Amplification of ERBB-2 (HER-2/NEU) Oncogene in Different Neoplasms of Patients from USSR

203 tumor specimens from 175 patients were studied. Amplification of ERBB-2 was detected in 14 out of 63 (22%) cases of breast carcinoma, in 1 out of 23 patients with ovarian cancers, in 1 out of 19 cases of colon carcinoma and in 1 out of 27 patients with thyroid cancer. We failed to find more than one copy of ERBB-2 in 34 patients with lung cancers, 6 with sarcomas and 3 with melanomas. There was tendency toward correlation between ERBB-2 amplification and lymph node involvement in patients with breast carcinoma. Thus, the oncogene ERBB-2 is often amplified in human tumors, but breast cancer is characterized by an especially high frequency of ERBB-2 amplification.

[Prevalence of widespread BRCA1 gene mutations in patients with familial breast cancer from St. Petersburg]

Ten variants different from the canonical nucleotide sequence (GenBank, U14680) has been identified when studying the mutation spectrum in gene BRCA1. Six of them (5382insC, 2963del10, 3819de15, 3875del4, 2274insA, and R1203X) cause premature termination of protein synthesis, thus predisposing to breast cancer. A missense mutation E1250K is presumed to be a factor of predisposition to cancer. We classified three variants of nucleotide sequence found in some patients as DNA polymorphisms S694S, L771L, and E1038G. The 5382insC and 3819de15 mutations have been detected in four and two families, respectively. Five of the mutations detected have not been found in Russia before. However, all mutations except for 2963del10 have been found in other populations of the world, which indicates their long evolutionary history. Two mutations found in patients from St. Petersburg (5382insC and 3875de14) have also been found in oncological patients from other regions of the Russian Federation.

Phase I/II trial of gene therapy with autologous tumor cells modified with tag7/PGRP-S gene in patients with disseminated solid tumors: miscellaneous tumors

BACKGROUND

The use of genetically modified autologous tumor cells appears to be a promising approach for cancer therapy. A phase I/II trial was undertaken to define the feasibility, safety and antitumor effects of the autologous vaccine prepared by transferring tag7/PGRP-S gene into malignant melanoma and renal cell carcinoma cells.

PATIENTS AND METHODS

Twenty-one patients (17 with disseminated malignant melanoma and four with metastatic renal cell carcinoma) were enrolled in this study. Cytoreduction was performed in all cases prior to therapy. Autologous tumor cells were transfected with the tag7/PGRP-S gene, irradiated and injected intradermally every 3 weeks.

RESULTS

Vaccinations were well tolerated by all patients, without clinically significant signs of toxicity. Delayed-type hypersensitivity was observed in 48% of cases. Antitumor immune response was observed in 95% of patients. There were no complete or partial responses; however, a minor response was achieved in one patient with renal cell carcinoma. The stabilization of neoplastic disease was observed in eight patients (seven with malignant melanoma and one with renal cell carcinoma). Median time to tumor progression was 3 months.

CONCLUSIONS

The approach suggested here appears to be well tolerated and produces a number of durable clinical effects. Further studies are required to determine whether promising effects on immune activation will result in an actual clinical benefit for patients with malignant melanoma and renal cell carcinoma.

Distinct prevalence of the CYP19 Delta3(TTTA)(7) allele in premenopausal versus postmenopausal breast cancer patients, but not in control individuals

The CYP19 gene encodes the enzyme aromatase, which plays a key role in the conversion of androgens to oestrogens. A polymorphism in CYP19 in intron 4 (TTTA)n has been reported to be associated with breast cancer (BC) risk, although conflicting evidence has also been published. Here, we employ a non-traditional, highly demonstrative design of a molecular epidemiological study, where the comparison of BC cases and healthy middle-aged female donors was supplemented by an analysis of groups with extreme characteristics of either BC risk (bilateral breast cancer (biBC) patients) or cancer tolerance (tumour-free elderly women aged >or=75 years). None of the (TTTA)n polymorphic variants was significantly overrepresented among the affected women compared with any of the control groups. However, a 3-bp deletion/insertion CYP19 polymorphism, which is located in the same intron approximately 50 bp upstream to the (TTTA)n repeat, was evidently associated with the menopausal status in both the BC and biBC cohorts. In particular, the Delta3(TTTA)(7) allele occurred significantly more frequently in premenopausal than in postmenopausal BC patients (65/172 (38%) versus 67/310 (22%); P=0.0001; Odds Ratio (OR)=2.20 (95% Confidence Interval (CI) 1.46-3.32)), while the perimenopausal cases demonstrated an intermediate value (9/34 (26%)). In the biBC cohort, women who developed both tumours during their premenopausal period had a significantly higher prevalence of the Delta3(TTTA)(7) allele than patients with a postmenopausal onset of bilateral disease (16/46 (35%) versus 8/50 (16%); P=0.035; OR=2.80 (1.08-7.23)); those biBC patients, whose tumours were diagnosed before and after the cessation of menses, displayed an intermediate occurrence of the Delta3(TTTA)(7) allele (7/32 (22%)). Similar tendencies in the Delta3(TTTA)(7) allele distribution in BC and biBC patients suggest that its association with the menopausal status of the patients is truly non-random and thus this observation deserves further detailed investigation.

