Discovery of the Novel Entecavir-Resistant Hepatitis B Virus Reverse Transcriptase A181C Substitution From an Integrated Genotypic Analysis

Entecavir (ETV) is a first-line therapy for chronic hepatitis B virus (HBV), demonstrating potent suppression of HBV DNA and a high barrier to viral resistance. Previous studies revealed that ETV-resistant (ETVr) HBV DNA resulted from substitutions in the HBV reverse transcriptase (RT) at positions rtT184, rtS202, or rtM250 in combination with lamivudine resistance (LVDr) substitutions rtM204I/V±rtL180M. In vitro, viral variants exhibit varying degrees of ETV susceptibility and replication capacity depending on specific resistance substitutions. To explore the potential for additional pathways to ETVr, HBV RT sequences from 982 evaluable patients enrolled in 17 ETV clinical studies were analyzed. Thirty novel emergent substitutions at amino acid positions not previously associated with HBV nucleos(t)ide drug resistance were observed in at least 2 patients and were identified in patient-derived HBV with a wild-type, LVDr, or ETVr RT sequence. Phenotypic analysis of these substitutions indicated that they had no effect on ETV susceptibility. Phenotypic analysis was also performed on patient-derived HBV RT sequences from 10 LVD-naive and 13 LVD-experienced patients with virologic breakthrough and emergent novel substitutions while on ETV treatment. One LVD-experienced patient-derived HBV RT harboring LVDr substitutions rtL180M+rtM204V with rtA181C displayed reduced ETV susceptibility (122-fold greater than wild-type HBV) and remained susceptible to adefovir and tenofovir. HBV harboring the rtA181C substitution without LVDr substitutions rtL180M+rtM204V remained susceptible to inhibition by ETV, adefovir, and tenofovir, although cross-resistance to LVD and telbivudine was observed. Conclusion: An integrated genotypic analysis of HBV RT sequences from patients with chronic HBV treated with ETV led to the discovery of the novel ETVr substitution rtA181C. This substitution was always detected in combination with LVDr substitutions rtL180M+rtM204V in ETV-treated patients.

High-throughput screening and rapid inhibitor triage using an infectious chimeric Hepatitis C virus

The recent development of a Hepatitis C virus (HCV) infectious virus cell culture model system has facilitated the development of whole-virus screening assays which can be used to interrogate the entire virus life cycle. Here, we describe the development of an HCV growth assay capable of identifying inhibitors against all stages of the virus life cycle with assay throughput suitable for rapid screening of large-scale chemical libraries. Novel features include, 1) the use of an efficiently-spreading, full-length, intergenotypic chimeric reporter virus with genotype 1 structural proteins, 2) a homogenous assay format compatible with miniaturization and automated liquid-handling, and 3) flexible assay end-points using either chemiluminescence (high-throughput screening) or Cellomics ArrayScan™ technology (high-content screening). The assay was validated using known HCV antivirals and through a large-scale, high-throughput screening campaign that identified novel and selective entry, replication and late-stage inhibitors. Selection and characterization of resistant viruses provided information regarding inhibitor target and mechanism. Leveraging results from this robust whole-virus assay represents a critical first step towards identifying inhibitors of novel targets to broaden the spectrum of antivirals for the treatment of HCV.

A novel small molecule inhibitor of hepatitis C virus entry

Small molecule inhibitors of hepatitis C virus (HCV) are being developed to complement or replace treatments with pegylated interferons and ribavirin, which have poor response rates and significant side effects. Resistance to these inhibitors emerges rapidly in the clinic, suggesting that successful therapy will involve combination therapy with multiple inhibitors of different targets. The entry process of HCV into hepatocytes represents another series of potential targets for therapeutic intervention, involving viral structural proteins that have not been extensively explored due to experimental limitations. To discover HCV entry inhibitors, we utilized HCV pseudoparticles (HCVpp) incorporating E1-E2 envelope proteins from a genotype 1b clinical isolate. Screening of a small molecule library identified a potent HCV-specific triazine inhibitor, EI-1. A series of HCVpp with E1-E2 sequences from various HCV isolates was used to show activity against all genotype 1a and 1b HCVpp tested, with median EC50 values of 0.134 and 0.027 µM, respectively. Time-of-addition experiments demonstrated a block in HCVpp entry, downstream of initial attachment to the cell surface, and prior to or concomitant with bafilomycin inhibition of endosomal acidification. EI-1 was equally active against cell-culture adapted HCV (HCVcc), blocking both cell-free entry and cell-to-cell transmission of virus. HCVcc with high-level resistance to EI-1 was selected by sequential passage in the presence of inhibitor, and resistance was shown to be conferred by changes to residue 719 in the carboxy-terminal transmembrane anchor region of E2, implicating this envelope protein in EI-1 susceptibility. Combinations of EI-1 with interferon, or inhibitors of NS3 or NS5A, resulted in additive to synergistic activity. These results suggest that inhibitors of HCV entry could be added to replication inhibitors and interferons already in development.

