Phosphoserine inhibits neighboring arginine methylation in the RKS motif of histone H3.

The effects of phosphorylation of histone H3 at serine 10 have been studied in the context of other posttranslational modifications such as lysine methylation. We set out to investigate the impact of phosphoserine-10 on arginine-8 methylation. We performed methylation reactions using peptides based on histone H3 that contain a phosphorylated serine and compared the extent of arginine methylation with unmodified peptides. Results obtained via fluorography indicate that peptides containing a phosphorylated serine-10 inhibit deposition of methyl groups to arginine-8 residues. To further explore the effects of phosphoserine on neighboring arginine residues, we physically characterized the non-covalent interactions between histone H3 phosphoserine-10 and arginine-8 using 31P NMR spectroscopy. A salt bridge was detected between the negatively charged phosphoserine-10 and the positively charged unmodified arginine-8 residue. This salt bridge was not detected when arginine-8 was symmetrically dimethylated. Finally, molecular simulations not only confirm the presence of a salt bridge but also identify a subset of electrostatic interactions present when arginine is replaced with alanine. Taken together, our work suggests that the negatively charged phosphoserine maximizes its interactions. By limiting its exposure and creating new contacts with neighboring residues, it will inhibit deposition of neighboring methyl groups, not through steric hindrance, but by forming intrapeptide interactions that may mask substrate recognition. Our work provides a mechanistic framework for understanding the role of phosphoserine on nearby amino acid residues and arginine methylation.

High prevalence of X4/DM-tropic variants in children and adolescents infected with HIV-1 by vertical transmission.

BACKGROUND: We studied HIV coreceptor tropism in vertically HIV-infected children and adolescents with the objective of predicting the proportion of children and adolescents that could be treated with CCR5 (R5) antagonists. METHODS: One hundred eighteen multidrug-resistant pediatric patients (36 children and 82 adolescents) were enrolled in a cross-sectional study. Viral tropism was assessed using the new phenotypic HIV-1 tropism coreceptor assay information and Trofile. RESULTS: Of 118 antiretroviral-experienced HIV-infected children and adolescents, 49 (57.0%) had dual-tropic and 20 (23.3%) had X4-tropic viruses by tropism coreceptor assay information testing. Only 17 (19.7%) showed R5-tropic variants. HIV-1 coreceptor usage was not detectable in 32 of 118 (27%) patients. Among 24 children and 62 adolescents with tropism coreceptor assay information results, 17 (70.8%) children and 51 (82.2%) adolescents showed viruses with dual-tropic or X4-tropic variants. Additionally, Trofile (ES) was performed in 42 of 118 patients with HIV-1 RNA > 1000 copies/mL. No patient showed X4-tropic variants; dual-tropic viruses were observed in 12 (28.6%) patients. In 6 (14.3%) patients, HIV tropism could not be determined. X4-tropic variants were more common in children (P = 0.031). CD4 T cell percentage was significantly lower in children (P = 0.011) and adolescents (P = 0.027) with R5-tropic viruses than in those with X4-tropic viruses. CONCLUSIONS: The presence of X4-tropic variants in more than 80% of our cohort of antiretroviral-experienced children and adolescents with vertical HIV-1 infection indicates a very limited role for CCR5 antagonists as part of salvage regimens for highly treatment-experienced vertically HIV-1-infected patients with extensive antiretroviral drug resistance and limited treatment options.

Potent and sustained antiviral response of raltegravir-based highly active antiretroviral therapy in HIV type 1-infected children and adolescents.

