Effects of vinblastine on cell membrane fluidity and the growth of SA-1 tumor in mice

Schedule-dependent interaction between vinblastine and irradiation in experimental sarcoma

BACKGROUND AND PURPOSE

Prolonged vinblastine (VLB) infusion and irradiation (IR) lead to favourable results in certain tumours types; however the underlying biological mechanisms of interaction are not well known. The aim of our study was to evaluate the dose- and time-dependent interactions between split-dose VLB treatment (mimicking prolonged infusion) and IR of sarcoma SA-1 tumours in A/J mice.

METHODS

Antitumor effectiveness of different VLB-IR schedules was determined by a tumour growth delay assay, the VLB amount in the tumours by liquid chromatography coupled to mass spectrometry and DNA cell cycle analysis.

RESULTS

A positive antitumor effect was obtained when tumours were irradiated immediately after the first (0 h) or second (4 h) injection of VLB treatment, despite the lower amount of VLB in the tumours as well as decreased number of cells in the IR-sensitive G2M phase at these times points as opposed to the second half of VLB split-dose scheduling.

CONCLUSION

Preferential binding of VLB to microtubules (with consequent lack of available VLB to bind to DNA where it acts as a radioprotector) and the absence of radiobiologically relevant hypoxia are presumably leading to the observed therapeutic benefit of applying IR at the beginning of the prolonged VLB infusion.

Schedule-dependent interaction between vinblastine and cisplatin in Ehrlich ascites tumors in mice

Information on the in vivo antitumor efficiency of the combination of Vinca alkaloids in animal tumor models, especially vinblastine (VLB) with cisplatin [cis-diamminedichloroplatinum(II); CDDP] is very limited. Therefore, the aim of our study was to explore whether antitumor schedule dependence exists for the combination of CDDP and VLB on i.p. Ehrlich ascites tumors in mice. Animals were treated 3 days after tumor transplantation with VLB (0.006 mg/kg) or CDDP (0.05 mg/kg) alone, VLB followed by CDDP, and CDDP followed by VLB. The time interval between i.p. injections of the drugs was 24 h. Cell number was measured by counting viable cells using the trypan blue exclusion assay, cell platinum content by electrothermal atomic absorption spectrometry, DNA distribution pattern using flow cytometry, apoptosis by flow-cytometric terminal deoxynucleotidyl transferase dUTP nick-end labeling assay, and cell morphology. Combination of CDDP and VLB resulted in additive interaction when VLB preceded CDDP as determined from cell survival data 24 h after completion of the therapy and in increased platinum content (two times) compared with the same combination in a reverse schedule (CDDP given before VLB), which resulted in antagonism. None of the treatment combinations induced apoptosis. We propose that the observed increase in antitumor effectiveness is mainly due to higher platinum accumulation in tumor cells, which we unambiguously demonstrated by measurement of platinum content in the tumor cells, leading to increased cytotoxicity as well as to cell cycle-dependent effects of VLB and CDDP.

Effect of vinblastine on cell membrane fluidity in vinblastine-sensitive and -resistant HeLa cells

The electron paramagnetic resonance method (EPR) was used to study the effects of vinblastine (VLB) on cell membrane fluidity in wild-type HeLa cells (HeLa K) and its subclone, which is resistant to several drugs (HeLa CA). HeLa CA cells, obtained by treatment of HeLa K with CDDP, were found to be more resistant to VLB than to CDDP. The experimentally observed EPR spectra were correlated with the calculated spectra obtained by computer simulation. The results indicate that the cell membrane of HeLa K and HeLa CA cells is heterogeneous and can be described with at least three types of coexisting domains with different fluidity characteristics. The two more fluid domains of HeLa CA cells were found to be more fluid than in HeLa K cells. The fluidity of the less fluid domain remained unchanged but its portion in the membrane was increased. VLB treatment did not affect the membrane fluidity of HeLa CA cells significantly. On the other hand, 1 h of treatment of HeLa K cells with 1 ng/ml VLB did not change the fluidity characteristics of membrane domains but decreased the portion of the less fluid domains. This was also reflected in an average increase of the entire membrane fluidity. The observed changes were detected at VLB concentrations which were far below the cytotoxic level.