High doses of synthetic antioxidants induce premature senescence in cultivated mesenchymal stem cells.

Stress-induced premature senescence program is known to be activated in cells by various genotoxic stressors, and oxidative stress is considered to be the main of those. To this end, many studies discover antioxidants as protective anti-aging agents. In the current study, we examined the effects of different antioxidants (Tempol, resveratrol, NAC, DPI) on the mesenchymal stem cells maintained in normal physiological conditions. We used high, but non-cytotoxic antioxidant doses which are widely used in laboratory practice to protect cells from oxidative damage. We show that these substances induce reversible block of cell proliferation and do not cause any genotoxic effects when applied to the quiescent cells. However, the same doses of the same substances, when applied to the proliferating cells, can induce irreversible cell cycle arrest, DNA strand breaks accumulation and DNA damage response activation. As a consequence, antioxidant-induced DNA damage results in the stress-induced premature senescence program activation. We conclude that high doses of antioxidants, when applied to the proliferating cells that maintain physiological levels of reactive oxygen species, can cause DNA damage and induce premature senescence which suggests to re-estimate believed unconditional anti-aging antioxidant properties.

Quiescent Human Mesenchymal Stem Cells Are More Resistant to Heat Stress than Cycling Cells.

Quiescence is the prevailing state of many cell types under homeostatic conditions. Yet, surprisingly, little is known about how quiescent cells respond to environmental challenges. The aim of the present study is to compare stress responses of cycling and quiescent mesenchymal stem cells (MSC). Human endometrial mesenchymal cells (eMSС) were employed as adult stem cells. eMSC quiescence was modeled by serum starvation. Sublethal heat shock (HS) was used as a stress factor. Both quiescent and cycling cells were heated at 45°C for 30 min and then returned to standard culture conditions for their recovery. HS response was monitored by DNA damage response, stress-induced premature senescence (SIPS), cell proliferation activity, and oxidative metabolism. It has been found that quiescent cells repair DNA more rapidly, resume proliferation, and undergo SIPS less than proliferating cells. HS-enforced ROS production in heated cycling cells was accompanied with increased expression of genes regulating redox-active proteins. Quiescent cells exposed to HS did not intensify the ROS production, and genes involved in antioxidant defense were mostly silent. Altogether, the results have shown that quiescent cells are more resistant to heat stress than cycling cells. Next-generation sequencing (NGS) demonstrates that HS-survived cells retain differentiation capacity and do not exhibit signs of spontaneous transformation.

Molecular Genetic Analysis of Human Endometrial Mesenchymal Stem Cells That Survived Sublethal Heat Shock.

High temperature is a critical environmental and personal factor. Although heat shock is a well-studied biological phenomenon, hyperthermia response of stem cells is poorly understood. Previously, we demonstrated that sublethal heat shock induced premature senescence in human endometrial mesenchymal stem cells (eMSC). This study aimed to investigate the fate of eMSC-survived sublethal heat shock (SHS) with special emphasis on their genetic stability and possible malignant transformation using methods of classic and molecular karyotyping, next-generation sequencing, and transcriptome functional analysis. G-banding revealed random chromosome breakages and aneuploidy in the SHS-treated eMSC. Molecular karyotyping found no genomic imbalance in these cells. Gene module and protein interaction network analysis of mRNA sequencing data showed that compared to untreated cells, SHS-survived progeny revealed some difference in gene expression. However, no hallmarks of cancer were found. Our data identified downregulation of oncogenic signaling, upregulation of tumor-suppressing and prosenescence signaling, induction of mismatch, and excision DNA repair. The common feature of heated eMSC is the silence of MYC, AKT1/PKB oncogenes, and hTERT telomerase. Overall, our data indicate that despite genetic instability, SHS-survived eMSC do not undergo transformation. After long-term cultivation, these cells like their unheated counterparts enter replicative senescence and die.

[DNA CONTENT IN INDIVIDUAL CHROMOSOMES OF NORMAL CHINESE HAMSTER KARYOTYPE AND CHROMOSOMES OF CONSTANT HAMSTER CELL LINES CHL V-79 RJK AND Vebr-5].

