite all the evidence, people continue to doubt the safety and efficacy of vaccines, opting out from vaccinating their children. The drop in the number of vaccinations has caused outbreaks of diseases that were previously very well contained, as to be effective at least 95% of the population needs to be vaccinated. One of the most recent is the spread of measles across Europe (> 500 cases reported in January 2017) and US (61 cases in the first quarter of 2017), where it was eliminated in 2000. In a world facing a post-antibiotic era and the increasing instances of cancer amongst several other diseases, there is no space to worry about life-threatening diseases that have been already defeated.

Blog written by Marco Derudas 

 

 

 

 

UK Dementia Research gains momentum


In March of 2012, then Prime Minister David Cameron announced the Prime Minister’s Dementia Challenge (see here), which included the pledge to “More than doubling overall funding for dementia research to over £66m by 2015.” The following year, and in recognition of the looming “tsunami of dementia” as a consequence of an aging global population the world’s first G8 dementia summit was held in London on the 11th December. This meeting involved researchers, drug companies and government ministers and set the ambitious target of identifying a cure, or a disease-modifying therapy, for dementia by 2025 (see here). The Prime Minister maintained momentum with the Prime Minister’s Challenge on Dementia 2020 (see here) “in order for England to be:

  • the best country in the world for dementia care and support and for people with dementia, their carers and families to live
  • the best place in the world to undertake research into dementia and other neurodegenerative diseases”
  • These lofty words and aspirations are actually being matched by actions, such as the establishing of the Dementia Platform UK (DPUK; see here) and the UK Dementia Research Institute (UK DRI; see here) as well as the National Institute for Health Research (NIHR) Dementia Translational Research Collaboration (TRC) which comprises four NIHR Dementia Biomedical Research Units as well as six NIHR Biomedical Research Centres with dementia-related research themes (see here).

JA 1For example, the DPUK (see Figure 1), which is led by Professor John Gallacher at the University of Oxford, aims to study different patients cohorts in order to characterise people with different types and stages of dementias. These population studies have the power to provide insights into the role of health and lifestyle on dementias by using the latest imaging and other technologies.

The DPUK is a public-private partnership established in 2014, with the MRC providing £12m funding over an initial period of five years with an additional £4m being contributed by six industry partners (Araclon Biotech, MedImmune, GlaxoSmithKline, Ixico, Janssen Pharmaceuticals and SomaLogic). In addition, an additional £37m has been contributed to fund networks of clinical research infrastructure focussed around Imaging, Informatics and Stem Cell Networks. An example of a major project that is using the DPUK is the NIHR-MRC Deep and Frequent Phenotyping study, a £6.9m project which aims to identify a combination of biomarkers that change in prodromal Alzheimer’s disease for use in proof of concept phase clinical trials.

The UK DRI is a network of research institutes (see Figure 2)

JA 2

established on the basis of £250m in funding from a combination of the Medical Research Council, the Alzheimer’s Society and Alzheimer’s Research UK (see here). The Head of the UK DRI, Prof. Bart de Strooper, and the hub of this research network, UCL, were announced in December 2016 (see here) with additional centres in Cardiff University, University of Edinburgh, University of Cambridge, Imperial College London and King’s College London being announced last month (see here). The initial round of UK DRI £55 million will fund 27 foundation programmes (details of which are available via links on the website). With the foundation programmes in place, the plan will be to attract additional scientists and rising stars from all over the world in order to integrate expertise across different areas of biomedical and translational research. Importantly, in addition to the existing focus on disease mechanisms as the basis for developing novel therapeutics, the DRI will add research into caring to its portfolio in 2018.

In an era when political words are seldom matched by significant actions, David Cameron’s commitment to dementia research has proved to be transformative and will continue in his recently-announced role as President of Alzheimer’s Research UK (see here). It is encouraging that Theresa May appears to be raising the profile of mental health (see here and here) yet only time will tell if her actions can come close to matching those of her predecessor.

Blog written by John Atack

 

Careers away from the laboratory bench


 

Over recent years there have been several articles and reports featuring graphics to highlight the careers taken by PhDs. You know the ones, with only the tiniest arrow leading to a professorial position (like the one below). Disheartening though this can be, what has always struck me the most is that the arrow with the greatest proportion of jobs is usually composed of the rather unhelpful “Careers outside science”. As I am currently considering my options I thought it would be useful to try and answer the question on my lips: “Just what are all these jobs and where can I find them?”

IB 1

Image adapted from “The Scientific Century: securing our future prosperity” produced by the Royal Society in 2010.

As luck would have it, I spotted an email for a careers event held at the Society of Chemical Industry (SCI) in London that offered a broad selection of presenters, which I hoped would shed some light on my query so I booked my (free) place and headed into London. The talks were highly illuminating, with each speaker detailing the steps of their career paths so far in addition to giving insights on what their jobs entail and how to go about getting into their field. For my part, I was most interested in the speakers whose careers had steered away from the laboratory though, if you are interested in following the academic route, I would highly recommend having a chat with Prof. Joe Sweeney, who delivered one of the best talks I have ever seen about what is (and isn’t) important about being an academic in the current research climate. I took the opportunity to network with a few of the presenters and have tried to highlight below what I learned about some of these “alternative” career pathways.

