Genotoxic Anti-Cancer Agents and Their Relationship to DNA Damage, Mitosis, and Checkpoint Adaptation in Proliferating Cancer Cells

Abstract

When a human cell detects damaged DNA, it initiates the DNA damage response (DDR) that permits it to repair the damage and avoid transmitting it to daughter cells. Despite this response, changes to the genome occur and some cells, such as proliferating cancer cells, are prone to genome instability. The cellular processes that lead to genomic changes after a genotoxic event are not well understood. Our research focuses on the relationship between genotoxic cancer drugs and checkpoint adaptation, which is the process of mitosis with damaged DNA. We examine the types of DNA damage induced by widely used cancer drugs and describe their effects upon proliferating cancer cells. There is evidence that cell death caused by genotoxic cancer drugs in some cases includes exiting a DNA damage cell cycle arrest and entry into mitosis. Furthermore, some cells are able to survive this process at a time when the genome is most susceptible to change or rearrangement. Checkpoint adaptation is poorly characterised in human cells; we predict that increasing our understanding of this pathway may help to understand genomic instability in cancer cells and provide insight into methods to improve the efficacy of current cancer therapies.

Cancer cells that survive checkpoint adaptation contain micronuclei that harbor damaged DNA

“…Furthermore, the cisplatin treated group had IC 50 values of 1 mM at 120 hours to M059K cells and 18.5 mM to WI-38 cells, values that are clinically relevant. 3 Although S-23906 and CPT were both cytotoxic to M059K cells, WI-38 cells were either insensitive to the compounds as in the case of S23906-1, or only sensitive to concentrations above the pharmacological concentrations (Fig. 2D).…”

“…Our criteria for selection were: an agent that has an IC 50 concentration to cultured cells similar to pharmacological concentrations, and a difference in cell viability between early and late times after treatment, which is a feature of checkpoint adaptation. 3 We tested camptothecin (CPT), S23906-1, and cisplatin because each has a different mechanism of action. Increasing concentrations of either CPT, S23906-1, or cisplatin were added to cells and viability was measured at 48, 96, or 120 hours by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay (Fig.…”

“…3 Checkpoint adaptation is characterized by a cell-cycle arrest after detection of damaged DNA, overcoming this arrest, and entry into mitosis with damaged DNA. 4,5 The presence of damaged DNA is signaled by cells by activating histone gH2AX, 6 which leads to a series of pathways steps including the activation of DNA damage kinases ATM/ATR, which then phosphorylate checkpoint kinase 1 (Chk1) on serine 345.…”

When genome integrity and cell cycle decisions collide: roles of polo kinases in cellular adaptation to DNA damage

“…These agents are used at doses that would induce enough DNA damage to exceed (at least momentarily) the DNA repair capacity of cells, but not grossly so, in order to avoid the induction of immediate cell death. This approach is typically used to study adaptation in mammalian cells (Swift and Golsteyn 2014). The goal of both systems described above is to create a situation whereby cells could either maintain a checkpoint-induced cell cycle arrest, or take the decision to re-enter a proliferative state despite the presence of significant levels of DNA damage in their genome.…”

“…This cellular response is known as adaptation to DNA damage (reviewed in Bahassi el 2011; Bartek and Lukas 2007;Clemenson and Marsolier-Kergoat 2009;Swift and Golsteyn 2014;Syljuasen 2007). In this process, checkpoint-arrested cells re-enter a proliferative state even though they experience significant DNA damage.…”