Accelerating the development of innovative cellular therapy products for the treatment of cancer

The field of cell therapy is rapidly emerging as a priority area for oncology research and drug development. Currently, two chimeric antigen receptor T-cell therapies are approved by the US Food and Drug Administration and other agencies worldwide for two types of hematologic cancers. To facilitate the development of these therapies for patients with life-threatening cancers with limited or no therapeutic options, science- and risk-based approaches will be critical to mitigating and balancing any potential risk associated with either early clinical research or more flexible manufacturing paradigms. Friends of Cancer Research and the Parker Institute for Cancer Immunotherapy convened an expert group of stakeholders to develop specific strategies and proposals for regulatory opportunities to accelerate the development of cell therapies as promising new therapeutics. This meeting took place in Washington, DC on May 17, 2019. As academia and industry expand research efforts and cellular product development pipelines, this report summarizes opportunities to accelerate entry into the clinic for exploratory studies and optimization of cell products through manufacturing improvements for these promising new therapies.

Simulated Leaching (Migration) Study for a Model Container-Closure System Applicable to Parenteral and Ophthalmic Drug Products

A simulating leaching (migration) study was performed on a model container-closure system relevant to parenteral and ophthalmic drug products. This container-closure system consisted of a linear low-density polyethylene bottle (primary container), a polypropylene cap and an elastomeric cap liner (closure), an adhesive label (labeling), and a foil overpouch (secondary container). The bottles were filled with simulating solvents (aqueous salt/acid mixture at pH 2.5, aqueous buffer at pH 9.5, and 1/1 v/v isopropanol/water), a label was affixed to the filled and capped bottles, the filled bottles were placed into the foil overpouch, and the filled and pouched units were stored either upright or inverted for up to 6 months at 40 °C. After storage, the leaching solutions were tested for leached substances using multiple complementary analytical techniques to address volatile, semi-volatile, and non-volatile organic and inorganic extractables as potential leachables.The leaching data generated supported several conclusions, including that (1) the extractables (leachables) profile revealed by a simulating leaching study can qualitatively be correlated with compositional information for materials of construction, (2) the chemical nature of both the extracting medium and the individual extractables (leachables) can markedly affect the resulting profile, and (3) while direct contact between a drug product and a system's material of construction may exacerbate the leaching of substances from that material by the drug product, direct contact is not a prerequisite for migration and leaching to occur.LAY ABSTRACT: The migration of container-related extractables from a model pharmaceutical container-closure system and into simulated drug product solutions was studied, focusing on circumstances relevant to parenteral and ophthalmic drug products. The model system was constructed specifically to address the migration of extractables from labels applied to the outside of the primary container. The study demonstrated that (1) the extractables that do migrate can be correlated to the composition of the materials used to construct the container-closure systems, (2) the extent of migration is affected by the chemical nature of the simulating solutions and the extractables themselves, and (3) even though labels may not be in direct contact with a contained solution, label-related extractables can accumulate as leachables in those solutions.

Creating a Holistic Extractables and Leachables (E&L) Program for Biotechnology Products

The risk mitigation of extractables and leachables presents significant challenges to regulators and drug manufacturers with respect to the development, as well as the lifecycle management, of drug products. A holistic program is proposed, using a science- and risk-based strategy for testing extractables and leachables from primary containers, drug delivery devices, and single-use systems for the manufacture of biotechnology products. The strategy adopts the principles and concepts from ICH Q9 and ICH Q8(R2). The strategy is phase-appropriate, progressing from extractables testing for material screening/selection/qualification through leachables testing of final products. The strategy is designed primarily to ensure patient safety and product quality of biotechnology products. The holistic program requires robust extraction studies using model solvents, with careful consideration of solvation effect, pH, ionic strength, temperature, and product-contact surface and duration. From a wide variety of process- and product-contact materials, such extraction studies have identified and quantified over 200 organic extractable compounds. The most commonly observed compounds were siloxanes, fatty acid amides, and methacrylates. Toxicology assessments were conducted on these compounds using risk-based decision analysis. Parenteral permitted daily exposure limits were derived, as appropriate, for the majority of these compounds. Analysis of the derived parenteral permitted daily exposure limits helped to establish action thresholds to target high-risk leachables in drug products on stability until expiry. Action thresholds serve to trigger quality investigations to determine potential product impact. The holistic program also evaluates the potential risk for immunogenicity. This approach for primary drug containers and delivery devices is also applicable to single-use systems when justified with a historical knowledge base and understanding of the manufacturing processes of biotechnology products.

