Profile of bavituximab and its potential in the treatment of non-small-cell lung cancer.
ABSTRACT: Bavituximab is a an unconjugated, chimeric immunoglobulin G1 (IgG1) monoclonal antibody directed against the phosphatidylserine (PS) expressed on tumor endothelium, with a specific mechanism of action. PS is an anionic membrane phospholipid, physiologically restricted to the internal membrane leaflet; various pathophysiologic processes cause the exposure of PS on the external membrane leaflet. Bavituximab, once bound, starts up host effector activities, such as antibody dependent cellular cytotoxicity, causing vessel destruction and enhancing antitumor immunity. Phase I clinical trials of bavituximab administered as monotherapy or in combination with other chemotherapeutic agents in adults with pretreated solid tumors have been accomplished, indicating that bavituximab can be safely dispensed weekly, with a recommended dose of 1 and 3 mg/kg. A Phase II randomized, placebo-controlled trial of bavituximab plus docetaxel, in the second-line therapy setting of locally advanced or metastatic non-small-cell lung cancer, has been conducted and recently presented, suggesting a clinical benefit of the combination, with an overall response rate of 17% and median overall survival of more than 11 months. A Phase III trial is currently ongoing. Bavituximab has been studied in combination with platinum-based doublets with promising results. In the present paper we summarize the preclinical development and clinical experience with bavituximab in non-small-cell lung cancer.
Project description:Objective:Host derived markers on virally infected cells or virions may provide targets for the generation of antiviral agents. Recently, we identified phosphatidylserine (PS) as a host marker of virions and virally-infected cells. Methods and Materials:Under normal physiological conditions, PS is maintained on the inner leaflet of the plasma membrane facing the cytosol. Following viral infection, activation or pre-apoptotic changes cause PS to become externalized. We have previously shown that bavituximab, a chimeric human-mouse antibody that binds PS complexed with ?2-glycoprotein I (?2GP1), protected rodents against lethal Pichinde virus and cytomegalovirus infections. Results:Here, we determined the antiviral activity of a fully human monoclonal antibody, PGN632, that directly binds to PS. Treatment with PGN632 protected 20% of guinea pigs with advanced infections of the hemorrhagic arenavirus, Pichinde, from death. Combining PGN632 with ribavirin improved the antiviral activity of both agents, such that the combination rescued 50% of animals from death. Conclusion:The major mechanisms of action of PGN632 appear to be opsonization of virus and antibody-dependent cellular cytotoxicity of virally-infected cells. PS-targeting agents may have utility in the treatment of viral diseases.
Project description:Background:Bavituximab is a monoclonal antibody that targets phosphatidylserine in the presence of ?2 glycoprotein 1 (?2GP1) to exert an antitumor immune response. This phase III trial determined the efficacy of bavituximab combined with docetaxel in patients with previously treated advanced non-small-cell lung cancer (NSCLC). Patients and methods:Key eligibility criteria included advanced non-squamous NSCLC with disease progression after treatment with platinum-based doublet chemotherapy, evidence of disease control after at least two cycles of first-line therapy, presence of measurable disease, ECOG performance status 0 or 1, adequate bone marrow and organ function, and no recent history of clinically significant bleeding. Eligible patients were randomized 1 : 1 to receive up to six 21-day cycles of docetaxel plus either weekly bavituximab 3?mg/kg or placebo until progression or toxicity. The primary end point was overall survival (OS). Results:A total of 597 patients were enrolled. Median OS was 10.5?months in the docetaxel?+?bavituximab arm and was 10.9?months in the docetaxel?+?placebo arm (HR 1.06; 95% CI 0.88-1.29; P?=?0.533). There was no difference in progression-free survival (HR 1.00; 95% CI 0.82-1.22; P?=?0.990). Toxicities were manageable and similar between arms. In subset analysis, among patients with high baseline serum ?2GP1 levels??200?µg/ml, a nonsignificant OS trend favored the bavituximab arm (HR 0.82; 95% CI 0.63-1.06; P?=?0.134). Among patients who received post-study immune checkpoint inhibitor therapy, OS favored the bavituximab arm (HR 0.46; 95% CI 0.26-0.81; P?=?0.006). Conclusions:The combination of bavituximab plus docetaxel is not superior to docetaxel in patients with previously treated advanced NSCLC. The addition of bavituximab to docetaxel does not meaningfully increase toxicity. The potential benefit of bavituximab observed in patients with high ?2GP1 levels and in patients subsequently treated with immune checkpoint inhibitors requires further investigation. Clinical trial number:NCT01999673.
