[The blood-brain barrier: implications for chemotherapy in brain tumors]

Abstract

The blood-brain barrier (BBB) is located between the blood and the extracellular space of the brain. This barrier is formed by the brain capillaries whose endothelial cells have tight intercellular junctions. Transcellular passage of drugs from the bloodstream to the brain occurs selectively, in a manner dependent on the ability of the molecules to penetrale through cell membranes. The blood-brain barrier is one of the main factors of chemotherapy failure in central nervous system tumors. Penetration of a molecule from the bloodstream to the brain is dependent on the compound's liposolubility, expressed by the octanol-water separation coefficient. Following intravenous administration, most drugs fail to achieve adequate levels in the central nervous system for a sufficiently long period of time. A variety of techniques have been used in an attempt to increase CNS penetration of drugs normally shut out by the blood-brain barrier: high-dose chemotherapy, intrathecal injections, intraarterial injections, induction of hyperosmolarity to make the blood-brain barrier permeable. The best results are obtained using liposoluble drugs with optimal octanol-water separation coefficients, such as fotemustine. This compound given as single drug therapy in brain metastases from malignant melanomas has yielded response rates of up to 28.2%.