Using cytometry and an microfluorimetry, we have determined the genome size in Chinese hamster Cricetulus griseus, as well as absolute and relative DNA content of its individual chromosomes and of chromosomes in the transformed Chinese hamster cell lines V-79 RJK and Vebr-5 after prolonged cultivation. It has been shown that the genome size in male and female Chinese hamster is 6.660 and 6.746 pg, respectively. Absolute content of chromosomal DNA of both studied cell lines differed significantly from the content of the corresponding chromosomal DNA of the Chinese hamster normal karyotype. During long-term cellular cultivation, changes in the DNA content of certain chromosomes in both cell lines (generally upward) reached 20-25 %. The level of DNA amplification in the p-arm of chromosome Z6, registered at the beginning of the experiment, in the course of further cellular cultivation (over 20 years) remained stable. The data obtained allow us to conclude that the malignant transformation of cells and subsequent adaptation to the conditions in vitro leads to a profound restructuring of its genome, which affects almost all chromosomes.

[CHARACTERISTIC OF ENDOMETRIAL MESENCHYMAL STEM CELLS IN CULTURE OBTAINED FROM PATIENT WITH ADENOMYOSIS].

Adenomyosis is form of endometriosis, common diseases of female reproductive system, which can lead to infertility in women. in this study we are obtained and characterized cell line endometrial mesenchymal stem cells from a patient with adenomyosis, and compare obtained cells with the cell line of healthy donor. Aim of this study was to assesses the extent of differences between cells from donor with adenomyosis and cells from healthy donor. Was established that compared lines had morphology like fibroblasts, were differentiated in adipocytes, were expressed mesenchymal markers and didn't expressed haematopoietic markers. Cytogenetic analysis of differentially stained metaphase chromosomes on G-banding (passage 6-7) showed that healthy donor's cells had predominantly normal karyotype. The cellular line from a patient with diagnosis of "adenomyosis" had a lot of cells with changes in karyotype's structure. These changes were related with aneuploidy of cellular population and the presence non-random chromosomal breaks, often in chromosomes 7 and 11. Analysis of this data allows the cells from adenomyosis characterized physiological stability in culture and karyotypic instability with non-random involvement certain chromosomal set. The cellular line obtained from donor with adenomyosis showed signs destabilization of he genome, typical for cell transformation. Division of adenomyosis cells to the 26th passage is stopped and these cells entered into a phase of replicative aging. Based on this, we can conclude that founded karyotype's hanges do not lead to transformation and immortalization of cells in vitro.

[BDNF secretion in human mesenchymal stem cells isolated from bone marrow, endometrium and adipose tissue].

The ability of mesenchymal stem cells (MSCs) to differentiate into neuronal lineage determines the potential of these cells as a substrate for a cell replacement therapy. In this paper we compare the neurogenic potential of MSCs isolated from bone marrow (BMSC), subcutaneous adipose tissue (AD MSC) and menstrual blood (eMSC). It was found that the native eMCSs, BMSCs and AD MSCs express neuronal marker ß-III-tubulin with a frequency of 90, 50 and 14%, respectively. We also showned that eMSCs have a high endogenous level of brain-derived neurotrophic factor (BDNF), whereas the BMSCs and the AD MSCs are characterized by low basal BDNF levels. As induction of neuronal differentiation in the studied MSCs using differentiation medium containing B27 and N2 supplements, 5-azacytidine, retinoic acid, IBMX and dbcAMF caused changes in the cells morphology, the increased expression of ß-III-tubulin, and the appearance of neuronal markers GFAP, NF-H, NeuN and MAP2. BDNF secretion during differentiation was significantly enhanced in the BMSCs and decreased in the eMSCs cultures. However, no correlation between the basal and induced levels of the neuronal markers expression and BDNF secretion in the studied MSCs has been established.

[Long-term cultivation of Chinese hamster fibroblasts of line V-79 RJK under elevated temperature leads to karyotype structure destabilization].

In this article we show that long-term cultivation of Chinese hamster fibroblasts of line V-79 RJK at elevated temperature resulted in the selection of variants with genetic changes at the level of karyotype. From the first steps of resistance selection to elevated temperature we identified population of cells with changes in karyotype (polyploidy cells, deletions, inversions, translocations of chromosomes, and some cells with DM-chromosomes). Further cultivation was accompanied with selection of cells with paracentrical chromosome breakages and HSR's on chromosomes. Nonspecific destabilization of the karyotype (on first steps of selection) was associated with increased expression of hsc70 and pgp. After long-term incubation at an elevated temperature, the cells with karyotypic changes had the basal level of hsc70 and pgp expression.

