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Background Imatinib shows limited efficacy in patients with gastrointestinal stromal tumors (GISTs) carrying secondary KIT mutations. HQP1351, an orally bioavailable multikinase BCR-ABL inhibitor, is currently in clinical trials for the treatment of T315I mutant chronic myelogenous leukemia (CML), but the potential application in imatinib-resistant GISTs carrying secondary KIT mutations has not been explored. Methods The binding activities of HQP1351 with native or mutant KIT were first analyzed. Imatinib-sensitive GIST T1 and imatinib-resistant GIST 430 cells were employed to test the in vitro antiproliferative activity. Colony formation assay, cell migration assay and cell invasion assay were performed to evaluate the clonogenic, migration and invasion ability respectively. Flow cytometry and western blot analysis were used to detect cell apoptosis, cell cycle and signaling pathway. In vivo antitumor activity was evaluated in mouse xenograft models derived from GIST cell lines. Results HQP1351 potently inhibited both wild-type and mutant KIT kinases. In both imatinib-resistant and sensitive GIST cell lines, HQP1351 exhibited more potent or equivalent antiproliferative activity compared with ponatinib, a third generation BCR-ABL and KIT inhibitor. HQP1351 led to more profound inhibition of cell colony formation, cell migration and invasion, cell cycle arrest and cell apoptosis than ponatinib. Furthermore, HQP1351 also inhibited p-KIT, p-AKT, p-ERK1/2, and p-STAT3 to a higher extent than ponatinib. Finally, in xenograft tumor models derived from imatinib-resistant GIST cancer cell lines, HQP1351 exhibited antitumor activity superior to ponatinib. Conclusions Collectively, our in vitro and in vivo results suggest that the therapeutic application of HQP1351 in imatinib-resistant GIST patients deserves further investigation in clinical trials.

Liposarcoma is a rare but highly recurrent soft tissue neoplasm. Combination of surgery and radiotherapy is the main treatment for liposarcoma patients while chemotherapy remains experimental and limited depends on disease subtypes. Well-differentiated and dedifferentiated liposarcoma (WDLPS/DDLPS) represents ~50% of all diagnosed liposarcoma and their benefit from chemotherapy has been documented to be minimal. Concomitant amplifications of MDM2 and CDK4 are frequently found in WDLPS/DDLPS patients, suggesting that the combination with two targeted agents may worth further development for the treatment. APG-115 is a potent, selective, orally bioavailable small molecule inhibitor of MDM2-p53 protein-protein interaction and thus activates tumor suppression activity of p53 in p53 wild-type tumors. Currently, APG-115 is in clinical development as a single agent or in combination with PD-1 blockade immunotherapy for solid tumors, including sarcoma. To further explore the sensitive patient population and predictive biomarkers for APG-115, in this study, we evaluated the effect of the combined MDM2/CDK4 inhibition in p53 wild-type, MDM2 and CDK4 amplified liposarcoma using a preclinical xenograft tumor model derived from a dedifferentiated liposarcoma patient (PDX). Tumor-bearing mice were treated with MDM2 inhibitor APG-115, CDK4 inhibitors palbociclib/ribociclib, or their combinations. In the first experiment, APG-115 administered at 40 mg/kg as a single agent demonstrated antitumor activity in the DDLPS PDX model. In comparison with the single agents, the combination treatment with APG-115 and palbociclib or APG-115 and ribociclib exerted synergistic antitumor effects, resulting in T/C values of 16.9% and 27.1%, respectively (T/C value, average tumor volumes in treatment group vs. the vehicle control group). Partial tumor regression (PR) was achieved in 1/5 animals in both combination treatment groups but not in single arms. Another independent experiment with a higher dose of APG-115 (80 mg/kg) combined with palbociclib showed further improved antitumor activity with T/C value of 7.0% (2/5 PR). Collectively, our results suggest that the combination therapy of APG-115 and a CDK4 inhibitor may benefit WDLPS/DDLPS patients with p53 wild-type, and MDM2 and CDK4 amplifications clinically. Citation Format: Douglas D. Fang, Guoqin Zhai, Chunhua Xu, Qingyang Gu, Jingwen Wang, Saijie Zhu, Dajun Yang, Yifan Zhai. MDM2 inhibitor APG-115 synergizes with CDK4/6 inhibitors in a patient-derived xenograft model of dedifferentiated liposarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1253.