Evaluating the extravascular penetration and distribution of anti-cancer drugs using a novel application of the multilayered cell culture model

The inefficient distribution of anti-cancer drugs in the tumour extravascular compartment may be an important mechanism of drug resistance in solid tumours. However, gaining an understanding of diffusion limitations of existing drugs and developing new drugs with improved tumour penetration is limited by a lack of techniques with which to evaluate drugs. The purpose of this research project was to assess the extravascular penetration and distribution of anti-cancer drugs using a novel application of the multilayered cell culture (MCC) model. MCC is a planar analogue of spheroidal cell culture, in which tumour cells are instead grown into discs of tissue. Due to their 3-D conformation they model many characteristics of the tumour extravascular compartment. A unique property of MCC is that it possesses two populations of rapidly proliferating cells, one on each side of the culture, that are separated by a known thickness of tissue. In tumours and spheroids proliferation status falls off with distance from the vasculature (tumours) or tissue edge (spheroids), which in turn modifies cellular response to drugs. Hence, visualizing the distribution of a drug's effect within these tissues cannot be used to directly determine its actual distribution. The hypothesis of this project was that the symmetrical proliferation seen in MCCs could be applied to measure the ability of anti-cancer drugs to penetrate and distribute within tissue using a biological endpoint. Based on this hypothesis an effect-based assay was devised and applied to assess the tissue distribution of a selection of anti-cancer drugs from several distinct classes. Using the assay, drug exposure to cells 150 μm into tissue (a diffusion distance commonly observed in solid tumours) was estimated to vary from as low as 3-10% of the reservoir exposure (anthracyclines) to cases where no reduction in exposure could be detected (5-FU and cisplatin). The MCC-based assay was validated by comparing the predicted drug distributions with direct visualization of the drugs themselves. Results from this study suggest that an MCC effect-based assay could be used as a simple drug penetration screen in the development of new anti-cancer drugs.Medicine, Faculty ofMedicine, Department ofExperimental Medicine, Division ofGraduat