LAY ABSTRACT

In the development of a drug product, careful consideration is given to impurities that may originate from manufacturing equipment, process components, and packaging materials. The majority of such impurities are common chemical additives used to improve the physicochemical properties of a wide range of plastic materials. Suppliers and drug manufacturers conduct studies to extract chemical additives from the plastic materials in order to screen and predict those that may leach into a drug product. In this context, the term extractables refers to a profile of extracted compounds observed in studies under harsh conditions. In contrast, the term leachables refers to those impurities that leach from the materials under real-use conditions and may be present in final drug products. The purpose of this article is to present a holistic approach that effectively minimizes the risk of leachables to patient safety and product quality.

The Product Quality Research Institute (PQRI) Leachables and Extractables Working Group Initiatives for Parenteral and Ophthalmic Drug Product (PODP)

The Product Quality Research Institute (PQRI) is a non-profit consortium of organizations working together to generate and share timely, relevant, and impactful information that advances drug product quality and development. The collaborative activities of PQRI participants have, in the case of orally inhaled and nasal drug products (OINDPs), resulted in comprehensive and widely-accepted recommendations for leachables assessments to help ensure patient safety with respect to this class of packaged drug products. These recommendations, which include scientifically justified safety thresholds for leachables, represent a significant milestone towards establishing standardized approaches for safety qualification of leachables in OINDP. To build on the success of the OINDP effort, PQRI's Parenteral and Ophthalmic Drug Products (PODP) Leachables and Extractables Working Group was formed to extrapolate the OINDP threshold concepts and best practice recommendations to other dosage forms with high concern for interaction with packaging/delivery systems. This article considers the general aspects of leachables and their safety assessment, introduces the PODP Work Plan and initial study Protocol, discusses the laboratory studies being conducted by the PODP Chemistry Team, outlines the strategy being developed by the PODP Toxicology Team for the safety qualification of PODP leachables, and considers the issues associated with application of the safety thresholds, particularly with respect to large-volume parenterals. Lastly, the unique leachables issues associated with biologics are described.

LAY ABSTRACT

The Product Quality Research Institute (PQRI) is a non-profit consortium involving industry organizations, academia, and regulatory agencies that together provide recommendations in support of regulatory guidance to advance drug product quality. The collaborative activities of the PQRI Orally Inhaled and Nasal Drug Products Leachables and Extractables Working Group resulted in a systematic and science-based approach to identify and qualify leachables, including the concept of safety thresholds. Concepts from this widely accepted approach, formally publicized in 2006, are being extrapolated to parenteral and ophthalmic drug products. This article provides an overview of extractables and leachables in drug products and biologics and discusses the PQRI Work Plan and Protocols developed by the PQRI Parenteral and Ophthalmic Drug Products Leachables and Extractables Working Group.

Characteristics of local recurrence of lung cancer and possibilities for surgical management

PURPOSE

To investigate the correlation between stage and histopathological characteristics of patients with lung cancer and local recurrence, as well as the incidence and the characteristics of local recurrence along with the possibility of surgical retreatment.

METHODS

Studied were 51 patients with locally relapsing lung cancer, initially treated surgically from 2003 to 2007. The operations performed ranged from conservative wedge resections, standard lobectomies and pneumonectomies to extensive resections of the entire lung and chest wall. All patients underwent regular follow-up including thoracic CT scan every 3 months.

RESULTS

All patients were diagnosed with local recurrence after a median of 10 months (range 1-30) after primary surgery with curative intent. There was no statistically significant link between type of surgery and time to local recurrence. Patients with pathological stage I,II, and IIIa had a significantly longer time to local recurrence than those with stage IIIb and IV. Local recurrence sites were the bronchial stump, mediastinal lymph nodes, the remaining lung parenchyma, chest wall and a combination of these. Surgical retreatment was possible in 20 of 51 patients (39.27percnt;). Chest wall was the commonest localization (20 of 51; 39.2%), also the most frequent in the group of surgically retreated patients (13 of 20; 65%). Squamous cell cancer (SCC) was the predominant histological type (38 of 51; 74.5%), followed by adenocarcinoma (9 of 51; 17.7%).

