HER2-targeted antibody-drug conjugate induces host immunity against cancer stem cells.

We previously tested HER2-targeted antibody-drug conjugates (ADCs) in immunocompromised (SCID) mice, precluding evaluation of host immunity, impact on cancer stem cells (CSCs), and potential benefit when combined with PD-L1 blockade. In this study, we tested HER2-targeted ADC in two immunocompetent mouse tumor models. HER2-targeted ADC specifically inhibited the growth of HER2-expressing tumors, prolonged animal survival, and reduced HER2+ and PD-L1+ cells. ADC + anti-PD-L1 antibody augmented therapeutic efficacy, modulated immune gene signatures, increased the number and function of CD3+ and CD19+ tumor-infiltrating lymphocytes (TILs), induced tumor antigen-specific immunological memory, stimulated B cell activation, differentiation, and IgG1 production both systemically and in the tumor microenvironment. In addition, ADC therapy modulated T cell subsets and their activation in TILs. Furthermore, HER2-targeted ADC reduced the number and tumorigenicity of ALDHhi CSCs. This study demonstrates that HER2-targeted ADC effectively targets ALDHhi CSCs and this effect is augmented by co-administration of anti-PD-L1 antibody.

A Biparatopic HER2-Targeting Antibody-Drug Conjugate Induces Tumor Regression in Primary Models Refractory to or Ineligible for HER2-Targeted Therapy.

Antibody-drug conjugate (ADC) which delivers cytotoxic drugs specifically into targeted cells through internalization and lysosomal trafficking has emerged as an effective cancer therapy. We show that a bivalent biparatopic antibody targeting two non-overlapping epitopes on HER2 can induce HER2 receptor clustering, which in turn promotes robust internalization, lysosomal trafficking, and degradation. When conjugated with a tubulysin-based microtubule inhibitor, the biparatopic ADC demonstrates superior anti-tumor activity over ado-trastuzumab emtansine (T-DM1) in tumor models representing various patient subpopulations, including T-DM1 eligible, T-DM1 ineligible, and T-DM1 relapsed/refractory. Our findings indicate that this biparatopic ADC has promising potential as an effective therapy for metastatic breast cancer and a broader patient population may benefit from this unique HER2-targeting ADC.

The CEA/CD3-bispecific antibody MEDI-565 (MT111) binds a nonlinear epitope in the full-length but not a short splice variant of CEA.

MEDI-565 (also known as MT111) is a bispecific T-cell engager (BiTE®) antibody in development for the treatment of patients with cancers expressing carcinoembryonic antigen (CEA). MEDI-565 binds CEA on cancer cells and CD3 on T cells to induce T-cell mediated killing of cancer cells. To understand the molecular basis of human CEA recognition by MEDI-565 and how polymorphisms and spliced forms of CEA may affect MEDI-565 activity, we mapped the epitope of MEDI-565 on CEA using mutagenesis and homology modeling approaches. We found that MEDI-565 recognized a conformational epitope in the A2 domain comprised of amino acids 326-349 and 388-410, with critical residues F(326), T(328), N(333), V(388), G(389), P(390), E(392), I(408), and N(410). Two non-synonymous single-nucleotide polymorphisms (SNPs) (rs10407503, rs7249230) were identified in the epitope region, but they are found at low homozygosity rates. Searching the National Center for Biotechnology Information GenBank® database, we further identified a single, previously uncharacterized mRNA splice variant of CEA that lacks a portion of the N-terminal domain, the A1 and B1 domains, and a large portion of the A2 domain. Real-time quantitative polymerase chain reaction analysis of multiple cancers showed widespread expression of full-length CEA in these tumors, with less frequent but concordant expression of the CEA splice variant. Because the epitope was largely absent from the CEA splice variant, MEDI-565 did not bind or mediate T-cell killing of cells solely expressing this form of CEA. In addition, the splice variant did not interfere with MEDI-565 binding or activity when co-expressed with full-length CEA. Thus MEDI-565 may broadly target CEA-positive tumors without regard for expression of the short splice variant of CEA. Together our data suggest that MEDI-565 activity will neither be impacted by SNPs nor by a splice variant of CEA.