New version of obesity drug could help people reduce weight without experiencing anxiety, depression

In continuation of my update on Rimonabant

A new version of an obesity drug that caused serious psychiatric side effects could help people lose pounds without experiencing the anxiety, depression and suicidal thoughts previously associated with it. The research, published in Bioorganic and Medicinal Chemistry, shows that the new version of the drug can still work without reaching the brain in rats, avoiding the side effects.

The researchers behind the study, from RTI International in the US, say this means the new version of the drug could be used in the future for treating obesity. And their approach could also support the development of drugs to tackle liver disease, metabolic conditions and high blood cholesterol.

In our bodies we have cannabinoid receptors that control appetite, mood, memory and pain. The obesity drug Rimonabant stops these receptors from working. But the drug was found to have serious psychiatric side effects in a small number of the people who took it. Because of this, the drug was never approved in the US and manufacturer Sanofi-Aventis pulled from the European market voluntarily.

In the new study, the researchers altered the drug so it no longer gets into the brain, which stops it from having psychiatric side effects.

Study author Dr. Rangan Maitra, from RTI International in the US, explained: "There is a real need for new medicines to treat metabolic conditions like obesity. We are working with chemists to alter the drug Rimonabant and create compounds that cannot get into the brain. We hope this will help create drugs that can treat people with these conditions, without them having to suffer the side effects."

Dr. Maitra and colleagues modified the original Rimonabant compound by changing its weight, polarity and other properties to try to stop it from getting into the brain.

Tests in rats found that one of the versions, called 8c, blocks the target receptor and is much less likely than the original drug to get into the brain and affect the central nervous system.

The researchers found that 8c mostly stays in the blood and works on cannabinoid receptors found in parts of the body other than the brain. In comparison, more than half of the original drug Rimonabant entered the brain.

It's early days for the research, and the new version of the drug will need to go through testing before it can be used to treat people, but the researchers say it's a step in the right direction. Their study also outlines how scientists can test drugs designed to target cannabinoid receptors to make sure they are working outside the brain.

"Drug development is a long and arduous process," said Dr. George Amato, co-author of the study. "You have to develop hundreds, if not thousands, of compounds before you get the right one. The challenge is that some medicines that are absorbed in the gut also get into the brain. We set out to find compounds that absorb across the gut barrier but not the brain barrier. We've identified some, and they'll now serve as lead structures for further refinement."

New version of obesity drug could help people reduce weight without experiencing anxiety, depression

Scientists develop obesity drug without neurological side effects....

We know the side effects of Rimonabant, (see structure) the first selective CB1 receptor blocker to be approved for use anywhere in the world. In Europe, it was indicated for use in conjunction with diet and exercise for patients with a body mass index greater than 30 kg/m², or patients with a BMI greater than 27 kg/m² with associated risk factors, such as type 2 diabetes or dyslipidaemia. In the UK, it was available beginning in July 2006. As of 2008, the drug was available in 56 countries. On October 23, 2008, the European Medicines Agency (EMEA) issued a press release stating that its Committee for Medical Products for Human Use (CHMP) had concluded that the benefits of Acomplia no longer outweighed its risks and subsequently recommended that the product be suspended from the UK market. Sanofi-Aventis later released a press statement stating that the drug had been suspended. Approval of the drug was officially withdrawn by the EMEA on January 16, 2009. But never approved for use in the US because of serious neurological side effects including depression and anxiety.

Now researchers from National Institutes of Health, Bethesda, and Alexandros Makriyannis, at Northeastern University, Boston lead by Dr. George Kunos, have developed a drug (see structure AM6545)  that has the same positive effects in mice on levels of glucose and fats in the blood as rimonabant but none of the neurological side effects.

As per researchers claim AM6545 is a non-brain-penetrant neutral CB1R antagonist. First-generationCB1R antagonists, such as rimonabant, are highly lipid soluble and readily penetrate the blood-brain barrier. In order to reduce brain penetrance, we introduced several modifications into the structure of rimonabant. AM6545 is less lipid soluble than rimonabant (estimated partition coefficient [log P], 3.3 vs. 6.4 for rimonabant) but retains high affinity and selectivity for CB1R. In radioligand displacement assays, AM6545 has a KI of 3.3 nM for CB1R, which is similar to that of rimonabant and greater than 100-fold CB1/CB2 selectivity. Unlike rimonabant, AM6545 does not reduce GTPγS binding in mouse brain membranes and is therefore a neutral antagonist.

As per the claim by the researchers, this drug did not cause weight loss or neurological side effects, which rimonabant does, but did have effects on levels of glucose and fats in the blood that should reduce the risk of the serious health consequences of obesity.

The authors therefore hope that this approach of targeting only peripheral CB1R can be translated into the clinic to reduce health risks in obese patients..

Ref : http://www.jci.org/articles/view/42551/pdf