[Uric Acid Metabolism, Uric Acid Transporters and Dysuricemia].

Serum urate levels are determined by the balance between uric acid production and uric acid excretion capacity from the kidneys and intestinal tract. Dysuricemia, including hyperuricemia and hypouricemia, develops when the balance shifts towards an increase or a decrease in the uric acid pool. Hyperuricemia is mostly a multifactorial genetic disorder involving several disease susceptibility genes and environmental factors. Hypouricemia, on the other hand, is caused by genetic abnormalities. The main genes involved in dysuricemia are xanthine oxidoreductase, an enzyme that produces uric acid, and the urate transporters urate transporter 1/solute carrier family 22 member 12 (URAT1/SLC22A12), glucose transporter 9/solute carrier family 2 member 9 (GLUT9/SLC2A9) and ATP binding cassette subfamily G member 2 (ABCG2). Deficiency of xanthine oxidoreductase results in xanthinuria, a rare disease with marked hypouricemia. Xanthinuria can be due to a single deficiency of xanthine oxidoreductase or in combination with aldehyde oxidase deficiency as well. The latter is caused by a deficiency in molybdenum cofactor sulfurase, which is responsible for adding sulphur atoms to the molybdenum cofactor required for xanthine oxidoreductase and aldehyde oxidase to exert their action. URAT1/SLC22A12 and GLUT9/SLC2A9 are involved in urate reabsorption and their deficiency leads to renal hypouricemia, a condition that is common in Japanese due to URAT1/SLC22A12 deficiency. On the other hand, ABCG2 is involved in the secretion of urate, and many Japanese have single nucleotide polymorphisms that result in its reduced function, leading to hyperuricemia. In particular, severe dysfunction of ABCG2 leads to hyperuricemia with reduced extrarenal excretion.

Targeting ABCG2 transporter to enhance 5-aminolevulinic acid for tumor visualization and photodynamic therapy.

5-Aminolevulinic acid (ALA) has been approved by the U. S. FDA for fluorescence-guided resection of high-grade glioma and photodynamic therapy (PDT) of superficial skin precancerous and cancerous lesions. As a prodrug, ALA administered orally or topically is metabolized in the heme biosynthesis pathway to produce protoporphyrin IX (PpIX), the active drug with red fluorescence and photosensitizing property. Preferential accumulation of PpIX in tumors after ALA administration enables the use of ALA for PpIX-mediated tumor fluorescence diagnosis and PDT, functioning as a photo-theranostic agent. Extensive research is currently underway to further enhance ALA-mediated PpIX tumor disposition for better tumor visualization and treatment. Particularly, the discovery of PpIX as a specific substrate of ATP binding cassette subfamily G member 2 (ABCG2) opens the door to therapeutic enhancement with ABCG2 inhibitors. Studies with human tumor cell lines and human tumor samples have demonstrated ABCG2 as an important biological determinant of reduced ALA-PpIX tumor accumulation, inhibition of which greatly enhances ALA-PpIX fluorescence and PDT response. These studies strongly support targeting ABCG2 as an effective therapeutic enhancement approach. In this review, we would like to summarize current research of ABCG2 as a drug efflux transporter in multidrug resistance, highlight previous works on targeting ABCG2 for therapeutic enhancement of ALA, and provide future perspectives on how to translate this ABCG2-targeted therapeutic enhancement strategy from bench to bedside.

5-Aminolevulinic Acid as a Theranostic Agent for Tumor Fluorescence Imaging and Photodynamic Therapy.

5-Aminolevulinic acid (ALA) is a naturally occurring amino acid synthesized in all nucleated mammalian cells. As a porphyrin precursor, ALA is metabolized in the heme biosynthetic pathway to produce protoporphyrin IX (PpIX), a fluorophore and photosensitizing agent. ALA administered exogenously bypasses the rate-limit step in the pathway, resulting in PpIX accumulation in tumor tissues. Such tumor-selective PpIX disposition following ALA administration has been exploited for tumor fluorescence diagnosis and photodynamic therapy (PDT) with much success. Five ALA-based drugs have now received worldwide approval and are being used for managing very common human (pre)cancerous diseases such as actinic keratosis and basal cell carcinoma or guiding the surgery of bladder cancer and high-grade gliomas, making it the most successful drug discovery and development endeavor in PDT and photodiagnosis. The potential of ALA-induced PpIX as a fluorescent theranostic agent is, however, yet to be fully fulfilled. In this review, we would like to describe the heme biosynthesis pathway in which PpIX is produced from ALA and its derivatives, summarize current clinical applications of ALA-based drugs, and discuss strategies for enhancing ALA-induced PpIX fluorescence and PDT response. Our goal is two-fold: to highlight the successes of ALA-based drugs in clinical practice, and to stimulate the multidisciplinary collaboration that has brought the current success and will continue to usher in more landmark advances.

A Novel 89Zr-labeled DDS Device Utilizing Human IgG Variant (scFv): "Lactosome" Nanoparticle-Based Theranostics for PET Imaging and Targeted Therapy.

