The Nonclinical Safety Assessment of a Novel Anti-CEACAM5 Antibody Exatecan Conjugate Predicts a Low Risk for Interstitial Lung Disease (ILD) in Patients—The Putative Mechanism Behind ILD

The therapeutic window of antibody drug-conjugates (ADC) remains challenging due to safety issues such as interstitial lung disease (ILD) observed with specific deruxtecan-based ADCs. To avoid ILD, we designed M9140 by conjugating the maleimide-containing hydrophilic β-glucuronide linker to exatecan and our anti-CEACAM5 (CarcinoEmbryonic Antigen-related Cell Adhesion Molecule 5) specific antibody. Following repeated iv-infusion at 3 to 30 mg/kg of M9140 every 3 weeks, the pathological findings obtained in cynomolgus monkeys were confined to gastrointestinal and hematolymphoid tissues and resembled the toxicity of exatecan. At 24 mg/kg or higher, transient reductions in neutrophil and reticulocyte counts were observed with each dosing event along with reversible anemia throughout the study. The no observed adverse effect level was 24 mg/kg and the maximum tolerated dose was 30 mg/kg. The difference in toxicity by this small dose increment was correlated with a 2.5-fold difference in plasma exatecan exposure indicating antigen-independent toxicity. As anticipated, no lung toxicity was found with M9140 in these studies that were similar in study design to those used to confirm ILD with trastuzumab-deruxtecan in monkeys. Since the non-human primate model is regarded as predictive for the ILD risk in humans, this result indicates a low risk for ILD when applying M9140 to patients. The current M9140 safety data are discussed with special focus on the absence or presence of ILD with other antibody camptothecin-conjugates, for which a hypothetical pathogenic mechanism is postulated here. The favorable nonclinical profile of M9140 warrants further investigation in patients with CEACAM5-overexpressing tumors.