Ribonucleotide Reductase Large Subunit (RRM1) Gene Epression Predicts Efficacy of Adjuvant Mitotane in Adrenocortical Cancer
Marco Volante, Massimo Terzolo, Martin Fassnacht, Ida Rapa, Antonina Germano, Silviu Sbiera, Fulvia Daffara, Paola Sperone, Giorgio V Scagliotti, Bruno Allolio, Mauro Papotti, Alfredo Berruti. University of Turin, Orbassano, Turin, Italy; University Hospital Wurzburg, Wurzburg, Germany
Background: Mitotane is the most effective systemic therapy for adrenocortical carcinoma (ACC), but its mechanism of action and possible predictors of treatment response are currently poorly defined. Our aim was to evaluate the gene expression of ribonucleotide reductase large subunit 1 (RRM1) and excision repair cross-complementation group 1 (ERCC1) in ACC as potential biomarkers for clinical outcome, based on their prognostic relevance in other cancer types and on the sequential use of platinum and gemcitabine-based therapy in advanced ACC patients.
Design: Ninety-two tissue samples of completely resected ACC (44 treated with surgery alone, 38 receiving adjuvant mitotane) were centrally analyzed using Real Time PCR for RRM1 and ERCC1 expression. Expression levels were compared to clinical and pathological variables and disease-free (DSF) and overall (OS) survival by means of univariate and multivariate analyses. H295R and SW-13 ACC cell lines were also used for pharmacological tests at different mitotane concentrations. Cell viability was measured using WST-1 assay. RRM1 gene expression was analyzed by means of Real Time PCR. RRM1 silencing experiments were also performed in SW-13 cells.
Results: RRM1 and ERCC1 gene expression levels were reciprocally correlated in the study population (R; 0.4425, p=0.0021) and were not significantly associated with pathological features. ERCC1 gene expression was not significantly associated with DFS and OS neither at univariate nor multivariate analysis. Conversely, high RRM1 expression levels were associated with shorter DFS and OS at both univariate and multivariate analysis. Moreover, in patients with low RRM1 expression, mitotane treatment was associated with a significantly longer DFS than that of patients undergoing follow up only [HR: 0.37; p=0.016], whereas no effect of mitotane treatment on DFS was observed in patients with high RRM1 levels [HR: 1.07; p=0.83], thus suggesting a predictive role of RRM1 gene expression in the mitotane adjuvant setting. In vitro, mitotante-induced RRM1 gene upmodulation was associated to dicreased mitotane sensitivity, and silencing of RRM1 gene in SW-13 cells induced a significant increase in mitotane sensitivity.
Conclusions: Our in vitro and in vivo data indicate that RRM1 gene expression is functionally associated to mitotane sensitivity and represents the first biomarker in ACC predicting the response to adjuvant mitotane.
Monday, March 19, 2012 2:30 PM
Platform Session: Section H, Monday Afternoon