sarcophytol-a and canventol

Tumor promotion is a critical point in multistage carcinogenesis in humans. We have identified a common biochemical and molecular tumor promotion mechanism, the okadaic acid pathway, applicable in various organs. Tumor promotion by the okadaic acid class of compounds is mediated through inhibition of protein phosphatases 1 and 2A, resulting in an increase of protein phosphorylation and a subsequent expression of cell proliferation genes. Recently, we demonstrated that okadaic acid induced the release of mouse tumor necrosis factor-alpha (mTNF-alpha) from BALB/3T3 cells. The first part of this review discusses the link between the okadaic acid pathway and TNF-alpha as endogenous tumor promoters in vivo. Inhibitors of tumor promotion are varied. For the purpose of cancer chemoprevention in humans, the inhibitors sarcophytol A, canventol, and (-)-epigallocatechin gallate (EGCG) were studied and the results are presented. The inhibitory mechanisms also were varied: sarcophytol A inhibited H2O2 formation by TPA-activated human polymorphonuclear leukocytes; canventol inhibited protein isoprenylation in the cells; and EGCG, which is a main constituent of Japanese green tea, is an antioxidant. These inhibitors are promising cancer chemopreventive agents. Study of the essential tumor promotion mechanisms will facilitate the development of cancer chemopreventive agents.

Topics: Anticarcinogenic Agents; Catechin; Cyclohexanols; Diterpenes; Ethers, Cyclic; Humans; Neoplasms; Okadaic Acid; Tumor Necrosis Factor-alpha

The small molecule S9a was derived from an established tumor necrosis factor-alpha (TNF-alpha) inhibitor (Canventol) by replacement of the isopropylidine group with a phenyl ring. S9a at 10 to 100 nM inhibited HIV production as potently as 3'-azido-3'-deoxythymidine (AZT), an inhibitor of viral reverse transcriptase. Furthermore, S9a and AZT in combination, at noncytoxic concentrations strongly inhibited HIV-1 replication that was more than additive and substantially prolonged the appearance of virus both in acutely infected CD4+ lymphocytes (SupT) in culture and in peripheral blood mononuclear cells (PBMCs) infected with a primary HIV-1 isolate. S9a inhibited TNF-alpha promoter-driven reporter gene activity. It was proposed that the mechanism of antiviral action of S9a was on the host cell, by blocking TNF-alpha transcription via a Tat-induced tar-independent loop, which decreases downstream NF-kappaB activation of HIV-1 long terminal repeat (LTR). S9a was superior to the first generation compound Canventol, which was superior to the natural compound sarcophytol A, demonstrating that further structure-based enhancement of potency of these compounds is feasible. This study suggests a therapeutic approach against AIDS by application of two drugs, one against a cellular and the other a viral target, which may provide an approach to the problem of frequent emergence of resistant variants to combinations of drugs that target only HIV genes.

Topics: Anti-HIV Agents; Anticarcinogenic Agents; Antineoplastic Agents; CD4-Positive T-Lymphocytes; Cell Line; Cyclohexanols; Diterpenes; Drug Combinations; Drug Synergism; Gene Products, tat; HIV-1; Humans; Jurkat Cells; NF-kappa B; Repetitive Sequences, Nucleic Acid; Reverse Transcriptase Inhibitors; tat Gene Products, Human Immunodeficiency Virus; Transfection; Tumor Necrosis Factor-alpha; Virus Replication; Zidovudine

Mechanisms of cancer prevention were studied using structurally different cancer-preventive agents, sarcophytol A, canventol, (-)-epigallo-catechin gallate, and tamoxifen, based on our evidence that tumor necrosis factor alpha (TNF-alpha) acts as an endogenous tumor promoter relevant to human carcinogenesis. Pretreatment with the four preventive agents commonly inhibited TNF-alpha mRNA expression and TNF-alpha release in BALB/3T3 cells induced by a tumor promoter, okadaic acid, whereas the expression of early response genes (c-jun, junB, c-fos, and fosB) was enhanced. These results strongly suggest that inhibition of TNF-alpha mRNA expression and its release is a new process of cancer prevention.

Topics: 3T3 Cells; Animals; Anticarcinogenic Agents; Base Sequence; Catechin; Cyclohexanols; Diterpenes; Humans; Mice; Molecular Sequence Data; Proto-Oncogenes; Tamoxifen; Tumor Necrosis Factor-alpha

A synthetic compound named canventol, 2-isopropyl-4-isopropylidencyclohex-2-ene-1-ol, inhibited tumor promotion of okadaic acid on mouse skin initiated with 7,12-dimethylbenz(a)anthracene in two-stage carcinogenesis experiments more strongly than sarcophytol A, isolated from a soft coral, although canventol has a simpler structure than sarcophytol A. Their mechanisms of action were studied based on our recent evidence that tumor necrosis factor alpha release induced by okadaic acid is an essential mechanism of tumor promotion. Canventol inhibited mouse tumor necrosis factor alpha release from BALB/3T3 cells less strongly than sarcophytol A, indicating that canventol has additional activity. Canventol inhibited isoprenylation of proteins with various molecular weights, such as M(r) 22,000, 17,000, and 13,000, whereas sarcophytol A did not show significant inhibition. Thus, a potent anticarcinogenic activity of canventol is mediated through the inhibitory bifunctions of tumor necrosis factor alpha release and of protein isoprenylation. Since canventol is less toxic to cells than sarcophytol A, these bifunctions are useful markers for screening for new cancer chemopreventive agents.

Topics: 3T3 Cells; 9,10-Dimethyl-1,2-benzanthracene; Animals; Anticarcinogenic Agents; Cyclohexanols; Diterpenes; Ethers, Cyclic; Female; Mevalonic Acid; Mice; Okadaic Acid; Protein Prenylation; Skin Neoplasms; Tumor Necrosis Factor-alpha