3099 Background: Phosphatidylinositol-3 kinase (PI3K) pathways are important elements of tumor survival and progression, and PIK3C genes are often mutated or overexpressed in many cancers. Additionally, PIK3D (PI3Kδ) modulates immune cell functions in tumors, elaborating another PI3Kδ inhibition feature with a potential clinical benefit. Linperlisib, an oral and highly selective PI3Kδ inhibitor, demonstrated potent anti-tumor activity in syngeneic animals from previous research. In this Phase 1b study, the safety, tolerability, and efficacy of linperlisib is under investigation for patients with advanced solid tumors. Methods: Linperlisib was given orally once daily (QD) in 28-day cycle until disease progression, unacceptable toxicity, or withdrawal from the study. Adverse events (AEs) were graded by NCI-CTCAE v5.0. Efficacy was assessed according to RECIST1.1 criteria. Results: As of December 28, 2020, 70 patients were enrolled in the Phase1b study, with advanced cancers, including colorectal (n = 22), breast (n = 8), lung (n = 8), kidney (n = 5), liver (n = 4), ovarian (n = 1), head and neck (n = 5), and esophageal (n = 1) cancers; sarcomas, (n = 4), small intestinal stromal tumor (n = 3), thymic (n = 2), gallbladder (n = 2), gastric (n = 4), and pancreatic (n = 1) carcinomas. The patients were heavily pretreated with an average of 4 previous lines of therapy. Among the 70 patients, the most common nonhematologic TEAEs (all grades/grade≥3) were proteinuria (37.14%/0%), elevated aspartate aminotransferase (20%/0%), nausea (20%/0%), oral mucositis (2.8%/2.8%), diarrhea (2.8%/2.8%). The most common hematological TEAEs were leukopenia (24.28%/0%) and neutropenia (17.14%/4.28%). There were no unexpected toxicities in this study. Of 42 patients evaluable for response, the overall response rate was 2.38%. Notably, the disease control rate (DCR) was 45.24% from monotherapy treatment. One patient with thymic carcinoma obtained a partial response (80.8% reduction of the target lesion), with a duration of response of more than 6 cycles. The treatment of this subject is continuing. A lung adenocarcinoma subject reached radiological stable disease associated with 13.7% reduction in the target lesion and disease control for approximately 6 months. Conclusions: In this study, the PI3K inhibitor, linperlisib exhibited a favorable safety profile as was previously seen in lymphoma patients. Monotherapy treatment with linperlisib was observed to impart a high DCR in advanced solid cancers of many types. Available data from linperlisib and other PI3K inhibitors suggests that linperlisib may limit tumor growth directly, but also by affecting the tumor immune microenvironment. With these promising indications of clinical tolerability and activity, further investigation of linperlisib alone or in key therapeutic combinations is warranted. Clinical trial information: NCT04049929.
DDRE-09. DEVELOPING IDO-PROTACS TO IMPROVE IMMUNOTHERAPEUTIC EFFICACY IN PATIENTS WITH GLIOBLASTOMA
