Branched pegylated linker-auristatin to control hydrophobicity for the production of homogeneous minibody-drug conjugate against HER2-positive breast cancer.

Trastuzumab emtansine (Kadcyla®) was the first antibody-drug conjugate (ADC) approved by the Food and Drug Administration in 2013 against a solid tumor, and the first ADC to treat human epidermal growth factor receptor 2 positive (HER2+) breast cancer. However, this second generation ADC is burden by several limitations included heterogeneity, limited activity against heterogeneous tumor (regarding antigen expression) and suboptimal tumor penetration. To address this, different development strategies are oriented towards homogeneous conjugation, new drugs, optimized linkers and/or smaller antibody formats. To reach better developed next generation ADCs, a key parameter to consider is the management of the hydrophobicity associated with the linker-drug, increasing with and limiting the drug-to-antibody ratio (DAR) of the ADC. Here, an innovative branched pegylated linker was developed, to control the hydrophobicity of the monomethyl auristatin E (MMAE) and its cathepsin B-sensitive trigger. This branched pegylated linker-MMAE was then used for the efficient generation of internalizing homogeneous ADC of DAR 8 and minibody-drug conjugate of DAR 4, targeting HER2. Both immunoconjugates were then evaluated in vitro and in vivo on breast cancer models. Interestingly, this study highlighted that the minibody-MMAE conjugate of DAR 4 was the best immunoconjugate regarding in vitro cellular internalization and cytotoxicity, gamma imaging, ex vivo biodistribution profile in mice and efficient reduction of tumor size in vivo. These results are very promising and encourage us to explore further fragment-drug conjugate development.

The proteolytic airway environment associated with pneumonia acts as a barrier for treatment with anti-infective antibodies.

Like pneumonia, coronavirus disease 2019 (COVID-19) is characterized by a massive infiltration of innate immune cells (such as polymorphonuclear leukocytes) into the airways and alveolar spaces. These cells release proteases that may degrade therapeutic antibodies and thus limit their effectiveness. Here, we investigated the in vitro and ex vivo impact on anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) IgG1s and other IgG subclasses (IgG2 and IgG4) of the neutrophil elastase, proteinase 3 and cathepsin G (the three main neutrophil serine proteases) found in endotracheal aspirates from patients with severe COVID-19. Although the IgGs were sensitive to neutrophil serine proteases, IgG2 was most resistant to proteolytic degradation. The two anti-SARS CoV2 antibodies (casirivimab and imdevimab) were sensitive to the lung's proteolytic environment, although neutrophil serine protease inhibitors only partly limited the degradation. Overall, our results show that the pneumonia-associated imbalance between proteases and their inhibitors in the airways contributes to degradation of antiviral antibodies.

Anticalin N- or C-Terminal on a Monoclonal Antibody Affects Both Production and In Vitro Functionality.

Bispecific antibodies (BsAbs) represent an important advance in innovative therapeutic strategies. Among the countless formats of BsAbs, fusion with molecules such as anticalins linked to a monoclonal antibody (mAb), represents an easy and low-cost way to obtain innovative molecules. We fused an anticalin against human fibronectin to a molecule biosimilar to trastuzumab (H0) or rituximab (R0), in four different positions, two on the N terminal region of heavy or light chains and two on the C terminal region. The eight BsAbs (H family (HF) 1 to 4 and R family (RF) 1 to 4) were produced and their affinity parameters and functional properties evaluated. The presence of anticalin did not change the glycosylation of the BsAb, shape or yield. The antigenic recognition of each BsAb family, Her2 for HF1 to 4 and CD20 for RF1 to 4, was slightly decreased (HF) or absent (RF) for the anticalin N-terminal in the light chain position. The anticalin recognition of FN was slightly decreased for the HF family, but a dramatic decrease was observed for RF members with lowest affinity for RF1. Moreover, functional properties of Abs, such as CD16 activation of NK, CD32-dependent phagocytosis and FcRn transcytosis, confirmed that this anticalin position leads to less efficient BsAbs, more so for RF than HF molecules. Nevertheless, all BsAbs demonstrated affinities for CD16, CD32 and FcRn, which suggests that more than affinity for FcRs is needed for a functioning antibody. Our strategy using anticalin and Abs allows for rapid generation of BsAbs, but as suggested by our results, some positions of anticalins on Abs result in less functionality.

Intra-Domain Cysteines (IDC), a New Strategy for the Development of Original Antibody Fragment-Drug Conjugates (FDCs).

Antibody-drug conjugates (ADCs) derived from a full immunoglobulin-G (IgG) are associated with suboptimal solid-tumor penetration and Fc-mediated toxicities. Antibody fragment-drug conjugates (FDCs) could be an alternative. Nevertheless, innovative solutions are needed to implant cysteines as conjugation sites in the single-chain fragment variable (scFv) format, which is the backbone from which many other antibody formats are built. In addition, the bioconjugation site has the utmost importance to optimize the safety and efficacy of bioconjugates. Our previous intra-tag cysteine (ITC) strategy consisted of introducing a bioconjugation motif at the C-terminal position of the 4D5.2 scFv, but this motif was subjected to proteolysis when the scFv was produced in CHO cells. Considering these data, using three intra-domain cysteine (IDC) strategies, several parameters were studied to assess the impact of different locations of a site-specific bioconjugation motif in the variable domains of an anti-HER2 scFv. In comparison to the ITC strategy, our new IDC strategy allowed us to identify new fragment-drug conjugates (FDCs) devoid of proteolysis and exhibiting enhanced stability profiles, better affinity, and better ability to kill selectively HER2-positive SK-BR-3 cells in vitro at picomolar concentrations. Thus, this work represents an important optimization step in the design of more complex and effective conjugates.

