Induction of partial synchronization of leukemia cells by continuous infusion of low-dose methotrexate followed by citrovorum factor

Improved retroviral suicide gene transfer in colon cancer cell lines after cell synchronization with methotrexate

Background

Cancer gene therapy by retroviral vectors is mainly limited by the level of transduction. Retroviral gene transfer requires target cell division. Cell synchronization, obtained by drugs inducing a reversible inhibition of DNA synthesis, could therefore be proposed to precondition target cells to retroviral gene transfer. We tested whether drug-mediated cell synchronization could enhance the transfer efficiency of a retroviral-mediated gene encoding herpes simplex virus thymidine kinase (HSV-tk) in two colon cancer cell lines, DHDK12 and HT29.

Methods

Synchronization was induced by methotrexate (MTX), aracytin (ara-C) or aphidicolin. Gene transfer efficiency was assessed by the level of HSV-TK expression. Transduced cells were driven by ganciclovir (GCV) towards apoptosis that was assessed using annexin V labeling by quantitative flow cytometry.

Results

DHDK12 and HT29 cells were synchronized in S phase with MTX but not ara-C or aphidicolin. In synchronized DHDK12 and HT29 cells, the HSV-TK transduction rates were 2 and 1.5-fold higher than those obtained in control cells, respectively. Furthermore, the rate of apoptosis was increased two-fold in MTX-treated DHDK12 cells after treatment with GCV.

Conclusions

Our findings indicate that MTX-mediated synchronization of target cells allowed a significant improvement of retroviral HSV-tk gene transfer, resulting in an increased cell apoptosis in response to GCV. Pharmacological control of cell cycle may thus be a useful strategy to optimize the efficiency of retroviral-mediated cancer gene therapy.

Etoposide (VP-16): cytogenetic studies in mice

Etoposide (VP 16-213), the epipodophyllotoxin derivative that is widely used in the treatment of cancer, forms complexes with DNA-topoisomerase type II alpha to exert its cytotoxicity. The drug was evaluated in vivo in Swiss albino mouse bone marrow cells for its ability to induce clastogenicity and sister chromatid exchanges (SCEs). Doses of 5, 10, 15, and 20 mg/kg body weight etoposide given intraperitoneally induced a dose-dependent significant increase of clastogenicity (Trend test, alpha < or = 0.05). The aberrations induced were predominantly chromatid types. The drug shows specificity for S-phase cells: cells harvested 6 and 12 hr posttreatment showed a significantly increased number of damaged cells and aberrations per cell. Doses of 0.5, 1.0, 2.5, 5.0, and 10.0 mg etoposide/kg body weight induced a dose-dependent significant induction of SCEs (Trend test, alpha < or = 0.05). The minimal effective concentration was 0.5 mg/kg body weight. Etoposide significantly prolonged the cell cycle time at all concentrations tested: 12-13 hr in treated animals vs. 11 hr in control. The results confirm in vivo cell cycle phase specificity of the drug and further designate etoposide as a potent clastogen and a genotoxic agent in mice.

Studies of the differentiation properties of camptothecin in the human leukaemic cells K562

Camptothecin, a specific inhibitor of topoisomerase I, caused erythroid differentiation of the human leukaemia cell-line K562, as assessed by benzidine staining at 70 h recovery following a 60 min treatment of the cells. Differentiation was confirmed by increased levels of epsilon-globin and gamma-globin mRNA in the treated cells and was accompanied by down-regulation of c-myb mRNA. Synchronisation of K562 cells by non-cytotoxic doses of methotrexate increased the differentiation induced by camptothecin, without affecting the camptothecin-induced inhibition of cellular proliferation. Camptothecin induction of differentiation and inhibition of proliferation may occur by independent mechanisms.

Synchronisation of cancer cell lines of human origin using methotrexate

U937 human histiocytic lymphoma cell line and SW626 ovarian carcinoma line of human origin were synchronised using very low, nontoxic concentrations (0.04-0.08 microM for 16-24 h) of methotrexate (MTX) under standard culture conditions. Satisfactory synchrony was achieved to study S phase events. Various kinetic behaviours and biological properties of the synchronised cells are considered for characterisation of the system. MTX-synchronisation was compared with that induced by aphidicolin (APC) alone and by serum deprivation and APC. In some cancer cell lines MTX appears to be the best choice for obtaining highly synchronised cell populations without cytotoxicity or physiological perturbations.