Overexpression of heat-shock protein 27 (HSP27) increases gemcitabine sensitivity in human pancreatic cancer cells through cell cycle arrest and apoptosis

Aims: We previously established a role for HSP27 as a prognostic and predictive marker in pancreatic cancer: Tissue-microarray studies showed increased HSP27 expression in pancreatic cancer specimens to be associated with better patient survival, while HSP27 overexpression unexpectedly increased susceptibility specifically towards gemcitabine in a pancreatic cancer cell line model.

Purpose: To further elucidate the underlying mechanisms of HSP27- mediated gemcitabine sensitivity in pancreatic cancer cells.

Methods: Cell cycle analyses (FACS), apoptosis assessment (FACS, nuclear staining, immunoblotting, mitochondrial membrane potential), drug sensitivity studies (proliferation assays).

Results: Upon gemcitabine treatment, stably HSP27-overexpressing cell clones displayed increased cell cycle arrest in S-phase followed by increased apoptosis as compared to isogenic control cells. Apoptosis (˜80%) was quantitatively and qualitatively validated by an increased subG1-fraction, mitochondrial membrane potential loss, caspase activation, upregulation of pro-apoptotic proteins and was blocked through treatment with caspase inhibitors. Additionally, heat shock-induced acute HSP27 upregulation also increased gemcitabine sensitivity in pancreatic cancer cells, amounting to at least additive if not synergistic effects. Interestingly, HSP27-overexpressing cell clones displayed increased sensitivity also towards direct receptor-mediated apoptosis via treatment with TRAIL-receptor targeting agents, establishing more specifically a pro-apoptotic function of HSP27 in pancreatic cancer cells.

Conclusion: In contrast to the well-established anti-apoptotic role of HSP27, our data point at less well-understood pro-apoptotic roles of HSP27 in certain subsets of cancer cells, which could have direct clinical implications: First, HSP27 could represent a predictive marker of therapeutic response and a tool for stratification of pancreatic cancer patients. Second, our data further substantiate the molecular basis for ongoing clinical studies applying the combination of gemcitabine and HSP27-modulating regional hyperthermia for the treatment of pancreatic cancer.