CONCLUSION

SCC is the commonest locally relapsing lung cancer. The type of the initial surgical procedure didn't have any impact on the incidence of local recurrence, but the extent and completeness of surgery did. The time to local recurrence heavily depended on the primary tumor pathological stage. Chest wall was the commonest relapse site, and the most suitable for surgical retreatment, which was related to the quality of surgery.

Hyperprolactinemia: different clinical expression in childhood

BACKGROUND

Hyperprolactinemia is the most common disturbance in pituitary gland secretion. Functional diversity of prolactin action is responsible for different initial clinical expressions of hyperprolactinemia.

PATIENTS AND METHODS

We investigated causes of hyperprolactinemia in 11 children and adolescents (6 females and 5 males), aged from 1.5 to 17.5 years. Children with primary hypothyroidism, iatrogenic hyperprolactinemia and adolescents with polycystic ovaries were excluded.

RESULTS

Four patients had short stature or growth deceleration, the same number were clinically obese, 2 adolescent girls had secondary amenorrhea, 1 girl had premature thelarche and gynecomastia, and hypogonadism was the indication for the endocrinologic examination of two adolescent boys. Delayed pubertal development was present in both sexes. Hyperprolactinemia was also found in the youngest girl with multiple ovarian cysts. A very high prolactin (PRL) level was documented in the PRL profile of all patients (mean 2,553.00 +/- 1,020.97 mU/l). MRI of the pituitary was indicated and revealed 4 microprolactinomas, one congenital hypophyseal cyst and one tumor of the hypothalamus. Dopamine agonist treatment was efficacious in almost all the patients.

CONCLUSION

Hyperprolactinemic children expressed a wide variety of initial clinical presentations. The most common were growth and puberty disorders and obesity. PRL determination should be included in investigation protocols of obese and short stature children.

Evaluation of safety and quality impact of extractable and leachable substances in therapeutic biologic protein products: a risk-based perspective

Leachables are chemical entities that migrate spontaneously from the final container closure system, packaging components and/or processing equipment under recommended conditions of product use and storage. Unlike leachables, extractables are generated under exaggerated temperature and time conditions in the presence of an appropriate solvent. Increasing evidence suggests that leachables may pose a safety risk by causing toxicity, carcinogenicity, immunogenicity and/or endocrine dysregulation. These substances may also alter product physico-chemical properties via interaction with the active pharmaceutical ingredient or the excipients in product vehicle, thereby adversely affecting the final product quality. The evaluation of leachable compounds begins with a thorough identification of extractable compounds released from the production and packaging components under exaggerated conditions. The set of observed extractables helps to identify possible targets to be monitored in a subsequent leachables study over extended time periods. Although extractables and leachables also present a challenge for the safe use of device components (e.g., metered dose inhalers, dry powder inhalers, nasal spray devices or various implants), this review focusses on a safety risk assessment for specified therapeutic biological protein products. Regulatory, safety and scientific considerations in evaluating extractables and leachables are discussed, along with strategies for the analytical identification, quantification and monitoring.

Influence of calcium on lipid mixing mediated by influenza hemagglutinin

We studied the influence of calcium on lipid mixing mediated by influenza hemagglutinin (HA). Lipid mixing between HA-expressing cells and liposomes containing disialoganglioside, influenza virus receptor, was studied at 37 degrees C and neutral pH after a low-pH pulse at 4 degrees C. With DSPC/cholesterol liposomes, calcium present after raising the temperature significantly promoted lipid mixing only when it was triggered by a short low-pH application. In case of DOPC/cholesterol liposomes, calcium promotion was observed regardless of the duration of the low-pH pulse. Calcium present during a short, but not long, low-pH application to HA-expressing cells with bound DSPC/cholesterol liposomes at 4 degrees C inhibited subsequent lipid mixing. We hypothesize that calcium influences lipid mixing because it binds to a vestigial esterase domain of hemagglutinin or causes expulsion of the fusion peptide from an electronegative cavity. We suggest that calcium promotes the transition from early and reversible conformation(s) of low pH-activated HA towards an irreversible conformation that underlies both HA-mediated lipid mixing and HA inactivation.

