On the existence of AgM9(VO4)6I (M = Ba, Pb)

Attempts to synthesize “AgM₉(VO₄)₆I” (M = Ba, Pb), potential waste form materials for radioiodine, were unsuccessful, demonstrating that AgI incorporation into an iodine-deficient apatite phase is not feasible under the reported conditions.

Thiopurine Prodrugs Mediate Immunosuppressive Effects by Interfering with Rac1 Protein Function

6-Thiopurine (6-TP) prodrugs include 6-thioguanine and azathioprine. Both are widely used to treat autoimmune disorders and certain cancers. This study showed that a 6-thioguanosine triphosphate (6-TGTP), converted in T-cells from 6-TP, targets Rac1 to form a disulfide adduct between 6-TGTP and the redox-sensitive GXXXXGK(S/T)C motif of Rac1. This study also showed that, despite the conservation of the catalytic activity of RhoGAP (Rho-specific GAP) on the 6-TGTP-Rac1 adduct to produce the biologically inactive 6-thioguanosine diphosphate (6-TGDP)-Rac1 adduct, RhoGEF (Rho-specific GEF) cannot exchange the 6-TGDP adducted on Rac1 with free guanine nucleotide. The biologically inactive 6-TGDP-Rac1 adduct accumulates in cells because of the ongoing combined actions of RhoGEF and RhoGAP. Because other Rho GTPases, such as RhoA and Cdc42, also possess the GXXXXGK(S/T)C motif, the proposed mechanism for the inactivation of Rac1 also applies to RhoA and Cdc42. However, previous studies have shown that CD3/CD28-stimulated T-cells contain more activated Rac1 than other Rho GTPases such as RhoA and Cdc42. Accordingly, Rac1 is the main target of 6-TP in activated T-cells. This explains the T-cell-specific Rac1-targeting therapeutic action of 6-TP that suppresses the immune response. This proposed mechanism for the action of 6-TP on Rac1 performs a critical role in demonstrating the capability to design a Rac1-targeting chemotherapeutic agent(s) for autoimmune disorders. Nevertheless, the results also suggest that the targeting action of other Rho GTPases in other organ cells, such as RhoA in vascular cells, may be linked to cytotoxicities because RhoA plays a key role in vasculature functions.

A phase 3b study of sofosbuvir plus ribavirin in treatment-naive and treatment-experienced Korean patients chronically infected with genotype 2 hepatitis C virus

In Korea, patients with chronic hepatitis C virus (HCV) infection are typically treated with pegylated interferon-alpha plus ribavirin, but interferons are contraindicated in many patients and are often poorly tolerated, particularly by the elderly and those with advanced liver disease. No interferon-free treatment regimens are approved in Korea. Sofosbuvir is an oral nucleotide analog inhibitor of the HCV nonstructural 5B RNA polymerase. It is approved in the USA, European Union and Japan for treating a number of HCV genotypes, including genotype 2. Genotype 2 has a seroprevalence of 38-46% in Korea. This single-arm, phase 3b study (NCT02021643) examined the efficacy and safety of sofosbuvir plus ribavirin (12-week duration) in chronic genotype 2 HCV-infected treatment-naive and treatment-experienced Korean patients with and without cirrhosis. The proportion of patients with sustained virologic response 12 weeks after treatment discontinuation (SVR12) was 97% (125/129), with 96% (101/105) of treatment-naive and 100% (24/24) of treatment-experienced patients achieving SVR12. Two patients experienced virologic failure (n = 1, on-treatment failure; n = 1, relapse). No patient discontinued study treatment due to an adverse event (AE). The most common treatment-emergent AEs were headache (18%, 23/129) and pruritus (15%, 19/129). Few patients had grade 3 AEs (5%, 6/129) or grade 3 laboratory abnormalities (12%, 15/129). No grade 4 AE was reported. These data suggest that 12 weeks of treatment with the all-oral, interferon-free regimen of sofosbuvir plus ribavirin is effective and well tolerated in Korean patients with chronic genotype 2 HCV infection.

Kinetic Mechanism of Formation of Hyperactive Embryonic Ras in Cells

Embryonic Ras (ERas)--a new subset of Ras proteins--are characterized by a unique p-loop residue, unique Switch II residues, and an unusual extended N-terminus. When expressed, both murine and human ERas are highly populated in their GTP-bound forms. The expression of murine ERas is linked to the development of murine embryonic cells, and the expression of human ERas is correlated to certain human cancers. Mutation-based kinetic analyses, in combination with assessments of the kinetic parameter-based calculation of the fraction of the GTP-bound active form of ERas proteins, explain the kinetic mechanism that produces the unprecedented hyperactive ERas. The ERas-specific p-loop residue contributes ERas proteins to intrinsically populate their GTP-bound form in cells. Furthermore, the ERas-specific Switch II residues block the catalytic action of p120GAP on ERas proteins. This blockage sustains the previously mentioned GTP-bound ERas proteins. In essence, the combined work of the ERas-specific p-loop and Switch II residues populates the exceedingly high GTP-bound form of ERas in cells. This study also rules out any kinetic function of the unique ERas-specific N-terminus in the production of the hyperactive GTP-bound ERas in cells. The biological role of this N-terminus remains uninvestigated. Intriguingly, the ERas-specific p-loop residue matches the mutated Ser residue of the Costello Syndrome G12S HRas mutant that also intrinsically populates its GTP-bound form in cells. However, because the effector protein of ERas differs from that of G12S HRas, this kinetic similarity does not confer on ERas biological and/or pathophysiological similarity to G12S HRas.

