Protein Toxin Synthesis Service

As a leader in recombinant antibody engineering and production, Creative Biolabs now offers services that integrate protein toxins into full antibody, antibody Fab regions, scFv, single-domain antibodies… as a novel form of antibody-drug conjugates (ADCs) for targeted drug developments.

Protein toxins are usually produced by bacteria or plants. Many bacterial toxins are comprised of two parts: the cell binding portion interacts with cell surface while the enzymatic portion enters the cytosol and generates toxicity. Common protein toxins include pseudomonas exotoxin (PE), diphtheria toxin (DT) and ribosome-inactivating proteins (RIPs). Protein toxins are potential payload candidates for immunotoxin conjugates (ITCs) and ADCs.

Fig.1 Pathways for protein toxin mediated cell death.^1,2

Diphtheria Toxin (DT)

DT is an extracellular protein from Corynebacterium diphtheriae that restrains protein synthesis and kills suspected cells. The essential factor of the protein synthesis machinery restrained by DT has been confirmed as elongation factor 2 (EF-2), while the presence of nicotinamide adenine dinucleotide (NAD) is required for DT protein synthesis inhibition. Furthermore, DT was proved to act catalytically through transferring the adenosine diphosphate ribose (ADPR) portion from NAD to EF-2, therefore inactivating EF-2 and restraining chain elongation during protein synthesis.

Pseudomonas Exotoxin (PE)

PE is an exotoxin produced by Pseudomonas aeruginosa and belongs to the two-component AB toxin family that contains an A domain with enzymatic activity and a B domain as cell binding subunit. PE has an extremely hydrophobic leader peptide of 25 aa at its N-terminus, followed by the receptor binding domain Ia (aa 1-252) that is comprised of antiparallel β-sheets. The second part of PE, Domain II (aa 253–364), contains six consecutive α-helices and allows the translocation of the toxin across cell membranes. PE also affects protein synthesis and doing so by restraining EF-2 via ADP-ribosylation, resulting in the termination of polypeptides elongation.

Ribosome-inactivating Protein (RIP)

Ribosome-inactivating proteins (RIPs), including ricin, abrin, and saporins, etc, are catalytic toxins which irreversibly inactivate protein synthesis. Most RIPs were isolated from plants and they were also discovered in fungi, algae and bacteria. They have been demonstrated to exert RNA N-glycosidase activity and depurinate the 28S rRNA of the large 60S ribosomal subunit in eukaryotic cells. Among these RIPs, the toxin ricin derived from Ricinus communis has been studied most extensively as cytotoxic payloads. For example, combotox, an ADC consists of two murine monoclonal IgG1 antibodies: a CD22 antibod (RFB4) and a CD19 antibody (HD37), both of which are individually conjugated to a ricin-based toxin: deglycosylated ricin-A chain (dgRTA), through a heterobifunctional, thiol-containing cross-linker. Combotox has been shown to be effective in a Daudi-Lymphoma (CD19+/CD22+) SCID mouse model, and the combined use of antibodies revealed a synergistic killing effect.

With our well-established recombinant antibody engineering and "DrugLnk" organic synthesis platforms, the experienced scientists here at Creative Biolabs is dedicated to help our clients develop antibody-targeted drugs containing protein toxin in a timely and cost-effective manner. Our customarily tailored services and high quality products will contribute greatly to the success of your projects.

Creative Biolabs also provides other various services regarding ADC development. Please feel free to contact us for more information and a detailed quote.

References:

1. Simon, Nathan, and David FitzGerald. "Immunotoxin therapies for the treatment of epidermal growth factor receptor-dependent cancers." Toxins 8.5 (2016): 137.
2. Distributed under Open Access License CC BY 4.0, without modification.