Intrinsic and induced drug resistance mechanisms: in silico investigations at the cellular and tissue scales.

Multiple cellular drug resistance mechanisms are present in a broad range of tumour types and act to counteract the effects of drugs. There are independent mechanisms by which drug resistance occurs; these include (i) the multi-drug resistance mechanism involving upregulation of ABC transporter proteins and (ii) intracellular mechanisms which sequester/degrade/detoxify drugs. In addition, drug resistance mechanisms could be either intrinsic, or directly induced by the drug. In this paper we focus on the behaviour of intrinsic and induced variants of these resistance mechanisms in solid tumours, by systematically elucidating their cellular and tissue level effects with an aim to bridge the gap between cell and tissue levels. This is achieved in a controlled in silico setting, which allows for an investigation of the interplay between transport, resistance pathways, and tissue level effects. Overall the paper (i) provides insights into the tissue level functioning of widespread classes of intracellular resistance mechanisms, showing important differences, (ii) systematically elucidates the difference between intrinsic and induced drug resistance mechanisms at the cell and tissue levels, (iii) demonstrates how spatial heterogeneity in intrinsic resistance in cells can significantly affect the response of solid tumours to drugs, and (iv) examines how different independent resistance mechanisms work in concert, to counteract drug dosages in tumours.