Abstract 822: Thienoindoles, a novel class of DNA minor groove alkylating agents highly suited for the generation of novel antibody drug conjugates (ADCs)

Abstract

Abstract The rapidly growing field of Antibody-Drug Conjugates (ADCs) has recently spurred the study of novel drug payloads. In particular, much interest has been paid to the identification of novel cytotoxic agents, which differ in mechanism from anti-tubulin agents, currently the most commonly employed class of drug for ADC coupling. Novel drug payloads for ADC-based therapy should thus ideally possess highly potent cytotoxic activity with a diverse mechanism from tubulin agents, as well as physicochemical properties, which facilitate coupling to antibodies. Duocarmycins are a widely-described class of DNA minor groove binding alkylating agents, examples of which can exhibit picomolar activity against human tumor cell lines, as well as high activity in preclinical tumor models. The clinical development of duocarmycins as drugs in their own right has however been hampered by an extremely limited therapeutic window. Duocarmycins also typically exhibit poor physicochemical profiles, most importantly generally possessing limited aqueous solubility and a propensity to induce protein aggregation, which renders these molecules poorly tractable as optimal ADC payloads. Based on the premise that opportune modification of the duocarmycin scaffold could lead to the discovery of compounds better suited to antibody conjugation, we describe the identification and related proof of concept studies for a novel chemical series based on a proprietary thienoindole scaffold, characterized both by potent antitumor activity and by physicochemical properties that are highly compatible with deployment as antibody payloads. Extensive in vitro profiling within the thienoindole series led to selection of potent cytotoxic compounds suitable for test conjugation to humanized monoclonal antibodies, which were then submitted to in vitro/in vivo profiling. Typically, average drug/antibody ratios (DARs) of 4 could readily be achieved without induction of antibody aggregation/precipitation and without affecting natural antibody-ligand affinity. Efficacy and mechanism of action studies were carried out for thienoindole-ADCs prepared with trastuzumab and with rituximab showing target driven effects in Her2 positive vs. negative breast cancer cell lines and against CD20 positive vs. negative hematological cell lines. PK data indicated long, essentially unaffected plasma half life of our novel ADCs in the mouse. In vivo efficacy studies in the Her2-positive HCC1954 human breast cancer model showed complete tumor regression in mice treated with trastuzumab-ADC with no effects on body weight gain, while unarmed trastuzumab and armed control antibody had little and no effect, respectively. Citation Format: Barbara Valsasina, Fabio Gasparri, Italo Beria, Nicoletta Colombo, Paolo Orsini, Rita Perego, Simona Rizzi, Ulisse Cucchi, Clara Albanese, Aurelio Marsiglio, Ivan Fraietta, Marina Ciomei, Sabrina Cribioli, Carlo Visco, Eduard R. Felder, Antonella Isacchi, Enrico A. Pesenti, Arturo Galvani, Daniele Donati, Michele Caruso. Thienoindoles, a novel class of DNA minor groove alkylating agents highly suited for the generation of novel antibody drug conjugates (ADCs). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 822. doi:10.1158/1538-7445.AM2014-822