Monday, July 6, 2009

Anticancer Compound from a Tumor-Promoter

ResearchBlogging.orgThe title of this article caught my eye because of the irony of designing an anticancer drug by modifying a known tumor promoter. Aplysiatoxin is a tumor promoter, while Compound 1 from the paper is not. In fact, Compound 1 is just a simpler version of Aplysiatoxin: the hemiacetal has become an ether and several side groups have been lost. There are also fewer stereocenters in Compound 1 than in Aplysiatoxin.

First a little background. Both compounds affect cancerous cells the way they do because they bind to Protein Kinase C (PKC). PKC is an enzyme that contributes to a number of signaling pathways within the cell, particularly having to do with cell differentiation, proliferation and apoptosis. PKC's involvement in cellular growth cycles also results in its involvement in carcinogenesis, and it has been a target for developing anti-cancer drugs for this reason.

The curious thing about PKC is that some molecules that bind to PKC activate the enzyme, while others de-activate it. Even stranger, some activators promote tumor formation and other activators do not.

PKC activators have shown some promise for treating diseases such as Alzheimers or AIDS, but their tumor-promoting behavior is a big drawback. Ideally you would want to find a PKC activator that was also non-tumor promoting. Bryostatins fit this description, but the compounds are too complex to be easily made in the laboratory. In nature, bryostatins are
made by a coral-like organism but in extremely small amounts. According to Wikipedia, you would need a ton (2000 lb) of bryozoans to obtain just one gram of bryostatin.

Aplysiatoxin binds to PCK as a tumor promoting activator. Compound 1 was designed as a simpler version of aplysiatoxin that might be a PKC activator without also being a tumor promoter. As it turns out, compound 1 shows minimal tumor-promoting activity, and it counteracts the effects of the tumor-promoter 12-O-tetradecanoylphorbol-13 acetate. It's anti-cancer activity as well as it's mode of binding to PKC seems to be comparable to the bryostatins. The authors report that they can make Compound 1 in only 22 steps, which makes it a promising alternative to bryostatins as a potential therapeutic agent.

Nakagawa, Y., Yanagita, R., Hamada, N., Murakami, A., Takahashi, H., Saito, N., Nagai, H., & Irie, K. (2009). A Simple Analogue of Tumor-Promoting Aplysiatoxin Is an Antineoplastic Agent Rather Than a Tumor Promoter: Development of a Synthetically Accessible Protein Kinase C Activator with Bryostatin-like Activity Journal of the American Chemical Society, 131 (22), 7573-7579 DOI: 10.1021/ja808447r

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