A possible immunosuppressant, cycloprodigiosin hydrochloride, obtained from Pseudoalteromonas denitrificans

Cycloprodigiosin hydrochloride (cPrG·HCl), a member of the prodigiosin family, is a red pigment obtained from the marine bacterium Pseudoalteromonas denitrificans. cPrG·HCl markedly suppressed ³H-thymidine incorporation by concanavalin A stimulated murine splenocytes but had little effect on lipopolysaccharide dependent ³H-thymidine incorporation, indicating that cPrG·HCl acts as a selective inhibitor of T cell proliferation in the same way as other members of the prodigiosin family. cPrG·HCl inhibited the proliferation of the PMA stimulated Jurkat cells through an apoptotic process. Intriguingly, cPrG·HCl inhibited the H⁺ translocation by vacuolar type ATPase in chromaffin granule membranes without any effect on either its ATPase activity nor on the membrane conductance of phospholipid bilayers, suggesting that cPrG·HCl selectively uncouples H⁺ translocation from the ATPase reaction rather than acting as a non-specific ionophore. Since crystalline cPrG·HCl is highly stable, it raises the possibility of its therapeutic use as an immunosuppressant.