Medico-genetic and cytogenetic investigation in family with high predisposition to diffuse intestine polyposis

We revealed a family consisting of 25 persons which displayed high predisposition to malignant diseases of the gastrointestinal tract (GIT): rectal cancer (RC) was diagnosed in 2 patients, large intestine malignant polyposis (LIMP) in 1 patient, large intestine diffuse polyposis (LIDP) in 3 and uterus fibromyoma in 1 patient. Six members of the family were examined cytogenetically with the methaphase method on blood lymphocytes following G-banding of chromosomes. In 2 patients with LIDP was detected 8.7 and 16.7% of hyperaneuploid cells, respectively, and 20% of cells with double minute chromosomes (DMS) were detected in 1 LIDP patient. We suppose, that LIDP development in members of the family is related to the significant increase of proportion of hyperaneuploid and DMS-containing cells.

[Molecular portrait of human kidney carcinomas: the gene expression profiling of protein-tyrosine kinases and tyrosine phosphatases which controlled regulatory signals in the cells]

Hybridization with cDNA arrays was used to obtain expression profiles of 214 protein-tyrosine kinase, protein-tyrosine phosphatase, dual-specific phosphatase, and other genes for kidney carcinomas (KC) and normal kidney tissues of 34 patients and for seven carcinoma cell lines. Computer analysis revealed three clusters of genes coexpressed in KC. A proliferating-cell gene cluster included MET, VIM, MYC, TOP2A, PCNA, etc. A neoangiogenesis and blood-cell gene cluster included LCK, HCK, FGR, MMP9, CSFR1, VEGF, FLT1, and KDR. A cluster corresponding to normal, differentiated kidney cells included ERBB2 (HER2) for receptor protein-tyrosine kinase, several phosphatase genes (PTPRE, PTPRB, DUSP9), and EGF. The results suggested that MET, DUSP9, PCNA, TOP2A, and VIM may serve as diagnostic and prognostic markers in KC. Tubulin and topoisomerase II were assumed to be promising targets for cell proliferation inhibitors in KC.

[Search for frequently encountered mutations in genes predisposing to breast cancer]

DNA of oncological patients, including Ashkenazi Jews and Slavs, living in St. Petersburg was collected, and the resultant collection was screened for three common mutations of genes BRCA1 and BRCA2 by means of heteroduplex analysis. The mutation 5382insC in exon 20 of the BRCA1 gene was found in four unrelated patients, including three Slavs and one Ashkenazi Jew, with a positive family history of breast cancer. The mutations 185delAG and 6174delT in the BRCA1 and BRCA2 genes, respectively, which are typical of Ashkenazi Jewish patients with breast cancer, were not found in the patients of either ethnicity living in St. Petersburg, although the 6174delT mutation was found in the control group of Ashkenazi Jews. A new 12-nucleotide duplication g.71741ins12nt found in intron 20 of the BRCA1 gene was described. The high frequency of the 5382insC mutation in the BRCA1 gene in patients with familial breast cancer in both St. Petersburg and Moscow indicates that Russian families with the history of breast cancer should be primarily tested for this mutation.