"Theranostics," a new concept of medical advances featuring a fusion of therapeutic and diagnostic systems, provides promising prospects in personalized medicine, especially cancer. The theranostics system comprises a novel 89Zr-labeled drug delivery system (DDS), derived from the novel biodegradable polymeric micelle, "Lactosome" nanoparticles conjugated with specific shortened IgG variant, and aims to successfully deliver therapeutically effective molecules, such as the apoptosis-inducing small interfering RNA (siRNA) intracellularly while offering simultaneous tumor visualization via PET imaging. A 27 kDa-human single chain variable fragment (scFv) of IgG to establish clinically applicable PET imaging and theranostics in cancer medicine was fabricated to target mesothelin (MSLN), a 40 kDa-differentiation-related cell surface glycoprotein antigen, which is frequently and highly expressed by malignant tumors. This system coupled with the cell penetrating peptide (CPP)-modified and photosensitizer (e.g., 5, 10, 15, 20-tetrakis (4-aminophenyl) porphyrin (TPP))-loaded Lactosome particles for photochemical internalized (PCI) driven intracellular siRNA delivery and the combination of 5-aminolevulinic acid (ALA) photodynamic therapy (PDT) offers a promising nano-theranostic-based cancer therapy via its targeted apoptosis-inducing feature. This review focuses on the combined advances in nanotechnology and material sciences utilizing the "89Zr-labeled CPP and TPP-loaded Lactosome particles" and future directions based on important milestones and recent developments in this platform.

The ABCG2 mRNA Synthesized in vitro Promoted Uric Acid Excretion in Mice / 中国生物化学与分子生物学报

Hyperuricemia is a chronic metabolic disease caused by the accumulation of uric acid in the body caused by purine metabolism disorder. In recent years, the incidence of hyperuricemia has increased and the age of onset is showing a younger trend. Finding effective therapeutic targets and treatment methods is a hot spot of current research. The urate transporter ATP-binding cassette subfamily G member 2 (ABCG2) is mainly expressed in the kidney and promotes uric acid excretion. In this study, ABCG2 mRNA was synthesized in vitro and transfected into hyperuricemia model mice to observe its effect on mouse uric acid levels. Firstly, the DNA template of ABCG2 mRNA was chemically synthesized, and then transcribed into mRNA in vitro, followed by modification and transfection into mouse TCMK-1 renal tubular epithelial cells. Finally, the protein expression in the cells was detected by Western blot. The results showed that the amount of protein expression in TCMK-1 cells was positively correlated with the amount of transfected mRNA (P < 0. 01), indicating a successful transfection. In animal experiments, twenty-four SPF mice were randomly divided into four groups (n = 6): control group, hyperuricemia model group, benzbromarone group [20 mg/(kg•d)] and mRNA group [2 mg/(kg•3d)]. The mice have been modeled and treated for 28 days. During this period, the body weight and growth status of the mice were monitored daily. After the treatment, the levels of serum uric acid, urine uric acid, serum creatinine, blood urea nitrogen and liver xanthine oxidase were analyzed. The results showed that compared with the model group of mice, mRNA treatment can significantly reduce the levels of serum uric acid (100. 38 ± 10. 94), blood urea nitrogen (6. 30 ± 1. 10), and serum creatinine (30. 86 ± 5. 78, P<0. 05 or P<0. 01). It can also increase the level of urine uric acid (617. 48 ± 50. 34, P<0. 05) in mice and promote the excretion of uric acid. But it has no significant effect on the activity of xanthine oxidase (26. 19 ± 2. 58) in the liver. The pathological changes of mice kidney were observed by HE staining. The results showed that compared with mice in the model group, pathological damages such as renal tubular cell edema and inflammatory cell infiltration in the mRNA treatment group were significantly improved. The relative expression of mRNA in mice kidney was detected by qRT-PCR, and the protein expression of ABCG2 in mice kidney was detected by immunohistochemistry and Western blot. The results showed that the relative expression of ABCG2 mRNA and its protein were significantly up-regulated in the kidney tissues of mice in the mRNA group (P < 0. 01), indicating that the transfection was successful in vivo. In conclusion, ABCG2 mRNA synthetized and modified in vitro can be successfully expressed in hyperuricemia mice and promote excretion of uric acid and other organic ions, as well as improvement of renal injury in mice. These results provide experimental basis for the clinical application of ABCG2 as a target for the treatment of hyperuricemia related diseases.

Association between the ABCG2 C421A polymorphism and Alzheimer's disease.

ATP binding cassette subfamily G member 2 (ABCG2) is involved in amyloid-ß transport and was found to be significantly up-regulated in Alzheimer's disease (AD) brain. A functional polymorphism of the ABCG2 gene (C421A; rs2231142) was genotyped in a sample of 299 Hungarian late-onset AD patients and 259 elderly, non-demented controls to investigate for the first time its association with AD, either alone or in combination with apolipoprotein E (APOE) ɛ2/ɛ3/ɛ4 polymorphism. A significantly increased susceptibility to AD (OR=1.741, 95% CI: 1.075-2.819, p=0.024) associated with ABCG2 C/C genotype was found when compared with the variant allele containing genotypes (CA and AA) as the reference category. Logistic regression analysis revealed a significant interaction effect between the ABCG2 C/C genotype and APOE ɛ4 allele on AD risk (p=0.003). It seems that the potential modest risk effect of the ABCG2 C/C genotype on AD risk is more pronounced in combination with the APOE ɛ4 allele. Further independent replications of our findings are required.