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Even though lung cancer is the leading cause of cancer death in both men and women in California, current therapies are largely ineffective, and are laden with devastating side effects for the patient. Lung cancer tumors cannot grow larger than the size of a pinhead without first attracting new blood vessels (angiogenesis) to supply nutrients and oxygen to the dividing cells. In addition, lung cancer cells cannot spread (metastasize) to other organs of the body without these vascular conduits. The higher the density of blood vessels feeding a tumor the poorer the prognosis for the patient. However, if new growth of blood vessels is halted, tumors shrink because cancer cells die, and metastasis is prevented. Logically, therapies that disrupt growth of new blood vessels in tumors should drastically improve patient prognoses. Unfortunately, current anti-angiogenesis treatments have proven unsuccessful, perhaps because the wrong blood vessel cell type has been targeted for therapy. New blood vessels are composed of two types of cells: endothelial cells that form the inner lining of the tube, and pericyte cells that form an outer sheath around the tube. There is substantial evidence documenting the effect of nicotine, the addictive component of tobacco smoke, on endothelial cells in new blood vessel formation in lung cancer. However, little is known about pericytes and their potential as targets for new lung cancer treatments. Detailed information about the localization of pericytes in growing vessel buds, and the effect of nicotine on pericyte growth is needed.
Pilot experiments on mouse lung cancer show that new vessel buds are extensively covered with pericytes. Some experiments also show that the pericytes carry receptors, called nicotinic acetylcholine receptors (nAchR), which can attract and bind nicotine. Most lung cancers develop in tobacco smokers. Lung cancers have a very long subclinical period during which they grow and metastasize before the patient develops symptoms. In chronic smokers, by the time lung cancer becomes symptomatic and reaches a detectable size, the new vessels have been exposed to nicotine circulating in the blood throughout the lengthy subclinical period. The proposed experiments will simulate the effect of nicotine on new blood vessel buds in lung cancer. This study aims at understanding the effect of nicotine on pericytes, which form the new vessel buds, and will establish pericytes and nicotinic acetylcholine receptors on pericytes as novel targets for drug discovery and lung cancer treatment.
The overall goal of this proposal is organized to three sub-divisions:
Goal 1. Investigate the stimulatory effect of nicotine on pericyte buds in newly forming vessels.
Goal 2. Investigate the nicotinic acetylcholine receptors on pericyte buds in newly forming vessels.
Goal 3. Investigate the effect of preventing nicotine from acting on pericytes via nAchRs in order to discover a treatment method to decrease pericyte proliferation.
To achieve Goal 1, we will use mice as experimental models. Angiogenesis will be stimulated, and then the mice will be exposed to nicotine. We will determine if pericytes in the resulting vessel buds of nicotine-exposed mice multiply faster compared to mice that did not receive nicotine (control). We will “tag” pericytes and endothelial cells with specific, fluorescent markers that will allow us to distinguish these two cell types. Using a microscope that detects fluorescence, we will compare the density and pericyte content of vessel buds from nicotine-exposed and control mice. A plastic cast of the tumor’s blood vessel network will be made by injecting liquid plastic into the newly formed blood vessels. Through microscopic examination of these casts, the shape and density of the new vessel buds will be compared between the nicotine-exposed and control mice. To achieve Goal 2, the presence of nAchRs on pericytes from human and mouse lung cancer tissue will be examined by using fluorescent markers that bind specifically only to these receptors. To achieve Goal 3, we will block the nAchRs on pericytes by genetic and pharmacological methods to see if angiogenesis is halted as a result of decreased pericyte proliferation. These studies will elucidate the mechanism whereby nicotine stimulates lung cancer growth via its action on pericyte proliferation. Understanding the mechanisms of nicotine action on pericytes will enable us to develop new strategies for the treatment of lung cancer by targeting pericytes in new tumor vessels. This type of therapy may prove more effective in saving lives than conventional therapies, and may improve the quality of life of lung cancer victims during and after their treatment by reducing the need for surgery, radiation, and chemotherapy. |