I first spoke to Dr. Samantha Alsbury, Head of Professional Development at The Organisation of Professionals in Regulatory Affairs (TOPRA). Interestingly, Samantha moved into her position at TOPRA after serving as a lecturer at the University of Greenwich. By gaining a teaching qualification and experience in co-ordinating academic programmes, she was in a strong position when the opportunity to join TOPRA came up. In addition to outreach, she is also responsible for the creation of training and development programmes for all career levels in the regulatory affairs (RA) profession. When speaking about careers in RA, Samantha neatly summarised it as “science, in a suit”. Along with the need to delve into the literature to get accurate data on drug efficacy and safety, most RA projects also include a significant amount of interaction with people; willingness to travel and strong communications skills are required to liaise between the various regulatory agencies, stakeholders, and even marketing departments involved in the drug development life cycle. Understandably, new entrants to the field often work on “lower” risk aspects, such as requests for amendments to clinical trial authorisations, or answers to questions posed by regulatory authorities. Once you have demonstrated competency at this level, exposure to higher risk projects such as Investigational New Drug filings where often millions of dollars are on the line. Later on, specialisation in areas such as compliance, operations, publishing, or even consulting, offer interesting career development pathways.

The same could be said for a career in publishing. Samantha Foskett, a Publisher at John Wiley & Sons, went over a couple of different career pathways available to scientists with an interest in gaining commercial experience but who also want to remain in direct contact with science and scientists. Samantha recommended looking for roles as an Assistant editor to start learning the ropes and building up contacts, then progressing to either, the more commercial-minded Journal Editors, or the more scholarly Associate Editors (more involved with peer review and manuscript decisions). She also made a point to mention the opportunities for growth currently in the industry because of the take up of new media and publishing technologies.

At the next networking opportunity, I spoke with Dr. Darren Smyth, a partner at IP firm EIP who offered an illuminating view on the kind of work involved in his career as a patent attorney. Darren emphasised the importance of detail and accuracy, as well as the flexibility to engage with a wide range of stakeholders in his day-to-day activities. A patent attorney will find themselves dealing with investors, large and small businesses, other patent examiners, and even liaising with solicitors and barristers if a dispute goes to trial. As with regulatory affairs, communication and strong research skills are very important, but the rewards are certainly worth the effort. Darren advised that, although the field is notoriously difficult to get into, these days there are numerous boutique firms in addition to the larger pharmaceutical companies where someone from a life sciences background could apply for a training position. Even then, it is a long road to becoming fully accredited, 4 to 6 years in most cases, and a large amount of private study would be expected in addition to working office hours. The exams are tough, with higher failure rates than you might be used to, and mostly essay based, however most firms are often supportive of good candidates and would try to help them overcome these difficulties.

Finally, I managed to have a chat with Dr. Nathalie Huther, a Business Development Manager for Arcinova, a contract research and development organisation based in Northumberland. Nathalie’s role is to serve as an intermediary between clients and company headquarters, using her technical knowledge to propose solutions to clients’ problems while also identifying areas of expertise or new technologies that could be used to enhance the services her company provides. In addition to technical experience, a willingness to travel, a talent for scouting new opportunities, and negotiating skills are key aspects of this role. In Nathalie’s case, these were acquired in her various roles as a laboratory scientist, then in marketing and sales force training in industry. Nathalie pointed out that a variety of job experience helps accelerate progression on this career pathway but, as it is a sales role, being able to deal with the pressure to make sales, as well as the pain of lost sales, is another key component to consider.

As you may have guessed, I left the SCI with a lot to think about! Please bear in mind that there are several career pathways I did not get to dive into on this occasion, including: Technical or Application Specialists, Clinical or Medical Science Liaisons, Clinical Trials Associates, and Data Analysts. I would say the take home message is to keep an open mind when thinking of alternatives careers choices. You might be surprised by what you find.

I would like to end with just a few pointers on how to approach a job search.

  • First and foremost is probably to update your online profile, be it on LinkedIn or ResearchGate. You never know who might be looking for someone just like you! Make sure to include the link on your CV, which should also be formatted appropriately for the type of job you are looking for.
  • Do a thorough analysis of your skills and try to categorise them in terms that recruiters in your field of interest will use, such as “Communication”, and “Project Management”. The Careers and Employability Centre at Sussex offers a range of tools that can help with this, including a Skills Checklist, and you can also arrange one-to-ones with advisors. Another resource recommended to me by a friend is the “Individual Development Plan” hosted at Science Careers. This is a free resource tailored for Life Scientists that are really unsure (yep, that’s me!) of what they would like to do, offering a prediction of what careers might suit their particular set of skills and interests.
  • Reach out to people in fields you are interested in via LinkedIn (remember that from the first point?) or ResearchGate and ask for “informational interviews”. These serve numerous purposes, principally, to provide you with information about what a job entails, and what skills you might want to brush up on before applying. These also allow you to start building up a network that can help you to land a job, offer career support when you get one, and perhaps even offer you bigger opportunities further down the line.
  • Keep your eyes peeled for opportunities in your network and don’t be afraid to apply, even if you don’t think you have enough experience. Recruiters have a habit of hanging onto CVs that catch their eye and can come back to you with alternatives that may not be openly advertised.

