Synthesis and preliminary cytotoxicity study of a cephalosporin-CC-1065 analogue prodrug

A CC-1065 analogue was conjugated to a cephalosporin affording prodrug 2. The prodrug and its corresponding free drug, 1, have IC50 values of 0.9 and 0.09 nM, respectively, against U937 leukemia cells in vitro.For the first time, a prodrug comprised of a cephalosporin and a CC-1065 analogue has been synthesized. The preliminary in vitro studies show that the prodrug was 10-fold less toxic than the free drug. Prodrug 2 has the potential to be useful in cancer treatment using the ADEPT approach.Antibody-directed enzyme prodrug therapy (ADEPT) [1-5] is one of the promising new approaches that selectively target tumor cells, thus reducing toxic side effects to patients. In this approach, an enzyme is conjugated to a tumor-specific antibody. The antibody selectively localizes the enzyme to the tumor cell surface. Subsequent administration of a prodrug substrate of the enzyme leads to the enzyme-catalyzed release of the free drug at the tumor site. This strategy addresses the stoichiometry, controlled drug release and poor antibody penetration problems associated with the use of monoclonal antibody-drug conjugates [6-8]. In addition, because the process of drug release is enzymatic, a single enzyme can generate a large amount of free drug. Consequently, a small amount of antibody can be used to reduce immunogenicity.It is important that the free drug in the ADEPT approach be highly toxic. Using highly toxic agents can reduce the amount of the monoclonal antibody required, thereby reducing side effects. CC-1065 (Figure 1) is among the most potent antitumor agents discovered [9-13]. It binds to double-stranded B-DNA within the minor groove with a sequence preference for 5'-d(A/GNTTA)-3' and 5'-d(AAAAA)-3', and alkylates the N3 position of the 3'-adenine with its left-hand CPI segment [14,15]. CC-1065 also inhibits gene transcription by interfering with binding of the TATA box-binding protein to its target DNA [16]. Despite its high potency and broad spectrum of antitumor ac