Cancer drug Nexavar has made its point. It can help people with liver cancer survive longer.Bayer Pharmaceuticals and Onyx Pharmaceuticals announced Monday that advanced stage clinical trials for this drug will end early. And now patients in the placebo arm of the study can begin treatment with the actual drug.
It's been a long road for researchers who have been searching for a liver cancer treatment that can target tumors with minimal side effects while extending life for months or even years.
It is estimated that 16,780 people in the United States will die from liver cancer in 2007 -- and it seems Nexavar, a drug initially predicted to fail when used for liver cancer -- may help save some of these lives.
Bayer and Onyx are planning to pursue FDA approval for this drug that has already been approved for kidney cancer.
1. Do Targeted Cancer Drugs Always Work?
The "targets" that the new "smart drugs" go after can be located on the "inside" or "outside" of a cancer cell. The most common targets on the outside are receptors, proteins that help relay chemical messages. And many targets on the inside are enzymes, proteins that help speed up chemical reactions in the body.
What Nexavar, Iressa, Tarceva, Sutent and Tykerb have in common is that they are small molecule drugs. Exciting results have come from studies of multitargeted tyrosine kinase inhibitors, small molecules that act on multiple receptors in the cancerous cells.
Cells are the most basic structure of the body. Cells make up tissues, and tissues make up organs, such as the lungs or liver. Each cell is surrounded by a membrane, a thin layer that separates the outside of the cell from the inside.
For a cell to perform necessary functions for the body and respond to its surroundings, it needs to communicate with other cells in the body. Communication occurs through chemical messages in a process called signal transduction. The purpose of these signals is to tell the cell what to do, such as when to grow, divide into two new cells, and die.
Targeted cancer therapies use drugs that block the growth and spread of cancer by interfering with specific molecules involved in carcinogenesis (the process by which normal cells become cancer cells) and tumor growth. By focusing on molecular and cellular changes that are specific to cancer, targeted cancer therapies may be more effective than current treatments and less harmful to normal cells.
However, monoclonal antibodies are "large" molecules. These very large molecules don't have a convenient way of getting access to the large majority of cells. Plus, there is multicellular resistance, the drugs affecting only the cells on the outside may not kill these cells if they are in contact with cells on the inside, which are protected from the drug. The cells may pass small molecules back and forth.
Even if clinical trials end early, each of these new targeted drugs are not for everybody. The study of cell function analysis tells us that even when the disease is the same type, different patients' tumors respond differently to the same agents. So it doesn't matter if there is a "target" molecule in the cell that the "targeted" drug is going after, if the drug either won't "get in" in the first place or if it gets pumped out/extruded or if it gets immediately metabolized inside the cell, drug resistance is multifactorial.
Posted at 12:48PM on Feb 17th 2007 by Gregory D. Pawelski