Angiogenesis Inhibitors
Scientists have peered into the genetics of cells comprising blood vessels which nourish tumors. They have discovered several genes (at least 46) that are turned on in vessels induced by tumors, but not on in normal vessels. The genetic differences between tumor induced and normal vessels could in theory, be used as a target. Drugs could be developed to interfere with the genes on the tumor induced vessels to halt their formation. Thus, the tumor would not grow any larger.
The theory behind this centers around the cells that make-up the blood vessels. The cells lining a tumor-induced blood vessel should have a special receptor (or protein) on their surface not found on normal blood vessels. A drug could be made that would only bind to the receptors found on tumor vessel cells.
For a moment, let’s assume a drug is made that only binds to the tumor vessel cell receptors. This compound could have a toxin bound to it. Once the compound bound to the receptor on the cell, it would destroy only that particular cell. In this way, all the tumor induced blood vessels could be destroyed and the tumor would never grow any larger. Instead, it might actually shrink since parts of it would be undernourished.
A growing tumor constantly needs new vessels to supply nutrients. If physicians could cut off its existing blood flow, it would essentially “starve”. Drugs fighting angiogenesis are easy to deliver since a chemical injected into the bloodstream can quite easily reach the blood vessels. Many drugs fail because they never reach all if any of the tumor. Angiogenesis inhibitors would completely by-pass that problem. In theory, it should be possible to create compounds capable of turning off the genes that allow these tumor vessels to grow.
Today, there are at least 30 potential angiogenesis inhibitors. A very promising drug of this sort is Endostatin (Folkman). Phase I of the trials gave very promising results. There is much enthusiasm that this trend may continue with future phases. If it works as expected, Endostatin could potentially keep cancers in check. For a patient, this might mean taking the Endostatin for the rest of his or her life. If the side effects are minimal, this would be a small price to pay.
