Novel HDL-Targeted Therapies -- The Search Continues

Linda Brookes, MSc


June 12, 2007

In This Article

Studies With D-4F, an Orally Administered ApoA-I Mimetic

D-4F is an 18-amino acid peptide that mimics the tertiary structure of ApoA-I. Developed by Bruin Pharma (Los Angeles, California), D-4F comprises D-amino acids only and thus is not degraded by mammalian gastrointestinal enzymes, so it can be administered orally. Its name refers to the D-amino acids and the 4 phenylalanines contained in the compound. It was shown in vitro to promote macrophage efflux, bind and sequester fatty acid hydroperoxides and proinflammatory oxidized phospholipids, and to inhibit atherosclerosis in mice and improve anti-inflammatory function of HDL in several species.[5,6]

A double-blind, placebo-controlled, phase 1 study that evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of a single oral dose of D-4F or matching placebo in patients with coronary heart disease showed that a single oral dose of D-4F is absorbed and well tolerated.[7] Bioavailability of D-4F was low, but improved when food was delayed for 2 hours post dose. It was noted that the anti-inflammatory function of HDL cholesterol improved significantly after a single dose of D-4F.

Another study of D-4F by researchers at the University of Pennsylvania was presented by Richard L. Dunbar, MD.[8] The study was completed in January 2006 and was the last of 3 studies performed there with the compound. The objectives of the phase 2, double-blind, randomized, placebo-controlled clinical trial were to evaluate the safety and tolerability of 13 consecutive daily doses of oral D-4F in patients at high risk for cardiovascular events; evaluate the acute pharmacokinetics before and after multiple daily dosing of oral D-4F; and assess pharmacodynamic changes with the HDL inflammatory index. An HDL inflammatory index > 1 indicates inflammatory HDL.

The subjects in the study were high-risk adults aged 21-80 years with stable coronary heart disease, treated with statins, but not with niacin or fibrates. Individuals with uncontrolled hypertension, uncontrolled diabetes, renal failure, transaminasemia, or who were using warfarin or other anticoagulants were excluded.

Subjects were randomized 3:1 to active D-4F (lyophilized powder dissolved in 60 mL of sucrose solution to give a D-4F concentration ranging from 1.66 mg/mL for the 100-mg dose to 8.33 mg/mL for the 500-mg dose) or to matching placebo (60 mL of 25% sucrose solution). Pharmacokinetic and pharmacodynamic effects were assessed in 8-hour blood samples taken on the last day of dosing (day 13), and subjects were followed up 1 and 3 weeks after the final dose to assess safety.

Plasma D-4F levels showed modest oral bioavailability. There was a proportional increase in plasma concentration with increasing dose, with plasma D-4F levels rising rapidly to a tmax of 1.5-2 hours post dose in all groups. Examination of mean plasma levels 2 hours following a dose on days 1, 3, 7, and 13 showed that 2-hour levels peaked between days 3 and 7 and did not increase thereafter. Dosing for 13 days resulted in plasma D-4F levels similar to those on day 1. Dr. Dunbar explained that the investigators had expected prolonged dosing to increase plasma levels, and they believe that the absence of this effect might indicate that the half-life of the drug is < 24 hours and that a longer dosing period might be required or that multiple dosing does not have that effect.

The investigators found an interaction between sex and the area under the curve (AUC) of D-4F, confirmed by ANOVA. This suggested that given the same dose, women would achieve higher plasma levels of D-4F compared with men. On average, plasma levels in women revealed a (nonsignificant) 5-fold increase over men in the 100-mg group and a 2-fold increase in the 300-mg group. The female AUC superiority was driven by a highly significant difference in the 500-mg dose group (2.5 times higher AUC). "We do not have any mechanistic explanation for this based on our data. We have a rather small data set. It is conceivable that there is a 1.63% possibility that this is a chance finding. So if we repeated this experiment 100 times, probably 1% of the time we would find this result," Dr. Dunbar explained ( Table 4 ).

All subjects started the study with an HDL cholesterol inflammatory index > 1. This fell with time in all subjects, but fell more with D-4F. There was a trend toward a greater decrease in HDL inflammatory index with ascending doses of D-4F. D-4F significantly lowered (improved) the postdose HDL inflammatory index in the 500-mg group (-0.15, P = .05) and the 300-mg group (-0.21, P = .01), compared with placebo. The magnitude of these changes was greatest at 4 and 8 hours post dose. The plasma D-4F AUC was also negatively correlated with the HDL inflammatory index. Dividing D-4F AUC into tertiles suggested a threshold effect for D-4F and possibly an effect modification by sex.

Subjects tolerated D-4F at doses up to 500 mg for 13 days. A total of 33 subjects (53%) reported a total of 74 adverse events, the majority of which were mild to moderate in intensity. Adverse effect frequency did not appear to be associated with the dose. The most frequently reported adverse events were nasopharyngitis (11%), urinary tract infection (8%), pain in an extremity (8%), and myalgia (7%). Six patients reported 10 events rated as severe. One serious adverse event was reported, which was believed to be unrelated to D-4F.

The Future of D-4F Compounds?

These effects seem to be beneficial, but the effect of D-4F on atherosclerosis has not been demonstrated in humans, Dr. Dunbar cautioned. He confirmed that he and his colleagues have no plans to do further studies on D-4F. In 2005 Novartis (Basel, Switzerland) reported that it had licensed D-4F from Bruin. Novartis has since said that the drug, designated APP018, is in exploratory phase 1 studies and that regulatory filing would not be done before 2010.

Elsewhere at the meeting, Dr. Rader called D-4F "the best example of an intervention that improves HDL anti-inflammatory function but does not really affect HDL levels at all." He said, "This is an area that requires a lot more attention." This and other methods that target the functional capacity, particularly the inflammatory functional capacity of HDL, to improve its function and ultimately translate into reduced atherosclerosis will become a topic of substantial investigation over the coming years, he predicted.


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