Supplementary Fig. S1. Structure and characterization of ADCT-602. (A) Full-length amino acid sequence of light and heavy chains of hLL2-C220, with the mutations C219S in the light chain and C225V and C228V in the heavy chain indicated in bold. (B) Structure of ADCT-602 with the PBD dimer payload tesirine (SG3249) conjugated at C219 of hLL2-CC20 (C220 according to the EU numbering system) in the heavy chain. (C) ADCT-602 characterized by size exclusion chromatography and by (D) reduced reversed-phase chromatography. L indicates elution of the light chain, whereas H0 and H1 indicate elution of the unconjugated H-chain or H-chain conjugated to SG3249, respectively. (E) RP-HPLC analysis of the reduced tryptic digest of 2 batches of ADCT-602 (red and black traces). Ala alanine; PABC poly(A)-binding protein C-terminal; PBD pyrrolobenzodiazepine; Val valine.
ARTICLE ABSTRACT
Relapsed or refractory B-cell acute lymphoblastic leukemia (R/R B-ALL) and lymphomas have poor patient outcomes; novel therapies are needed. CD22 is an attractive target for antibody–drug conjugates (ADCs), being highly expressed in R/R B-ALL with rapid internalization kinetics. ADCT-602 is a novel CD22-targeting ADC, consisting of humanized mAb hLL2-C220, site specifically conjugated to the pyrrolobenzodiazepine dimer–based payload tesirine. In preclinical studies, ADCT-602 demonstrated potent, specific cytotoxicity in CD22-positive lymphomas and leukemias. ADCT-602 was specifically bound, internalized, and trafficked to lysosomes in CD22-positive tumor cells; after cytotoxin release, DNA interstrand crosslink formation persisted for 48 hours. In the presence of CD22-positive tumor cells, ADCT-602 caused bystander killing of CD22-negative tumor cells. A single ADCT-602 dose led to potent, dose-dependent, in vivo antitumor activity in subcutaneous and disseminated human lymphoma/leukemia models. Pharmacokinetic analyses (rat and cynomolgus monkey) showed excellent stability and tolerability of ADCT-602. Cynomolgus monkey B cells were efficiently depleted from circulation after one dose. Gene signature association analysis revealed IRAK1 as a potential marker for ADCT-602 resistance. Combining ADCT-602 + pacritinib was beneficial in ADCT-602–resistant cells. Chidamide increased CD22 expression on B-cell tumor surfaces, increasing ADCT-602 activity. These data support clinical testing of ADCT-602 in R/R B-ALL (NCT03698552) and CD22-positive hematologic cancers.
