MECHANISM OF RESISTANCE TO ACTINOMYCIN IN BACILLUS SUBTILIS

Doxorubicin resistance in P388 leukemia--evidence for reduced drug influx

Multi-drug resistance (MDR) in cancer cells is associated with reduced drug accumulation. Although intensively studied, the mechanism of this process remains ill-defined. We have now developed a new, rapid and quantitative method of measuring uptake of doxorubicin by these cells, in which the fluorescence of accumulated drug is rapidly quenched by DNA in the cell nucleus. Pre-treatment of cells with deoxyribonuclease eliminates DNA from non-viable, permeable cells, and this obviates the spurious fluorescence quenching that made previous application of this technique useless. Our data strongly suggest that the drug passively diffuses into cells. The rate of this diffusion into drug-resistant cells is considerably lower than that found in drug-sensitive cells. The ratio of the rates of drug entry in these cell types could fully account for the differences between the cell lines in doxorubicin growth-inhibitory activity. In these experiments no evidence for the previously proposed active efflux mechanism was found in either cell line.

Pentamidine transport and sensitivity in brucei-group trypanosomes

Sensitivity to pentamidine of bloodstream forms and culture forms of Trypanosoma brucei brucei, strains of this subspecies, and strains of T. brucei rhodesiense characteristically differs in vitro. Analyses of transport parameters for pentamidine uptake in these organisms show differences that correspond with drug sensitivity. Long slender bloodstream forms of T. b. brucei have a high affinity for the drug and high rates of uptake at indicated by Km and Vmax values for [3H]pentamidine transport. Although pentamidine and stilbamidine resistance is associated with dyskinetoplasty, this condition does not itself confer resistance to pentamidine nor does it affect pentamidine transport. However, drug-resistant strains show lower rates for pentamidine transport as does T. b. rhodesiense, which is characteristically less sensitive to the drug. Of all the forms and strains studied, procyclic trypomastigotes were least sensitive to pentamidine and had a remarkable ability to exclude the drug.

Actinomycin-D-resistant in vitro mouse cell line derived from a methylcholanthrene-induced sarcoma: decrease of malignancy and antigenic characteristics

The tumorigenic EPO clonal cell line, derived from a methylcholanthrene-induced murine sarcoma, was exposed to increasing concentrations of actinomycin D and gave rise to a subline, resistant to 0.02 mug of actinomycin D per ml of medium, which was designated EPO/ADj. Drug resistance was accompained by a striking decrease of tumorigenic capacity as determined by the tumor take incidence and tumor growth rate in syngeneic C57BL/6 mice (normal and X-irradiated), as well as by tumor take incidence in the cheek pouch of cortisone-treated weanling Syrian hamsters. One of the tumors obtained after inoculation of EPO/ADj cells into syngeneic mice was reexplanted in culture and developed as the EPO/ADj/T subline. It was found to be relatively resistant to actinomycin D as compared to the parental EPO cells. The morphology of cells changed with actinomycin-D-resistance: EPO/ADj cells were more spread and flattened and less overlapping than the original fibroblast-like EPO cells. EPO/ADj/T cells, however, had an aspect similar to that of EPO cells. No major differences were seen between the karyotypes of EPO, EPO/ADj and EPO/ADj/T cells. Tumor-specific antigen(s), characteristic of drug-sensitive, parental EPO line, was expressed in the resistant EPO/ADj and EPO/ADj/T lines, as shown by: (a) transplantation resistance to challenge with EPO cells in syngeneic mice pretreated with EPO/ADj cells; and (b) cross-reactivity in indirect immunofluorescence tests performed with sera from syngeneic animals hyperimmunized with EPO or EPO/ADj cells. Furthermore, an additional surface antigen(s), absent from EPO cells, was demonstrated in EPO/ADj and EPO/ADj/T cells by means of immunofluorescence tests performed with specific anti-EPO/ADj syngeneic sera previously absorbed on EPO or EPO/ADj cells.

Accumulation of 14C-streptomycin by streptomycin-sensitive and streptomycin-resistant group H streptococci

Three streptomycin-resistant mutants of group H streptococcus, strain Challis, were examined for ability to accumulate (14)C-streptomycin. Although the mutants exhibited different levels of transformation, only the streptomycin-sensitive parent Challis strain accumulated significant amounts of (14)C-streptomycin. It appears that impermeability to streptomycin does not necessarily result in reduction or loss of transformability. The amount of label accumulated by strain Challis was correlated with a loss of viability. In addition, accumulation of label was influenced by the concentration of (14)C-streptomycin, the time of exposure, and the type of medium employed.

Relationship between competence for transfection and for transformation

Deoxyribonucleic acid (DNA) extracted from phage SPP1 is highly infectious on Bacillus subtilis competent cells; the efficiency of infection is 5 x 10(3) to 6 x 10(3) phage equivalents per plaque-forming unit. This DNA was used to study the relationship between competence for transfection and for transformation. The experiments were concerned with the frequency of infection and transformation in mutants exhibiting different levels of competence, the effect of periodate on competence for infection and for transformation, the competition between phage and bacterial DNA, the transformation of cells preinfected with phage DNA, and the infection of cells pretreated with bacterial DNA. The data show that B. subtilis cells competent for transformation are also competent for transfection and vice versa; transfection with phage DNA represents, therefore, a simple way to measure the total number of competent cells in a culture. The fraction of competent cells, determined by SPP1 DNA infection, varied from 10(-2) to 7 x 10(-2).

Transformability of streptomycin-resistant group H streptococci

Several resistant mutants of a transformable group H streptococcus, strain Challis, were isolated from media containing high concentrations of streptomycin. Mutants SR5a and SR5 exhibited high and low transformability, respectively, when exposed to deoxyribonucleic acid (DNA) from a novobiocin-resistant Challis strain. With similar exposure, mutant SR30 exhibited loss of transformability. The mutants further differed from the parent strain in time of appearance of optimal competence, and, in the case of SR5 and SR30, total growth was somewhat less than that of the parent. The rapidity with which transformants appeared upon initial exposure to DNA was approximately the same in the mutants and the parent strain. The decrease or loss of transformability of mutants SR5 and SR30 was found to be due to an alteration in capacity to take up DNA. Mutant SR5a (highly transformable) was further differentiated from mutants SR5 and SR30 in that it was somewhat more sensitive to high concentrations of streptomycin. Transformants obtained by treating strain Challis with the three types of mutant DNA, on the other hand, exhibited similar degrees of resistance to increasing concentrations of streptomycin. The additional decrease in transforming ability of mutant SR5a and the loss of transforming ability of mutant SR5 after a second exposure to streptomycin may indicate a stepwise process in the change from transformability to nontransformability. Although streptomycin resistance may not be directly related to inability to transform, results indicate that streptomycin greatly increases the chances of selecting these mutants and also can be of value in serving as a marker in studies of this nature.