Friday, June 14, 2013

Small molecule could have big impact on cancer


Androgen receptors are found inside cells and have complex surfaces with multiple "docking points" where various proteins can bind to the receptor. Each docking point has a unique shape, so only a correctly shaped molecule will fit.


Androgen hormones, such as testosterone, are the primary molecules that bind to androgen receptors. Such binding sets off a chain of events that activates several different processes in the human body, including stimulating the development and maintenance of male characteristics.


Looking for a new approach to battle prostate cancer, Ahn and his colleagues keyed in on blocking a critical docking point on the androgen receptor.


"When a tumor is trying to grow, activation of this location provides what the tumor needs," Ahn said. "There are other surfaces on the androgen receptor that are free to continue working with their respective proteins and to continue functioning. We sought to block only one set of interactions that contribute to prostate cancer growth. That's why we thought our approach might lead to potent efficacy with fewer side effects."


Using computer-assisted molecular modeling, Ahn designed a helix-mimicking small molecule (see structure)
that fits precisely into a pocket on the androgen receptor that is associated with prostate cancer. Collaborating with senior study author Dr. Ganesh Raj, associate professor of urology at UT Southwestern and a specialist in treating urologic cancers, the researchers tested the compound in animal and isolated human tissue. Without exhibiting noticeable toxicity, the compound prevented the androgen receptor from recruiting its protein partners and it blocked the growth of prostate cancer cells.

According to the researchers, D2 (Methyl 4-(3-isobutoxy-4-nitrobenzamido)-3-isobutoxybenzoate, above structure)  is stable, non-toxic and efficiently taken up by prostate cancer cells. Importantly, D2 blocks androgen-induced nuclear uptake and genomic activity of the androgen receptor. Furthermore, D2 abrogates androgen-induced proliferation of prostate cancer cells in vitro with an IC50 of 40 nM, and inhibits tumour growth in a mouse xenograft model. D2 also disrupts androgen receptor–coregulator interactions in ex vivo cultures of primary human prostate tumours. These findings provide evidence that targeting androgen receptor–coregulator interactions using peptidomimetics may be a viable therapeutic approach for patients with advanced prostate cancer.


"We have shown that our molecule binds very tightly, targeting the androgen receptor with very high affinity," Ahn said. "We also have confirmed that it inhibits androgen function in these cells, which is a promising finding for drug development. We showed that it does work through these mechanisms, and it is as effective in inhibiting the proliferation of prostate cancer cells as other compounds currently in clinical trials."

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Ref : http://www.nature.com/ncomms/journal/v4/n5/full/ncomms2912.html

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