Combining purification and bioconjugation has the potential to unlock and drive major cost savings and speed time to market. Downstream integrated bioconjugation is a highly promising advanced manufacturing concept—now under development—that has the potential to achieve huge efficiencies in the ADC production pipeline. 

Background, market challenges and drivers for process innovation
The drive to bring such innovation to the market comes directly from biopharmaceutical companies seeking suppliers who can transform the efficiency of what has emerged as a highly complex set of manufacturing processes within a multi-faceted supply chain. Biopharma is under constant pressure to drive down development time and cost of goods, but to still meet demands for increasing amounts of drug required for extended pre-clinical and clinical programs; enabling clinicians to develop the safest and most effective therapeutic regimes prior to drug approval.

In the typical Antibody Drug Conjugate (ADC) supply chain each core element is treated as a discrete activity, which ends in a fully tested and released product. The elements are then linked, typically, via high risk material shipment between different contract development and manufacturing organizations (CDMOs). This approach includes a high degree of redundancy, risk, cost and time penalty for the ADC product. Analysis by CDMOs suggests that delivery of multiple elements of the supply chain from a single source and location coupled with abbreviated release testing could save months in development time; up to three months for two elements combined and up to six months for three elements combined. This equates to saving six months of additional patent protection that, in the case of blockbuster drugs, would otherwise costs biopharmaceutical companies millions of dollars.

A paradigm shift in approach where the entire supply chain is considered as a continuum with only the final ADC considered as a product could revolutionize the industry.  Adoption of such forward-thinking concepts requires specialist knowledge, engagement at the research and early development phase and is likely to be pioneered by early phase specialist CDMOs. CDMO’s who specialize in commercial product manufacture arrive too late to drive such innovation.

Innovator CDMOs could exploit one or more promising generic process optimization solutions; single use systems, continuous processing or Process Analytical Technologies (PAT) for example. Or, they could use tools developed specifically for ADC development and manufacturing such as Lock-Release. This technology streamlines bioconjugation into four simple steps. Lock the antibody (mAb) to a resin, perform the conjugation, wash the locked ADC free of residuals and then release the purified ADC. Originally developed to limit ADC aggregation and improve residual clearance when starting with purified mAbs—problems common with the emerging toxin linker classes—this technology has been a huge step forward for the industry. Consider then that this technology is also well suited to downstream integrated bioconjugation where mAb purification and conjugation are achieved in one integrated process.

Downstream integrated bioconjugation: the transformative process method
Downstream integrated bioconjugation represents a new paradigm in ADC development. The new approach provides for bioconjugation concurrent with the mAb purification process negating the need for mAb testing, release, storage and shipping before a conjugate can be made.

The major benefit, and the reason this approach will prove so disruptive to the manufacturing industry is that it will save up to three months of manufacturing time and up to 25% of the overall costs, due to shorter manufacturing runs and importantly replacement of protein A. As ever with process innovation, there will be challenges to overcome if the benefits of this method are to be brought to the market. Implementation of the groundbreaking approach will require much of the industry to reevaluate its current ingrained manufacturing methods and to establish precisely how it structures the supply chain which at present often uses three CMOs.

With this new process, the starting point for the conjugation will no longer be constrained to the use of purified antibodies but can instead begin anywhere between first capture of the mAb from the cell culture supernatant onto a mimetic Lock-Release resin and the final stage mAb process operations typically employed. As this involves handling of highly potent cytotoxins, it will require the conjugation and purifications is carried out by integrated bioconjugation CDMOs. 

The Protein A capture step is the ‘work-horse’ in a mAb downstream process. Protein A is a highly specific binder of antibodies and results in a significantly purified mAb bulk and reduction in total process volume in a single step. It is conceivable to consider conjugation of the mAb while bound to the protein A resin, but this has several limitations which mean this is not viable. Protein A like the mAb is a protein and as such can be conjugated when employing certain conjugation chemistries. This would render the Protein A resin single use and would consume extra toxin linker; both cost prohibitive scenarios.

The answer: replacing protein A with specially developed mimetic resins that lie at the heart of the innovative Lock-Release technology. These small molecule mimetics retain the beneficial properties of protein A of specificity, capacity and scalability, and have the added and unique benefit of being compatible with conjugation chemistries. Combined with resin costing about a third to half the cost of protein A, the savings in time, complexity and materials are expected to be significant.

Starting with antibody supernatants, Lock-Release facilitates both the antibody capture step and subsequent conjugation of the toxin-linker to generate the ADC. The regulatory requirements for viral inactivation, viral clearance and final polishing steps can then be met post-conjugation. However, if an ADC proved not to be stable during certain processes, the innovators are looking into the possibility of carrying out some of these processes prior to conjugation.

Conceptually, the developers would capture the antibodies on the mimetic resins, perform the required mAb downstream processing, capture the purified antibody again on the mimetic ligand and then perform the conjugation as the penultimate downstream process. The final process being a simple formulation of the ADC into the correct solution. This approach is not possible with protein A, even when compatible with the conjugation chemistry, as protein A leaches from the column during mAb release. Protein A is known to cause immunogenic responses in humans and therefore its removal is mandatory and generally requires multiple purification steps to remove it to safe levels. The simple formulation process which can be used with Lock-Release has no capability for protein A reduction.

Driving innovation
ADC Bio has established a Specialist Process Innovation Group to assess the viability of its new conjugation process in comparison with conventional approaches. The aim of this group will be to drive and develop technical innovation and its first task is to establish proof of concept for the downstream bioconjugation method—demonstrating that the original antibody production process can be taken and grafted into the new conjugation process, technically how it works and how a sensible amount of product can be recovered from the process—equivalent to what would be amassed from a process which sees production of the antibody first and then the conjugation carried out in a separate step.

The group contains experts who possess relevant skills and knowledge in downstream antibody processing, as well as innovations already in use like Lock-Release. The intention is to carry out a side-by-side case study comparing the traditional antibody first and then conjugation second approach carried out at a different service provider—with the new production process demonstrating significant productivity and economic advantages. The technical proof-of-concept work is being carried out over a 12 to 18 month period. 

Conclusion
In summary, the new development process telescopes antibody downstream processing and conjugation to provide just one set of manufacturing, analytical development and release processes. At the same time, the innovation brings in the use of much more cost effective and safer resins. Once this revolutionary technique is successfully validated, its benefits will be brought to the market before long. It would represent a compelling change for the industry that would take manufacturers away from tried and tested conventional techniques and to embrace a new system with a highly compelling set of benefits. 

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Charlie Johnson is chief executive officer of ADC Bio. He brings over 20 years of experience in strategic development, commercialization and management of service businesses within the oncology sector. Charlie has a notable track record in the ADC segment going back to 2004 when he established Avecia’s ADC manufacturing operations when the segment was in its infancy. He joined ADC Biotechnology as CEO in early 2012. For more information visit www.adcbio.com/bcs.