The tyrosine kinase inhibitor genistein blocks HIV-1 infection in primary human macrophages

Binding of HIV-1 envelope glycoprotein (Env) to its cellular receptors elicits a variety of signaling events, including the activation of select tyrosine kinases. To evaluate the potential role of such signaling, we examined the effects of the tyrosine kinase inhibitor, genistein, on HIV-1 entry and infection of human macrophages using a variety of assays. Without altering cell viability, cell surface expression of CD4 and CCR5 or their abilities to interact with Env, genistein inhibited infection of macrophages by reporter gene-encoding, beta-lactamase containing, or wild type virions, as well as Env-mediated cell-fusion. The observation that genistein blocked virus infection if applied before, during or immediately after the infection period, but not 24h later; coupled with a more pronounced inhibition of infection in the reporter gene assays as compared to both beta-lactamase and p24 particle entry assays, imply that genistein exerts its inhibitory effects on both entry and early post-entry steps. These findings suggest that other exploitable targets, or steps, of the HIV-1 infection process may exist and could serve as additional opportunities for the development of new therapeutics.

Heterogeneity of early intermediates in cell-liposome fusion mediated by influenza hemagglutinin

To explore early intermediates in membrane fusion mediated by influenza virus hemagglutinin (HA) and their dependence on the composition of the target membrane, we studied lipid mixing between HA-expressing cells and liposomes containing phosphatidylcholine (PC) with different hydrocarbon chains. For all tested compositions, our results indicate the existence of at least two types of intermediates, which differ in their lifetimes. The composition of the target membrane affects the stability of fusion intermediates at a stage before lipid mixing. For less fusogenic distearoyl PC-containing liposomes at 4 degrees C, some of the intermediates inactivate, and no intermediates advance to lipid mixing. Fusion intermediates that formed for the more fusogenic dioleoyl PC-containing liposomes did not inactivate and even yielded partial lipid mixing at 4 degrees C. Thus, a more fusogenic target membrane effectively blocks nonproductive release of the conformational energy of HA. Even for the same liposome composition, HA forms two types of fusion intermediates, dissimilar in their stability and propensity to fuse. This diversity of fusion intermediates emphasizes the importance of local membrane composition and local protein concentration in fusion of heterogeneous biological membranes.

Advances in HIV-1 entry inhibitors: strategies to interfere with receptor and coreceptor engagement

The present armamentarium of 19 antiretroviral drugs licensed for treatment of HIV-1 infection in the U.S. exemplifies preponderance of scientific evidence, which led to improved understanding of the structural and functional, viral and cellular attributes driving HIV-1 infection. The majority of approved drugs (with exception of enfuvirtide), however, focus on two steps of the viral life cycle: reverse transcription and viral maturation. Therefore, it appears there is ample opportunity for the development of a third drug class that has been extensively researched in recent years known as entry inhibitors. Currently, this class of compounds targets steps involved in virion attachment to CD4 or to an appropriate chemokine receptor on the cell surface as well as subsequent conformational rearrangements induced in the envelope glycoprotein (gp120/gp41; Env). These inhibitors preclude the fusion of the virion envelope with the host cell membrane thereby preventing the release of viral capsid into the cytosol. Antiviral agents interfering with receptor (i.e., CD4) or coreceptor (e.g., CCR5 and/or CXCR4) engagement comprise a special subset of viral entry inhibitors. While drugs targeting viral entry offer certain advantages over other classes of compounds, they also pose specific challenges. This review focuses on compounds blocking viral attachment to CD4, CCR5 or CXCR4, highlights the challenges they present, and attempts to offer possible solutions.

