Improving the paradigm of approaches to adolescent sexual and reproductive health.

Traditional approaches to improving adolescent sexual and reproductive health (ASRH) have focused on changing individual behavior, with little emphasis on addressing the factors that contribute to this behavior: biological changes; the influence of family and friends; the communities in which young people live; and access to economic and academic opportunities. This article provides an overview of the various factors that influence ASRH behaviors and outcomes and suggests an approach grounded in the principles of positive youth development to reduce risk factors and improve the protective factors that contribute to adolescents' successful and healthy transition into adulthood.

Structural and functional characterization of methicillin-resistant Staphylococcus aureus's class IIb fructose 1,6-bisphosphate aldolase.

Staphylococcus aureus is one of the most common nosocomial sources of soft-tissue and skin infections and has more recently become prevalent in the community setting as well. Since the use of penicillins to combat S. aureus infections in the 1940s, the bacterium has been notorious for developing resistances to antibiotics, such as methicillin-resistant Staphylococcus aureus (MRSA). With the persistence of MRSA as well as many other drug resistant bacteria and parasites, there is a growing need to focus on new pharmacological targets. Recently, class II fructose 1,6-bisphosphate aldolases (FBAs) have garnered attention to fill this role. Regrettably, scarce biochemical data and no structural data are currently available for the class II FBA found in MRSA (SaFBA). With the recent finding of a flexible active site zinc-binding loop (Z-Loop) in class IIa FBAs and its potential for broad spectrum class II FBA inhibition, the lack of information regarding this feature of class IIb FBAs, such as SaFBA, has been limiting for further Z-loop inhibitor development. Therefore, we elucidated the crystal structure of SaFBA to 2.1 Å allowing for a more direct structural analysis of SaFBA. Furthermore, we determined the KM for one of SaFBA's substrates, fructose 1,6-bisphosphate, as well as performed mode of inhibition studies for an inhibitor that takes advantage of the Z-loop's flexibility. Together the data offers insight into a class IIb FBA from a pervasively drug resistant bacterium and a comparison of Z-loops and other features between the different subtypes of class II FBAs.

Enhanced tumor cell radiosensitivity and abrogation of G2 and S phase arrest by the Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin.

PURPOSE: Because of the potential for affecting multiple signaling pathways, inhibition of Hsp90 may provide a strategy for enhancing tumor cell radiosensitivity. Therefore, we have investigated the effects of the orally bioavailable Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) on the radiosensitivity of human tumor cells in vitro and grown as tumor xenografts. EXPERIMENTAL DESIGN: The effect of 17-DMAG on the levels of three proteins (Raf-1, ErbB2, and Akt) previously implicated in the regulation of radiosensitivity was determined in three human solid tumor cell lines. A clonogenic assay was then used to evaluate cell survival after exposure to 17-DMAG followed by irradiation. For mechanistic insight, the G(2)- and S-phase checkpoints were evaluated in 17-DMAG-treated cells. Finally, the effect of in vivo administration of 17-DMAG in combination with radiation on the growth rate of xenograft tumors was determined. RESULTS: 17-DMAG exposure reduced the levels of the three radiosensitivity-associated proteins in a cell line-specific manner with ErbB2 being the most susceptible. Corresponding concentrations of 17-DMAG enhanced the radiosensitivity of each of the tumor cell lines. This sensitization seemed to be the result of a 17-DMAG-mediated abrogation of the G(2)- and S-phase cell cycle checkpoints. The oral administration of 17-DMAG to mice bearing tumor xenografts followed by irradiation resulted in a greater than additive increase in tumor growth delay. CONCLUSIONS: These data indicate that 17-DMAG enhances the in vitro and in vivo radiosensitivity of human tumor cells. The mechanism responsible seems to involve the abrogation of radiation-induced G(2)- and S-phase arrest.

Flavopiridol enhances human tumor cell radiosensitivity and prolongs expression of gammaH2AX foci.

Flavopiridol is a cyclin-dependent kinase (CDK) inhibitor, which has recently entered clinical trials. However, when administered as a single agent against solid tumors, the antitumor actions of flavopiridol have been primarily cytostatic. Given its reported effects on cell cycle regulation, transcription, and apoptosis, flavopiridol may also influence cellular radioresponse. Thus, to evaluate the potential for combining this cyclin-dependent kinase inhibitor with radiation as a cancer treatment strategy, we have investigated the effects of flavopiridol on the radiation sensitivity of two human prostate cancer cell lines (DU145 and PC3). The data presented here indicate that exposure to flavopiridol (60-90 nM) after irradiation enhanced the radiosensitivity of both DU145 and PC3 cells. This sensitization occurred in the absence of significant reductions in cell proliferation, retinoblastoma protein phosphorylation, or P-TEFb activity. Moreover, the post-irradiation addition of flavopiridol had no effect on radiation-induced apoptosis or the activation of the G2 cell cycle checkpoint. However, flavopiridol did modify the time course of gammaH2AX expression in irradiated cells. Whereas there was no significant difference in radiation-induced gammaH2AX foci at 6 h, at 24 h after irradiation, the number of cells expressing gammaH2AX foci was significantly greater in the flavopiridol-treated cells. These results indicate that flavopiridol can enhance radiosensitivity of human tumor cells and suggest that this effect may involve an inhibition of DNA repair.

Gleevec-mediated inhibition of Rad51 expression and enhancement of tumor cell radiosensitivity.

Rad51 is an essential component of the homologous DNA repair pathway and has been implicated as a determinant of cellular radiosensitivity. Gleevec is a relatively specific inhibitor of c-Abl, a tyrosine kinase that can play a role in the regulation Rad51. The aim of this study was to determine the effects of Gleevec on Rad51 levels and the radiosensitivity of two human glioma cell lines and a nonimmortalized normal human fibroblast cell line. Exposure of both glioma cell lines to radiation resulted in an increase in Rad51 expression; Gleevec treatment alone reduced Rad51 expression. When glioma cells were pretreated with Gleevec, radiation-induced Rad51 expression and nuclear foci formation were reduced. Accordingly, pretreatment of the glioma cells with Gleevec resulted in an enhancement in their radiosensitivity. These data indicate that Gleevec enhances radiation-induced tumor cell killing and suggest that the mechanism involves the reduction in Rad51 levels. In contrast to the glioma cell lines, radiation or Gleevec treatments had no effect on Rad51 expression or foci formation in the normal fibroblast cells. Consistent with these observations, Gleevec did not modify the radiosensitivity of the normal cell line. These results suggest that Rad51 expression is subject to different regulatory processes in the glioma and normal cell lines and further suggest that Rad51 may be an appropriate target for selectively enhancing the radiosensitivity of brain tumor cells.