Date of Award

Spring 4-23-2026

Embargo Period

4-23-2028

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Molecular and Cellular Biology and Pathobiology

College

College of Graduate Studies

First Advisor

Robin Muise-Helmericks

Second Advisor

G. Aaron Hobbs

Third Advisor

Tim Barnoud

Fourth Advisor

Casey Langdon

Abstract

KRAS is mutated in approximately 95% of pancreatic ductal adenocarcinoma (PDAC) cases, with the most frequent alterations occurring at glycine 12, including G12D (42%), G12V (31%), and G12R (15%). Standard PDAC treatment relies on cytotoxic chemotherapy regimens such as FOLFIRINOX; however, clinical outcomes remain poor, with 5-year survival near 13%. Recently, direct RAS targeting therapies have emerged, including daraxonrasib. Although patients initially respond to daraxonrasib, clinical data indicate that resistance develops within approximately one year, underscoring the need for combination strategies that improve efficacy and limit resistance.

To investigate mechanisms of resistance, we developed an isogenic model derived from a human pancreatic cancer cell line engineered to express KRAS G12D or G12R. This system revealed mutation specific resistance mechanisms: in PANC1G12R, upregulation of the receptor tyrosine kinase EGFR drove resistance. Consistent with this model, blockade of SOS1, a RAS guanine exchange factor capable of activating wildtype RAS, attenuated MAPK signaling selectively in G12D cell lines. We further demonstrated that PANC1G12R cells do not activate wildtype RAS, suggesting that the G12R mutant lacks the ability to transactivate wildtype isoforms.

To determine whether these mechanisms were conserved across PDAC, we generated daraxonrasib resistant PDAC cell lines through continuous drug exposure. In contrast to the isogenic models, all established PDAC lines developed resistance through increased activation of wildtype RAS isoforms, independent of KRAS mutation status. Suppression of HRAS and NRAS using siRNA induced compensatory upregulation of KRAS in both G12D and G12R mutants, indicating that human PDAC cell lines do not acquire mutation specific resistance mechanisms to daraxonrasib.

Finally, we examined the role of receptor tyrosine kinases in mediating resistance. Genetic knockout of IGF1R, as well as pharmacologic inhibition of IGF1R, increased MAPK signaling and promoted resistance across PDAC models. Together, these findings identify mutation independent resistance mechanisms and highlight compensatory MAPK activation as a key driver of resistance to panRAS inhibition.

Rights

Copyright is held by the author. All rights reserved.

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Available for download on Sunday, April 23, 2028

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