Article

RRM1 Modulated In Vitro and In Vivo Efficacy of Gemcitabine and Platinum in Non–Small-Cell Lung Cancer

University of South Florida, Tampa, Florida, United States
Journal of Clinical Oncology (Impact Factor: 18.43). 11/2006; 24(29):4731-7. DOI: 10.1200/JCO.2006.06.1101
Source: PubMed

ABSTRACT RRM1 encodes the regulatory subunit of ribonucleotide reductase and is a molecular target of gemcitabine. Previous studies showed increased RRM1 expression on continuous exposure of cell lines to gemcitabine and suggested improved survival for patients with low as opposed to high tumoral RRM1 expression when treated with gemcitabine-containing chemotherapy. However, the principal hypothesis that intratumoral levels of gene expression are associated with disease response has not been addressed.
We constructed genetically modified lung cancer cell lines with increased and decreased RRM1 expression to investigate the in vitro 50% inhibitory concentration (IC50) for gemcitabine, cisplatin, and carboplatin. A prospective phase II clinical trial in patients with locally advanced non-small-cell lung cancer was conducted with pretreatment tumor collection for determination of RRM1 and ERCC1 expression by real-time reverse transcriptase polymerase chain reaction. The levels of gene expression were correlated with tumor response after two cycles of gemcitabine and carboplatin.
In cell lines with a genetically engineered 15-fold RRM1 expression range, the gemcitabine IC50 had a 100-fold range, and the cisplatin and carboplatin IC50 had a two-fold range. They were highest in constructs with high RRM1 expression. In the prospective clinical trial, RRM1 expression was significantly (P = .002) and inversely correlated (r = -0.498) with disease response. ERCC1 expression showed a similar trend (P = .099).
The results strongly suggest that tumoral RRM1 expression is a major predictor of disease response to gemcitabine/platinum chemotherapy. ERCC1 expression is predictive of response albeit to a lesser degree.

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    • "Because 5 -NT reduces phosphorylated metabolites of GEM, the activity level of 5 -NT might also be a target for evaluation as the one factor most affecting the clinical outcome of GEM chemotherapy [22]. Although RRM1, dCK, and 5 -NT are useful predictors of GEM resistance [23], the individual actions of each of RR, dCK, and 5 -NT have not been reported as useful predictors of prognosis in pancreatic cancer chemotherapy . Namely, pancreatic cancer cells with a higher ratio of hENT1×dCK/RRM1×RRM2 showed higher cytotoxicity, and those cells with a lower ratio showed lower cytotoxicity [21]. "
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    • "The ribonucleotide reductase regulatory subunit M1 (RRM1) may also contribute to cisplatin resistance when delivered in combination with gemcitabine [24] [25]. However, although preclinical data suggests increased RRM1 expression levels are associated with resistance to cisplatin in vitro, the effect is less pronounced than that observed for gemcitabine [24]. It may be that in this doublet combination the relationship to gemcitabine resistance is more clinically relevant in determining outcomes for patients. "
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    • "Low level of human MutS homolog 2 (MSH2), a mismatch repair enzyme, was linked with sensitivity to cisplatin [22]. Low expression of regulatory subunit of ribonucleotide reductase (RRM1) was associated with sensitivity to gemcitabine in cell lines as well as in a clinical setting [23]. Low expression of BRCA1 seems to predict sensitivity to cisplatin [24], whereas high expression may be associated with sensitivity to antimicrotubule drugs such as taxanes and vinorelbine [25]. "
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