Long-term monitoring shows hepatitis B virus resistance to entecavir in nucleoside-naïve patients is rare through 5 years of therapy

Patients with chronic hepatitis B virus (HBV) infection who develop antiviral resistance lose benefits of therapy and may be predisposed to further resistance. Entecavir (ETV) resistance (ETVr) results from HBV reverse transcriptase substitutions at positions T184, S202, or M250, which emerge in the presence of lamivudine (LVD) resistance substitutions M204I/V +/- L180M. Here, we summarize results from comprehensive resistance monitoring of patients with HBV who were continuously treated with ETV for up to 5 years. Monitoring included genotypic analysis of isolates from all patients at baseline and when HBV DNA was detectable by polymerase chain reaction (> or = 300 copies/mL) from Years 1 through 5. In addition, genotyping was performed on isolates from patients experiencing virologic breakthrough (> or = 1 log(10) rise in HBV DNA). In vitro phenotypic ETV susceptibility was determined for virologic breakthrough isolates, and for HBV containing novel substitutions emerging during treatment. The results over 5 years of therapy showed that in nucleoside-naïve patients, the cumulative probability of genotypic ETVr and genotypic ETVr associated with virologic breakthrough was 1.2% and 0.8%, respectively. In contrast, a reduced barrier to resistance was observed in LVD-refractory patients, as the LVD resistance substitutions, a partial requirement for ETVr, preexist, resulting in a 5-year cumulative probability of genotypic ETVr and genotypic ETVr associated with breakthrough of 51% and 43%, respectively. Importantly, only four patients who achieved < 300 copies/mL HBV DNA subsequently developed ETVr.

CONCLUSION

Long-term monitoring showed low rates of resistance in nucleoside-naïve patients during 5 years of ETV therapy, corresponding with potent viral suppression and a high genetic barrier to resistance. These findings support ETV as a primary therapy that enables prolonged treatment with potent viral suppression and minimal resistance.

Hepatitis B virus quasispecies susceptibility to entecavir confirms the relationship between genotypic resistance and patient virologic response

BACKGROUND/AIMS

The efficacy of anti-viral therapy for chronic hepatitis B virus (HBV) is lost upon the emergence of resistant virus. Using >500 patient HBV isolates from several entecavir clinical trials, we show that phenotypic susceptibility correlates with genotypic resistance and patient virologic responses.

METHODS

The full-length HBV or reverse transcriptase gene was amplified from patient sera, sequenced, and cloned into an HBV expression vector. Entecavir susceptibilities of individual virus clones and patient quasispecies populations were analyzed in conjunction with the sequenced resistance genotype and the patient's virologic response.

RESULTS

Entecavir susceptibility decreased approximately 8-fold for isolates with various constellations of lamivudine resistance substitutions. The spectrum of additional substitutions that emerged during therapy at residues rtT184, rtS202, or rtM250 displayed varying levels of entecavir susceptibility according to the specific resistance substitutions and the proportion of resistant variants in the quasispecies. Phenotypic analyses of samples associated with virologic breakthrough confirmed the role of these residue changes in entecavir resistance. Additional longitudinal phenotypic analyses showed that decreased susceptibility correlated with both genotypic resistance and increased circulating HBV DNA.

CONCLUSIONS

HBV phenotypic analysis provides additional insight as part of a resistance monitoring program that includes genotypic analysis and quantification of circulating virus.

