Phase I study to assess the effect of adavosertib (AZD1775) on the pharmacokinetics of substrates of CYP1A2, CYP2C19, and CYP3A in patients with advanced solid tumors.

PURPOSE: Adavosertib may alter exposure to substrates of the cytochrome P450 (CYP) family of enzymes. This study assessed its effect on the pharmacokinetics of a cocktail of probe substrates for CYP3A (midazolam), CYP2C19 (omeprazole), and CYP1A2 (caffeine). METHODS: Period 1: patients with locally advanced or metastatic solid tumors received 'cocktail': caffeine 200 mg, omeprazole 20 mg, and midazolam 2 mg (single dose); period 2: after 7- to 14-day washout, patients received adavosertib 225 mg twice daily on days 1-3 (five doses), with cocktail on day 3. After cocktail alone or in combination with adavosertib administration, 24-h pharmacokinetic sampling occurred for probe substrates and their respective metabolites paraxanthine, 5-hydroxyomeprazole (5-HO), and 1'-hydroxymidazolam (1'-HM). Safety was assessed throughout. RESULTS: Of 33 patients (median age 60.0 years, range 41-83) receiving cocktail, 30 received adavosertib. Adavosertib co-administration increased caffeine, omeprazole, and midazolam exposure by 49%, 80%, and 55% (AUC0-12), respectively; AUC0-t increased by 61%, 98%, and 55%. Maximum plasma drug concentration (Cmax) increased by 4%, 46%, and 39%. Adavosertib co-administration increased 5-HO and 1'-HM exposure by 43% and 54% (AUC0-12) and 49% and 58% (AUC0-t), respectively; paraxanthine exposure was unchanged. Adavosertib co-administration decreased Cmax for paraxanthine and 5-HO by 19% and 7%; Cmax increased by 33% for 1'-HM. After receiving adavosertib, 19 (63%) patients had treatment-related adverse events (six [20%] grade ≥ 3). CONCLUSION: Adavosertib (225 mg bid) is a weak inhibitor of CYP1A2, CYP2C19, and CYP3A. CLINICALTRIALS: GOV: NCT03333824.

Adavosertib (AZD1775) does not prolong the QTc interval in patients with advanced solid tumors: a phase I open-label study.

PURPOSE: Adavosertib is a small-molecule, ATP-competitive inhibitor of Wee1 kinase. Molecularly targeted oncology agents have the potential to increase the risk of cardiovascular events, including prolongation of QT interval and associated cardiac arrhythmias. This study investigated the effect of adavosertib on the QTc interval in patients with advanced solid tumors. METHODS: Eligible patients were ≥ 18 years of age with advanced solid tumors for which no standard therapy existed. Patients received adavosertib 225 mg twice daily on days 1-2 at 12-h intervals and once on day 3. Patients underwent digital 12-lead electrocardiogram and pharmacokinetic assessments pre-administration and time-matched assessments during the drug administration period. The relationship between maximum plasma drug concentration (Cmax) and baseline-adjusted corrected QT interval by Fridericia (QTcF) was estimated using a prespecified linear mixed-effects model. RESULTS: Twenty-one patients received adavosertib. Concentration-QT modeling of ΔQTcF and the upper limit of the 90% confidence interval corresponding to the geometric mean of Cmax observed on days 1 and 3 were below the threshold for regulatory concern (not > 10 ms). No significant relationship between ΔQTcF (vs baseline) and adavosertib concentration was identified (P = 0.27). Pharmacokinetics and the adverse event (AE) profile were consistent with previous studies at this dose. Eleven (52.4%) patients experienced 17 treatment-related AEs in total, including diarrhea and nausea (both reported in six [28.6%] patients), vomiting (reported in two [9.5%] patients), anemia, decreased appetite, and constipation (all reported in one [4.8%] patient). CONCLUSION: Adavosertib does not have a clinically important effect on QTc prolongation. CLINICALTRIALS: GOV: NCT03333824.

Phase I Study of SYNB1891, an Engineered E. coli Nissle Strain Expressing STING Agonist, with and without Atezolizumab in Advanced Malignancies.

