Molecular aspects of cancer cell resistance to chemotherapy.

Cancer cell resistance to chemotherapy is still a heavy burden that impairs treatment of cancer patients. Both intrinsic and acquired resistance results from the numerous genetic and epigenetic changes occurring in cancer cells. Most of the hallmarks of cancer cells provide general mechanisms to sustain stresses such as the ones induced by chemotherapeutic drugs. Moreover, specific changes in the target bring resistance to specific drugs like modification in nucleotide synthesis enzymes upon anti-metabolite exposure, in microtubule composition upon spindle poison treatment, in topoisomerase activity upon topoisomerase inhibitor incubation or in intracellular signaling pathways when targeting tyrosine kinase receptors. Finally, the stemness properties of a few cancer cells as well as components of the tumor stroma, like fibroblasts and tumor-associated macrophages but also hypoxia, also help tumor to resist to anticancer agents. These processes provide an additional level of complexity to the understanding of the tumor resistance phenomenon. This review aims to describe the different general mechanisms as well as some examples of specific on target modifications inducing cancer cell resistance to chemotherapy at the molecular level. Perspectives to develop more efficient treatment, using genomic signature or more specific biomarkers to characterize putative resistance mechanisms in patients before choosing the more appropriate treatment, will also be discussed.