Pamela Trail

Therapeutic Mechanism and Efficacy of the Antibody Drug-Conjugate BAY 79-4620 Targeting Human Carbonic Anhydrase 9

Carbonic anhydrase IX (CAIX) is a cell surface glycoprotein that is expressed in many different tumors and yet restricted in normal tissues to the gastrointestinal tract. It is upregulated by hypoxia and correlates with tumor grade and poor survival in several tumor indications. Monoclonal antibodies (mAb) with single digit nanomolar binding affinity for CAIX were derived by panning with the recombinant ectodomain of CAIX against the MorphoSys HUCAL Gold library of human Fabs. Highest affinity Fabs were converted to full-length IgGs and subjected to further characterization based upon their avidity and selectivity for CAIX, their capacity to undergo internalization in CAIX-expressing cell lines, and their selective localization to CAIX-positive human xenografted tumors when administered to mice as fluorescent conjugates. Through this selection process, the 3ee9 mAb was identified, which upon conjugation to monomethyl auristatin E through a self-immolative enzyme-cleavable linker yielded the potent and selective CAIX antibody–drug conjugate CAIX-ADC (BAY 79-4620). In preclinical human xenograft models in mice representing several tumor indications, BAY 79-4620 showed potent antitumor efficacy and in some models showed partial and complete tumor shrinkage even following a single dose. The mechanism of action was shown by histology to involve the sequelae of events typical of antitubulin agents. Efficacy in murine preclinical models correlated semiquantitatively, with CAIX expression levels as determined by immunohistochemistry and ELISA. These preclinical data collectively support the development of BAY 79-4620 for the treatment of cancer patients with CAIX overexpressing tumors. Mol Cancer Ther; 11(2); 340–9. ©2011 AACR.

Antibody Drug Conjugates for Treatment of Breast Cancer: Novel Targets and Diverse Approaches in ADC Design.

Breast cancer is a heterogeneous group of malignancies with a spectrum of molecular subtypes, pathologies and outcomes that together comprise the most common non-cutaneous cancer in women. Currently, over 80% of breast cancer patients are diagnosed at relatively early stages of disease where there are encouraging data on outcomes and long term survival. However, there is currently no curative option for those patients with metastatic disease and there is a substantial medical need to identify effective and safe treatment options for these patients. One approach to improve cancer therapy is by designing therapeutics directed against targets with differential levels of expression on malignant versus normal cells with the goal of improving tumor selectivity and reducing damage to normal tissues. Antibody drug conjugates (ADCs) are a rapidly evolving therapeutic class that exploits the target-selectivity of monoclonal antibodies (MAbs) to deliver cytotoxic drugs to antigen-expressing cells (Lambert & Morris, 2017; Senter, 2009; Thomas, Teicher, & Hassan, 2016; Trail, 2013). The regulatory approval of ADCs for both hematologic malignancies (brentuximab vedotin) (Younes et al., 2010) and solid tumors (ado-trastuzumab emtansine) (Amiri-Kordestani et al., 2014; Verma et al., 2012) clearly demonstrates the clinical potential of ADCs. This review will focus on targets under consideration for breast cancer directed ADCs and on the technology modifications being considered to improve ADC efficacy and safety.

A phase I first-in-human study of Nesvacumab (REGN910), a fully-human anti-Angiopoietin-2 (Ang2) monoclonal antibody, in patients with advanced solid tumors.

Purpose: Nesvacumab (REGN910) is a fully human immunoglobulin G1 (IgG1) monoclonal antibody that specifically binds and inactivates the Tie2 receptor ligand Ang2 with high affinity, but shows no binding to Ang1. The main objectives of this trial were to determine the safety, tolerability, dose-limiting toxicities (DLT), and recommended phase II dose (RP2D) of nesvacumab. Experimental Design: Nesvacumab was administered intravenously every two weeks with dose escalations from 1 to 20 mg/kg in patients with advanced solid tumors. Results: A total of 47 patients were treated with nesvacumab. No patients in the dose escalation phase experienced DLTs, therefore a maximum tolerated dose (MTD) was not reached. The most common nesvacumab-related adverse events were fatigue (23.4%), peripheral edema (21.3%), decreased appetite, and diarrhea (each 10.6%; all grade ≤ 2). Nesvacumab was characterized by linear kinetics and had a terminal half-life of 6.35 to 9.66 days in a dose-independent manner. Best response by RECIST 1.1 in 43 evaluable patients included 1 partial response (adrenocortical carcinoma) of 24 weeks duration. Two patients with hepatocellular carcinoma had stable disease (SD) > 16 weeks, with tumor regression and >50% decrease in α-fetoprotein. Analyses of putative angiogenesis biomarkers in serum and tumor biopsies were uninformative for treatment duration. Conclusions: Nesvacumab safety profile was acceptable at all dose levels tested. Preliminary antitumor activity was observed in patients with treatment-refractory advanced solid tumors. On the basis of cumulative safety, antitumor activity, pharmacokinetic and pharmacodynamic data, the 20 mg/kg dose was determined to be the RP2D. Clin Cancer Res; 22(6); 1348–55. ©2015 AACR.