Randomised clinical trial: alisporivir combined with peginterferon and ribavirin in treatment-naïve patients with chronic HCV genotype 1 infection (ESSENTIAL II)

BACKGROUND

Alisporivir (ALV) is an oral, host-targeting agent with pangenotypic anti-hepatitis C virus (HCV) activity and a high barrier to resistance.

AIM

To evaluate efficacy and safety of ALV plus peginterferon-α2a and ribavirin (PR) in treatment-naïve patients with chronic HCV genotype 1 infection.

METHODS

Double-blind, randomised, placebo-controlled, Phase 3 study evaluating ALV 600 mg once daily [response-guided therapy (RGT) for 24 or 48 weeks or 48 weeks fixed duration] or ALV 400 mg twice daily RGT with PR, compared to PR alone. Following a Food and Drug Administration partial clinical hold, ALV/placebo was discontinued and patients completed treatment with PR only. At that time, 87% of patients had received ≥12 weeks and 20% had received ≥24 weeks of ALV/PR triple therapy.

RESULTS

A total of 1081 patients were randomised (12% cirrhosis, 55% CT/TT IL28B). Addition of ALV to PR improved virological response in a dose-dependent fashion. Overall, sustained virological response (SVR12; primary endpoint) was 69% in all ALV groups vs. 53% in PR control. Highest SVR12 (90%) was achieved in patients treated with ALV 400 mg twice daily and PR for >24 weeks. Seven cases of pancreatitis were reported, with similar frequency between ALV/PR and PR control groups (0.6% vs. 0.8% respectively). Adverse events seen more frequently with ALV/PR than with PR alone were anaemia, thrombocytopenia, hyperbilirubinaemia and hypertension.

CONCLUSIONS

Alisporivir, especially the 400 mg twice daily regimen, increased efficacy of PR therapy in treatment-naïve patients with HCV genotype 1 infection. The mechanism of action and pangenotypic activity suggest that alisporivir could be useful in interferon-free combination regimens.

Failure of Helicobacter pylori eradication and age are independent risk factors for recurrent neoplasia after endoscopic resection of early gastric cancer in 283 patients

BACKGROUND

Whether the incidence of metachronous gastric dysplasia and cancer could be decreased by eradication of Helicobacter pylori after endoscopic submucosal dissection (ESD) for early gastric cancer (EGC).

AIM

To compare the incidence of metachronous gastric lesion in the eradicated group and the persistent group. Second end point is to evaluate the risk factors for metachronous gastric lesions after ESD for EGC.

METHODS

In a single centre, between May 2007 and May 2010, the patients who had evidence of H. pylori infection at the time of ESD for EGC were included, and the follow-up data were analysed retrospectively.

RESULTS

We enrolled 283 patients who have shown H. pylori infection at the time of ESD for EGC. Successful eradication was achieved for 214 patients (75.6%) (Eradicated group), and 69 patients (24.4%) showed persistent H. pylori infection (Persistent group). Metachronous gastric lesions developed in 13 (18.8%) in the persistent group and 18 (8.4%) in the eradicated group (P = 0.016). In the ≥60-year-old group, the cumulative incidence of metachronous gastric cancer showed a significant increase (P = 0.012). Cumulative hazard ratio of subsequent gastric metachronous lesions differed between the eradication group and the persistent infection group (OR = 2.322, 95% CI = 1.136-4.744, P = 0.021), and ≥60 age at the time of endoscopic resection (OR = 2.803, 95% CI = 1.207-6.509, P = 0.016).

CONCLUSIONS

Both persistent H. pylori infection and old age (≥60) are independent risk factors for the increased incidence of metachronous gastric cancer.

Superoxide inhibits guanine nucleotide exchange factor (GEF) action on Ras, but not on Rho, through desensitization of Ras to GEF

Ras and Rho GTPases are molecular switches for various vital cellular signaling pathways. Overactivation of these GTPases often causes development of cancer. Guanine nucleotide exchange factors (GEFs) and oxidants function to upregulate these GTPases through facilitation of guanine nucleotide exchange (GNE) of these GTPases. However, the effect of oxidants on GEF functions, or vice versa, has not been known. We show that, via targeting Ras Cys(51), an oxidant inhibits the catalytic action of Cdc25-the catalytic domain of RasGEFs-on Ras. However, the enhancement of Ras GNE by an oxidant continues regardless of the presence of Cdc25. Limiting RasGEF action by an oxidant may function to prevent the pathophysiological overactivation of Ras in the presence of both RasGEFs and oxidants. The continuous exposure of Ras to nitric oxide and its derivatives can form S-nitrosated Ras (Ras-SNO). This study also shows that an oxidant not only inhibits the catalytic action of Cdc25 on Ras-SNO but also fails to enhance Ras-SNO GNE. This lack of enhancement then populates the biologically inactive Ras-SNO in cells, which may function to prevent the continued redox signaling of the Ras pathophysiological response. Finally, this study also demonstrates that, unlike the case with RasGEFs, an oxidant does not inhibit the catalytic action of RhoGEF-Vav or Dbs-on Rho GTPases such as Rac1, RhoA, RhoC, and Cdc42. This result explains the results of the previous study in which, despite the presence of an oxidant, the catalytic action of Dbs in cells continued to enhance RhoC GNE.