An effective strategy for the humanization of antibody fragments under an accelerated timeline.

The use of monoclonal antibodies (mAbs) in therapy is gradually advancing and discussions entail its safety, rentability and effectiveness. To this date, around a hundred mAbs have been approved by the FDA for the treatment of various diseases. Aiming for their large-scale production, recombinant DNA technology is mainly employed, and antibodies can be expressed in various eukaryotic and prokaryotic systems. Moreover, considering their heterologous origin and potential immunogenicity, various strategies have been developed for mAb humanization, considering that around 50 % of commercial mAbs are humanized. Hence, we introduce LimAb7, a mouse mAb capable of binding and neutralizing brown spider's Loxosceles intermedia dermonecrotic toxins in vivo/in vitro. This antibody has been produced in mouse and humanized scFv and diabody formats, however results indicated losses in antigen-binding affinity, stability, and neutralizing ability. Intending to develop evolved, stable, and neutralizing antibody fragments, we report for the first time the design of humanized antibody V-domains produced as Fab fragments, against spider venom toxins. Improvements in constructs were observed regarding their physicochemical stability, target binding and binding pattern maintenance. As their neutralizing features remain to be characterized, we believe this data sheds new light on antibody humanization by producing a parental molecule in different recombinant formats.

Exploration and Modulation of Antibody Fragment Biophysical Properties by Replacing the Framework Region Sequences.

In order to increase the successful development of recombinant antibodies and fragments, it seems fundamental to enhance their expression and/or biophysical properties, such as the thermal, chemical, and pH stabilities. In this study, we employed a method bases on replacing the antibody framework region sequences, in order to promote more particularly single-chain Fragment variable (scFv) product quality. We provide evidence that mutations of the VH- C-C' loop might significantly improve the prokaryote production of well-folded and functional fragments with a production yield multiplied by 27 times. Additional mutations are accountable for an increase in the thermal (+19.6 °C) and chemical (+1.9 M) stabilities have also been identified. Furthermore, the hereby-produced fragments have shown to remain stable at a pH of 2.0, which avoids molecule functional and structural impairments during the purification process. Lastly, this study provides relevant information to the understanding of the relationship between the antibodies amino acid sequences and their respective biophysical properties.

Loxoscelism: Advances and Challenges in the Design of Antibody Fragments with Therapeutic Potential.

Envenoming due to Loxosceles spider bites still remains a neglected disease of particular medical concern in the Americas. To date, there is no consensus for the treatment of envenomed patients, yet horse polyclonal antivenoms are usually infused to patients with identified severe medical conditions. It is widely known that venom proteins in the 30-35 kDa range with sphingomyelinase D (SMasesD) activity, reproduce most of the toxic effects observed in loxoscelism. Hence, we believe that monoclonal antibody fragments targeting such toxins might pose an alternative safe and effective treatment. In the present study, starting from the monoclonal antibody LimAb7, previously shown to target SMasesD from the venom of L. intermedia and neutralize its dermonecrotic activity, we designed humanized antibody V-domains, then produced and purified as recombinant single-chain antibody fragments (scFvs). These molecules were characterized in terms of humanness, structural stability, antigen-binding activity, and venom-neutralizing potential. Throughout this process, we identified some blocking points that can impact the Abs antigen-binding activity and neutralizing capacity. In silico analysis of the antigen/antibody amino acid interactions also contributed to a better understanding of the antibody's neutralization mechanism and led to reformatting the humanized antibody fragment which, ultimately, recovered the functional characteristics for efficient in vitro venom neutralization.

Evaluation of immunogenicity and protection of the Mic1-3 knockout Toxoplasma gondii live attenuated strain in the feline host.

Toxoplasmosis is a zoonotic disease caused by the parasite Toxoplasma gondii. Up to a third of the global human population is estimated to carry a T. gondii infection, which can result in severe complications in immunocompromised individuals and pregnant women. Humans and animals can become infected by ingesting either tissue cysts containing T. gondii bradyzoites, from raw or undercooked meat, or sporulated oocysts from environmental sources. T. gondii oocysts are released in the faeces of cats and other felids, which are the parasite's definitive hosts, leading to environmental contamination. Therefore, vaccination of the feline host against T. gondii is an interesting strategy to interrupt the parasitic life cycle and subsequently limit contamination of intermediate hosts. With this goal in mind, we tested in cats, an attenuated live strain of T. gondii deleted for the Mic1 and Mic3 genes (Mic1-3KO) that was previously shown to be an efficient vaccine candidate in mouse and sheep models. Subcutaneous or oral vaccination routes induced a high specific antibody titer in the cat sera, indicating that the Mic1-3KO strain is immunogenic for cats. To assess protection induced by the vaccine candidate strain, we followed oocysts shedding by vaccinated cats, after oral challenge with a T. gondii wild-type strain. Surprisingly, a high antibody titer did not prevent cats from shedding oocysts from the challenge strain, regardless of the vaccination route. Our results show that the Mic1-3KO vaccine candidate is immunogenic in the feline host, is well tolerated and safe, but does not confer protection against oocysts shedding after natural infection with wild type T. gondii. This result highlights the particular relationship between T. gondii and its unique definitive host, which indicates the need for further investigations to improve vaccination strategies to limit environmental and livestock contaminations.