An unusually large eccrine poroma: a case report and review of the literature.

The eccrine poroma is an uncommon benign neoplasm previously thought to originate solely from the eccrine sweat gland. Initially believed to present on hairless acral surfaces, a more extensive distribution has been described. We report a case of a 55-year-old man with a slowly growing, 6-cm eccrine poroma on the medial aspect of his right foot of 40 years' duration. Clinicians should be aware that poromas can be of either eccrine or apocrine origin and can occur in areas other than acral skin. They also should understand the subclassification of the poroma family of neoplasms.

Useof anti-phosphohistone H3 immunohistochemistry to determine mitotic rate in thin melanoma.

The seventh edition of the American Joint Committee on Cancer (AJCC) melanoma staging system, slated for release in 2010, will introduce mitotic rate (MR) as one of the primary criteria for staging thin melanoma (< or = 1.0 mm). Accurate counts are essential because the finding of a single mitotic figure (MF) will alter the staging and management of these patients. The traditional manner of counting of mitotic figures (MFs) using a X40 objective is time consuming and prone to inter- and intraobserver variability. We employed an antibody to phosphohistone H3 (pHH3, ser10) that labels MFs in all stages of mitosis, to evaluate mitotic counts at X20 in tissue sections from 30 melanoma patients with thin lesions 0.45 to 1.2 mm in depth, and compared results with routine hematoxylin and eosin (H&E) in a double-blind fashion. The mean MR was 1.63 by antipHH3, and 0.67 for H&E, representing a mean increase of 243%. The Spearman correlation coefficient for MR in H&E and anti-pHH3 sections was 0.88 (P < 0.0001). When melanomas were designated as "mitotically active," if the MR by anti-pHH3 was > or = 2 and > or = 1 by H&E, the correlation coefficient increased to 1.0. No thin melanomas were mitotically inactive on anti-pHH3 but active on H&E. Results indicate that anti-pHH3 is a useful immunostain for labeling melanocytes in mitosis. Subsequent studies will be needed confirm the accuracy of this staining technique, which has the potential to be used as a screening method for counting MFs before conventional H&E methodology in the microstaging of thin melanoma.

Mapping cooperative activity of the hepatitis C virus RNA-dependent RNA polymerase using genotype 1a-1b chimeras.

The nonstructural protein 5B (NS5B) of hepatitis C virus (HCV) encodes an RNA-dependent RNA polymerase (RdRp) which is essential for viral replication. NS5B expression in bacteria generated 20- to 50-fold lower yield and 100-fold less product per mol of enzyme for gentoype 1a RdRp than type 1b. Further, unlike type 1b RdRp, type 1a enzyme failed to exhibit cooperative properties in the assays described herein. Differences in thermal stability may partially account for the inability to efficiently oligomerize. Superose gel filtration analyses confirm differences between these RdRp preparations, although affinity for the column rather than size may account for the differences in migration. To further address this complexity, a panel of RdRp type 1a-type 1b chimeras were evaluated and implicate a role for the thumb subdomain of genotype 1b RdRp as critical for cooperative function.

HIV-1 evades antibody-mediated neutralization through conformational masking of receptor-binding sites.

The ability of human immunodeficiency virus (HIV-1) to persist and cause AIDS is dependent on its avoidance of antibody-mediated neutralization. The virus elicits abundant, envelope-directed antibodies that have little neutralization capacity. This lack of neutralization is paradoxical, given the functional conservation and exposure of receptor-binding sites on the gp120 envelope glycoprotein, which are larger than the typical antibody footprint and should therefore be accessible for antibody binding. Because gp120-receptor interactions involve conformational reorganization, we measured the entropies of binding for 20 gp120-reactive antibodies. Here we show that recognition by receptor-binding-site antibodies induces conformational change. Correlation with neutralization potency and analysis of receptor-antibody thermodynamic cycles suggested a receptor-binding-site 'conformational masking' mechanism of neutralization escape. To understand how such an escape mechanism would be compatible with virus-receptor interactions, we tested a soluble dodecameric receptor molecule and found that it neutralized primary HIV-1 isolates with great potency, showing that simultaneous binding of viral envelope glycoproteins by multiple receptors creates sufficient avidity to compensate for such masking. Because this solution is available for cell-surface receptors but not for most antibodies, conformational masking enables HIV-1 to maintain receptor binding and simultaneously to resist neutralization.

Mutagenic stabilization and/or disruption of a CD4-bound state reveals distinct conformations of the human immunodeficiency virus type 1 gp120 envelope glycoprotein.

The human immunodeficiency virus type 1 (HIV-1) gp120 exterior envelope glycoprotein is conformationally flexible. Upon binding to the host cell receptor CD4, gp120 assumes a conformation that is recognized by the second receptor, CCR5 and/or CXCR4, and by the CD4-induced (CD4i) antibodies. Guided by the X-ray crystal structure of a gp120-CD4-CD4i antibody complex, we introduced changes into gp120 that were designed to stabilize or disrupt this conformation. One mutant, 375 S/W, in which the tryptophan indole group is predicted to occupy the Phe 43 cavity in the gp120 interior, apparently favors a gp120 conformation closer to that of the CD4-bound state. The 375 S/W mutant was recognized as well as or better than wild-type gp120 by CD4 and CD4i antibodies, and the large decrease in entropy observed when wild-type gp120 bound CD4 was reduced for the 375 S/W mutant. The recognition of the 375 S/W mutant by CD4BS antibodies, which are directed against the CD4-binding region of gp120, was markedly reduced compared with that of the wild-type gp120. Compared with the wild-type virus, viruses with the 375 S/W envelope glycoproteins were resistant to neutralization by IgG1b12, a CD4BS antibody, were slightly more sensitive to soluble CD4 neutralization and were neutralized more efficiently by the 2G12 antibody. Another mutant, 423 I/P, in which the gp120 bridging sheet was disrupted, did not bind CD4, CCR5, or CD4i antibodies, even though recognition by CD4BS antibodies was efficient. These results indicate that CD4BS antibodies recognize conformations of gp120 different from that recognized by CD4 and CD4i antibodies.

Identification and biological characterization of heterocyclic inhibitors of the hepatitis C virus RNA-dependent RNA polymerase.

The hepatitis C virus (HCV) NS5B protein encodes an RNA-dependent RNA polymerase (RdRp), the primary catalytic enzyme of the HCV replicase complex. We established a biochemical RNA synthesis assay, using purified recombinant NS5B lacking the C-terminal 21 amino acid residues, to identify potential polymerase inhibitors from a high throughput screen of the GlaxoSmithKline proprietary compound collection. The benzo-1,2,4-thiadiazine compound 1 was found to be a potent, highly specific inhibitor of NS5B. This agent interacts directly with the viral polymerase and inhibits RNA synthesis in a manner noncompetitive with respect to GTP. Furthermore, in the absence of an in vitro-reconstituted HCV replicase assay employing viral and host proteins, the ability of compound 1 to inhibit NS5B-directed viral RNA replication was determined using the Huh7 cell-based HCV replicon system. Compound 1 reduced viral RNA in replicon cells with an IC(50) of approximately 0.5 microm, suggesting that the inhibitor was able to access the perinuclear membrane and inhibit the polymerase activity in the context of a replicase complex. Preliminary structure-activity studies on compound 1 led to the identification of a modified inhibitor, compound 4, showing an improvement in both biochemical and cell-based potency. Lastly, data are presented suggesting that these compounds interfere with the formation of negative and positive strand progeny RNA by a similar mode of action. Investigations are ongoing to assess the potential utility of such agents in the treatment of chronic HCV disease.