No abstract

Aldehyde drugs are gaining increasing research interest, considering that aldehyde dehydrogenases overexpression is characteristic of cancer stem cells. Here, we describe the traceless site-specific coupling of a novel potent drug, containing an aldehyde moiety, to recombinant antibodies, which were engineered to display a cysteine residue at their N-terminus, or a 1,2-aminothiol at their C-terminus. The resulting chemically defined antibody-drug conjugates represent the first example in which a thiazolidine linkage is used for the targeted delivery and release of cytotoxic agents.

Conventional cancer chemotherapy heavily relies on the use of cytotoxic agents, which typically do not preferentially localize at the tumor site and cause toxicity to normal organs, preventing dose escalation to therapeutically active regimens. In principle, antibodies and other ligands could be used for the selective pharmacodelivery of cytotoxic agents to the neoplastic mass. For many years, the availability of ligands, capable of selective internalization into tumor cells, has been considered to be an essential requirement for the development of targeted cytotoxics. This assumption, however, has recently been challenged on the basis of therapeutic data obtained with noninternalizing drug conjugates. Moreover, quantitative evaluations of the tumor targeting properties of antibodies and of small organic ligands have provided new insights for the implementation of optimal strategies for the development of targeted cytotoxics. In this article, we highlight opportunities and challenges associated with the clinical and industrial development of antibody-drug conjugates and small molecule-drug conjugates for cancer therapy.

It is generally thought that the anticancer efficacy of antibody-drug conjugates (ADC) relies on their internalization by cancer cells. However, recent work on an ADC that targets fibronectin in the tumor microenvironment suggests this may not be necessary. The alternatively spliced extra domains A and B (EDA and EDB) of fibronectin offer appealing targets for ADC development, because the antigen is strongly expressed in many solid human tumors and nearly undetectable in normal tissues except for the female reproductive system. In this study, we describe the properties of a set of ADCs based on an antibody targeting the alternatively spliced EDA of fibronectin coupled to one of a set of potent cytotoxic drugs (DM1 or one of two duocarmycin derivatives). The DM1 conjugate SIP(F8)-SS-DM1 mediated potent antitumor activity in mice bearing DM1-sensitive F9 tumors but not DM1-insensitive CT26 tumors. Quantitative biodistribution studies and microscopic analyses confirmed a preferential accumulation of SIP(F8)-SS-DM1 in the subendothelial extracellular matrix of tumors, similar to the pattern observed for unmodified antibody. Notably, we found that treatments were well tolerated at efficacious doses that were fully curative and compatible with pharmaceutical development. Our findings offer a preclinical proof-of-concept for curative ADC targeting the tumor microenvironment that do not rely upon antigen internalization. Cancer Res; 74(9); 2569-78. Ó2014 AACR.