Abstract B4: Evaluation of VEGFxxxb isoforms as a predictive biomarker for anti-VEGF cancer therapy.

Biomarkers are critical tools for measuring efficacy of treatments or predicting which patients are mostly likely to respond to a particular therapy. Recently, the VEGF isoform, VEGF165b, was proposed to be a predictive marker for bevacizumab in metastatic colorectal cancer patients. VEGF165b is an anti-angiogenic splice variant that differs from its pro-angiogenic counterpart, VEGF165, by only six amino acids at the C-terminal end of the protein. Members of the VEGFxxxb isoform family are produced by alternative splicing of the 3’ untranslated region (UTR) to generate exon 8b, instead of the conventional exon 8 which produces exon 8a. The study of VEGF165b in colorectal cancer (Bates et al, Clinical Cancer Research, 2012) reported that patients with low VEGF165b:VEGFtotal ratio had improved PFS following bevacizumab + FOLFOX4 treatment, while individuals with higher VEGF165b:VEGFtotal ratios did not benefit. On the other hand, another recent study (Harris et al, PLoS One, 2012) reported that VEGFxxxb isoforms may be a RT-PCR artifact. In this study, we sought to test the role of VEGF165b in the response to anti-VEGF therapy using preclinical human tumor models, and to evaluate the prevalence of VEGFxxxb isoform in human cancer cells and normal tissues using RNA-Seq, a next generation sequencing (NGS) platform that is independent of RT-PCR. Our results show that xenograft tumors engineered to overexpress VEGF165b had similar growth kinetics, tumor vascular density and were equally sensitive to aflibercept or bevacizumab treatment in humanized VEGF SCID mice compared to their parental counterparts. These results indicate that VEGF165b does not have anti-angiogenic properties, and VEGF165b levels did not correlate with the efficacy of anti-VEGF therapy. Furthermore, although we were able to detect VEGF165b splice variants by NGS profiling in cells engineered to overexpress VEGF165b, no NGS evidence supporting the VEGFxxxb isoforms was found in a panel of 24 human cancer cell lines and 12 different types of human normal tissues. To our knowledge, this is the first report to survey VEGFxxxb isoforms using NGS RNA-seq technology. Overall, these studies suggest that closer inspection of VEGFxxxb isoforms may be required before employing VEGF165b as a predictive biomarker for anti-VEGF therapy. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B4. Citation Format: Wen Zhang, Cristina Abrahams, Ying Huang, Baosheng Li, Asma Parveen, Min Ni, Yi Wei, Yueming Ding, Eric Zhang, Hsin Chieh Lin, Gavin Thurston, Qing Zhang. Evaluation of VEGFxxxb isoforms as a predictive biomarker for anti-VEGF cancer therapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B4.