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PURPOSE Pirtobrutinib is a highly selective, noncovalent (reversible) Bruton tyrosine kinase inhibitor (BTKi). We report the safety and efficacy of pirtobrutinib in patients with covalent Bruton tyrosine kinase inhibitor (cBTKi) pretreated mantle-cell lymphoma (MCL), a population with poor prognosis. METHODS Patients with cBTKi pretreated relapsed/refractory (R/R) MCL received pirtobrutinib monotherapy in a multicenter phase I/II trial (BRUIN; ClinicalTrials.gov identifier: NCT03740529 ). Efficacy was assessed in the first 90 consecutively enrolled patients who met criteria for inclusion in the primary efficacy cohort. The primary end point was overall response rate (ORR). Secondary end points included duration of response (DOR) and safety. RESULTS The median patient age was 70 years (range, 46-87), the median prior lines of therapy was 3 (range, 1-8), 82.2% had discontinued a prior cBTKi because of disease progression, and 77.8% had intermediate- or high-risk simplified MCL International Prognostic Index score. The ORR was 57.8% (95% CI, 46.9 to 68.1), including 20.0% complete responses (n = 18). At a median follow-up of 12 months, the median DOR was 21.6 months (95% CI, 7.5 to not reached). The 6- and 12-month estimated DOR rates were 73.6% and 57.1%, respectively. In the MCL safety cohort (n = 164), the most common treatment-emergent adverse events (TEAEs) were fatigue (29.9%), diarrhea (21.3%), and dyspnea (16.5%). Grade ≥3 TEAEs of hemorrhage (3.7%) and atrial fibrillation/flutter (1.2%) were less common. Only 3% of patients discontinued pirtobrutinib because of a treatment-related adverse event. CONCLUSION Pirtobrutinib is a first-in-class novel noncovalent (reversible) BTKi and the first BTKi of any kind to demonstrate durable efficacy after prior cBTKi therapy in heavily pretreated R/R MCL. Pirtobrutinib was well tolerated with low rates of treatment discontinuation because of toxicity.

Abstract Background: Isocitrate dehydrogenase 1/2 (IDH1/2) is mutated in a subset of cholangiocarcinoma (CCA), gliomas, and other solid tumors. LY3410738 is a potent, selective, covalent, dual inhibitor of IDH1/2 mutations (IDH1/2m). LY3410738 binds covalently at a novel binding site, enabling continued potency in preclinical models in the setting of second site IDH resistance mutations. We present initial results from the first-in-human phase 1 study of oral LY3410738 in patients (pts) with IDH1/2m CCA, and IDH1m glioma or other solid tumors. Methods: Dose escalation (3+3 design) evaluated LY3410738 monotherapy in advanced IDHm CCA and other solid tumors (NCT04521686). Key objectives included determining the RP2D, safety, PK, PD (inhibition of plasma D-2-HG), and preliminary antitumor activity. Results: As of 28 July 2022, 80 pts including 42 with CCA (33 IDH1m, 9 IDH2m), 27 with glioma (IDH1m), and 11 other tumor types (IDH1m) received LY3410738 dosed at 25-600 mg QD or 300 mg BID. Pts were median 52 years of age (range, 23-80) with a median of 2 prior therapies (range, 1-7). 19% of CCA pts had received prior IDH1 inhibitor. Median time on treatment was 3.7 months (range, 0.1-19). No DLTs or treatment related deaths were observed; the MTD was not reached. Treatment emergent adverse events (TEAEs) ≥15% included nausea (35%), vomiting (21%), and decreased appetite (19%) and were mostly grade 1-2. Most frequent grade ≥3 TEAEs >2% were anemia (4%), cholangitis (3%), headache (3%), decreased lymphocyte count (3%), and hyponatremia (3%). LY3410738 exposure was dose proportional. In pts with IDH1m cancers, LY3410738 achieved sustained D-2-HG inhibition at all dose levels, including in pts who received prior IDH1 inhibitor. In pts with IDH2m cancers, a higher dose (≥150 mg daily dose) was required for D-2-HG inhibition. Among the 42 pts with R/R CCA, the best response included 1 PR and 22 SD. Of the 22 glioma pts with contrast enhancing tumors, best response included 3 PR and 9 SD. Conclusions: LY3410738 demonstrated a favorable safety profile with potent and sustained D-2-HG inhibition in pts with IDH1/2m advanced solid tumors. Consistent with the expectations for IDH inhibitor monotherapy in this setting, CCA and glioma pts exhibited prolonged stable disease. RP2D evaluation is ongoing. Updated data on LY3410738 monotherapy will be presented at the meeting. Citation Format: Jordi Rodon, Lipika Goyal, Teresa Macarulla Mercade, Masafumi Ikeda, Shunsuke Kondo, Do-Youn Oh, Li-Yuan Bai, Makoto Ueno, Antoine Italiano, Kyriakos Papadopoulos, David Spigel, Sani H. Kizilbash, Rasha Cosman, Joon Oh Park, Li-Tzong Chen, Tomoya Yokota, Anita A. Turk, Chih-Yi Liao, Rachna Shroff, Anthony El-Khoueiry, Taroh Satoh, Antoine Hollebecque, Mitesh J. Borad, Nilofer Azad, Kurt A. Jaeckle, Herbert H. Loong, Jorge Adeva, Wei Peng Yong, Junjie Zhao, Hui Liu, Anna M. Szpurka, Ivelina Gueorguieva, Kamnesh R. Pradhan, Xiaojian Xu, James J. Harding. A first-in-human phase 1 study of LY3410738, a covalent inhibitor of mutant IDH, in advanced IDH-mutant cholangiocarcinoma and other solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT098.

In cancer cells, endogenous or therapy-induced DNA damage leads to the abnormal presence of DNA in the cytoplasm, which triggers the activation of cGAS (cyclic GMP–AMP synthase) and STING (stimulator of interferon genes). STAT2 suppresses the cGAMP-induced expression of IRF3-dependent genes by binding to STING, blocking its intracellular trafficking, which is essential for the full response to STING activation. STAT2 reshapes STING signaling by inhibiting the induction of IRF3-dependent, but not NF-κB–dependent genes. This noncanonical activity of STAT2 is regulated independently of its tyrosine phosphorylation but does depend on the phosphorylation of threonine 404, which promotes the formation of a STAT2:STING complex that keeps STING bound to the endoplasmic reticulum (ER) and increases resistance to DNA damage. We conclude that STAT2 is a key negative intracellular regulator of STING, a function that is quite distinct from its function as a transcription factor.