PCA062, a P-cadherin Targeting Antibody-Drug Conjugate, Displays Potent Antitumor Activity Against P-cadherin-expressing Malignancies

The cell surface glycoprotein P-cadherin is highly expressed in a number of malignancies, including those arising in the epithelium of the bladder, breast, esophagus, lung, and upper aerodigestive system. PCA062 is a P-cadherin specific antibody-drug conjugate that utilizes the clinically validated SMCC-DM1 linker payload to mediate potent cytotoxicity in cell lines expressing high levels of P-cadherin in vitro, while displaying no specific activity in P-cadherin-negative cell lines. High cell surface P-cadherin is necessary, but not sufficient, to mediate PCA062 cytotoxicity. In vivo, PCA062 demonstrated high serum stability and a potent ability to induce mitotic arrest. In addition, PCA062 was efficacious in clinically relevant models of P-cadherin-expressing cancers, including breast, esophageal, and head and neck. Preclinical non-human primate toxicology studies demonstrated a favorable safety profile that supports clinical development. Genome-wide CRISPR screens reveal that expression of the multidrug-resistant gene ABCC1 and the lysosomal transporter SLC46A3 differentially impact tumor cell sensitivity to PCA062. The preclinical data presented here suggest that PCA062 may have clinical value for treating patients with multiple cancer types including basal-like breast cancer.

Abstract 2696: Genetic and pharmacologic evaluation of the ubiquitin ligase CBL-B as a small-molecule, tumor immunotherapy target

E3 ubiquitin ligases play critical roles in directing cellular protein fate by controlling the specificity of ubiquitin conjugation to substrate proteins and targeting them for cellular relocalization or degradation by the ubiquitin proteasome system. The E3 ubiquitin ligase CBL-B is expressed in immune cell lineages and negatively regulates activity of the T-cell receptor (TCR) by imposing a requirement for a costimulatory signal to mount a productive immune response upon TCR engagement. Mice deficient in Cbl-b, and more specifically in the RING Zn-finger ligase domain of Cbl-b, demonstrate a tumor rejection phenotype mediated by CD8+ T cells (Paolino et al., JI, 2011). We have reproduced these results and demonstrate that Cbl-b deficient mice show enhanced anti-tumor activity. In addition, we show that CD4+ and CD8+ T cells from mice deficient in Cbl-b have 5 to 10-fold enhanced secretion of IL-2 and IFN γ when stimulated ex vivo. These data provide a genetic rationale for the development of a small molecule inhibitor of CBL-B ligase activity for use in patients with tumor-mediated immune suppression of effector T cells.

We have identified a series of small molecule inhibitors of CBL-B activity with biochemical potency at low nanomolar concentrations. CBL-B inhibitors increased cytokine secretion in vitro at low nanomolar concentrations, as measured by IL-2 and IFN γ secretion, in primary human and mouse T cells stimulated with CD3/CD28 or CD3 alone. The compounds also stimulated proliferation and elevated levels of the T cell surface activation markers CD25 and CD69. CBL-B inhibitors enhanced an antigen recall response in human PBMCs ex vivo, as measured by approximately 5-fold higher secretion of GM-CSF, TNF-α and RANTES, and demonstrated effects in an ex vivo model of exhausted T cell function.

Oral dosing of an optimized CBL-B inhibitor enhanced anti-CD3 stimulated T cell activation in mouse CD4+ and CD8+ T cells, demonstrating a dose proportional pharmacodynamic effect. Oral administration over 28 days in the syngeneic CT-26 tumor model was well tolerated and resulted in single agent tumor growth inhibition.

These data support the continued advancement of small molecule oral CBL-B inhibitors for future development in immuno-oncology.

