Peculiarities of Molecular Mechanisms Involved in Modification of the Structural and Molecular Organization of the Cell Genome.

Within the framework of the previously proposed model of structural organization of DNA that supplements the Watson-Crick model and is based on a mathematical regulation - Fibonacci sequence, we suppose the existence of nucleotides without nitrogenous base and acting as linkers connecting DNA subunits.

Biodistribution of Alpha-Fetoprotein-Containing Noncovalent Complex Aimpila with Antitumor Activity.

Biodistribution of [125I]Aimpila (20 mg/kg) in the tumor and normal tissues, including the mammary gland tissue, after single oral dose was studied in BALB/c nude mice with T47D/ReCAF+++ human breast tumor sensitive to this drug and in closely related BALB/c nude+mice without tumors. The maximum concentration of [125I]Aimpila was in fact the same in the tumor and in the mammary gland, while the time course of its accumulation/elimination differed. The time of the maximum accumulation of the drug in the tumor was shorter and its persistence longer than in normal tissue. After 24 h, label concentration in the tumor was 4.5 times higher (p=0.002). Differences in the time course of label accumulation in the tumor were detected. The maximum ratio of tumor/blood concentrations of the preparation was recorded in 1 h after administration. [125I]Aimpila and [125I]alpha-fetoprotein accumulated in the tumor in comparable concentrations and were eliminated simultaneously at the same rate. The results of comparative analysis of accumulation of the labeled compounds in Aimpila-sensitive T47D/RECAF+++ tumor from 0.5 to 9.0 h after drug administration could be interpreted as a result of possible receptor-mediated binding of the complex with the tumor at the expense of the alpha-fetoprotein transporting part. Differences in the parameters of [125I]Aimpila biodistribution in the tumor and normal mammary tissue indirectly attested to selective antiproliferative activity of the complex.

Changes in the Quantitative Composition of the Population in Delayed Periods After γ-Radiation Exposure of the Cells in Various Phases of S Period of the First Mitotic Cycle.

Using the autoradiographic method, we studied the kinetics of DNA synthesis over the mitotic cycle in mouse corneal epithelium cells in delayed periods after γ-irradiation in different points of the S phase of the first mitotic cycle. The index labeled cells during 1-3 periods of DNA synthesis most adequately reflects quantitative changes in the cell population composition after cell exposure during the first S period. The relative number of labeled S phase cells in the second mitotic cycle in experiments where the cells were irradiated in the S1 phase of the first S period was 4-fold lower than in experiments where the cells were exposed during S2 phase. This effect is determined by inhibition of the transcription factors activation. It seems that two territorially different sites of the genome controlling the regulatory stimuli and involved in modification of the quantitative composition of the population are responsible for changes in its quantitative balance.

Fibonacci Sequence and Supramolecular Structure of DNA.

We proposed a new model of supramolecular DNA structure. Similar to the previously developed by us model of primary DNA structure [11-15], 3D structure of DNA molecule is assembled in accordance to a mathematic rule known as Fibonacci sequence. Unlike primary DNA structure, supramolecular 3D structure is assembled from complex moieties including a regular tetrahedron and a regular octahedron consisting of monomers, elements of the primary DNA structure. The moieties of the supramolecular DNA structure forming fragments of regular spatial lattice are bound via linker (joint) sequences of the DNA chain. The lattice perceives and transmits information signals over a considerable distance without acoustic aberrations. Linker sequences expand conformational space between lattice segments allowing their sliding relative to each other under the action of external forces. In this case, sliding is provided by stretching of the stacked linker sequences.

Delayed Consequences of Changes in DNA Synthesis in Cells Exposed to Single Irradiation at the End of S Phase of the Mitotic Cycle.

