Design and synthesis of a cephalosporin-retinoic acid prodrug activated by a monoclonal antibody–β-lactamase conjugate Original Research Article

Two novel series of all-trans-β-retinoic acid derivatives were synthesized and found to possess anticancer activity. The first series, cephalosporin 3′-retinoic esters 6 and 7 were, respectively, obtained by the condensation of all-trans-β-retinoic acid (2) with cephalosporins 4 and 5. The second series, 7-(retinamido)cephalosporins 11 and 12, were synthesized, respectively, by the condensation of 2 with cephalosporins 9 and 10. These four heretofore undescribed compounds 6, 7, 11, and 12 showed inhibitory activity against murine leukemias (L1210 and P388), sarcoma 180, breast carcinoma (MCF7), and human T-lymphocytes (Molt4/C8 and CEM/0). They also inhibited squamous metaplasia and keratinization in tracheal organ cultures derived from vitamin-A-deficient hamsters. Moreover, cephalosporin 3′-retinoic ester 7 exhibited enhanced activity against keratinization with ED50=3.91×10−11 M in the presence of a β-lactamase from Staphylococcus aureus 95. A tumor targeting fusion protein (dsFv3–β-lactamase) was also used in conjunction with cephem-based retinoid 7 and the potency of 7 toward L1210, P388, and MCF7 was found to approach that of the free retinoic acid (2). In the presence of dsFv3–β-lactamase, tumor cells were found to be much more susceptible to retinoid 7 than normal human embryonic lung cells. These notions provide a new approach to the use of β-retinoic acid for antitumor therapy.