Methotrexate resistance in vitro is achieved by a dynamic selectionprocess of tumor cell variants emerging during treatment

Abstract

Genetic instability leads to tumor heterogeneity, which in turn provides a source of cell variants responsible for drug resistance. However, the source of resistant cells during the process of acquired resistance is poorly understood. Our aim has been to characterize the mechanism by which acquired resistance to methotrexate emerges during the course of cancer cell treatment in vitro. We recently demonstrated that, in vitro, HT-29 colon cancer cells become transiently sensitive to methotrexate by depleting the extracellular milieu of survival factors; on the other hand, the cell population under treatment can reversibly adapt to grow below a critical cell density in the presence of the drug. Here, we show that this adapted cell population gives rise to permanent resistant populations through repeated cycles of cell death and growth. This increased cell turnover, but not merely cell proliferation, is required for the appearance of increasing degrees of stable resistance that are progressively selected by drug pressure. Such a process, taking place in multiple steps, is here designated ''dynamic selection.'' The analysis of sensitive and resistant HT-29 cell populations revealed that methotrexate induces genomic instability-characterized by centrosome amplification and aberrant chromosome recombination-leading to a low-level amplification of the 5q chromosome arm as one of the earliest genetic events selected during treatment. Therefore, this model provides a mechanism by which a tumor cell population lacking resistant subpopulations before treatment is able to acquire the genetic changes required for stable drug resistance. ' 2006 Wiley-Liss, Inc.

Dihydrofolate reductase amplification and sensitization to methotrexate of methotrexate-resistant colon cancer cells

“…Gene amplification as a mechanism of drug resistance is a stepwise selection process in which cells become resistant through repeated cycles of cell death and proliferation accompanied by genomic instabilization and successive cycles of gene copy number gains (29). Most chemotherapeutic failures are due to the development of drug resistance by the tumor cells (3), which usually leads to giving up the chemotherapy regimen.…”

Aberrant Posttranscriptional Processing of Hyaluronan Synthase 1 in Malignant Transformation and Tumor Progression

“…For any given protein, both over-and underexpression can be detrimental, whereas levels that are "just right" allow passage through normal cell division (the "Goldilocks" hypothesis) (Adamia, Pilarski, Belch, et al, 2013;Pilarski et al, 2005). Aneuploid cells arising from RHAMMmediated mitotic abnormalities may be encouraged by "dynamic selection" (de Anta et al, 2006) for resistance e.g. Thus, acquisition by cancer cells of molecular adaptations that can modulate RHAMM overexpression are predicted to result in a biological balance that promotes malignant progression.…”

Differential oxidative response to fluoropyrimidines in colorectal cancer cell lines

“…Established and characterized cell lines were classified into different groups based on their morphological features, growth rate, and other functional parameters, implicating a broad range of systemic heterogeneity and drug response (Leibovitz et al, 1976;Brattain et al, 1981;McBain et al, 1984;Ribas et al, 2003;Flatmark et al, 2004;de Anta et al, 2006).…”

“…display important differences in tumor growth and metastatic capacity, leading to heterogeneity, possibly in a clinical relevant manner (Flatmark et al, 2004). Heterogeneity resulting from any system in cancer cells may bring about resistance to chemotherapeutic drugs (de Anta et al, 2006). However, understanding the mechanism of the heterogeneity creates an opportunity to increase the efficacy of drugs in the treatment of tumor cells.…”