CHICAGO– A single set of intramuscular injections of stromal cell–derived factor-1 in patients with critical limb ischemia showed safety as well as evidence of efficacy through 12 months of follow-up in the STOP-CLI trial.
“Patients treated with JVS-100 demonstrated dose-dependent improvement across multiple patient-centered outcomes, including pain, quality of life, and wound healing, with less change in macrovascular objective measures in this small study,” Dr. Melina R. Kibbe reported at the American Heart Association scientific sessions. JVS-100 is a nonviral plasmid encoding human stromal cell–derived factor-1 (SDF-1), a natural chemokine protein that promotes angiogenesis by recruiting endothelial progenitor cells from the bone marrow to ischemic sites, explained Dr. Kibbe, professor and vice chair of surgical research and deputy director of the Simpson Querrey Institute for BioNanotechnology at Northwestern University, Chicago.
Dr. Melina R. Kibbe
STOP-CLI was an exploratory, phase IIa, double-blind, first-in-humans study involving 48 patients with Rutherford classification 4 or 5 critical climb ischemia (CLI). All had an ankle-brachial index of 0.4 or lower, an ankle systolic blood pressure of 70 mm Hg or less or a toe systolic blood pressure of 50 or less, and were poor candidates for surgical revascularization. None had Buerger’s disease.
Participants were randomized to one of four study arms, and within each study arm further randomized 3:1 to stromal cell–derived factor-1 (SDF-1) or placebo injections. The patients received either 8 or 16 injections, each containing either 0.5 or 1.0 mg of SDF-1 or placebo. The injections, given in a single session, were placed at least 0.5 cm apart throughout the ischemic area of the affected limb.
By chance, most patients randomized to the placebo group were Rutherford 4, a category of CLI defined by rest pain, while the majority in the active treatment arms were Rutherford 5, a more severe disease manifestation characterized by ulcers. As a consequence, the SDF-1 recipients also had far larger nonhealing wounds, with an average area of 6.4 cm2, compared with 1.5 cm2, in controls.
The SDF-1 injections proved safe and were well tolerated, with no treatment-related serious adverse events and no safety signals evident in the laboratory results.
Turning to efficacy endpoints, Dr. Kibbe said self-rated visual analog scale pain scores showed clear, dose-dependent improvement over time in the SDF-1 treatment cohorts and no change in controls.
Similarly, the active treatment groups showed improved quality of life scores on all domains of the Short Form-36: physical functioning, bodily pain, general health, social functioning, energy/fatigue, emotional well-being, and overall physical and mental health, the surgeon continued.
Wound area decreased significantly in the SDF-1-treated groups, with the biggest reduction – more than 8 cm2 – being noted in the three patients who received eight 1-mg injections. That was also the group with the largest wounds at baseline, with an average area of 11.4 cm2.
Of note, the major limb amputation rate was “remarkably low” for patients with such severe CLI, according to Dr. Kibbe. The rate was less than 10% over the course of 12 months, with one patient in each of the four active treatment arms having a major amputation at time intervals of 58-112 days post injection. No major limb amputations occurred in the control group.
There was a hint of improvement with SDF-1 therapy over placebo in ankle-brachial index and transcutaneous oxygen pressure, but the between-group differences were too narrow in this study to allow for any conclusions. That must await planned much larger phase III trials, according to Dr. Kibbe.
Audience members, citing the numerous failures of once-promising stem cell therapies for CLI at phase III testing over the last 10-15 years, wondered why Dr. Kibbe thinks SDF-1 will fare any better.
“This is much debated and discussed among all the people involved in these kinds of trials,” she replied. “I’d say, briefly, that a lot of it has to do with patient selection. I think when you have a mixed bag of patients in a trial, including patients with Buerger’s disease, treated in multiple different countries, using different definitions of when to amputate, all those things come into play and could account for why those phase III trials were not successful.”
“Having been involved in lots of the different gene- and cell-based therapy trials, I think one of the unique benefits of this therapy is that it kind of bridges between the two. SDF-1 basically homes your endothelial progenitor cells to the site of ischemic injury for enhanced vasculogenesis. But SDF-1 also has direct effects on endothelial cells, including stimulating proliferation and preventing apoptosis,” she added.