Cancer Cell Fitness Is Dynamic.

Several phenotypes that impact the capacity of cancer cells to survive and proliferate are dynamic. Here we used the number of cells in colonies as an assessment of fitness and devised a novel method called Dynamic Fitness Analysis (DynaFit) to measure the dynamics in fitness over the course of colony formation. DynaFit is based on the variance in growth rate of a population of founder cells compared with the variance in growth rate of colonies with different sizes. DynaFit revealed that cell fitness in cancer cell lines, primary cancer cells, and fibroblasts under unhindered growth conditions is dynamic. Key cellular mechanisms such as ERK signaling and cell-cycle synchronization differed significantly among cells in colonies after 2 to 4 generations and became indistinguishable from randomly sampled cells regarding these features. In the presence of cytotoxic agents, colonies reduced their variance in growth rate when compared with their founder cell, indicating a dynamic nature in the capacity to survive and proliferate in the presence of a drug. This finding was supported by measurable differences in DNA damage and induction of senescence among cells of colonies. The presence of epigenetic modulators during the formation of colonies stabilized their fitness for at least four generations. Collectively, these results support the understanding that cancer cell fitness is dynamic and its modulation is a fundamental aspect to be considered in comprehending cancer cell biology and its response to therapeutic interventions. SIGNIFICANCE: Cancer cell fitness is dynamic over the course of the formation of colonies. This dynamic behavior is mediated by asymmetric mitosis, ERK activity, cell-cycle duration, and DNA repair capacity in the absence or presence of a drug.

A guide for the analysis of long-term population growth in cancer.

Although cancer is a chronic disease, most of the in vitro experiments to assess the effectiveness of intervention are performed in hours or a few days. Moreover, none of the available methodologies to measure cell proliferation are adapted to provide information about the growth kinetic during and after treatment. Thus, the objective of this work is to provide a guide to assess long-term changes in cell population size to be used mainly in cancer research. Cumulative population doubling (CPD) graphs based on cell counting for in vitro or tumor volume for in vivo assays were used to calculate four parameters: relative end CPD (RendCPD), to quantify the end point analysis of proliferation; relative area under curve (rAUC), to describe the global chronic effect of a treatment; relative time to cross a threshold (RTCT), to indicate the delay in cell population recovery produced by a treatment; and relative proliferation rate (RPR), to describe the relative regrowth velocity of the cells that survived after treatment. These parameters describe not only the acute and chronic effects of a treatment but also the behavior of cells that are not eliminated by the treatment, providing crucial information about the growth kinetic of the surviving population. Moreover, the proposed analysis allowed the grouping of independent CPD experiments quantified at different time points and even the direct comparison of in vitro and in vivo experiments. Therefore, this new way to analyze long-term outcomes provides a global view of the effectiveness of an intervention, as an important tool for long-term studies.

Sensitization of glioma cells by X-linked inhibitor of apoptosis protein knockdown.

OBJECTIVE: Glioblastomas are a kind of cancer with high resistance to treatments, requiring more efficient alternatives of treatment. X-linked inhibitor of apoptosis (XIAP) is highly expressed in gliomas and, due to its inhibition of caspases, can participate in resistance to therapy. Here we test the sensitization of glioma cells with XIAP gene knockdown (KD) to drugs used in chemotherapy. METHODS: We silenced XIAP expression in U87MG glioblastoma using stable shRNA, and cells were treated with taxol, BCNU, temozolomide, cisplatin, etoposide, resveratrol (Rsv), vincristine and doxorubicin. We analyzed cell viability, cell cycle, apoptosis and senescence. RESULTS: XIAP KD cells were more sensitive to etoposide, Rsv, vincristine and doxorubicin compared to wild-type (WT) cells. Doxorubicin 1 µM and vincristine 100 nM induced higher activation of caspases after 24 h and doxorubicin induced a higher degree of senescence induction in XIAP KD cells in relation to WT cells. Phospho-p53 and phospho-H2Ax Western blot indicate subsequent DNA damage as an important effector of doxorubicin-induced death. CONCLUSIONS: This study suggests that XIAP inhibitors may sensitize gliomas to certain drugs and induce death and that the mechanisms of sensitization involve apoptosis, senescence and p53 signaling.