Human fetal islet transplantation in type 1 diabetics: comparison of immunological effects between multiple implantation regimens

Previous studies have suggested that the multiple transplants might be equally metabolically efficient to a single regimen for human adult islets. The aim of this study was to compare immunological and metabolic parameters after each of the two regimens of human fetal islets (HFI). Group A single transplants (n = 9) had 180 +/- 20 x 1000 HFI equivalents (IEQs) implanted via a single intramuscular injection. In group B multiple transplants (n = 8) islets were implanted by three consecutive injections of 60 +/- 10 x 1000 IEQs at 7-day intervals. We analyzed the immunological parameters of CD4/CD8 T lymphocyte ratios; islet cell antibodies (ICAs) and insulin antibodies (IAs). We estimated insulin secreting capacity (ISC) as the metabolic parameter. We observed that the CD4+/CD8+ T-cell ratio increased, peaking on day 90, in similar fashion in both groups: day -1: A = 1.18 +/- 0.03 versus B = 1.19 +/- 0.04; on day 90: A = 1.79 +/- 0.09, versus B = 1.75 +/- 0.08 (P = NS) immediately before the decrease in C-peptide levels. Thereafter the ratios rapidly decreased without statistical differences. The levels of ICAs did not change. The levels of IAs, which were increased before transplant, then decreased without statistical differences between the groups. The values of ISC increased after transplant and then decreased similar to the T-cell ratio. Our results demonstrated that regimens of multiple and single HFIs did not show differences in the kinetics of the immunological response presumably mediating graft destruction. The CD4/CD8 ratio increased as the C-peptide level decreased, peaking on day 90 at the time of a decrease in C-peptide. These results may be useful for clinical studies of HFIs for type 1 diabetic patients.

Human fetal islet transplantation in type 1 diabetic patients: Comparison of metabolic effects between single and multiple implantation regimens

Previous studies suggest that multiple transplantations might be equally efficient to a single regimen for human adult islets. The aim of this study was to compare metabolic parameters after each of the two regimens of human fetal islet (HFI) transplantation in type 1 diabetics. In group A (single transplant, n = 9), 180 +/- 20 x 1000 HFI equivalents (IEQs) were implanted by a single IM injection; in group B (multiple transplants, n = 8) islets were implanted as three consecutive injections (60 +/- 10 x 1000 IEQs) at 7-day intervals. We analyzed the metabolic parameters on days -1, 30, 60, 90, 120, 150, and 180 after the procedure. Among the metabolic parameters, we evaluated insulin secretion capacity-ISC (C peptide, RIA), metabolic control (HbA1c, chromatography), and insulin daily dose IDD. We found that C peptide levels increased, peaking on day 90 (A: 0.38 +/- 0.15; B: 0.34 +/- 0.19 nmol/L, P = NS) and then rapidly decreasing without differences, the HbA1c levels and IDD decreased in the same manner without differences between the groups. Our results demonstrate that multiple and single islet transplant regimens are equally efficient to temporarily restore a significant ISC with improvement of metabolic and clinical parameters. The results imply that the two regimens have an equal clinical value.

Recent Advances in Understanding the Molecular Mechanisms of HIV-1 Entry and Fusion: Revisiting Current Targets and Considering New Options for Therapeutic Intervention

Recent advances in our understanding of the cellular and molecular mechanisms of HIV-1 entry provide the basis for novel therapeutic strategies that prevent viral penetration of the target cell-membrane, while reducing detrimental virus and treatment effects on cells and prolonging virion exposure to immune defenses. A number of potential sites for therapeutic intervention become accessible during the narrow window between virus attachment and the subsequent fusion of viral envelope with the cell membrane. Initial approaches considered for prevention of HIV-1 entry included the use of natural ligands, small-molecule inhibitors and/or monoclonal antibodies, which could interfere with gp120-CD4 and/or gp120-CXCR4/CCR5 interaction. Others avenues pursued were the use of agents that interfere with the conformational changes of gp120 or gp41 leading to subsequent fusion of viral and cellular membranes. More recently, strategies have emerged that involve inhibition of thiol/disulfide oxidoreductases (factors which facilitate Env transition from an inactive to a fusion-competent conformation) to block redox exchange, thereby impeding the entry process. This review provides a summary of the cellular and viral factors mediating the HIV-1 entry process, with an emphasis on novel therapeutics targeting Env-receptor/coreceptor interaction, Env conformational change and the membrane fusion process.

