The Content of ROS in Blood Lymphocytes of Healthy Individuals, Individuals Irradiated as a Result of Chernobyl Disaster and Patients with Prostate Cancer.

The ROS concentration and proliferation activity (Ki67 expression.marker) have been studied in the periphery blood lymphocytes of Moscow and Obninsk citizens, donors, Chernobyl disaster liquidators, inhabitants of the region contaminated after Chernobyl disaster (Klincy) and individuals with prostate cancer. It was shown that ROS concentration in lymphocytes of the liquidators and residents of the polluted region was lowered. But in lymphocytes of patients with tumors the ROS content was higher in comparison with the control. The cell content with Ki67 expression in lymphocytes of the individuals resided in the polluted region and tumor patients was lowered.

[Relationship between the induction of MDR1, a multidrug resistance gene in tumor cells, and apoptosis]. / Sviaz' mezhdu inductsiei aktivnosti gena mnozhestvennoi lekarstvennoi ustoichivosti opukholevykh kletok MDR1 i apoptozom.

Gene MDR1 coding for P-glycoprotein belongs to a group of genes responsible for cell defense. Overexpression of this gene determines the resistance of tumor cells to a series of chemotherapeutic drugs known as multidrug resistance. Many chemotherapeuticals induce both apoptosis and transcriptional activity of the MDR1 gene in tumor cells. It is not known, however, how these two processes are associated with each other. In order to elucidate a possible link between them, we have studied the sphyngomyelinic pathway of signal transduction. This pathway is activated in response to various stress factors and includes the hydrolysis of sphyngomyelin of cytoplasmic membrane resulting in an accumulation of intracellular ceramide, which activates cascades of enzymatic reactions leading to various cell responses, including apoptosis. C2 ceramide (N-acetyl-D-sphyngosine) and cytosar (1 beta-D-arabinosylcytosine, or ara C) were used to induce the sphyngomyelinic pathway. Their effects on human hemoblastosis cell lines (K562 and H9 cell lines) were examined. C2 ceramide and ara C induced apoptosis in both cell lines over an 18-h incubation. C2 ceramide also induced an increase in the expression of the gene MDR1 in both cell lines, while ara C increased the activity of the gene MDR1 only in H9 cells. The results obtained provide evidence for the contribution of ceramide-mediated signal pathway to the control of MDR1 activity.

[Adaptation of reverse transcriptase polymerase chain reaction for clinical diagnosis of expression of MDR1 gene]. / Adaptatsiia metoda obratnotranskriptaznoi tsepnoi reaktsii dlia klinicheskoi diagnostiki ékspressii gena MDR1.

Chemotherapy of malignant tumors is ineffective usually because of tumor cell resistance to it. Two types of resistance are known: cell resistance to a certain drug and multiple drug resistance (MDR). MDR covers a wide spectrum of drugs with different chemical structure and mechanisms of action. The most frequent cause of MDR is hyperexpression in the plasma membrane of P glycoprotein cells, which is coded for by MDR1 gene realizing active release of many cytotoxic substances from cells (Pgp-MDR). Acquisition of MDR phenotype by patient's cells impedes therapy and is often a poor prognostic sign, and therefore testing of material from cancer patients for MDR phenotype is important for selecting tumor therapy. We adapted the reverse transcriptase polymerase chain reaction (RT-PCR) to evaluating the MDR1 gene expression in peripheral blood cells of patients with hemoblastosis, assessed its sensitivity and specificity, and carried out clinical trials with blood samples from patients with MDR. Comparison of the results of RT-PCR with the findings of other methods used for detection of Pg-MDR showed their good correlation in the majority of cases. These results recommend these method for clinical practice in patients with hemoblastosis.

Differential effects of the MDR1 (multidrug resistance) gene-activating agents on protein kinase C: evidence for redundancy of mechanisms of acquired MDR in leukemia cells.

Human leukemia cells may acquire MDR1/P-glycoprotein-mediated multidrug resistance (MDR) in the course of short-term (within hours) exposure to many stress stimuli. This effect is thought to be associated with the activity of protein kinase C (PKC) (Chaudhary, Roninson, 1992. 1993). However, we show here that cytosine beta-D-arabinofuranoside (Ara C) and 12-O-tetradecanoylphorbol 13-acetate (TPA), agents that activated the MDR1 gene in the H9 T-cell leukemia line, caused different effects on PKC. Namely, TPA activated PKC whereas Ara C was without the effect. Furthermore, cell permeable ceramide, a lipid messenger known to mediate cellular effects of chemotherapeutic drugs and TPA, activated the MDR1 gene and down-regulated PKC. These results suggest that the MDR1 gene can be activated via the pathway(s) that requires PKC activity as well as via bypass of PKC. The redundancy of signaling pathways that regulate the acquisition of MDR should be taken into consideration for prevention of secondary drug resistance in hematological malignancies.

Induction of P-glycoprotein functional activity and multidrug resistance by a soluble factor(s) produced by some mammalian cells.

In the previous study we have found that Djungarian hamster fibroblasts with high levels of multidrug resistance (MDR) (colchicine-resistance index RI of 1000 to 42000) produce soluble factor(s) communicating MDR to the drug-sensitive cells of the same species by elevating the functional activity of P-glycoprotein (Pgp). Here we have shown that these cells can influence human tumor cells in the same fashion. Rat hepatoma McA RH7777 cells and their colchicine-resistant derivatives are shown to produce a factor with similar effects (induction of MDR and Pgp functional activity in the drug-sensitive cells). These effects seem to depend on the drug resistance level of the donor cells. Our results show that induction of the Pgp-mediated MDR is not species-specific and the tumor cells with intrinsic MDR (arising from the tissue with a high level of Pgp expression) can produce a factor(s) communicating this type of drug resistance to the sensitive cells.