I’ve been covering the pharma and biotech worlds long enough now that I remember when one of the last “big things” was: RNA interference (RNAi). Before CRISPR came along and captured the headlines, it was the CRISPR of its time. Which, frankly, wasn’t that long ago. Fact is, RNAi is still important and still drives a number of therapeutic pipelines. Recently, Dr. Geert Cauwenbergh, president and CEO of RXi Pharmaceuticals, answered some questions from former DDNews Managing Editor Lloyd Dunlap about RNAi and its part in RXi’s efforts.
DDNews: Despite having been around for a number of years, RNAi technology continues to be a bit of an enigma to many of us. Would you explain where it fits into the drug discovery universe?
Geert Cauwenbergh: It is well known that in order for a gene to guide the production of a protein, it must first be copied into a single-stranded mRNA, which is then translated into a protein. Abnormal expression of certain genes (too much or too little) can result in disease, as can expression of an abnormal protein from a gene with a mutation.
There is a naturally occurring process, known as RNAi (short for RNA interference), by which a particular messenger RNA (mRNA) molecule can be destroyed before it is translated into a protein. The process of RNAi can be artificially induced by introducing into the cells a small double-stranded fragment of RNA that corresponds to a particular mRNA. A protein complex within the cell called RISC (RNA-induced silencing complex) recognizes this double-stranded RNA fragment and uses one strand, the guide strand, to bind to and destroy its corresponding cellular mRNA target. If the mRNA is destroyed in this way, the encoded protein cannot be made. Thus, RNAi provides a way to potentially block the expression of specific proteins. Since the overexpression of certain proteins plays a role in many diseases—from lung cancer to kidney disease—the ability to inhibit gene expression with RNAi provides a potentially powerful tool to treat human disease.
RXi Pharmaceuticals is fortunate to be working with Dr. Craig Mello, who received the Nobel Prize for the co-discovery of RNAi. Dr. Mello serves as the chairman of our scientific advisory board and has been instrumental in the development of the company’s self-delivering RNAi (sd-rxRNA) platform.
Since its discovery, delivery of RNAi compounds has been an ongoing challenge for many companies. One conventional solution involves encapsulation into a lipid-based particle, such as a liposome, to improve circulation time and cellular uptake. At RXi, we have used an alternative approach to delivery in which drug-like properties were built into the RNAi compound itself. These novel compounds are termed “self-delivering” RNAi compounds or sd-rxRNA. These sd-rxRNA compounds incorporate advanced features of both RNAi and antisense technologies.
DDNews: How does sd-rxRNA include the positive features of RNAi and antisense? What are these features?
Cauwenbergh: sd-rxRNA compounds incorporate drug-like properties that provide a distinct advantage over traditional RNAi compounds. RNAi compounds have high intracellular potency but are difficult to deliver into target cells and tissues because of their duplex structure and hydrophilic character. Single-stranded compounds such as antisense have favorable tissue distribution and cellular uptake properties but they are less potent than RNAi compounds. In an attempt to combine the best properties of both technologies, sd-rxRNA has a single-stranded phosphorothioate region, a short duplex region and contains a variety of nuclease-stabilizing and lipophilic chemical modifications. These sd-rxRNA compounds are taken up efficiently and cause target gene silencing in diverse cell types (cell lines and primary cells) as well as tissues in vivo following direct administration. This novel class of RNAi compounds may afford a broad opportunity for therapeutic development.
DDNews: What is meant by “sd-rxRNA reduces the level of mRNAs and long non-coding RNAs, nuclear and cytoplasmic, in a target-specific manner?”
Cauwenbergh: RNAi is a naturally occurring process and can be harnessed to destroy, or silence, a targeted mRNA before it is translated into protein. We have demonstrated that all cell types tested (primary, neuronal and non-adherent) internalize sd-rxRNA compounds uniformly and efficiently, resulting in effective silencing of target mRNAs. This targeted approach to specifically reduce particular mRNAs occurs in the cytoplasm of the cell.
Another class of cellular RNA called long non-coding RNAs, or lncRNAs, are often located in the nucleus, contain more than 200 nucleotides, and do not code for proteins. lncRNAs are known to be involved in the regulation of various biological processes, such as cell proliferation, differentiation and the regulation of gene expression. Importantly, dysregulation of lncRNA expression has been shown to be associated with the progression of many diseases, including cancer, cardiovascular diseases, neurological disorders, diabetes and HIV/AIDS. Therefore, targeting and reducing specific lncRNAs may result in therapeutic benefit.
Recently, in collaboration with Biogazelle, we have shown that specifically-designed sd-rxRNAs demonstrated potent and target-specific silencing of multiple lncRNAs, including lncRNAs that are strictly localized in the nucleus such as MALAT1. These findings dramatically expand the number of potential sequences RXi is capable of targeting by approximately fourfold.
Together, mRNAs and lncRNAs encompass a broad spectrum of RNAs, for both protein coding and non-protein regulatory targets, that our sd-rxRNAs can effectively silence. This ability to target lncRNAs opens up new areas of research and collaboration potential.
DDNews: RXI-109 is in development to regulate fibrosis and scar formation in the skin and the eye. How does reduction of connective tissue growth factor by RXI-109 reduce scar formation?
