Abstract 2941: Physiologic epidermal growth factor modeling improves sensitivity of KRASG12Dinhibitor MRTX1133

Abstract Background: Pancreatic Ductal Adenocarcinoma (PDAC) remains a formidable cancer type with a median 5-year survival rate of 13%, largely due to ineffective systemic therapy. MRTX1133 is an emerging small molecule inhibitor of KRASG12D which has been shown to be effective across multiple treatment settings. Epidermal growth factor (EGF) is often integrated at supraphysiologic levels in models of luminal cancer types. Here, we evaluate KRASG12D targeting as a function of EGF supplementation to understand both sensitivity and selectivity across EGFR signaling. Methods: Organoids were seeded in low volume 10uL 96 well plate (Ibidi, Inc) with a density of 500 cells per microliter across experimental groups. Organoids were treated with MRTX1133 in serial dilutions with either standard EGF concentrations (50 ug/mL) or physiological (0.5 ug/mL). Brightfield imaging was captured using time course data from 0h to 144h via Cytation 5. Viability was assessed 144 hours post treatment via Cell-Titer Glo assay, to calculate IC50 of MRTX1133 (n= 8). Response to MRTX1133 was tracked via effect size Glass’s Delta, which is defined by difference between the mean of control and treatment group normalized to the standard deviation of the control. Protein analysis was performed by western blot for MAP kinase effector signaling. Results: Removal of EGF in media lead to growth arrest over the course of 5 weeks (+17.8% v. + 120% in control; GΔ = 0.64 ). Indicating that its addition is required for proper organoid propagation. When established across 5 weeks, physiologic levels of EGF in cultures did not impact the growth of KRASG12D pancreatic organoids (+101.3% v. 102% in control; GΔ = 0.005). However, the use of physiologic EGF had improved sensitivity to MRTX1133 (IC50 0.46± 11.03 nM) when compared to standard media (IC50=33.6±3.40 nM), which shows a 60-fold decrease in sensitivity. At lower concentrations of MRTX1133 (0.5nM), resistance was observed in standard EGF conditions (+133.8% v. +106.4% in control; GΔ = 0.437), in comparison to physiological EGF media which reduced proliferation (+55.8% v. +85.7% in control; GΔ= -0.47). Western blot analysis revealed few changes between standard media conditions and physiologic when probing for effectors in Ras signaling, such as AKT and EGFR. Treatment of MRTX1133 (10nM) over 72 hours, also did not yield improved inhibition at either media conditions. Conclusion: Physiologic EGF stimulation yielded improved sensitivity to MRTX1133 in a manner independent of organoid growth rate. While resistance to MRTX1133 can be observed in organoid models, understanding this as a function of accurate EGF stimulation remains a critical need particularly at informing relevant resistance mechanisms. Future work includes evaluating this across a diversity of KRASG12D cancer models and comparing physiologic EGF across therapeutic screening applications in combination. Citation Format: Lauryn Elise Flannagan, Michela Cadarso, Eleanor Riedl, Md Shahadat Hossan, Ethan S. Lin, Jeremy D. Kratz. Physiologic epidermal growth factor modeling improves sensitivity of KRASG12Dinhibitor MRTX1133 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2941.