Blog written by Iain Barrett

References:

“The Scientific Century: securing our future prosperity” ISBN: 978-0-85403-818-3 © The Royal Society, 2010

(https://royalsociety.org/~/media/Royal_Society_Content/policy/publications/2010/4294970126.pdf)

 

TRPV6 In Prostate Cancer: What is the significance?


The transient receptor potential proteins (TRPs) are a family of ion channels involved in different cellular functions. TRP channels are ubiquitously distributed throughout the mammalian system. And based on their sequence homology they have been divided into six families: TRPC, TRPV, TRPM, TRPN, TRPA, and TRPP. TRP subunits assemble as homo- or hetero-tetramers to form cation selective channels which are activated by a wide range of stimuli including intra- and extracellular messengers, chemical, mechanical and osmotic stress, temperature, growth factors and by the depletion of intracellular calcium stores.

TRPV6 channel cDNA was cloned in 1999 from rat duodenum by expression cloning using Xenopus oocytes (Peng et al. 1999). Like other TRP family members it is necessary for a wide variety of physiological functions. TRPV6 expression is mainly confined to epithelial tissue of different organs such as digestive tract, kidney, testis, ovaries and skin. TRPV6 has a high calcium selectivity and is involved in the regulation of calcium homeostasis in the body. Published data have demonstrated its upregulation in cancer and correlation with the advanced stages in prostate cancer (stage pT2a and pT2b). However its role in the initiation or progression of most cancers is not yet understood. The in vitro oncogenicity of TRPV6 in prostate cancer has been proposed to operate via calcium signalling control of processes such as proliferation and resistance to apoptosis (Prevarskaya et. al., 2007)

Many publications over the years have demonstrated a correlation between TRV6 expression in prostate tissue and prostate cancer. Lehen (2007) have shown that Ca2+ entry via TRPV6 controlled proliferation directly and promoted apoptotic resistance in prostate cancer cells and concluded that the upregulation of TRPV6 may represent a mechanism for maintaining a higher proliferation rate. In view of the strong correlation between TRPV6 expression levels with the Gleason score >7 tumor grading, the channel represents a promising new therapeutic target prostate cancer treatment.

Conversely, other studies have shown that in healthy and benign human prostate tissue the expression levels of TRPV6 mRNA are very low if not undetectable. In 2012 Raphael et al used in situ hybridization methods to demonstrate that TRPV6 mRNA transcripts were undetectable in high-grade prostatic neoplasia and incidental adenocarcinoma but were increased in prostate adenocarcinoma (1B). Additionally, work by Wissenbach et al., (2004) on biopsies of prostate cancer tissue has shown that TRPV6 mRNA expression increases with the degree of aggressiveness of the cancer (1A), as assessed by the Gleason score and the degree of metastasic spread. Both studies suggest that expression levels of TRPV6 could be an excellent marker to predict the clinical outcome of prostate cancer.

Figure 1: Expression of TRPV6 in prostate cancer.

1A                                         1B

 

Figure 1 A. Northern blot analysis using cDNA probes of human TRPV6, TRPM4 and TRPM8 cDNA. (Ref). Both TRPm4 and TRPV6 transcripts are detectable in prostate cancer but not in benign prostate tissue (Biochemical and biophysical Research communication 322 (2004) 1359-1363).

Figure 1B. Immuno-histochemical staining of human prostate tissue using Anti-TRPV6 antibody. Very low expression of TRPV6 is observed in normal and benign hyperplasia (BHP) as opposed to significant expression in prostate adenocarcinoma (ADC 7). Adapted from Raphael, M. et al. (2014) Proc. Natl. Acad. Sci. U.S.A. 111, E3870.

In summary, the specific expression pattern in prostate cancer coupled with its physiological function as a calcium selective channel suggests that TRPV6 may be a promising drug discovery target for the possible treatment of prostate cancer.

 Blog written by H I Choudhury (Shamim)

References:

  • Maylis Raphael¨ et. al. (2012); Role of the TRPV6 channel in cancer. J Physiol 590.6 pp 1369–1376 1369
  • V Lehen’Kyi et al., (2007) TRPV6 channel controls prostate cancer cell proliferation via Ca2+/NFAT-dependent pathways Oncogene 26, 7380–7385
  • Wissenbach et al., (2004) TRPV6 and prostate cancer: growth beyond the prostate correlates with increase TRPv6 Ca+ channel expression. Biochemical and biophysical Research communication 322, 1359-1363
  • Thomas Fixemer et al., (2003) Expression of the Ca2þ-selective cation channel TRPV6 in human prostate cancer: a novel prognostic marker for tumor progression. Oncogene (2003) 22, 7858–7861
  • Natalia Prevarskaya et. al., (2007) TRP channels in cancer Biophysica Acta 1772, 937–946

 

 

Spoilt by choice – Which CYP-specific probe to use?


