Zotarolimus, a novel sirolimus analogue with potent anti-proliferative activity on coronary smooth muscle cells and reduced potential for systemic immunosuppression.

Sirolimus (rapamycin) is an immunosuppressant used in preventing allograft rejection and in drug-eluting stents to prevent restenosis after angioplasty. Zotarolimus, an analogue of sirolimus, was designed to have a shorter in vivo half-life. Zotarolimus was found to be mechanistically similar to sirolimus in having high-affinity binding to the immunophilin FKBP12 and comparable potency for inhibiting in vitro proliferation of both human and rat T cells. Rat pharmacokinetic studies with intravenous dosing demonstrated terminal elimination half-lives of 9.4 hours and 14.0 hours for zotarolimus and sirolimus, respectively. Given orally, T1/2 values were 7.9 hours and 33.4 hours, respectively. Consistent with its shorter duration, zotarolimus showed a corresponding and statistically significant 4-fold reduction in potency for systemic immunosuppression in 3 rat disease models. Pharmacokinetic studies in cynomolgus monkey underpredicted the half-life difference between zotarolimus and sirolimus apparent from recent clinical data. In vitro inhibition of human coronary artery smooth muscle cell proliferation by zotarolimus was comparable to sirolimus. Drug-eluting stents for local delivery of zotarolimus to the vessel wall of coronary arteries are in clinical development. The pharmacological profile of zotarolimus suggests it may be advantageous for preventing restenosis with a reduced potential for causing systemic immunosuppression or other side effects.

Zotarolimus (ABT-578) eluting stents.

Drug-eluting stents have revolutionized the field of interventional cardiology and have provided a significant innovation for preventing coronary artery restenosis. Polymer coatings that deliver anti-proliferative drugs to the vessel wall are key components of these revolutionary medical devices. This article focuses on the development of stents which elute the potent anti-proliferative agent, zotarolimus, from a synthetic phosphorylcholine-based polymer known for its biocompatible profile. Zotarolimus is the first drug developed specifically for local delivery from stents for the prevention of restenosis and has been tested extensively to support this indication. Clinical experience with the PC polymer is also extensive, since more than 120,000 patients have been implanted to date with stents containing this non-thrombogenic coating. This review provides background on pre-clinical studies with zotarolimus, on the development of the biocompatible PC polymer and on the clinical trials conducted using two stent platforms which deliver this drug to patients with coronary artery disease.

Zotarolimus-eluting stents reduce experimental coronary artery neointimal hyperplasia after 4 weeks.

AIMS: The addition of drug elution to coronary stents plays an integral role in coronary restenosis prevention. The present study was undertaken to determine the mechanism of action and the in vitro and in vivo efficacy of zotarolimus, a new chemical entity designed specifically for elution from phosphorylcholine (PC)-coated stents, for the reduction of neointimal hyperplasia in porcine coronary arteries. METHODS AND RESULTS: In vitro studies of Zotarolimus bound to FKBP-12 potently inhibited smooth muscle cells (SMCs) and endothelial cell (EC) proliferation. Twenty PC-only and 20 stents eluting zotarolimus 10 microg/mm were implanted in the coronary arteries of 20 domestic juvenile swine. After 28 days, zotarolimus stents exhibited less area stenosis (22.4+/-8.6 vs. 35.7+/-13%, P = 0.01), less neointimal area (1.69+/-0.55 vs. 2.78+/-1.07 mm(2), P = 0.01), less neointimal thickness (0.25+/-0.07 vs. 0.38+/-0.13 mm, P = 0.01), and greater lumen area (6.07+/-1.39 vs. 5.02+/-1.3 mm2, P = 0.01). All arteries in both the polymer-only and polymer/drug stent showed near-complete healing and minimal toxicity. Zotarolimus did not affect the extrastent segments nor alter the overall artery size (external elastic lamina cross-sectional area 9.18+/-1.19 vs. 9.06+/-1.28 mm2, P = 0.7). CONCLUSION: Zotarolimus binds to FKBP-12 and in vitro inhibits SMC and EC proliferation. Zotarolimus applied to PC-coated stents reduces neointima in the swine coronary model after 28 days. These results suggest potentially promising human clinical application for coronary stenting with this polymer/drug combination.

Hypertension induced by blockade of ET(B) receptors in conscious nonhuman primates: role of ET(A) receptors.

