Cytotoxic effects of vincristine on tumour subpopulations separated from pulmonary nodules

Abstract

The cytotoxic and stathomokinetic effects of vincristine (VCR) on murine fibrosarcoma (FSa) cells, grown either in vitro as primary cultures or in vivo as micro- or macroscopic pulmonary nodules, were determined and compared. FSa cells were separated and synchronized on the basis of size by centrifugal elutriation. Flow microfluorometry (FMF) was used to determine the cell-cycle parameters and the relative synchrony of the separated populations, thus allowing determination of age-dependent cytotoxicity. The colony-forming efficiencies (CFE) of these cells were determined using a lung colony assay. Synchronized cell population of FSa cells, separated by centrifugal elutriation, were injected into recipient animals and exposed 20 min later to a single dose of VCR to determine their age-specific sensitivity. Under these conditions there appeared to be a suggestion of an enhanced killing of cells enriched in the G2 + M phase. However, following prolonged VCR exposure in vitro (e.g., 2.5 micrograms ml-1; 25 ml for 24 h) to primary cultures of FSa cells or in vivo (e.g., 0.25 mg kg-1 per fraction i.p.; 5 fractions in 24 h) to macroscopic pulmonary tumour nodules, elutriated FSa cell populations most enriched with G1 phase cells exhibited the lowest CFE. If under either condition exposed cells were allowed to recover in the absence of VCR for 24 h prior to their removal and separation, FSa cell survival increased in each of the elutriated populations. In contrast, while G1 enriched cell populations from in vitro exposed cultures still exhibited a significant reduction in CFE, no such age-specific response was observed for in vivo exposed macroscopic pulmonary nodules. The stathomokinetic effect of VCR on FSa cells was also readily observed in vitro using FMF analysis (e.g., an increase of from 20 to 38% in the G2 + M phase compartment). While no such effect was observed in vivo using FMF analysis, cluster of mitotic figures were observed. The mitotic indices (MI) of the in vivo exposed FSa cells increased from 2.5 to 8.4%.