Torcetrapib is a CETP inhibitor with IC50 of 37 nM, elevates HDL-C and reduces nonHDL-C in plasma. Inhibition of cholesteryl ester transfer protein (CETP) has been shown to have a substantial effect on plasma lipoprotein levels.
In vitro: Torcetrapib dose-dependently increases aldosterone release from H295R cells after either 24 or 48 h of treatment, this effect is mediated by calcium channel as calcium channel blockers completely blocks torcetrapib-induced corticoid release and calcium increase. Torcetrapib (1 μM) significantly increases the expression of steroidogenic gene, CYP11B2 and CYP11B1, in H295R cell lines [1].
In vivo: Researchers tested torcetrapib in rabbits fed an atherogenic diet at a dose sufficient to increase HDL-C by at least 3-fold. CETP activity was inhibited by 70–80% throughout the study. Non-HDL-C increased in both groups, but there was no difference apparent by the study’s end [2].
Clinical trial: Torcetrapib therapy resulted in an increased risk of mortality and morbidity of unknown
mechanism. Although there was evidence of an off-target effect of torcetrapib, adverse effects related to CETP inhibition cannot be ruled out [3].
References:
[1] Hu X, Dietz JD, Xia C, Knight DR, Loging WT, Smith AH, Yuan H, Perry DA, Keiser J. Torcetrapib induces aldosterone and cortisol production by an intracellular calcium-mediated mechanism independently of cholesteryl ester transfer protein inhibition. Endocrinology. 2009;150(5):2211-9.
[2] Morehouse LA, Sugarman ED, Bourassa PA, Sand TM, Zimetti F, Gao F, Rothblat GH, Milici AJ. Inhibition of CETP activity by torcetrapib reduces susceptibility to diet-induced atherosclerosis in New Zealand White rabbits. J Lipid Res. 2007;48(6):1263-72.
[3] Barter PJ, Caulfield M, Eriksson M, Grundy SM, Kastelein JJ, Komajda M, Lopez-Sendon J, Mosca L, Tardif JC, Waters DD, Shear CL, Revkin JH, Buhr KA, Fisher MR, Tall AR, Brewer B; ILLUMINATE Investigators. Effects of torcetrapib in patients at high risk for coronary events. N Engl J Med. 2007;357(21):2109-22.