[Neurogenic potential of human mesenchymal stem cells isolated from bone marrow, adipose tissue and endometrium: a comparative study].

Mesenchymal stem cells (MSCs) can be isolated from many adult tissue sources. These cells are a valuable substrate in cell therapy for many diseases and injuries. Different types of MSCs vary in plasticity. We performed a comparative study of the neurogenic potential of three types of human MSCs derived from bone marrow (BMSCs), subcutaneous adipose tissue (ADSCs) and endometrium (isolated from the menstrual blood) (eMSCs). It was shown that all three types of MSC cultures demonstrate multipotent plasticity and predisposition to neurogenesis, based on the expression of pluripotency markers SSEA-4 and neuronal precursors' markers nestin and beta-III-tubulin. Further analysis revealed the transcription of the neuronal marker MAP2 and neurotrophin-3 in undifferentiated BMSCs and ADSCs. Additionally, a significant basal level of synthesis of brain-derived neurotrophic factor (BDNF) in eMSC culture was also observed. Stimulation of neural induction with such agents as 5-azacytidine, recombinant human basic fibroblast growth factor (bFGF), recombinant human epidermal growth factor (EGF), a recombinant human fibroblast growth factor 8 (FGF8), morphogen SHH (sonic hedgehog), retinoic acid (RA) and isobutyl-methyl-xanthine (IBMX), showed further differences in the neurogenic potential of the MSCs. The components of the extracellular matrix, such as Matrigel and laminin, were also the important inducers of differentiation. The most effective neural induction in BMSCs proceeded without the RA participation while the cells pretreated with 5-azacytidine. In contrary, in the case of eMSCs RA was a necessary agent of neural differentiation as it stimulated the transcription of neurotrophin-4 and the elevation of secretion level of BDNF. The use of laminin as the substrate in eMSCs appeared to be critical, though an incubation of the cells with 5-azacytidine was optional. As far as ADSCs, RA in combination with 5-azacytidine caused the elevation of expression of MAP2, but reduced the secretion of BDNF. Thus, the effect of RA on neural differentiation of ADSCs in ambiguous and, together with the study of its signaling pathways in the MSCs, requires further research. The therapeutic effect of transplanted MSCs is commonly explained by their paracrine activity. The high basal level of BDNF synthesis in the eMSCs, along with their high proliferative rate, non-invasive extraction and neural predisposition, is a powerful argument for the use of the intact eMSCs as a substrate in cell therapy to repair nerve tissue.

[Menstrual blood stem cells as a potential substrate of cell therapy].

Cell replacement and restorative therapies have great perspectives in the treatment of various diseases and traumas. Various types of stem cells, most different in the biological properties, are evaluated as the potential substrates of cell therapy for such diseases. Mesenchymal stem cells (MSC) posses relatively high proliferative activity and high level of plasticity, and can be differentiated not only to the cells of the mesenchymal lineage, but also to the neurons. Among the MSC populations, a population of endometrial stem cells, including that present in the menstrual blood, is available most readily. In the current study, we analyze biological properties of the menstrual blood stem cells and evaluate those cells as a potential substrate of cell therapy.

[Mesenchymal stem cells of human endometrium do not undergo spontaneous transformation during long-term cultivation].

Mesenchymal stem cells isolated from human endometrium (eMSC) are perspective source of stem cells for regenerative medicine. Large amount of these cells accumulated by in vitro cultivation is usually required for transplantation into patients. We established several cell eMSC lines and cultivated them during long period of time to examine the possibility of their spontaneous transformation. All cell lines demonstrate limited lifespan, undergo replicative senescence and die. Karyotypic analysis on different passages reveals that most cells display karyotypic stability. Thus, extended in vitro cultivation of eMSCs does not lead to spontaneous transformation that makes therapeutic application of these cells safety for patients. During long-term cultivation eMSCs sustain the expression of surface markers.

[Examination of cytotoxic effect of anti-cancer drug doxorubicin on human embryonic stem cells].

Cytotoxic effect of anti-cancer drug, doxorubicin (DR), has been examined on human embryonic stem cells (ESC) C910 and fibroblasts spontaneously differentiated from these cells. The fibroblasts retained diploid karyotype. It was found that ESC are more sensitive to DR than fibroblasts: DR dose killing 20% cells was 0.01 and 0.1 microg/ml, respectively. DR induced ESC apoptotic death and reduced both ESC and fibroblast proliferation. Unlike fibroblasts DR reversibly inhibited ESC proliferation. Thus, we have demonstrated that ESC and their differentiated derivates differ their sensitivity and response to the genotoxic agent.

