George Kulik Lab
Research in my laboratory is focused on signal transduction mechanisms that protect prostate cancer cells from apoptosis. This information is necessary to design more effective therapies for advanced prostate cancer and other therapy-resistant cancers.
Recently, we have identified BAD as a convergence point of several anti-apoptotic pathways downstream from PI3K/Akt, EGFR, and GPCRs (Fig. 1). Detailed analysis of these signaling pathways revealed a complex network of remarkable redundancy that connects signals from the tumor microenvironment with BAD phosphorylation.
These findings have formed a foundation for several research projects described below.
1. Emotional stress and prostate cancer.
Almost two millennia ago, Galen observed that emotional stress may lead to cancer. However, results of modern-day epidemiological studies that address the connections between stress and cancer remain controversial. This controversy is largely due to the lack of mechanistic understanding of how stress could influence tumor development and therapy resistance.
While analyzing the anti-apoptotic network in prostate cancer, we have found that epinephrine (at concentrations observed after chronic emotional stress) protects prostate cancer cells from apoptosis via the PKA/BAD mechanism. Recent experiments show that injections of epinephrine or emotional stress counteract the anti-tumor effects of PI3K inhibitors on prostate cancer xenografts in mice. Based on these observations, we hypothesize that emotional stress activates anti-apoptotic signaling in prostate cancer cells and, as a result, contributes to the progression of prostate cancer and resistance of advanced prostate cancer to therapies. If this hypothesis is confirmed, it will provide a mechanistic explanation for the connection between emotional stress and cancer.
The project will be developed in the following directions: a) prostate cancer xenografts and a transgenic mouse model of prostate cancer will be used to test the role of emotional stress and depression in cancer development and therapeutic sensitivity; b) the signaling pathways activated by stress hormones and their role in apoptosis regulation will be analyzed; and c) stress hormone levels in prostate cancer patients and their responses to therapies will be assessed.
2) The role of BAD phosphorylation in prostate tumor development in vivo.
Use of a prostate cancer xenograft model and genetically modified mice are proposed in these experiments. For experiments with xenograft tumors, we generated C42Luc prostate cancer cells that express firefly luciferase and either wild-type BAD or BAD2SA with mutated phosphorylation sites. Growth of C42Luc xenografts was followed in live mice by noninvasive optical imaging. To test the role of BAD phosphorylation in mouse models of prostate cancer, genetically modified mice in which endogenous BAD is replaced by mutant BAD3SA (BAD3SA knock-in mice) will be bred with mice that develop prostate cancer due to prostate-restricted expression of PTENp-/- or c-myc. If expression of phosphorylation-deficient BAD prevents prostate cancer development, then signaling pathways that control BAD are plausible targets for anti-cancer therapy. Subsequent efforts will be focused on identification of kinases that control BAD in prostate cancer cells and testing effects of inhibition of these kinases on tumor growth.
3) Prostate tumor-targeted kinase inhibitors.
This interdisciplinary project provides a unique training opportunity by including all stages of drug discovery: computer modeling of drug-enzyme interaction (with biophysicist Dr. Freddie Salsbury), chemical synthesis of candidate drugs (with chemist Dr. Mark Welker); in vitro and invivo testing of synthesized drugs in mouse models of prostate cancer (with Dr. George Kulik). The goal is to synthesize prostate tumor-specific inhibitors of signaling pathways that control BAD phosphorylation and apoptosis. Prostate tumor specificity will be achieved by a) generating an inactive pro-drug activated by prostate tumor-secreted protease (PSA); and b) targeting pro-drug to prostate tumors by prostate-specific antibodies. Computer modeling will be used to analyze interactions between activated pro-drugs and target kinases; candidate pro-drugs selected based on this modeling will be synthesized and tested in vitro and in vivo using luminescent xenografts models of prostate cancer.