BACKGROUND: There are pediatric patients receiving many highly active antiretroviral therapy (HAART) regimens entailing drug resistance mutations that complicate HAART effective therapies. METHODS: This was a multicenter retrospective study of 19 multidrug-resistant children and adolescents enrolled from July 2007 to October 2009. Patients were nonresponders because no reduction in HIV type 1 (HIV-1) RNA to undetectable levels was observed during their previous antiretroviral treatment history. The long-term effectiveness of raltegravir (RAL)-based salvage therapy was assessed through a longitudinal analysis of immunologic, virologic, and clinical status of the patients. RESULTS: Median age was 16.0 (15.0-18.0) years. At baseline, median HIV-1 RNA was 10,000 (4.0 log10 copies/mL) (interquartile range [IQR]: 4300-83,000), and median CD4T-cell count was 329 (18.2% cells/µL) (IQR: 175-452). The backbone regimen included at least 1 fully active drug in 17/19 (89%) patients. Median follow-up with HAART including RAL was 80.1 weeks (IQR: 49.4-96.4): 16/19 (84%) exposed for >120 weeks and 6/19 (32%) >100 weeks. After RAL-based therapy, 4/19 (21%) patients achieved HIV-1 RNA <400 copies and 13/17 (68%) reached HIV-1 RNA <50 copies: 6 (32%) within the first month and 7 (37%) within the first 4 months. CD4+ T-cell recovery (70% to 90% of the baseline values) was observed in 17/19 (89%) patients. No deaths, AIDS-defining illnesses, or symptoms of severe intolerance were recorded. Only 2 patients experienced mild-moderate short-term skin rash. Two (11%) patients had sustained and optimum adherence to HAART. No patients showed resistance mutations to RAL after follow-up. CONCLUSIONS: We observed a sustained antiviral response and improved immunologic indices in multidrug-resistant pediatric patients, most of whom had received RAL as part of salvage regimens with at least 1 fully active drugs.

Long-term efficacy and safety of fosamprenavir in human immunodeficiency virus-infected pediatric patients.

Fosamprenavir (FPV) efficacy in human immunodeficiency virus (HIV)-infected pediatric patients is still being evaluated in ongoing clinical trials. The long-term efficacy and safety of FPV boosted with ritonavir (FPV/r) was evaluated in 20 antiretroviral-naive and antiretroviral-experienced HIV-vertically infected pediatric patients. Analyses of CD4(+) T-cells, HIV-ribonucleic acid (RNA), and clinical status were performed during a median of 180 weeks. Initially, median HIV-RNA was 4.6 log(10) in naive and 4.4 log(10) in pretreated patients. Median CD4(+) T-cell was 17% and 31%, respectively. After FPV/r treatment, 18 of 20 patients achieved undetectable HIV-RNA and 4 of 20 experienced adverse events. To date, FPV/r treatment has shown sustained antiviral response and immunologic improvement in our 20 patients.

Salvage therapy with abacavir and other reverse transcriptase inhibitors for human immunodeficiency-associated encephalopathy.

BACKGROUND: HIV-associated encephalopathy (HIV-AE) is a severe neurologic condition that affects HIV-infected children. The potential benefit of antiretroviral (ARV) agents with good cerebrospinal fluid (CSF) penetration remains to be defined. Abacavir (ABC) achieves good CSF concentrations and studies of high-dose ABC showed benefit in adults with HIV dementia. The present study evaluated the safety and virologic, immunologic and neuropsychological responses of an ARV regimen including high-dose ABC in children with HIV-AE. METHODS: Children between 3 months and 18 years old and abacavir-naive with HIV-AE and virologic failure were eligible. RESULTS: : Seventeen children (16 ARV-experienced) were enrolled and 14 children completed 48 weeks of therapy. The overall tolerability was good; 2 children had a possible hypersensitivity reaction. At week 48, 53% and 59% of the children achieved HIV RNA levels below the limit of quantitation in plasma and CSF, respectively. The median (25%-75% range) change of HIV RNA from baseline to week 48 was -2.29 (-0.81 to -2.47) log10 copies/mL in plasma and -0.94 (0 to -1.13) log10 copies/mL in CSF. The mean increases in CD4 (+/-standard error of mean) cell count and CD4% were 427 (+/-169) cells/mm and 8% (+/-2), respectively. Concentrations of soluble tumor necrosis factor receptor II were reduced in plasma and CSF. Children less than 6 years of age demonstrated significant neuropsychological improvement at week 48. CONCLUSIONS: In the present study with a limited number of children, highly active ARV therapy including high-dose ABC showed a safety profile similar to standard dose ABC and provided clinical, immunologic and virologic response in children with HIV-AE at week 48. Children less than 6 years of age also demonstrated significant neuropsychological improvement.