Translational Predictive Biomarker Analysis of the Phase 1b Sorafenib and Bevacizumab Study Expansion Cohort

Predictive biomarkers are needed to triage patients to the best therapy. We prospectively planned examination of sequential blood, biopsy, and functional imaging with which to confirm the mechanism and to identify potential predictive biomarkers in a phase Ib clinical trial expansion of patients with solid tumors receiving sorafenib/bevacizumab. The maximally tolerated doses of sorafenib at 200 mg twice daily with bevacizumab at 5 mg/kg every other week were given to biopsiable patients. Patients were randomized to receive either sorafenib or bevacizumab monotherapy for the first 28-day cycle with the second drug added with cycle 2. Biopsies, dynamic contrast-enhanced MRI, and fluorodeoxyglucose-proton emission tomography were done pre-therapy and at 2 and 6 weeks (2 weeks into combination therapy). Tumor and serum proteomics, Ras/Raf mutational analysis, and functional imaging results were examined individually and across the dataset to identify potential changes predictive of response to therapy and those that confirm the biochemical drug mechanism(s). Therapy with sorafenib/bevacizumab resulted in clinical benefit in 45% of this mixed solid tumor group. ERK activation and microvessel density were decreased with monotherapy treatment with sorafenib or bevacizumab, respectively; whereas a decreased signal over the group of total AKT, phospho(p)-VEGF receptor2, p-endothelial nitric-oxide synthase, b-RAF, and cleaved poly(ADP-ribose) polymerase was associated with earlier progression of disease. Tumor metabolic activity decreased in those patients with clinical benefits lasting longer than 4 months, and activity increased with progression of disease. Cleavage of caspase 3 and poly(ADP-ribose) polymerase was increased, and Ki67 expression decreased in patients with prolonged clinical benefits, consistent with decreased proliferation and increased apoptosis. The conglomerate analysis, incorporating pharmacodynamic and tumor biochemistry, demonstrated sorafenib/bevacizumab-targeted vascular activity in the tumor. Results suggest potential biomarkers for which changes, as a group, during early therapeutic exposure may predict clinical benefit.Sorafenib and bevacizumab have demonstrated clinical utility as single agents or in combination with chemotherapy for solid tumors. Sorafenib, initially developed as a c-Raf kinase inhibitor, also has potent inhibitory activity against the vascular endothelial growth factor receptor-2 (VEGFR2).¹ Clinical activity has been shown for bevacizumab, the humanized neutralizing monoclonal antibody against VEGF, also alone and in chemotherapy combinations (1–5). The role of combining two agents with overlapping target biology had not yet been studied.We tested the clinical hypothesis that signal interruption at collaborative pathway points, both vertical and horizontal interactions, may yield equal or greater effect than the agents in isolation in a phase I trial combining bevacizumab and sorafenib ({"type":"clinical-trial","attrs":{"text":"NCT00095459","term_id":"NCT00095459"}}NCT00095459), and we now report the translational analyses (6). Sorafenib was selected for its ability to target both receptor and cytosolic kinases important in a variety of activated cells in the tumor microenvironment, including stromal, endothelial, and malignant cells. Because such kinase inhibitor treatment has been shown to up-regulate production of proangiogenic cytokines, we added bevacizumab to reduce VEGF ligand availability and augment inhibition of endothelial cells. We observed the clinical benefit, including partial response and prolonged disease stabilization, using attenuated doses of the individual agents as determined by safety assessments during the trial; partial response or disease stabilization of at least 4 months occurred in 59% of the daily sorafenib cohort and in 55% of those on the intermittent, 5 of 7 days, sorafenib schedule (6, 7). These benefits lasted up to 37+ months with over 25% of patients receiving 12 or more months of therapy. The trial prospectively planned comprehensive translational assessment using a randomized drug addition design (Fig. 1A) to evaluate individual drug target specificity and combination drug effects to identify potential predictive biomarkers to examine in the ongoing phase II study of sorafenib/bevacizumab in ovarian cancer.Open in a separate windowFig. 1.Treatment schema (A) and Consort diagram (B).Predictive biomarkers are increasingly important for the advancement of targeted therapies. Such knowledge should allow more effective triage of patients to interventions more likely to provide clinical benefit. Biomarkers that predict drug response may consist of direct measures of activity, such as modulation of biochemical signals in the tumor (8) or those that yield pharmacodynamic measures, such as functional imaging (9, 10). Changes in metabolic activity and/or blood flow using dynamic imaging may fall into both categories with decreased glucose uptake due to reduced glucose delivery and/or reduced glucose metabolism and altered vascular permeability in response to attenuation of the VEGF drive. Aggregate analysis of these varied translational measures may yield a more detailed view of the cancer and the drug combination, allowing broader dissection into potential predictive biomarkers. Linking modulation of activity with clinical benefit is a first step in validating prospective biomarkers.We designed a novel drug administration schema from which to examine the contribution of both sorafenib and bevacizumab on the modulation of tumor and the tumor microenvironment behavior. The biochemical and imaging data demonstrate changes consistent with alteration of tumor vascularity, demonstrate direct association of target effect with clinical outcome across solid tumor types, and confirm the benefit of complementary pathway targeting. Reduction in blood flow, up-regulation of cytokine production, and inhibition of a set of anti-apoptotic anti-proliferative signaling events together may define potentially predictive changes to examine in early drug administration in subsequent trials.