PURPOSE: SYNB1891 is a live, modified strain of the probiotic Escherichia coli Nissle 1917 (EcN) engineered to produce cyclic dinucleotides under hypoxia, leading to STimulator of INterferon Genes (STING) activation in phagocytic antigen-presenting cells in tumors and activating complementary innate immune pathways. PATIENTS AND METHODS: This first-in-human study (NCT04167137) enrolled participants with refractory advanced cancers to receive repeat intratumoral injections of SYNB1891 either alone or in combination with atezolizumab, with the primary objective of evaluating the safety and tolerability of both regimens. RESULTS: Twenty-four participants received monotherapy across six cohorts, and 8 participants received combination therapy in two cohorts. Five cytokine release syndrome events occurred with monotherapy, including one that met the criteria for dose-limiting toxicity at the highest dose; no other SYNB1891-related serious adverse events occurred, and no SYNB1891-related infections were observed. SYNB1891 was not detected in the blood at 6 or 24 hours after the first intratumoral dose or in tumor tissue 7 days following the first dose. Treatment with SYNB1891 resulted in activation of the STING pathway and target engagement as assessed by upregulation of IFN-stimulated genes, chemokines/cytokines, and T-cell response genes in core biopsies obtained predose and 7 days following the third weekly dose. In addition, a dose-related increase in serum cytokines was observed, as well as stable disease in 4 participants refractory to prior PD-1/L1 antibodies. CONCLUSIONS: Repeat intratumoral injection of SYNB1891 as monotherapy and in combination with atezolizumab was safe and well tolerated, and evidence of STING pathway target engagement was observed.

Mocetinostat in Combination With Durvalumab for Patients With Advanced NSCLC: Results From a Phase I/II Study.

BACKGROUND: Histone deacetylase (HDAC) inhibitors have potential to augment the effectiveness of immune checkpoint inhibitors and overcome treatment resistance. This dose-escalation/expansion study (NCT02805660) investigated mocetinostat (class I/IV HDAC inhibitor) plus durvalumab in patients with advanced non-small cell lung cancer (NSCLC) across cohorts defined by tumor programmed death-ligand 1 (PD-L1) expression and prior experience with anti-programmed cell death protein-1 (anti-PD-1) or anti-PD-L1 regimens. PATIENTS AND METHODS: Sequential cohorts of patients with solid tumors received mocetinostat (starting dose: 50 mg TIW) plus durvalumab at a standard dose (1500 mg Q4W) to determine the recommended phase II dose (RP2D: phase I primary endpoint), based on the observed safety profile. RP2D was administered to patients with advanced NSCLC across 4 cohorts grouped by tumor PD-L1 expression (none or low/high) and prior experience with anti-PD-L1 /anti-PD-1 agents (naïve, clinical benefit: yes/no). The phase II primary endpoint was objective response rate (ORR, RECIST v1.1). RESULTS: Eighty-three patients were enrolled (phase I [n = 20], phase II [n = 63]). RP2D was mocetinostat 70 mg TIW plus durvalumab. ORR was 11.5% across the phase II cohorts, and responses were durable (median 329 days). Clinical activity was observed in NSCLC patients with disease refractory to prior checkpoint inhibitor treatment: ORR 23.1%. Across all patients, fatigue (41%), nausea (40%), and diarrhea (31%) were the most frequent treatment-related adverse events. CONCLUSION: Mocetinostat 70 mg TIW plus durvalumab at the standard dose was generally well tolerated. Clinical activity was observed in patients with NSCLC unresponsive to prior anti-PD-(L)1 therapy.

Phase 1b study of pan-AKT inhibitor vevorisertib alone or with paclitaxel or fulvestrant in PIK3CA/AKT/PTEN-mutated advanced solid tumors.

