Synthesis and Immunosuppressive Activity of Novel Prodigiosin Derivatives Roberto D’Alessio,* ,† Alberto Bargiotti, † Orlando Carlini, † Francesco Colotta, ‡ Mario Ferrari, ‡ Paola Gnocchi, ‡ Annamaria Isetta, ‡ Nicola Mongelli, † Pietro Motta, † Arsenia Rossi, † Mario Rossi, † Marcello Tibolla, † and Ermes Vanotti † Departments of Chemistry and Pharmacology, Discovery Research Oncology, Pharmacia & Upjohn SpA, Viale Pasteur 10, 20014 Nerviano (MI), Italy Received January 4, 2000 Prodigiosins (Ps) represent a family of naturally occurring red pigments characterized by a common pyrrolylpyrromethene skeleton. Some members of this family have been shown to possess interesting immunosuppressive properties exerted with a novel mechanism of action, different from that of currently used drugs. In fact, Ps inhibit phosphorylation and activation of JAK-3, a cytoplasmic tyrosine kinase associated with a cell surface receptor component called common γ-chain, which is exclusive of all IL-2 cytokine family receptors. Blocking common γ-chain transduction activity results in a potent and specific immunosuppressive activity. With respect to the interesting and unexploited immunomodulating properties of this family of compounds we initiated a medicinal chemistry program aimed at finding novel prodigiosin derivatives with improved immunosuppressive activity and lower toxicity. Utilizing an unprecedented and flexible way of assembling the prodigiosin frame, a number of new derivatives have been prepared and tested leading to the choice of 4-benzyloxy-5-[(5-undecyl- 2H-pyrrol-2-ylidene)methyl]-2,2′-bi-1H-pyrrole (PNU-156804, 16) as a lead immunosuppressant. Introduction Immunosuppression is required to reduce detrimental immune reactions and has a potential role in the therapy of autoimmune diseases. Main indications of immunosuppressive therapy are prevention and treat- ment of acute and chronic allogeneic organ transplant rejection and graft-versus-host disease (GVHD) result- ing from transplantation of foreign organs or tissues, a practice that is becoming increasingly commonplace, with renal transplantation the most frequently per- formed transplant. Although the use of cyclosporin A (CyA) has been a major advance in the progress of organ transplanta- tion, 1,2 current immunosuppressive therapies 3 still have strong limitations because of low efficacy and relevant side effects on transplant recipients. Present strategies seek to use low-dose combinations of drugs able to target different crucial steps of lymphocyte proliferation, to improve rejection prophylaxis and reduce cumulative toxicity. Prevention of solid organ transplant rejection is presently accomplished with the combination of steroids, a noncytotoxic immunosuppressant, 4 and a cytotoxic drug. 5 The above combination acts by inhibiting differ- ent steps in the cascade of events which lead to lymphocyte proliferation that represents the primary target of immunosuppression. Even with the best treatment available, up to 50% of patients receiving a solid organ graft experience at least one acute rejection episode within 6-12 months after transplantation and GVHD still occurs in 40% of the patients undergoing allogeneic bone marrow transplan- tation. Since toxicity and efficacy are unsolved problems in immunosuppression, a real breakthrough in the field would be a drug with a mechanism of action different from that of currently available immunosuppressive drugs, thus providing the rationale for its use in combination with current therapy, at lower doses and reduced cumulative toxicity. 6 Prodigiosins (Ps) represent a family of naturally occurring red pigments 7 produced by microorganisms including Streptomyces and Serratia and characterized by the common pyrrolylpyrromethene skeleton shown in Figure 1. Prodigiosin 8 and some related compounds isolated in the 1960s have been originally studied as antibiotic and cytotoxic compounds but have never been developed due to their high systemic toxicity. 9 During the past decade some members of this class, particularly undecylprodigiosin (Prodigiosin 25-C, UP), 10 methacycloprodigiosin, 11 and, more recently, prodigi- osin 12 have been found to possess interesting immuno- suppressive properties, acting through a novel mecha- nism of action, different from that of currently used drugs. Competitive antagonism studies have shown that Ps interact neither with the binding site for CyA nor with the common binding site for FK506 and Rapamycin on FK binding protein. * To whom correspondence should be addressed. Phone: ++39 02 4838 5349. Fax: ++39 02 4838 3833. E-mail: roberto.dalessio@ eu.pnu.com. † Department of Chemistry. ‡ Department of Pharmacology. Figure 1. 2557 J. Med. Chem. 2000, 43, 2557-2565 10.1021/jm001003p CCC: $19.00 © 2000 American Chemical Society Published on Web 05/17/2000