PBD-Dimer Payloads for Antibody Drug Conjugates A Robust Approach to cGMP Production
Bertrand Cottineau, Rachel De Luca, Mélanie Derde, and Francois D’Hooge
rom the 1960s when monomeric computer-generated graphic (Figure 2), PBD- pyrrolobenzodiazepines (PBDs) such as dimer minor groove binding does not change anthramycin were isolated and DNA geometry, which makes this modification Fcharacterized, to the dramatic increase of hard to identify and repair. PBD-dimer geometry potency induced by dimerization in the 2000s, is induced by the two H11a stereochemistries, so PBD dimers have evolved as one of the leading stereochemical control is absolutely necessary for classes of antibody drug conjugate (ADC) biological activity. payloads (Figure 1). Currently, 17 ADCs are in clinical trials involving PBD-dimers — second Specific Challenges of only to auristatins (23 ADCs), and more than PBD Synthesis and Purification those with maytansines (16 ADCs). Four different PBD-dimer payloads are ultrapotent molecules PBD-dimer ADC payloads are in clinical trials: that require very high containment (occupational Talirine (SGD-1910) from Seattle Genetics; exposure limits below 30 ng/m3/8 h). Novasep’s Tesirine (SG3249) from Spirogen, MedImmune, chemical and bioconjugation laboratories and ADC Therapeutics, and Abbvie; and DGN462 production suites offer a consistent set of and DGN549 from Immunogen. With the most equipment fitted with the best available barrier advanced PBD-ADC program, Abbvie- technology allowing for ultracontained handling StemCentrx’ Rovalpituzumab-tesirine (Rova-T) and transfer of PBD samples and bulk product. closing to commercial launch, we summarize Combined with essential know-how of specially herein the production challenges and solutions trained staff, exposure can be as low as a few ng/ presented by the PBD-dimer platform. m3, as demonstrated by periodical sampling at the Several other companies also are involved in workstations. preclinical development of PBD-dimers ADC From a process standpoint, the principal payloads, either through a license from Spirogen challenge is that PBD-dimers are highly unstable (Genentech, Mitsubishi Tanabe Pharma, in acidic and basic media as well as under Regeneron, and Gamamabs Pharma) or through nucleophilic conditions. To produce a robust proprietary internal payload development process and highly pure PBD-dimers, experience programs (Sanofi, Bristol-Myers Squibb, Cellerant in PBD chemistry and expertise in process Therapeutics, and Abzena). development are essential. For such compounds, PBD-dimers are DNA crosslinkers or Novasep’s approach is to perform a detailed alkylators. Upon ADC internalization and process characterization on key steps of the lysosomal processing, PBD-dimer payloads are process using design of experiment (DoE) tools. released in the cytosol, then diffuse through the The main impurities to control include nuclear membrane and bind in the minor groove diastereomers, aromatized impurities, and of DNA. After binding, the imine then can maleimide and conjugable impurities. alkylate or crosslink the two DNA strands and Diastereomers: As described by Tiberghien, the block DNA replication. As shown on the possible epimerization of H11a can occur under 2 BioProcess International 16(6)i June 2018 Sponsored Report Figure 1: History of PBD-dimer ADC payload Structure ear
Anthramycin 1965
Spirogen SJG136 / SG2000 2001 epin e Seattle Genetics SGD‐1910 / Talirine 2010 dia z o (PBDs) oloben z r y P
Spirogen SG3249 / Tesirine 2013 s Immunogen DGN462 2014 pin e e ia z o d z (IBDs)
Immunogen DGN549 2016 Indolinoben
basic conditions, for example using TBAF Conjugation of PBD-Dimer Payloads deprotection of the TBS group (2). It can be Four commercial ADCs are available currently: controlled by using TBAF buffered with acetic Pfizer’s Mylotarg (gemtuzumab ozogamicin) and acid. Besponsa (inotuzumab ozogamicin), Seattle Aromatized Impurities: On highly aromatic Genetics’ Adcetris (brentuximab vedotin), and compounds such as SGD-1910, the H11a position Roche/Genentech’s Kadcyla (ado-trastuzumab is very sensitive to elimination, leading to a flat emtansine). Figure 4 shows that they are produced pi-conjugated system in which DNA binding using two different conjugation technologies: potency is widely reduced. This elimination needs stochastic lysine conjugation and stochastic cysteine to be under control for the whole process. conjugation (Figure 4a, 4b). For PBD-dimer Maleimide and Conjugable Impurities: The last payloads, the same conjugation technologies were steps of the synthesis of SG3249 or SGD-1910 used, along with a more advanced site-specific (Figure 3) involve introduction of a maleimide cysteine conjugation for Seattle Generics’ moiety for the antibody-cysteine conjugation. vadastuximab talirine, where an antibody is Extra care must be taken to ensure that no other engineered with extra cysteines at specific site for maleimide-bearing impurity is present. Expertise conjugation purpose only (Figure 4c). in high-pressure chromatography is key to developing a robust process, guaranteeing high Drug-to-Antibody Ratio (DAR) and consistent purity of PBD-dimer payload when and Conjugation Process the process is transferred to the manufacturing For each of the three processes illustrated in facilities. Figure 5, the main critical quality attributes are drug-to-antibody ratio (DAR) and monomeric Sponsored Report June 2018 16(6)i BioProcess International 3 Figure 2: Mode of action (1)
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