Modulation of angiogenic biomarkers in patients treated on a phase I study of TRC105 (anti-CD105 antibody) monotherapy for advanced solid tumors

Abstract

BACKGROUND: CD105 (endoglin) is an important mediator of tumor angiogenesis that is upregulated by hypoxia and VEGF inhibitors. TRC105 is an anti-CD105 monoclonal antibody currently being evaluated in clinical trials as an anti-angiogenic cancer therapy. METHODS: In this first-in-human phase I study, pts with advanced, incurable solid tumors were treated with escalating doses of TRC105, iv every 2 wks, until disease progression. Serial plasma samples were analyzed via a novel multiplex ELISA platform optimized for cancer patients. 39 candidate biomarkers related to tumor growth, angiogenesis, and inflammation were assayed at baseline (BL), after 1 month, and at end of study (EOS). RESULTS: 19 pts treated with TRC105 at 0.01-1 mg/kg were evaluable for biomarker analysis. Spearman’s rank correlation coefficients were calculated for pairs of analytes with known interactions. Wilcoxon signed rank tests indicated that the following analytes were significantly down-regulated at one month when compared with baseline: IGFBP-3 (p=0.001), VEGF-C (p=0.002), VEGF-D (p=0.003), FGFb (p=0.008), PDGF-AA (p=0.011), PDGF-BB (p=0.039), and PIGF (p=0.045). By EOS, significant increases from the 1 month nadir were observed for the following analytes: VEGF-C (p=0.027), VEGF-D (p=0.034), and IGFBP-3 (p=0.043). CONCLUSIONS: This is the first systematic investigation of the effect(s) of TRC105 on angiogenic biomarkers in the clinical setting. Multiplex analyses indicate that TRC105 therapy is associated with down-regulation of key modulators of angiogenesis that later increase at the time of disease progression. Based on these preliminary findings, additional analyses are planned for pts treated at higher TRC105 doses as well as pts treated on phase Ib and phase II studies of TRC105 in combination with VEGF inhibitors and other standard-of-care cancer therapies.