Tissue transglutaminase expression in breast carcinomas

Tissue transglutaminase (tTG) is known to participate in multiple cellular processes, including apoptosis, cellular adhesiveness etc. Alterations of tTG expression could contribute to the development of several categories of diseases, including AIDS, cancer etc. The aim of the study was to test the pattern and relevance of tTG expression in a subset of breast carcinomas. RT-PCR has detected tTG-specific RNA message in 11 out of 25 (44%) breast cancer samples. tTG message was detected in 6/8 (75%) breast carcinomas with high apoptotic index, but only in 5/17 (29%) with the low one (p = 0.03). Immunohistochemical analysis revealed that only 15% of breast carcinomas displayed tTG protein in tumor cells, while the staining of the stromal components occurred in approximately one-half of the tumours tested. Surprisingly, there was no significant association between tTG RNA expression and protein positivity. Moreover, there was no evident relationships between tTG immunostaining and apoptotic index or clinical parameters of breast neoplasms. There are at least 2 alternative explanations for the poor concordance between RNA and protein data. It is likely that the sensitivity of immunohistochemistry is not sufficient to detect functionally relevant tTG enzyme in all breast cancer sections. Otherwise, tTG RNA expression does not always lead to accumulation of its product in the tumor cells, but reflects the transcriptional activation of other pro-apoptotic genes due to common triggering mechanisms.

CYP19 gene polymorphism in endometrial cancer patients

PURPOSE

Initiation/promotion of endometrial cancer is known to be associated with estrogenic influence. Therefore, it is possible that some allelic polymorphisms of the genes involved in steroidogenesis or steroid metabolism contribute to endometrial cancer susceptibility.

METHODS

Here, we compared CYP19 (aromatase) gene polymorphism in 85 endometrial cancer patients and in 110 non-affected women.

RESULTS

The genotypes containing the longest alleles (A6 and A7) of CYP19 were found to be over-represented in patients as compared to controls. In addition, these genotypes demonstrated a tendency to be associated with increased concentrations of estradiol and testosterone in postmenopausal patients.

CONCLUSIONS

Thus, CYP19 polymorphism might be one of the genetic risk factors for endometrial cancer development.

GSTM1 genotypes in elderly tumour-free smokers and non-smokers

Cancer is known to be an extremely common disease, with the life-time risks reaching close to 0.5 for men and to 0.4 for women. Hence those individuals, who succeeded to achieve a reasonably old age without a history of malignancy, represent a distinct group of interest, which apparently can be defined as 'tumour-tolerant'. Focus on the genetic features of these subjects may significantly facilitate the research of cancer-predisposing polymorphisms: first, a fundamental understanding of molecular mechanisms conferring the phenomena of cancer resistance appears to be outstandingly important; second, it is promising to involve non-affected geriatric cohorts in the molecular epidemiological studies as a tumour-free control of especial value. Here we analysed the GSTM1 genotype frequencies in the individuals with seemingly different degrees of resistance or susceptibility to neoplasms, such as elderly tumour-free smokers and non-smokers (> or = 75-years-old), healthy middle-aged donors, and lung cancer patients. The proportion of GSTM1-deficient individuals gradually increased from elderly controls (70/157; 45%) to middle-aged ones (77/140; 55%) to lung cancer sufferers (34/58; 59%), showing the minimal estimates in elderly non-affected smokers (35/81; 43%) and the maximal ones in the affected non-smokers (7/7, 100%). These data have led to the two groups of conclusions. First, the broad protective role of GSTM1 has been confirmed in this report. In particular, GSTM1-deficiency appeared to reduce the chances of entering an elderly age without a history of malignancy (OR=0.66 (0.42-1.04); P=0.073). Second, the efficiency of 'tumour patients versus elderly donors' comparative analysis has been exemplified. Indeed, the long-debated fact of overrepresentation of GSTM1(-) genotypes among lung cancer sufferers was clearly demonstrated by comparison of the affected individuals to the geriatric controls (OR=1.76 (0.96-3.23); P=0.068), whereas the same patients failed to produce any convincing deviations towards the middle-aged donors (OR=1.16 (0.63-2.14); P=0.641).

