The Role of Solute Carrier Transporters in Efficient Anticancer Drug Delivery and Therapy

Transporter-mediated drug resistance is a major obstacle in anticancer drug delivery and a key reason for cancer drug therapy failure. Membrane solute carrier (SLC) transporters play a crucial role in the cellular uptake of drugs. The expression and function of the SLC transporters can be down-regulated in cancer cells, which limits the uptake of drugs into the tumor cells, resulting in the inefficiency of the drug therapy. In this review, we summarize the current understanding of low-SLC-transporter-expression-mediated drug resistance in different types of cancers. Recent advances in SLC-transporter-targeting strategies include the development of transporter-utilizing prodrugs and nanocarriers and the modulation of SLC transporter expression in cancer cells. These strategies will play an important role in the future development of anticancer drug therapies by enabling the efficient delivery of drugs into cancer cells.

Nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) in autophagy-induced hepatocellular carcinoma

Autophagy, an evolutionarily conserved catabolic process, is the most important pathogenic events in the development and progression of liver diseases. Deregulation of Nrf2 is proposed to play a key pathogenic role in hepatocellular carcinoma (HCC). Under certain pathophysiological conditions, such as oxidative stress, impaired autophagy is accompanied by the Nrf2 activation that leads to the detrimental effects favoring the proliferation and survival of HCC. Elucidating its role and potential mechanism is essential for understanding tumorigenesis and the development of effective clinical application. Nrf2 is participated in HCC proliferation, migration and invasion through autophagy pathways. These includes the negatively regulated-Nrf2 by Keap1 that participates in HCC tumorigenesis via regulating ROS production, in which autophagy may contribute to oxidant metabolic reprogramming of HCC cells. Post-transcriptional modifications, such as phosphorylation and ubiquitination of Nrf2, can be positively or negatively induced by multiple transcription factors. Nrf2 exhibits chemoresistance through its binding sites in the promoter region of the target genes. Nrf2 may be a valuable potential biomarker and therapeutic strategy for diagnostics, prognostics and treatment of HCC.

Role of breast cancer resistance protein in gastrointestinal tumors

The breast cancer resistance protein, also known as ABCG2, is a member of the drug efflux membrane transporters. As a drug discharge pump, ABCG2 can reduce the concentration of intracellular drugs and protect cells from toxic substances. ABCG2 is not only able to protect normal cells, but also to influence the chemotherapy effect by making tumor cells resistant to various anti-cancer drugs. In order to provide a reference for the basic and clinical research of gastrointestinal tumors, we review the physiological function of ABCG2, factors affecting ABCG2 expression, and its relationship with gastrointestinal tumors.

Association between DNA methylation and multidrug resistance in human glioma SHG-44 cells

The aim of the present study was to evaluate the association between DNA methylation and multidrug resistance (MDR) in glioma and identify novel effectors responsible for MDR in human gliomas. An MDR glioma cell line, SGH-44/ADM, was developed using adriamycin (ADM) impulse treatment. Cryopreservation, recovery and withdrawal were performed to evaluate the stability of SGH-44/ADM cells. The adherence rate and cellular morphology were observed by microscopy, and the cell growth curve and doubling time were determined. DNA methylation was analyzed using a methylated DNA immunoprecipitation microarray chip (MeDIP-Chip). The cell cycle, Rh123 ingestion and exudation, and SGH-44/ADM apoptosis were analyzed by flow cytometry. SGH-44/ADM cells showed little difference as compared with parental cells, except that SGH-44/ADM cells were bigger in size with a wizened nucleus. Compared to SGH-44 cells, a larger proportion of SGH-44/ADM cells remained in G1 and S phase, as measured by flow cytometry. The MDR of SGH-44/ADM was associated with the upregulation of multi-drug resistance 1, prostaglandin-endoperoxide synthase 2 (COX-2); protein kinase C α (PKCα); however, the expression of these genes was not associated with DNA methylation. In the MeDIP-Chip analysis, 74 functions were markedly enhanced, and seven significant pathways were observed. Genes including SNAP47, ARRB2, PARD6B, TGFB1, VPS4B and CBLB were identified by gene ontology analysis. The predominant molecular mechanism of MDR in SGH-44/ADM cells was identified as exocytosis and efflux. The expression of COX-2, PKCα and P-glycoprotein (Pgp) was not found to be associated with DNA methylation. Genes including SNAP47, VAMP4 and VAMP3 may serve as the downstream effectors of Pgp, COX-2 or PKCα; however, further experiments are required to verify these observations.

Heme transport and erythropoiesis

In humans, systemic heme homeostasis is achieved via coordinated regulation of heme synthesis, transport and degradation. Although the heme biosynthesis and degradation pathways have been well characterized, the pathways for heme trafficking and incorporation into hemoproteins remain poorly understood. In the past few years, researchers have exploited genetic, cellular and biochemical tools, to identify heme transporters and, in the process, reveal unexpected functions for this elusive group of proteins. However, given the complexity of heme trafficking pathways, current knowledge of heme transporters is fragmented and sometimes contradictory. This review seeks to focus on recent studies on heme transporters with specific emphasis on their functions during erythropoiesis.