PHARMACOLOGICAL MODULATION OF BLOOD-BRAIN BARRIER: FUTURE STRATEGY FOR TREATMENT OF BRAIN TUMORS

A prerequisite for the efficacy of chemotherapy is that it reaches the tumor mass at a therapeutic concentration. In brain tumors this phenomenon is hampered by the presence of the blood brain barrier (BBB) which limits the spread of chemotherapeutic agents within the brain. It is lately emerged as this Multi Drug Resistance (MDR) phenomenon is explained through the cooperation of P-glycoprotein (P-gp, ABCB1) and breast cancer resistance protein (BCRP, ABCG2), two “gatekeeper" transporters that work in tandem on the BBB and are also present on the plasma membrane of certain brain tumors. Recently, we have attempted to improve the therapeutic efficacy of pharmacological treatment in malignant braintumorsbysafeand temporaryBBBpermeabilization. We have demonstrated that morphine and, to a lower level, ondansetron and dexamethasone allow an accumulation of doxorubicin within the rat brain byLC-MS/MSmass spectrometry. All these drugs are substrates of P-gp and BCRP efflux pumps. The aim of the current proposal is to expand our preliminary observation, to understand the mechanism of action of BBB “permeabilization” induced by morphine or other drugs, and to exploit this method for the “treatment” of brain tumour in an animal model. i) Quantifying the level drugs that do not usually cross the BBB (mitoxantrone or melphalan) after morphine pre-treatment in a preclinical model. Verifying the cytotoxic effect ofmorphine plus doxorubicin (and other chemotherapeutic agents) treatment by usingMTTand TUNEL analysis in glioblastoma cell lines ii) Quantifying the level of drugs that do not usually cross the BBB after morphine pre-treatment in an artificial BBB through a monolayer of MDCKII cells over-expressing the human P-gp or BCRP. iii) Investigating the regulatory role of certain microRNA in MDR mechanism by RT-PCR and western blot analysis of P-gp, BCRP, miR-21, miR-27a and miR-451. Our data suggest that blocking efflux transporters by pretreatment with morphine, ondansetron or desamethasone is able to allowdoxorubicin penetration inside the brain. This is not associated with acute cardiac or renal toxicity. These preliminary results will enable us to novel therapeutic approaches to refractory or recurrent brain tumors in which molecules usually stopped by the BBB may have a therapeutic impact.