Abstract C134: Inhibition of KRAS-G12D as a radiosensitization strategy for KRAS-G12D-mutant pancreatic ductal adenocarcinoma cells

Abstract Introduction: KRAS is the most frequently mutated oncogene in pancreatic ductal adenocarcinoma (PDAC) (>90%), making it an attractive therapeutic target. Indeed, KRASG12C inhibitors have been approved by the FDA. However, the most common KRAS mutation in PDAC is KRASᴳ12ᴰ(>40%). The preclinical success of novel KRASᴳ12ᴰ inhibitors like MRTX1133 initiated a Phase 1/2 clinical trial, which, however, was halted due to formulation challenges. Even with improved formulations, acquired resistance to KRAS inhibitors remains a major challenge, underscoring the need for combination strategies to enhance therapeutic durability. Radiotherapy, included in treatment guidelines for borderline resectable and locally advanced PDAC, is one potential combination partner. However, the survival benefits of radiotherapy are limited in PDAC due to its inherent radioresistance. Prior studies indicated that oncogenic KRAS may contribute to this resistance. Thus, we hypothesize that combining radiotherapy with KRASᴳ12ᴰ inhibition is an effective strategy to overcome PDAC resistance to either treatment alone. Methods: We assessed the synergistic potential of the KRASᴳ12ᴰ inhibitor MRTX1133 and irradiation in three KRASG12D murine PDAC cell lines: AK4.4, KPC001S, and 6649c2 (KPCY). MTT assays were performed to assess sensitivity to MRTX1133 for a range of concentrations, with or without irradiation (0–10 Gy) as a short-term viability readout. Additionally, long-term colony formation assays (CFA) were conducted to assess clonogenic survival after treatment with MRTX1133, irradiation, or their combination. Survival curves were fitted using the linear-quadratic model and analyzed via F-tests and Sensitizer Enhancement Ratios (SER). SynergyFinderPlus was used to evaluate synergy between MRTX1133 and irradiation. Results: Across all cell lines, combining MRTX1133 with irradiation significantly reduced cell viability (MTT assay) and clonogenic potential (CFA) compared to either treatment alone. SynergyFinder analysis revealed additive (score 0–10) to synergistic effects (>10) for both assays. F-tests on CFA survival data revealed significant radiosensitization in all cell lines. SER analysis showed the strongest radiosensitization in KPCY cells (SER0.3 1.38–1.60 at 1–1000 nM), followed by AK4.4 (SER0.5 1.22–1.30 at 10–1000 nM) and KPC001S (SER0.5 1.06–1.24 at 10–1000 nM). KPCY cells were the most sensitive to both MRTX1133 (IC50 6.9 nM) and irradiation, and the combination yielded the greatest cytotoxic effect (e.g., 76% survival reduction in CFA at 100 nM, 8 Gy; Bliss Score: 13.8). Notably, despite high resistance to MRTX1133 (IC50 ∼3 μM) and irradiation, AK4.4 cells exhibited pronounced synergy when combined - though overall cytotoxicity remained moderate (48% survival reduction at 100 nM, 8 Gy; Bliss Score 20.8). Conclusion: Combining the KRASG12D inhibitor MRTX1133 with irradiation induces synergistic cytotoxic effects in KRASG12D-mutant murine PDAC cells, warranting further testing of multimodality strategies to overcome resistance and improve therapeutic outcomes in PDAC. Citation Format: Halil I. Corbali, Rieke Schleinhege, Schuyler R. Fuller, Kento Miyazaki, Praveena R. George, Henning Willers, Dan G. Duda. Inhibition of KRAS-G12D as a radiosensitization strategy for KRAS-G12D-mutant pancreatic ductal adenocarcinoma cells [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 C134.