[Multipotent mesenchymal stem cells of desquamated endometrium: isolation, characterization and use as feeder layer for maintenance of human embryonic stem cell lines].

In this study, we characterize new multipotent human mesenchymal stem cell (MSC) lines derived from desquamated (shedding) endometrium in menstrual blood. The isolated endometrial MSC (eMSC) is an adhesive to plastic heterogeneous population composed mainly of endometrial glandular and stromal cells. The established cell lines meet the criteria of the International Society for Cellular Therapy for defining multipotent human MSC of any origin. The eMSCs have positive expression of CD73, CD90, CD105, CD13, CD29, CD44 markers and the absence of expression of the hematopoietic cell surface antigens CD19, CD34, CD45, CD117, CD130 and HLA-DR (class II). Multipotency of the established eMSC is confirmed by their ability to differentiate into other mesodermal cell types such as osteocytes and adipocytes. Besides, the isolated eMSC lines partially (over 50%) express the pluripotency marker SSEA-4, but do not express Oct-4. Immunofluorescent analysis of the derived cells revealed the expression of the neural precursor markers nestin and beta-III-tubulin. This suggests a neural predisposition of the established eMSC. These cells are characterized by high rate of cell proliferation (doubling time 22-23 h) and high cloning efficiency (about 60%). In vitro the eMSCs undergo more than 45 population doublings revealing normal karyotype without karyotipic abnormalilies. We demonstrate, that the mititotically inactivated eMSCs are perfect feeder cells for human embryonic stem cell lines (hESC) C612 and C910. The eMSC being a feeder culture maintain the pluripotent status of the hESC, which is revealed by the expression of Oct-4, alkaline phosphatase and SSEA-4. When co-culturing, hESC retain their morphology, proliferative rate for more than 40 passages and capability for spontaneous differentiation into embryoid bodies comprising the three embryonic germ layers. Thus, an easy and non-invasive extraction of the eMSC in menstrual blood, their multipotency and high proliferative activity in vitro without karyotypic abnormalities demonstrate the potential of use of these stem cells in regenerative medicine. Using the derived eMSCs as the feeder culture eliminates the risks associated with animal cells while transferring hESC to clinical setting.

[The effect of synthetic polycation polyallylamine on adhesion and viability of CHL V-79 RJK Chinese hamster fibroblasts with different heat resistance].

The effects of synthetic polycation polyallylamine (PAA) on adhesion of CHL V-79 RJK fibroblasts and CHL V-79 RJK40 cells resistant to 40 degrees C, and attachment to these cells to polycation immobilized on polystyrene surface were studied. We have also investigated the cytotoxicity of PAA. It was shown that cell adherence to polystyrene plastic coated with PAA was enhanced or decreased in dependence of the PAA concentration used for surface coating and did not depend on heat resistance of investigated cell lines. The effect of PAA on cell adhesion to uncoated polystyrene surface after cell exposure with PAA depended not only on the polycation concentration, but also on the extent of heat resistance of investigated cell lines. Pretreatment of CHL V-79 RJK cells with PAA at the nontoxic concentrations led to inhibition of cell adhesion, and no change in adhesive properties of thermoresistant cells was found under the same conditions. PAA was toxic for CHL V-79 RJK and CHL V-79 RJK40 cells only at concentrations of 100 microg/ml (MTT assay). PAA-induced acute toxicity was accompanied by necrotic-like cell damage. Possible mechanisms of the PAA effect on the behaviour of cells with different structural and metabolic characteristics that are due to the temperature of cell cultivation are discussed.

[Characteristic of tumors developed after transplantation of transgenic GFP-positive C57BL/6 mice bone-marrow mesenchymal stem cells to mdx mice muscle].

