Effect of mast cells on efficacy of anti-angiogenic therapy by secreting matrix-degrading granzyme b.

Abstract

11522 Background: Resistance towards anti-angiogenic therapy (AAT) still represents a substantial clinical challenge. As mast cell (MC) density is known to correlate with tumor angiogenesis, we analyzed if inhibition of MC holds potential to increase efficacy of AAT in mice and cancer patients. Methods: C57BL/6J (WT), NSG or MC-deficient KitW-sh(Wsh) mice were subcutaneously injected with Panc02, EL4 or BxPC3 cells with or without bone marrow-derived MC. Tumors were treated with 20 mg/kg of anti-VEGFR2 antibodies (DC101) or 25 mg/kg cromoglicic acid. Tissue microarrays from n = 299 breast cancer patients from the GeparQuinto Phase 3 clinical trial were stained for MC and MC numbers were correlated with clinical data. Results: We observed that absence of MC reduced tumor growth and increased the efficacy of AAT in different tumor models. Intriguingly, AAT only initially reduced microvessel proliferation but this was abrogated over time as a result of MC-mediated resistance. We show that MC secrete increased amounts of granzyme b upon therapy, which mobilizes alternative pro-angiogenic factors from the tumor matrix. These factors act beside the targeted VEGFA-VEGFR2-axis and reinduce angiogenesis despite the presence of AAT. Importantly, MC-mediated resistance could be overcome using the FDA-approved MC inhibitor cromoglicic acid. In line with our preclinical data, high intratumoral MC density correlated with disease progression in HR+ breast cancer patients when Bevacizumab was added to standard neodjuvant chemotherapy (HR 8.45, p = 0.006). Accordingly, Kaplan-Meier curves indicated that disease free survival of patients with high tumoral MC density was numerically shorter in the whole cohort and significantly shorter in the HR+ cohort upon addition of AAT to chemotherapy (p = 0.168 and p = 0.004, respectively). Conclusions: Here we unravel a novel resistance mechanism, by which MC hamper efficacy of AAT in mice and cancer patients. In preclinical models this effect could be overcome by combining AAT with an FDA-approved MC inhibitor indicating high clinical relevance. Thus, combination of FDA-approved MC inhibitors with AAT might be a suitable approach to increase efficacy of AAT in the clinic.