CYP17 polymorphism in the groups of distinct breast cancer susceptibility: comparison of patients with the bilateral disease vs. monolateral breast cancer patients vs. middle-aged female controls vs. elderly tumor-free women

The CYP17 gene encodes an enzyme involved in several critical steps of steroidogenesis. The promoter region of the CYP17 displays a single-nucleotide polymorphism, which is suspected to modulate the expression of the gene and thus may contribute in the interindividual variations of hormonal background. In agreement with this functional hypothesis, the MspA1+ allele (designated as A2) of the CYP17 was shown to render an increased risk of breast cancer (BC). However, the latter observation was disputed by a series of negative reports. Here, we re-evaluated the role of CYP17 MspA1 polymorphism in the BC susceptibility, using a non-traditional design of a case-control study. In addition to randomly selected 183 BC patients and 107 female middle-aged donors, we examined the groups with apparently extreme characteristics of either BC risk or BC resistance, namely the 57 bilateral breast cancer (biBC) patients and 75 elderly (>/=75 years old) tumor-free women. Neither BC nor biBC patients showed increased prevalence of 'unfavorable' A2 allele as compared with the non-affected cohorts. Moreover, the A2 variant was not significantly associated with the tumor size, nodal involvement and menopausal status in the patients either with the monolateral or bilateral disease. Thus, our data argue against the earlier reported role of the CYP17 in BC predisposition and progression. In addition, usual distribution of the CYP17 alleles in the elderly group indicates a neutral effect of this polymorphism on the longevity in females.

L-MYC and GSTM1 polymorphisms are associated with unfavourable clinical parameters of gliomas

L-MYC and GSTM1 genotypes were analysed in glioma patients (GP) and healthy donors (HD). None of these genes appeared to influence the risk of this disease, however both polymorphisms correlated with unfavourable clinical parameters of gliomas. In particular, S allele of the L-MYC was overrepresented in the relapsed patients (P < 0.05), and GSTM1-null genotype was associated with the advanced tumour grade (P < 0.05). Patients, but not donors, demonstrated frequent combination of SS L-MYC homozygosity with GSTM1(-) variant (P < 0.01 ), as well as a correlation between LL L-MYC homozygosity and GSTM1 (+) genotype (P < 0.05).

Evidence for microsatellite instability in bilateral breast carcinomas

The molecular pathogenesis of various categories of breast cancer (BC) has been well described, but surprisingly few reports have appeared on analysis of somatic mutations in bilateral BC. We have performed a polymerase chain reaction (PCR)-driven investigation of chromosomal regions showing common loss of heterozygosity (LOH) in 23 cases (46 tumors) from patients diagnosed with bilateral BC. LOH was observed in 15/46 (33%) informative tumors for chromosome 1p, 5/32 (16%) for 5q, 12/44 (27%) for 11q, 15/40 (38%) for 13q and 4/24 (17%) for 17p. These values are within the range of interlaboratory variations reported for unilateral BC. There was no strong evidence for concordance of LOH within the same patient for any of the chromosomal loci tested. Atypical for breast carcinomas, 7/46 (15%) tumors accumulated a high frequency (ranging from 11 to 29%) of shortened dinucleotide CA repeats, implying microsatellite instability (MI). Further analysis with the highly informative BAT-26 marker allowed for the classification of two of these tumors as having a replication error positive (RER(+)/MSI-H) phenotype, whereas the remaining five carcinomas harbored so-called borderline MI. Thus an involvement of both RER(+) and borderline MI appears to be a distinct feature of bilateral breast carcinomas compared to unilateral lesions.

L-myc polymorphism in cancer patients, healthy blood donors and elderly, tumor-free individuals in Russia

L-myc polymorphism was investigated in 95 breast cancer (BC), 63 colorectal cancer (CC) and 58 lung cancer (LC) patients, as well as in 122 healthy, middle-aged blood donors (HBDs) and 184 elderly, tumor-free individuals. The occurrence of the S allele in the BC cohort (57%) was significantly higher than that in middle-aged, healthy females (41%) and elderly, non-affected women (47%), implying involvement of the L-myc genotype in BC susceptibility (age-adjusted OR = 1.74, 95% CI 1.11-2.73, p = 0.016). L-myc allele distribution in CC and LC was similar to that in controls. Contrary to earlier reports, L:S allele frequencies ratio in elderly blood donors (EBDs) did not significantly differ from that in HBDs (0.49:0. 51 and 0.54:0.46, respectively). However, the S allele had a tendency to be over-represented among elderly compared with middle-aged smokers (55% vs. 44%; OR = 1.57, 95% CI 0.98-2.50, p = 0. 059), which implies that it may be linked with tolerance to smoking effects.