Project description:Abstract BACKGROUND Glioblastoma and tumor endothelial cells express phosphatidylserine, a highly immunosuppressive membrane phospholipid. Bavituximab a chimeric monoclonal antibody binds to 2-glycoprotein 1 (2-GP1) to form a complex of 2-GP1 with phosphatidylserine, resulting in immune activation against tumor cells and anti-angiogenic effects. Phase I/II trials in other solid cancers have demonstrated response rates up to 85% when bavituximab was given with cytotoxic chemotherapy. Pre-clinical data in glioblastoma models suggested synergistic effects of phosphatidylserine blockade, radiation, and temozolomide (TMZ). METHODS In this ongoing phase II trial (NCT03139916), adult patients with IDH-wild-type newly diagnosed glioblastoma receive 6 weeks of chemoradiation, followed by 6 cycles of adjuvant TMZ (C1-C6 aTMZ). Bavituximab (3 mg/kg) is given weekly, starting week 1 of chemoradiation, for 18 weeks with the option to continue if tolerated. Physiologic MRIs are performed pre-treatment, pre-C1, pre-C3, and pre-C5 aTMZ. Within the enhancing tumor region, we measured median tumor Ktrans (reflecting vascular permeability) and relative cerebral blood volume (rCBV). Median percent changes during treatment were compared to pre-treatment values. RESULTS To date, 25 of 36 anticipated patients have enrolled (10 with MGMT promoter methylation). All patients underwent pre-treatment scans. 13 have evaluable pre-C1 and 8 pre-C3 aTMZ scans. On the pre-C1 MRIs, enhancing volume decreased by 39% and median tumor Ktrans and rCBV did not change significantly. On the pre-C3 MRIs, enhancing volume decreased by 11% and Ktrans and rCBV decreased by 17% and 21%, respectively. Five patients experienced radiographic disease progression after a median of 2.6 months and 1 patient died 76 days after diagnosis due to disease progression. Bavituximab was generally well tolerated. CONCLUSIONS: Combining bavituximab with radiation and temozolomide results in decreased enhancing tumor volume, permeability, and cerebral perfusion. Continued patient accrual and imaging marker evaluation are underway to investigate the correlation between bavituximab, MRI changes, and survival.
Project description:There is a pressing need for antiviral agents that are effective against multiple classes of viruses. Broad specificity might be achieved by targeting phospholipids that are widely expressed on infected host cells or viral envelopes. We reasoned that events occurring during virus replication (for example, cell activation or preapoptotic changes) would trigger the exposure of normally intracellular anionic phospholipids on the outer surface of virus-infected cells. A chimeric antibody, bavituximab, was used to identify and target the exposed anionic phospholipids. Infection of cells with Pichinde virus (a model for Lassa fever virus, a potential bioterrorism agent) led to the exposure of anionic phospholipids. Bavituximab treatment cured overt disease in guinea pigs lethally infected with Pichinde virus. Direct clearance of infectious virus from the blood and antibody-dependent cellular cytotoxicity of virus-infected cells seemed to be the major antiviral mechanisms. Combination therapy with bavituximab and ribavirin was more effective than either drug alone. Bavituximab also bound to cells infected with multiple other viruses and rescued mice with lethal mouse cytomegalovirus infections. Targeting exposed anionic phospholipids with bavituximab seems to be safe and effective. Our study demonstrates that anionic phospholipids on infected host cells and virions may provide a new target for the generation of antiviral agents.