Comprehensive evaluation of hepatitis B virus reverse transcriptase substitutions associated with entecavir resistance

Virologic resistance emerging during entecavir (ETV) therapy for hepatitis B virus (HBV) requires three substitutions in the viral reverse transcriptase (RT), signifying a high barrier to resistance. Two of these substitutions are associated with lamivudine resistance (LVDr) in the tyrosine-methionine-aspartate-aspartate (YMDD) motif (rtM204V and rtL180M), whereas the other occurs at one or more positions specifically associated with ETV resistance (ETVr): rtT184, rtS202, or rtM250. Although a variety of substitutions at these primary ETVr positions arise during ETV therapy, only a subset give rise to clinical virologic breakthrough. To determine the phenotypic impact of observed clinical and potential new ETVr substitutions, a comprehensive panel of clones containing every possible amino acid at the three primary ETVr positions in LVDr HBV was constructed and analyzed in vitro. A range of replication capacities was observed for the panel, but none of the mutations rescued replication of the LVDr mutant to the wild-type level. More clones with residue rtS202 substitutions were severely impaired than those at rtT184 or rtM250. A wide variety of ETV susceptibilities was observed, ranging from approximately eight-fold (no increase over the LVDr parent) to greater than 400-fold over the wild-type. A correlation was identified between clinically observed substitutions and those displaying higher in vitro replication and resistance, especially those from virologic breakthrough patients.

CONCLUSION

The high number of tolerated and resistant ETVr substitutions is consistent with models predicting that the mechanism for ETVr is through enhancement of LVDr changes in the RT deoxyribonucleotide triphosphate (dNTP)-binding pocket.

X-ray crystal structures of human immunodeficiency virus type 1 protease mutants complexed with atazanavir

Atazanavir, which is marketed as REYATAZ, is the first human immunodeficiency virus type 1 (HIV-1) protease inhibitor approved for once-daily administration. As previously reported, atazanavir offers improved inhibitory profiles against several common variants of HIV-1 protease over those of the other peptidomimetic inhibitors currently on the market. This work describes the X-ray crystal structures of complexes of atazanavir with two HIV-1 protease variants, namely, (i) an enzyme optimized for resistance to autolysis and oxidation, referred to as the cleavage-resistant mutant (CRM); and (ii) the M46I/V82F/I84V/L90M mutant of the CRM enzyme, which is resistant to all approved HIV-1 protease inhibitors, referred to as the inhibitor-resistant mutant. In these two complexes, atazanavir adopts distinct bound conformations in response to the V82F substitution, which may explain why this substitution, at least in isolation, has yet to be selected in vitro or in the clinic. Because of its nearly symmetrical chemical structure, atazanavir is able to make several analogous contacts with each monomer of the biological dimer.

Inhibition of hepatitis B virus polymerase by entecavir

Entecavir (ETV; Baraclude) is a novel deoxyguanosine analog with activity against hepatitis B virus (HBV). ETV differs from the other nucleoside/tide reverse transcriptase inhibitors approved for HBV therapy, lamivudine (LVD) and adefovir (ADV), in several ways: ETV is >100-fold more potent against HBV in culture and, at concentrations below 1 microM, displays no significant activity against human immunodeficiency virus (HIV). Additionally, while LVD and ADV are obligate DNA chain terminators, ETV halts HBV DNA elongation after incorporating a few additional bases. Three-dimensional homology models of the catalytic center of the HBV reverse transcriptase (RT)-DNA-deoxynucleoside triphosphate (dNTP) complex, based on the HIV RT-DNA structure, were used with in vitro enzyme kinetic studies to examine the mechanism of action of ETV against HBV RT. A novel hydrophobic pocket in the rear of the RT dNTP binding site that accommodates the exocyclic alkene moiety of ETV was predicted, establishing a basis for the superior potency observed experimentally. HBV DNA chain termination by ETV was accomplished through disfavored energy requirements as well as steric constraints during subsequent nucleotide addition. Validation of the model was accomplished through modeling of LVD resistance substitutions, which caused an eightfold decrease in ETV susceptibility and were predicted to reduce, but not eliminate, the ETV-binding pocket, in agreement with experimental observations. ADV resistance changes did not affect the ETV docking model, also agreeing with experimental results. Overall, these studies explain the potency, mechanism, and cross-resistance profile of ETV against HBV and account for the successful treatment of naive and LVD- or ADV-experienced chronic HBV patients.