Features of HPV infection among the healthy attendants of gynecological practice in St. Petersburg, Russia

Prevalence of human papillomavirus (HPV) infection was estimated in women from St. Petersburg, Russia. The study included 309 attendants of gynecological practice, who met the following criteria: (1) history of sexual activity; (2) reproductive age; (3) lack of evidence for a specific disease of the genital tract or a current pregnancy; and (4) no cervical abnormalities revealed by cytological examination. Papillomavirus detection was carried out by PCR using MY09/11 primers. Ninety (29%) females turned out to be HPV-positive. HPV presence did not correlate with the current age, age at the sexual debut, or time interval since the first intercourse. However, women with the history of more than two contraceptive abortions had a higher prevalence of papillomavirus infection as compared to the remaining group (30/66 (45%) vs. 56/207 (27%); P = 0.005; OR = 2.25 (1.27-3.97)). HPV genotyping procedure involved reverse dot-blot hybridization and restriction endonuclease analysis. High-risk, low-risk and non-identified viruses were detected in 58, 26, and 16% of the positive samples, respectively. HPV16 was the most prevalent type, being present alone in 21% of the infected women, and in combination with other HPVs in 5% of the virus-positive females. No other papillomavirus types showed exceptionally prominent prevalence. The data suggest that HPV occurrence among Russian women is within the range of world-wide variations.

Medico-genetic and cytogenetic study of a family with high predisposition to malignant disease in gastro-intestinal tract

In a family consisting of 48 persons with high predisposition to familial stomach cancer (SCr), SCr was diagnosed in 8 persons (I-2; II-1,3,4; III-1,2,3,4). Moreover, one woman (III-8) had bilateral breast cancer and two (proband: IV-1 and her father's cousin: III-10) chronic gastritis. The proband, her father's cousin, his sister (III-11) and the proband's sister (IV-2) were examined clinically and cytogenetically (with the metaphase method on blood lymphocytes with G-banding of chromosome 21: (p12-pter) in 100% of cells on the basis of chromosomal instability; besides, the complex translocation in chromosome 2 in 4% of cells and the increase of q-arm of chromosome 21 was found in 2% of cells. The proband's sister (IV-2) had 3% of cells with polyploidy, the del 1 (p34-pter) in 1% of cells and the del 7 (p21-pter) in 4% of cells. The cytogenetic examination of the proband's uncle (III-10), carried out 3 times, revealed the case of the proband, endomitosis in 2% of cells, polyploidy in 2% of cells and hyperaneuploidy in 4% of cells. His sister (III-11) had 4% of cells with endomitosis, 3% of cells with chromosome and chromatid breaches, an increase of the p-arm of chromosome 21 in 100% of cells and the loss of 7p in 2% of cells. The nature of the phenomenon in chromosome 21 and the translocations in the members of this family is here discussed. The cytogenetic examination is currently ongoing.

Experimental gastrocarcinogenesis: the dynamics of morphological and biochemical changes

In many cases of stomach disease, specific epithelial changes of the mucous membrane have already been detected and staged in the past. An attempt has been made in this study to assess with a more up-to-date approach the data concerning the possible molecular biological mechanisms of tumor proliferation in stomach epithelial cells.

Supportive care in cancer patients in St. Petersburg

The supportive care programme in St. Petersburg has existed for more than 10 years and works mainly with breast cancer patients. It includes physical procedures, psychotherapy and support given by volunteers of the Hope/ Nadezhda Association, who operate in accordance with the Reach to Recovery International Programme. In the last stages the pain relief service is activated and has good results. The Anticancer/Antirak Society in St. Petersburg provides cancer patients with help and information. Our experience with this kind of care is described and some outcomes are reported.

Nuclear protein synthesis in thymocytes of X-irradiated rats

The biosynthesis and phosphorylation of nuclear proteins of thymocytes were investigated in rats after 4.0 Gy whole-body X-irradiation during the period which precedes DNA degradation in lymphoid cells. Proteins were separated by two-dimensional gel-electrophoresis, detected by Coomassie blue staining. Incorporation of [35S]methionine into proteins and phosphorylation of proteins with [32P]inorganic phosphate were determined by scanning densitometry of autofluorograms and autoradiograms, respectively. No change in the quantity of proteins was observed 1 h after irradiation. Decrease in specific activity of [35S]methionine-labelled proteins was seen in most protein fractions. Significant enhancement of phosphorylation of three proteins was established, characterized by molecular weight and pH: MW 20 kD, pH 6.8; MW 35 kD, pH 5.8 and MW 48 kD, pH 5.8. These results suggest that immediately after X-irradiation a short-term increase of chromatin-bound non-histone protein phosphorylation occurs. This finding, along with the previously described enhancement of RNA polymerase II in thymocytes (Zhivotovsky et al. 1982) suggests a temporary gene activation shortly after X-irradiation of the rat.