Cauwenbergh: During wound healing, connective tissue growth factor, or CTGF, modulates signals from a wide range of factors in the skin and, in this way, controls critical cellular pathways including scar tissue deposition and remodeling. CTGF is involved in the differentiation of fibroblasts to contractile myofibroblasts which are the main cells responsible for the deposition of collagen, a major structural protein of a scar. Elevated levels of CTGF-dependent signaling can prolong the tissue repair process and lead to deposition of too much collagen, causing raised hypertrophic scars on the skin. Elevated CTGF can also lead to pathological scarring or fibrosis of other organs, and may even be involved in cancer. In the eye, damage to the retina is caused by various ocular diseases, one of them being the wet form of age-related macular degeneration, or wet AMD. As a consequence of retinal damage, CTGF becomes elevated and can lead to sub-retinal fibrosis, or scarring of the retina and permanent loss of vision.
RXI-109, our lead sd-rxRNA compound, was designed to specifically silence CTGF. Reduction of CTGF back to more normal levels is expected to reduce or inhibit scar formation in the skin and in the eye, two areas where visible scars form and can be monitored and tracked in our ongoing clinical trials. As you can imagine, reducing CTGF could also be beneficial for other fibrotic diseases, such as those known to occur in the liver or lung, and these are potential areas of focus after we establish proof of concept.
DDNews: How will treatments with RXI-109 help to preserve vision over a longer period of time than anti-VEGF treatment alone?
Cauwenbergh: A Phase 1/2 clinical study, RXI-109-1501, is underway to evaluate the safety and clinical activity of RXI-109 to prevent the progression of subretinal fibrosis, or retinal scarring, a harmful component of numerous retinal diseases.
In our current trial for retinal scarring, we are enrolling patients who already have subretinal fibrosis as a consequence of wet AMD. Patients with wet AMD are primarily treated with anti-VEGF therapies to block elevated vascular endothelial growth factor (VEGF) from causing blood vessel leakiness and the consequential damage to the retina and potential vision loss. However, as the disease progresses, many advanced patients also experience retinal scarring which leads to further vision loss. In fact, over 50 percent of patients develop subretinal fibrosis within two years of initiating anti-VEGF treatments. We believe that by blocking CTGF in the eye with RXI-109 on a continuing basis, the formation of subretinal fibrosis may be diminished. Our ultimate goal is to reduce the scarring that is secondary to advanced wet AMD or other ocular diseases and, in doing so, preserve vision for a longer period time.
In addition to the ocular trial, a Phase 2 clinical trial, RXI-109-1402, is currently evaluating RXI-109 for the ability to reduce the recurrence of hypertrophic scars following scar revision surgery. Multiple intradermal injections have been well tolerated at all dose levels tested, and over 100 subjects have been treated with RXI-109 by intradermal injection in our trials to date. In early trials, RXI-109 was shown to cause a dose-dependent silencing of CTGF messenger RNA and protein levels in the treated areas of the skin compared to placebo. In the ongoing trial, subjects will be treated over the course of six months in an effort to interfere with the long process by which hypertrophic scars are formed. One major endpoint is the direct comparison of RXI-109 treated vs. untreated areas. Preliminary results from previous clinical work indicated a positive clinical effect on scar appearance by three months.
DDNews: What is on tap from RXi in terms of both research projects and clinical trials?
Cauwenbergh: The results from clinical trials to date have helped guide the selection of dose timing and dose level. In Q4 2015, we initiated two new cohorts in a Phase 2 clinical trial to help define best treatment length and number of doses. The company expects to report early results from these two cohorts later this year. We also expect to share initial safety readouts in the second half of this year in our ocular trial.
In addition to our clinical development programs, we have also harnessed the capabilities of our sd-rxRNA platform to develop cosmetic product candidates. RXI-185 targets collagenase, an enzyme that breaks down the peptide bonds in collagen. If collagenase is reduced, the collagen necessary for skin firmness will be maintained rather than destroyed, and this may be beneficial in the treatment of skin aging disorders including photo aging, wrinkles, acne scarring and blistering skin disorders. RXI-231 targets tyrosinase, a key enzyme involved in the synthesis of melanin, the protein that gives color to your skin, hair and eyes. Reduction of melanin may be useful in a number of areas including cutaneous hyperpigmentation disorders such as age spots, liver spots and freckles. These two targets were selected because they have great potential as clinically relevant pharmaceutical gene targets as well as cosmetic product development targets.
The selection of these two cosmetic product candidates opens the door for additional business development opportunities with both small and large companies that are focusing on non-therapeutic skin health. The company is actively testing other sd-rxRNAs targeting tyrosinase and collagenase for possible therapeutic development or out-licensing.
RXi has also in-licensed a small molecule called Samcyprone. This topical immunotherapy is a proprietary formulation of diphenylcyclopropenone (DPCP). Recent publications support the use of DPCP and its use as an immunomodulator for the treatment of alopecia areata, warts and cutaneous metastases of malignant melanoma. RXi initiated a Phase 2 trial with Samcyprone for the treatment of cutaneous warts (RXI-SCP-1502) in the last quarter of 2015. The trial is designed to evaluate the ability of Samcyprone to clear common warts in healthy subjects. The trial is expected to fully enroll by the end of 2016 and early readouts are expected by the second half of 2016.
Dr. Geert Cauwenbergh was appointed president and CEO of RXi Pharmaceuticals in April 2012. Prior to joining RXi, Cauwenbergh served as chairman and CEO of Barrier Therapeutics Inc., a publicly-traded biopharmaceutical company he founded in 2001 that focused on dermatology drug development. Barrier was acquired by Stiefel Laboratories Inc. in 2008 (now Stiefel, a GSK company). Prior to founding Barrier, he held a number of ascending senior management positions at Johnson & Johnson, where he was employed for 23 years.