Antranik Shahinian

Evaluation of 9-[(3-18F-fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]-FHPG) in vitro and in vivo as a probe for PET imaging of gene incorporation and expression in tumors

Preparation of 9-[(3-18F-fluoro-1-hydroxy-2-propoxy)methyl]-guanine ([18F]-FHPG) for clinical use, and its evaluation as a positron emission tomography (PET) imaging agent for gene incorporation and expression in tumors are reported. In vitro studies in human colon cancer cells, HT-29, transduced with the retroviral vector G1Tk1SvNa and nontransduced (wild type) showed 4, 8, 12, and 15 times higher uptake of the probe in 1, 3, 5, and 7 h, respectively, in transduced cells compared with the controls. In vivo studies in tumor-bearing nude mice demonstrated that the tumor uptake of the radiotracer is three and six-fold higher in 2 and 5 h, respectively, in transduced cells compared with the control cells. These results suggest that [18F]-FHPG is a potential in vivo PET imaging agent for monitoring gene incorporation and expression in gene therapy of cancer.

Receptor mediated uptake of a radiolabeled contrast agent sensitive to β-galactosidase activity

Radiolabeling of the MRI contrast agent 1-[2-(beta-galactopyranosyloxy)propyl]-4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane with (111)In, and its evaluation is reported. Radiolabeling was performed in acetate buffer with 50-78% radiochemical yield. In vitro studies revealed that the asialoglycoprotein receptor-poor cell line MH1C1 has low uptake, while the receptor-rich cell lines BNL-CL2 and Hep G2 have higher uptake. In vivo, the uptake of the compound in receptor-rich organ liver was very high. Blocking the receptor in vivo, reduced liver uptake by 90% suggesting that the compound localizes in receptor-enriched tissues by binding to the asialoglycoprotein receptor.

Choline autoradiography of human prostate cancer xenograft: effect of castration.

Microcalcifications are an important diagnostic marker for breast cancer on mammograms, yet the mechanism of their formation is poorly understood. Indeed, there is presently no short-latency, high-...The purpose of this study was to investigate the effects of castration and tracer uptake time interval on the level of radiolabeled choline accumulation in murine-implanted human prostate tumor xenografts using quantitative autoradiography. We implanted androgen-dependent (CWR22) and androgen-independent (PC3) human prostate cancer cells in castrated (n = 9) and noncastrated (n = 9) athymic male mice and allowed tumors to grow to 1 cm3. The mice were euthanized at 5, 10, and 20 minutes after injection of 5 µCi [14C]-choline. Mice were prepared for quantitative autoradiography with density light units of viable tumor sections converted to units of radioactivity (nCi/mm2) using calibration. Two-group comparisons were performed using a two-tailed Student t-test with unequal variance and with a significance probability level of less than .05. Two-group comparisons between the means of the tracer uptake level for each tumor type at each of three time points for each of two host types showed that (1) the level of tracer localization in the two tumor types was affected little in relation to the host type and (2) PC3 tumor uptake level tended to increase slowly with time only in the noncastrated host, whereas this was not observed in the castrated host or with CWR22 tumor in either host type. The uptake time interval and castration do not appear to significantly affect the level of radiolabeled choline uptake by the human prostate cancer xenograft.

Validation of fluorouracil metabolite analysis in excised tumor: Lability of anabolites

Rapid excision and freezing of tissue commonly is assumed to preserve the molecular composition of the tissue just prior to its removal from the host. We examined the lability of radiolabeled 5-fluorouracil (FUra) and its anabolites during excision and freeze-clamping in a rat tumor model. Acid-soluble metabolites were identified by HPLC. Two rats, each bearing multiple, subcutaneously-implanted colon tumors, were treated with eniluracil (an inactivator of dihydropyrimidine dehydrogenase) to prevent catabolism of FUra and then injected intravenously with [(3)H]FUra. After 2 hr, tumors were harvested sequentially and segmented. The tumor pieces were kept at room temperature for various times up to 4 min prior to freezing. These specimens showed a decrease (P < 0.01) in labeled nucleoside triphosphate content of 13 +/- 2%/min and commensurate increases (P < 0.005) in labeled nucleoside monophosphates and nucleosides with increasing time-to-freeze. The amounts of labeled macromolecules, nucleoside diphosphates, and FUra each remained approximately constant. The study indicates that substantial errors may occur in measured tissue concentrations of pyrimidine nucleosides and nucleotides due to lability during tissue excision and freeze-clamping. Such errors can be corrected using data of the type obtained in this study.