Mechanistic Insights of an Immunological Adverse Event Induced by an Anti-KIT Antibody Drug Conjugate and Mitigation Strategies

Abstract

Hypersensitivity reactions (HSRs) were observed in three patients dosed in a phase I clinical trial treated with LOP628, a KIT targeted antibody drug conjugate. Mast cell degranulation was implicated as the root cause for the HSR. Underlying mechanism of this reported HSR was investigated with an aim to identifying potential mitigation strategies. Biomarkers for mast cell degranulation were evaluated in patient samples and in human peripheral blood cell-derived mast cell (PBC-MC) cultures treated with LOP628. Mitigation strategies interrogated include pretreatment of mast cells with small molecule inhibitors that target KIT or signaling pathways downstream of FcεR1, FcγR, and treatment with Fc silencing antibody formats. Transient elevation of serum tryptase was observed in patients 1-hour posttreatment of LOP628. In agreement with the clinical observation, LOP628 and its parental antibody LMJ729 induced degranulation of human PBC-MCs. Unexpectedly, KIT small molecule inhibitors did not abrogate mast cell degranulation. By contrast, small molecule inhibitors that targeted pathways downstream of Fc receptors blunted degranulation. Furthermore, interference of the KIT antibody to engage Fc receptors by pre-incubation with IgG or using engineered Fc silencing mutations reduced or prevented degranulation. Characterization of Fcγ receptors revealed human PBC-MCs expressed both FcγRII and low levels of FcγRI. Interestingly, increasing the level of FcγRI upon addition of IFNγ, significantly enhanced LOP628-mediated mast cell degranulation. Our data suggest LOP628-mediated mast cell degranulation is the likely cause of HSR observed in the clinic due to co-engagement of the FcγR and KIT, resulting in mast cell activation. .

Preclinical Antitumor Activity of a Novel Anti–c-KIT Antibody–Drug Conjugate against Mutant and Wild-type c-KIT–Positive Solid Tumors

“…This led to cessation of the phase I clinical trial. The clinical findings and mechanism behind this hypersensitivity reaction are explored elsewhere (29). These data highlight the potential benefit of targeting c-KIT via an ADC approach, but also the challenges of translating preclinical safety findings to the clinic.…”

Anti-KIT DNA Aptamer for Targeted Labeling of Gastrointestinal Stromal Tumor

“…In addition, the aptamer concentrations tested here were several log-fold higher than the concentration used for cell binding experiments (400 nmol/L). This strongly suggests that the aptamer has negligible adverse cytotoxic effect when utilized for in vitro or in vivo applications (24).…”

Non-genotoxic conditioning facilitates hematopoietic stem cell gene therapy for hemophilia A using bioengineered factor VIII

“…A clinical trial testing an LMJ729-based antibody-drug conjugate (LOP628) for acute myelogenous leukemia ( ClinicalTrials.gov identifier: NCT02221505) was discontinued in 2015 during phase 1 when three participants developed hypersensitivity reactions attributed to co-engagement of FcγR and CD117 present on mast cells. 49 Promising preclinical results were later obtained by Shizuru and colleagues 50 using SR-1 to deplete both normal and myelodysplastic syndrome (MDS) human HSCs in murine xenograft models, as well as endogenous HSPCs in cynomolgus macaques using the humanized version AMG191. 51 A current phase 1 dose-escalation trial sponsored by Jasper Therapeutics testing JSP191 (formerly AMG191) as a conditioning agent in patients undergoing HSCT for severe combined immune deficiency (SCID) has shown encouraging early results for this indication, achieving up to 7% donor granulocyte chimerism 24 weeks post-transplantation ( ClinicalTrials.gov identifier: NCT02963064).…”