A study presented last month by Quark Pharmaceuticals at Beyond Genome 2007 in San Francisco suggests that an siRNA-based drug can minimize kidney ischemic injury in a rodent model.
Also at the conference, RNAi drugs newcomer Cequent Pharmaceuticals presented a poster showing that its so-called transkingdom RNAi technology shows potential for RNAi-based cancer drugs.
Quark Pharmaceuticals, formerly Quark Biotech, presented unpublished data showing that its systemically administered, siRNA-based acute renal failure drug AKli-5 was able to minimize kidney ischemic injury in a rodent model.
The research sheds additional light on Quark’s decision to develop AKIi-5 as its lead in-house RNAi drug candidate.
AKIi-5, which was licensed from Silence Therapeutics, is designed to temporarily inhibit the expression of the transcription factor human p53, which is associated with DNA repair and apoptosis. According to Quark, this strategy in acute settings such as acute kidney injury is expected to delay apoptosis and thereby allow “natural repair mechanisms to restore normal DNA and cellular integrity.”
In the poster, company researchers and collaborators from Indiana University School of Medicine presented rodent data indicating that siRNA-mediated pharmacological inhibition of p53 is a “safe and efficient” way to treat and prevent acute kidney injury caused by ischemia-reperfusion.
This condition, also known as I/R, is dangerous because tissue that has been deprived of blood for a certain period and then suddenly regains circulation will cause the newly re-introduced free radicals rather than contribute to cellular energy production.
In an ongoing phase I, dose-escalating study, Quark is evaluating AKIi-5 in patients undergoing cardiac surgery. The trial is expected to conclude by the end of the year.
“Previous studies have indicated that apoptosis, following ischemia reperfusion injury to the kidneys, plays an important pathophysiologic role in epithelial cell dropout and the ensuing dysfunction,” the researchers wrote in Quark’s poster. “In particular, p53 has been shown to mediate a major pathway of apoptosis in tubular epithelial cells and its inhibition by [the] small molecule pifithrin minimized the injury following ischemia.”
In order to assess the therapeutic potential of AKIi-5, 1 mg/kg doses of the drug were administered to three groups of rats whose renal arteries were clamped to induce ischemic kidney injury, as well as a control group.
The first treated group received two injections of AKIi-5 prior to clamping; the second received two injections prior to clamping and one injection after the clamp was released; and the third group received two injections before clamping and two after clamp release.
Rats in the third treated group showed a statistically significant reduction in serum levels of creatinine, a byproduct of creatine phosphate breakdown used to evaluate kidney function, compared with no change in control animals, the researchers stated.
The researchers also said they observed a similar effect in a partial aortic clamp model of renal hypoperfusion.
“Reduction of serum creatinine levels in … treat groups was accompanied by improvement in both cortical and medullary histology scores and reduction in the number of … apoptotic cells,” the researchers wrote.
To verify the creatinine-lowering effect of AKIi-5, the researchers compared a four-dose regimen of the drug to siRNAs targeting GFP. “The latter had no effect on post-injury serum creatinine levels, reassuring specificity of p53 siRNA action,” they noted.
Meantime, in its poster presentation, Cequent Pharmaceuticals described a delivery approach that involves engineering non-pathogenic Escherichia coli to transcribe shRNAs from a plasmid containing the invasin gene Inv and the listeriolysin O gene HlyA. to transcribe shRNAs from a plasmid containing the invasin gene
According to Cequent, these two genes encode two bacterial factors needed for the shRNAs to be successfully transferred into mammalian cells.
Although several different research groups have shown that using RNAi to silence oncogenes can slow tumor growth or trigger apoptosis, delivering siRNA “remains one of the biggest challenges to overcome before RNAi-based therapies can be achieved,” according to researchers from Cequent and Harvard Medical School’s Beth Israel Deaconess Medical Center, which contributed to the study.
The preclinical data indicated that “siRNA-mediated pharmacological inhibition of p53 is a safe and efficient strategy for [the] treatment [and] prevention of [ischemia reperfusion]-induced acute kidney injury.”
Transkingdom RNAi “has important advantages” over other carrier systems, according to the Cequent poster. For instance, E. coli can be controlled with antibiotics and they can be “easily” manipulated, stored, and grown.
The poster added that in vivo animal studies suggest the approach is safe and effective through different routes of administration.
To demonstrate how transkingdom RNAi can deliver siRNA, the Cequent team used it to deliver shRNA targeting the oncogene beta-catenin into two mouse models.
According to Cequent’s poster, oral administration of E. coli expressing shRNAs against mouse beta-catenin resulted in decreased catenin expression in the intestinal epithelium. Intravenous administration of the transkingdom RNAi drug to mice carrying colon cancer xenograft tumors, meanwhile, resulted in a significant drop in beta-catenin expression and reduced cell proliferation.
Though most of these data were published in Nature Biotechnology last year, the Cequent poster was voted “people’s choice” from among all the posters presented at the event. in last year, the Cequent poster was voted “people’s choice” from among all the posters presented at the event.
Cequent, which recently closed a $9 million financing round (see RNAi News, 6/21/2007), expects to begin phase I testing of a transkingdom RNAi-based treatment for familial adenomatous polyposis next year.
The company has also licensed an option to its earlier-stage inflammatory bowel disease program to Novartis. This effort is still in the target-screening stage.