The purpose of the study was the morphological and histochemical characteristics of differentiation of tumors developed after transplantation of GFP-positive mesenchymal bone-marrow stem cells (MSC) of transgenic mice C57BL/6 into M. quadriceps femoris of mdx mice. The tumors occurred only after transplantation of MSCs of 43-45th passages and did not arise after transplantation of MSCs of the 15th passage. No tumors developed also after transplantation of MSCs of 43-45th passages into muscle of C57BL/6 mice. The average weight of tumors appeared in 4 mdx mice studied was 1.3 +/- 0.5 g. All four tumors were classified as mesenchymomas because they originated from mesenchymal stem cells. Most of the periphery of the tumors was classified as fibrosarcomas with mitotic index 0.9 +/- 0.1%. The central parts of tumors had areas with epithelial like morphology of cells. Such cells showed positive reactivity for alcyan blue staining at pH 2.5, which indicated chondrocyte nature of the cells. No mitosis was observed in epithelial like cells. In the tumors, there were also areas with bone trabeculae containing megacaryocytes and foci of myeloid and erythrocyte hematopoiesis. There were also areas with neuronal and glial cells, and accumulations of adipocytes. One of the tumors was classified as a round cells sarcoma. The observed types of tumor cell differentiation in vivo were in accordance with described in literature types of MSCs differentiation after induction in vitro with special inductors. The spectrum of in vivo differentiation of transgenic GFP-positive MSCs after transplantation to mdx mice was broader than the spectrum of in vivo differentiation of transfected or transformed in vitro adult MSCs after transplantation to immunodeficient mice and mdx mice.

[Generation of dopamine neurons from human embryonic stem cells in vitro].

The aim of the study was to generate dopaminergic (DA) neurons from human embryonic stem cells (ESC) in vitro. It was shown that human ESCs are able to differentiated into DA neurons without co-culture with stromal cells. Terminal differentiation into DA neurons was reached by successive application of noggin and bFGF growth factors on collagen and matrigel substrates during 3-4 weeks. Differentiation efficiency was evaluated by the number of colonies with cells expressing tyrosine hydroxylase (TH), a DA neuron marker, and by the number of TH-positive cells in cell suspension using flow cytometry. No cells with pluripotent markers were detected in DA-differentiated cultures. It makes possible to propose that the protocol of human ESC differentiation might be applied to generate DA neurons for their transplantation into the animals modeling neurodegenerative (Parkinson) disease without the risk of tumor growth.

[Novel human embryonic stem cell lines C612 and C910].

Novel human embryonal stem cell lines C612 and C910 have been established from hatching blastocytes. Cells were cultivated in mTeST medium on mouse fibroblast feeder-layers. They express common pluripotent markers such as alkaline phosphatase, Oct 3/4, SEEA-4, Nanog, Rex1. Immunophenotyping of these cells by flow cytometry revealed expression of CD90 (Thy-1) and CD117 (c-kit) antigens and weak or no expression of CD13, CD34, CD45, CD130, HLA class I and HLA class II antigens. This pattern of surface antigen expression is common for human embryonic stem cells. G-banding assay of C612 and C910 metaphase plates showed that karyotypic structure of these cells was normal both in chromosome number and structure. The cells are pluripotent because of their capability to generate embryoid bodies, undergo spontaneous differentiation and express markers of all germ layers: nestin, keratin, vimentin (ectoderm), alpha-fetoprotein (entoderm), and muscle alpha-actinin (mesoderm). Thus, C612 and C910 cells have all attributes of typical human embryonic stem cells (diploid, capable of self-renewal, express pluripotent markers and differentiate into three germ layers) and may be of potential use for fundamental and regenerative medicine researches.

[Spontaneous transformation and immortalization of mesenchymal stem cells in vitro].

Mesenchymal stem cells (MXC) possess plasticity and unlimited proliferative activity in vitro that makes them an attractive subject of the studies focused on searching new resources for regenerative medicine. The usage of MSC is effective for treatment of patients with degenerative and traumatic diseases of different tissues, however, biological basis of therapeutic efficacy of MSC are still obscure. We found that long term culture of MSC expressing transgenic green fluorescence protein (GFP) led to increase in their proliferative activity, decrease in adhesion, and loss of differentiation potential and production of the GFP. MSC at the first passages showed karyotipic features of transformation, that at the later passages were complicated with developing of tumorigenic abilities detected after transplantation into normal syngenic recipients. When explanted into cell culture conditions the cells of the tumor tissue originated from the MSC did not express GFP and were not inducible to differentiation, but in contrast to the parent cells showed decreased clonogenic and proliferative activities. We suggest that growth of MSC in vitro results in their spontaneous transformation at early passages. Immortalization making physiological basis for the unlimited proliferation of MSC in vitro may be a feature of MSC transformation but not an initial characteristic of the stem cells.

