Tumor Suppression Through Oxidized Glycerophosphocholines

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DESCRIPTION (provided by applicant): Oxidative stress has long been known to be an important trigger for neoplastic development. The importance of oxidative stress in carcinogenesis is seen in the ability of chemical and environmental tumor promoters to induce the production of reactive oxygen species. Not surprisingly, a number of antioxidants have been examined for potential chemopreventive activity. While there is strong pre-clinical and epidemiologic evidence to support the idea that antioxidants have antineoplastic properties, more recent human studies have shown mixed results. If successful, the studies proposed in this grant application will provide key insights into cellular responses to oxidative stress, particularly in regards to tumor promotion. Importantly, these insights may lead to better chemopreventive approaches to neoplastic development. Studies by our group and others have indicated that oxidative stress results in the production of oxidized glycerophosphocholines (ox-GPC) that act as agonists for the platelet-activating factor receptor (PAF-R) and the peroxisome proliferator activated receptor gamma (PPAR?) systems. Moreover, we and others provide evidence that the PAF-R and PPAR? act to suppress the tumor promoter-induced hyperproliferative response as well as long-term cutaneous neoplasia. We hypothesize that ox-GPCs with PAF-R and PPAR? agonist activity have evolved as a cellular defense against tumor promoter-induced neoplastic development. They do this by acting as a brake on tumor promoter- induced hyperplastic responses and subsequent tumor development. We further propose that antioxidants suppress this protective response by blocking the production of ox-GPCs; thus, we expect that adding back these ox-GPCs or specific agonists for the PAF-R and/or PPAR? would augment the chemopreventive activity of antioxidant therapy. Three specific aims are designed to test these hypotheses. 1.) We will first verify that two different chemical tumor promoters induce the production of these ox-GPCs in mouse epidermis. We will then verify in mouse epidermis that topically applied ox-GPCs, as well as defined PAF-R and PPAR? agonists, are capable of activating the PAF-R and PPAR?. The specificity of these responses will be verified in gene knockout mice lacking the PAF-R (PAF-R(-/-)) or epidermal PPAR? (PPAR?(-/-)). 2.) We will next demonstrate that the PAF-R and PPAR? suppress tumor-promoter induced growth using these knockout mouse models. We will then verify that adding back exogenous ox-GPCs, a PAF-R agonist, or a PPAR? agonist all act to augment the ability of antioxidants to block tumor promoter-induced hyperproliferative responses. 3.) Finally, using normal mice as well as these knockout mice, we will directly determine whether the chemopreventive activity of antioxidants can be boosted by adding back exogenous ox-GPCs or specific PAF-R and/or PPAR? agonists. These studies are part of my long-term goals to define the receptor based mechanisms through which lipid hormones are involved in neoplastic development. PUBLIC HEALTH RELEVANCE: Two common features of all tumor promoters are the production reactive oxygen species and the induction of a sustained hyperproliferative response in the epidermis. Recent studies by our group have demonstrated that reactive oxygen species induce the production of oxidized glycerophosphocholines (ox-GPC) that can act as agonists for the growth inhibitory platelet-activating factor receptor (PAF-R) and peroxisome proliferator activated receptor gamma (PPAR?) systems. The proposed studies will determine whether tumor promoters induce ox-GPCs that serve a protective function in neoplastic development by activating growth-inhibitory PAF-R and/or PPAR?.