Targeting myeloid derived suppressor cells: Phase 0/1 trial of low dose capecitabine + bevacizumab in patients with recurrent glioblastoma.

Abstract

e13507 Background: Glioblastoma (GBM) creates an immunosuppressive environment that allows tumor growth. Myeloid derived suppressor cells (MDSCs), a heterogeneous class of immunosuppressive cells, mediate immune suppression in GBMs. MDSCs are up-regulated in the blood of patients with GBM and multiple other tumor types. We have developed a novel strategy to target GBM immunosuppression using low dose 5-fluorouracil (5-FU) that, targets immune cells and does not depend on blood brain or blood tumor barrier penetration. Marked MDSC depletion occurs at 5-FU doses in mice equivalent to < 10% of the normal human dosing. Goal: proof of concept that MDSC suppression in feasible in GBM pts with low-dose capecitabine [cap], an oral 5-FU analogue). Methods: Eligibility: Recurrent GBM in need of surgical resection; no prior cap or bevacizumab (bev). Cohorts of 3-6 patients receive low-dose cap 150 mg/m2/d (dose level [DL] 1) for 7 days before surgery. After surgery, patients resume cap for one cycle after which bev is added. Blood MDSC, immune cell levels, and relevant secreted factors are measured at baseline; pre- and post-op; and after the addition of bev. Tumors are assayed for MDSCs and glioma stem-like cells (GSCs). Primary endpoint: MDSC and T-Regulatory cell reduction after cap. Secondary endpoints: Tumor concentrations of MDSCs, GSCs, and T-reg cells; safety; and PFS6. Results: Three of the 4 patients enrolled have data available. All patients received 5 days of pre-op cap at DL 1 with MDSC reductions of 20, 26, and 79% from baseline. The first patient reached a reduction of 93% (measured 2 days after pre-op course) whereas the other 2 experienced return to baseline. The regulatory T cells (T-reg) also fell approximately 15, 20, and 50%, respectively. CD8 concentrations appeared to rise at the time of MDSC and T-reg reduction. No patient experienced grade 3 or higher toxicity. Conclusions: Low dose capecitabine appears to reduce MDSC concentrations with minimal toxicity. During this course T-regs also fell and CD8 concentrations rose. Dose escalation continues. (NCT02669173) (Supported by Musella Foundation, Blast GBM, Sontag Foundation, Velosano, Mylan Pharmaceuticals) Clinical trial information: NCT02669173.