Two-year assessment of entecavir resistance in Lamivudine-refractory hepatitis B virus patients reveals different clinical outcomes depending on the resistance substitutions present

Entecavir (ETV) is a deoxyguanosine analog approved for use for the treatment of chronic infection with wild-type and lamivudine-resistant (LVDr) hepatitis B virus (HBV). In LVD-refractory patients, 1.0 mg ETV suppressed HBV DNA levels to below the level of detection by PCR (<300 copies/ml) in 21% and 34% of patients by Weeks 48 and 96, respectively. Prior studies showed that virologic rebound due to ETV resistance (ETVr) required preexisting LVDr HBV reverse transcriptase substitutions M204V and L180M plus additional changes at T184, S202, or M250. To monitor for resistance, available isolates from 192 ETV-treated patients were sequenced, with phenotyping performed for all isolates with all emerging substitutions, in addition to isolates from all patients experiencing virologic rebounds. The T184, S202, or M250 substitution was found in LVDr HBV at baseline in 6% of patients and emerged in isolates from another 11/187 (6%) and 12/151 (8%) ETV-treated patients by Weeks 48 and 96, respectively. However, use of a more sensitive PCR assay detected many of the emerging changes at baseline, suggesting that they originated during LVD therapy. Only a subset of the changes in ETVr isolates altered their susceptibilities, and virtually all isolates were significantly replication impaired in vitro. Consequently, only 2/187 (1%) patients experienced ETVr rebounds in year 1, with an additional 14/151 (9%) patients experiencing ETVr rebounds in year 2. Isolates from all 16 patients with rebounds were LVDr and harbored the T184 and/or S202 change. Seventeen other novel substitutions emerged during ETV therapy, but none reduced the susceptibility to ETV or resulted in a rebound. In summary, ETV was effective in LVD-refractory patients, with resistant sequences arising from a subset of patients harboring preexisting LVDr/ETVr variants and with approximately half of the patients experiencing a virologic rebound.

Molecular basis for increased susceptibility of isolates with atazanavir resistance-conferring substitution I50L to other protease inhibitors

Protease inhibitors (PIs) are highly effective drugs against the human immunodeficiency virus (HIV), yet long-term therapeutic use is limited by emergence of HIV type 1 (HIV-1) protease substitutions that confer cross-resistance to multiple protease inhibitor drugs. Atazanavir is a highly potent HIV protease inhibitor with a distinct resistance profile that includes effectiveness against most HIV-1 isolates resistant to one or two PIs. The signature resistance substitution for atazanavir is I50L, and it is frequently (53%) accompanied by a compensatory A71V substitution that helps restore viability and increases atazanavir resistance levels. We measured the binding affinities of wild-type (WT) and I50L/A71V HIV-1 proteases to atazanavir and other currently approved PIs (ritonavir, lopinavir, saquinavir, nelfinavir, indinavir, and amprenavir) by isothermal titration calorimetry. Remarkably, we find that all of the PIs have 2- to 10-fold increased affinities for I50L/A71V protease, except for atazanavir. The results are also manifested by thermal stability measures of affinity for WT and I50L/A71V proteases. Additional biophysical and enzyme kinetics experiments show I50L/A71V protease is a stable enzyme with catalytic activity that is slightly reduced (34%) relative to the WT. Computational modeling reveals that the unique resistance phenotype of I50L/A71V protease likely originates from bulky tert-butyl groups at P2 and P2' (specific to atazanavir) that sterically clash with methyl groups on residue L50. The results of this study provide a molecular understanding of the novel hypersusceptibility of atazanavir-resistant I50L/A71V-containing clinical isolates to other currently approved PIs.

A dose-ranging study of the efficacy and tolerability of entecavir in Lamivudine-refractory chronic hepatitis B patients

BACKGROUND & AIMS

Entecavir is a nucleoside analogue with potent in vitro activity against lamivudine-resistant hepatitis B virus (HBV). This randomized, dose-ranging, phase 2 study compared the efficacy and safety of entecavir with lamivudine in lamivudine-refractory patients.

METHODS

Hepatitis B e antigen (HBeAg)-positive and -negative patients (n = 182), viremic despite lamivudine treatment for > or =24 weeks or having documented lamivudine resistance substitutions, were switched directly to entecavir (1.0, 0.5, or 0.1 mg daily) or continued on lamivudine (100 mg daily) for up to 76 weeks.

RESULTS

At week 24, significantly more patients receiving entecavir 1.0 mg (79%) or 0.5 mg (51%) had undetectable HBV DNA levels by branched chain DNA assay compared with lamivudine (13%; P < .0001). Entecavir 1.0 mg was superior to entecavir 0.5 mg for this end point (P < .01). After 48 weeks, mean reductions in HBV DNA levels were 5.06, 4.46, and 2.85 log(10) copies/mL on entecavir 1.0, 0.5, and 0.1 mg, respectively, significantly higher than 1.37 log(10) copies/mL on lamivudine. Significantly higher proportions of patients achieved normalization of alanine aminotransferase levels on entecavir 1.0, 0.5, and 0.1 mg (68%, 59%, and 47%, respectively) than on lamivudine (6%). One virologic rebound due to resistance occurred (in the 0.5-mg group).

