Nonclinical Characterization of the Pharmacokinetics and Disposition of Inotuzumab Ozogamicin, a Calicheamicin-Containing Antibody-Drug Conjugate

Purpose. Inotuzumab ozogamicin (InO) is an antibody-drug conjugate (ADC) in clinical development for the treatment of patients with relapsed or refractory acute lymphoblastic leukemia (ALL). A series of in vitro and in vivo nonclinical studies were conducted to characterize the pharmacokinetics (PK), distribution, metabolism, and excretion of InO and it released cytotoxic payload, N-Ac-γ-calicheamicin DMH, as conduct of traditional human ADME studies are not feasible for ADCs. Findings from these nonclinical studies were used to inform an understanding of the likely clearance mechanism of InO in humans and, as a result, the potential contributors to inter-patient variability and drug interactions.

Methods. PK, tissue distribution, mass balance, and metabolic profiling/identification were assessed in rats following a single i.v. dose of [³H]InO. The stability of [³H]InO in rat, monkey and human plasma was evaluated in vitro, and metabolic profiles were determined following incubation of [³H]N‑Ac-γ-calicheamicin DMH in rat, monkey and human liver S9 and plasma. Additional in vitro studies were conducted to further characterize [³H]InO-related material in circulation.

Results. Distribution of [³H]InO radioequivalents into tissues of rats was limited, consistent with its low volume of distribution. In rats, most circulating drug-related material was unchanged InO, and in vitro and in vivo studies suggested that hydrolytic release of N‑Ac-γ-calicheamicin DMH in circulation was limited. The primary elimination pathway of [³H]InO in rats was hepatic clearance/biliary excretion, with limited excretion of unchanged N‑Ac-γ-calicheamicin DMH in bile or urine. Released N‑Ac-γ-calicheamicin DMH was extensively metabolized, with non-enzymatic reduction of the disulfide moiety identified as the primary metabolic pathway.

Conclusions. Based on these nonclinical studies, InO is anticipated to be cleared from circulation, with concomitant deconjugation, in humans by both target (CD22)- and non-target (catabolism/FcRn recycling)-mediated pathways. In addition, released N‑Ac-γ-calicheamicin DMH is expected to be extensively metabolized in humans, with calicheamicin-related metabolites eliminated via hepatic clearance/biliary excretion. Drug interactions are not anticipated when InO is co-administrated with inhibitors or inducers of the major CYP or UGT drug metabolizing enzymes.