Tsuguo Kubota

Engineered therapeutic antibodies with improved effector functions

In the past decade, more than 20 therapeutic antibodies have been approved for clinical use and many others are now at the clinical and preclinical stage of development. Fragment crystallizable (Fc)‐dependent antibody functions, such as antibody‐dependent cell‐mediated cytotoxicity (ADCC), complement‐dependent cytotoxicity (CDC), and a long half‐life, have been suggested as important clinical mechanisms of therapeutic antibodies. These functions are primarily triggered through direct interaction of the Fc domain with its corresponding receptors: FcγRIIIa for ADCC, C1q for CDC, and neonatal Fc receptor for prolongation of the clearance rate. However, current antibody therapy still faces the critical issues of insufficient efficacy and the high cost of the therapeutic agents. A possible solution to these issues could be to engineer antibody molecules to enhance their antitumor activity, leading to improved therapeutic outcomes and reduced doses. Here, we review advanced Fc engineering approaches for the enhancement of effector functions, some of which are now ready for evaluation of their effectiveness in clinical trials. (Cancer Sci 2009; 100: 1566–1572)

Generation and Improvement of Effector Function of a Novel Broadly Reactive and Protective Monoclonal Antibody against Pneumococcal Surface Protein A of Streptococcus pneumoniae.

A proof-of-concept study evaluating the potential of Streptococcus pneumoniae Pneumococcal Surface Protein A (PspA) as a passive immunization target was conducted. We describe the generation and isolation of several broadly reactive mouse anti-PspA monoclonal antibodies (mAbs). MAb 140H1 displayed (i) 98% strain coverage, (ii) activity in complement deposition and opsonophagocytic killing (OPK) assays, which are thought to predict the in vivo efficacy of anti-pneumococcal mAbs, (iii) efficacy in mouse sepsis models both alone and in combination with standard-of-care antibiotics, and (iv) therapeutic activity in a mouse pneumonia model. Moreover, we demonstrate that antibody engineering can significantly enhance anti-PspA mAb effector function. We believe that PspA has promising potential as a target for the therapy of invasive pneumococcal disease by mAbs, which could be used alone or in conjunction with standard-of-care antibiotics.

Potent Therapeutic Activity Against Peritoneal Dissemination and Malignant Ascites by the Novel Anti-Folate Receptor Alpha Antibody KHK2805

Many ovarian cancer patients often show peritoneal metastasis with malignant ascites. However, unmet medical needs remain regarding controlling these symptoms after tumors become resistant to chemotherapies. We developed KHK2805, a novel anti-folate receptor α (FOLR1) humanized antibody with enhanced antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). The primary aim of the present study was to evaluate whether the anti-tumor activity of KHK2805 was sufficient for therapeutic application against peritoneal dissemination and malignant ascites of platinum-resistant ovarian cancer in preclinical models. Here, both the ADCC and CDC of KHK2805 were evaluated in ovarian cancer cell lines and patient-derived samples. The anti-tumor activity of KHK2805 was evaluated in a SCID mouse model of platinum-resistant peritoneal dissemination. As results, KHK2805 showed specific binding to FOLR1 with high affinity at a novel epitope. KHK2805 exerted potent ADCC and CDC against ovarian cancer cell lines. Furthermore, primary platinum-resistant malignant ascites cells were susceptible to autologous ADCC with KHK2805. Patient-derived sera and malignant ascites induced CDC of KHK2805. KHK2805 significantly reduced the total tumor burden and amount of ascites in SCID mice with peritoneal dissemination and significantly prolonged their survival. In addition, the parental rat antibody strongly stained serous and clear cell-type ovarian tumors by immunohistochemistry. Overall, KHK2805 showed cytotoxicity against both ovarian cancer cell lines and patient-derived cells. These translational study findings suggest that KHK2805 may be promising as a novel therapeutic agent for platinum-resistant ovarian cancer with peritoneal dissemination and malignant ascites.

Abstract C123: A novel anti-FOLR1 antibody developed with AccretaMab® technology, KHK2805, exhibits markedly high ADCC/CDC activity and a tolerable safety profile in preclinical models

Introduction: Folate receptor alpha (FOLR1) is a member of the folate transporter family expressed on normal tissues and overexpressed in multiple types of tumors, such as ovarian cancer, uterine cancer, non-small cell lung cancer, gastric cancer, breast cancer and kidney cancer. Currently, several clinical trials of FOLR1-targeting drugs [conventional IgG1 antibodies, which exhibit antibody-dependent cellular cytotoxicity/complement-dependent cytotoxicity (ADCC/CDC) activities, folic acid or antibody-drug conjugates and vaccines] have been conducted for ovarian and lung cancer. Therefore, FOLR1 is a remarkable target for cancer therapy under ongoing investigation. AccretaMab® technology involves combining both the POTELLIGENT®, a clinically validated ADCC-enhanced technology, and COMPLEGENT®, a new CDC-enhanced technology, systems to result in a superior technology for enhancing the killing activity of antibodies. KHK2805 is a novel humanized and CDR-altered anti-FOLR1 antibody developed with AccretaMab® technology. In this study, we evaluated the anti-cancer activity of KHK2805 in preclinical ovarian cancer models, both in vitro and in vivo, and confirmed the safety profile of KHK2805 in cynomolgus monkeys, since KHK2805 cross-reacts to cynomolgus monkey FOLR1. Materials and Methods: The binding kinetics of KHK2805 against recombinant FOLR1 (rFOLR1) were measured using the Biacore system. The epitope was determined with an ELISA against rFOLR1s. The in vitro ADCC and CDC activities against FOLR1-positive ovarian cancer cells were evaluated using PBMCs and serum from healthy volunteers. The in vivo anti-tumor activity of KHK2805 was examined using a SCID mouse model. The safety profile of KHK2805 was evaluated in cynomolgus monkeys. Results: KHK2805 induced potent ADCC and CDC activities against FOLR1-positive ovarian cancer cells. The ADCC activity of KHK2805 was significantly higher than that of the conventional anti-FOLR1 antibody. Furthermore, KHK2805 showed a potent ADCC activity against ovarian cancer cells with a low FOLR1 expression or low folic acid-uptake activity, which may be difficult to target with current FOLR1-targeting drugs. The results also showed that the markedly higher ADCC activity of KHK2805 was caused by its super-high affinity, unique epitope and use of AccretaMab® technology. In addition, the CDC activity of KHK2805 was also clearly higher than that of the conventional anti-FOLR1 antibody. This indicates that the higher CDC activity of KHK2805 is due to the application of protein engineering of CDR alterations and AccretaMab® technology. Moreover, the potent anti-tumor activity of KHK2805 was observed in a peritoneal dissemination model in SCID mice. Finally, we completed preliminary safety experiments with KHK2805. A repeated-dose toxicity study of KHK2805 (weekly 100 mg/kg for 4 weeks, intravenously) showed an acceptable tolerability profile in cynomolgus monkeys. Conclusions: KHK2805 may be a promising novel anti-FOLR1 therapeutic agent with a potent anti-tumor activity and tolerable safety profile for patients with the FOLR1 expression. Citation Format: Munetoshi Ando, Keiko Nagata, Hiroshi Ando, Mariko Nakano, Naoya Kameyama, Tsuguo Kubota, Maiko Adachi, Yui Suzuki, Kazuyasu Nakamura, Toshihiko Ishii, Ryuichiro Nakai, Takeshi Takahashi. A novel anti-FOLR1 antibody developed with AccretaMab® technology, KHK2805, exhibits markedly high ADCC/CDC activity and a tolerable safety profile in preclinical models. [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 C123.