Treatment of acute myeloid leukemia (AML) remains challenging. Enhancement of anti-tumor responses by blocking negative immune regulators is a promising strategy for novel effective leukemia therapeutics. V-domain Ig suppressor of T-cell activation (VISTA) is a recently defined negative regulator mediating immune evasion in cancer. To investigate the effect of VISTA on anti-leukemia immune response in AML, we initiated a study using clinical samples collected from AML patients. Here we report that VISTA is highly expressed on myeloid-derived suppressor cells (MDSCs) in the peripheral blood of AML patients. Both the frequency and intensity of VISTA expression on MDSCs are significantly higher in newly diagnosed AML than in healthy controls. Importantly knockdown of VISTA by specific siRNA potently reduced the MDSCs-mediated inhibition of CD8 T cell activity in AML, suggesting a suppressive effect of VISTA on anti-leukemia T cell response. Furthermore, we observed a strong positive association between MDSC expression of VISTA and T cell expression of PD-1 in AML. These results support the strategy of VISTA-targeted treatment for AML and underscore the strong potential for combined blockade of VISTA and PD-1 pathways in effective leukemia control.

Purpose mTOR inhibitors like temsirolimus may result in undesirable AKT upregulation. Metformin inhibits mTOR through different mechanisms and may enhance temsirolimus’s antitumor activity. We conducted an open-label phase I dose escalation trial of this drug combination in patients with advanced/refractory cancers. Methods Temsirolimus, 25 mg weekly, was combined with an escalating daily dose of metformin (level 1: 500; level 2: 1000; level 3: 1500; level 4: 2000 mg) by utilizing a standard 3+3 trial design. Treatment was administered in 28-day cycles following initial two-week metformin titration during the first cycle. Results Twenty-one patients (median age, 56 years) with sarcoma (n=8), colorectal (n=3), endometrial (n=4), uterine carcinosarcoma (n=2), ovarian (n=2), and other (n=2) cancers were enrolled. Patients had received median of 4 prior systemic treatments. Two dose limiting toxicities were observed (grade 3 mucositis, grade 3 renal failure); both patients continued treatment after dose modification. Fifty-six percent patients had stable disease as best response; clinical benefit rate was 22%. Patients continued treatment for median of 11 weeks. Conclusions Combination temsirolimus/metformin was well tolerated with modestly promising effectiveness among this heavily pretreated patient cohort. We recommend a dose of temsirolimus 25 mg weekly and metformin 2000 mg daily for phase II study.

Five candidate plasma biomarkers (ST2, REG3α, elafin, TNFR1, sIL2Rα) were measured at specific time-points following cyclophosphamide/fludarabine-based nonmyeloablative allotransplantation (NMAT) in patients who did or did not develop acute graft-versus-host-disease (aGVHD). Plasma samples from 34 patients were analyzed at days +7, +14, +21 and +30. At a median follow-up of 358 days, 17 patients had experienced aGVHD with a median time to onset of day +36. Risk of aGVHD was associated with elevated plasma ST2 concentrations at day +7 (c-stat=0.72, p=0.03), day +14 (c-stat=0.74, p=0.04), and day +21 (c-stat=0.75, p=0.02); elevated plasma REG3α concentrations at day +14 (c-stat=0.73, p=0.03), day +21 (c-stat=0.76, p=0.01) and day +30 (c-stat=0.73, p=0.03); and elevated elafin at day +14 (c-stat=0.71, p=0.04). Plasma concentrations of TNFR1 and sIL2Rα were not associated with aGVHD risk at any of the time-points studied. This study identified ST2, REG3α and elafin as prognostic biomarkers to evaluate risk of aGVHD following Cy/Flu-based NMAT. These results need to be confirmed in an independent validation cohort.

BACKGROUND. The combination of multikinase VEGF inhibitor regorafenib and anti-EGFR antibody cetuximab overcomes intrinsic and acquired resistance in both EGFR-sensitive and EGFR-resistant preclinical models of colorectal cancer (CRC). METHODS.Utilizing a standard 3+3 design, a phase I study was designed to determine safety, maximum tolerated dose (MTD), and dose-limiting toxicities (DLTs) of the regorafenib plus cetuximab combination among patients with advanced cancer including CRC. Comprehensive genomic profiling was performed on the exceptional responder. RESULTS.Among the 27 patients enrolled the median age was 54 years. None of 19 patients treated at dose level 1 (cetuximab i.v. 200 mg/m 2 followed by 150 mg/m 2 weekly + regorafenib 80 mg daily) experienced a DLT, and 2 of 5 patients treated at dose level 2 (cetuximab i.v. 200 mg/m 2 followed by 150 mg/m 2 weekly + regorafenib 120 mg daily) experienced a DLT (grade 3 thrombocytopenia [n = 1] and grade 3 intra-abdominal bleed [n = 1]). Most common adverse events were grade 1 or 2 rash (20 patients). Of 24 evaluable patients, 11 (46%) patients had clinical benefit (stable disease > 6 cycles or partial response [PR]) (CRC n = 8, one patient each with head and neck cancer, carcinoma of unknown primary, and glioblastoma). A CRC patient, who progressed on anti-EGFR and regorafenib, achieved a PR (46% decrease per RECIST v1.1) lasting 15 months. Genomic profiling of an exceptional responder with response for over 27 cycles revealed hypermutated genotype with microsatellite instability (MSI). CONCLUSION.Regorafenib 80 mg daily plus cetuximab 200 mg/m 2 loading dose, followed by 150 mg/m 2 every week is the MTD/recommended phase II dose. The combination demonstrated early signals of activity in wild-type CRC, including 1 exceptional responder with MSI high.