The use of in vitro metabolic surrogates (e.g. microsomes, recombinant CYP450s, cyro-preserved hepatocytes) is now widespread in drug discovery and evermore refined methods improving the utility of these model are in constant development. However, as any IVIV extrapolation is always subject to the reduced complexity of those model systems it is vital to understand their limitations (e.g. reduced expression of CYP3A4, PXR and CAR in CACO-2s; rapid loss of metabolic competence, canalicular and basolateral efflux transport in freshly isolated hepatocytes.) to avoid misinterpretation of data

In order to predict possible Drug-Drug Interactions (DDIs) it is necessary to understand the relative contribution of individual CYPs to the overall phase I metabolism of an NCE and to this end Relative Activity Factor (RAF), developed twenty years ago (1), has been used alongside inhibition approaches to elucidate the CYP reaction phenotype. Individual recombinant CYPs (rCYP), expressed in and isolated on bacterial membranes, can be used to measure the clearance (CLrCYP) of a CYP-selective probe.  The probe is then assayed in microsomes to obtain CLHLM and a correlation made of the relative levels of clearance in each system (RAF) for that particular CYP.  Once established the RAFs for each CYP can be used to assess the relative contribution of the individual CYPs to the metabolism of a NCE in microsomes.

Highly diverse RAFs are generated between various institutions due to the variability of microsome batches, rCYP expression levels and assay conditions but as long as these variables are maintained within any given laboratory the RAFs should generate internally consistent data. However, whilst it has been known for some time that the promiscuity of CYPs may be facilitated by multiple binding regions in the active site (2), until recently no one has directly assessed the effect of probe choice on whether the scaling from rP450 to HLMs is consistent between various P450-selective probe reactions and those of the test NCE by that P450 isoform.

To demonstrate this issue Sui et al (3) generated RAFs for 2C9 and 3A4 from three CYP-selective probes each.

CYP CYP-selective substrate
2C9 Diclofenac

Tolbutamide

Warfarin

3A4 Midazolam

Nifedipine

Testosterone

Using the RAF generated by one probe the predicted microsome clearance (CLHLM (p)) was calculated for the other two probes then compared with the directly measured CLHLM for those probes.  This was performed in a crossover manner for each of the probes.

The CLrCYP and CLHLM were derived using standard Michaelis-Menton kinetics

snip 1

The RAF was then generated as a ratio between CLHLM and CLrCYP.snip 2

In each crossover the CLHLM (p) was then simply calculated as the measured clearance of the test probe with rCYP multiplied by the RAF.

snip 3

These predicted CLHLM(p) values were then subsequently compared with the actual measured CLHLM to give a value for the Intersystem Clearance Ratio (ICR)

snip 4

Fig 1. Crossover analysis of ICRs based on the RAFs derived from A = Diclofenac, B = tolbutamide and C = Warfarin for 2C9 and D = Midazolam, E = Nifedipine and F = Testosterone for 3A4

marcus

Whilst it is clear to see the effects of probe choice on ICR this then has a knock on effect when determining the relative CYP contribution to the metabolism of a test NCE. Fig 2. Shows the comparison of % relative contributions for CYP metabolism of substrates with RAFs generated from various combinations of 2C9 and 3A4 probes (RAFs generated 1A2, 2C19, and 2D6 from single probe throughout)

Fig 2. Variations in relative CYP contribution (fm, fraction of total metabolism attributed to specific CYPs) calculations subject to probe choice

marcus second

With Physiologically based pharmacokinetic (PBPK) modelling and simulation playing an increasingly large role in drug development the accuracy of the input data is therefore crucial to the predictive accuracy of a model. Here, the generation of fm is demonstrably affected by probe choice and if the RAFs for a given probe/CYP pair are not appropriate for the test NCE, deviations in fm from the true value may significantly impact, for instance, generation of risk assessments for drugs as potential DDI victims.

This study would suggest that for test NCEs, fm should be generated using various combinations of a limited number of CYP-specific probes which represent the full range of specific substrate binding sites for a given CYP.  Presently our understanding of CYP binding site multiplicity is limited although studies indicate that we may soon have probe/inhibitor pairs for discreet pharmacophores (4, 5) facilitating increased accuracy of fm prediction.

Blog written by Marcus Hanley

References

  1. Clarke S. E. (1998) In vitro assessment of human cytochrome P450. xenobiotica, 1998, vol. 28, no. 12, 1167-1202
  2. Korzekwa, K R (1998) Evaluation of atypical cytochrome P450 kinetics with two-substrate models: evidence that multiple substrates can simultaneously bind to cytochrome P450 active sites. Biochemistry, 24 March 1998, Vol.37(12), pp.4137-47
  3. Siu Y.A (2017) Impact of Probe Substrate Selection on Cytochrome P450 ReactionPhenotyping Using the Relative Activity Factor. Drug Metab Dispos 45:183–189
  4. Kumar V. (2006) CYP2C9 Inhibition: Impact of Probe Selection and Pharmacogenetics on in Vitro Inhibition Profiles. Drug Metab Dispos Vol. 34 (12):1966-1975
  5. Foti R.S. (2008) CYP2C19 Inhibition: The Impact of Substrate Probe Selection on in Vitro Inhibition Profiles. Drug Metab Dispos Vol. 36 (3): 523-528

Organs-on-a-chip: The future of drug discovery?


Organs- on-a-chip were initially established at the Wyss Institute for Biologically Inspired Engineering located at Harvard University. The polymer chips containing microtubules are designed to recapitulate the structural, functional and mechanical attributes of human organs and they are only the size of a USB stick (Wyss Institute (2017)).