Project description:We used molecular dynamics simulations to explore the effects of asymmetric transbilayer distribution of anionic phosphatidylserine (PS) lipids on the structure of a protein on the membrane surface and subsequent protein-lipid interactions. Our simulation systems consisted of an amyloidogenic, beta-sheet rich dimeric protein (D42) absorbed to the phosphatidylcholine (PC) leaflet, or protein-contact PC leaflet, of two membrane systems: a single-component PC bilayer and double PC/PS bilayers. The latter comprised of a stable but asymmetric transbilayer distribution of PS in the presence of counterions, with a 1-component PC leaflet coupled to a 1-component PS leaflet in each bilayer. The maximally asymmetric PC/PS bilayer had a non-zero transmembrane potential (TMP) difference and higher lipid order packing, whereas the symmetric PC bilayer had a zero TMP difference and lower lipid order packing under physiologically relevant conditions. Analysis of the adsorbed protein structures revealed weaker protein binding, more folding in the N-terminal domain, more aggregation of the N- and C-terminal domains and larger tilt angle of D42 on the PC leaflet surface of the PC/PS bilayer versus the PC bilayer. Also, analysis of protein-induced membrane structural disruption revealed more localized bilayer thinning in the PC/PS versus PC bilayer. Although the electric field profile in the non-protein-contact PS leaflet of the PC/PS bilayer differed significantly from that in the non-protein-contact PC leaflet of the PC bilayer, no significant difference in the electric field profile in the protein-contact PC leaflet of either bilayer was evident. We speculate that lipid packing has a larger effect on the surface adsorbed protein structure than the electric field for a maximally asymmetric PC/PS bilayer. Our results support the mechanism that the higher lipid packing in a lipid leaflet promotes stronger protein-protein but weaker protein-lipid interactions for a dimeric protein on membrane surfaces.
Project description:Understanding how functional lipid domains in live cell membranes are generated has posed a challenge. Here, we show that transbilayer interactions are necessary for the generation of cholesterol-dependent nanoclusters of GPI-anchored proteins mediated by membrane-adjacent dynamic actin filaments. We find that long saturated acyl-chains are required for forming GPI-anchor nanoclusters. Simultaneously, at the inner leaflet, long acyl-chain-containing phosphatidylserine (PS) is necessary for transbilayer coupling. All-atom molecular dynamics simulations of asymmetric multicomponent-membrane bilayers in a mixed phase provide evidence that immobilization of long saturated acyl-chain lipids at either leaflet stabilizes cholesterol-dependent transbilayer interactions forming local domains with characteristics similar to a liquid-ordered (lo) phase. This is verified by experiments wherein immobilization of long acyl-chain lipids at one leaflet effects transbilayer interactions of corresponding lipids at the opposite leaflet. This suggests a general mechanism for the generation and stabilization of nanoscale cholesterol-dependent and actin-mediated lipid clusters in live cell membranes.
Project description:Polybia-MP1 (MP1) is a bioactive host-defense peptide with known anticancer properties. Its activity is attributed to excess serine (phosphatidylserine (PS)) on the outer leaflet of cancer cells. Recently, higher quantities of phosphatidylethanolamine (PE) were also found at these cells' surface. We investigate the interaction of MP1 with model membranes in the presence and absence of POPS (PS) and DOPE (PE) to understand the role of lipid composition in MP1's anticancer characteristics. Indeed we find that PS lipids significantly enhance the bound concentration of peptide on the membrane by a factor of 7-8. However, through a combination of membrane permeability assays and imaging techniques we find that PE significantly increases the susceptibility of the membrane to disruption by these peptides and causes an order-of-magnitude increase in membrane permeability by facilitating the formation of larger transmembrane pores. Significantly, atomic-force microscopy imaging reveals differences in the pore formation mechanism with and without the presence of PE. Therefore, PS and PE lipids synergistically combine to enhance membrane poration by MP1, implying that the combined enrichment of both these lipids in the outer leaflet of cancer cells is highly significant for MP1's anticancer action. These mechanistic insights could aid development of novel chemotherapeutics that target pathological changes in the lipid composition of cancerous cells.
