Cardiovascular profile of newly developed Diltiazem analogs

Abstract

Many diltiazem related L-VDCC blockers were developed using a multidisciplinary approach. This current study was to investigate and compare diltiazem with to the newly developed compounds by mouse Langendorff-perfused heart, Ca2+-transients and on recombinant L-VDCC. Five particular compounds were selected by the ligand-based virtual screening procedure (LBVS) (5B, M2, M7, M8 and P1). Wild-type human heart and rabbit lung α1 subunits were expressed (combined with the regulatory α2δ and β3 subunits) in Xenopus leavis oocytes using a two-electrode voltage clamp technique. Diltiazem is a benzothiazepine Ca2+ channel blocker used clinically for its antihypertensive and antiarrhythmic effects. Previous radioligand binding assays revealed a complex interaction with the benzothiazepine binding sites for M2, M7 and M8. (Carosati E. et al. J. Med Chem. 2006, 49; 5206). In agreement with this, the relative order of increased rates of contraction and relaxation at lower concentrations ( M2>M8>P1. Similar increases in Ca2+ transients were observed in cardiomyocytes. Diltiazem showed negative inotropic effects whereas 5B had no significant effect. Diltiazem blocks Ca2+ currents in a use-dependent manner and facilitates the channel by accelerating the inactivation and decelerating the recovery from inactivation. In contrast to diltiazem, the new analogs had no pronounced use-dependence. Application of 100 μM M8 and M2 showed ∼10% tonic block, shifted the steady-state inactivation in hyperpolarized direction and the current inactivation time was significantly decreased compared with control (219.6±11.5 ms, 226±14.5 vs. 269±12.9 ms). Contrary to diltiazem, the recovery from the block by M8 and M2 was comparable to control. All of the compounds displayed the same sensitivity on the Ca2+ channel rabbit lung α1 except P1. Taken together, these findings suggest that M8 and M2 might directly decrease the binding affinity or allow more rapid dissociation from the benzothiazepine binding site.