P08.09 Prostanoid metabolism as a potential target for improved drug response in gliomas

Introduction: Gliomas are difficult to treat primary brain tumours classified into grades I-IV by the WHO. One problem is the development of multiple drug resistance (MDR) in response to repeated cycles of chemotherapy. MDR occurs through the increased expression of ATP-binding cassette transporters (ABC transporters). Several ABC transporters are linked to drug resistance in human tumours and include MDR1/P-glycoprotein (ABCB1), breast cancer resistance protein (ABCG2) and the multiple drug resistance proteins, ABCC1 and ABCC2. Cyclooxygenase2 (COX-2) can cause up-regulation of ABCB1 and a correlation exists between COX-2 and ABCB1 in breast cancer. Considering the fact that gliomas can develop MDR and express high levels of COX-2, the aim of the study was to investigate the importance of COX-1 and COX-2 to the expression and activity of the ABC transporters ABCB1 and ABCC1-5 in the absence or presence of vincristine-induced MDR. Materials and Methods: The human glioma cell lines A172, T98G, U87MG, U138MG and U251MG were used. mRNA and protein expression of COX-1, COX-2, microsomal ­prostaglandin E synthase 1, 2 and cytosolic prostaglandin E synthase (mPGES1, mPGES2 and cPGES), ABCB1 and ABCC1-5 were determined by qPCR and Western blotting in the absence or presence of COX-1 inhibitor (SC-560), COX-2 inhibitor (NS-398) or gamma-linolenic acid (GLA). ABC transporter activity was determined using fluorescent probes. The response of vincristine-resistant cells was studied as vincristine is used in gliomas in PCV (procarbazine, CCNU, vincristine) treatment and is a known substrate for the ABC transporters ABCB1 and ABCC2. Tumour samples from grade II-IV gliomas were also analysed for ABCB1 and ABCC1-4 expression by immunohistochemical staining and compared with COX1, COX2, mPGES1, mPGES2 and cPGES expression. Results: The results showed constitutive expression of COX-1 and COX-2 in the panel of human glioma cells as well as the expression of all the ABC transporters studied, although considerable variations in expression were found among the different cell lines. Inhibition of COX-1 and COX-2 caused a decrease in the expression and activity of several ABC transporters. The presence of GLA also led to changes in COX-1, COX-2 and ABC transporter expression in the glioma cell lines. Vincristine-resistant cells showed an increase in expression of both COX enzymes and ABC transporters which was altered by COX inhibition. Patient samples had variable expression of COX enzymes and ABC transporters. Conclusions: The potential for altering the expression profile and activity of ABC transporters through the manipulation of COX-2 and/or prostaglandin metabolism may lead to improved tumour response to chemotherapy in the future. Financial support: FAPESP (15/08777-0), CNPq, CAPES.