Development of multidrug resistance due to multiple factors including P‐glycoprotein overexpression under K‐selection after MYC and HRAS oncogene activation

Abstract

Multistep tumorigenesis is a form of microevolution consisting of mutation and selection. To clarify the role of selection modalities in tumor development, we examined two alternative evolutionary conditions, r-selection in sparse culture, which allows cells to proliferate rapidly, and K-selection in confluent culture, in which overcrowding constrains cell proliferation. Using MYC-and EJ-RAS-transformed rat embryo fibroblasts, we found that K-selected cells acquired and stably maintained multidrug resistance (MDR) to DOX, VCR, MTX and Ara-C. Then, we examined the involvement of a number of factors potentially causal of the development of MDR, that is, ploidy, Tp53 mutation, doubling time and the expression levels of genes related to drug resistance. Although ploidy status and Tp53 mutations did not correlate with MDR, we found that Abcb1/Mdr1, encoding P-glycoprotein (Pgp), was significantly upregulated after K-selection. Cyclosporin A, a competitive inhibitor of Pgp, increased the intracellular accumulation of DOX and reduced the resistance to it. Indeed, the population of Pgp-transfected cells significantly expanded under K-, but not under r-selection. In addition to Pgp upregulation, altered expression of other genes such as Cda/cytidine deaminase and Slc29a1/equilibrative nucleoside transporter 1 and prolonged doubling times were associated with MDR. This system reproduces events associated with MDR in vivo and would be useful for analysis of MDR development. ' 2005 Wiley-Liss, Inc.Key words: natural selection; drug resistance; multistep tumorigenesis; clonal evolution While the original Darwinian theory of natural selection explains the evolution of species during millions of years, the theory has also been applied to explain the development of cancer, which occurs over a period of years, which is often called microevolution. Foulds proposed a theory of multistep tumorigenesis according to which a cancer originates from one single cell, from which a tumor develops in a stepwise fashion through qualitatively different stages. 1 Nowell further proposed that multistep tumorigenesis consists of mutation and selection, resulting in successive clonal evolution. 2 In recent years, numerous molecular events associated with the multistep tumorigenesis have been identified. 3 Although the functional involvement of these molecular events in tumorigenesis has been extensively investigated, what types of selection modalities contribute to cancer development is still not well understood.A rodent cell culture system was shown to recapitulate a variety of events frequently encountered in human tumors, such as the emergence of polyploid cells and genetic aberrations such as TP53 gene mutations. 4 We have been investigating the roles of different selection processes using such a culture system of rat embryo fibroblasts (REFs) transformed with MYC and activated HRAS (EJ-RAS) oncogenes. 5 Using this culture system, we previously applied two selection modalities, r-and K-selection, which were originally defined by MacArthur an...

TRAIL sensitize MDR cells to MDR-related drugs by down-regulation of P-glycoprotein through inhibition of DNA-PKcs/Akt/GSK-3β pathway and activation of caspases

“…The c-Myc is known to be involved in regulating expression of P-gp, the product of MDR1 gene [29,30] and renders cells sensitive to TRAIL-induced apoptosis [31]. Since the increased activity of DNA-PK participates in the development of MDR phenotype [10], we determined the relationships among P-gp, c-Myc and DNA-PKcs/Akt/GSK-3β molecules in MDR variants (Figure 3).…”

“…Previously, we have demonstrated that the increased expression of DNA-PKcs is associated with the development of drug resistance in MDR variants of CEM cells [10]. In addition, the c-Myc is known to be involved in regulating expression of P-gp, the product of MDR1 gene [29,30]. It has been reported that elevated P-gp expression in MDR cells is accompanied by increased level of pAkt [41].…”

Starvation, detoxification, and multidrug resistance in cancer therapy

“…In human cancer cells, mutations in the coding region of NRF2 cause constitutive induction of drug efflux pumps and cytoprotective enzymes (Shibata et al, 2008) such as NQO (Belinsky and Jaiswal, 1993). Further, IGF-I, and its downstream elements such as RAS/ERK (Nakamura et al, 2006) and PI3K/AKT (Abdul-Ghani et al, 2006; Han et al, 2007; Tazzari et al, 2007) promote MDR, in part, by modulating ABC transporter expression. Notably, DR increases Nrf2 in normal cells (Martin-Montalvo et al, 2011) and thus has the potential to be an important mediator of the differential effects of DR in the protection of normal and cancer cells (Lee and Longo, 2011; Raffaghello et al, 2008).…”

Survivin transcription is associated with P-glycoprotein/MDR1 overexpression in the multidrug resistance of MCF-7 breast cancer cells

“…Although chemotherapy plays an important role in the management of patients with breast carcinoma, the tumors subsequently are unresponsive to chemotherapy and result in death of patients (1,2). The progression of a tumor to an untreatable form is suggested to be associated with several genetic, morphological and phenotypical changes, which may involve the increased expression of inhibitors of apoptosis proteins (IAPs) such as survivin (3)(4)(5) and a dramatic increased expression of multidrug resistant P-glycoprotein (P-gp) (6)(7)(8).…”