Abstract 2792: Impact of hypoxia on tyrosine kinase activation in cancer cells
Authors: Dai Yao , Siemann Dietmar 
Published: July 2016

Purpose: Metastasis is the major cause of therapeutic failure and high mortality in cancer patients. Growing evidence has demonstrated that dysregulated intracellular tyrosine kinase (TK) activity can play an important role in promoting disease onset and progression, while low oxygen tensions (hypoxia) are a typical external driving force that facilitates tumor cell dissemination. However, whether hypoxia-induced metastasis is mediated by TK-signaling is largely unknown. In this study, we have identified potential TK(s) that can mediate hypoxia-induced cell functions associated with metastasis, and further determine the therapeutic potential of small molecule TK inhibitors in intervening these functional behaviors.

Methods: Cancer cells were exposed to low oxygen tensions (1% O2) for varied durations (0, 2, 6, 24 h), with or without treatment of desired molecular agents. To test cellular phenotypes, cells were seeded into appropriate culture vehicles and cell migration and invasion will be examined by scratch and transwell-based assays. At the molecular level, pan-TKs phosphorylation in malignant versus normal cells, as well as in cancer cells with or without hypoxic exposure were detected by Western blotting. To further investigate the association of p-Src and HIF-1α in patient tissues, tissue microarray (TMA) with prostate cancer patients was conducted by immunohistochemical staining followed by independent quantification on the H-score of the two proteins.

Results: TK phosphorylation in cancer cells is generally stronger than in normal cells. Similar observation is found in patient tumor tissues versus adjacent normal counterparts. When exposing cells to hypoxia, short term hypoxic exposure (2-6 h) generally induces greater cell migration and invasion than prolonged hypoxic exposure (24 h). Such functional behaviors tend to be associated with elevated tyrosine kinome activation, although the exact TKs in different cell lines may vary. Subsequent kinome screening reveals that the well-known oncoprotein c-Src is activated under particularly acute hypoxia. Further, small molecule inhibitors targeting these TKs have shown stronger inhibition on cell migration and invasion under hypoxia than normoxia. Finally, TMA analysis suggests that p-Src expression is significantly associated with HIF-1α particularly in prostate cancer patients with advanced disease.

Conclusion: The data reveal that short term hypoxia is able to enhance metastasis-associated phenotypes by activating a group of TKs such as p-Src. In addition, Src inhibitors are showing higher potential in impeding hypoxia-induced functional behaviors. These findings suggest that at least in some cancers over-activated TKs can be used as indirect markers for hypoxia and more importantly, molecular agents targeting hypoxia-activated TKs may hold therapeutic potential to prevent metastatic spread of cancer cells that have experienced particularly short-term oxygen depletion.

Citation Format: Yao Dai, Dietmar Siemann. Impact of hypoxia on tyrosine kinase activation in cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2792.