BACKGROUND: In this first-in-human phase 1b study (ClinicalTrials.gov identifier NCT02761694) of advanced solid tumors with PIK3CA/AKT/PTEN mutations, the authors investigated the safety and efficacy of the pan-AKT inhibitor vevorisertib (MK-4440; ARQ 751) as monotherapy or with paclitaxel or fulvestrant. METHODS: Patients with histologically confirmed, advanced or recurrent, PIK3CA/AKT/PTEN-mutated solid tumors, measurable disease according to Response Evaluation Criteria in Solid Tumors, version 1.1, and an Eastern Cooperative Oncology Group performance status ≤1 received vevorisertib (dose range, 5-100 mg) alone or with paclitaxel 80 mg/m2 or fulvestrant 500 mg. The primary end point was safety and tolerability. Secondary end points included pharmacokinetics and the objective response rate according to Response Evaluation Criteria in Solid Tumors, version 1.1. RESULTS: Of 78 patients enrolled, 58 received vevorisertib monotherapy, 10 received vevorisertib plus paclitaxel, and nine received vevorisertib plus fulvestrant. Dose-limiting toxicity occurred in three patients (vevorisertib monotherapy, n = 2 [grade 3 pruritic and maculopapular rashes]; vevorisertib plus paclitaxel, n = 1 [grade 1 asthenia]). Across doses, treatment-related AEs occurred in 46 patients (79%) with vevorisertib monotherapy, in 10 patients (100%) with vevorisertib plus paclitaxel, and in nine patients (100%) with vevorisertib plus fulvestrant; and grade 3 treatment-related AEs occurred in 13 (22%), 7 (70%), and 3 (33%) patients, respectively. No grade 4/5 treatment-related AEs occurred. Maximum vevorisertib concentrations were reached 1-4 hours after dosing; the elimination half-life ranged from 8.8 to 19.3 hours. The objective response rate was 5% with vevorisertib monotherapy (three partial responses), 20% with vevorisertib plus paclitaxel (two partial responses), and 0% with vevorisertib plus fulvestrant. CONCLUSIONS: Vevorisertib alone or with paclitaxel or fulvestrant had a manageable safety profile, and vevorisertib alone or with paclitaxel had minimal to modest antitumor activity in this patient population with PIK3CA/AKT/PTEN-mutated advanced solid tumors. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, NCT02761694.

Phase 1 first-in-human study of dalutrafusp alfa, an anti-CD73-TGF-ß-trap bifunctional antibody, in patients with advanced solid tumors.

BACKGROUND: Cluster of differentiation (CD)73-adenosine and transforming growth factor (TGF)-ß pathways are involved in abrogated antitumor immune responses and can lead to protumor conditions. This Phase 1 study (NCT03954704) evaluated the safety, pharmacokinetics, pharmacodynamics, and efficacy of dalutrafusp alfa (also known as GS-1423 and AGEN1423), a bifunctional, humanized, aglycosylated immunoglobulin G1 kappa antibody that selectively inhibits CD73-adenosine production and neutralizes active TGF-ß signaling in patients with advanced solid tumors. METHODS: Dose escalation started with an accelerated titration followed by a 3+3 design. Patients received dalutrafusp alfa (0.3, 1, 3, 10, 20, 30, or 45 mg/kg) intravenously every 2 weeks (Q2W) up to 1 year or until progressive disease (PD) or unacceptable toxicity. RESULTS: In total, 21/22 patients received at least one dose of dalutrafusp alfa. The median number of dalutrafusp alfa doses administered was 3 (range 1-14). All patients had at least one adverse event (AE), most commonly fatigue (47.6%), nausea (33.3%), diarrhea (28.6%), and vomiting (28.6%). Nine (42.9%) patients had a Grade 3 or 4 AE; two had Grade 5 AEs of pulmonary embolism and PD, both unrelated to dalutrafusp alfa. Target-mediated drug disposition appears to be saturated at dalutrafusp alfa doses above 20 mg/kg. Complete CD73 target occupancy on B cells and CD8+ T cells was observed, and TGF-ß 1/2/3 levels were undetectable at dalutrafusp alfa doses of 20 mg/kg and higher. Free soluble (s)CD73 levels and sCD73 activity increased with dalutrafusp alfa treatment. Seventeen patients reached the first response assessment, with complete response, partial response, stable disease, and PD in 0, 1 (4.8%), 7 (33.3%), and 9 (42.9%) patients, respectively. CONCLUSIONS: Dalutrafusp alfa doses up to 45 mg/kg Q2W were well tolerated in patients with advanced solid tumors. Additional evaluation of dalutrafusp alfa could further elucidate the clinical utility of targeting CD73-adenosine and TGF-ß pathways in oncology.

Effect of Pevonedistat, an Investigational NEDD8-Activating Enzyme Inhibitor, on the QTc Interval in Patients With Advanced Solid Tumors.