Citation Format: Jennifa Gosling, Ryan Rountree, Asad Taherbhoy, Chenbo Wang, Thomas Cummins, Frederick Cohen, Hiroko Tanaka, Dahlia Weiss, Mario Cardozo, Christopher Karim, May Tan, Joseph Juan, Austin Tenn-McClellan, Szerenke Kiss von Soly, Julie Sheung, Kathleen Boyle, Ketki Dhamnaskar, Katherine Kurylo, Jilliane Bruffey, Jennifer McKinnell, Dane Karr, Andria Christianson, Anne-Renee Van Der Vuurst de Vries, Pallavur Sivakumar, Mark Gallop, Paul A. Barsanti, Anjanabha Saha, Neil F. Bence, Christoph W. Zapf. Genetic and pharmacologic evaluation of the ubiquitin ligase CBL-B as a small-molecule, tumor immunotherapy target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2696.

Abstract 1682: Development and activity of a novel antibody-drug conjugate for the treatment of P-cadherin expressing cancers

The cell surface glycoprotein P-cadherin is an attractive target for an antibody-drug conjugate (ADC) therapy as it is known to be highly expressed in a number of malignancies, including those arising in the epithelium of the breast, lung, bladder, esophagus, stomach, endometrium and colon, among others. In breast cancer, P-cadherin is frequently overexpressed in high grade invasive tumors and is a reliable marker of the basal-like breast cancer molecular subtype, a disease with no effective therapeutic treatment options. Based on the expression profile of P-cadherin in human cancer, a highly selective and potent ADC was developed to target cancer types overexpressing this glycoprotein. This ADC consists of a fully human anti-P-cadherin-specific antibody conjugated to the potent maytansine-derived microtubule-disruptor, DM1, via an SMCC non-cleavable thioether linkage (technology licensed from ImmunoGen, Inc.). In vitro, the ADC was demonstrated to selectively bind P-cadherin expressing cell lines, to rapidly internalize and traffic to lysosomes, and to release a sufficient amount of activated payload to potently induce a cytotoxic response in cell viability assays. Profiling of activity in a cell line panel indicated that this ADC can effectively target and kill P-cadherin-positive cancer cells representing breast, head and neck, and bladder carcinomas. In vivo, the ADC was highly efficacious in numerous relevant xenograft models of P-cadherin expressing cancers, including breast, head and neck, bladder and lung. From this promising cellular and in vivo activity, this ADC may be an effective treatment for patients with P-cadherin positive cancers of high unmet medical need.

Citation Format: Daniel Menezes, Tinya J. Abrams, Christopher Karim, Yan Tang, Chi Ying, Kathy Miller, Christie Fanton, Majid Ghoddusi, Zhen Wang, Montesa Patawaran, Nancy Pryer, Emma Lees, Jason Damiano. Development and activity of a novel antibody-drug conjugate for the treatment of P-cadherin expressing cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1682. doi:10.1158/1538-7445.AM2015-1682

Abstract DDT02-02: Preclinical development of LFA102, a highly potent and selective neutralizing antibody against the prolactin receptor

