3080 - Translational Relevance of SOX2 and OCT4 as Mediators of Treatment Resistance in Pancreatic Cancer

05:00pm - 06:00pm PT

Hall F

Screen: 23

POSTER

Presenter(s)

Zachery Keepers, BS - University of Maryland School of Medicine, Baltimore, MD

Z. Keepers¹, S. Roy¹, H. Ryan III¹, B. Bhandary¹, N. Lamichhane², F. Carrier¹, J. K. Molitoris¹, W. F. Regine Jr¹, and H. D. Shukla¹; ¹Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, ²Department of Radiation Oncology, University of Maryland Medical Center, Baltimore, MD

Purpose/Objective(s):

SOX2 and OCT4 are transcription factors that contribute to stemness in pancreatic cancer (PC). We’ve previously shown changes in the expression of these markers in patient-derived pancreatic tumor organoids (PTOs) following treatment with radiation (RT), chemotherapies, and chemo-RT. Here, we aimed to clarify the clinical implications and molecular changes associated with altered expression of SOX2 and OCT4 in PC. We hypothesize that aberrant expression of SOX2 and OCT4 promotes aggressive phenotypes and resistance to therapies in pancreatic cancer.

Materials/Methods:

We used The Cancer Genome Atlas (TCGA) database to identify PC samples (n = 177) with amplifying mutations or upregulated mRNA expression (z-score threshold > 2.0) of SOX2 or OCT4. These samples were categorized as “altered.” Transcriptome, proteome, and clinical profiles of altered groups were compared to unaltered groups. Findings prompted further evaluation with patient-derived pathology specimens and PTOs.

Three PC pathology specimens with normal tissue controls were DAB-stained for SOX2 and OCT4. Representative images were obtained using an ECHO Revolution microscope and stain density was quantified by ImageJ. Tumor organoids from three additional patients were treated with patient-specific IC50 doses of FOLFIRINOX, gemcitabine + paclitaxel, RT, and chemo-RT. Immunoblot was performed using SOX2 and OCT4 antibodies. RNA was obtained with RNeasy Mini Kit, and sequencing was performed on NovaSeq X Plus Series (PE150).

Results:

In TCGA, expression of SOX2 and OCT4 were upregulated in 7% and 4% of patients, respectively. Analysis of these patients' transcriptome profiles revealed significantly increased expression of genes known to confer properties of stemness and several genes with unclear roles in PC. Patients with increased SOX2 showed upregulation of GBP3 (p = 1.80e-15), and increased OCT4 conferred upregulation of PSORS1C2 (p = 5.9e-14) and ELMO3 (p = 5.08e-11). Proteome analysis revealed significant changes (p < 0.05) in CDH and TFRC for SOX2-altered patients and CDKN1B, EGFR, and SMAD4 for OCT4-altered patients. Patients with SOX2 amplification mutations showed a decreased overall survival approaching significance (p = 0.079).

DAB-staining showed significantly increased and heterogeneous expression of SOX2 and OCT4 in tumor vs normal tissues. Moreover, tumor tissues with high expression of SOX2 had more aggressive pathology. Immunoblots showed increased expression of SOX2 and OCT4 in PTOs after RT, and the degree of increase varied across organoids. The expression of both markers was greatest 72 hours post-RT.

Conclusion:

Altogether, these results suggest SOX2 and OCT4 are aberrantly expressed in PC and may contribute to treatment resistance and poor outcomes. Further exploration of relevant pathways and newly identified genes implicated by TCGA analysis is warranted. These will be of particular focus in the analysis of RNAseq data.