Abstract A130: A preclinical study repurposing the proteasome inhibitor carfilzomib for use with radiotherapy and/or cetuximab for head and neck cancer

Abstract Background /Purpose: There is a great unmet need for new drugs that can be administered against squamous cell carcinoma of the head and neck (SCCCHN), with or without radiotherapy (RT). We preclinically studied the 2nd generation proteasome inhibitor carfilzomib (CFZ) in combination with RT +/- a proven biologic radiosensitizer, the anti-EGFR antibody Cetuximab (CTX). Materials/Methods: We studied two highly proliferative, HPV-negative human SCCHN cell lines in vitro, CAL-27 and SCC-25, using a metabolic assay (WST-1) and clonogenic survival assays. Cells in culture were exposed to varying concentrations of CFZ, with or without CTX, for 48 hours, with or without a single dose of RT given at 24 hrs. For subsequent in vivo experiments, we implanted CAL-27 cells into the hindleg of immunocompromised (NOD scid) mice. After tumors reached approximately 50-100 mm3 (7-10 days), cohorts of mice (N=5 per cohort) began treatment. Drug treatment consisted of DMSO (control), CFZ (2-4 mg/kg), and/or CTX (10 mg/kg), given twice per week x 5 doses. Half of the cohorts also received local tumor RT (3 Gy x 3 = 9 Gy delivered over 10 days, using an orthovoltage irradiator with custom shielding). Tumor size was measured 3x per week, and signs of mouse toxicity were monitored daily. Mice then were sacrificed at 35 days after the start of treatment. Tumors were harvested for macroscopic, microscopic, and molecular analyses. Results: By metabolic assay, the IC50 of CFZ was 17 nM in the CAL-27 cells and 14.5 nM in the SCC-25 cells. Combining CFZ with RT showed decreases in IC50's, to 6nM and 5 nM respectively. In CAL-27 clonogenic assays, CFZ (10 nM) reduced the # of colonies by about 50%, while the effects of single agent RT (5 Gy) or CTX (100 ug/ml) were minimal (p< 0.025 for comparison of CFZ vs. CTX). However, doublet treatment with CFZ/CTX was significantly more effective than single agent CFZ (p<0.0001) or single agent CTX (p<0.025). Similarly, CFZ/RT was significantly more effective than single agent CFZ (p<0.0001) or RT alone (p<0.005). The triple combination (CFZ/CTX/RT) was not evaluable (few if any colonies could be imaged). Results in SCC-25 showed similar trends (will be presented). In vivo results showed tumor growth delay with any of the 3 agents studied. Combination RT/CFZ or RT/CTX was superior to RT alone (p<0.002 and p<0.0001). Combination CFZ/CTX was superior to CFZ alone (p<0.002) or CTX alone (p<0.002). The triple combination demonstrated the ‘best’ results, with average tumor volume 47mm3 at Day 35, compared with 111 mm3 for RT/CTX and 149 mm3 for RT/CFZ. No signs of toxicity as assessed qualitatively and by mouse weight and serum creatinine were identified. Transcriptomic data will be presented. Summary/Conclusions: Carfilzomib (CFZ) has preclinical activity and radiosensitizes SCCHN, with or without Cetuximab (CTX). Given these results, and the non-overlapping toxicity profiles of CFZ and CTX, further translational studies with the goal of leading toward development of an early phase clinical trial(s), are justified. Citation Format: Hanif Khan, Suny Jang, Muhammed Danial, Todd Schell, Mitchell Machtay. A preclinical study repurposing the proteasome inhibitor carfilzomib for use with radiotherapy and/or cetuximab for head and neck cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr A130.