Abstract CT194: N-myristoylation inhibitor zelenirstat: New mechanistic insights and efficacy signals from a first in human phase I study
Authors: Berthiaume Luc Gerard , Beauchamp Erwan , Gamma Jay , Pain Rony , Kostiuk Morris A. , Cromwell Christopher R. , Moussa Eman W. , Julien Olivier , Hubbard Basil P. , Kuruvilla John , Sehn Laurie H. , Spratlin Jennifer , Jamal Rahima , Sangha Randeep , Mackey John R. 
Published: April 2024

Introduction. Zelenirstat (PCLX-001) is a small molecule inhibitor of N-myristoylation, a process that involves addition of the fatty acid myristate to over 200 proteins by two N-myristoyltransferases (NMT1 and 2). These include Src family kinases and c-Abl. Inhibition of N-myristoylation by zelenirstat leads to the degradation of non-myristoylated proteins and cancer cell death. We conducted a phase I trial to evaluate the safety, tolerability, and maximally tolerated dose (MTD) of zelenirstat in patients with refractory cancer.

Methods. Differential mass spectrometry was performed in NMT1 and NMT2 CRISPR/Cas9 KOs or zelenirstat-treated HAP1 cells to identify N-myristoylation-regulated proteins. Fully consented patients with advanced solid malignancies or refractory B-cell lymphomas were administered escalating doses of zelenirstat in 28-day cycles until progression or dose-limiting toxicity (DLT).

Results. Proteomic analysis of cells with genetic or pharmacological NMT inhibition was performed to gain insights into NMT substrates and function. In addition to the rapid degradation of SFKs, which disrupts the pro-survival signaling of RTKs, we identified multiple respiratory complex I proteins as the most degraded, including NDUFAF4. NMT1 KO and zelenirstat treatment disrupted complex I leading to oxidative phosphorylation (OXPHOS) inhibition, which is essential for both cancer stem cell survival and metastasis. Continuous once-daily zelenirstat at 20 mg to 210 mg was well tolerated, with no dose-limiting toxicities in 24 patients up to and including 210 mg. Gastrointestinal DLTs were observed in the 280 mg cohort, establishing 210 mg as the MTD. Oral absorption was rapid, and pharmacokinetics were suitable for once daily dosing. Seven patients had stable disease as best response, including pancreatic, ovarian and colon cancer patients; one colon cancer patient with 5 prior lines of therapy continues 210 mg beyond 11 cycles with reduction in carcinoembryonic antigen (CEA) and tumor dimensions. Kaplan-Meier analysis revealed longer progression-free survival (log-rank p=0.033) and overall survival (p=0.026) in the patients treated at 210 mg (n=7) when compared with patients treated in lower dose cohorts (n=17).

Conclusion. Zelenirstat has a unique dual impact on growth signaling and OXPHOS. Having previously demonstrated pre-clinical efficacy in hematologic cancers in vitro and in vivo, we now demonstrate the therapeutic potential of zelenirstat in patients with refractory advanced solid malignancies, warranting further clinical evaluation in these indications.

Citation Format: Luc Gerard Berthiaume, Erwan Beauchamp, Jay Gamma, Rony Pain, Morris A. Kostiuk, Christopher R. Cromwell, Eman W. Moussa, Olivier Julien, Basil P. Hubbard, John Kuruvilla, Laurie H. Sehn, Jennifer Spratlin, Rahima Jamal, Randeep Sangha, John R. Mackey. N-myristoylation inhibitor zelenirstat: New mechanistic insights and efficacy signals from a first in human phase I study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT194.