FDA grants SiSaf’s innovative siRNA Therapy SIS-101-ADO Orphan Drug Designation

Guildford, England – 15 May 2023SiSaf Ltd, an RNA delivery and therapeutics company, announces that SIS-101-ADO, its siRNA therapeutic for patients with Autosomal Dominant Osteopetrosis Type 2 (ADO2), has been granted Orphan Drug Designation by the U.S. FDA. In addition, due to the serious manifestations of this rare skeletal disorder in children, SIS-101-ADO has been granted Rare Pediatric Disease Designation for the treatment of Autosomal Dominant Osteopetrosis.

FDA Orphan Drug Designation provides SiSaf with incentives such as tax credits for clinical trials, exemption from user fees, and expanded marketplace exclusivity. The Rare Pediatric Disease Designation entitles SiSaf to apply for a priority review voucher that can be used to have the drug approval process expedited by the FDA.

The FDA awarded SIS-101-ADO Rare Pediatric Disease Designation on the basis of the serious or life-threatening manifestations of ADO that primarily affect children including blindness from optic nerve compression, anomalies in dental and craniofacial development, and scoliosis.

There are currently no approved treatments for Osteopetrosis ADO2 and no other treatments currently in clinical trials. If approved, SiSaf’s SIS-101-ADO would thus be the first treatment for Osteopetrosis ADO2 and could provide life-altering benefits for those who suffer from this debilitating disease. SiSaf is currently preparing for first-in-human clinical trials.

SIS-101-ADO combines an siRNA that suppresses the expression of CLCN7 with SiSaf’s Bio-Courier delivery technology. By downregulating the expression of CLCN7, a mutant gene expressed by osteoclasts and other cell types responsible for causing ADO2, the RNA therapy restores bone mass and quality to nearly normal levels. 

Genetic skeletal disorders such as ADO2 account for five percent of all birth defects globally, yet many unmet needs and challenges remain for providing safe and effective treatments. SiSaf’s proprietary Bio-Courier technology has the potential to accelerate the development of new RNA-based treatments. The technology addresses the limitations of other RNA delivery technologies by stabilizing lipid nanoparticles with bioabsorbable silicon.

SiSaf’s Founder and CEO, Dr. Suzanne Saffie-Siebert, said, “Being granted Orphan Drug Designation and Rare Pediatric Disease Designation is a major milestone in our drive to move our revolutionary siRNA treatment forward to alleviate the pain and suffering that Osteopetrosis ADO2 inflicts. SIS-101-ADO ushers in the potential for a new era of personalized care and treatment options for ADO2 and other rare bone and skeletal diseases.”

There has been an explosion of interest in RNA therapeutics for a wide range of medical conditions and SiSaf’s innovative Bio-Courier delivered siRNA technology holds the promise to address some of the most intractable diseases.

"SIS-101-ADO and other Bio-Courier formulated drugs will not only be able to treat rare skeletal disorders but can clear the way for therapeutics for other rare diseases once thought impossible to treat”, added Dr Saffie-Siebert.

Bio-Courier Technology Program and its Benefits

SiSaf’s Bio-Courier drug delivery platform builds upon lipid nanoparticle technology with the introduction of silicon, for structural integrity and durability. The result is a nanoparticle with improved RNA loading capacity and protection from hydrolysis, combined with efficient transfection and controlled release of the oligonucleotide payload.  Bio-Courier versatility is achieved by modifying particle size, surface charge and surface ligands for targeting to the desired site of drug action. Bio-Courier formulated drugs can be used for multiple routes of administration.

About Orphan Drug Designation

Orphan Drug Designation is a process designated by the FDA for therapeutics that have promising, but limited, efficacy in the marketplace. The FDA has authority to grant Orphan Drug Designation to a drug or biological product to prevent, diagnose or treat a rare disease or condition – typically affecting 200,000 people or less – through incentives such as tax credits for clinical trials, exemption from user fees, and expanded marketplace exclusivity.

About Rare Pediatric Disease Designation

Under Section 529 to the Federal Food, Drug, and Cosmetic Act (FD&C Act) the FDA will award priority review vouchers to sponsors of rare pediatric disease product applications that meet certain criteria. Under this program, a sponsor who receives an approval for a drug or biologic for a "rare pediatric disease" may qualify for a priority review voucher that can be redeemed to receive a priority review of a subsequent marketing application, including applications for a different product.

SiSaf is working with CSSi LifeSciences, a leader in shepherding emerging therapeutics through federal approval processes, to co-ordinate the complex regulatory process that is required for the clinical trials of SIS-101-ADO.


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