[Principles of lymph node surgery in differentiated thyroid carcinoma]

Surgery is the initial therapy in differentiated thyroid carcinoma (DTC). The surgery is performed on organ of tumor origin and regional lymphatic basins. The aim of surgery in DTC is to eradicate all tumor foci, cure the most number of patients, reduce recurrence and mortality rate, and provide good quality of life. There is no doubt between oncologists that the surgery for thyroid carcinoma has no alternative. The extent of surgery is matter of actual controversies. It should be performed by well trained surgeons. Dissection of central and biopsy of supraclavicular and lower third of jugulo-carotid chain of neck lymph nodes is the integral part of surgery in DTC, together with total thyroidectomy. If lymph node metastases are found in jugulo-carotid chain, modified radical neck dissection, unilateral or bilateral is indicated. Dissection of mediastinal lymph nodes should be performed too in cases of involvement. The extent of primary surgery should be dictated by stage of disease and prognostic factors. The quality of surgery and incidence of complications depends prognostic factors, as well as on surgeon's skill and experience. That is why the surgeon is factor of prognosis in treatment of patients with DTC.

Thiol/disulfide exchange is a prerequisite for CXCR4-tropic HIV-1 envelope-mediated T-cell fusion during viral entry

Attachment of gp120 to CD4 during HIV-1 entry triggers structural rearrangement in gp120 that enables binding to an appropriate coreceptor. Following coreceptor engagement, additional conformational changes occur in the envelope (Env), resulting in fusion of virion and cell membranes. Catalysts with redox-isomerase activity, such as protein disulfide isomerase (PDI), facilitate Env conversion from its inactive to its fusion-competent conformation. We report here that anti-PDI agents effectively block CXCR4 Env-mediated fusion and spread of virus infection. Exogenously added PDI, in turn, can rescue fusion from this blockade. We further find that PDI facilitates thiol/disulfide rearrangement in gp120 during conformational change, whereas inhibition of this redox shuffling prevents gp41 from assuming the fusogenic 6-helix bundle conformation. At the virus-cell contact site, gp120 induces assembly of PDI, CD4, and CXCR4 into a tetramolecular protein complex serving as a portal for viral entry. Our findings support the hypothesis that Env conformational change depends on a well-coordinated action of a tripartite system in which PDI works in concert with the receptor and the coreceptor to effectively lower the activation energy barrier required for Env conformational rearrangement.

Reversible stages of the low-pH-triggered conformational change in influenza virus hemagglutinin

The refolding of the prototypic fusogenic protein hemagglutinin (HA) at the pH of fusion is considered to be a concerted and irreversible discharge of a loaded spring, with no distinct intermediates between the initial and final conformations. Here, we show that HA refolding involves reversible conformations with a lifetime of minutes. After reneutralization, low pH-activated HA returns from the conformations wherein both the fusion peptide and the kinked loop of the HA2 subunit are exposed, but the HA1 subunits have not yet dissociated, to a structure indistinguishable from the initial one in functional, biochemical and immunological characteristics. The rate of the transition from reversible conformations to irreversible refolding depends on the pH and on the presence of target membrane. Importantly, recovery of the initial conformation is blocked by the interactions between adjacent HA trimers. The existence of the identified reversible stage of refolding can be crucial for allowing multiple copies of HA to synchronize their release of conformational energy, as required for fusion.

Synchronized activation and refolding of influenza hemagglutinin in multimeric fusion machines

At the time of fusion, membranes are packed with fusogenic proteins. Do adjacent individual proteins interact with each other in the plane of the membrane? Or does each of these proteins serve as an independent fusion machine? Here we report that the low pH-triggered transition between the initial and final conformations of a prototype fusogenic protein, influenza hemagglutinin (HA), involves a preserved interaction between individual HAs. Although the HAs of subtypes H3 and H2 show notably different degrees of activation, for both, the percentage of low pH-activated HA increased with higher surface density of HA, indicating positive cooperativity. We propose that a concerted activation of HAs, together with the resultant synchronized release of their conformational energy, is an example of a general strategy of coordination in biological design, crucial for the functioning of multiprotein fusion machines.

