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Resistance to cytosine arabinoside in cells transfected with activated Ha-ras oncogene
C Riva1, S el Khyari, Y Rustum
1Groupe de Recherche sur les Cancers du Poumon et des Voies Aériennes, Univ. Joseph Fourier, Institut Albert Bonniot, La Tronche, France.
Abstract:
The molecular basis for cancer cell resistance to 1-beta-D-arabinofuranosylcytosine (ara-C) is not well understood. Since aberrant expression and mutations of various ras oncogenes have been implicated in the poor prognosis of human cancers and in several mechanisms of drug resistance, we tested this hypothesis by determining the effect of varying level of c-Ha-ras expression and the presence of ras gene mutation on resistance to 1-beta-D-arabinofuranosylcytosine in rodent Rat-1a fibroblasts and human mammary HBL100 cells. We found that a) transfection of cells by Ha-ras renders cells resistance to ara-C, b) resistance was not associated either with a decrease of intracellular ara-CTP formation and retention or lack of incorporation of ara-C into DNA, c) resistance was due to deoxycytidine kinase inactivity and decrease of mRNA expression of the gene, d) the degree of ara-C resistance correlated directly with the level of Ha-ras expression, e) an inverse correlation was found between ras expression and kinase expression, f) the increased expression of ras mRNA rather than ras mutation influenced ara-C resistance. These findings suggest that c-Ha-ras levels may influence therapeutic success in some tumors and may regulate metabolic pathways of drug such as ara-C.
Insights
Increased c-Ha-ras expression, not mutation, confers resistance to 1-beta-D-arabinofuranosylcytosine (ara-C) chemotherapy. This resistance stems from reduced deoxycytidine kinase activity and expression, impacting cancer treatment strategies.
Area of Science:
- Molecular Biology
- Cancer Research
- Pharmacology
Background:
- Cancer cell resistance to 1-beta-D-arabinofuranosylcytosine (ara-C) is a significant clinical challenge.
- Ras oncogenes are implicated in cancer progression and drug resistance, but their specific role in ara-C resistance is unclear.
Purpose of the Study:
- To investigate the impact of c-Ha-ras expression levels and mutations on cellular resistance to ara-C.
- To elucidate the molecular mechanisms underlying ras-mediated ara-C resistance.
Main Methods:
- Transfection of rodent Rat-1a fibroblasts and human HBL100 cells with varying levels of c-Ha-ras.
- Assessing ara-C resistance, intracellular ara-CTP levels, DNA incorporation, deoxycytidine kinase activity, and gene expression.
Main Results:
- Ha-ras transfection conferred resistance to ara-C.
- Resistance was linked to deoxycytidine kinase inactivity and decreased mRNA expression, not altered ara-CTP metabolism or DNA incorporation.
- Higher c-Ha-ras expression correlated with increased ara-C resistance and decreased kinase activity.
- Ras mRNA levels, rather than mutations, were the primary driver of resistance.
Conclusions:
- c-Ha-ras expression levels significantly influence cellular sensitivity to ara-C.
- Ras oncogenes may regulate key metabolic enzymes, such as deoxycytidine kinase, impacting drug efficacy.
- Findings suggest c-Ha-ras levels could be a predictive biomarker for therapeutic success in ara-C treated cancers.