R. Marayati1, M. Anderson1,2, J. Yeh1,2,3,4 1University Of North Carolina At Chapel Hill,Lineberger Comprehensive Cancer Center,Chapel Hill, NC, USA 2University Of North Carolina At Chapel Hill,School Of Medicine,Chapel Hill, NC, USA 3University Of North Carolina At Chapel Hill,Department Of Surgery,Chapel Hill, NC, USA 4University Of North Carolina At Chapel Hill,Department Of Pharmacology,Chapel Hill, NC, USA
Introduction: Over half of all pancreatic cancer patients initially present to the clinic with metastatic disease and the 5-year overall survival rate for this cohort is less than 2%. Treatment options for these patients are limited, as they are not candidates for surgery and often prove to be unresponsive to chemotherapy. Current research efforts are, therefore, focused on understanding tumor biology with the goal of identifying new targets for therapy. Previous work in a genetically engineered mouse model of pancreatic cancer showed anabolic glucose metabolism to be essential for primary tumor growth. Hexokinase 2 (HK2) is a key enzyme necessary for glucose uptake and processing that is commonly dysregulated in solid tumors. We aimed to assess the role of HK2 in promoting pancreatic cancer tumor growth and metastasis.
Methods: Microarray gene expression data was analyzed from 149 primary and 61 metastatic pancreatic cancer tumors, and 47 normal pancreatic samples. Pancreatic cancer cell lines were stably transfected with doxycycline-inducible lentiviral shRNA constructs targeting either HK2 (shHK2) or a nonspecific control (shNS). Subcutaneous and tail vein injections of these lines were performed to monitor primary tumor growth and metastasis, respectively. Mice were treated with either doxycycline, to induce shRNA expression, or vehicle. Tumor growth was assessed biweekly using caliper measurements for 30 days of treatment, and mice were examined for lung metastasis using bioluminescence for 6 weeks after tail vein injection.
Results: HK2 was significantly upregulated in both primary and metastatic pancreatic tumors relative to normal pancreas. Kaplan-Meier survival analysis showed that patients with high expression of HK2 in primary pancreatic tumors had a significantly worse overall survival (13 vs 21 months, p=0.033). Mice subcutaneously injected with shHK2 and treated with doxycycline to induce HK2 knockdown (n=9) had a significant decrease in tumor volume compared to those treated with vehicle (n=8, p=0.049). This tumor growth inhibition was not observed with the induction of shNS expression (shNS doxycycline vs. vehicle, p=0.339), suggesting that HK2 expression is necessary for primary tumor growth in vivo. Furthermore, HK2 knockdown impaired the formation of lung metastasis. All control mice with tail vein injections of nonspecific shNS (n=7) developed lung metastasis during the six-week period, while only 2 out of 9 mice with HK2 knockdown developed metastasis (p=0.003).
Conclusion: Our results show that glycolytic enzyme HK2 has decreased expression in normal pancreas and is upregulated in pancreatic tumors. Furthermore, increased HK2 expression is associated with a poor clinical prognosis. In vivo studies support an important role for this gene in promoting both primary tumor growth and metastasis. Together, these results suggest HK2 may represent a good therapeutic target for the treatment of pancreatic cancer.