Altered cholesterol metabolism in human cancers unraveled by label-free spectroscopic imaging
Despite tremendous scientific achievements, cancer remains the second leading cause of death in the United States. Metabolic reprogramming has been increasingly recognized as a core hallmark of cancer. My dissertation work identified novel diagnostic markers and therapeutic targets for human cancers through the study of cholesterol in cancer cells. ^ Enabled by label-free Raman spectromicroscopy, we performed the first quantitative analysis of lipogenesis at single cell level in human patient cancerous tissues. Our imaging data revealed an unexpected, aberrant accumulation of esterified cholesterol in lipid droplets of high-grade prostate cancer and metastases, but not in normal prostate, benign prostatic hyperplasia, or prostatitis. Biochemical and molecular biological studies showed that such cholesteryl ester accumulation was a consequence of loss of tumor suppressor PTEN and subsequent activation of PI3K/AKT pathway in prostate cancer cells. Furthermore, we found that such accumulation arose from significantly enhanced uptake of exogenous lipoproteins and required cholesterol esterification. Depletion of cholesteryl ester storage using pharmacological inhibitors or RNA interference significantly reduced cancer proliferation, impaired cancer invasion capability, and suppressed tumor growth in mouse xenograft models with negligible toxicity. These findings open new opportunities for diagnosing and treating late-stage prostate cancer by targeting the altered cholesterol metabolism. ^ My thesis work also found that cholesterol-rich domains on plasma membranes can be used as a marker for the loss of basoapical polarity, one of the earliest changes observed in breast neoplasia. Raman microspectroscopy revealed that in polarized acini lipids were more ordered at the apical membranes compared to basal membranes, and that an inverse situation occurred in acini that lost apical polarity upon treatment with Ca2+-chelator EGTA. This method allowed us to detect the disruption of apical polarity by dietary breast cancer risk factor, &ohgr;6 fatty acid, even when the effect was too moderate to permit a conclusive assessment by traditional immunostaining method. Collectively, label-free Raman analysis of cholesterol-rich membrane domains in mammary acini provides an effective screening platform to identify risk factors that initiate breast cancer.^
Ji-Xin Cheng, Purdue University.
Engineering, Biomedical|Physics, Optics|Health Sciences, Oncology