Inhibition of hypoxic response decreases stemness and reduces tumorigenic signaling due to impaired assembly of HIF1 transcription complex in pancreatic cancer

Abstract

Pancreatic tumors are renowned for their extremely hypoxic centers, resulting in upregulation of a number of hypoxia mediated signaling pathways including cell proliferation, metabolism and cell survival. Previous studies from our laboratory have shown that Minnelide, a water-soluble pro-drug of triptolide (anti-cancer compound), decreases viability of cancer cells in vitro as well as in vivo. However, its mechanism of action remain elusive. In the current study we evaluated the effect of Minnelide, on hypoxia mediated oncogenic signaling as well as stemness in pancreatic cancer. Minnelide has just completed Phase 1 trial against GI cancers and is currently awaiting Phase 2 trials. Our results showed that upon treatment with triptolide, HIF-1α protein accumulated in pancreatic cancer cells even though hypoxic response was decreased in them. Our studies showed even though HIF-1α is accumulated in the treated cells, there was no decrease in HIF-1 binding to hypoxia response elements. However, the HIF-1 transcriptional activity was significantly reduced owing to depletion of co-activator p300 upon treatment with triptolide. Further, treatment with triptolide resulted in a decreased activity of Sp1 and NF-kB the two major oncogenic signaling pathway in pancreatic cancer along with a decreased tumor initiating cell (TIC) population in pancreatic tumor.

Long non-coding RNA GAS5 acts as proliferation “brakes” in CD133+ cells responsible for tumor recurrence

“…While they are probably not a population that is responsible for the origin of pancreatic tumors, our previously published study definitely show that they are responsible for therapeutic resistance, tumor initiation at very low dilution as well as extreme metastasis 2, 24, 26 . Our studies further show that this population is enriched upon nutritional deprivation, low dose chemotherapy as well as presence of hypoxia 21, 25, 26 . We and others have shown that CD133+ population are generally slow-cycling or quiescent 2, 6, 36 .…”

“…Similar observation was made in other pancreatic cancer cell line as well (Supplementary Figure 3A, B). Previously published results from our laboratory show that under all these conditions, CD133 expression was upregulated as well 21, 25 . Our previously published work has shown that chemotherapy selected for treatment refractory CD133+ population 25 .…”

“…We and others have shown that hypoxia increases expression and activity of self-renewal proteins like Sox2/Oct4 and Nanog 21 . Similarly, nutritional deprivation as well as chemotherapy also induced expression of Sox2, Oct4 and Nanog expression 25 .…”

“…This population correlated with invasiveness of the pancreatic cancer cells and tumors 24, 25, 27 and was found to be responsible for initiating tumors at very low dilutions 2 . Further, results from our lab showed that this CD133+ population was enriched upon stress conditions like nutritional deprivation, hypoxia as well as chemotherapeutic stress 21, 25, 26 , and was identified as a “tumor initiating cell” even though it was not the cell of origin for pancreatic cancer.…”

“…It is known that availability of nutrients regulates cell proliferation by affecting gene transcription. In this context, CD133+ cells that are typically enriched during hypoxia in pancreatic cancer 21, 25, 26 are nutritionally deprived. Studies have shown that both hypoxia as well as nutritional deprivation can result in quiescence in a cancer cell population leading to “senescence associated stemness” in a select population of tumor cells.…”