IKS03, a Novel CD19-Targeted Antibody Drug Conjugate, Induces Target Dependent In Vivo Cell Killing of B-Cell Lymphoma Xenografts By DNA Crosslinking

CD19 is widely expressed in B-cell non-Hodgkin lymphoma including diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL). IKS03 is a CD19-targeting antibody drug conjugate (ADC) with a novel linker payload design for tumor-selective payload release. Site-specific conjugation using farnesyltransferase-catalysed ConjuALL technology to a DNA crosslinking agent yields a homogenous ADC with drug-to-antibody ratio (DAR) of 2. To minimize systemic release of the highly potent payload in human plasma, IKS03 incorporates a linker specifically cleavable by the lysosomal enzyme beta-glucuronidase. In addition, the payload is a pro-drug with a protecting moiety cleavable by the same enzyme. Therefore, following CD19-dependent binding and uptake, IKS03 requires intracellular lysosomal processing in the target cell to both release and fully activate the free pyrrolobenzodiazepine (PBD) dimer payload which induces DNA crosslinking, blocks DNA replication and ultimately leads to tumor selective cell death. In vivo efficacy was evaluated in CD19-expressing preclinical human xenograft models representing different subtypes of B-NHL. IKS03 was highly active against Farage and OCI-LY10 DLBCL xenografts as well as Granta-519 MCL xenografts in SCID mice with durable tumor regressions observed following treatment with a single dose of 0.1 to 0.3 mg/kg. Likewise, in a Ramos lymphoma model a single IKS03 dose of 0.3 mg/kg significantly inhibited tumor growth. IKS03 demonstrated greater in vivo efficacy than the clinical benchmark ADCs polatuzumab vedotin and loncastuximab tesirine approved for the treatment of patients with B-cell non-Hodgkin lymphomas. PBD cytotoxic agents have been described to induce DNA crosslinking leading to DNA damage. To demonstrate that IKS03 in vivo activity is the result of targeted payload release, Ramos xenografts were established in immunodeficient mice and treated with up to 1 mg/kg of IKS03 in comparison with a non-targeted ADC utilizing the same linker payload format. Tumors were excised at 1 day and 3 days post-treatment and assessed for the presence of phospho-H2AX positive foci, a marker of DNA damage, by immunohistochemistry. IKS03 treatment increased both frequency and staining intensity of nuclear phospho-H2AX foci in Ramos xenografts in a dose- and time-dependent manner. In contrast, the non-targeted control ADC did not result in any changes as compared to a vehicle control. This confirms the specific induction of DNA damage i