Optimization of an Enzymatic Antibody–Drug Conjugation Approach Based on Coenzyme A Analogs

Phosphopantetheine transferases (PPTases) can be used to efficiently prepare site-specific antibody–drug conjugates (ADCs) by enzymatically coupling coenzyme A (CoA)-linker payloads to 11–12 amino acid peptide substrates inserted into antibodies. Here, a two-step strategy is established wherein in a first step, CoA analogs with various bioorthogonal reactivities are enzymatically installed on the antibody for chemical conjugation with a cytotoxic payload in a second step. Because of the high structural similarity of these CoA analogs to the natural PPTase substrate CoA-SH, the first step proceeds very efficiently and enables the use of peptide tags as short as 6 amino acids compared to the 11–12 amino acids required for efficient one-step coupling of the payload molecule. Furthermore, two-step conjugation provides access to diverse linker chemistries and spacers of varying lengths. The potency of the ADCs was largely independent of linker architecture. In mice, proteolytic cleavage was observed for some C-terminally linked auristatin payloads. The in vivo stability of these ADCs was significantly improved by reduction of the linker length. In addition, linker stability was found to be modulated by attachment site, and this, together with linker length, provides an opportunity for maximizing ADC stability without sacrificing potency

Synthesis, Structure–Activity Relationships, and in Vivo Efficacy of the Novel Potent and Selective Anaplastic Lymphoma Kinase (ALK) Inhibitor 5‑Chloro‑<i>N</i>2‑(2-isopropoxy-5-methyl-4-(piperidin-4-yl)phenyl)‑<i>N</i>4‑(2-(isopropylsulfonyl)phenyl)pyrimidine-2,4-diamine (LDK378) Currently in Phase 1 and Phase 2 Clinical Trials

The synthesis, preclinical profile, and in vivo efficacy in rat xenograft models of the novel and selective anaplastic lymphoma kinase inhibitor <b>15b</b> (LDK378) are described. In this initial report, preliminary structure–activity relationships (SARs) are described as well as the rational design strategy employed to overcome the development deficiencies of the first generation ALK inhibitor <b>4</b> (TAE684). Compound <b>15b</b> is currently in phase 1 and phase 2 clinical trials with substantial antitumor activity being observed in ALK-positive cancer patients