Impact of sirtuin genes expression on first-line treatment outcomes in patients (pts) with metastatic colorectal cancer (mCRC) enrolled in CALGB/SWOG 80405 (Alliance).

269 Background: Sirtuins (SIRT1-7) are class III histone deacetylases with different roles in CRC as tumor suppressive and oncogenic, mainly influencing proliferation, migration, invasion, DNA damage and chemoresistance. In the present study, we explored the association between tumor gene expression of sirtuins and first-line treatment outcomes in mCRC pts. Methods: We evaluated the impact of the tumor gene expression of sirtuin genes ( SIRT1 -7) on treatment outcomes (overall survival: OS; progression free survival: PFS) in 433 pts enrolled in the randomized, phase III CALGB/SWOG 80405 (NCT00265850) trial. RNA extracted from FFPE tumor samples was sequenced using the HiSeq 2500 (Illumina). Subgroup analyses were based on treatment (bevacizumab [bev] (N = 226) vs. cetuximab [cet] (N = 207)). For each gene, expression was divided into tertiles of high, medium and low. The associations between tumor gene expression and outcomes (PFS and OS) were assessed using log-rank test in univariate analysis. Multivariable Cox proportional hazards regression model was used to compute hazard ratios (HR) and 95% confidence intervals while adjusting for baseline characteristics. Treatment-gene interactions were analyzed using the likelihood ratio test. Results: Of the seven genes analyzed, SIRT3 high was associated with both longer PFS (HR: 0.59 [95% CI: 0.46-0.74], P < 0.001) and OS (HR:0.64 [95% CI: 0.50-0.83], P = 0.002) overall. Treatment-gene interaction testing found significant interactions for SIRT1 and SIRT5 with PFS ( P values: 0.021 and 0.016, respectively) and OS ( P values: 0.038 and 0.014, respectively) with targeted therapies (bev vs. cet). Multivariate analysis showed SIRT1 high associated with longer PFS (HR: 0.62 [95% CI: 0.42-0.89], P = 0.014) and OS (HR: 0.59 [95% CI: 0.40-0.89], P = 0.036) in cet-treated pts; in contrast with shorter observed PFS (HR: 1.38 [95% CI: 0.96-1.99], P = 0.22) and OS (HR: 1.31 [95% CI: 0.90-1.93], P = 0.23) in bev-treated pts. SIRT5 high showed similar results and associated with longer PFS (HR: 0.64 [95% CI: 0.45-0.91], P = 0.039) and OS (HR: 0.57 [95% CI: 0.39-0.83], P = 0.013) in cet-treated pts, with no similar associations in bev-treated pts. Conclusions: Our results highlight a potential role for SIRT3 as prognostic and, SIRT1 and SIRT5 as predictive biomarkers for first-line treatment in mCRC, with differential effects based on targeted agents. Significant interaction favored cet treatment in SIRT1 high and SIRT5 high tumors. However, previous reports suggest an opposite role of SIRT5 that has been linked to chemotherapy and/or cet resistance in CRC via the inactivation of succinate dehydrogenase complex subunit A. Therefore, further studies are warranted to dissect the mechanism behind the interaction of SIRT5 with cetuximab activity and establish the potential of targeting SIRT1/5 in CRC.