Safety, Tolerability, and Pharmacokinetics of NTM-1632, a Novel Mixture of Three Monoclonal Antibodies against Botulinum Toxin B

Monoclonal Antibody Therapies for Infectious Diseases

In contrast to therapy in oncology and immune-related diseases, where dozens of monoclonal antibodies (mAbs) have been introduced, often in transformative fashion, the use of mAbs for infectious diseases is generally underdeveloped, with fewer than a dozen mAbs currently licensed for the treatment of microbial diseases. This situation is paradoxical given that antibodies are major products of the immune system for protecting against infectious diseases. The underdevelopment of mAbs for infectious diseases has several causes including the availability of effective therapy against many microbial diseases, the fact that many pathogenic microbes are antigenically diverse and thus all strains are not covered by a single mAb, and the high expense of mAb therapies. Despite these hurdles the number of mAbs licensed for infectious disease indications is slowly increasing and there are numerous opportunities for the development of mAbs in the prevention and treatment of microbial diseases.

Isolation and characterization of Hc-targeting chimeric heavy chain antibodies neutralizing botulinum neurotoxin type B

Background

Botulinum neurotoxin (BoNT) produced by Clostridium botulinum is one of the most potent known toxins. Moreover, BoNT is classified as one of the most important biological warfare agents that threatens the biosafety of the world. Currently, the approved treatment for botulism in humans is the use of polyvalent horse serum antitoxins. However, they are greatly limited because of insufficient supply and adverse reactions. Thus, treatment of human botulism requires the development of effective toxin-neutralizing antibodies. Considering their advantages, neutralizing nanobodies will play an increasing role as BoNTs therapeutics.

Methods

Herein, neutralizing nanobodies binding to the heavy chain (Hc) domain of BoNT/B (BHc) were screened from a phage display library. Then, BoNT/B-specific clones were identified and fused with the human Fc fragment (hFc) to form chimeric heavy chain antibodies. Finally, the affinity, specificity, and neutralizing activity of antibodies against BoNT/B in vivo were evaluated.

Results

The B5-hFc, B9-hFc and B12-hFc antibodies demonstrated high affinity for BHc in the nanomolar range. The three antibodies were proven to have potent neutralizing activity against BoNT/B in vivo.

Conclusion

The results demonstrate that inhibiting toxin binding to the host receptor is an efficient strategy and the three antibodies could be used as candidates for the further development of drugs to prevent and treat botulism.

Recent Advancements and Novel Approaches Contributing to the Present Arsenal of Prophylaxis and Treatment Strategies Against Category A Bacterial Biothreat Agents

Bacterial pathogens have always been a part of the ecosystem in which we thrive. Some pathogens have caused deadly outbreaks in the past and have been exploited as an agent of threat. Natural hotspots for these biological pathogens are widely distributed throughout the world and hence they remain clinically important. Technological advancement and change in general lifestyle has driven the evolution of these pathogens into more virulent and resistant variants. There has been a growing concern over the development of multidrug-resistant bacterial strains that could be used as bioweapons. This rapid change in pathogens also propels the field of science to develop and innovate new strategies and methodologies which are superior and safer to the existing ones. Some bacterial agents like-Bacillus anthracis, Yersinia pestis, Francisella tularensis and toxins produced by strains of Clostridium botulinum, have been segregated as Category A substances as they pose imminent threat to public health with a history of life threatening and catastrophic disease. This review highlights some encouraging developments and value additions in the current plan of action for protection against these select biothreat bacterial pathogens.