The chips are not just incredibly cool but also provide an innovative platform for drug discovery, which was recognised by the National Centre for the Replacement, Refinement and Reduction of animals in research (NC3Rs) back in 2012 (3Rs (2012)). The fact that the organs-on-a-chip mimic multiple aspects of the human body means that they could one day be used as an alternative approach to in vivo testing – a controversial but currently essential aspect of drug development.

The lung-on-a-chip, just one of the many organs developed, reconstructs the alveolar-capillary interface of the lung (Huh, D.et al (2010)). A central porous membrane is coated in extracellular matrix proteins that are present in the human lung. One side of the membrane is lined with alveolar epithelial cells isolated from a human lung and human pulmonary microvascular endothelial cells cover the other. The principal compartment allows for air to flow over the epithelial cells and for a blood-like solution containing nutrients to run beneath the endothelial cells. A vacuum on either side of the membrane causes the cells to stretch, in term conveying the movement experienced in the lung when we breathe.

 

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Figure 1: Lung-on-a-chip diagram From Keane, J. (2013)

This model has proven to replicate a lung infection, where white blood cells migrate from the blood-like solution through onto the epithelial side and are observed engulfing bacteria present in the air space using time-lapse fluorescence microscopy (Huh, D.et al (2010)). Small airways-on-a-chip with its goblet and ciliated epithelial cells can be used to model diseases like chronic obstructive pulmonary disease (COPD) and asthma. Addition of interleukin 13 (IL-13) to the epithelium further replicates an asthmatic phenotype inducing goblet cell hyperplasia and cytokine hypersecretion. A paper in Nature has reported to be able to reverse this response with an inhibitor of the JAK-STAT pathway involved in the signalling of IL-13, showing the application of these models in the screening of new treatments (Benam, K. Villenave, R. et al. (2016)).

The next focus is the humans-on-a-chip, which utilize an automated device to connect multiple organs-on-a-chip via a shared vascular network (figure 2). This platform would enable scientist to investigate the pharmacokinetics and pharmacodynamics of a drug in a relevant system (Abaci, H.E. Shuler, M.L. (2015)). Whereby drugs could be administered via the lung-on-a-chip, absorbed by the gut-on-a-chip, metabolised by the liver-on-a-chip and excreted by the kidney-on-a-chip while accessing the efficacy and any toxicity throughout.

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Figure 2: Human-on-a-chip schematic From Mok, J. (2015)

An interesting application of this technology is in the scope of personalized drugs. A chip can be developed with an individual’s cell to determine personal response to a drug, providing a tailor made drug with optimal efficacy (Hamilton, G. (2016)). This notion can also be implemented to clinical trials, where potential new drugs could be tested on cells from a certain genetic populations or on cells from children for paediatric medicines. This technology still has a way to go but one day it may transform the drug discovery process.

Blog written by Olivia Simmonds

References

Abaci, H.E. Shuler, M.L. (2015). Human-on-a-chip design strategies and principles for physiologically based pharmocokinetics/pharmacodynamics modeling. Integr Biol (Camb). 7 (4), 383-391.

Benam, K. Villenave, R. et al. (2016) Small airway-on-a-chip enables analysis of human lung inflammation and drug responses in vitro Nature Methods. 13 (2), 151-157

Hamilton, G. (2016). Body parts on a chip. Available:  https://www.ted.com/talks/geraldine_hamilton_body_parts_on_a_chip. Last accessed 20th April 2017.

Huh, D.et al (2010) Reconstituting Organ-Level Lung Functions on a Chip Science. 328, 1662-1668

Keane, J. (2013) The End of Drug Testing on Animals, Lung-on-a-Chip Device. Available: http://www.industrytap.com/lung-on-a-chip-device-to-end-drug-testing-on-animals/2160. Last accessed 21st April 2017

Mok, J. (2015) Organs-on-Chips Emulates Human Organs for Better Biomedical Testing. Available: https://thenewstack.io/organs-on-chips-emulates-human-organs-for-better-biomedical-testing/. Last accessed 21st April 2017

Wyss Institute (2017)Human organs on a chip. Avalible: https://wyss.harvard.edu/technology/human-organs-on-chips/. Last accessed 21st April 2017.

3Rs (2012). 3Rs Prize winners. Available: https://www.nc3rs.org.uk/3rsprizewinners. Last accessed 21st April 2017.

 

Towards a Heat-Stable Rapid-Acting Insulin


Introduction

Insulin is a small globular protein hormone secreted by the pancreas to lower blood glucose levels. Subcutaneous injection of insulin has long been established as a treatment for diabetes mellitus in which either the pancreas ceases to produce insulin (type 1) or in which the tissues become insensitive to the action of insulin (type 2).

Structurally, the Insulin monomer consists of two chains, an A chain, containing 21 residues and a B-chain containing 30 residues (fig. 1a).

Raj 1

a

 

 

Raj 2

b

 

Figure 1. (a) The disposition of the two chains in the insulin molecule indicating the three disulphide bridges. (b) The hydrogen-bonds (dashed lines) of the antiparallel b-sheet formed between the two molecules of the insulin dimer and the cluster of non-polar residues at the interface [1].

Both chains pack to form a compact globular domain stabilized by three disulphide bridges (A6-A11, A7-B7, and A20-B19). PheB24 lies at the classical receptor-binding surface with its aromatic ring packed against the hydrophobic core (fig. 1b) and has been proposed to direct a change in conformation on receptor binding, with residues B24–B30 detaching from the core (a). It is this propensity for conformational change which makes the insulin monomer susceptible to fibrillation whereupon the structure changes from a predominantly α-helical state to a β-sheet rich conformation (fig. 2).

