TUMOR-PROMOTING EFFECTS OF OKADAIC ACID AND PALYTOXIN

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The biochemistry of tumor promotion by okadaic acid (OKA) and palytoxin (PAL) will be studied in mouse epidermis in vivo. Complete and stage 2 skin tumor promoters increase the hydroperoxide (HPx)-producing activity of the epidermis. Ornithine decarboxylase (ODC) induction and cell proliferation are early and late events of stage 2, respectively. HPx production and ODC induction are essential for stage 2 but not correlated. Beside ODC induction in early stage 2, the production of HPx caused by 12- O-tetradecanoylphorbol-13-acetate (TPA) during the early inhibition (EI) of epidermal DNA synthesis may be crucial to trigger a greater compensatory stimulation of DNA synthesis required to achieve hyperplasia in late stage 2. OKA induces ODC activity but PAL does not. Since the non-TPA type tumor promoters OKA and PAL neither bind to the phorbol ester receptor nor activate protein kinase C (PKC), the hypothesis to be tested is that common induction of HPx production by OKA, PAL and TPA may be the key event involved in tumor promotion. The objective is to determine if there is a correlation between HPx production and the 2nd peak of DNA synthesis (P2) after OKA, PAL and TPA treatment. The following aims will be examined over the next 4 years: 1) characterize and compare the HPx responses to OKA, PAL and TPA treatments and determine if these HPx responses have different requirements for, and/or are differently modulated by, macromolecule synthesis, Ca2+ mobilization, protease, PKC and phospholipase activities, and arachidonic acid metabolism; 2) study the relationships between the increased production of HPx and the sequential EI and compensatory stimulation of epidermal DNA synthesis, especially P2, caused by OKA, PAL and TPA; 3) determine if OKA and PAL induce tumor promotion synergistically with TPA or mimic the promoting activities of TPA and mezerein during stages 1 and 2, respectively; and 4) determine if the tumor-promoting activity of PAL can be improved by pretreatment with an ODC inducer and if the promotion of skin tumors by OKA and PAL can be inhibited by the antioxidant diethyldithiocarbamate. This project should demonstrate that if all tumor promoters share the ability to increase HPx production, the drugs inhibiting this HPx response, therefore, may have the best potential for inhibiting tumor promotion, a finding which could lead to the development of new means of cancer prevention.