CONCLUSIONS

In HBeAg-positive and HBeAg-negative lamivudine-refractory patients, treatment with entecavir 1.0 and 0.5 mg daily was well tolerated and resulted in significant reductions in HBV DNA levels and normalization of alanine aminotransferase levels. One milligram of entecavir was more effective than 0.5 mg in this population.

Replication-competent chimeric hepatitis C virus subgenomic replicons

OBJECTIVE

To utilize chimeric hepatitis C virus (HCV) replicons to select adaptive mutation(s) that allow replication of a genotype 1a replicon.

METHODS

We used a genetic approach to gradually apply selective pressure by generating chimeric replicons through sequential replacement of nonstructural genes of a 1b replicon with genotype 1a sequences.

RESULTS

A chimeric replicon containing a genotype 1a NS5A protein did not replicate in a transient assay, but could be used to establish stable cell lines using G418 selection. The cell lines contained a K1846T mutation in NS4B which functioned as an adaptive mutation that now allowed the chimera to replicate at levels similar to wild-type replicons. Similarly, replication of a 1a NS5A5B chimera was only observed after establishment of stable cell lines, even in the presence of the K1846T mutation. Sequence analysis of this cell line revealed an additional adaptive mutation of M1496L in NS3. Lastly, by including the K1846T mutation in a replicon that was entirely genotype 1a sequence, stable 1a cell lines could be established.

CONCLUSION

These studies identify an NS4B adaptive mutation, K1846T, which allows establishment of a replication-competent 1a replicon and demonstrate the utility of this chimeric approach for establishing replicons for various HCV genotypes.

Clinical emergence of entecavir-resistant hepatitis B virus requires additional substitutions in virus already resistant to Lamivudine

Entecavir (ETV) exhibits potent antiviral activity in patients chronically infected with wild-type or lamivudine (3TC)-resistant (3TC(r)) hepatitis B virus (HBV). Among the patients treated in phase II ETV clinical trials, two patients for whom previous therapies had failed exhibited virologic breakthrough while on ETV. Isolates from these patients (arbitrarily designated patients A and B) were analyzed genotypically for emergent substitutions in HBV reverse transcriptase (RT) and phenotypically for reduced susceptibility in cultures and in HBV polymerase assays. After 54 weeks of 3TC therapy, patient A (AI463901-A) received 0.5 mg of ETV for 52 weeks followed by a combination of ETV and 100 mg of 3TC for 89 weeks. Viral rebound occurred at 133 weeks after ETV was started. The 3TC(r) RT substitutions rtV173L, rtL180M, and rtM204V were present at study entry, and the additional substitutions rtI169T and rtM250V emerged during ETV-3TC combination treatment. Reduced ETV susceptibility in vitro required the rtM250V substitution in addition to the 3TC(r) substitutions. For liver transplant patient B (AI463015-B), previous famciclovir, ganciclovir, foscarnet, and 3TC therapies had failed, and RT changes rtS78S/T, rtV173L, rtL180M, rtT184S, and rtM204V were present at study entry. Viral rebound occurred after 76 weeks of therapy with ETV at 1.0 mg, with the emergence of rtT184G, rtI169T, and rtS202I substitutions within the preexisting 3TC(r) background. Reduced susceptibility in vitro was highest when both the rtT184G and the rtS202I changes were combined with the 3TC(r) substitutions. In summary, infrequent ETV resistance can emerge during prolonged therapy, with selection of additional RT substitutions within a 3TC(r) HBV background, leading to reduced ETV susceptibility and treatment failure.

Routine prophylactic antibiotics for arthroplasty patients receiving dental care. Is it necessary?

Much of the debate regarding the prophylactic use of antibiotics for patients who have had a total joint replacement has focussed on their use before dental procedures. Despite the fact that almost all orthopaedic surgeons routinely recommend antibiotics for patients with prosthetic joints who require dental treatment, there is little evidence of a definitive link between transient bacteraemia occurring during dental procedures and late infections around prosthetic joints. An extensive review of the literature reveals that most authors recommend prophylactic antibiotics in high-risk patients or in those who undergo extensive dental surgery.

