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Are CETP inhibitors kaput?

Posted Aug 26 2008 4:16pm

Was torcetrapib’s crash and burn fatal for this class of drug?

At the 2007 American Heart Association meetings in Orlando, Florida, Dr. Philip Barter of Sydney, Australia, presented an update of the ILLUMINATE drug trial for the once-promising drug, torcetrapib, the billion-dollar bet that Pfizer made on its first entry into the new drug class.

You may recall that the crash and burn of Pfizer’s torcetrapib in December 2006 made headlines and prompted enormous disappointment for many patients and doctors who had hoped for a new drug choice to raise HDL cholesterol. Pfizer executives (heads flew!) and investors were also disappointed, anticipating release of a drug that might have become the number one biggest selling drug in the world—ever, surpassing even Lipitor's® $13 billion annual sales.

Torcetrapib is the first among the “cholesteryl-ester transfer protein inhibitors,” or CETP-inhibitors, drugs that block the exchange of cholesterol and triglycerides between HDL and VLDL particles and prevent formation of the unwanted small LDL particles. Preliminary efforts suggested that effects were positively enormous.

However, the 15,000-participant trial was abruptly terminated after 550 days when an excess of deaths were identified among the group taking the experimental drug: 59 deaths in control group; 93 deaths in the torcetrapib group.

In addition, cardiovascular events were 24% greater in the torcetrapib group, numbering 373 compared to 464 in the no-torcetrapib group, including a substantially greater number of heart attacks and hospitalizations. Another surprise came in the way of cause of death among some of the torcetrapib patients, with an excess of deaths due to cancers (twice as many in the torcetrapib group), strokes, and infections.

Why the divergence: enormous improvements in cholesterol values, yet increase in adverse effects including more heart attack? Deeper digging by the principal investigators uncovered unexpected distortions of electrolytes like sodium and potassium. They then re-analyzed blood samples from participants on both sides of the trial and discovered that participants taking torcetrapib experienced significant rise in the blood pressure hormone, aldosterone. This, they surmised, also likely accounted for the 4 mmHg average rise in blood pressure among those taking the experimental drug. (This is the same pathway blocked by blood pressure drugs like ACE inhibitors lisinopril and enalapril, ARBs like losartan.)

Simultaneously (what a coincidence!) with the torcetrapib data, investigators at competing drug manufacturer, Merck, reported encouraging data with their version of CETP inhibitor, anacetrapib. In a phase II FDA trial of 589 patients, anacetrapib reduced LDL-C levels by up to 40% and increased HDL-C up to 139%.

Spokesman Daniel Bloomfield, M.D., of Merck Research Laboratories reported that "The favorable lipid effects seen in this study with multiple doses of anacetrapib were significant, and confirm the continued evaluation of the clinical benefits of CETP inhibitors in the treatment of dyslipidemia." Quick to distinguish this drug from torcetrapib’s track record of dangerous effects on blood pressure, he added that "the decreased LDL-C concentrations, increased HDL-C concentrations and no demonstrable increase in blood pressure seen with anacetrapib are particularly encouraging results of this study."

However, the data reported only an 8 week expereince. Given the experience with torcetrapib, longer term data will obviously be required to assess safety. After Pfizer spent over $1 billion and sacrificed lives to obtain this experience, Merck will need to tread carefully.

It will clearly be many years before we have a confident answer on whether the CETP-inhibitor class of drugs will be a safe choice for correction of cholesterol abnormalities, especially low HDL. Are we helpless until then?

Though CETP inhibitors offer the potential for a one-stop opportunity to raise HDL substantially, there are still many strategies available to raise HDL.

Strategies that raise HDL and are available today include:

• Weight loss—to your ideal weight. A very effective strategy.

• Reduction in processed carbohydrates—like breads, pasta, cookies, pretzels, etc. Note that very low-fat diets reduce HDL. Often a huge effect.

• Fish oil—A small effect, more dramatic when triglycerides are high.

• Niacin—Vitamin B3, the best we have at present. Doses of 500-1500 mg per day raise HDL 20–50%; work with your doctor if you are contemplating niacin. We use this agent everyday and have had great success; good hydration is key to minimize the annoying “hot-flush” effect.

• Dark chocolate—40 grams, or about 2 inches square, a delicious way to squeeze out a little rise in HDL.

• Alcoholic beverages—Red wines are almost certainly the preferred route, rich in flavonoids.

• Exercise—HDL-raising effects vary, but can sometimes be as much as 10–20 mg.

• Other drugs—Though not commonly used for this effect, drugs like pioglitazone (for diabetes and pre-diabetes); fibrates (Tricor® or fenofibrate; Lopid® or gemfibrozil); and Pletal® or cilostazol are occasionally prescribed.

• Vitamin D—You won’t find validation of this effect in any scientific study, but our emerging experience in our heart disease reversal program is suggesting that this neglected nutrient can exert powerful HDL-raising effects. In fact, supplementing vitamin D has made my life much easier.

And, last I checked, none of these HDL-raising strategies are ever fatal.

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