Organs on a Chip – The next step in 3D culture


Methods of modelling complex diseases have developed dramatically in recent years. Co-cultures as well as 3D cultures are now widely used in the drug discovery process, but with advances in microfluidics more complex co-culture systems are being developed that permit the investigation of complex biological processes. In these models biomimetic devices are used that are engineered to represent the structural and functional units found in organs such as bone, heart, liver, lung, intestine, brain and kidney. Also engineered within these devices is the ability to assay the result, therefore these devices are transparent enabling visualisation of the cells and immunological staining as well as being able to sample the media for assaying secreted factors (2).

Device for studying interaction of neuronal and astrocytes by metabolic communication (3)

Device for studying interaction of neuronal and astrocytes by metabolic communication (3)

One example of this is a model from Kunze et al., (3) where they used such a device for an astrocyte neuronal co-culture. Astrocyte neuronal co-cultures are not new, but these typically use an astrocyte feeder layer and therefore measure physical interactions between neuronal cells and astrocytes. In this model however, the group wanted to measure the effect of non-physical interactions between these cell types, i.e. secreted factors, or metabolic communication as described by the group. This microfluidic device is designed with two side channel in which astrocytes and neurons are seeded, separated by a central ‘contact’ area. The contact area in the middle enables fluid movement between the two cell types and neurite outgrowth, but the distance of 0.9mm means there is no physical contact between the cell types. Using this set-up the team was able to observe that astrocytes stably expressing mutant SOD (super-oxide dismutase) reduce neuronal survival in the ‘contact area’ compared to when the astrocytes express wild-type SOD, with no physical interaction between the astrocytes and neurons. Although this was a case-study for the device it demonstrates that this system can clearly be used for compounds targeting non-physical cross-talk between astrocytes and neurons as well as other cell-types. Additionally read-outs using both immunological staining of neurons or astrocytes as well looking at factors secreted can be used demonstrating the flexibility of the system.

Another example is a model that enables endothelial function to be observed in a 3D microenvironment (1). Here, a microfluidic device has an inner channel that in the study was lined with HUVECs (human umbilical vein endothelial cells). Inside the channel was a matrix gel where the group cultured A549 lung cancer spheroids. The device itself was clear and therefore enabled direct visualisation of the spheroids in the channel, therefore the group was able to measure EMT (Epithelial-mesenchymal transition)-induced spheroid dispersal due to the interaction of the HUVECs and the A549s. A number of FDA approved compounds known to inhibit EMT were applied to the inner matrix and their ability to inhibit EMT measured. Interestingly these compounds were as much as three fold more potent in the 3D assay than the conventional 2D equivalent. Interestingly the efficacious concentrations identified in the 3D micro-device were more similar to those measured in human trials than those in the 2D model.

To study epithelial-mesenchymal transition A549 spheroids are cultured in a gel-filled inner channel lined with HUVECs (1)

To study epithelial-mesenchymal transition A549 spheroids are cultured in a gel-filled inner channel lined with HUVECs (1)

These are simply two examples of sophisticated devices capable of modelling diseases or cell interactions that normal 2D or even 3D culture is unable to do. As the accessibility of microfluidics is expanding, so are the number and complexity of these devices. The limitations are clear; current throughput is low, labour intensive, and cost is high in comparison to traditionally screening. They do, however, provide possibilities for use in drug discovery such as late stage screening as well as target validation.

References

  1. Aref AR, Huang RY-J, Yu W, Chua K-N, Sun W, Tu T-Y, Bai J, Sim W-J, Zervantonakis IK, Thiery JP, Kamm RD. Screening therapeutic EMT blocking agents in a three-dimensional microenvironment. Integr. Biol. (Camb). 5: 381–9, 2013.
  2. Esch EW, Bahinski A, Huh D. Organs-on-chips at the frontiers of drug discovery. Nat. Rev. Drug Discov. 14: 248–60, 2015.
  3. Kunze A, Lengacher S, Dirren E, Aebischer P, Magistretti PJ, Renaud P. Astrocyte-neuron co-culture on microchips based on the model of SOD mutation to mimic ALS. Integr. Biol. (Camb). 5: 964–75, 2013.

Blog written by Trevor Askwith

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