Cytotoxic effects of vincristine on tumour subpopulations separated from pulmonary nodules

The in vivo interaction between vincristine and radiation in a C3H mammary carcinoma and the feet of CDF1 mice

PURPOSE

Evaluation of the interaction between vincristine (VCR) and X rays in a murine tumor and its surrounding skin.

METHODS AND MATERIALS

End points were local tumor control and moist desquamation using the C3H mammary carcinoma and the mouse foot skin in vivo. Cell cycle effects of VCR was studied by dual parameter flowcytometry. Vincristine was administered as a single IP injection at various time intervals from 4 days before to 4 days after irradiation.

RESULTS

Flowcytometric studies of cell cycle distribution showed that VCR caused a temporary blockage of cells in the mitotic phase; the proportion of cells in G2M increased three-fold at intervals up to 48 h after VCR treatment. The radiation enhancement peaked when VCR was administered 24 h before X rays in tumors, and when given 15 min before X rays in skin. A significant therapeutic gain was observed at the 24 h preirradiation of postirradiation intervals--the therapeutic gain factors being 1.19 and 1.24, respectively (p < 0.005). Analysis of the tumor data suggested an additive cytotoxic effect rather than VCR radiosensitization. In contrast to what was expected from the single dose data, a significant loss of therapeutic effect was found for the addition of VCR administered at the first day of a fractionated irradiation regime with five fractions in 5 days (p < 0.025).

CONCLUSION

The tumor control studies showed a lack of correlation between the VCR-induced accumulation of cells in G2M cell cycle phase and enhancement of tumor radiation response. Preirradiation VCR caused radiosensitization both in tumors and skin, whereas postirradiation VCR mostly resulted in responses equal to radiation only.

Effectiveness of AMSA alone or in combination with radiation on murine fibrosarcoma pulmonary nodules

The cytotoxic effects in vivo of 4'-(9-acridinylamino) methanesulfon-m-anisidide (AMSA), radiation or both modalities in combination on murine fibrosarcoma (FSa) cells grown as pulmonary tumors were determined. Fourteen days following the i.v. injection of viable FSa cells, recipient mice developed between 100 and 150 visible pulmonary nodules. At that time, tumor-bearing animals were exposed to either single or combined modality treatments, as well as single and fractionated dose regimens. Animals were sacrificed 1 hour after the last treatment. Tumor nodules were excised, made into a single cell suspension and separated on the basis of cell size by centrifugal elutriation. Flow microfluorometry (FMF) was used to determine the cell-cycle parameters and the relative synchrony of the separated populations, as well as the percentage contamination by normal diploid cells in each of the tumor cell populations. Known numbers of viable cells from each elutriator fraction were injected into recipient mice to determine their colony-forming efficiency (CFE). Surviving fractions were determined by comparing the CFEs of treated FSa cells from each of the separated elutriator fractions with those of appropriate untreated controls. Following a single i.v. dose of AMSA (30 mg/kg), populations of cells enriched in S phase were the most sensitive. When a single dose of AMSA was combined with a single dose of radiation (100 rad), there was a marked schedule dependence with the more effective sequence, especially if a 12 hour interval was chosen between doses, being AMSA followed by irradiation. No schedule dependence was observed if both modalities were combined and administered under a fractionated protocol of four fractions of AMSA (5 mg/kg per fraction) and four fractions of radiation (300 rad per fraction). Under these conditions the greatest reduction in CFE was in cell subpopulations most enriched in S and G2 + M phase cells.