O6-Methyl-2'-deoxyguanosine (O6-MedG), a novel inhibitor of O6-alkylguanine-DNA alkyltransferase (O6-AGT), has been synthesized. The ability of O6-MedG to deplete the O6-AGT activity in leukemia L1210 and melanoma B16 cells in vivo has been studied. After intraperitoneal administration of O6-MedG to mice bearing leukemia L1210 or melanoma B16, the activity of O6-AGT in tumour cells decreased by 50%. Pretreatment of leukemia L1210 bearing mice with O6-MedG (200 mg/kg) 24 hours prior to ACNU (15 mg/kg) administration resulted in six out of seven 60-day survivors. Treatment of mice with ACNU (15 mg/kg) alone increased the life span by 200%. Treatment of melanoma B16 bearing mice with O6-MedG and 3 hours thereafter with ACNU resulted in a 50% inhibition of tumour growth, whereas the inhibiting effect of ACNU alone was 16%. There was no difference in leukemia growth when L1210/BCNU bearing mice were treated with O6-MedG followed by ACNU treatment. In vivo ACNU (15 mg/kg) produced a deep and prolonged inhibition of DNA, RNA and protein synthesis in leukemia L1210 cells. The DNA synthesis in leukemia L1210/BCNU cells was shown to recover more rapidly than in L1210 cells. The activities of DNA-polymerases alpha and beta and, especially, of O6-AGT were elevated in ACNU-resistant leukemia cells as compared with ACNU-sensitive cells. The activation of some repairing enzymes, such as O6-AGT, DNA-polymerases alpha and beta as well as increased levels of GSH may play a role in the development of drug resistance to ACNU.

O-Quinaldoyl derivatives of thymidine, 2'-deoxyuridine, and 5-trimethylsilyl-2'-deoxyuridine were synthesized. 5'-Deoxy-5'-(quinoline-2-carbonylamino)- and 5'-deoxy-5'-[(quinoline-2-carbonylamino)butyroylamino]thymidine were obtained by the reaction of 5'-amino-5'-deoxythymidine with pentafluorophenyl ester of quinaldic acid, or with 4-(quinoline-2-carbonylamino)butyric acid. Antiproliferative properties in respect to CaOv cells in vitro were found in most of the synthesized quinaldoyl derivatives of nucleosides (CE50 approximately 10(-5) M). 3'-O-Quinaldoylthymidine exhibited an antitumor activity in vivo. The interaction of 3'- and 5'-O-quinaldoyl- as well as 3',5'-di-O-quinaldoylthymidine with DNA was investigated by the method of fluorescent probes.

Interaction of 3'-amino-3'-deoxy-2',3'-secoadenosine with the N-hydroxysuccinimide esters of nicotinic or quinaldic acids and with 1-nitroanthraquinone-2-carboxylic acid in the presence of 2-ethoxy-1-ethoxy-carbonyl-1,2-dihydroquinoline led to the corresponding amides. To obtain 5'-modified 2',3'-secoadenosine analogs, 5'-deoxy-5'-nicotinoylamido-, 5'-deoxy-5'-(quinoline-2- carbonylamido)-, and 5'-deoxy-5'-[3-(3-indolyl)propionylamido]adenosine were subjected to the periodate oxidation--sodium borohydride reduction procedure. Structures of the synthesized compounds were was confirmed by 1H NMR spectroscopy, 2',3'-Diamino-2',3'-deoxy-, 3'-deoxy-3'-(quinoline-2-carbonylamido)-, and 5'-deoxy-5'-[3-(3-indolyl)propionylamido]-2',3'-secoadenosines+ ++ exhibited a cytotoxic effect on CaOv cells in vitro (CE50 10-30 microM).

Cytogenetic effects of ultra low doses of nitrosomethylurea in the range 10(-12)-10(-17) mol/(kg x day) on the chromosome structure were studied in the Ehrlich tumor and leucosis L-12110 cells. It was shown that nitrosomethylurea at an ultra low dose of 10(-17) mol/(kg x day) induces chromosome aberrations in the cells of the both studied tumors after a single and multiple injections to random bred and linear animals. The recorded effect suggests that with the decrease of therapeutic dose by 13 orders of magnitude the cytogenetic activity of the drug decreases by no more than one order of magnitude.

