Faculty Mentor: Conan Kinsey (Internal Medicine, University of Utah)

The majority of pancreatic adenocarcinoma (PDAC) cases arise from mutations in KRAS, a GTPase involved in the MAP Kinase (MAPK) pathway. Inhibition of the MAPK pathway upregulates autophagy, a process in which cells recycle their intracellular components to sustain nutrient demands under stressful conditions and can render targeted therapies ineffective. Combining trametinib, a MEK1/2 inhibitor (MEKi), with an autophagy inhibitor such as chloroquine leads to regression in in vivo mouse xenograft experiments as well as a response in a single pancreatic cancer patient (Kinsey et al., 2019). Chloroquine is a relatively weak autophagy inhibitor at FDA approved maximum doses and has many off-target effects. We are searching for drugs that are FDA-approved or in clinical trials and modulate autophagy for potential repurposing in novel combinations for rapid clinical translation. A preliminary FDA- approved drug screen suggested that cyclin-dependent kinase 9 (CDK9) inhibition has an inhibitory effect on autophagy. CDK9 regulates transcription elongation by RNA polymerase-2 and is a negative prognostic marker for PDAC patient outcomes (Kretz et al., 2017). We demonstrate that the CDK9 inhibitors (CDK9i), AZD4573 and BAY1251152, inhibit autophagy in PDAC cell lines expressing an autophagic flux reporter (AFR) to a similar extent as chloroquine. To validate this finding, we used a HiBiT-LC3 autophagy reporter which also demonstrated a potent inhibition of basal and trametinib-induced autophagy in multiple PDAC cell lines. Combination of MAPKi with CDK9i in PDAC AFR cell lines showed that both AZD4573 and BAY1251152 significantly blunt trametinib and KRAS inhibitor-induced autophagy. After determining synergism between trametinib and AZD4573 in vitro, a mouse xenograft pilot was initiated in which mice treated with a combination of trametinib and AZD4573 reached a stable disease phenotype after three weeks. MEKi in combination with CDK9i has potential to be an effective combination treatment and warrants further exploration to determine the most efficacious treatment settings in preclinical models.

Bibliography

Kinsey, C. G., Camolotto, S. A., Boespflug, A. M., Guillen, K. P., Foth, M., Truong, A., Schuman, S. S., Shea, J. E., Seipp, M. T., Yap, J. T., Burrell, L. D., Lum, D. H., Whisenant, J. R., Gilcrease, G. W., Cavalieri, C. C., Rehbein, K. M., Cutler, S. L., Affolter, K. E., Welm, A. L., McMahon, M. (2019). Protective autophagy elicited by RAF→MEK→ERK inhibition suggests a treatment strategy for Ras-driven cancers. Nature Medicine, 25(4), 620–627. https://doi.org/10.1038/s41591-019-0367-9

Kretz, A.-L., Schaum, M., Richter, J., Kitzig, E. F., Engler, C. C., Leithäuser, F., Henne- Bruns, D., Knippschild, U., & Lemke, J. (2017). CDK9 is a prognostic marker and therapeutic target in pancreatic cancer. Tumor Biology, 39(2), 101042831769430. https://doi.org/10.1177/1010428317694304