Clinical significance of MUC4 isoforms in pancreatic cancer patients.

Abstract

742 Background: Pancreatic adenocarcinoma (PC) is a highly aggressive cancer with a 5-year survival rate around 9% with majority of patients diagnosed at advanced stage. Prior studies describe transcriptomic alterations during tumorigenesis, of which novel and progressive expression of mucins are significant. Mucins are large secreted or membrane-tethered glycoproteins that have been shown to be of pathogenic importance in PC. Methods: We explored differential expression and survival outcomes based on mucin expression using TCGA PC patients (n = 150). RNA-Seq. reads were realigned to all known mucin splice variant (SV) sequences. Hazard ratios (HR) were calculated for all SVs (n = 123), and SVs with significant HRs were plotted on Kaplan-Maier survival curves comparing expression about the median. The MUC4 SV (MUC4Δ6) was selected for validation in patient tumor samples (n = 17) due to PC tumor cell-specific expression and in-frame deletion of a single exon. After discovery of significant mucin SVs, we designed a gold-nanoparticle (GNP) assay to specifically detect MUC4Δ6 in circulation from PC patient plasma. Results: In the absence of significant mucin-based survival differences, we expanded our analysis to include mucin SV transcripts. Through hazard and survival analyses, we identified 3 MUC1 SVs with better survival (SV1 HR = .61, p = .033; SV2 HR = .64, p = .05; SV3 HR = .62, p = .04), and one each of MUC4 (HR = 1.93, p = .028) and MUC16 (HR = 1.90, p = .027) with worse prognosis. In a validation cohort, we found 10 samples had a high cellularity (HC) gene signature. Expression of MUC4Δ6 was 4804.7 copies/100,000 GPI copies in the HC population and expressors above the median had a median survival of 397 days compared to1964.5 days (p = .191) in low expressors. Our novel GNP assay detected MUC4∆6 transcripts at minimum concentrations of 100 fM with a synthetic RNA. Uniquely, our assay detects the MUC4∆6 SV but not wild-type variant. Conclusions: We were able to determine that expression of specific mucin SV are prognostic in PC patients. We developed technology to detect MUC4Δ6 transcript in circulation using a novel GNP assay. Future studies will seek to stabilize the nanoparticles and modify them for potential diagnostic purposes in a clinical setting.