Long-term Tumor Regression Induced by an Antibody–Drug Conjugate That Targets 5T4, an Oncofetal Antigen Expressed on Tumor-Initiating Cells

Abstract

Antibody-drug conjugates (ADC) represent a promising therapeutic modality for the clinical management of cancer. We sought to develop a novel ADC that targets 5T4, an oncofetal antigen expressed on tumorinitiating cells (TIC), which comprise the most aggressive cell population in the tumor. We optimized an anti-5T4 ADC (A1mcMMAF) by sulfydryl-based conjugation of the humanized A1 antibody to the tubulin inhibitor monomethylauristatin F (MMAF) via a maleimidocaproyl linker. A1mcMMAF exhibited potent in vivo antitumor activity in a variety of tumor models and induced long-term regressions for up to 100 days after the last dose. Strikingly, animals showed pathologic complete response in each model with doses as low as 3 mg antibody/kg dosed every 4 days. In a non-small cell lung cancer patient-derived xenograft model, in which 5T4 is preferentially expressed on the less differentiated tumor cells, A1mcMMAF treatment resulted in sustained tumor regressions and reduced TIC frequency. These results highlight the potential of ADCs that target the most aggressive cell populations within tumors, such as TICs. In exploratory safety studies, A1mcMMAF exhibited no overt toxicities when administered to cynomolgus monkeys at doses up to 10 mg antibody/kg/ cycle  2 and displayed a half-life of 5 days. The preclinical efficacy and safety data established a promising therapeutic index that supports clinical testing of A1mcMMAF. Mol Cancer Ther; 12(1); 38-47. Ó2012 AACR.

A general approach to site-specific antibody drug conjugates

“…In the low-5T4-expressing cell line, MDAMB468, A1 HC-S115pAF-NC-D1 is twofold more potent than conventional A1 mc-D1. The significant difference in the in vitro potency between 3+ (MDA MB435/5T4, cells expressing high levels of 5T4) and 2+ (MDA MB468, endogenously expressed 5T4) is likely due to different levels of 5T4 expression in the two cell lines (25).…”

A Priori Prediction of Tumor Payload Concentrations: Preclinical Case Study with an Auristatin-Based Anti-5T4 Antibody-Drug Conjugate

“…Detailed protocols to determine the affinity of mAb A1 towards 5T4 antigen and internalization rate of surface bound mAb in 5T4 expressing cell is presented in the supplementary material of (4). Briefly, Biacore® analysis was performed to determine the binding constants between A1 and 5T4 at pH 7.4.…”

“…The anti-5T4 ADC is termed A1mcMMAF and comprises the humanized anti-5T4 antibody (A1) linked to the potent microtubule-disrupting agent monomethylauristatin F (MMAF) a noncleavable maleimidocaproyl (mc) linker. A1mcMMAF has been shown to be highly potent in a variety of tumor models and did not cause any overt toxicity in nonhuman primates at comparable exposures (4). As such, A1mcMMAF is a promising clinical candidate that targets TICs, with the goal of providing long-term therapeutic benefit to patients with cancer.…”

“…There are more than 30 ADCs currently in the clinical development for the treatment of various malignant disease (3). We are developing a novel ADC that targets 5T4, an oncofetal antigen expressed on tumor initiating cells (TIC), which comprise the most aggressive cell population in the tumor (4). The anti-5T4 ADC is termed A1mcMMAF and comprises the humanized anti-5T4 antibody (A1) linked to the potent microtubule-disrupting agent monomethylauristatin F (MMAF) a noncleavable maleimidocaproyl (mc) linker.…”

Novel Anti-TM4SF1 Antibody–Drug Conjugates with Activity against Tumor Cells and Tumor Vasculature

“…Together these findings suggested that therapy could be enhanced by targeting TM4SF1 with an ADC approach. ADCs have entered the clinic and are currently used to target tumors expressing many different antigens, including CD33 (40), Her2 (41), and CD30 (42); more than 100 additional ADCs directed against different tumor cell targets populate the preclinical and clinical pipelines (43)(44)(45)(46). An ADC against a target expressed by both tumor cells and the tumor vasculature would be expected to offer exceptional therapeutic benefit.…”