In Vitro Activity of Alkylating Agents on Human Tumors as Measured by a Short-term Antimetabolic Assay

Sensitization of Chronic Myeloid Leukemia Cells to Adriamycin Cytotoxicity by Clofibrate

Clofibrate (CPIB), an antihyperlipidemic agent, was employed as a drug response modulator in this study to evaluate its action, if any, on adriamycin (ADR) cytotoxicity in adriamycin insensitive chronic myeloid leukemia (CML) cells in vitro. Inhibition of (3H)-thymidine incorporation was used as a measure of DNA biosynthesis inhibition. A marginally toxic concentration of CPIB [0.001 % (v/v)] was utilized to evaluate the cytotoxicity in CML cells exposed to ADR 5 and 10 μg/ml. A heterogeneous response was observed in 16 different CML blood samples, 9 samples displaying a synergistic, 3 an additive and 4 a less than additive inhibition of DNA biosynthesis when exposed to the combination of ADR and CPIB. The cytotoxic effect induced by ADR alone and in combination with CPIB was found to be irreversible. The data suggest that the cell membrane modulating drug CPIB is effective as an adjuvant to enhance the antiproliferative action of ADR.

Combined 4-hydroxy-ifosfamide and vinorelbine treatment in established and primary human breast cell cultures

BACKGROUND

Vinorelbine and ifosfamide are active drugs against breast cancer, but the best treatment schedule has yet to be defined by preclinical or clinical studies. The antitumor activity of 4-hydroxy-ifosfamide (4-OH-IF), the active form of ifosfamide, and vinorelbine (VNB) and their interaction were investigated in two established breast cancer cell lines (MCF-7 and BRC-230) and in 10 primary breast cancer cultures.

MATERIALS AND METHODS

Cytotoxic activity was evaluated by a highly efficient clonogenic assay (HECA). The median-effect principle was applied to evaluate synergistic and antagonistic interactions and the corresponding combination index values were calculated. Cell cycle perturbations were analysed by flow cytometry.

RESULTS

In MCF-7 and BRC-230 cell lines the sequence VNB for 4 hours followed by 4-OH-IF for 24 hours produced an antagonistic effect. Conversely, the inverse sequential scheme, 4-OH-IF-->VNB provided synergistic effects on both cell lines. The synergism was associated with a strong block in the G2-M phase. Synergistic activity of 4-OH-IF-->VNB sequence was confirmed in 7 of 10 primary breast cancer cultures.

CONCLUSIONS

In conclusion, the sequence 4-OH-IF-->VNB appeared to be the most effective scheme both in established cell lines and in primary breast cancer cultures.