Abstract A149: NMS-P945, a highly active payload for antibody drug conjugates generation

Antibody-drug conjugates (ADCs) are increasingly employed in different oncology settings with more than forty products in clinical evaluation at present, and two approved drugs, ado-trastuzumab emtansine and brentuximab vedotin, respectively targeting Her2 and CD30 positive tumors. Although many different antibody targets have been so far considered for this approach, only a handful of toxins have been exploited, and more than 50% of ADCs result to be conjugated to two well known tubulin binding agents, auristatin and maitansine. New toxins with a different cellular mechanism of action, possibly acting also on quiescent or slowly proliferating cells, are thus strongly needed. Duocarmycins, classical DNA minor groove alkylating agents, were studied in clinical trials as chemotherapy drugs in the nineties, but were abandoned few years later due to the poor therapeutic index of the free drugs. In this context we approached a new proprietary class of thienoindole duocarmycins derivatives as novel promising toxins for ADC generation. Here we describe the identification and related proof of concept studies for this novel chemical series, characterized by both potent antitumor activity and physicochemical properties highly compatible with deployment as antibody payloads. Extensive in vitro profiling within the thienoindole series led to the selection of a potent cytotoxic compound suitable for conjugation to humanized monoclonal antibodies upon introduction of a linker moiety (NMS-P945). Efficacy and mechanism of action studies were carried out for NMS-P945-ADCs prepared with trastuzumab showing target-directed and target-enhanced (“bystander”) cytotoxicity in Her2 positive vs. negative cancer cell lines. In vitro and in vivo activity of NMS-P945-ADC is strictly correlated to the target presence, the internalization and the lysosomal digestion of the ADC inside the tumor cells. In addition we generated and validated selective antidrug antibodies and using this tool we followed the fate of the toxin upon release from the ADC clearly showing chromatin localization, as expected for duocarmycin based molecules. In animal efficacy studies against a Her2-positive human breast cancer model, trastuzumab-NMS-P945 ADC administration yielded complete tumor regression in treated mice, with no effects on body weight gain, while unarmed trastuzumab and armed control antibody showed little and no effect, respectively. These results support further development of NMS-P945 as a new interesting payload for conjugation with targeted antibodies. Citation Format: Fabio Gasparri, Michele Caruso, Italo Beria, Nicoletta Colombo, Paolo Orsini, Rita Perego, Simona Rizzi, Ulisse Cucchi, Sonia Troiani, Federico Riccardi Sirtori, Clara Albanese, Aurelio Marsiglio, Ivan Fraietta, Francesco Sola, Marina Ciomei, Sabrina Cribioli, Carlo Visco, Eduard Rudolf Felder, Antonella Isacchi, Enrico Pesenti, Arturo Galvani, Daniele Donati, Barbara Valsasina. NMS-P945, a highly active payload for antibody drug conjugates generation. [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 A149.