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Figure 2. (a) Native structure of the insulin dimer. (b) View of insulin fibril model, looking down fibril axis [2]. (c) The protofilament structure of insulin amyloid fibrils [3]. (d) Insulin fibrils formed after incubation at 65°C for 2 days in the presence of 1 mM NaCl (pH 2.0)[4].

Possibly for this reason, in the pancreatic β-cell insulin has evolved to be stored as Zn2+-stabilized hexamers, arranged in crystalline arrays within mature storage granules (b).

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Figure 3. The 2-zinc insulin hexamer of monomers (or a trimer of dimers). Each axial Zn2+ ion is coordinated by three B10 His side chains [1].

Upon secretion from the pancreas in response to rising blood glucose levels, the insulin Zn2+-hexamers dissociate into Zn2+-free dimers and monomers for immediate passage into blood capillaries. The rate of absorption of injected insulin is also limited by the time required for dissociation of the hexamers into the monomer. Recombinant DNA technology has made it possible to prepare rapid-acting insulin analogs with accelerated heaxmeric disassembly that remain dimeric or even monomeric at high concentration by introducing amino acid substitutions into the molecule.

Insulin KP (lispro – Humalog) is one such rapid-acting analog developed by Eli Lilly that can be injected just before meals. Lispro contains the substitutions ProB28→Lys and LysB29→Pro, which destabilise the classical dimer-forming C-terminal anti-parallel β-sheet, an inversion that mimics the sequence of the homologous insulin-Iike growth factor-1 (IGF-1)(Fig. 4).

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Fig. 4. The hydrogen-bonds of the antiparallel b-sheet formed at the dimer interface of native insulin and insulin lispro[1].

However, despite destabilisation of the dimer interface insulin lispro still forms Zn2+ insulin hexamers in the presence of the phenolic excipients present in commercial pharmaceutical formulations (c). This provides the necessary stability against fibrillation during storage in the vial but absorption is still not as rapid as could be provided by a zinc-free formulation. Additionally lispro and other meal-time insulin analogs have reduced shelf life upon dilution by the patient or health-care provider.

There is a great need for an insulin analog which augments the stability of the insulin monomer while retaining the weakened dimer-related β-sheet of lispro.

Halogen stabilization in medicinal chemistry

Halogen atoms have long been used for compound optimization in medicinal chemistry (d). The utility of halogen substitutions in amino acids is also well established in medicinal chemistry. Of all the halogens, the effect of fluorine (with an atomic radius of 42 pm similar to that of hydrogen at 53 pm) incorporation on the physical and chemical properties of proteins is the most characterized in the scientific literature (e). Such observations have motivated the study of fluorinated amino acids for the structural stabilization of proteins, with the provisio that in the case of a biologically active polypeptide at least a significant proportion of the activity must also be maintained.

Thermalin Fluorolog

Fluorolog (f) is a rapid-acting, ultra-concentrated insulin that is in pre-clinical development by Thermalin Diabetes (Cleveland, Ohio). In this lispro analog B24 Phe has been substituted with ortho-monofluorophenylalanine (2F-Phe)(fig. 5).

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Figure 5. (a) A vial of rapid-acting, ultraconcentrated U-500 Fluorolog. (b) Ortho-monofluoro-phenylalanine (2F-Phe). (c) The disposition of 2F-Phe against the body of the Fluorolog molecule [5].

The large inductive effects of the fluorine atom act to thermodynamically stabilize the entire molecule yielding an analog that no longer needs to form a hexamer to be stable. Fluorolog is not prone to clumping and can be formulated at high concentrations (500 units/mL) without the risk of fibrillation and targets three market niches [5]:

1) Fibrillation of insulin is enhanced by agitation and can result in blockage of insulin pumps used by some type 1 diabetics. In miniaturized insulin pumps, pump size is currently constrained by the size of the insulin reservoir which if shrunk by 80% could yield a pump that lasts a whole week. Insulin fibrillation is of even greater concern in implantable insulin pumps, where the insulin may be contained for up to 3 months at high concentration and at physiological temperature.

2) In developed countries some highly insulin resistant type 2 diabetics – often members of underprivileged minority communities- currently inject several hundred units of insulin each day (g). Injecting up to 0.5 mL of the standard lispro 100 units/mL (U-100) formulation is not only uncomfortable but also delays mealtime insulin absorption. Highly concentrated Fluorolog will allow these diabetics to inject smaller quantities at one site and closer to meals.

3) Because fibrillation is also enhanced at higher temperatures, insulin must optimally be kept refrigerated prior to use. For both type 1 and type 2 diabetics in underdeveloped parts of Africa and the Middle East there is a great need for an insulin that does not degrade without refrigeration. Fluorolog is stable for up to 3 months in warm climates without refrigeration.(h)

Phase 1 & 2 trials

Phase I studies have confirmed that the introduction of a single fluorine atom at the receptor-binding surface of Fluorolog stabilizes the monomer and protects it from degradation. Fluorolog exhibited the expected rapid-acting pharmacokinetic properties (even at U-500 formulation) in contrast to the impaired pharmacokinetic properties of native insulin. Furthermore, fluorination of B24Phe was able to mitigate the untoward effects of AspB10 in the DKP homolog on cellular proliferation in culture and on cross-binding to the IGF-1 receptor.

