Correlation of BMAL1 expression in colorectal cancer with resistance to anti-VEGFA therapy with bevacizumab.

Abstract

705 Background: Mechanisms underlying failure of colorectal cancer (CRC) patients to respond to anti-vascular endothelial growth factor A (VEGFA) therapy with bevacizumab in combination with chemotherapy are largely unknown, and novel predictive markers required. Methods: Tumours from patients/mice and CRC cell lines were analysed by IHC, PCR, EMSA, ChIP, ELISA and Western blot. Statistics of (pre)clinical data was calculated with SAS and Graphpad Prism. Response outcomes including progression-free survival (PFS) and restaging according to RECIST (PR/SD/PD) were analyzed. Results: Circadian rhythm transcription factor and heme receptor REVERBA and its target gene BMAL1 promoted binding to and activation of the -700kB RORE DNA-element in the VEGFA promoter resulting in increased VEGFA mRNA expression and VEGFA protein secretion from human CRC cell lines. Conversely, REVERBA siRNA and its antagonist (Fe3+) hemin inhibited VEGFA synthesis. In C57BL/6J Apcmin/+ mice treated with murinized VEGFA Ab (n=11 mu_chimeric_B20-4.1 vs. n=42 mock; 10 mg/kg*week; i.p.; 4 weeks), Vegfa mRNA was reduced, as was incidence (*p=0.0411 Fisher Exact Test) and multiplicity (*p=0.0157 Cochran Armitage Trend Test) of vascularized CRCs. However, Bmal1 mRNA was up-regulated, and high BMAL1 protein expression in tumor cells positively correlated with Ki67+ proliferation (n=3 B20 vs. n=3 mock; *p<0.05 t-test) in treated Apcmin/+ CRCs. BMAL1 protein was also induced in xenografts from BALB/c nude mice s.c. implanted with the human CRC cell line HCT116 and treated with humanized VEGFA Ab (n=4 bevacizumab vs. n=4 vehicle; 10 mg/kg*week; i.p.; 3 weeks; *p<0.05 t-test). In CRC patients, high BMAL1 protein expression in tumor cells was associated with clinical non-response to bevacizumab (n=15 SD vs. n=29 PD: BMAL1- vs. BMAL1+, *p=0.0061 Cochran Armitage Trend Test,*p=0.0130 Fisher Exact Test) and reduced PFS (BMAL1- [671 days] vs. BMAL1+ [368 days], *p=0.0030 log rank test, HR=0.4792 [95%CI 0.3103-0.7871], n=74). Conclusions: BMAL1 may represent a predictive marker for bevacizumab non-response. Due to its drugability, the REVERBA-BMAL1-VEGFA axis may be a potential target to prevent resistance to anti-angiogenic therapy in CRC.