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Background: Ataxia-telangiectasia is a pleiotropic autosomal recessive disorder caused by mutations in the ATM gene. In addition to a profound cancer predisposition, another hallmark of ataxia-telangiectasia is radiosensitivity. Recently, p53-null mouse fibroblasts have been reported to be radiosensitised by the concurrent loss of ATM., Materials and Methods: We compared the sensitivity of atm(+/+)/p53(-/-) and atm(-/-)/p53(-/-) mouse embryonic fibroblasts to different classes of chemotherapeutic agents using the MTT assay, Trypan Blue exclusion and fluorescence-activated cell sorting for cell cycle and apoptosis analyses., Results: Loss of ATM function in p53-deficient cells resulted in a 2- to 4-fold increase in sensitivity to the topoisomerase I poisons camptothecin and topotecan, to the topoisomerase II poisons doxorubicin, epirubicin and etoposide, and to the antimetabolites 5-fluorouracil and gemcitabine, but not to the platinum compounds cisplatin, carboplatin and oxaliplatin, the taxanes docetaxel and paclitaxel, or to busulfan. Loss of ATM function did not result in increased apoptosis, but resulted in increased Trypan Blue staining in response to epirubicin, suggesting that processes other than apoptosis may mediate cytotoxicity. ATM deficiency did not alter the extent of G(1)/S or G(2)/M cell cycle phase accumulation produced by epirubicin, suggesting that enhanced sensitivity was not due to failure of checkpoint activation., Conclusions: We provide further evidence that ATM is involved in regulating cellular defences against some cytotoxic agents in the absence of p53. Tumour-targeted functional inhibition of ATM may be a valuable strategy for increasing the efficacy of anticancer agents in the treatment of p53-mutant cancers.

TAPET-CD, a genetically engineered Salmonella strain with chromosomal-incorporated cytosine deaminase (CD) gene, has been shown to selectively accumulate tumors, suppress tumor growth, and convert 5-fluorocytosine (5-FC, an antifungal agent) to the antitumor agent 5-fluorouracil (5-FU) in animals. The current studies investigated the safety of TAPET-CD, and TAPET-CD/5-FC combination, in animals. In C57BL/6 mice (n = 10 females/dose), the maximum nonlethal dose of TAPET-CD (intravenous [IV] bolus) was 1 x 10(6) colony-forming units (cfu)/mouse, or > 10,000 x that of wild-type Salmonella. In Sprague-Dawley rats (n = 4/sex/group), after treatment with 4 weekly cycles of TAPET-CD (an IV injection/cycle at 1 x 10(5), 3 x 10(5), 1 x 10(6), 3 x 10(6), or 1 x 10(7) cfu/rat on day 1) and 5-FC (per os twice daily [PO b.i.d.], 250 mg/kg on days 2-7/cycle), clinical signs and mortality were evaluated daily, body weight and clinical pathology weekly, and gross necropsy on day 29. No treatment-related toxicity, although occasional and mild clinical signs (e.g., dehydration), increased hepatic enzyme/function values and white blood cells, splenic enlargement, and bilateral red discoloration of the kidneys, were observed. In cynolmogus monkeys, Experiment 1 involved treatment with TAPET-CD (IV injection at 1 x 10(9) cfu/monkey). Clinical signs and mortality were evaluated daily, body weight weekly, and gross necropsy on days 2, 7, and 31 (1/sex/time point). Experiment 2 involved treatment with TAPET-CD (IV injection at 1 x 10(9) and 1 x 10(10) cfu/monkey in Groups 1 to 3 and Groups 4 to 6, respectively) on day 1 and 5-FC (PO b.i.d. at 250, 500, and 1000 mg/kg in Groups 1 to 3, and 500, 1500, and 0 mg/kg in Groups 4 to 6, respectively) on days 4 to 17 (n = 1/sex/group). Clinical signs and mortality were evaluated daily; body weight and clinical pathology on days 1, 2, 4, 14, and 18; body temperature on days 1, 4, and 18; ophthalmic examinations on days 3 and 17; and gross necropsy and histopathology on day 18. Experiment 1 indicated that TAPET-CD at 1 x 10(9) or 1 x 10(10) cfu/monkey was well tolerated, with only occasional mild clinical signs (i.e., emesis, vomiting, inappetance, loose/infrequent/absence of stool), increases in hepatic enzyme/function values, and splenic enlargement. Experiment 2 indicated that TAPET-CD/5-FC combination had a maximum tolerated dose (MTD) of 1 x 10(10) cfu/monkey for TAPET-CD and 500 mg/kg for 5-FC in monkeys. Supra-MTDs induced renal toxicity. In conclusion, TAPET-CD had a good safety profile (reflected by the extremely large amount of TAPET-CD needed to induce mortality or toxicity) in mice, rats, and monkeys. More adverse events were observed with TAPET-CD/5-FC combination when compared to TAPET-CD and these events were similar to the reported effects of 5-FU, suggesting the involvement of 5-FU.

