Eric J. Niesor, Christine Magg, Naoto Ogawa, Hiroshi Okamoto, Elisabeth von der Mark, Hugues Matile, Georg Schmid, Roger G. Clerc, Evelyne Chaput, Denise Blum-Kaelin, Walter Huber, Ralf Thoma, Philippe Pflieger, Makoto Kakutani, Daisuke Takahashi, Gregor Dernick, Cyrille Maugeais

Objective The increased mortality observed with the cholesteryl ester transfer protein inhibitor torcetrapib is partly due to increased aldosterone production and blood pressure. The mechanisms underlying these effects were investigated. Methods Cytochrome P450 subunit 11B2 (aldosterone synthase), extracellular signal-regulated kinase (p44/42) and voltage-gated Ca²⁺channel alpha subunit mRNA profiling, aldosterone production, cytosolic calcium and RNA interference were assessed in adrenocarcinoma human cells (H295R). Telemetry was conducted in spontaneously hypertensive rats. Results Torcetrapib and angiotensin II (Ang II) but not dalcetrapib (a structurally different cholesteryl ester transfer protein inhibitor) elevated both cytochrome P450 subunit 11B2 mRNA and aldosterone production in H295R cells at 6 h. At days 1–5, torcetrapib produced a sustained increase of cytochrome P450 subunit 11B2 mRNA, unlike Ang II. Although torcetrapib and Ang II potentiated the effect of 25-OH cholesterol and raised pregnenolone levels, torcetrapib increased neither cytosolic Ca²⁺ at 5 min nor extracellular signal-regulated kinase1/2 phosphorylation, suggesting initially divergent pathways. Unlike Ang II, torcetrapib steroidogenesis was not affected by Ang II type 1 receptor antagonism or voltage-gated T-type Ca²⁺ channel antagonism, but was blocked by several L-type Ca²⁺channel antagonists. In unbiased genome-wide screening, Ang II and torcetrapib modulated an overlapping but distinct set of genes in H295R cells. Torcetrapib, but not Ang II, upregulated mRNA levels of the L-type Ca²⁺ channel alpha 1C subunit. In spontaneously hypertensive rat, torcetrapib had a potent hypertensive effect mediated by the L-type Ca²⁺ channel. Conclusion The unique steroidogenic and hypertensive side effects of torcetrapib may be linked and involve voltage-gated L-type Ca²⁺ channels. Structurally unrelated cholesteryl ester transfer protein inhibitors such as dalcetrapib do not share this effect.

Review literature on the effect of decreasing cholesteryl ester transfer protein (CETP) activity through pharmacological inhibition or modulation in preclinical and clinical settings compared to human CETP deficiency on lipoprotein characteristics, HDL remodelling and function. Torcetrapib, anacetrapib and dalcetrapib inhibited the heterotypic transfer of cholesteryl ester from HDL to LDL and/or VLDL with similar potency, although the potency of dalcetrapib was time dependent. Homotypic transfer of cholesteryl ester from HDL3 to HDL2 via recombinant human CETP was inhibited by torcetrapib and anacetrapib (CETP inhibitors, CETPi) but not by dalcetrapib (CETP modulator, CETPm). In a hamster model of reverse cholesterol transport, only dalcetrapib increased efflux of fecal sterols from macrophages to feces. In clinical studies, dose-responses of CETPi and CETPm demonstrate qualitative and quantitative changes in HDL and LDL particle composition and distribution. Recent studies of the CETPi torcetrapib and anacetrapib and the CETPm dalcetrapib have shown differences in the resulting increase in HDL-cholesterol and in the level of HDL remodelling and potential for effective reverse cholesterol transport. Results from ongoing clinical outcomes studies with anacetrapib and dalcetrapib will clarify the relevance of CETP inhibition versus modulation towards HDL remodelling in the treatment of cardiovascular diseases.