Antitumor Activity of Dual BCL-2/BCL-Xl Inhibitor Pelcitoclax (APG-1252) in Natural Killer/T-Cell Lymphoma (NK/TCL)

Natural killer/T-cell lymphoma (NK/TCL) is one of the most common subtypes (10.4%) of peripheral T-cell lymphoma, which in turn accounts for 10% to 15% of all cases of non-Hodgkin lymphoma. NK/TCL occurs more frequently in Asia and Latin America than other regions, and although associated with Epstein-Barr virus (EBV) infection, NK/TCL has an unclear pathogenesis of genetic and molecular alterations. Asparaginase-based chemotherapy regimens are frequently used, typically with unsatisfactory outcomes. Novel targeted therapies, such as histone deacetylase (HDAC) inhibitors and programmed death-1 antibodies, are reported effective either as single agents or in combination with other agents. Studies have also shown that EBV-positive NK/TCL cell lines are B-cell lymphoma-extra large (BCL-xL) dependent. Other preclinical experiments have shown that BH3-mimetic drugs targeting BCL-xL-induced cell death in NK/TCL cell lines were effective in NK/TCL xenograft models. BCL-xL inhibitors have shown narrow therapeutic windows in clinical trials because of dose-limiting on-target thrombocytopenia. Pelcitoclax (APG-1252) is a novel dual BCL-2/BCL-xL inhibitor under clinical development for solid tumors. As a result of its unique prodrug design, APG-1252 can overcome the undesired platelet toxicity. This study evaluated the potential antitumor effect of APT-1252 in preclinical models of NK/TCL. Cell-based antiproliferation studies showed activity of APG-1252 and its more potent metabolite APG-1252-M1 toward NK/TCL cell lines that overexpressed BCL-xL. Half-maximal inhibitory concentrations (IC ₅₀) for APG-1252 in SNK-1, SNK-6, and SNK-8 (EBV-positive NK/TCL) cell lines were 2.652 ± 2.606 µM, 1.568 ± 1.109 µM, and 0.557 ± 0.383 µM, respectively. Corresponding values for APG-1252-M1 were 0.133 ± 0.056 µM, 0.064 ± 0.014 µM, and 0.020 ± 0.008 µM, respectively. Mechanistic studies demonstrated that APG-1252 and APG-1252-M1 disrupted the complex of BCL-xL/BCL-2-associated X protein (Bax) and BCL-xL/BCL-2 homologous antagonist killer protein (Bak) in SNK-6 cells, thereby liberating these proapoptotic proteins and further activating downstream apoptosis pathways by cleaving poly-ADP ribose polymerase-1 (PARP-1) and caspase-3. In an SNK-6 xenograft model, administration of APG-1252 at 65 mg/kg and 100 mg/kg either twice or once weekly resulted in significant antitumor effects, with tumor growth rate (T/C%) values ranging from 13.7% to 30.7%. Furthermore, the combination of APG-1252 with HDAC inhibitor chidamide or DDGP (dexamethasone, cisplatin, gemcitabine, and pegaspargase) chemotherapy demonstrated synergistic effects. Pharmacokinetic assessment in mice showed that APG-1252 had a long half-life in plasma (127 hours) and tumor tissues (25.2 hours), justifying intermittent dosing schedules used in vivo. Importantly, the transformation of APG-1252 to APG-1252-M1 was 16 times higher in tumor tissues compared to plasma (22% vs. 1.3%) after administration of APG-1252, thereby suggesting that APG-1252 can reduce platelet toxicity caused by APG-1252-M1 in plasma. In conclusion, APG-1252 has promising antitumor effects in NK/TCL, either as a single agent or in combination with an HDAC inhibitor or chemotherapy. These findings provide evidence to further evaluate APG-1252 as a potential treatment for NK/TCL.