The prolactin receptor (PRLR) is a class I cytokine receptor frequently expressed in breast and prostate cancer. The polypeptide hormone prolactin (PRL) has been demonstrated to induce PRLR signaling through the Jak/Stat, PI3-kinase/AKT and MAPK pathways, leading to cell proliferation and survival. Breast- and prostate-specific overexpression of PRL in transgenic mice leads to a higher incidence of mammary and prostate tumors, respectively. In addition, the PRLR locus is the site of frequent viral integrations in MMTV-derived mammary tumors. Elevated serum PRL levels in humans have been correlated with an increased risk for breast cancer, and an analysis of more than 3000 breast tumor specimens indicates that PRLR is expressed with high prevalence (60-70% of tumors) across all breast cancer subtypes. In prostate cancer specimens, the presence of prolactin and phosphorylated Stat5 have been reported to be associated with high-grade tumors and poor clinical outcomes, suggesting a role of the PRL/PRLR signaling pathway in the pathology of this disease as well. All of these lines of evidence support the hypothesis that targeting the PRL/PRLR axis may be a new approach for addressing unmet medical need in these tumor types. LFA102 is a Human Engineered™ anti-PRLR antibody of the IgG1 isotype that neutralizes the function of PRLR through a nonligand competitive binding interaction. LFA102 blocks PRL-induced signaling and proliferation in T47D and MCF7 human breast cancer cells in vitro, and abolishes PRL-induced phospho-Stat5 signaling in T47D xenograft tumors in vivo. This antibody also cross-reacts with and neutralizes rat PRLR and is capable of potently regressing PRL-dependent Nb2-C11 pre-T cell lymphoma tumors in vivo. In vitro studies have shown that LFA102 can mediate antibody-dependent cellular cytotoxicity (ADCC) and inhibit the PRL-dependent release of the proangiogenic factor VEGF from breast cancer cells. Thus, there are multiple potential mechanisms through which LFA102 could show antitumor activity in vivo. Preclinical toxicological studies of LFA102 indicate that this therapeutic is well tolerated and exhibits a normal pharmacokinetic profile in relevant animal species. The safety and pharmacokinetics of LFA102 in humans are currently being evaluated in a phase I healthy volunteer trial. A phase 1b trial in breast and prostate cancer is planned to evaluate the efficacy of this antibody in patient populations predicted to have the highest probability of benefiting from an anti-PRLR therapeutic. This presentation will provide a summary of the preclinical data supporting the clinical development of LFA102.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr DDT02-02. doi:10.1158/1538-7445.AM2011-DDT02-02

Mapping the interaction surface of a membrane protein: unveiling the conformational switch of phospholamban in calcium pump regulation

We have used magnetic resonance to map the interaction surface of an integral membrane protein for its regulatory target, an integral membrane enzyme. Phospholamban (PLN) regulates cardiac contractility via its modulation of sarco(endo)plasmic reticulum calcium ATPase (SERCA) activity. Impairment of this regulatory process causes heart failure. To map the molecular details of the PLN/SERCA interaction, we have functionally reconstituted SERCA with labeled PLN in dodecylphosphocholine micelles for high-resolution NMR spectroscopy and in both micelles and lipid bilayers for EPR spectroscopy. Differential perturbations in NMR linewidths and chemical shifts, measured as a function of position in the PLN sequence, provide a vivid picture of extensive SERCA contacts in both cytoplasmic and transmembrane domains of PLN and provide structural insight into previously reported functional mutagenesis data. NMR and EPR data show clear and complementary evidence for a dynamic (micros-to-ms) equilibrium between two conformational states in the cytoplasmic domain of PLN. These results support the hypothesis that SERCA attracts the cytoplasmic domain of PLN away from the lipid surface, shifting the preexisting equilibrium of PLN conformers toward a structure that is poised to interact with the regulatory target. EPR shows that this conformational switch behaves similarly in micelles and lipid membranes. Based on structural and dynamics data, we propose a model in which PLN undergoes allosteric activation upon encountering SERCA.

Interaction of glyceraldehyde-3-phosphate dehydrogenase with AMP as studied by means of a spin-labeled analog

The binding of a spin-labeled AMP analog to tetrameric glyceraldehyde-3-phosphate dehydrogenase from rabbit muscle is described. The spin label, perdeuterated and 15N-substituted 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, was attached to C-8 of AMP (C8-SL-AMP). Up to 8 equivalents of C8-SL-AMP bind per enzyme tetramer, i.e., 2 per monomer. Combining sites are the adenine subsite of the coenzyme-binding domain and the phosphate site. Glyceraldehyde 3-phosphate causes a conformational change in the enzyme that brings C8-SL-AMP molecules bound to adjacent R-axis-related subunits closer to one another by 0.2-0.3 nm and allows for spin-spin interaction between the nitroxide radicals. Similar, but less pronounced structural changes take place upon lowering the pH from 8 to 7. Addition of a single equivalent of NAD+ to a complex of the enzyme with 7.6 equivalents of C8-SL-AMP leads to the release of almost 4 C8-SL-AMP molecules. This supports our previous findings that binding of just one NAD+ molecule induces conformational changes in all four subunits.