Experimental treatment of neuroblastoma using [131I]meta-iodobenzylguanidine and topotecan in combination.

The radiopharmaceutical [(131)I]meta-iodobenzylguanidine ([(131)I]MIBG) and the topoisomerase I inhibitor topotecan are both effective as single-agent treatments of neuroblastoma. Our purpose was to assess the therapeutic potential of [(131)I]MIBG and topotecan in combination using SK-N-BE(2c) neuroblastoma cells and UVW/NAT glioma cells expressing the noradrenaline transporter transgene. Topotecan treatment was given (i) before, (ii) after or (iii) simultaneously with [(131)I]MIBG. DNA fragmentation was evaluated by comet assay and cell cycle redistribution was determined by fluorescence-activated cell sorting. Combination index analysis indicated that delivery schedules (ii) and (iii) were more effective than schedule (i) with respect to clonogenic cell kill. Similarly, significant DNA damage was observed following treatment schedules (ii) and (iii) (p <0.005), but not (i). Prior exposure to topotecan did not significantly enhance [(131)I]MIBG uptake in athymic mice bearing tumour xenografts. We conclude that the enhancement of the efficacy of [(131)I]MIBG by combining it with topotecan was the result of inhibition of DNA damage repair rather than an increase in expression of the noradrenaline transporter by tumour.

Dose-response relationship for radiation-induced mutations at micro- and minisatellite loci in human somatic cells in culture.

PURPOSE: The study was designed to determine the dose-response relationship for radiation induction of mutations at mini- and microsatellite loci in human somatic cells. Mutations induced by graded doses of gamma-irradiation were quantified by screening clones derived from single irradiated cells for micro- and minisatellite alterations following irradiation with 1, 2 or 3 Gy. MATERIALS AND METHODS: After irradiation, the moderately radioresistant glioma cell line UVW was seeded at low density into Petri dishes to allow formation of discrete colonies, 100 of which were examined at each dose. All the cells within a colony were presumed to have arisen from a single irradiated cell. Radiation-induced microsatellite alterations were determined at 16 different loci, by PCR amplification and visualization on polyacrylamide gels. Minisatellite alterations were identified at four different minisatellite loci by restriction enzyme digestion and Southern blotting. RESULTS: A dose-response curve for mutation frequency was obtained by analysis of 100 clones, yielding a minisatellite mutation rate of 5.5x10(-3) mutations/locus/Gy/cell and a microsatellite mutation rate of 8.75x10(-4) mutations/locus/ Gy/cell. At microsatellite loci, alterations were predominantly simple loss or gain of repeat units and loss of heterozygosity (LOH). The mutations in minisatellite loci resulted predominantly in LOH and variation in repeat number. The background instability at each locus was determined by analysis of non-irradiated clones. Only 2% and 1% of the micro-and minisatellite loci respectively showed altered bands. CONCLUSIONS: This is the first report of a dose-response relationship for radiation-induced micro- and minisatellite mutations in human somatic cells. Described is a sensitive method for analysis of low-dose radiation mutagenesis in somatic cells that may prove to be a useful tool for radiation protection and dosimetry.

Experimental targeted radioiodide therapy following transfection of the sodium iodide symporter gene: effect on clonogenicity in both two-and three-dimensional models.

To evaluate the potential of the expression of the sodium/iodide symporter (NIS) as a means of targeting radioiodine to tumor cells, we have employed plasmid-mediated transfection of the NIS gene into a range of mammalian cell hosts. We observed perchlorate-inhibitable iodide uptake up to 41-fold over control in all NIS-transfected cells. We assessed the effect of NIS expression followed by exposure to 131I- on the clonogenic survival of UVW glioma cells. After exposure of two-dimensional monolayer cultures of UVW-NIS cells to 131I- at a radioactive concentration of 4 MBq/mL, clonogenic survival was reduced to 21%. Similar treatment of UVW-NIS cells in three-dimensional spheroid cultures resulted in a reduction of clonogenic survival to 2.5%. This increase in sensitivity to 131I- exposure is likely to be due to a radiological bystander effect. These results are very encouraging for the development of a novel cytotoxic gene-therapy strategy in which a radiological bystander effect plays a significant role in tumor cell sterilization.