Unbiased analysis of pancreatic cancer radiation resistance reveals cholesterol biosynthesis as a novel target for radiosensitisation

Abstract

Background:Despite its promise as a highly useful therapy for pancreatic cancer (PC), the addition of external beam radiation therapy to PC treatment has shown varying success in clinical trials. Understanding PC radioresistance and discovery of methods to sensitise PC to radiation will increase patient survival and improve quality of life. In this study, we identified PC radioresistance-associated pathways using global, unbiased techniques.Methods:Radioresistant cells were generated by sequential irradiation and recovery, and global genome cDNA microarray analysis was performed to identify differentially expressed genes in radiosensitive and radioresistant cells. Ingenuity pathway analysis was performed to discover cellular pathways and functions associated with differential radioresponse and identify potential small-molecule inhibitors for radiosensitisation. The expression of FDPS, one of the most differentially expressed genes, was determined in human PC tissues by IHC and the impact of its pharmacological inhibition with zoledronic acid (ZOL, Zometa) on radiosensitivity was determined by colony-forming assays. The radiosensitising effect of Zol in vivo was determined using allograft transplantation mouse model.Results:Microarray analysis indicated that 11 genes (FDPS, ACAT2, AG2, CLDN7, DHCR7, ELFN2, FASN, SC4MOL, SIX6, SLC12A2, and SQLE) were consistently associated with radioresistance in the cell lines, a majority of which are involved in cholesterol biosynthesis. We demonstrated that knockdown of farnesyl diphosphate synthase (FDPS), a branchpoint enzyme of the cholesterol synthesis pathway, radiosensitised PC cells. FDPS was significantly overexpressed in human PC tumour tissues compared with healthy pancreas samples. Also, pharmacologic inhibition of FDPS by ZOL radiosensitised PC cell lines, with a radiation enhancement ratio between 1.26 and 1.5. Further, ZOL treatment resulted in radiosensitisation of PC tumours in an allograft mouse model.Conclusions:Unbiased pathway analysis of radioresistance allowed for the discovery of novel pathways associated with resistance to ionising radiation in PC. Specifically, our analysis indicates the importance of the cholesterol synthesis pathway in PC radioresistance. Further, a novel radiosensitiser, ZOL, showed promising results and warrants further study into the universality of these findings in PC, as well as the true potential of this drug as a clinical radiosensitiser.

The Landscape of Prognostic Outlier Genes in High-Risk Prostate Cancer

“…In addition, SMC4/condensin interacts with the genomic transcriptional insulator CTCF, and thus may be required for oncogenic gene silencing (48). SQLE is a cholesterol biosynthesis enzyme that has been implicated in several cancers other than prostate, and, interestingly, is located in the chromosome 8q24 Myc oncogene amplicon (49)(50)(51). SQLE knockdown had an impact in LNCaP-AR but not DU145 cells, which is likely reflective of the much more significant role of steroid hormone signaling in LNCaP-AR cells.…”

Squalene epoxidase (SQLE) promotes the growth and migration of the hepatocellular carcinoma cells

“…Dysregulation of SQLE has been observed in several cancer types, including breast cancer, lung cancer, and colorectal cancer [11][12][13][14][15]. However, the expression profile and the function of SQLE in hepatocellular carcinoma remain largely unknown.…”

“…Frequent Myc gene amplification and DNA hypomethylation of SQLE promoter were observed in aggressive breast cancer and indicated poor outcome [11]. Also, SQLE and other genes involved in cholesterol biosynthesis were important for the radioresistance in pancreatic cancer [12,13]. In colorectal cancer, low expression level of SQLE was associated with a better prognosis in patients [14].…”

MUC1-Mediated Metabolic Alterations Regulate Response to Radiotherapy in Pancreatic Cancer

“…Colonies containing >50 cells for each well were counted (in triplicate). Surviving fraction at each dose was determined by using the formula: [(number of surviving colonies in dose X)/(number of cells seeded for dose X (average colonies arising from the non-irradiated cells (0Gy)/number of non-irradiated cells seeded)] (25). …”