[The role of the collagen tripeptide fragment GER in the adhesion activation and modification of fatty acid composition in membrane phospholipids of CHO-K1 cells].

It has been found that multiply repeated tripeptide fragment GER (Gly-Glu-Arg) from different collagen types stimulates nonspecific adhesion of CHO-K1 cells. Activation of cell adhesion is accompanied by modifications in fatty acid composition of cell membrane phospholipids. Cell incubation with the synthetic peptide increases the unsaturation indexes of phosphatidylcholin (PC), phosphatidylethanolamine (PEA) and phosphatidylinositol (PI). Arachidonic (C20:4omega6) acid is mainly contributed to the increased unsaturation index of PI. In the case of PC and PEA not only arachidonic acid but also other unsaturated fatty acids: docosatetraenoic (C22:4omega6), docosapentaenoic (C22:5omega3) and docosahexaenoic (C22:6omega3) acids are implicated in the index increasing. Besides, the elevation of relative content of molecules with polyenoic fatty acids in the group of PI molecules is accompanied by decrease in monoenoic fatty acids caused mainly by decrease in the oleic (C18:1) acid level. The role of the investigated peptide: 1) in the activation of cell adhesion as a regulator of active or non active state of integrin receptors: 2) in the alterations of fatty acid composition in main classes of phospholipids as modulator of fluidity level in annular lipid zones around these adhesive molecules is discussed.

[Characterization of cultured murine mesenchymal stem cell line expressing GFP].

We have developed and characterized a murine mesenchymal stem cell line from the bone marrow of transgenic mouse C57BL ubiquitously expressing GFP. Immunostaining analysis revealed the presence of several markers typically found in fibroblasts such as smooth muscle cells actin in the form of stress fibrils and vimentin--the protein of intermediate filaments. These cells maintained capability to differentiate into adipocytes or osteoblasts under appropriate conditions. Karyotypic features include changes in the ploidy level between 2n and 8n and multiple chromosomal aberrations. After six passages 80% of the cell population was aneuploid with chromosomal numbers between 50 and 85 without well defined modal class. Differential G-staining of metaphase spreads showed variability in copy numbers of individual chromosomes and the presence of aberrations such as ectopic associations of non-homologous chromosomes. All analyzed cells contained unique dicentric marker chromosome and some of them also had numerous microchromosomes which might indicate gene amplification. These cells could be useful in the future work directed at the investigation of stem cells spontaneous oncogenic transformation in vivo and in vitro.

[Microfluorimetric analysis of dynamics of genomic changes of Chinese hamster fibroblasts CHL V-79 RJK with multidrug resistance].

Results of karyological analysis of cells CHL V-79 RJK selected for resistance to ethidium bromide (EB) causing multidrug resistance (MDR) (line Vebr-5) were compared with the data of microfluorimetric determination of DNA content in individual chromosomes of the karyotype. The analysis was performed at the 11th and 88th passages. Karyotyping of Vebr-5 has shown the presence of an additional genetic material (ADM) in the form of homogenously or differentially stained regions (HSRs and DSRs, respectively) in two chromosomes (Z1 and Z6, loci 1 p29-31 and 1q26, respectively). HSRs in Z6, in the region of localization of the wild type of gene mdr, had unstable length and structure characteristic of morphological markers of amplification of genes of the family mdr. During long cultivation of Vebr-5 in the presence of EB (88 passages), the instability of HSRs in Z6 increased. Results of microfluorimetric analysis of Vebr-5 at the 11th passage have shown an increase in the DNA content not only in chromosomes Z1 and Z6 marked by HSRs, but also in three chromosomes (Z5, Z12 and Z13) that have no visual morphological changes. The corresponding analysis at the 88th passage has also revealed non-random changes in the DNA content in four more chromosomes: an increase in Z14, while a decrease in chromosomes 8, Z7, and Z9. A decrease of the DNA content in chromosomes is considered to be a result of a partial loss of genetic material, while its increase is a result of its translocation and (or) amplification. Coefficient of variation of the DNA content changes for large chromosomes amounted to about 9%. while for small chromosomes it is about 26%, which indicates that small chromosomes have greater potential for instability than the large ones. The data obtained not only confirm, but also enlarge the concept of directions and character of destabilization of the cell genetic apparatus in the process of neoplastic transformation due to the MDR acquisition by cells.