Background:
Matrix metalloproteinases (MMPs) are activated in myocardial ischemia, digesting key
structural components in cardiac muscle in the setting of myocardial infarction and
myocardial ischemia-reperfusion injury (Schulz, 2007, Annu. Rev. Pharmacol. Toxicol. 47,
211-42).
The antibiotic doxycycline is the only drug approved as an MMP inhibitor by Health Canada
and the U.S. FDA for the treatment of periodontitis and rosacea at sub-antimicrobial
doses.
Doxycycline decreases intracellular proteolysis, improves cardiac function, and reduces
infarct size in animal models of ischemia-reperfusion injury (Cheung et al, 2002,
Circulation 101:1833-39; Villarreal et al, 2003, Circulation 208:1487-92).
TIPTOP (Cerisano et al, 2014, Eur Heart J 35: 184-91) was a randomized open-label trial
(110 patients) that studied the effect of 1-week doxycycline given post-percutaneous
coronary intervention (PCI) in patients with anterior STEMI. Patients who received
doxycycline showed improved echocardiographic indices at 6 months relative to untreated
controls: left ventricular end diastolic volume index (LVEDVi) -8 mL ± 14 mL (P=0.004),
left ventricular end systolic volume index (LVESVi) -6 mL ± 12 mL (P=0.02), and left
ventricular ejection fraction (LVEF) +5% ± 12% (P=0.04). They also showed decreased
infarct sizes (-6%, P=0.05) by single photon emission computed tomography (SPECT).
Rationale for study:
The TIPTOP pilot study showed promise for doxycycline therapy to decrease adverse
ventricular remodeling post-PCI in STEMI patients. Animal models suggest that MMP
activation occurs early in reperfusion (within 5 minutes) following severe ischemia, and
the TIPTOP pilot showed that early treatment may result in measurable clinical benefit.
However, the TIPTOP pilot was an open label study and used a low resolution approach to
measure clinical outcomes.
This is a small-scale, single-centre Phase II trial with double blinding, and includes
the use of magnetic resonance imaging to measure primary (LVESVi) and secondary outcomes
(LVEF ad LVEDVi). The investigators anticipate beneficial effects of doxycycline, with
patients showing lower levels of LVESVi and LVEDVi, increased LVEF by MRI, and reduced
infarct sizes, compared to placebo at 3 months. The investigators also expect
hospitalization and mortality rates due to cardiac events to be reduced in these
patients.
If successful, the overarching goal is to develop a multi-center randomized, blinded,
placebo-controlled trial to examine the effect of early doxycycline therapy in the
setting of STEMI.