Biochemical and genetic characterizations of a novel human immunodeficiency virus type 1 inhibitor that blocks gp120-CD4 interactions

BMS-378806 is a recently discovered small-molecule human immunodeficiency virus type 1 (HIV-1) attachment inhibitor with good antiviral activity and pharmacokinetic properties. Here, we demonstrate that the compound targets viral entry by inhibiting the binding of the HIV-1 envelope gp120 protein to cellular CD4 receptors via a specific and competitive mechanism. BMS-378806 binds directly to gp120 at a stoichiometry of approximately 1:1, with a binding affinity similar to that of soluble CD4. The potential BMS-378806 target site was localized to a specific region within the CD4 binding pocket of gp120 by using HIV-1 gp120 variants carrying either compound-selected resistant substitutions or gp120-CD4 contact site mutations. Mapping of resistance substitutions to the HIV-1 envelope, and the lack of compound activity against a CD4-independent viral infection confirm the gp120-CD4 interactions as the target in infected cells. BMS-378806 therefore serves as a prototype for this new class of antiretroviral agents and validates gp120 as a viable target for small-molecule inhibitors.

In vitro resistance profile of the human immunodeficiency virus type 1 protease inhibitor BMS-232632

BMS-232632 is an azapeptide human immunodeficiency virus (HIV) type 1 (HIV-1) protease inhibitor that displays potent anti-HIV-1 activity (50% effective concentration [EC(50)], 2.6 to 5.3 nM; EC(90), 9 to 15 nM). In vitro passage of HIV-1 RF in the presence of inhibitors showed that BMS-232632 selected for resistant variants more slowly than nelfinavir or ritonavir did. Genotypic and phenotypic analysis of three different HIV strains resistant to BMS-232632 indicated that an N88S substitution in the viral protease appeared first during the selection process in two of the three strains. An I84V change appeared to be an important substitution in the third strain used. Mutations were also observed at the protease cleavage sites following drug selection. The evolution to resistance seemed distinct for each of the three strains used, suggesting multiple pathways to resistance and the importance of the viral genetic background. A cross-resistance study involving five other protease inhibitors indicated that BMS-232632-resistant virus remained sensitive to saquinavir, while it showed various levels (0. 1- to 71-fold decrease in sensitivity)-of cross-resistance to nelfinavir, indinavir, ritonavir, and amprenavir. In reciprocal experiments, the BMS-232632 susceptibility of HIV-1 variants selected in the presence of each of the other HIV-1 protease inhibitors showed that the nelfinavir-, saquinavir-, and amprenavir-resistant strains of HIV-1 remained sensitive to BMS-232632, while indinavir- and ritonavir-resistant viruses displayed six- to ninefold changes in BMS-232632 sensitivity. Taken together, our data suggest that BMS-232632 may be a valuable protease inhibitor for use in combination therapy.

The CRE-binding protein dCREB-A is required for Drosophila embryonic development

We have previously described the cloning of a cyclic AMP response-element (CRE)-binding protein, dCREB-A, in Drosophila melanogaster that is similar to the mammalian CRE-binding protein CREB. dCREB-A is a member of the bZIP family of transcription factors, shows specific binding to the (CRE), and can activate transcription in cell culture. In this report, we describe the gene structure for dCREB-A, protein expression patterns throughout development and the necessary role for this gene in embryogenesis. The 4.5-kb transcript is encoded in six exons that are distributed over 21 kb of DNA. There are seven start sites and no TATA consensus sequences upstream. The dCREB-A protein is expressed in the nuclei of the embryonic salivary gland, proventriculus and stomadeum. Late in embryogenesis, tracheal cell nuclei and specific nuclei within the segments show staining with anti-dCREB-A antibodies. In adult female ovaries, dCREB-A is expressed in the stage 9 through stage 11 follicle cell nuclei. Null mutations of the dCREB-A gene give rise to animals that no longer express dCREB-A protein and die late in embryogenesis before or at hatching. The absolute requirement of dCREB-A for embryogenesis demonstrates a nonredundant function for a CRE-binding protein that will be useful in studying the role of specific signal transduction cascades in development.