Antibody Directed Delivery for Treatment of Cancer: Antibody Drug Conjugates and Immunotoxins

A major goal in the development of cancer therapeutics is to identify agents that will effectively eradicate tumors while having minimal effects on cells of normal tissues. Unfortunately, the majority of anticancer agents developed to date have substantial side effect profiles and a narrow therapeutic index. One means to improve the selectivity and efficacy of cancer therapy is by choosing therapeutic targets with altered levels of expression on malignant versus normal cells. Following the introduction of monoclonal antibody (MAb) technology by Kohler and Milstein (Nature 256:495–497, 1975), the potential to utilize the antigen-selectivity of MAbs to deliver toxic agents initiated an extensive effort to design antibody-targeted therapeutics. The clinical utility of MAb-based therapeutics was substantially improved by both the chimerization and humanization of murine MAbs, both of which substantially reduced immunogenicity and improved MAb half-life. The ability to obtain fully human MAbs from transgenic mice and by phage display has further enhanced the clinical potential of these approaches (Nat Rev Immunol 6:343–357, 2006; Expert Opin Investig Drugs 7:607–614, 1998; Nat Biotechnol 23:1117–1125, 2005). Monoclonal antibodies and fragments of MAbs have been used to effectively deliver radionuclides (Hosp Pract (Minneap) 38:82–93, 2010; Clin Cancer Res 17:6406–6416, 2011), cytokines (Integr Biol (Camb) 3:468–478, 2011; Int J Cancer 102:109–116, 2002), plant and bacterial toxins (FEBS J 278:4683–4700, 2011; Expert Opin Drug Deliv 8:605–621, 2011; Drug Discov Today 16:495–503, 2011), and a variety of cytotoxic drugs (Nat Biotechnol 21:778–784, 2003; Cancer Res 53:3336–3342, 1993; Expert Opin Investig Drugs 6:169–172, 1997; Science 261:212–215, 1993). Although simple in concept, the design of effective targeting agents has required substantial investigation and modification in the selection of MAbs and their targets, the types of linkers used, and the potency of the toxic agents that are delivered. This chapter focuses on MAb-directed delivery of plant and bacterial toxins (immunotoxins) and MAb-directed delivery of cytotoxic drugs (antibody–drug conjugates: ADCs).

Abstract C126: PRLR ADC: A novel antibody drug-conjugate for the treatment of PRLR positive breast cancer

Breast cancer is a heterogeneous disease comprised of various subtypes based on pathology and molecular profiling. Expression of hormone receptors (HR) and HER2 biomarkers are important determinants of therapy choice, due to the established role of these proteins as drivers of disease. Prolactin Receptor (PRLR) is a type 1 cytokine receptor that is expressed on a subset of breast cancers and may contribute to pathogenesis. Functionally, activation of PRLR by the hormone ligand Prolactin (PRL) induces PRLR dimerization and signaling resulting in cell proliferation and differentiation. While PRLR is expressed at low levels in some normal human tissues including the mammary gland, it is relatively overexpressed in ∼25% of human breast tumors and importantly, is rapidly internalized upon binding of anti-PRLR antibodies. We developed an anti-PRLR antibody-drug conjugate (ADC), PRLR ADC, to target PRLR positive breast cancer. PRLR ADC is comprised of a fully human high affinity function-blocking anti-PRLR IgG1 antibody conjugated via a non-cleavable SMCC linker to the cytotoxic maytansine derivative DM1. Both unconjugated anti-PRLR antibody and the PRLR ADC block PRL mediated activation in vitro and induce rapid internalization of the receptor into lysosomes. PRLR ADC induces potent cell cycle arrest and cytotoxicity in several PRLR-expressing cell lines. The in vivo efficacy of PRLR ADC was explored in breast cancer cell line xenograft models expressing both endogenous PRLR (MCF7, T47D) or transfected receptor (MCF7/PRLR). Treatment of tumor bearing SCID (T47D) or NCr Nude (MCF7) animals was initiated approximately 15 days post implantation of cells where tumor volumes averaged 150-200 mm3. In both T47D and MCF7/PRLR xenograft models, where PRLR is expressed highly, single or multiple (once weekly x 3) doses of 2.5-15 mg/kg resulted in significant inhibition of tumor xenograft growth. In the MCF7 model that expresses low levels of PRLR, inhibition and regression of tumors was observed at 10 and 15 mg/kg dose levels. In all models, higher doses resulted in greater and more prolonged repression of tumor growth. Conjugation of DM1 to anti-PRLR antibody was required for efficacy, as unconjugated antibody had no effect on tumor growth. Anti-tumor efficacy of PRLR ADC was also assessed in NSG mice bearing breast cancer Patient Derived Xenograft (PDXs) tumors with moderate and heterogeneous expression of PRLR. Treatment was initiated 21 days after implantation of the PDX tumors where the average tumor volume was ∼500mm3. Anti-tumor efficacy was observed following 10 or 20 mg/kg PRLR ADC dosed once weekly x 4. These studies demonstrate the promising anti-tumor activity of the PRLR ADC against PRLR positive breast cancers and support the continued development of this agent. Citation Format: Marcus P. Kelly, Sandra Coetzee, Carlos Hickey, Sosina Makonnen, Frank Delfino, Julian Andreev, Arthur Kunz, Christopher D9Souza, Jason Giurleo, Thomas Nittoli, Pamela A. Trail, Nicholas Papadopoulos, Gavin Thurston, Jessica R. Kirshner. PRLR ADC: A novel antibody drug-conjugate for the treatment of PRLR positive breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C126.