A Three-Monoclonal Antibody Combination Potently Neutralizes BoNT/G Toxin in Mice

Equine-derived antitoxin (BAT^®) is the only treatment for botulism from botulinum neurotoxin serotype G (BoNT/G). BAT^® is a foreign protein with potentially severe adverse effects and is not renewable. To develop a safe, more potent, and renewable antitoxin, humanized monoclonal antibodies (mAbs) were generated. Yeast displayed single chain Fv (scFv) libraries were prepared from mice immunized with BoNT/G and BoNT/G domains and screened with BoNT/G using fluorescence-activated cell sorting (FACS). Fourteen scFv-binding BoNT/G were isolated with K_D values ranging from 3.86 nM to 103 nM (median K_D 20.9 nM). Five mAb-binding non-overlapping epitopes were humanized and affinity matured to create antibodies hu6G6.2, hu6G7.2, hu6G9.1, hu6G10, and hu6G11.2, with IgG K_D values ranging from 51 pM to 8 pM. Three IgG combinations completely protected mice challenged with 10,000 LD₅₀s of BoNT/G at a total mAb dose of 6.25 μg per mouse. The mAb combinations have the potential for use in the diagnosis and treatment of botulism due to serotype G and, along with antibody combinations to BoNT/A, B, C, D, E, and F, provide the basis for a fully recombinant heptavalent botulinum antitoxin to replace the legacy equine product.

Antimicrobial Resistance and Recent Alternatives to Antibiotics for the Control of Bacterial Pathogens with an Emphasis on Foodborne Pathogens

Antimicrobial resistance (AMR) is one of the most important global public health problems. The imprudent use of antibiotics in humans and animals has resulted in the emergence of antibiotic-resistant bacteria. The dissemination of these strains and their resistant determinants could endanger antibiotic efficacy. Therefore, there is an urgent need to identify and develop novel strategies to combat antibiotic resistance. This review provides insights into the evolution and the mechanisms of AMR. Additionally, it discusses alternative approaches that might be used to control AMR, including probiotics, prebiotics, antimicrobial peptides, small molecules, organic acids, essential oils, bacteriophage, fecal transplants, and nanoparticles.

Safety of Ceftazidime-Avibactam in Combination with Aztreonam (COMBINE) in a Phase I, Open-Label Study in Healthy Adult Volunteers

This phase I study evaluated the safety of the optimal ceftazidime-avibactam (CZA) with aztreonam (ATM) regimens identified in hollow fiber infection models of MBL-producing Enterobacterales. Eligible healthy subjects aged 18 to 45 years were assigned to one of six cohorts: 2.5 g CZA over 2 h every 8 h (approved dose), CZA continuous infusion (CI) (7.5 g daily), 2 g ATM over 2 h every 6 h, ATM CI (8 g daily), CZA (approved dose) with 1.5 g ATM over 2 h every 6 h, and CZA (approved dose) with 2 g ATM over 2 h every 6 h. Study drug(s) were administered for 7 days. The most frequently observed adverse events (AEs) were hepatic aminotransferase (ALT/AST) elevations (n = 19 subjects). Seventeen of the 19 subjects with ALT/AST elevations received ATM alone or CZA-ATM. The incidence of ALT/AST elevations was comparable between the ATM-alone and CZA-ATM cohorts. Two subjects in the ATM CI cohort experienced severe ALT/AST elevation AEs. All subjects with ALT/AST elevations were asymptomatic with no other findings suggestive of liver injury. Most other AEs were of mild to moderate severity and were similar across cohorts, except for prolonged prothrombin time (more frequent in CZA-ATM cohorts). These results suggest that CZA-ATM administered as 2-h intermittent infusions is safe and that some caution should be exercised with the use of ATM CI at an ATM dose of 8 g daily. If CZA-ATM is prescribed, clinicians are advised to monitor liver function, hematologic, and coagulation parameters. Future controlled studies are required to better define the safety and efficacy of the CZA-ATM regimens evaluated in this phase I study.

Multicolor fluorescence activated cell sorting to generate humanized monoclonal antibody binding seven subtypes of BoNT/F

