Functional Genome-wide Screening Identifies Targets and Pathways Sensitizing Pancreatic Cancer Cells to Dasatinib.

This study is an unbiased genomic screen to obtain functional targets for increased effectiveness of dasatinib in pancreatic cancer. Dasatinib, a multi-targeted tyrosine kinase inhibitor, is used in clinical trials for treatment of pancreatic cancer; however, intrinsic and acquired resistance often occurs. We used a dasatinib-resistant pancreatic cancer cell line SU8686 to screen for synthetic lethality that synergizes with dasatinib using a pooled human shRNA library followed by next generation sequencing. Novel genes were identified which when silenced produced a prominent inhibitory effect with dasatinib against the pancreatic cancer cells. Several of these genes are involved in the regulation of epigenetics, as well as signaling pathways of the FOXO and hedgehog families. Small molecule inhibitors of either histone deacetylases or nuclear exporter had marked inhibitory effect with dasatinib in pancreatic cancers, suggesting their potential therapeutic effectiveness in this deadly cancer.

Activation of protein phosphatase 2A tumor suppressor as potential treatment of pancreatic cancer.

We utilized three tiers of screening to identify novel therapeutic agents for pancreatic cancers. First, we analyzed 14 pancreatic cancer cell lines against a panel of 66 small-molecule kinase inhibitors and dasatinib was the most potent. Second, we performed RNA expression analysis on 3 dasatinib-resistant and 3 dasatinib-sensitive pancreatic cancer cell lines to profile their gene expression. Third, gene profiling data was integrated with the Connectivity Map database to search for potential drugs. Thioridazine was one of the top ranking small molecules with highly negative enrichment. Thioridazine and its family members of phenothiazine including penfluridol caused pancreatic cancer cell death and affected protein expression levels of molecules involved in cell cycle regulation, apoptosis, and multiple kinase activities. This family of drugs causes activation of protein phosphatase 2 (PP2A). The drug FTY-720 (activator of PP2A) induced apoptosis of pancreatic cancer cells. Silencing catalytic unit of PP2A rendered pancreatic cancer cells resistant to penfluridol. Our observations suggest potential therapeutic use of penfluridol or similar agent associated with activation of PP2A in pancreatic cancers.

Growth inhibition of pancreatic cancer cells by histone deacetylase inhibitor belinostat through suppression of multiple pathways including HIF, NFkB, and mTOR signaling in vitro and in vivo.

Pancreatic ductal adenocarcinoma is a devastating disease with few therapeutic options. Histone deacetylase inhibitors are a novel therapeutic approach to cancer treatment; and two new pan-histone deacetylase inhibitors (HDACi), belinostat and panobinostat, are undergoing clinical trials for advanced hematologic malignancies, non-small cell lung cancers and advanced ovarian epithelial cancers. We found that belinostat and panobinostat potently inhibited, in a dose-dependent manner, the growth of six (AsPc1, BxPc3, Panc0327, Panc0403, Panc1005, MiaPaCa2) of 14 human pancreatic cancer cell lines. Belinostat increased the percentage of apoptotic pancreatic cancer cells and caused prominent G2 /M growth arrest of most pancreatic cancer cells. Belinostat prominently inhibited PI3K-mTOR-4EBP1 signaling with a 50% suppression of phorphorylated 4EBP1 (AsPc1, BxPc3, Panc0327, Panc1005 cells). Surprisingly, belinostat profoundly blocked hypoxia signaling including the suppression of hypoxia response element reporter activity; as well as an approximately 10-fold decreased transcriptional expression of VEGF, adrenomedullin, and HIF1α at 1% compared to 20% O2 . Treatment with this HDACi decreased levels of thioredoxin mRNA associated with increased levels of its endogenous inhibitor thioredoxin binding protein-2. Also, belinostat alone and synergistically with gemcitabine significantly (P = 0.0044) decreased the size of human pancreatic tumors grown in immunodeficiency mice. Taken together, HDACi decreases growth, increases apoptosis, and is associated with blocking the AKT/mTOR pathway. Surprisingly, it blocked hypoxic growth related signals. Our studies of belinostat suggest it may be an effective drug for the treatment of pancreatic cancers when used in combination with other drugs such as gemcitabine.