Kinetics of DNA synthesis throughout the mitotic cycle in mouse corneal epithelial cells after single γ-irradiation of cells (4 Gy) at the end of S phase was studied by the method of radioautography. It was found that single irradiation increased the duration of S phase due to reparation of damage in the cell at the expense of time that normally falls on g1 phase. During reparation, two parallel DNA synthesis processes occur in the damaged cells: de novo synthesis at the site of injury after excision of the damaged fragments (reparative synthesis) and supplementary synthesis during the repair period in the remaining undamaged genome competent for replication. During supplementary synthesis, repeats appear in DNA structure, which increases the amount of genetic material in the cell and affect S phase duration. All reparative processes take place in the cell population consisting of subpopulations of "differentiated", "resting", and "proliferating" cells. The changes in the proportions between the subpopulations under the influence of extreme factors can induce the appearance of metastatic cells in the population.

Reparation as a factor contributing to genetic variability of the biological system.

Kinetics of DNA synthesis in mitotic cycle of in mouse corneal epithelial cells after γ-irradiation in different S phase points was studied by the method of autoradiography. Normally, S phase of corneal epithelial cells consists of two phases (S1 and S2) separated by an interval without DNA synthesis. Each phase, in turn, includes two subphases with a pause in DNA synthesis. It was hypothesized that pauses in DNA synthesis, similar to that during presynthetic g1 phase, correspond to periods of cell preparation to the next stage of their development. After irradiation, reparation proceeds during pauses at different phases of the cell cycle. The mechanism of reparation induces cell genome rearrangement.

Dynamics of DNA synthesis disturbance and recovery after fractionated irradiation of S phase cells.

Using the autoradiographic method we studied the kinetics of DNA synthesis during themitotic cycle of mouse corneal epithelial cells after γ-irradiation in a dose of 2 Gy at different S-phase points. Normally, S phase in corneal epitheliocytes includes S1 and S2 phases separated by an interval during which DNA is not synthesized. Double exposure modifies the pattern of DNA synthesis in the cell due to reparation of injuries. The reparative processes in the cell are realized during the interval between the S1 and S2 phases and at the expense of g1 period of the mitotic cycle. If the cell has no time for reparation, the injuries are transferred into the class of "latent" injuries.

Comparative analysis of the kinetics of DNA synthesis after exposure during different phases of the cell cycle S period.

The kinetics of DNA synthesis in the mitotic cycle of mouse corneal epithelial cells was studied after a single γ-irradiation of cells in a dose of 4 Gy at different S-phase points. Normally, corneal epitheliocyte S phase consists of S1 and S2 phases separated by an interval during which no DNA is synthesized. The duration of each phase was lengthened after single irradiation due to reparation of injuries in the cells at the expense of the time normally occupied by g1 period of the mitotic cycle. The first event during reparation is excision of damaged complex from the DNA molecule; this complex consists of labeled daughter fragment and matrix site of DNA chain that was used for the synthesis of the daughter fragment. Presumably, the entire reparation process in the cell consists of two stages: "reparative" synthesis and "additional" synthesis. The reparative synthesis, in turn, includes two stages: de novo synthesis of matrix fragment in the DNA chain at the site of the gap formation and de novo synthesis of the daughter fragment after the synthesis of the new matrix fragment is over.

Effect of irradiation on DNA synthetic period of the mitotic cycle in cells.

Kinetics of DNA synthesis in mitotic cycle of mouse corneal epithelial cells after single γ-irradiation (4 Gy) at the end of S period was studied by the method of radioautography. Normally, S period of corneal epithelial cells consists of several stages separated by intervals without DNA synthesis. The estimated mean duration of the first (S(1)) and second (S(2)) phases of S period was 16 and 10 h, respectively, and the interval between them was 7 h. Single irradiation at the end of S period changed the duration of mitotic cycle periods: S(2) phase became 2.2-longer than S(1) phase and the duration of g(1) period decreased, because the time for reparation in irradiated cell increases at the expense of g(1) period. Shortening of g(1) period is a factor promoting the appearance of transformed cells.