Antibacterial effect of antibiotics modified by their interaction with antitumor preparations on the cellular level

Abstract

Interaction of antitumor and antibacterial drugs seems to be a very important factor probably influencing the efficacy of treating bacterial infections in patients in the course of antitumor chemotherapy. As is known, lethality in patients with a cancer diagnosis, resulting from a secondary infection on the background of special antitumor chemotherapy, is a rather common phenomenon [1 -3]. These cases frequently involve the intracell occurrence of pathogens, which is quite understandable if we take into account the immune deficiency arising in these cases, including that on the phagocyte level [4]. EXPERIMENTAL PARTThe experiments were performed on leukocytes from peripheral blood of healthy volunteers aged 18 -40, both intact and inoculated with St. aureus, and on leukocytes from patients with a diagnosis of breast cancer. The St. aureus strain was taken from clinical isolates. The minimum inhibiting concentration (MIC) and minimum bactericidal concentration (MBC) of antibiotics were determined by the method of double serial dilutions in an AGV medium [5]. According to these data, the MIC and MBC values for the antibiotics studied under a standard microbial load of 106 cells per ml AGV medium were as follows: gentamicin, 0.125 and 0.5 lag/ml; rifampicin, 0. I and 0.4 lag/ml; and erythromycin, 0.2 and 0.5 lag/ml, respectively. We have used the suspensions of 24-h cultures with the cell concentration characterized by the optical density. The bacteria were preliminarily opsonized with a normal blood serum. The antibiotics were represented by the following commercial drugs: rifampicin, erythromycin, gentamicin, doxorubicin, and dactinomycin. Their activities were referenced to the standard obtained from the Laboratory of Antibiotics Quality Control (State Research Institute of Drug Standardization and Control). 186The binding of antibiotics to polymorphonuclear human leukocytes was studied by incubating the cells (5 x 106 mi-l) with drug preparations at 37~ in a l-ml volume of medium 199 containing additives of gelatin (0. I%) and blood serum (5%) under aseptic conditions. The concentrations of the antibiotics tested were selected in accordance with their average therapeutic level in the blood serum [5,6]. The initial concentration of antibiotics was I0 lag/ml for the antibacterial drugs and 1 lag/ml for the antitumor ones. The samples were incubated for 30 min in plastic tubes placed in a temperaturecontrolled shaker. During this experiment, the viability of the cells was monitored using the Trypan Blue test. The cells were separated from the extracell liquid by filtration through Millipore SM membrane filters with a pore diameter of 5 lam. The residue was washed and the cells were lysed by repeated freezing-defreezing cycles in distilled water. The concentration of antibiotic was determined both in the cell lysate and in the filtrate. The coefficient of the antibiotic binding in the cell was calculated as the ratio of the drug concentrations inside and outside the cells. The ratio of intracell to extracell phases...