CONSEQUENCES OF ALKYLATION FOR THE BEHAVIOR OF DNA

Optimized viral dose and transient immunosuppression enable herpes simplex virus ICP0-null mutants To establish wild-type levels of latency in vivo

The reduced efficiency with which herpes simplex virus type 1 (HSV-1) mutants establish latent infections in vivo has been a fundamental obstacle in efforts to determine the roles of individual viral genes in HSV-1 reactivation. For example, in the absence of the "nonessential" viral immediate-early protein, ICP0, HSV-1 is severely impaired in its ability to (i) replicate at the site of inoculation and (ii) establish latency in neurons of the peripheral nervous system. The mouse ocular model of HSV latency was used in the present study to determine if the conditions of infection can be manipulated such that replication-impaired, ICP0-null mutants establish wild-type levels of latency, as measured by viral genome loads in latently infected trigeminal ganglia (TG). To this end, the effects of inoculum size and transient immunosuppression on the levels of acute replication in mouse eyes and of viral DNA in latently infected TG were examined. Following inoculation of mice with 2 x 10(3), 2 x 10(4), 2 x 10(5), or 2 x 10(6) PFU/eye, wild-type virus replicated in mouse eyes and established latency in TG with similar efficiencies at all four doses. In contrast, increasing the inoculum size of the ICP0-null mutants n212 and 7134 from 2 x 10(5) to 2 x 10(6) PFU/eye significantly decreased the levels of infectious virus detected in the tear films of mice from days 4 to 9 postinfection. In an attempt to establish the biological basis for this finding, the effect of viral dose on the induction of the host proinflammatory response was examined. Quantitative reverse transcription-PCR demonstrated that increasing the inoculum of 7134 from 2 x 10(4) to 2 x 10(6) PFU/eye significantly increased the expression of proinflammatory (interleukin 6), cell adhesion (intercellular adhesion molecule 1), and phagocyte-associated (CD11b) genes in mouse eyes 24 h postinfection. Furthermore, transient immunosuppression of mice with cyclophosphamide, but not cyclosporin A, significantly enhanced both the levels of acute n212 and 7134 replication in the eye and the levels of mutant viral genomes present in latently infected TG in a dose-dependent manner. Thus, the results of this study demonstrate that acute replication in the eye and the number of ICP0-null mutant genomes in latently infected TG can be increased to wild-type levels for both n212 and 7134 by (i) optimization of inoculum size and (ii) transient immunosuppression with cyclophosphamide.

Effects of ultraviolet radiation and immunosuppressive therapy on mouse epidermal cell kinetics

The effects of immunosuppressive drugs on epidermal cell mitotic activity and the proliferative response of epidermis following ultraviolet radiation (UVR) were tested. Hairless (Skh-hr 1) mice were treated with immunosuppressive drugs at equivalent clinical doses with or without concomitant UVR (290-400 nm). Epidermal parameters measured were mitotic index (Im), rate of entry into mitosis (Fm), flash labelling index (FLI), rate of entry into DNA synthesis (Fs) and DNA content (flow cytometric analysis). In non-irradiated skin, prednisolone therapy depressed both mitotic activity and DNA synthesis; azathioprine and cyclosporin A had no effect; cyclophosphamide therapy increased the Fm and FLI values. Following repeated doses of UVR, there were enhanced mitotic activity and DNA synthesis in epidermis. Prednisolone therapy moderately depressed both proliferative responses; cyclophosphamide enhanced mitotic activity; azathioprine and cyclosporin A had no effect on these responses. The significance of these findings in relation to potential for increased susceptibility of skin to UV-induced carcinogenesis is discussed.

Membrane and cytoplasmic changes in 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU)-sensitive and resistant human malignant glioma-derived cell lines

Human glioma-derived cell lines previously determined by a microtiter chemotherapy assay to be either 'sensitive' or 'resistant' to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) were treated with BCNU (1-80 micrograms/ml) and observed using microcinematography, scanning electron microscopy, and transmission electron microscopy. Striking bleb formation and cell retraction were observed to occur in a dose-dependent relationship within minutes in the cells known to be BCNU-sensitive. At 15 micrograms/ml, 69% of cells showed blebs by 30 min, 87% by 90 min, and 100% by 4 hr. This activity was not seen in BCNU-resistant cells. These morphological changes occur at a time too early to be accounted for by the known BCNU mechanism of DNA alkylation and cross-link formation and suggest that cytoplasmic and/or membrane events may be significant initial events in the cytotoxic actions of BCNU.

The effect of dibromodulcitol on resting and dividing lymphoid cells

The effect of dibromodulcitol (DBD) on the incorporation of labelled precursors into DNA and RNA fractions of PHA-stimulated human lymphocytes and of P388F lymphoma cells at various stages of their growth was studied. Both cell systems showed sensitivity to the drug within the concentration rage of 1-10 mug/ml. When DBD was added before phytohaemagglutinin (PHA), h.han RNA. In contrast, by adding DBD after PHA, RNA labelling was much more inhibited than DNA. In the latter case, the decrease in DNA labelling occurred only 24 h after drug treatment whereas RNA labelling was decreased 1 h after treatment. Levels of DBD which normally produced 30% inhibition in plating efficiency of P388F lymphoma cells affected uridine-5-T incorporation to a different extent at different stages of growth of the culture. Enhanced RNA labelling occurred in early exponential stage while at later stages of growth, RNA synthesis was depressed.