For its phase 2 trial Thermalin Diabetes is seeking to extend the pilot stability data to include individual aspects of chemical and physical degradation (such as disulphide cleavage, covalent polymer formation, and fibrillation) in preparation for an Investigational New Drug (IND) Application

Notes

a. In single-chain insulin (SCI: the recombinant precursor expressed in yeast) B29Lys and A1Gly are linked by a peptide bond. SCI crystallizes with the same fold as native insulin but is inactive.

b. In the early days insulin could only be crystallized if acid-ethanol extracted from pancreatic tissue in a galvanized bucket.

c.  DKP- insulin with the additional HisB10→Asp substitution is monomeric under a wide range of conditions. Although this insulin-like growth factor-1 equivalent substitution eliminates zinc binding it does raise the possibility of mitogenicity.

d. The activities of the widely prescribed statin atorvastatin (Liptor) and the SSRI antidepressant fluoxetine hydrochloride (Prozac) are both enhanced by the covalent incorporation of a fluorine atom.

e. Fluorine is distinguished from the normal C,H,O,N and S constituents of proteins by its atomic radius, electronegativity, stereo-electronic distribution of partial charges, and transmitted effects on the stereo-electronic properties of neighboring atoms.

f.  US Patent 20140128319 A1 (2008).

g.  As pre-filled insulin pens can only inject 60–80 units of insulin at a time, some highly insulin-resistant diabetics must inject up to 9 times a day or more.

h. Ideal for airmail.

Blog written by Raj Gill.

References

  1. Gill, R. & Wood, S. (2003) Structure and Phylogeny of Insulin. Chapter 12 in International Textbook of Diabetes Vol. 1, ed. Pickup, J.C. & Williams, G., Blackwell Scientific, Oxford.
  2.  Ivanova, M.I., Sievers, S.A., Sawaya, M.R., Wall, J.S. & Eisenberg, D. (2009) Molecular Basis for Insulin Fibril Assembly. Proc Natl Acad Sci USA 106, 18990–18995.
  3.  Landreh, M., Johansson, J., Rising, A., Presto, J. &Jörnvall, H. (2012) Control of Amyloid Assembly by Autoregulation. Biochemical J. 447, 185-192.
  4. Dyukov, M.I., Grudinin, M.P., Sirotkin, A.K., & Kiselev, O.I. (2008) Insulin Fibrillogenesis In vitro. Doklady Biochem. Biophys. 419, 79-81.
  5. http://www.thermalin.com/lead-product—fluorologtrade.hl

 

 

An update on the progress of PARP inhibitors in the clinic


An article published at the beginning of 2016 titled ‘ PARP Inhibitors: The race is on’, describes the race to exploit single agent PARP inhibitors for the treatment of cancer by exploiting the concept of synthetic lethality to selectively target cancer cells deficient in the repair of DNA double strand breaks by the homologous recombination (HR) pathway1. The most studied defects in HR are associated with inactivating mutations in the proteins BRCA1 and BRCA2, which have essential roles in the pathway. Inhibition of PARP during the repair of damaged DNA bases by the base excision repair (BER) pathway causes single strand breaks in DNA that later become double strand breaks during DNA replication. The breaks are repaired by the error prone non-homologous end joining (NHEJ) pathway in cells deficient in homologous recombination (HR) repair mechanisms. The high burden of mutations in the DNA of rapidly proliferating cells caused by error prone NHEJ leads to cell death. Therefore, in accordance with the synthetic lethality concept, PARP inhibition in tumours that have deleterious mutations in BRAC1/2 should lead to cancer cell death and tumour shrinkage.2 Olaparib is the first example of a PARP inhibitor that is well tolerated in patients and clinically validates the synthetic lethality concept 3,4. The drug has been approved as a monotherapy for the treatment of ovarian cancer patients with germline BRCA mutations. Its success has encouraged the development of other PARP inhibitor programmes from Clovis, Tesaro, AbbVie and Medivation. So, as we end the first quarter of 2017, who is leading the race?

Clovis took an early lead with Rucaparib after submitting a new drug application to the FDA in June 2016 for patients with advanced ovarian cancer that have been treated with two or more chemotherapies and have either somatic or germline BRCA1/2 mutations. An efficacy study measuring the percentage of patients to experience complete or partial shrinkage of their tumors (progression free survival) was completed in a cohort of 106 patients with Rucaprib dosed twice per day (600mg). The company posted favorable comparative data showing a high response rate (54% vs 34% for Olaparib) with a marginally longer duration of response at 9.7 months compared to Olaparib’s 7.2 months. In December 2016 the FDA granted accelerated approval for Rucaparib. Furthermore, unlike Olaparib that is restricted to germline BRCA mutations, Rucaparib was approved for germline and/or somatic mutations in ovarian tumours.