The role of endothelin-B (ET(B)) receptors in circulatory homeostasis is ambiguous, reflecting vasodilator and constrictor effects ascribed to the receptor and diuretic and natriuretic responses that could oppose the hypertensive effects of ET excess. With the use of conscious, telemetry-instrumented cynomolgus monkeys, we characterized the hypertension produced by ET(B) blockade and the role of ET(A) receptors in mediating this response. Mean arterial pressure (MAP) and heart rate (HR) were measured 24 h/day for 24 days under control conditions and during administration of the ET(B)-selective antagonist A-192621 (0.1, 1.0, and 10 mg/kg bid, 4 days/dose) followed by coadministration of the ET(A) antagonist atrasentan (5 mg/kg bid) + A-192621 (10 mg/kg bid) for another 4 days. High-dose ET(B) blockade increased MAP from 79 +/- 3 (control) to 87 +/- 3 and 89 +/- 3 mmHg on the first and fourth day, respectively; HR was unchanged, and plasma ET-1 concentration increased from 2.1 +/- 0.3 pg/ml (control) to 7.24 +/- 0.99 and 11.03 +/- 2.37 pg/ml. Atrasentan + A-192621 (10 mg/kg) decreased MAP from hypertensive levels (89 +/- 3) to 75 +/- 2 and 71 +/- 4 mmHg on the first and fourth day, respectively; plasma ET-1 and HR increased to 26.64 +/- 3.72 and 28.65 +/- 2.89 pg/ml and 113 +/- 5 (control) to 132 +/- 5 and 133 +/- 7 beats/min. Thus systemic ET(B) blockade produces a sustained hypertension in conscious nonhuman primates, which is mediated by ET(A) receptors. These data suggest an importance clearance function for ET(B) receptors, one that influences arterial pressure homeostasis indirectly by reducing plasma ET-1 levels and minimizing ET(A) activation.

Evaluation of tissue perfusion in a rat model of hind-limb muscle ischemia using dynamic contrast-enhanced magnetic resonance imaging.

PURPOSE: To evaluate the feasibility of using dynamic contrast-enhanced magnetic resonance imaging (MRI) for assessment of muscle perfusion in a rat model of hind-limb ischemia. MATERIALS AND METHODS: The acute alteration and chronic recovery in muscle perfusion and perfusion reserve after femoral artery ligation were quantified using the maximum Gd-DTPA uptake rate obtained by a T(1)-weighted gradient-recalled echo sequence. Radionuclide-labeled microsphere blood flow measurements were performed for comparison with the MR perfusion measurement on a separate set of animals. RESULTS: After femoral artery ligation, a significant reduction in resting muscle perfusion was only observed at 1 hour post-ligation during the 28-day follow-up period. Muscle perfusion reserve was severely diminished following the ligation. Despite significant recovery over time, perfusion reserve to the ligated limb reached only 63% of the perfusion capacity in the unaffected limb by 42 days post ligation. A strong correlation (r = 0.86) between MR perfusion and microsphere blood flow measurements was observed for evaluation of relative changes in muscle perfusion. CONCLUSION: Dynamic contrast-enhanced MRI with Gd-DTPA is useful to assess time-dependent changes in muscle perfusion and perfusion reserve in this hind-limb ischemia model.

Oral bimoclomol elevates heat shock protein 70 and reduces myocardial infarct size in rats.

Bimoclomol has been shown to increase an inducible member of the heat shock protein 70 family (HSP70) and cytoprotect in vitro. Here, we addressed whether oral pretreatment of rats with bimoclomol could elevate myocardial HSP70 and reduce infarct size in a rat model of ischemia and reperfusion. Rats were pretreated with bimoclomol at 3, 6 or 18 h or with 42 degrees thermal stress 24 h before ischemia. Infarct size was significantly decreased 6 h after oral administration of bimoclomol and 24 h after thermal stress. Left ventricles from a separate group of rats were examined for HSP70 levels. Western blots showed a significant increase in HSP70 6 h after oral administration of bimoclomol and 24 h after thermal stress. There was a significant correlation (P<0.05) between HSP70 induction and infarct size reduction, whether produced by thermal stress or oral administration of bimoclomol. Thus, bimoclomol can increase HSP70 and reduce infarct size in a rat model of ischemia and reperfusion.