Human immunodeficiency virus type 1 viral background plays a major role in development of resistance to protease inhibitors

The observed in vitro and in vivo benefit of combination treatment with anti-human immunodeficiency virus (HIV) agents prompted us to examine the potential of resistance development when two protease inhibitors are used concurrently. Recombinant HIV-1 (NL4-3) proteases containing combined resistance mutations associated with BMS-186318 and A-77003 (or saquinavir) were either inactive or had impaired enzyme activity. Subsequent construction of HIV-1 (NL4-3) proviral clones containing the same mutations yielded viruses that were severely impaired in growth or nonviable, confirming that combination therapy may be advantageous. However, passage of BMS-186318-resistant HIV-1 (RF) in the presence of either saquinavir or SC52151, which represented sequential drug treatment, produced viable viruses resistant to both BMS-186318 and the second compound. The predominant breakthrough virus contained the G48V/A71T/V82A protease mutations. The clone-purified RF (G48V/A71T/V82A) virus, unlike the corresponding defective NL4-3 triple mutant, grew well and displayed cross-resistance to four distinct protease inhibitors. Chimeric virus and in vitro mutagenesis studies indicated that the RF-specific protease sequence, specifically the Ile at residue 10, enabled the NL4-3 strain with the triple mutant to grow. Our results clearly indicate that viral genetic background will play a key role in determining whether cross-resistance variants will arise.

Characterization of siamycin I, a human immunodeficiency virus fusion inhibitor

The human immunodeficiency virus (HIV) fusion inhibitor siamycin I, a 21-residue tricyclic peptide, was identified from a Streptomyces culture by using a cell fusion assay involving cocultivation of HeLa-CD4+ cells and monkey kidney (BSC-1) cells expressing the HIV envelope gp160. Siamycin I is effective against acute HIV type 1 (HIV-1) and HIV-2 infections, with 50% effective doses ranging from 0.05 to 5.7 microM, and the concentration resulting in a 50% decrease in cell viability in the absence of viral infection is 150 microM in CEM-SS cells. Siamycin I inhibits fusion between C8166 cells and CEM-SS cells chronically infected with HIV (50% effective dose of 0.08 microM) but has no effect on Sendai virus-induced fusion or murine myoblast fusion. Siamycin I does not inhibit gp120 binding to CD4 in either gp120- or CD4-based capture enzyme-linked immunosorbent assays. Inhibition of HIV-induced fusion by this compound is reversible, suggesting that siamycin I binds noncovalently. An HIV-1 resistant variant was selected by in vitro passage of virus in the presence of increasing concentrations of siamycin I. Drug susceptibility studies on a chimeric virus containing the envelope gene from the siamycin I-resistant variant indicate that resistance maps to the gp160 gene. Envelope-deficient HIV complemented with gp160 from siamycin I-resistant HIV also displayed a resistant phenotype upon infection of HeLa-CD4-LTR-beta-gal cells. A comparison of the DNA sequences of the envelope genes from the resistant and parent viruses revealed a total of six amino acid changes. Together these results indicate that siamycin I interacts with the HIV envelope protein.

Acute carpal tunnel syndrome secondary to thrombosis of a persistent median artery

An unusual case of thrombosis of a persistent median artery as a cause of acute carpal tunnel syndrome is reported. The sudden onset of numbness in the median nerve distribution and pain in the fingers were the main symptoms. The embryonic development of the median nerve vascular supply and the reported incidence of persistent median artery are reviewed.

Genotypic and phenotypic analysis of human immunodeficiency virus type 1 isolates from patients on prolonged stavudine therapy

Development of stavudine resistance was studied using human immunodeficiency virus type 1 isolates from 13 patients treated with stavudine for 18-22 months. Drug sensitivity testing on 11 of these pre- and posttherapy isolates identified only 2 posttreatment isolates with decreased stavudine sensitivity (ED50s < 4-fold higher than the average pretreatment ED50). Genotypic analysis of all 13 pairs of isolates identified multiple mutations in the reverse transcriptase (RT) gene. However, no genetic basis was identified to account for the observed changes in stavudine susceptibility. A recombinant virus containing the entire RT gene of the posttherapy isolate displaying the greatest resistance remained sensitive to stavudine. Five of the stavudine posttreatment isolates developed resistance (9- to 176-fold) to zidovudine, although the relationship between stavudine treatment and the appearance of zidovudine resistance remains unexplained. Analysis of 10 additional pairs of isolates did not confirm this relationship. The low frequency and modest degree of change in stavudine sensitivity following prolonged treatment is very encouraging.

