Recurrent growth factor starvation promotes drug resistance in human leukaemic cells

Abstract

Multi-drug resistance can be induced by various environmental stresses including an exposure to chemical drugs and X-ray irradiation. In addition, hypo-nutritive conditions are known to promote multi-drug resistance in solid tumours. To understand the importance of nutritive conditions in the development of drug resistance in non-solid tumours and to know whether a transient malnutrition could induce a permanent reduction in drug sensitivity, leukaemic cells were transiently cultured under growth factor-starved conditions. Granulocyte-macrophage colony-stimulating factor-dependent human leukaemic MO7e cells were cultured in the absence of granulocyte-macrophage colon-stimulating factor for 2 weeks, during which the majority of the cells died, and the minor viable cells were expanded in the presence of granulocyte-macrophage colon-stimulating factor for following 1 week. This procedure was repeated three times, and the surviving cells were cloned by limiting dilution. These clones underwent G1 arrest in the absence of granulocyte-macrophage colon-stimulating factor, while parental cells underwent apoptosis. Interestingly, activities of the downstream targets of granulocyte-macrophage colon-stimulating factor receptor were regulated in a granulocyte-macrophage colon-stimulating factor-independent manner, indicating that the ligand-independent activation of granulocyte-macrophage colon-stimulating factor receptor had not taken place. Moreover, the 4 -7-fold increases in IC 50 for etoposide and the 2 -6-fold increase in IC 90 for doxorubicin was observed. Furthermore, Bcl-2 protein expression was significantly up-regulated in the clones while no significant changes in Bax, Bcl-xL , P-glycoprotein and Hsp70 protein expression and no consistent changes in p53 expression were detected. We propose that recurrent growth factor starvation, which may occur in vivo when stromal function is damaged after intensive chemotherapy or bone marrow occupation by malignant cells, causes selection of drug resistant leukaemia cells that will expand when the growth factor supply recovers.

Evaluation of Cytotoxic and Cytostatic Effects in Saccharomyces cerevisiae by Poissoner Quantitative Drop Test

“…Many toxic compounds introduce DNA damage and cause formation of bulky lesions that block DNA replication and/or RNA transcription, leading to cell cycle arrest and the inability of the cells to form colonies [6]. Current colony counting techniques and methods used to measure the size of yeast colonies have drawbacks that include: (i) inadequate sensitivity to determine the effect of low doses of cytotoxic/cytostatic compounds; (ii) high expense due to the need for specialized equipment or chemical substances [5]; and (iii) induction of starvation in treated yeast cells over time, an effect that has been shown to increase cellular resistance to chemical agents in mammalian cells [7]. For this study, we developed an improved assay method, the poissoner quantitative drop test (PQDT) based on the poissoner assay [8], to evaluate the sensitivity of yeast cells to genotoxic and cytotoxic compounds.…”

A importância do gene p53 na carcinogênese humana

“…Também, condições de hipo-nutrição são sabidamente reconhecidas por promover tal resistência em tumores sólidos. Contudo, estas condições não alteram a expressão do p53 (18). Por outro lado, Liu et al (19) concluíram que a resposta inicial à quimioterapia em crianças com leucemias é variável e envolve tanto as vias que dependem da p53, quanto as que não dependem dela.…”