Laboratory and clinical evidence of synergistic cytotoxicity of sequential treatment with gemcitabine followed by docetaxel in the treatment of sarcoma.

PURPOSE: A recent report of the combination of gemcitabine and docetaxel described favorable results in patients with uterine leiomyosarcoma. The objective of this report is to describe experience with this combination in a variety of histologic subtypes of sarcoma. Additionally, cell-culture studies were performed to assess the effect of the sequence of drug administration on colony formation. PATIENTS AND METHODS: A medical record review of 35 patients receiving the gemcitabine/docetaxel combination was undertaken. Gemcitabine 675 mg/m(2) intravenously was administered over 90 minutes on days 1 and 8, and docetaxel 100 mg/m(2) intravenously was administered over 60 minutes on day 8 of a 21-day cycle. Cell culture studies using the SAOS-2 osteosarcoma cell line and MCF-7 breast cancer cell line were also performed. Gemcitabine and docetaxel were added to cells either simultaneously for 24 hours, gemcitabine for 24 hours followed by docetaxel for 24 hours, or the reverse sequence. RESULTS: Thirty-five patients were treated. Five complete responses and 10 partial responses were observed for an overall response rate of 43%. Responses occurred in uterine, extremity, and retroperitoneal leiomyosarcoma, osteosarcomas, angiosarcomas, malignant fibrous histiocytomas, malignant peripheral-nerve sheath tumors, and Ewing's sarcoma. In the cell culture studies, gemcitabine followed by docetaxel provided synergy. In contrast, the administration of drugs simultaneously resulted in antagonism, and docetaxel followed by gemcitabine provided mixed results. CONCLUSION: The combination of gemcitabine and docetaxel seems to be active in a variety of sarcomas. A multicenter, randomized clinical trial in soft tissue sarcoma comparing gemcitabine alone with this combination, is ongoing.

The role of DNA synthesis inhibition in the cytotoxicity of 2',2'-difluoro-2'-deoxycytidine.

PURPOSE: Cytotoxicity from the anticancer drug 2',2'-difluoro-2'-deoxycytidine (dFdCyd) has been correlated with its incorporation into DNA. However, cytotoxicity may also result from inhibition of DNA synthesis, due to either (1) dFdCyd diphosphate-mediated inhibition of ribonucleotide reductase, or (2) direct inhibition of DNA polymerases by the 5'-triphosphate of dFdCyd (dFdCTP). To elucidate the role of DNA synthesis inhibition in the cytotoxicity of dFdCyd, we compared dFdCyd to hydroxyurea (HU), a ribonucleotide reductase inhibitor, and aphidicolin, an inhibitor of DNA polymerases, in the U251 and D54 human glioblastoma cell lines. METHODS: Sensitivity to dFdCyd, HU, and aphidicolin were determined using a colony formation assay. The effects of these drugs on DNA synthesis were measured by dual parameter flow cytometry, while the effects on nucleotide pool levels were analyzed by high-performance liquid chromatography. RESULTS: HU and aphidicolin elicited substantially less cytotoxicity than the multi-log killing with dFdCyd. When used at equitoxic concentrations (24-h IC50 values), dFdCyd and HU decreased purine dNTP pools primarily, but dFdCyd was less effective than HU. dFdCyd had decreased dATP by about 80% after 4-12 h, and required 8-24 h to decrease DNA synthesis by 50%. In contrast, HU rapidly depleted dATP by >98% within 2 h, which resulted in >90% inhibition of DNA synthesis. Aphidicolin at a concentration similar to its Ki values for DNA polymerases (1 microM) decreased DNA synthesis by >70% within 2 h. However, this decreased cell survival by only 10% (U251 cells) and 40% (D54 cells). CONCLUSIONS: These results demonstrate that HU and aphidicolin produced a more rapid and profound inhibition of DNA synthesis than dFdCyd, but resulted in significantly less cytotoxicity. This suggests that inhibition of DNA synthesis accounted for less than one log of the multi-log cytotoxicity observed with dFdCyd, whereas incorporation of dFdCTP into DNA is a more lethal event.