Surface proteomic analysis of osteosarcoma identifies EPHA2 as receptor for targeted drug delivery.

BACKGROUND: Osteosarcoma (OS) is the most common bone tumour in children and adolescents. Despite aggressive therapy regimens, treatment outcomes are unsatisfactory. Targeted delivery of drugs can provide higher effective doses at the site of the tumour, ultimately improving the efficacy of existing therapy. Identification of suitable receptors for drug targeting is an essential step in the design of targeted therapy for OS. METHODS: We conducted a comparative analysis of the surface proteome of human OS cells and osteoblasts using cell surface biotinylation combined with nano-liquid chromatography - tandem mass spectrometry-based proteomics to identify surface proteins specifically upregulated on OS cells. This approach generated an extensive data set from which we selected a candidate to study for its suitability as receptor for targeted treatment delivery to OS. First, surface expression of the ephrin type-A receptor 2 (EPHA2) receptor was confirmed using FACS analysis. Ephrin type-A receptor 2 expression in human tumour tissue was tested using immunohistochemistry. Receptor targeting and internalisation studies were conducted to assess intracellular uptake of targeted modalities via EPHA2. Finally, tissue micro arrays containing cores of human OS tissue were stained using immunohistochemistry and EPHA2 staining was correlated to clinical outcome measures. RESULTS: Using mass spectrometry, a total of 2841 proteins were identified of which 156 were surface proteins significantly upregulated on OS cells compared with human primary osteoblasts. Ephrin type-A receptor 2 was highly upregulated and the most abundant surface protein on OS cells. In addition, EPHA2 was expressed in a vast majority of human OS samples. Ephrin type-A receptor 2 effectively mediates internalisation of targeted adenoviral vectors into OS cells. Patients with EPHA2-positive tumours showed a trend toward inferior overall survival. CONCLUSION: The results presented here suggest that the EPHA2 receptor can be considered an attractive candidate receptor for targeted delivery of therapeutics to OS.

Fiber-chimeric adenoviruses expressing fibers from serotype 16 and 50 improve gene transfer to human pancreatic adenocarcinoma.

Survival of patients with pancreatic cancer is poor. Adenoviral (Ad) gene therapy employing the commonly used serotype 5 reveals limited transduction efficiency due to the low amount of coxsackie-adenovirus receptor on pancreatic cancer cells. To identify fiber-chimeric adenoviruses with improved gene transfer, a library of Ad vectors based on Ad5 and carrying fiber molecules consisting of 16 other serotypes were transduced to human pancreatic carcinoma cell lines. Adenoviruses containing fibers from serotype 16 and 50 showed increased gene transfer and were further analyzed. In a gene-directed prodrug activation system using cytosine deaminase, these adenoviruses proved to be effective in eradicating primary pancreatic tumor cells. Fiber-chimeric Ad5 containing fiber 16 and wild-type Ad5 were also transduced ex vivo to slices of normal human pancreatic tissue and pancreatic carcinoma tissue obtained during surgery. It was shown that fiber-chimeric Ad5 with fiber 16 revealed an improved gene delivery to primary pancreatic tumor tissue compared to Ad5. In conclusion, fiber-chimeric adenoviruses carrying fiber 16 and 50 reveal a significantly enhanced gene transfer and an increased specificity to human pancreatic adenocarcinoma compared to Ad5, whereas transduction to normal pancreatic tissue was decreased. These findings expand the therapeutic window of Ad gene therapy for pancreatic cancer.

Canalicular multispecific organic anion transporter/multidrug resistance protein 2 mediates low-affinity transport of reduced glutathione.

The canalicular multispecific organic anion transporter (cMOAT), a member of the ATP-binding cassette transporter family, mediates the transport of a broad range of non-bile salt organic anions from liver into bile. cMOAT-deficient Wistar rats (TR-) are mutated in the gene encoding cMOAT, leading to defective hepatobiliary transport of a whole range of substrates, including bilirubin glucuronide. These mutants also have impaired hepatobiliary excretion of GSH and, as a result, the bile flow in these animals is reduced. In the present work we demonstrate a role for cMOAT in the excretion of GSH both in vivo and in vitro. Biliary GSH excretion in rats heterozygous for the cMOAT mutation (TR/tr) was decreased to 63% of controls (TR/TR) (114+/-24 versus 181+/-20 nmol/min per kg body weight). Madin-Darby canine kidney (MDCK) II cells stably expressing the human cMOAT protein displayed >10-fold increase in apical GSH excretion compared with wild-type MDCKII cells (141+/-6.1 pmol/min per mg of protein versus 13.2+/-1.3 pmol/min per mg of protein in wild-type MDCKII cells). Similarly, MDCKII cells expressing the human multidrug resistance protein 1 showed a 4-fold increase in GSH excretion across the basolateral membrane. In several independent cMOAT-transfectants, the level of GSH excretion correlated with the expression level of the protein. Furthermore, we have shown, in cMOAT-transfected cells, that GSH is a low-affinity substrate for the transporter and that its excretion is reduced upon ATP depletion. In membrane vesicles isolated from cMOAT-expressing MDCKII cells, ATP-dependent S-(2,4-dinitrophenyl)glutathione uptake is competitively inhibited by high concentrations of GSH (Ki approximately 20 mM). We concluded that cMOAT mediates low-affinity transport of GSH. However, since hepatocellular GSH concentrations are high (5-10 mM), cMOAT might serve an important physiological function in maintenance of bile flow in addition to hepatic GSH turnover.