Abstract B050: ERK1 splicing switch triggers lethal hyperactivation and overcomes KRAS inhibitor resistance in pancreatic cancer
Luisa F. Escobar-Hoyos, Md Siraj Afjalus, Deanne Yugawa, Gilbert Giri, Ching Siang Ong, Priyabrata Mukherjee, Resham Bhattacharya, Daniel DominguezAbstract
Background:
Pancreatic ductal adenocarcinoma (PDAC) is projected to become the second leading cause of cancer death in the United States by 2040. Oncogenic KRAS, present in ∼90% of PDACs, drives tumor growth through MAPK signaling and ERK1/2 activation. While pan-RAS and mutant-selective KRAS inhibitors can produce initial responses, most tumors develop resistance within 6–12 months, frequently through ERK1/2 reactivation via both genetic and non-genetic mechanisms. Direct ERK inhibition has been limited by toxicity and the high similarity between ERK1 and ERK2, motivating alternative strategies. We identified an ERK1-specific regulatory “switch” in which alternative splicing generates a hyperactive ERK1 isoform that is intrinsically lethal to PDAC cells.
Methods:
Deep RNA-seq was performed in PDAC cells with experimentally altered expression of the splicing factor SMNDC1 (overexpressed in ∼16% of PDACs). This revealed an ERK1 transcript lacking exon 4 (E4), which encodes the activation loop. We defined biological and mechanistic differences between canonical ERK1 and the E4-skipped isoform using gain- and loss-of-function studies, biochemical assays, and in silico structural analyses, coupled with manipulation of SMNDC1. To test therapeutic relevance in KRAS-inhibitor resistance, we targeted SMNDC1 with novel degraders and enforced ERK1 E4 skipping using exon 4 splice-switching oligonucleotides (E4-SSOs). Antitumor activity was evaluated in mice bearing orthotopic PDAC tumors with acquired resistance to multiple next-generation KRAS inhibitors using a systemic delivery approach optimized for PDAC.
Results:
SMNDC1 promoted oncogenic signaling and tumor growth by favoring ERK1 E4 inclusion, preserving the full activation loop. Enforcing E4 skipping with splice-switching morpholinos/SSOs suppressed tumor growth. Mechanistically, E4 exclusion produced an alternative ERK1 isoform that retained a bilobular kinase structure despite lacking the activation loop and was constitutively active, with ∼2-fold higher activity than canonical ERK1. This hyperactive isoform was tightly constrained by proteasome-dependent degradation, and its expression triggered PDAC cell death. Therapeutically, inducing E4 exclusion—via SMNDC1 degradation or E4-SSOs—reduced tumor burden and approximately doubled survival in orthotopic models with acquired resistance to next-generation KRAS inhibitors.
Conclusions:
Reprogramming ERK1 splicing to enforce exon 4 skipping induces a lethal hyperactive ERK1 state and overcomes KRAS-inhibitor resistance in PDAC. Targeting this ERK1 splicing switch may offer a distinct therapeutic strategy for PDAC and other RAS/MAPK-driven malignancies.
Citation Format:
Luisa F. Escobar-Hoyos, Md Siraj Afjalus, Deanne Yugawa, Gilbert Giri, Ching Siang Ong, Priyabrata Mukherjee, Resham Bhattacharya, Daniel Dominguez. ERK1 splicing switch triggers lethal hyperactivation and overcomes KRAS inhibitor resistance in pancreatic cancer [abstract]. In: Proceedings of the AACR Conference on Pancreatic Cancer: New Frontiers in Biology and Therapeutic Development; 2026 Sep 25-28; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(18_Suppl_2):Abstract nr B050.