Generating specific monoclonal antibodies (mAbs) that neutralize multiple antigen variants is challenging. Here, we present a strategy to generate mAbs that bind seven subtypes of botulinum neurotoxin serotype F (BoNT/F) that differ from each other in amino acid sequence by up to 36%. Previously, we identified 28H4, a mouse mAb with poor cross-reactivity to BoNT/F1, F3, F4, and F6 and with no detectable binding to BoNT/F2, F5, or F7. Using multicolor labeling of the different BoNT/F subtypes and fluorescence-activated cell sorting (FACS) of yeast displayed single-chain Fv (scFv) mutant libraries, 28H4 was evolved to a humanized mAb hu6F15.4 that bound each of seven BoNT/F subtypes with high affinity (KD 5.81 pM to 659.78 pM). In contrast, using single antigen FACS sorting, affinity was increased to the subtype used for sorting but with a decrease in affinity for other subtypes. None of the mAb variants showed any binding to other BoNT serotypes or to HEK293 or CHO cell lysates by flow cytometry, thus demonstrating stringent BoNT/F specificity. Multicolor FACS-mediated antibody library screening is thus proposed as a general method to generate multi-specific antibodies to protein subtypes such as toxins or species variants.

First-in-Human Clinical Trial to Assess the Safety, Tolerability and Pharmacokinetics of Single Doses of NTM-1633, a Novel Mixture of Monoclonal Antibodies against Botulinum Toxin E

Botulism is a rare, life-threatening paralytic disease caused by botulinum neurotoxin (BoNT). Available treatments including an equine antitoxin and human immune globulin are given postexposure and challenging to produce and administer. NTM-1633 is an equimolar mixture of 3 human IgG monoclonal antibodies, E1, E2, and E3, targeting BoNT serotype E (BoNT/E). This first-in-human study assessed the safety, tolerability, pharmacokinetics (PK), and immunogenicity of NTM-1633. This double-blind, single-center, placebo-controlled dose escalation study randomized 3 cohorts of healthy volunteers to receive a single intravenous dose of NTM-1633 (0.033, 0.165, or 0.330 mg/kg) or saline placebo. Safety monitoring included physical examinations, clinical laboratory studies, and vital signs. Blood sampling was performed at prespecified time points for PK and immunogenicity analyses. Twenty-four subjects received study product (18 NTM-1633; 6 placebo), and no deaths were reported. An unrelated serious adverse event was reported in a placebo subject. Adverse events in the NTM-1633 groups were generally mild and similar in frequency and severity to the placebo group, and no safety signal was identified. NTM-1633 has a favorable PK profile with a half-life >10 days for the 0.330 mg/kg dose and an approximately linear relationship with respect to maximum concentration and area under the concentration-time curve (AUC_0→t). NTM-1633 also demonstrated low immunogenicity. NTM-1633 is well tolerated at the administered doses. The favorable safety, PK, and immunogenicity profile supports further development as a treatment for BoNT/E intoxication and postexposure prophylaxis.

Neutralizing Concentrations of Anti-Botulinum Toxin Antibodies Positively Correlate with Mouse Neutralization Assay Results in a Guinea Pig Model

Botulinum neurotoxins (BoNT) are some of the most toxic proteins known and can induce respiratory failure requiring long-term intensive care. Treatment of botulism includes the administration of antitoxins. Monoclonal antibodies (mAbs) hold considerable promise as BoNT therapeutics and prophylactics, due to their potency and safety. A three-mAb combination has been developed that specifically neutralizes BoNT serotype A (BoNT/A), and a separate three mAb combination has been developed that specifically neutralizes BoNT serotype B (BoNT/B). A six mAb cocktail, designated G03-52-01, has been developed that combines the anti-BoNT/A and anti-BoNT/B mAbs. The pharmacokinetics and neutralizing antibody concentration (NAC) of G03-52-01 has been determined in guinea pigs, and these parameters were correlated with protection against an inhalation challenge of BoNT/A1 or BoNT/B1. Previously, it was shown that each antibody demonstrated a dose-dependent mAb serum concentration and reached maximum circulating concentrations within 48 h after intramuscular (IM) or intraperitoneal (IP) injection and that a single IM injection of G03-52-01 administered 48 h pre-exposure protected guinea pigs against an inhalation challenge of up to 93 LD₅₀s of BoNT/A1 and 116 LD₅₀s of BoNT/B1. The data presented here advance our understanding of the relationship of the neutralizing NAC to the measured circulating antibody concentration and provide additional support that a single IM or intravenous (IV) administration of G03-52-01 will provide pre-exposure prophylaxis against botulism from an aerosol exposure of BoNT/A and BoNT/B.