We studied sensitivity of various types of clonogenic hemopoietic cells (CFU-S-7, CFU-S-11, and CFU-ep) on the liver of 14-days embryos and from the bone marrow and spleen of adult mice to the cytotoxic agent 5-fluorouracil (5-FU) in vitro and in vivo. We discovered that different types of CFU-S of the embryos and adult mice has similar sensitivity to 5-FU in vitro. At the same time in vivo the bone marrow CFU-S-7 display a higher sensitivity to 5-FU than CFU-S-11, thus agreeing with the published data (Hodgson and Bradley, 1979). The differences between the 5-FU effects in vitro and in vivo are related to the hemopoietic microenvironment, which modulates the cytotoxic 5-FU effect in vivo.

The reaction of 5'-amino-2',5'-dideoxyuridine and 5'-amino-5'-deoxy-2',3'-O-ethoxymethyliden-6- azauridine with 3-(3-indolyl)propionic or 1-nitroanthraquinon-2-carboxylic acids in THF in the presence of 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ) resulted in the corresponding amide derivatives. The reaction conditions of the standard procedure for the removal of the O-alkylidene protecting group turned out to be too severe for the 5'-N-acylamide derivatives of 6-azauridine. 5'-Deoxy-5'-[3-(3-indolyl)propionyl-amino]-6-azauridine was synthesized from 5'-amino-5'-deoxy-6-azauridine and 3-(3-indolyl)propionic acid in THF in the presence of EEDQ. A reaction between 5'-O-tosyl-2',3'-O-ethoxymethyliden-6-azauridine and 3-aminopropanol gave 3-(3-hydroxypropylamino)-2-(2',3'-O-ethoxymethylidene-beta- D-ribofuranosyl)-as-triazine-5(2H)-one, the structure of which was confirmed also by synthesis from O2,5'-anhydronucleoside and 3-aminopropanol followed by further chemical transformations. A reaction of 3-(3-hydroxypropylamino) derivative obtained with nicotinoyl chloride prepared in situ, or with 1-nirtoanthraquinon-2-carboxylic acid in the presence of DCC with subsequent deprotection, afforded 3-[(3-pyridin-3-ylcarboxy)propylamino]- or 3-[3-(1-nitroanthraquinon-2-carboxy)propylamino]-2-beta-D-ribof ura nosyl-as- triazine-5(2H)-one, respectively. Structures of the nucleosides prepared were examined by 1H NMR spectroscopy. 2',5'-Dideoxy-5'-[(1-nitroanthraquinon-2-carbonyl)amino]uridine at a 10(-4) M concentration was shown to inhibit thymidine incorporation into cell DNA (CE50 10(-5) M) by 72%.

Interaction of nicotinoyl chloride in situ with 2'-deoxyuridine, its 3'-O-acetyl-, or 5'-O-trityl derivatives led to 3'-O-nicotinoyl-, 5'-O-nicotinoyl-, 3',5'-di-O-nicotinoyl-, and N3,3'-di-O-nicotinoyl-2'-deoxyuridine. Similarly, 5'-O-nicotinoyl-6-azauridine resulted from the reaction of 2',3'-O-ethoxymethylidene-6-azauridine followed by the deprotection. Reaction of 5'-amino-5'-deoxy-2',3'-O-ethoxymethylidene-6-azauridine with nicotinic acid in the presence of 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline followed by the cleavage of the 2',3'-O-protecting group gave 5'-deoxy-5'-nicotinamido-6-azauridine. The same compound was obtained from 5'-amino-5'-deoxy-6-azauridine and N-succinimidyl nicotinate. Structures of the compounds obtained were corroborated by 1H NMR spectra. It is shown that 3',5'-di-O-nicotinoyl-2'- deoxyuridine and 5'-deoxy-5'-O-nicotinamido-6-azauridine are cytotoxic toward CaOv cells in vitro (CE50 10(-5) M).