The purpose of this study was to assess the effect of pevonedistat, a neural precursor cell expressed, developmentally down-regulated protein 8 (NEDD8)-activating enzyme inhibitor, on the heart rate-corrected QT (QTc) interval in cancer patients. Patients were randomized 1:1 to receive pevonedistat 25 or 50 mg/m2 on day 1 and the alternate dose on day 8. Triplicate electrocardiograms were collected at intervals over 0-11 hours and at 24 hours via Holter recorders on days -1 (baseline), 1, and 8. Changes from time-matched baseline values were calculated for QTc by Fridericia (QTcF), PR, and QRS intervals. Serial time-matched blood samples for analysis of pevonedistat plasma pharmacokinetics were collected and a concentration-QTc analysis conducted. Safety was assessed by monitoring vital signs, physical examinations, and clinical laboratory tests. Forty-four patients were included in the QTc analysis. Maximum least square (LS) mean increase from time-matched baseline in QTcF was 3.2 milliseconds at 1 hour postdose for pevonedistat at 25 mg/m2 , while the LSs mean change from baseline in QTcF was -1.7 milliseconds 1 hour postdose at 50 mg/m2 . The maximum 2-sided 90% upper confidence bound was 6.7 and 2.9 milliseconds for pevonedistat at 25 and 50 mg/m2 , respectively. Pevonedistat did not result in clinically relevant effects on heart rate, nor on PR or QRS intervals. Results from pevonedistat concentration-QTc analysis were consistent with these findings. Administration of pevonedistat to cancer patients at a dose of up to 50 mg/m2 showed no evidence of QT prolongation, indicative of the lack of clinically meaningful effects on cardiac repolarization. ClinicalTrials.gov identifier: NCT03330106 (first registered on November 6, 2017).

Manufacturing-dependent change in biological activity of the TLR4 agonist GSK1795091 and implications for lipid A analog development.

A phase I trial (NCT03447314; 204686) evaluated the safety and efficacy of GSK1795091, a Toll-like receptor 4 (TLR4) agonist, in combination with immunotherapy (GSK3174998 [anti-OX40 monoclonal antibody], GSK3359609 [anti-ICOS monoclonal antibody], or pembrolizumab) in patients with solid tumors. The primary endpoint was safety; other endpoints included efficacy, pharmacokinetics, and pharmacodynamics (PD). Manufacturing of GSK1795091 formulation was modified during the trial to streamline production and administration, resulting in reduced PD (cytokine) activity. Fifty-four patients received GSK1795091 with a combination partner; 32 received only the modified GSK1795091 formulation, 15 received only the original formulation, and seven switched mid-study from the original to the modified formulation. Despite the modified formulation demonstrating higher systemic GSK1795091 exposure compared with the original formulation, the transient, dose-dependent elevations in cytokine and chemokine concentrations were no longer observed (e.g., IP-10, IL10, IL1-RA). Most patients (51/54; 94%) experienced ≥1 treatment-emergent adverse event (TEAE) during the study. Safety profiles were similar between formulations, but a higher incidence of TEAEs associated with immune responses (chills, fatigue, pyrexia, nausea, and vomiting) were observed with the original formulation. No conclusions can be made regarding GSK1795091 anti-tumor activity due to the limited data collected. Manufacturing changes were hypothesized to have caused the change in biological activity in this study. Structural characterization revealed GSK1795091 aggregate size in the modified formulation to be twice that in the original formulation, suggesting a negative correlation between GSK1795091 aggregate size and PD activity. This may have important clinical implications for future development of structurally similar compounds.

Therapeutic targeting of SLC6A8 creatine transporter suppresses colon cancer progression and modulates human creatine levels.

Colorectal cancer (CRC) is a leading cause of cancer mortality. Creatine metabolism was previously shown to critically regulate colon cancer progression. We report that RGX-202, an oral small-molecule SLC6A8 transporter inhibitor, robustly inhibits creatine import in vitro and in vivo, reduces intracellular phosphocreatine and ATP levels, and induces tumor apoptosis. RGX-202 suppressed CRC growth across KRAS wild-type and KRAS mutant xenograft, syngeneic, and patient-derived xenograft (PDX) tumors. Antitumor efficacy correlated with tumoral expression of creatine kinase B. Combining RGX-202 with 5-fluorouracil or the DHODH inhibitor leflunomide caused regressions of multiple colorectal xenograft and PDX tumors of distinct mutational backgrounds. RGX-202 also perturbed creatine metabolism in patients with metastatic CRC in a phase 1 trial, mirroring pharmacodynamic effects on creatine metabolism observed in mice. This is, to our knowledge, the first demonstration of preclinical and human pharmacodynamic activity for creatine metabolism targeting in oncology, thus revealing a critical therapeutic target.

