Effect of calcium influx blocker verapamil on adriamycin-induced cytotoxicity in leukemia cells in vitro.

The effect of verapamil (calcium influx blocker) on adriamycin-induced cytotoxicity against sensitive and resistant subline of K 562 acute myelogenous human leukemia cells has been evaluated. Verapamil by itself at a concentration of 0.5 microgram/ml did not affect the cell growth. It was found that the nontoxic concentration of verapamil moderately enhanced adriamycin cytotoxicity against K 562 cells, showing enhancement ratio of 1.3-1.4 according to the schedule used. A significant enhancement of adriamycin cytotoxicity (enhancement ratio of 5.8) was observed when verapamil and adriamycin were administered simultaneously against resistant subline of K 562/ADM cells. The results obtained give grounds to assume that verapamil could be used to overcome drug resistance in tumor cells.

On the in vitro cytotoxicity of 1-chloroethyl-2-chloromethyl-2-imidazoline hydrochloride.

The cytotoxic activity of the monofunctional alkylating agent 1-chloroethyl-2-chloromethyl-2-imidazoline hydrochloride (chlorimidazine), synthesized according to predetermined properties, is characterized. The data obtained show that the substance has a cell-cycle state nonspecific cytotoxic effect. The interaction of chlorimidazine with cellular DNA is traced. It is found that the substance does not induce a break in the macromolecule, apurine sites or intercalation. Ensuing from the chemical structure of the compound, the probable mechanism of its cytotoxic action is discussed.

Dependence of bleomycin-induced cytotoxicity and DNA damage on the in vitro culture growth phase of mouse tumour cells.

EMT 6/Ca/VJAC cells have been treated with various doses of bleomycin and the effects of these treatments in terms of cell killing and DNA damage have been determined. The experiments have been carried out with exponentially growing and plateau-phase cultures. Dose-response curves have been obtained using a clonogenic cell survival assay. Bleomycin-induced DNA damage was quantitated by a fluorescence procedure, based upon the time-dependent partial unwinding of cellular DNA under alkaline conditions. Although cells in exponential-phase of culture growth were more sensitive to bleomycin than those in plateau-phase, this could only be attributed to enhanced drug-DNA interaction at high (greater than 40 micrograms/ml) drug concentration. Thus factors other than DNA damaging potential and related to culture growth status control drug sensitivity.

Potentiation of sensitivity to bleomycin and the drug-induced DNA damage in EMT6 cells by the calmodulin inhibitor trifluoperazine.

It has been shown that inhibitors of calmodulin can increase the sensitivity of rodent cells to Bleomycin by interfering with DNA repair functions. As a result of this study we have found that treatment of plateau-phase EMT6 cells with Bleomycin causes a decrease in cell survival due to DNA damage. This toxic effect can be potentiated by the addition of a nonlethal dose of the calmodulin inhibitor Trifluoperazine. Furthermore, it was found that Trifluoperazine greatly potentiated Bleomycin-induced DNA breakage. Considering the results obtained by alkaline-denaturation assay (detects single-strand breaks, including these arising from alkali-labile lesions) and nucleoid sedimentation (in neutral sucrose gradients) assay (detects only frank breaks), a difference, presumably due to the Trifluoperazine-produced discrete block in the repair of Bleomycin-induced DNA alkali-labile lesions was found. These data suggest a role for calmodulin in the DNA repair pathway and provide a rational basis for the use of calmodulin inhibitors in cancer chemotherapy.

Modification of the balance between damage and repair of bleomycin-induced DNA-strand breakage by hyperthermia.

It is well recognized that hyperthermia can greatly enhance the cytotoxic effect of bleomycin. It has been suggested that the mechanism of hyperthermic potentiation of bleomycin toxicity involves the inhibition of DNA repair function. We have investigated how hyperthermia can modify the repair capacity of bleomycin treated cells by monitoring the induction of DNA damage and repair, using two essentially different techniques (DNA unwinding assay and nucleoid sedimentation assay). We have also investigated whether the enhancement of DNA-damaging potential of bleomycin was related to the availability of new sites within chromatin for drug attack. We have found that heat treatment (even for non-toxic exposures of 30 min at 44 degrees C) restricts the access of active drug to DNA, probably by the increase in nuclear protein content. The results obtained show that the increase in drug-induced DNA damage in heat-treated cells probably represents an underestimation of the predominant effect of hyperthermia on reducing cellular DNA repair capacity.

Antitumour activity of chlorimidazine on transplantable mouse tumour systems.

The antitumour activity of the newly synthesized compound, chlorimidazine (1-chlorethyl-2-chlormethyl-2-imidazoline hydrochloride), has been investigated on mouse tumour systems including L 1210 and P 388 leukaemias and Lewis lung carcinoma. It has been found that optimum treatment schedules resulted in 153% T/C in mice with L 1210 leukaemia, 159% T/C in mice bearing P 388 leukaemia and 68% TWI for Lewis lung carcinoma. Due to the results obtained the compound acts as a novel potential antitumour agent that warrants further evaluation.

Testing of 2,3-dihydro-1,3-6H-oxazine-dione (3-oxauracil) in mouse L1210 leukemia and 37 sarcoma.

The antimetabolite 2,3-dihydro-1,3-6H-oxazine-dione (3-oxauracil) has been investigated in an attempt to elucidate its effects on survival time of DBA/2 and B6D2F1 mice with L1210 leukemia and of outbred albino mice with 37 sarcoma. A significant increase in survival time was observed in mice with 37 sarcoma and slight effects were observed in mice with L1210 leukemia when treated with 3 x 12.5 or 3 x 25 mg/kg of 3-oxauracil. No toxic side effects were observed when large therapeutic doses of the drug were given.