ADC or antibody-drug conjugates have recently been at the forefront of cancer research, and according to the experts presenting their latest data during the the 2017 Cambridge Healthcare Institute’s PepTalk, the Protein Engineering Week, held January 8-13, 2017 in San Diego, CA, the role for ADCs is quickly expanding.
At PepTalk, scientists and researchers participated in the Antibody-drug Conjugate conference ‘pipeline’ to discuss the most current technology and innovations in the development of these novel, targeted, agents. During the presentations on Wednesday, January 11, speakers discussed some important innovations helping to advance more ADCs into the clinic.
Dorin Toader, Ph.D., Senior Scientist of Antibody Discovery and Protein Engineering at MedImmune gave an informative presentation on the discovery and development of a fully synthetic tubulysin analog MMETA (MethylMep-N-Ethyl-TubulysinAniline) and it’s application in ADC’s.
Tubulysins are a class of highly cytotoxic peptides that occur naturally from fungus, and due to their picomolar activity on a range of cancer cell lines, they are a great candidate for use as an ADC payload. According to Toader, MMETA is at least as potent as MMAE (MethylMep-N-Ethyl-Aniline), and potent activity has already been shown in MDR over-expressing cell lines.
When MMETA is connected to a protease cleavable mc-Lys linker, it forms a great choice for generation of antibody-drug conjugates because it is highly water soluble and has low lipophiliity. Importantly, mc-Lys-MMETA when conjugated at the appropriate position via site-specific conjugation, yields ADCs that are homogenous and stable in serum. Furthermore, MMETA’s aniline group can be used for linking proteins with a protease cleavable linker, and hydrolysis of the acetyl ester group, which generates dMMETA, has lead to a significant loss in toxicity. 
Toader went on to discuss MEDI4276, an HER2 biparatopic ADC using MMETA that has demonstrated broad antitumor activity in vitro , as well as the ability to kill neighboring HER2-negative tumor cells via a bystander effect. MEDI4276 has shown potency in a variety of cancer cell lines in vitro and is currently being investigated in the clinic.
Also during Wednesday’s program was a presentation regarding Ablynx’s technology platform which generates antibody derived drugs termed Nanobodies®. Carlo Boutton, Ph.D., the Director of Technology & Information Management at Ablynx nv, explained the use of the Nanobody technology platform in producing multiparatopic and multispecific Nanobody-based drug conjugates.
Nanobodies are derived from heavy-chain only antibodies which are stable, fully functional, and which, according to Boutton, represent the next generation of antibody-derived biologics. Ablynx’s nanobodies are smaller than conventional antibodies, easily linked together, have nano- to picomolar affinities, and have a sequence homology that is comparable to humanized/human monoclonal antibodies. They can also be easily manufactured with yeast, bacteria, and mammalian cells.
Boutton note the chemical uniformity, great chemical, physical, and storage stability, and an intrinsic low aggregation propensity of these nanobodies. These biophysical properties, Boutton explained, provide an excellent CMC profile, thanks to the inherent properties of Nanobodies in combination with the expert work at Ablynx.
In developing nanobody-drug conjugates, researchers focus on improving the therapeutic index when compared to the current, mainly IgG based ADC development. Researchers at Ablynx hope that their platform will reduce toxicity while, at the same time, improving efficacy.
The small size of nanobodies provides a potential for better penetration of the tumor and tumor accumulation. Having no Fc domain means there will be reduced toxicity due to no non-specif uptake by Fc receptors. Efficacy compared to conventionally antibodies is improved through multi-valency, and improved tumor specificity is reached with the use of bispecific Nanobodies. Finally, a tunable half life and chemical stability means pharmacokinetics may be tailored, and the ability to couple chemistries is simplified. Boutton went on to present several key studies that show an ability to control DAR for a homogenous product, an extension in half life, and target-specific cell killing both in vitro and in vivo. 
Ablynx platform has various formatting applications that they believe can change the paradigm of cancer treatment, and the company is in partnership with multiple top-tier pharma companies. They currently have a late stage clinical pipeline with 8 Nanobodies in development.
Another impactful presentation on the development of next-generation of antibody-drug conjugates came form Ulf Grawunder, Ph.D., the CEO and Founder of NBE-Therapuetics. The company, a privately owned Swiss Biotech company founded in 2012, currently has three proprietary ADC development platforms. Grawunder’s presentation, titled “Leveraging Ultra-Potent Toxins in Novel ADCs for Highly Effective Anti-Tumor Therapy,” discussed the main challenges associated with ADC development , and presented data on their Sortase Mediated Antibody Conjugation, or SMAC Technology, and their novel ultra-potent anythracycline toxin, PNU-159682, to create PNU ADCs.
Currently, ADCs have presented challenges like unstable malemide linker chemistry, insufficient potency of tubulin inhibiting drugs, and issues with heterogeneous conjugation. These conventionally conjugated ADC’s with chemical linkers create the result of a drug that is not uniform – some of the ADCs in a particular mix may be more or less active than others, while some may be inactive or an altered species altogether.
According to Grawunder, SMAC-Technology can solve many of these issues through their use of stable peptide-based linkers and ultra potent warheads. This technology can work with many payloads, and can also attach more that one different toxin to generate a dual conjugated ADC. Grawunder went on to provide HPLC anaysis data that showed high homogeneity in their SMAC-technology manufactured Tras-ADC of DAR4.0, when compared to commercially available Kadcyla. Additionally, NBE-Therapeutics is using their SMAC-Technology with a PNU-derivative to construct PNU ADCs with high in vitro serum stability and favorable in vivo PK.