Impact of Diabetes and Insulin Use on Prognosis in Patients With Resected Pancreatic Cancer: An Ancillary Analysis of NRG Oncology RTOG 9704.

PURPOSE: Diabetes mellitus (DM) has been proposed to be tumorigenic; however, prior studies of the association between DM and survival are conflicting. The goal of this ancillary analysis of RTOG 9704, a randomized controlled trial of adjuvant chemotherapy in pancreatic cancer, was to determine the prognostic effects of DM and insulin use on survival. METHODS AND MATERIALS: Eligible patients from RTOG 9704 with available data on DM and insulin use were included. Overall survival (OS) and disease-free survival (DFS) were estimated using the Kaplan-Meier method, and variable levels were compared using log-rank test. Cox proportional hazards models were created to assess the associations among DM, insulin use, and body mass index phenotypes on outcomes. RESULTS: Of 538 patients enrolled from 1998 to 2002, 238 patients were eligible with analyzable DM and insulin use data. Overall 34% of patients had DM and 66% did not. Of patients with DM, 64% had insulin-dependent DM, and 36% had non-insulin-dependent DM. On univariable analysis, neither DM nor insulin dependence were associated with OS or DFS (P > .05 for all). On multivariable analysis, neither DM, insulin use, nor body mass index were independently associated with OS or DFS. Nonwhite race (hazard ratio [HR], 2.18; 95% confidence interval [CI], 1.35-3.50; P = .0014), nodal involvement (HR, 1.74; 95% CI, 1.24-2.45; P = .0015), and carbohydrate antigen 19-9 (CA19-9) ≥90 U/mL (HR, 3.61; 95% CI, 2.32-5.63; P < .001) were associated with decreased OS. Nonwhite race (HR, 1.67; 95% CI, 1.05-2.63; P = .029) and CA19-9 ≥90 U/mL (HR, 2.86; 95% CI, 1.85-4.40; P < .001) were associated with decreased DFS. CONCLUSIONS: DM and insulin use were not associated with OS or DFS in patients with pancreatic cancer in this study. Race, nodal involvement, and increased CA19-9 were significant predictors of outcomes. These data might apply to the more modern use of neoadjuvant therapies for potentially resectable pancreatic cancer.

Incidentally discovered distant cutaneous metastasis of sacral chordoma: a case with variation in S100 protein expression (compared to the primary tumor) and review of the literature.

Chordomas represent rare malignant primary bone tumors most often occurring in the sacral area. These tumors uncommonly involve the skin and often follow a progressive course with multiple recurrences, metastases and eventual death. Reports of cutaneous metastases from chordoma are very rare. The immunohistochemical staining characteristics of these cutaneous metastases with comparison to the primary tumors are similarly rarely addressed in the literature. We report a rare case of incidentally discovered, small, solitary distant cutaneous metastasis of sacral chordoma that developed on the right upper back of a 44-year-old man with a history of multiple completely excised melanomas who had also been previously diagnosed with chordoma involving the sacrum 12 years earlier. We describe its pathologic features with comparison to the primary tumor and briefly review the literature. Immunohistochemically, the cutaneous metastasis and primary tumor both stained positively for pancytokeratin and vimentin, as expected. However, the cutaneous metastasis unexpectedly lacked S100 protein expression, whereas the primary tumor was S100 positive. This phenomenon has only been documented in one other case report. We demonstrate that late, incidentally discovered cutaneous metastasis with unexpected immunohistochemical staining features rarely occur and can present a diagnostic challenge.

The gemcitabine, docetaxel, and capecitabine (GTX) regimen for metastatic pancreatic cancer: a retrospective analysis.

