Modulation of MDR1 isoform of P-glycoprotein efflux transporter increases permeability of doxorubicin into the brain of the rat

MG Giovannini1, G La Marca1, S Malvagia3, M Da Ros2, V Fratoni1, I Sardi2. 1University, Pharmacology 50139, Italy, 2Meyer\'s Children Hospital, Onco-Hematology 50139, Italy, 3Meyer\'s Children Hospital, Neuroscience 50139, Italy

Despite recent advances in the cure of childhood cancer, brain tumor still lags behind other cancer types. Based on in vivo and in vitro studies, brain tumors might be expected to be sensitive to chemotherapy agents, as anthracyclines . Yet, most patients fail to achieve adequate disease control due to insuffcient cytoreduction of unresectable tumors, or develop tumor relapse despite apparent gross-total resection and/or irradiation. One major obstacle to efficient tumor cytoreduction may be insuffcient drug delivery to the tumor site. The blood– brain barrier (BBB) is a physical and metabolic barrier between systemic circulation and the brain. BBB maintains homeostasis and protects the brain from toxic insults but it may represent a real limiting factor to delivering chemotherapy agents within the brain tumor mass. We have demonstrated (Sardi et al., 2010) that doxorubicin concentration in the rat brain is greatly enhanced when doxorubicin is administered in the presence of therapeutic plasma levels of morphine. Morphine is a substrate of the MDR1 isoform of P-glycoprotein (P-gp) efflux transporter, which very efficiently removes several molecules and drugs from the CNS, thus limiting their entry into the brain. Morphine mediated “accumulation” of doxorubicin into the brain might result from its reduced efflux mediated by P-gp at the level of the BBB cells. Therefore, aim of this study was to verify whether other drugs, known to be substate of the MDR1 isoform of P-glycoprotein share the effect of morphine in allowing accumulation of anthracycline within the brain. We checked whether ondansetron or desamethasone might be more effective than morphine in allowing accumulation of doxorubicin within the brain. Rats (n=3-5) were pretreated with ondansetron (2 mg/kg i.p., 3 injections, spaced by 12 h) or desamethasone (2 mg/kg i.p., 3 injections, spaced by 12 h) before injection of doxorubicin (12 mg/kg). Quantitative analysis of doxorubicin was performed by mass spectrometry using an LC-MS-MS method in the positive ion mode, using tritiated doxorubicin as internal standard. The concentration of doxorubicin was signficantly higher in the cerebral cortex (+ 159%, P<0.05, Student’s t test), in the brainstem (+ 62%, P<0.05, Student’s t test) or in the cerebellum (+ 82%, P<0.05, Student’s t test) of rats pretreated with ondansetron than in matched control brain areas of rats treated with doxorubicin alone at the same dose. Preliminary results show that in the cerebral cortex of rats treated desamethasone doxorubicin levels were significantly higher than in controls (+ 195%, P<0.05, Student’s t test). Pretreatment with ondansetron or desamethasone did not induce an elevation of LDH activity or of lipid peroxidation compared to controls. Our data suggest that blocking MDR1 isoform of P-glycoprotein (P-gp) efflux transporter by pretreatment with ondansetron or desamethasone is able to allow doxorubicin 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 blood–brain barrier may have a therapeutic impact.