Early Development, Scale-Up, and Reverse-Phase Purification of a Highly Potent Pyrrolobenzodiazepine Dimer, SG3259, for Use in Antibody–Drug Conjugates

Abstract

Pyrrolobenzodiazepine (PBD) dimers, such as that found in SG3259, are fully synthetic highly potent (subnanomolar) small molecules currently being developed as warheads for antibody–drug conjugates (ADCs). The complete synthetic route toward the linker drug SG3259 has 17 steps, and 10–20 g of drug was needed prior to antibody conjugation for IND-enabling toxicological studies and Phase I clinical trials. Herein, we disclose the enabling route to SG3259, with the final four steps being conducted under GMP conditions. Significant effort was spent developing the preparatory scale reverse-phase HPLC purification of the final linker drug. SG3259 suffers from poor solubility; acid-, light-, and oxygen-sensitivity; and extremely high potency, factors which make this a challenging target for gram-scale development.

Development of Dual Practical Manufacturing Routes to Cognate Pyrrolobenzodiazepine-Based Linker-Drugs

“…A synthesis of the prominent dimeric PBD warhead tesirine has been described, with efforts to improve on the complex supply chain outlined in a separate disclosure . Whereas tesirine utilizes the native aminal for the attachment site of an extended peptidic poly­(ethylene glycol)–maleimide linker, other clinical ADCs have used PBD toxins with cleavable linker connections at pendent aniline attachment sites, including talirine and SG3259 . Genentech licensed a series of PBD dimers for its internal ADC program with in-house-designed linkers; this article conveys the small-molecule process development work that was conducted to move these self-immolative disulfide-linked payloads into the clinic …”

“…8 Whereas tesirine utilizes the native aminal for the attachment site of an extended peptidic poly(ethylene glycol)−maleimide linker, other clinical ADCs have used PBD toxins with cleavable linker connections at pendent aniline attachment sites, including talirine 9 and SG3259. 10 Genentech licensed a series of PBD dimers for its internal ADC program with inhouse-designed linkers; this article conveys the small-molecule process development work that was conducted to move these self-immolative disulfide-linked payloads into the clinic. 11 The assembly of a full ADC construct is achieved by merging the antibody, a water-soluble biologic, with the organic-soluble linker-drug in an accommodating milieu via a site-specific conjugation to the desired drug/antibody ratio.…”