PURPOSE: We developed a laboratory based regimen called GTX which induces synergistic apoptosis in human pancreatic cancer cells. This retrospective review summarizes our clinical experience with GTX in an initial group of 35 patients; 66% untreated and 34% failed prior therapies. METHODS: All patients treated with GTX for metastatic pancreatic cancer, prior to initiation of a prospective phase II trial of GTX were assessed and followed until death. GTX consisted of capecitabine (X), 750 mg/m(2) p.o. BID on days 1-14, gemcitabine (G) (750 mg/m(2)) over 75 min and docetaxel (T) (30 mg/m(2)) on days 4 and 11. Thus one cycle of GTX was 14 days with 7 days off for a 21 day cycle. Tumor assessments were repeated every 3 cycles. RESULTS: All 35 patients had metastatic pancreatic cancer (94% liver, 6% lung sites). Grade 3-4 hematological toxicities were: leukopenia and thrombocytopenia-both 14%, and anemia 9%, respectively. The overall response rate of all 35 patients treated with GTX (from 0.5 cycles onward) was 29% (CR/PR) by WHO criteria, and 31% had a minor response or stable disease (MR, SD). At the metastatic sites for the 35 patients, there were 9% complete (CR) and 31% partial (PR) responses (total 40%). For the 31 patients who had their primary tumor (4 patients had a prior Whipple resection), there were 13% CR and 19% PR for a response rate of 32% at the primary tumor site. Overall median progression free survival of responders was 6.3 months (95% C.I. 4.4-10.4 months) and median survival was 11.2 months (95% C.I. 8.1-15.1 months). Survival after initiation of GTX at 12, 18, 24 and 30 months was 43, 29, 20, and 11%, respectively. CONCLUSION: Our retrospective review suggests that GTX has potential as a regimen for untreated and treated metastatic pancreatic cancer.

QTL influencing baseline hematocrit in the C57BL/6J and DBA/2J lineage: age-related effects.

Baseline serum hematocrit varies substantially in the population. While additive genetic factors account for a large part of this variability, little is known about the genetic architecture underlying the trait. Because hematocrit levels vary with age, it is plausible that quantitative trait loci (QTL) that influence the phenotype also show an age-specific profile. To investigate this possibility, hematocrit was measured in three different age cohorts of mice (150, 450, and 750 days) of the C57BL/6J (B6) and the DBA2/J (D2) lineage. QTL were searched in the B6D2F(2) intercross and the BXD recombinant inbred (RI) strains. The effects of these QTL were explored across the different age groups. On the phenotypic level, baseline serum hematocrit declines with age in a sex-specific manner. In the B6D2F(2) intercross, suggestive QTL that influence the phenotype were located on Chromosomes (Chr) 1, 2, 7, 11, 13, and 16. With the exception of the QTL on Chr 2, all of these QTL exerted their largest effect at 750 days. The QTL on Chr 1, 2, 7, 11 and 16 were confirmed in the BXD RIs in a sex- and age-specific manner. Linkage analysis in the BXD RIs revealed an additional significant QTL on Chr 19. Baseline serum hematocrit is influenced by several QTL that appear to vary with the age and sex of the animal. These QTL primarily overlap with QTL that have been shown to regulate hematopoietic stem cell phenotypes.

Mapping the structure and function of the E1 and E2 glycoproteins in alphaviruses.

The 9 A resolution cryo-electron microscopy map of Sindbis virus presented here provides structural information on the polypeptide topology of the E2 protein, on the interactions between the E1 and E2 glycoproteins in the formation of a heterodimer, on the difference in conformation of the two types of trimeric spikes, on the interaction between the transmembrane helices of the E1 and E2 proteins, and on the conformational changes that occur when fusing with a host cell. The positions of various markers on the E2 protein established the approximate topology of the E2 structure. The largest conformational differences between the icosahedral surface spikes at icosahedral 3-fold and quasi-3-fold positions are associated with the monomers closest to the 5-fold axes. The long E2 monomers, containing the cell receptor recognition motif at their extremities, are shown to rotate by about 180 degrees and to move away from the center of the spikes during fusion.

Conformational changes of the flavivirus E glycoprotein.

