What is temsirolimus? Temsirolimus is a mTOR inhibitor, where mTOR stands for mammalian target of rapamycin. In normal cells, the pathway called PI3-AKT pathway plays an important role in regulation of cell growth. In studies scientists have found that in cancerous cells, PI3 and AKT proteins (kinase enzymes) are present in large amounts, resulting in constant signaling to cell to continue to multiply (a cancerous cell is essentially a cell that does not know when to stop multiplying). What has also been found that if you block or inhibit mTOR enzyme, this prevents the signaling to the nucleus to continue to multiply. A drug that seems to have this property is Rapamycin, an old macrolid antibiotic. Since this discovery, scientists have been trying to develop Rapamycin like drugs that would have better activity, and could be given easily to patients. Temsirolimus is one of the first such drugs to get to the market. So, Temsirolimus inhibits the mTOR enzyme in P13-AKT pathway to prevent the multiplication of cancer cells.An activated PI3-AKT pathway is found in a lot of tumors, such as renal cell cancer, mantle cell cancer etc. Thus there is hope that mTOR inhibitors will be useful broadly. More importantly, it is thought that if mTOR inhibitors are combined with other traditional cytotoxics, and newer targeted therapies, they might be even more effective.
Naturally, like most drugs, Temsirolimus in not devoid of side effects. For instance, temsirolimus is known to have an impact on liver, can cause diabetes like symptoms (high blood sugar) which needs to be managed with insulin, and the FDA has asked Wyeth to provide more data on Temsirolimus' action on the heart (QTc prolongation).
Some people might also be hypersensitive to Temsirolimus, so this drug may not be for every renal cancer patient. But the good news is, just in last couple of years, Renal Cancer patients have seen significant improvement in treatments available to them. Sutent, Nexxavar, and now Temsirolimus are all important additions to the arsenal of drugs an oncologist needs for treatment of this dreadful disease which affects 50,000 patients annually in the US alone.
Temsirolimus provides modest benefit - in clinical trials, compared to interferon (which is a tough drug to take) it was shown to increase survival from 7.3 months to 10.9 months in patients with a very aggressive disease. But these additional 3 months are very valuable months for Renal cancer patients, so I hope that the drug proves to be useful to a lot of patients.
