ABCC drug efflux pumps and organic anion uptake transporters in human gliomas and the blood-tumor barrier.

Delivery of therapeutic agents to the brain and its neoplasms depends on the presence of membrane transport proteins in the blood-brain barrier and in the target cells. The cellular and subcellular localization of these membrane transporters determines the drug accessibility to the brain and its tumors. We therefore analyzed the expression and localization of six members of the multidrug resistance protein family of ATP-dependent efflux pumps (ABCC1-ABCC6, formerly MRP1-MRP6) and of six organic anion uptake transporters (OATP1A2, OATP1B1, OATP1B3, OATP1C1, OATP2B1, and OATP4A1) in 61 human glioma specimens of different histologic subtypes. Real-time PCRs indicated expressions of ABCC1, ABCC3, ABCC4, and ABCC5. In addition, we detected expressions of the OATP uptake transporter genes SLCO1A2, SLCO1C1, SLCO2B1, and SLCO4A1. At the protein level, however, only OATP1A2 and OATP2B1 were detectable by immunofluorescence microscopy in the luminal membrane of endothelial cells forming the blood-brain barrier and the blood-tumor barrier, but not in the glioma cells. ABCC4 and ABCC5 proteins were the major ABCC subfamily members in gliomas, localized both at the luminal side of the endothelial cells and in the glioma cells of astrocytic tumors and in the astrocytic portions of oligoastrocytomas. These results indicate that expression of ABCC4 and ABCC5 is associated with an astrocytic phenotype, in accordance with their expression in astrocytes and with the higher chemoresistance of astrocytic tumors as compared with oligodendrogliomas. Our data provide a basis for the assessment of the role of uptake transporters and efflux pumps in the accessibility of human gliomas for chemotherapeutic agents.

Dehydroepiandrosterone causes hyperplasia and impairs regeneration in rat liver.

DHEA, a steroid of the adrenal gland, is a non-genotoxic hepatocarcinogen of the peroxisome proliferator type in rodents. However, DHEA also exerts anti-carcinogenic effects by reducing the number and proliferation of preneoplastic and neoplastic lesions induced by N-nitrosomorpholine. The mechanism underlying this growth-modulating effect is unclear, and no data are available on DHEA effects on normal liver. Here, we show that DHEA is a liver mitogen, increasing proliferation in rat liver after 3 days of treatment (100 mg/kg body weight per day) as indicated by significantly enhanced expression of cyclin E, PCNA and Ki-67 and an elevated number of mitotic figures. Histological observation of the liver and biochemical evaluation of serum transaminases and bilirubin did not reveal any evidence for cell death, demonstrating that increased proliferation was not due to liver damage. After 2 weeks of DHEA-treatment, proliferation parameters returned to control values and, after 4 weeks, cyclin E and Ki-67 were even lower than in controls. To study the DHEA effect on regenerating liver, we performed partial hepatectomy (PHx) on rats pretreated for 4 weeks with DHEA and analyzed the kinetics of the cell cycle. DHEA-treatment delayed the entry of hepatocytes into G1 phase by about 6 h indicated by a later rise in Ki-67 and cyclin E expression. Reduced STAT-3 activation before G1-phase entry indicates an impaired recruitment of hepatocytes to regenerative proliferation in DHEA-treated livers. The rise in proliferation observed after PHx in DHEA-treated livers was more flat and, in contrast to controls, did not show a peak value within the first 35h as indicated by Ki-67, PCNA, cyclin E and BrdU-incorporation levels in hepatocytes. In conclusion, the results show that DHEA acts as a mitogen in rat liver but reduces the regenerative capacity of the liver.

Human hepatobiliary transport of organic anions analyzed by quadruple-transfected cells.

Hepatobiliary elimination of many organic anions is initiated by OATP1B1 (OATP2, LST-1, OATP-C), OATP1B3 (OATP8), and OATP2B1 (OATP-B), which are the predominant uptake transporters of human hepatocytes. Thereafter, the unidirectional efflux pump ABCC2 (multidrug resistance protein 2) mediates the transport of organic anions, including glutathione conjugates and glucuronosides, into bile. In this study, we generated a Madin-Darby canine kidney (MDCKII) cell line stably expressing recombinant OATP1B1, OATP1B3, and OATP2B1 in the basolateral membrane and ABCC2 in the apical membrane. Double-transfected MDCKII cells stably expressing ABCC2 together with OATP1B1, OATP1B3, or OATP2B1 served as control cells. The quadruple-transfected cells exhibited high rates of vectorial transport of organic anions, including bromosulfophthalein, cholecystokinin peptide (CCK-8), and estrone 3-sulfate. The quadruple-transfected cells enabled the identification of substrates for uptake or vectorial transport that may be missed in studies with a double-transfected cell line, as exemplified by CCK-8, which is a substrate for OATP1B3 but not for OATP1B1 or OATP2B1. The broad substrate spectrum covered by the three hepatocellular OATP transporters enables representative analyses of the uptake of many organic anions into human hepatocytes. The broad spectrum of organic anions transported vectorially by the quadruple-transfected cells also provides valuable information on the substrate selectivity of ABCC2, without the need for studies in inside-out membrane vesicles containing the ABCC2 protein. The quadruple-transfected MDCKII-ABCC2/OATP1B1/1B3/2B1 cells may thus be useful for the identification of substrates and inhibitors, including drug candidates, undergoing uptake and secretion by human hepatocytes, under conditions that may be better defined than in primary cultures of human hepatocytes.

Induction and modulation of hepatic preneoplasia and neoplasia in the rat by dehydroepiandrosterone.

Dehydroepiandrosterone (DHEA), the main adrenal steroid in humans and a precursor in androgen and estrogen biosynthesis, acts as a peroxisome proliferator and as a hepatocarcinogen in rats. Neoplasms emerge from a glycogenotic/amphophilic/basophilic preneoplastic cell lineage. A higher female tumor incidence suggests a relevant influence of sex hormones. DHEA enhances hepatocarcinogenesis induced by N-nitrosomorpholine (NNM), which is characterized by the glycogenotic/basophilic cell lineage. The tumor promoting effect is related to an additional amphophilic/basophilic preneoplastic lesion sequence and to faster proliferation of the basophilic preneoplastic lesions. Nevertheless, hepatocellular carcinomas provided under DHEA treatment seem to have a less malignant phenotype compared to tumors induced by NNM only. Further, DHEA treatment reduces growth and generation of glycogen storage foci (GSF) in initial NNM-treated rats. Thus, DHEA treatment results in both, a growth stimulation of the late basophilic lesion type with an additional amphophilic lesion sequence, and in a growth inhibition of early preneoplastic lesions, addressing especially GSF. DHEA also inhibits the growth of physiologically proliferating liver tissue. This might be explained by a DHEA related cellular metabolism, which results in significant energy consumption. Additionally, a DHEA-induced alteration of cytokine levels might contribute to this growth inhibition as well.