Conclusion: These results show that eight pancreatic cancer cell lines are broadly sensitive to CDDP, and that chemotherapy for pancreatic cancer may improve the prognosis by more effective drug delivery to cancer cells., Background: Chemotherapy for pancreatic cancer does not satisfactorily improve prognosis. The efficacy of chemotherapy depends on choosing sensitive anticancer drugs., Methods: The in vitro chemosensitivity of eight human pancreatic cancer cell lines was investigated. Growth inhibition was measured by 3H-thymidine incorporation assays for doxorubicin hydrochloride (ADM), mitomycin C (MMC), cisplatin (CDDP), and etoposide (VP-16), and by Alamar Blue assay for (AB assay) 5-fluorouracil (5-FU). The cells were exposed to ADM, MMC, CDDP, and VP-16 for 2 h, and 5-FU for 72 h. From the dose-response curves, the 50% growth inhibition (IC50) level for each drug was estimated., Results: The IC50 after 2 h of exposure of each of the eight kinds of cell lines to each anticancer drug ranged from 0.12-8.2 micrograms/mL for ADM, 0.066-25 micrograms/mL for MMC, 0.57-7 micrograms/mL for CDDP, 0.68-300 micrograms/mL for VP-16. IC50 after 72 h of exposure to 5-FU ranged from 1.8-23 micrograms/mL.

Herpes simplex virus thymidine kinase (HSV-tk)/ganciclovir (GCV) viral-directed enzyme prodrug gene therapy causes potent, tumor-selective cytotoxicity in animal models in which HSV-tk gene transduction is limited to a minority of tumor cells. The passage of toxic molecules from HSV-tk+ cells to neighboring HSV-tk- cells during GCV therapy is one mechanism that may account for this "bystander" cytotoxicity. To investigate whether gap junction-mediated intercellular coupling could mediate this bystander effect, we used a flow cytometry assay to quantitate the extent of heterocellular coupling between HSV-tk+ murine fibroblasts and both rodent and human tumor cell lines. Bystander tumor cytotoxicity during GCV treatment in a coculture assay was highly correlated (P < 0.001) with the extent of gap junction-mediated coupling. These findings show that gap junction-mediated intercellular coupling contributes to the in vitro bystander effect during HSV-tk/GCV therapy and that retroviral transduction of tumor cells is not required for bystander cytotoxicity.

Diacetyldianhydrogalactitol (DADAG), a new alkylating sugar alcohol derivative, was administered as single, 30-min infusions in doses ranging from 390 to 1200 mg/m2. The dose-limiting toxicity was myelosuppression. The median times to WBC nadir and regeneration were 16 and 21 days, and to platelet nadir and recovery 20 and 27, respectively. Nausea and vomiting occurred frequently and were of moderate severity. For phase II studies 900 mg/m2 DADAG given every 4-6 weeks is recommended. The area under the plasma concentration time curve (AUC) for DADAG did not increase in proportion with dose escalation; it changed only from 235.5 +/- 70.7 to 262.4 +/- 71.5 micrograms h ml-1 between doses of 690 and 1050 mg/m2. No correlations between the dose administered and the nadir values for haemoglobin concentration, WBC and platelet counts, or the number of episodes of vomiting were demonstrable in this dose range. Such an association was revealed, however, when the above biological variables were related to the individual AUC for DADAG.