Degree of chromatin fragmentation and frequency of nuclear pyknosis in Percoll-fractionated thymocytes of irradiated rats

The relationship between nuclear chromatin degradation to polydeoxyribonucleotides (PDN) and other features of interphase death were studied using thymocytes of normal and X-irradiated rats. Fractionation of the thymic cells in Percoll gradients was performed in order to separate dead from intact cells. The degree of radiation-induced chromatin fragmentation, as assessed by electrophoresis, was similar for PDN from all Percoll bands. Following irradiation 87-98 per cent of 'heavy' thymocytes were pyknotic and almost devoid of receptors to autologous erythrocytes thus comprising a dead cell population. A direct relationship between PDN content and nuclear pyknosis was noted throughout the gradient. The loss of autologous rosette-forming ability was directly related to other indices of interphase death. The possibility of PDN originating from pyknosis-prone cells and the capacity of radiosensitive thymocytes to form autologous rosettes are discussed.

Effects in vitro of cadmium ions on some membrane and nuclear parameters of normal and irradiated thymic lymphoid cells

Effects of cadmium chloride upon 3H-Con A binding, number of autologous rosette-forming cells (ARFC), cell viability and the degree of DNA supercoiling were studied in normal and irradiated thymic lymphoid cells, isolated from rats and incubated up to 6 h in vitro. Cd (10-100 microM) did not significantly alter the patterns of surface markers and viability of normal thymocytes, as measured by supravital staining or nuclear pyknotic criteria. The following effects of Cd were noted for irradiated thymic cells: 1) Cd ions (25 microM) caused elimination of radiation-induced increase of Con A binding; 2) the characteristic loss of ARFC receptors, like development of nuclear pyknosis, was prevented in the presence of CdCl2 (10-100 microM); 3) the postradiation relaxation of nuclear supercoiled DNA was distinctly less pronounced with Cd. Possible reasons for these effects of Cd are discussed. Irradiated lymphoid cells are proposed as a suitable experimental model for the studies of different toxic actions of Cd and other heavy metals.

Distribution of nuclease attack sites and complexity of DNA in the products of post-irradiation degradation of rat thymus chromatin

The distribution of nuclease attack sites in chromatin has been studied on the basis of the quantitative relationship of the single- and double-stranded fragments of various lengths in the products of post-irradiation degradation of chromatin (PDN). It has been shown that in irradiated thymocytes internucleosome degradation of chromatin occurs and the products of the enzymic digestion of chromatin derive from randomly distributed genome areas accumulate. Analysis of the reassociation curves has not shown any differences in the complexity of the PDN fractions and total DNA.

Effects of X-irradiation on the hybridization of rat thymus nuclear RNA with repeated and unique DNA sequences

The kinetics of DNA hybridization with heterogeneous nuclear RNA (hnRNA) from normal and phytohaemagglutinin (PHA)-stimulated thymocytes has been studied in control rats and in animals 30 min after exposure to whole-body X-radiation with 400 rad. Irradiation results in a diminished ability of hnRNA to form hybrids with DNA at all C0t values ranging from 10(-3) to 10(4). Since this effect is most pronounced in the regions of low repetitive and unique DNA sequences, it is concluded that whole-body X-irradiation of animals may also suppress the transcription, particularly, in these regions.

Reassociation kinetics of DNA from x-irradiated ascites hepatoma cells of the rat

The kinetics of the reassociation fo DNA from ascites hepatoma cells has been studied. The curve exhibited three zones corresponding to 'fast', 'intermediate' and 'slow' speeds of DNA reassociation. The difference was observed in the DNA reassociation curves of the control and irradiated (1500 rad) cells which was particularly expressed in the 'slow' zone (10(2) less than C0t less than 10(4). The same dose, however, does not qualitatively effect the secondary DNA structure, which was estimated by the method of thermal elution from the hydroxyapatite column.