Dengue virus, a member of the Flaviviridae family, has a surface composed of 180 copies each of the envelope (E) glycoprotein and the membrane (M) protein. The crystal structure of an N-terminal fragment of E has been determined and compared with a previously described structure. The primary difference between these structures is a 10 degrees rotation about a hinge relating the fusion domain DII to domains DI and DIII. These two rigid body components were used for independent fitting of E into the cryo-electron microscopy maps of both immature and mature dengue viruses. The fitted E structures in these two particles showed a difference of 27 degrees between the two components. Comparison of the E structure in its postfusion state with that in the immature and mature virions shows a rotation approximately around the same hinge. Flexibility of E is apparently a functional requirement for assembly and infection of flaviviruses.

Regulation of Semliki Forest virus RNA replication: a model for the control of alphavirus pathogenesis in invertebrate hosts.

Alphavirus nonstructural proteins are translated as a polyprotein that is ultimately cleaved into four mature proteins called nsP1, nsP2, nsP3, and nsP4 from their order in the polyprotein. The role of this nonstructural polyprotein, of cleavage intermediates, and of mature proteins in synthesis of Semliki Forest virus (SFV) RNA has been studied using mutants unable to cleave one or more of the sites in the nonstructural polyprotein or that had the arginine sense codon between nsP3 and nsP4 changed to an opal termination codon. The results were compared with those obtained for Sindbis virus (SINV), which has a naturally occurring opal codon between nsP2 and nsP3. We found that (1) an active nonstructural protease in nsP2 is required for RNA synthesis. This protease is responsible for all three cleavages in the nonstructural polyprotein. (2) Cleavage between nsP3 and nsP4 (the viral RNA polymerase) is required for RNA synthesis by SFV. (3) SFV mutants that are able to produce only polyprotein P123 and nsP4 synthesize minus-strand RNA early after infection as efficiently as SF wild type but are defective in the synthesis of plus-strand RNA. The presence of sense or opal following nsP3 did not affect this result. At 30 degrees C, they give rise to low yields of virus after a delay, but at 39 degrees C, they are nonviable. (4) SFV mutants that produce nsP1, P23, nsP4, as well as the precursor P123 are viable but produce an order of magnitude less virus than wild type at 30 degrees C and two orders of magnitude less virus at 39 degrees C. The ratio of subgenomic mRNA to genomic RNA is much reduced in these mutants relative to the parental viruses. (5) At 30 degrees C, the variants containing an opal codon grow as well as or slightly better than the corresponding virus with a sense codon. At 39 degrees C, however, the opal variants produce significantly more virus. These results support the conclusion that SFV and SINV, and by extension all alphaviruses, regulate their RNA synthesis in the same fashion after infection. P123 and nsP4 form a minus-strand replicase that synthesizes plus-strand RNA only inefficiently, especially at the higher temperatures found in mammals and birds. A replicase containing nsP1, P23, and nsP4 can make both plus and minus strands, but prefers the promoter for genomic plus sense RNA to that for subgenomic mRNA. The fully cleaved replicase can make only plus-strand RNA, and prefers the promoter for subgenomic mRNA to that for genomic RNA. Alphaviruses alternate between infection of hematophagous arthropods and higher vertebrates. Although the infection of higher vertebrates is acute and often accompanied by disease, continuing transmission of the virus in nature requires that infection of arthropods be persistent and relatively asymptomatic. We propose that this mechanism for control of RNA synthesis evolved to moderate the pathogenicity of the viruses in their arthropod hosts.

Visualization of membrane protein domains by cryo-electron microscopy of dengue virus.

Improved technology for reconstructing cryo-electron microscopy (cryo-EM) images has now made it possible to determine secondary structural features of membrane proteins in enveloped viruses. The structure of mature dengue virus particles was determined to a resolution of 9.5 A by cryo-EM and image reconstruction techniques, establishing the secondary structural disposition of the 180 envelope (E) and 180 membrane (M) proteins in the lipid envelope. The alpha-helical 'stem' regions of the E molecules, as well as part of the N-terminal section of the M proteins, are buried in the outer leaflet of the viral membrane. The 'anchor' regions of E and the M proteins each form antiparallel E-E and M-M transmembrane alpha-helices, leaving their C termini on the exterior of the viral membrane, consistent with the predicted topology of the unprocessed polyprotein. This is one of only a few determinations of the disposition of transmembrane proteins in situ and shows that the nucleocapsid core and envelope proteins do not have a direct interaction in the mature virus.