Novel strategies for prevention of prostate cancer are highly desirable because of high mortality associated with this malignancy in American men. During the funded period of this grant, we showed that garlic constituent diallyl trisulfide (DATS) selectively inhibits growth of cultured human prostate cancer cells by causing apoptosis regardless of their androgen responsiveness or the p53 status. We also demonstrated, for the first time, that oral DATS administration not only retards growth of PC-3 human prostate cancer xenografts in athymic mice but also offers significant protection against prostate cancer development in a transgenic mouse model (TRAMP) without any signs of overt toxicity. Furthermore, we discovered that the DATS-mediated proapoptotic signal transduction in prostate cancer cells is intimately linked to the production of reactive oxygen species (ROS) due to ferritin (light chain) degradation and an increase in labile (chelatable) iron pool. Our more recent preliminary unpublished studies have revealed that treatment of human prostate cancer cells with apoptosis-inducing concentrations of DATS results in up-regulation of survivin, an anti-apoptotic protein frequently overexpressed in human cancers. The present renewal application, building upon these exciting and novel observations, largely shifts emphasis from molecularly-oriented cellular studies to in vivo validation of the mechanistic findings with tremendous translational value. Hypothesis: Central hypothesis unifying the specific aims of the renewal application is that favorable pharmacokinetic attributes empower DATS to prevent prostate cancer development via labile iron-ROS- mediated apoptosis, which is amenable to augmentation by pharmacologic suppression of survivin.
Specific Aims :
The specific aims of the renewal application are to: (1) determine the pharmacokinetic parameters and oral bioavailability of DATS using non-transgenic male mice;(2) determine the contribution of labile iron-mediated ROS production in proapoptotic and chemopreventive response to DATS using cellular (PC-3, LNCaP, and PrEC) and in vivo models (TRAMP mice);(3) gain insight into the molecular circuitry of DATS-induced apoptosis downstream of ROS production using cultured cells (PC-3, LNCaP, and PrEC) and prostate/tumor tissues from TRAMP mice (from specific aim 2);and (4) determine the effect of survivin knockdown on proapoptotic and chemopreventive response to DATS using cellular (PC-3, LNCaP) and in vivo models (TRAMP mice). Translational Impact of the Proposed Research: Even though the studies conducted during the funded period of this project provide compelling preclinical evidence for efficacy of DATS against prostate cancer, efficient translation of these findings into a clinical setting is critically dependent on in vivo validation of the cellular observations. Clinical trials without a full appreciation of the factors influencing biological effects of DATS inherit risk of failure. For example, in vivo validation of the contribution of labile iron-ROS in proapoptotic and chemopreventive response to DATS (Specific Aim 2) is essential for optimization of DATS-based chemopreventive regimens to eliminate potential adverse drug-drug interactions between DATS and other anti- oxidants or agents interfering with iron homeostasis. Similarly, intrinsic value of Specific Aim 4 resides in potential design of combination regimens involving DATS and inhibitors of survivin for efficient chemoprevention of human prostate cancer.
Prostate cancer is one of the most commonly diagnosed visceral malignancies and a leading cause of cancer- related deaths among men in the United States. Therefore, novel strategies to hinder inception and/or progression of prostate cancer are highly desirable to reduce the disease-related cost, morbidity and mortality associated with this neoplasm. The ultimate goal of this project is to develop a safe and inexpensive but effective strategy for chemoprevention of human prostate cancer using garlic constituent diallyl trisulfide (DATS). Even though the studies conducted thus far provide compelling preclinical evidence for efficacy of DATS against prostate cancer, efficient translation of these findings into a clinical setting is critically dependent on in vivo validation of the cellular findings. In summary, the immediate and future intrinsic value of the studies proposed in this renewal application resides in optimization of DATS-based regimens for chemoprevention of prostate cancer.
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