To: Cheryl Galt who wrote (28290 ) 2/21/1999 6:24:00 AM From: Henry Niman Read Replies (1) | Respond to of 32384
Cheryl, I've answered your questions previously, but I'll give it another try staring with the science and technology. All three rexinoids (Targretin, LGD1268 and LGD1324) activate all three RXRs (alpha, beta, gamma). They are classified as rexinoids because the don't activate the three RARs (alpha, beta, gamma). The various receptors are involved in different processes (and the RAR activation has been associated with elevated triglycerides). The two rexinoid that had not entered the clinic (LGD1268 and LGD1324) were called second generation because the had a stronger affinity for the RXRs. However, I don't think that they were more selective (they still activated all three RXRs). For type II diabetes, PPARgamma combines with RXRalpha. Thus to specifically target that disease, a rexinoid specific for RXRalpha (doesn't activate RXR beta or gamma) would be desirable. Thus, LGND is using a more strict definition of "second generation", which means that the compound is more restrictive in subtype activation. Since the specific compounds are not defined, that is one definition of "second generation". I had heard that a problem with Targretin was its in vivo conversion to a metabolite that does activate RARs. Elvelated triglycerides is a common side effect of retinoids (vitamin-A derivatives that activate RARs). Thus the "second generation" terminology may apply to compounds that don't metabolize into RAR activating compounds. When LGND split up the AGN, AGN had the more specific rexinoids. However, there were hundreds of molecules split up, so I'm sure that LGND has its own sub-type specific compounds. Although LGND gets a royalty from AGN's compounds, they would get more from the ones that they develop, so they are not going to give AGN and WLA (and everyone else in the world) the details behind the "second generation" compounds. The LGND/AGN joint venture was grossly under-funded. The initial $100 million was used up well ahead of the initial 5 year time frame, and drug development is very expensive. The LLY deal allows LGND to make considerable progress. AGN has no rexinoid in the clinic, so I don't think that LGND wants to give out info that will help AGN beat them to the market. I think it's clear that many of the readers of this board still lack a clear understanding of the science and technology behind drug development.