Delay of influenza hemagglutinin refolding into a fusion-competent conformation by receptor binding: a hypothesis

Two subunits of influenza hemagglutinin (HA), HA1 and HA2, represent one of the best-characterized membrane fusion machines. While a low pH conformation of HA2 mediates the actual fusion, HA1 establishes a specific connection between the viral and cell membranes via binding to the sialic acid-containing receptors. Here we propose that HA1 may also be involved in modulating the kinetics of HA refolding. We hypothesized that binding of the HA1 subunit to its receptor restricts the major refolding of the low pH-activated HA to a fusion-competent conformation and, in the absence of fusion, to an HA-inactivated state. Dissociation of the HA1-receptor connection was considered to be a slow kinetic step. To verify this hypothesis, we first analyzed a simple kinetic scheme accounting for the stages of dissociation of the HA1/receptor bonds, inactivation and fusion, and formulated experimentally testable predictions. Second, we verified these predictions by measuring the extent of fusion between HA-expressing cells and red blood cells. Three experimental approaches based on 1) the temporal inhibition of fusion by lysophosphatidylcholine, 2) rapid dissociation of the HA1-receptor connections by neuraminidase treatment, and 3) substitution of membrane-anchored receptors by a water-soluble sialyllactose all provided support for the proposed role of the release of HA1-receptor connections. Possible biological implications of this stage in HA refolding and membrane fusion are being discussed.

Membrane fusion mediated by baculovirus gp64 involves assembly of stable gp64 trimers into multiprotein aggregates

The baculovirus fusogenic activity depends on the low pH conformation of virally-encoded trimeric glycoprotein, gp64. We used two experimental approaches to investigate whether monomers, trimers, and/or higher order oligomers are functionally involved in gp64 fusion machine. First, dithiothreitol (DTT)- based reduction of intersubunit disulfides was found to reversibly inhibit fusion, as assayed by fluorescent probe redistribution between gp64-expressing and target cells (i.e., erythrocytes or Sf9 cells). This inhibition correlates with disappearance of gp64 trimers and appearance of dimers and monomers in SDS-PAGE. Thus, stable (i.e., with intact intersubunit disulfides) gp64 trimers, rather than independent monomers, drive fusion. Second, we established that merger of membranes is preceded by formation of large (greater than 2 MDa), short-lived gp64 complexes. These complexes were stabilized by cell-surface cross-linking and characterized by glycerol density gradient ultracentrifugation. The basic structural unit of the complexes is stable gp64 trimer. Although DTT-destabilized trimers were still capable of assuming the low pH conformation, they failed to form multimeric complexes. The fact that formation of these complexes correlated with fusion in timing, and was dependent on (a) low pH application, (b) stable gp64 trimers, and (c) cell-cell contacts, suggests that such multimeric complexes represent a fusion machine.

Chemical correlates of α-tocopherol (Vitamin E) alteredMalacosoma disstria herbivory inFraxinus pennsylvanica var.Subintegerrinia, green ash

The antioxidant α-tocopherol (vitamin E), applied in a basal trunk band to the green ash tree,Fraxinus pennsylvanica var.subintergerrinia, elicited an alteration of foliar feeding byMalacosoma disstria larvae (Lepidoptera: Lasiocampidae). The bioassayed effects were dependent on the dosage of elicitor, the time after elicitation, and the position in the tree. Leaves for chemical analysis were collected from trees receiving two dosages and at two intervals after elicitation. Compounds in the ethyl acetate extractables from the ash tree leaves were separated by TLC and HPLC. TLC separations showed differences in the nonhydrolyzed extractables attributable to elicitor dosage and time after elicitation. TLC-resolved differences were also evident among acid-hydrolyzed samples. HPLC-resolved profiles revealed eight peaks in the nonhydrolyzed extractables that were quantitatively negatively correlated with larval feeding preference between elicited versus control foliage on at least one of the two sampling dates. Results from this study and other investigations reported in the literature indicate that the antioxidantα-tocopherol (vitamin E) can function as an environmental-stress elicitor of alterable defensive chemistry in green ash and other plants.