ADCT-602, a Novel PBD Dimer-containing Antibody-Drug Conjugate for Treating CD22-positive Hematologic Malignancies

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.

Figure 1.

Mode-of-action studies with ADCT-602. A, Confocal microscopy images of Ramos cells treated with 2 μg/mL ADCT-602 and stained for nuclei (blue), lysosomal-associated membrane protein 1 (LAMP-1; red), and human IgG antibody (green). B, Time course of DNA interstrand crosslink formation in Ramos cells exposed to ADCT-602 or free warhead SG3199. Percentage reduction in OTM relative to untreated control in Ramos cells treated with either 10 nmol/L ADCT-602 or 10 pmol/L SG3199. For ADCT-602, the peak of DNA crosslinking occurred at around 12 hours and persisted for 48 hours. C, Histograms depicting the percentage of viable CD22-negative KARPAS-299 cells after exposure to conditioned media from Ramos cells (top) or NCI-N87 cells (bottom) treated with ADCT-602 for different days (unpaired t-test). *, Co-staining between LAMP-1 and IgG is observed as yellow. Crosslinking and bystander data are presented as the mean of at least three independent experiments. **, P < 0.05; ****, P < 0.0001. IgG, immunoglobulin G; OTM, Olive tail moment.

Figure 2.

In vivo antitumor activity of ADCT-602 in a range of xenograft models. A,In vivo antitumor activity of ADCT-602 in an subcutaneously implanted Burkitt lymphoma–derived Ramos xenograft model. ADCT-602 or an isotype-control ADC was administered intravenously at a group mean tumor volume of 116 mm³ as a single dose to treatment groups of 10 mice. A vehicle-treated group served as the control. B,In vivo antitumor activity of ADCT-602 in an subcutaneously implanted DLBCL-derived WSU-DLCL2 xenograft model. ADCT-602 or an isotype-control ADC was administered intravenously at a group mean tumor volume of 121 mm³ as a single dose to treatment groups of 10 mice. A vehicle-treated group served as the control. C,In vivo antitumor activity of ADCT-602 in a disseminated REH model. Kaplan–Meier survival plots show the percentage of animal survival over 62 days in an experiment in which ADCT-602 was administered either as a single dose of 0.45 mg/kg and 1.3 mg/kg or as multiple doses of 0.45 mg/kg Q4D × 3 and compared with the vehicle or nontargeting ADC administered as a single dose of 1.3 mg/kg (each group, n = 8). D, Lack of in vivo antitumor activity of ADCT-602 in CD22-negative KARPAS-299 ALCL xenograft. ADCT-602 was administered intravenously (day 1) to treatment groups of 8 mice. A vehicle-treated group served as the control. ADC, antibody–drug conjugate; ALCL, anaplastic large cell lymphoma; DLBCL, diffuse large B-cell lymphoma; QD, daily; Q4D, every 4 days; SC, subcutaneous(ly).

Figure 3.

Pharmacokinetics and pharmacodynamics in rats and cynomolgus monkies. A, Pharmacokinetics of ADCT-602 in rats (three in total) as measured by total antibody ECLIA, ADC (DAR ≥1) ECLIA, or total extracellular CD22-binding antibody ECLIA. B, B-cell depletion after dosing ADCT-602 in cynomolgus monkies (three in total). C, Pharmacokinetics of ADCT-602 in cynomolgus monkies as measured by the total antibody ECLIA, ADC (DAR ≥1) ECLIA, or total extracellular CD22-binding antibody ECLIA. *Indicates time of dosing. ADC, antibody–drug conjugate; DAR, drug-to-antibody ratio; ECLIA, electrochemiluminescence immunoassay; LLOQ, lower limit of quantification.

Figure 4.

Gene expression signature association analysis. Representative gene set enrichment analysis plots associated with resistance (A) to ADCT-602 [gene sets with higher expression in resistant cells (red)] and sensitivity (B) to ADCT-602 [gene sets with higher expression in sensitive cells (blue)] in B-cell lymphomas. NES, normalized enrichment score.

Figure 5.

Combination studies with ADCT-602. A, Box plots of the combination of ADCT-602 with pacritinib in eight lymphoma cell lines [four high IRAK1 expression levels resistant to ADCT-602 (red; KARPAS-422, REC1, SU-DHL-16, and TOLEDO) and four low IRAK1 expression levels sensitive to ADCT-602 (blue; FARAGE, OCI-LY-1, VAL, and SP49)]. Box plots represent the CI values obtained in individual cell lines. In each box plot, the line in the middle represents the median, and the box extends from the 25th to the 75th percentile; the whiskers extend to the upper and lower adjacent values. On the basis of the Chou–Talalay CI, the effect of the combinations was defined as synergistic (CI <0.9), additive (CI, 0.9–1.1), or antagonist (CI >1.1). CI thresholds are visualized with dotted lines. B, Cell-surface expression of CD22 following treatment with chidamide analyzed by flow cytometry in Ramos, TMD8, and SU-DHL-4 cell lines. Data represent the mean ± SE of at least two independent experiments, and they are expressed as MFI fold change (CD22 MFI chidamide/CD22 MFI DMSO). C,In vitro cytotoxicity of ADCT-602 following pretreatment with chidamide for 7 days. Data are presented as the mean IC₅₀ values of ADCT-602 from at least three independent experiments. Statistics were calculated using an unpaired t test. CI, combination index; DMSO, dimethyl sulfoxide; IC₅₀, 50% inhibitory concentration; MFI, mean fluorescence intensity.