S. P. O’Hare1, H. Guo1, B. Herring1, J. B. Rose1,2, H. Chen1,2, B. Ren1,2 1University Of Alabama at Birmingham, Department Of Surgery, Heersink School of Medicine, Birmingham, Alabama, USA 2University Of Alabama at Birmingham, O’Neal Comprehensive Cancer Center, Heersink School Of Medicine, Birmingham, Alabama, USA
Introduction: Pancreatic neuroendocrine tumors (pNETs) are heterogeneous neoplasms with robust angiogenic behavior. mTOR pathway targeting is second-line therapy for advanced pNETs but tumors develop chemoresistance, with cancer stem-like cells (CSCs) playing a major potential role. CD36, a membrane glycoprotein that mediates fatty acid (FA) metabolism, contributes to chemoresistance, and drives stem-like features in cancer cells. We hypothesize that CD36-mediated FA metabolism confers stem-like features in pNETs.
Methods: Immunohistochemistry of human pNET tissue microarrays (TMAs) was used to evaluate the association of CD36 expression with pNET progression. TMA samples were also imaged at magnified levels to identify individual cells with differential CD36 staining, and CD36 staining intensity was quantified at the single-cell level using NIH ImageJ. Drug-resistant BON cells (DR-BON) were developed via long-term exposure to an mTOR inhibitor. Lentiviral transduction of CD36 shRNAs and RT-qPCR were used to evaluate the association of CD36 with stem-like features. The association of CD36-mediated metabolic reprogramming with CSCs was studied by FA treatment and inhibition of FA oxidation with/without CD36 knockdown. Finally, BON cell invasion assays were used to evaluate functional endpoints in response to CD36-mediated FA oxidation.
Results: CD36 expression was positively associated with tumor grade upon TMA analysis (r = 0.263, p = 0.05), and tumor cells with high CD36 expression were more abundant near blood vessels and tumor nest borders than in tumor nest interiors (p < 0.001). Additionally, DR-BON cells exhibited increased expression of a CSC gene signature compared to the wild-type BON cells. Treatment of DR-BON cells with FAs demonstrated further upregulation of CSC-related genes. However, CD36 knockdown attenuated the CSC gene signature. Finally, inhibition of CD36-mediated FA oxidation reduced the relative number of invasive DR-BON cells.
Conclusion: CD36-mediated FA oxidation is critical for CSC features and may contribute to mTOR drug resistance and pNET progression.