Abstract 1929: Acquired resistance to sotorasib in KRASG12C mutant NSCLC is vulnerable to PI3K-mTOR pathway inhibition and regulated by 4E-BP1

Abstract Up to 40% of NSCLC patients with KRASG12C mutation respond to sotorasib. However, acquired resistance (AR) develops rapidly in all patients. The majority of AR is associated with unknown mechanisms. Twelve KRASG12C mutant NSCLC PDXs were developed from patient samples and characterized with WES, RNAseq, and RPPA analyses. Three PDXs treated with sotorasib showed complete tumor regression, and one showed growth inhibition. PDXs, PDX derived organoids (PDXO), and cell line derived xenografts (CDX) were with AR to sotorasib were generated. TC303AR and TC314AR PDXs were generated by prolonged continuous in-vivo treatment with sotorasib. Two isogeneic AR PDXOs from TC303 and TC314 PDXs were generated through continuous incremental dosing of sotorasib in organoid cultures. Both TC303AR and TC314AR PDXOs showed 100-fold resistance than sensitive counterparts. Over 100-fold resistance were also measured in two sotorasib resistant isogenic H23AR and H358AR cell lines. Both resistant PDXOs and cell lines showed resistance to adagrasib, another selective, KRASG12C inhibitor. H358AR CDXs were generated through continuous in-vivo treatment with sotorasib and multiple passages of CDX tissues. WES was performed for AR PDXs, CDX, PDXOs and cell lines and all retained the KRASG12C mutation, and no additional KRAS mutations were found. We performed RNAseq, RPPA, and mass spectrometry (MS) on TC303AR and TC314AR PDXs. Heatmaps showed significant sets of differentially regulated RNA and protein in AR vs. parental. Enrichment analysis found a significant upregulation of MTORC1 signaling in AR PDXs. Proteins involved in PI3K-AKT-mTOR pathway were significantly upregulated in AR. PI3K and AKT expression were also increased in H23AR and H358AR. Inhibition of PI3K, AKT and mTOR by copanlisib, MK2206 and everolimus respectively was synergistic with sotorasib in AR cells and PDXOs, with copanlisib being the most effective. Copanlisib significantly inhibited colony formation in AR cells. Downstream molecules in PI3K-AKT-mTOR pathway showed marked downregulation of pAKT, pmTOR, p70S6, pS6, pGSK3b, and pPRAS40 by copanlisib. The downstream 4E-BP1 and p4E-BP1 were remarkably high in AR cells, which was downregulated by copanlisib. To verify the role of PI3K, PI3Kα CRISPR-Cas9 knock-out clones were generated in both H23AR and H358AR cells. Absence of p4E-BP1 was associated with restoration of sotorasib sensitivity while high levels of p4E-BP1 phosphorylated by an mTOR independent pathway restored sotorasib resistance in the knock-out clones. When copanlisib was combined with sotorasib in treating the resistant TC303AR, TC314AR PDXs, H358AR CDX and H23AR xenograft tumors, antitumor effects were observed in every model. Inhibition of the PI3K pathway at different nodes is a vulnerability in KRASG12C mutant NSCLC with sotorasib AR and p4E-BP1 is a mediator of sotorasib resistance Citation Format: Ismail M. Meraz, Shuhong Wu, Mourad Majidi, Chenghui Ren, Yi Xu, Feng Meng, Lihui Gao, Renduo Song, Ran Zhang, Bingliang Fang, Qi Wang, Yuanxin Xi, Jing Wang, Sung Yun Jung, Jack A. Roth. Acquired resistance to sotorasib in KRASG12C mutant NSCLC is vulnerable to PI3K-mTOR pathway inhibition and regulated by 4E-BP1 abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1929.