Project description:It is well known that lipids are heterogeneously distributed throughout the cell. Most lipid species are synthesized in the endoplasmic reticulum (ER) and then distributed to different cellular locations in order to create the distinct membrane compositions observed in eukaryotes. However, the mechanisms by which specific lipid species are trafficked to and maintained in specific areas of the cell are poorly understood and constitute an active area of research. Of particular interest is the distribution of phosphatidylserine (PS), an anionic lipid that is enriched in the cytosolic leaflet of the plasma membrane. PS transport occurs by both vesicular and non-vesicular routes, with members of the oxysterol-binding protein family (Osh6 and Osh7) recently implicated in the latter route. In addition, the flippase activity of P4-ATPases helps build PS membrane asymmetry by preferentially translocating PS to the cytosolic leaflet. This asymmetric PS distribution can be used as a signaling device by the regulated activation of scramblases, which rapidly expose PS on the extracellular leaflet and play important roles in blood clotting and apoptosis. This review will discuss recent advances made in the study of phospholipid flippases, scramblases and PS-specific lipid transfer proteins, as well as how these proteins contribute to subcellular PS distribution.
Project description:In mammalian cells, the internal and external leaflets of the plasma membrane (PM) possess different phospholipids. Phosphatidylserine (PS) is normally confined to the inner (cytoplasmic) membrane leaflet. Here we report that the adhesin CPn0473 of the human pathogenic bacterium Chlamydia pneumoniae (Cpn) binds to the PM of human cells and induces PS externalization but unexpectedly not apoptosis. PS externalization is increased in human cells exposed to infectious Cpn cells expressing increased CPn0473 and reduced in exposure to Cpn expressing decreased CPn0473. CPn0473 binds specifically to synthetic membranes carrying PS and stimulates pore formation. Asymmetric giant unilamellar vesicles (GUVs) in which PS is restricted to the inner leaflet reveal that CPn0473 induces PS externalization in the absence of other proteins. Thus our identification of CPn0473 as a bacterial PS translocator capable of specific and apoptosis-independent PS externalization during infection extends the spectrum of mechanisms intracellular pathogens use to enter host cells.
Project description:Phosphatidylserine (PS) is an anionic phospholipid maintained on the inner-leaflet of the cell membrane and is externalized in malignant cells. We previously launched a careful unbiased selection targeting biomolecules (e.g. protein, lipid or carbohydrate) distinct to cancer cells by exploiting HCC4017 lung cancer and HBEC30KT normal epithelial cells derived from the same patient, identifying HCC4017 specific peptide-peptoid hybrid PPS1. In this current study, we identified PS as the target of PPS1. We validated direct PPS1 binding to PS using ELISA-like assays, lipid dot blot and liposome based binding assays. In addition, PPS1 recognized other negatively charged and cancer specific lipids such as phosphatidic acid, phosphatidylinositol and phosphatidylglycerol. PPS1 did not bind to neutral lipids such as phosphatidylethanolamine found in cancer and phosphatidylcholine and sphingomyelin found in normal cells. Further we found that the dimeric version of PPS1 (PPS1D1) displayed strong cytotoxicity towards lung cancer cell lines that externalize PS, but not normal cells. PPS1D1 showed potent single agent anti-tumor activity and enhanced the efficacy of docetaxel in mice bearing H460 lung cancer xenografts. Since PS and anionic phospholipid externalization is common across many cancer types, PPS1 may be an alternative to overcome limitations of protein targeted agents.