Treatment of spinal tuberculosis by decompression and anterior spinal fusion. Case report and review of the literature

The treatment of a young man with lumbar spinal tuberculosis and neurological involvement is described. Decompression and anterior spinal fusion were performed. Dramatic improvement in the patient's condition was obtained following surgery. The literature on the treatment of tuberculosis of the spine is reviewed.

Chronic triangular fibrocartilage complex tears. A case report and review of the literature

The treatment of a young man with chronic symptomatic gross subluxation of the distal radio-ulnar joint of the right wrist secondary to traumatic disruption of the triangular fibrocartilage complex (TFCC) is described. At operation, a strip of tensor fascia lata was used to stabilize the distal radio-ulnar joint. Complete relief of pain and restoration of normal function was obtained following surgery. The literature on TFCC disorders is also reviewed.

Arthroscopic surgery of the knee

Seventy-nine arthroscopies of the knee were performed between January 1989 and March 1992. There were sixty-one males and eighteen females. The age range was from 12 to 78 years and the mean age was thirty-four years. Fifty patients had torn menisci. The menisci were removed arthroscopically in forty cases, arthrotomy being needed in the other ten cases. Following arthroscopic meniscectomies, patients returned to work in seven days, and to sporting activities in eight to ten weeks. Chondromalacia of the patella and femoral condyles were diagnosed in nineteen cases. These were treated by arthroscopic shaving and drilling of the irregular articular surfaces. In two cases, the procedure was used for assessment prior to other operations. Arthroscopy failed in two other patients due to pain and swelling and was normal in the remaining six cases.

A cyclic AMP-responsive element-binding transcriptional activator in Drosophila melanogaster, dCREB-A, is a member of the leucine zipper family

In this report, we describe the isolation and initial characterization of a Drosophila protein, dCREB-A, that can bind the somatostatin cyclic AMP (cAMP)-responsive element and is capable of activating transcription in cell culture. Sequence analysis demonstrates that this protein is a member of the leucine zipper family of transcription factors. dCREB-A is unusual in that it contains six hydrophobic residue iterations in the zipper domain rather than the four or five commonly found in this group of proteins. The DNA-binding domain is more closely related to mammalian CREB than to the AP-1 factors in both sequence homology and specificity of cAMP-responsive element binding. In embryos, dCREB-A is expressed in the developing salivary gland. A more complex pattern of expression is detected in the adult; transcripts are found in the brain and optic lobe cell bodies, salivary gland, and midgut epithelial cells of the cardia. In females, dCREB-A is expressed in the ovarian columnar follicle cells, and in males, dCREB-A RNA is seen in the seminal vesicle, ejaculatory duct, and ejaculatory bulb. These results suggest that the dCREB-A transcription factor may be involved in fertility and neurological functions.

Isolation and characterization of a fruit-specific cDNA and the corresponding genomic clone from tomato

Differential screening of a cDNA bank constructed from ripe tomato fruit mRNA allowed the isolation of cDNA clone 2A11 which is entirely fruit-specific, is expressed at steadily increasing levels from anthesis to breaker, and accounts for approximately 1% of the messenger RNA in mature tomato fruit. A genomic clone corresponding to the 2A11 cDNA was isolated from a tomato genomic library. Sequence comparison of the cDNA clone with the genomic clone shows they are identical over the shared region with the genomic clone possessing a single large intron near the 5' end of the message. The open reading frame of 2A11 would encode a sulfur-rich polypeptide 96 amino acids in length. The identity of the putative protein is unknown. In situ hybridization shows that the 2A11 message is found throughout the pericarp cells in a tomato fruit. In contrast, in situ hybridization of early ripening stages with a polygalacturonase probe shows higher mRNA levels in cells of the outer pericarp and cells surrounding the vascular regions of the pericarp.

Improved membrane filter method for fecal coliform analysis

A two-layer agar method has been developed which consistently yields higher recovery of fecal coliforms on membrane filters when compared to the existing membrane fecal coliform procedure. This method has been evaluated by three laboratories using samples of raw and chlorinated waste water, and reservoir, river, and marine waters. Verification of 1,013 fecal coliform colonies isolated from 61 water samples averaged 92% on this proposed procedure. Comparison with the Standard Methods membrane fecal coliform procedure revealed the two-layer agar method had an overall increased sensitivity to fecal coliform detection in these waters. It is therefore proposed that this procedure be evaluated as an alternative to the Standard Methods fecal coliform membrane Filter test in the examination of chlorinated secondary effluents, marine waters, and any natural waters that may contain pollutants with heavy metal ions.