ABBV-011, A Novel, Calicheamicin-Based Antibody-Drug Conjugate, Targets SEZ6 to Eradicate Small Cell Lung Cancer Tumors

Abstract

In the past year, four antibody-drug conjugates (ADC) were approved, nearly doubling the marketed ADCs in oncology. Among other attributes, successful ADCs optimize targeting antibody, conjugation chemistry, and payload mechanism of action. Here, we describe the development of ABBV-011, a novel SEZ6-targeted, calicheamicin-based ADC for the treatment of small cell lung cancer (SCLC). We engineered a calicheamicin conjugate that lacks the acid-labile hydrazine linker that leads to systemic release of a toxic catabolite. We then screened a patient-derived xenograft library to identify SCLC as a tumor type with enhanced sensitivity to calicheamicin ADCs. Using RNA sequencing (RNA-seq) data from primary and xenograft SCLC samples, we identified seizure-related homolog 6 (SEZ6) as a surface-expressed SCLC target with broad expression in SCLC and minimal normal tissue expression by both RNA-seq and IHC. We developed an antibody targeting SEZ6 that is rapidly internalized upon receptor binding and, when conjugated to the calicheamicin linker drug, drives potent tumor regression in vitro and in vivo. These preclinical data suggest that ABBV-011 may provide a novel treatment for patients with SCLC and a rationale for ongoing phase I studies (NCT03639194).

Figure 1.

A, Modified linker drug chemistry in LD19.10 to eliminate toxic DMZ catabolite from calicheamicin linker drug. Chemical structure and metabolic pathway for the 19.10 linker drug in ABBV-011 compared with the acid-labile linker drug used in clinically approved calicheamicin-based ADCs. B, RNA expression of ubiquitously expressed surface antigen CD46 across PDX of varying indications by microarray analysis. C, PDX tumor response to a single dose of anti-CD46 antibody conjugated to LD19.10 calicheamicin linker drug in murine tumor models derived from multiple tumor indications. Animals were dosed with 2 (SCLC PDX top half-filled circles), 4 (SCLC PDX filled circles), or 8 mg/kg (all others) as indicated.

Figure 2.

SEZ6 is expressed in NE SCLC with minimal expression in normal tissues. A, Comparison of pairwise Pearson correlation between CHGA and all cell surface markers in PDX setting (y-axis) and in human primary setting combined across three published human cohorts (refs. ; x-axis). B, Microarray data (Affymetrix Clariom D platform) of PDX shows SEZ6 expression is high in SCLC PDX, but low in normal tissues and other cancers. C, SEZ6 had upregulated expression in human SCLC tumors (n = 79) compared with the normal reference (n = 7) from the SCLC79 cohort (16). D, Hierarchical clustering with Euclidean distance and Ward linkage on expression of genes of interest in the Ucologne cohort (15).

Figure 3.

SEZ6 is expressed in primary SCLC samples by IHC. A, Representative images of SEZ6 IHC analysis of primary human SCLC tumor samples with a range of target expression (from left to right: sez6 negative, weakly positive, moderately positive, and strongly positive). Arrows indicate areas of brown SEZ6 staining, with arrow heads indicating specific membranous staining. B, Quantitative analysis of percent positivity (left) and H-score (right) across 73 primary human SCLC samples. Scatter plot indicates distribution, and horizontal bar indicates mean. C, Representative images of SEZ6 IHC staining across normal human tissues. Arrows indicate staining in parasympathetic ganglia of the large intestine.

Figure 4.

SC17 is a SEZ6-specific antibody that internalizes when bound to SEZ6 on the surface of SCLC cells. A, Parental 293T and 293T cells overexpressing human SEZ6, H69 cells and SEZ6 KO H69 cells, and SCLC PDX models, LU149, LU64, LU95, and LU505, were stained with SC17 or control IgG antibody conjugated to the fluorophore PE. Specific SEZ6 cell surface staining is observed with SC17-PE but not with IgG-PE in 293T cells overexpressing SEZ6, in naïve H69 cells, and in the two SCLC PDX models. B, Time course fluorescence microscopy with SC17-A647 in A549 cells engineered to express human SEZ6 and lysosomal protein LAMP1 fused to mRUBY (red signal). At time 0, SC17 localized to the outer membrane of the cell (green signal). After a 4-hour incubation period, we observed strong intracellular staining of SC17-A647 and colocalization with lysosomes (yellow signal). C, Time course quantitation of the lysosomal colocalization of SC17-A647 compared with CD46-A647 and IgG-A647 (negative control).

Figure 5.

ABBV-011 potently and selectively kills SEZ6-positive cells in vitro. A, Schematic depiction of the ABBV-011 ADC. ABBV-011 consists of mAb SC17 conjugated to two molecules of LD19.10 linker drug (DAR2). B, 293T-SEZ6 cells were exposed to increasing concentrations of ABBV-011, nontargeted control ADC, unconjugated SC17 antibody targeting SEZ6, a nontargeted control antibody, or free calicheamicin. Percentage of live cells was determined by a luminometric viability assay. C, Parental NCI-H69 cells and SEZ6-KO NCI-H69 cells were exposed to increasing concentrations of ABBV-011 or nontargeted control ADC. Percentage of live cells was determined by a luminometric viability assay.

Figure 6.

ABBV-011 induces dose-dependent tumor regression in SEZ6-positive SCLC PDX models. Antitumor activity in SEZ6-positive LU64 (A), LU95 (B), and LU149 (C) SCLC PDX models when mice are treated with indicated doses of ABBV-011 (red), cisplatin + etoposide (blue), or controls (gray). D, Lack of antitumor response in SEZ6-negative LU505 SCLC PDX. Mice treated with ABBV-011 (red), cisplatin + etoposide (blue), or CD46-targeted calicheamicin ADC (black).