In October 2016 Tesaro presented data on Niraparib at ESMO from a Phase III randomized clinical trial in patients with platinum responsive ovarian cancer. The study assessed progression free survival (PFS) in a cohort of 533 patients with or without BRCA mutations.5 Consistent with previous studies on PARP inhibitors, patients with germline BRCA1/2 mutations showed the greatest PFS at 21 months compared to placebo (5 months). Crucially, a statistically significant effect was demonstrated in non-germline BRCA mutant cancers with a PFS of 9.3 months vs 3 months for placebo. In December the FDA granted Niraparib priority review status and last week gave approval for the maintenance treatment for recurrent ovarian cancer in patients who are in complete or partial response to platinum based chemotherapy. Furthermore, the approval is not restricted to ovarian cancer patients with BRCA mutations, making the drug available to a larger population of ovarian cancer patients than either Rucaparib or Olaparib.

While PARP inhibitors have been tested in several types of solid tumour, the greatest response has been observed in ovarian cancer 6. AbbVie’s approach with Veliparib has focused on demonstrating sensitisation of classical chemotherapy drugs to combinations with PARP inhibitors in the more prevalent non-small cell lung cancer and breast cancer patient groups. The use of platinum based agents like carboplatin cause apoptosis of cancer cells by cross linking DNA, leading to tumour cell shrinkage 7. However, the DNA damage response can limit the effect of these agents. The resulting lesions are recognized by the DNA damage sensors and repaired by the base or nucleotide excision repair pathways. Inhibiting the role of PARP in these DNA repair pathways leads to the formation of single strand breaks, which are synthetically lethal in HR deficient cells. Studies in preclinical mouse models of breast cancer demonstrated a pronounced potentiation of cisplatin efficacy in combination with Veliparib 8. While PARP inhibitors are well tolerated, combination therapies risk narrowing the therapeutic window for both Veliparib and the chemotherapeutic agent. At the San Antonio Breast Cancer Symposium in December last year, AbbVie presented results from its phase II study of Veliparib in patients with locally recurrent or metastatic breast cancer with BRCA1 or BRCA2 mutations. While the addition of Veliparib to paclitaxel and carboplatin resulted in an improved overall response rate without an increase in adverse events, the study failed to show statistical significance in progression free survival. Despite the disappointing PFS data, the higher responder rate has encouraged continuation with the phase III trial (BROCADE) appropriately powered to detect improvements in PFS and overall survival. In addition to trails in Breast Cancer, AbbVie was given orphan drug status for Veliparib in NSCLC.

Of all the PARP inhibitors in late stage clinical trials, the most potent and selective is Talazaporib, recently acquired by Pfizer after its take-over of Medivation. While PARP inhibitors have been developed to potently inhibit the enzymatic activity of PARP, recent evidence suggests that the ability of the compounds to trap PARP at the DNA single strand break closely correlates with efficacy in preclinical models 9. Talazaporib has superior trapping ability than any other PARP inhibitor on the market, and with the promise of superior efficacy at a lower dose with fewer side effects, there is significant interest in the ongoing clinical studies. The drug is in a phase III clinical study for advanced and/or metastatic breast cancer with a BRCA mutation. Results from the study are keenly awaited.

PARP inhibitors are widely accepted as a clinically proven target class that validates the synthetic lethality concept. The future growth of PARP inhibitors will depend on the ability to combine it with other targeted approaches that can demonstrate synthetic lethality in tumour cell backgrounds while sparing normal cells. The good tolerability of PARP inhibitors in combination with other chemotherapy bodes well. Studies are ongoing for PARP inhibitors in different cancer populations in combination with radiation, Wee1 inhibitors, ATR inhibitors, Hsp90 inhibitors and drugs targeting the PI3K/Akt pathway. Studies may complete in 2017/18 and the results are eagerly awaited.

Blog written by Darren Le Grand

References

  1. Brown, J. S., Kaye, S. B. & Yap, T. A. PARP inhibitors: the race is on. Br. J. Cancer 114, 713–715 (2016).
  2. Farmer, H. et al. Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy. Nature 434, 917–21 (2005).
  3. Ledermann, J. et al. Olaparib Maintenance Therapy in Platinum-Sensitive Relapsed Ovarian Cancer. N. Engl. J. Med. 366, 1382–1392 (2012).
  4. Ledermann, J. A. et al. Articles Overall survival in patients with platinum-sensitive recurrent serous ovarian cancer receiving olaparib maintenance monotherapy: an updated analysis from a randomised, placebo-controlled, double-blind, phase 2 trial. Lancet Oncol (2016). doi:10.1016/S1470-2045(16)30376-X
  5. Mirza, M. R. et al. Niraparib Maintenance Therapy in Platinum-Sensitive, Recurrent Ovarian Cancer. N. Engl. J. Med. 375, 2154–2164 (2016).
  6. Ledermann, J. A. PARP inhibitors in ovarian cancer. Ann. Oncol. 27, i40–i44 (2016).
  7. Kelland, L. The resurgence of platinum-based cancer chemotherapy. Nat. Rev. Cancer 7, 573–584 (2007).
  8. Donawho, C. K. et al. ABT-888, an Orally Active Poly(ADP-Ribose) Polymerase Inhibitor that Potentiates DNA-Damaging Agents in Preclinical Tumor Models. Clin. Cancer Res. 13, (2007).
  9. Murai, J. et al. Trapping of PARP1 and PARP2 by Clinical PARP Inhibitors. Cancer Res. 72, 5588–99 (2012).