BOSTON – They've been around since the 1990s, but until recently were held back by unpredictability in manufacturing, inability to manufacture at scale, poor stability and a short half-life.

However, recent advances mean it has become possible to make bi-specific antibodies at scale in a way that finally makes them amenable to commercialization, and serious attention is now being given to experimenting with different formats and exploring the additional functionality that the ability to hit two receptors at once provides.

"We are now in an era of totally different molecules. The next generation of antibodies will be multivalent constructs, and many of these are starting to come through," David Goldenberg, founder and chief medical officer of Immunomedics Inc., told delegates on Wednesday at a session weighing up the state of play in dual-targeting antibodies.

While Munich, Germany-based Trion Pharma GmbH's Removab (catumaxomab), approved by the European Medicines Agency in 2009 for the treatment of malignant ascites, is the only marketed bi-specific antibody, 11 of the 15 largest pharma companies either have their own bi-specific platforms, or have licensing agreements around that format.

Fueled by that interest, data are beginning to emerge showing they not only deliver superior efficacy over mixtures of two antibodies, but also that new mechanisms of action arise when one molecule locks onto two targets simultaneously.

A case in point is the Dual-Variable-Domain-Ig format that is being developed by Abbott, which makes it possible to engineer bi-specific antibodies from any two monoclonal antibodies that preserve the activity of the parent antibodies.

"These make it possible to target two disease mechanisms with a single molecule," Tariq Ghayur, of Abbott, told delegates.

In one project, the modular assembly method behind Dual-Variable-Domain was used to design 90 different molecules based on anti-interleukin-1beta and anti-interleukin-17 monoclonal antibodies. Within months, those were synthesized, purified and run through high-throughput screens, and five to six candidates taken forward. "You can select a panel with a lot of diversity, so if anything fails at any stage, you've always got a backup product in place," Ghayur noted.

Among other programs, Abbott is applying the platform to increase the efficacy of anti-TNF-alpha monoclonal antibodies and thus build on its Humira (adalimumab) franchise in rheumatoid arthritis. While anti-TNF-alpha is effective, there are multiple symptoms of rheumatoid arthritis. "As a result, there's still unmet medical need, so we are adding functionality, to prevent pain, protect cartilage and prevent bone erosion. We can quickly generate candidates with new functions," Ghayur said.

In cancer, it is possible to engage with T cells and bind tumor cells, resulting in potent killing of tumor cells. "There are additive, synergistic effects of blocking two targets simultaneously," Ghayur said.

Furthermore, there is no evidence of any increase in immunogenicity from those combinations. "We don't find anything that stands out; they behave just like monoclonal antibodies," Ghayur said. Abbott's two lead programs from the Dual-Variable-Domain platform have now completed Phase I.

Immunomedics, of Morris Plains, N.J., is another company that is aiming to extract further returns from its investment in classical monoclonal antibodies by moving into bi-specific antibodies. Its Dock and Lock technology platform is a modular system that can be used to produce a wide variety of bioconjugates that cannot be made with traditional methods. Molecules generated by the platform retain the full binding specificity of the parent antibodies, but they have unique mechanisms of action, said Edmund Rossi, of Immunomedics. "They are considerably more potent than the parent antibodies in combination," he said.

For example, a combined anti-CD20 and anti-CD74 antibody generated by Immunomedics has been shown to trigger a number of signaling pathways, initiating events at an organelle level that induce apoptosis.

Early stage company Biotecnol Inc., of North Brunswick, N.J., takes the binding ability of its antibodies even further with its Tribody constructs, which use the natural in vivo heterodimerization of Fab fragments to form a scaffold on which additional proteins can be incorporated.

That Tribody scaffold can accommodate up to three different binders, allowing Tribodies to combine T-cell recruitment and dual targeting, for example. Nico Mertens, of Biotecnol, told delegates that this gives Tribodies the potential to address both tumor drug resistance and tumor heterogeneity.

As an example, Biotecnol has generated Tribodies that target both the EGFR and the HER2 tumor antigens and tested that in ex vivo tumors. "When you look at a treated tumor under a microscope, some [Tribodies] bind to one or to the other receptor, and only some bind to both. In other words, metastases are heterogeneic," Mertens said.

Biotecnol has overcome difficulties in manufacturing Tribodies and refined the platform to the point where it is possible to generate Tribody leads within three months. The company is looking for partners and is applying the technology in-house to develop Tribodies for treating triple-negative breast cancer, advanced metastatic melanoma and gastric cancer.