The "in vivo" effect of cycloplatam on DNA synthesis in leukemia P388/o (parent strain), P388/c (cycloplatam-resistant strain) and in some organs of tumour-bearing mice, such as spleen, kidney, gastrointestinal mucosa (GI mucosa) and bone marrow, has been studied. Cycloplatam induced a deep and stable inhibition of DNA synthesis in leukemia cells and kidney. DNA synthesis in normal dividing cells (GI mucosa, bone marrow, spleen) was shown to recover more rapidly than in leukemia cells and kidney after cycloplatam treatment. The GSH level was increased tenfold in leukemia P388/c cells in comparison with P388/o. The glutathione peroxidase and glutathione reductase activities were increased twofold in the resistant strain in comparison with the parent strain, while the activity of glutathione-S-transferase showed a 1.5-fold increase. Administration of cycloplatam to tumour-bearing mice caused a marked increase of the GSH level in the both leukemia strains. Alterations in GSH-dependent enzymes following cycloplatam therapy were expressed in a lesser degree. These data indicate that GSH and GSH-dependent enzymes may play an important role in the resistance of P388 leukemia cells to cycloplatam.

The effect of potential differentiation-inducing agent N-methylformamide on radiation response of murine normal and tumor cells (Lewis lung carcinoma, hematopoietic tissue and jejunum epithelial stem cells) was studied. The agent reduced or not altered radiation damage of tumor and epithelial cells in mice receiving NMF before irradiation. Sensitization to radiation was observed in endogenous spleen colony forming hemopoietic stem cells. When the agent was injected 15 min before irradiation the sensitizing effect was less pronounced. The highest effect was observed when agent was injected 24 h after irradiation of animals.

Stability of genome of children born to patients after antitumor radio- and chemotherapy was studied. For this aim the peripheral lymphocytes were irradiated in vitro at doses 0, 0.25, 0.50, 1.00, and 1.50 Gy of gamma-rays 137Cs, and induced chromosome aberrations on metaphases of cultivated lymphocytes were scored. The data obtained demonstrate an increased chromosomal radiosensitivity of patients' children as compared to the control children. A possible association between the chromosomal instability and the increased risk of cancer is discussed. The children prezygotically exposed to mutagenic factors are supposed to make a group of potentially increased risk of cancer.

The interaction of 3'-amino-2',3'-dideoxy- or 5'-amino-2',5'-dideoxy-5-substituted pyrimidine nucleosides with N-ethylmaleimide in DMF in the presence of Et3N gave two diastereomeric 2',3'-dideoxy-3'-(N-ethylsuccinimido)- or 2',5'-dideoxy-5'-(N-ethylsuccinimido)aminonucleosides in each reaction. For 3'-amino-5-trimethylsilyl- and 3'-amino-5-benzyloxymethyl-2',5'-dideoxyuridine diastereomeric 3'-(N-ethylsuccinimido)derivatives were separated by preparative TLC. Structures of synthesized analogs were confirmed by UV-, IR- and 1H-NMR spectra. It has been shown that modified nucleosides at 10(-5)-10(-4) M concentrations do not inhibit the thymidine incorporation into DNA of CaOv cells in vitro.

The results of fluorimetric spectral analysis of peripheral blood lymphocytes taken from patients with kidney tumors have suggested that data on the pattern of spectrum and particularly, parameter alpha--a ratio of one-spiral nucleinic acids to two-spiral ones in a cell--may be instrumental in assessing nonspecific resistance in cancer patients and prognosis. Also, these data may be used in working out strategies of treatment and, in particular, to reduce postoperative complications and side-effects of chemo- and radiation therapy. With high values of parameter alpha (0.16-0.4), activation reaction starts to counter stress, causing nonspecific resistance to increase. At lower values of the parameter (0.022-0.048), stress sits in, and nonspecific resistance level drops. Parameter alpha increases as a result of nonspecific activation therapy which leads to lower side-effects and fewer complications of postsurgical and chemoradiation treatment.