Medivir AB announced that its selective cathepsin K inhibitor, MIV-711, has been granted Rare Pediatric Disease Designation (RPDD) for the treatment of Legg-Calvé-Perthes Disease (LCPD). The FDA defines a rare pediatric disease as a serious or life-threatening disease in which the disease manifestations primarily affect individuals aged from birth to 18 years of age. Pediatric diseases recognized as "rare", affect fewer than 200,000 people in the United States.

With a RPDD, MIV-711 qualifies to receive fast track review and upon marketing approval in LCPD, the Company may be eligible to receive a Priority Review Voucher from the FDA. The voucher can be redeemed to receive priority review for any subsequent marketing application or may be sold to another company for their use. To gain RPDD, there must be supportive data suggesting that the drug may be effective in the disease.

MIV- 711 has shown, in an LCPD-specific animal model, the ability to prevent femoral head deformity and positive impact on biomarker of bone degradation without negatively impacting normal bone formation. Similarly, clinical studies have shown that MIV-711 prevents bone degradation in patients with osteoarthritis, further supporting the potential clinical benefit in LCDP. Cathepsin K is the main cysteine protease involved in bone resorption and cartilage degradation by osteoclasts, through the breakdown of key bone matrix proteins.

Cathepsin K inhibition protects the damaged bone by reducing bone resorption and promoting bone formation, thereby addressing the key mechanisms causing pathological changes in LCPD, with potential to minimize long-term negative effects. Selective inhibition of cathepsin K has the potential to provide clinical benefit in diseases characterized by excessive bone resorption, including additional pediatric bone disorders. Legg­Calvé­Perthes disease (LCPD) is a childhood hip disorder initiated by a disruption of blood flow to the head of the femur.

Due to the lack of blood flow, the bone dies (osteonecrosis or avascular necrosis) and stops growing. Over time, healing occurs by new blood vessels infiltrating the dead bone and removing the necrotic bone which leads to a loss of bone mass and a weakening of the femoral head. The condition is most commonly found in children between the ages of 4 and 8, but it can occur in children between the ages of 2 and 15.

It is estimated to affect about 10 in 100.000 children per year in the USA. It results in permanent deformity of the femoral head in many children, which increases the risk of developing osteoarthritis in adults. MIV-711 is a potent and selective inhibitor of cathepsin K, the principal protease involved in breaking down collagen in bone and cartilage.

It has been shown to slow, stop or reverse the progressive degeneration of joints affected by osteoarthritis. By inhibiting cathepsin K and increased/excessive activity of osteoclasts, MIV- 711 has the potential to prevent degradation of bone and cartilage and counteract the osteonecrosis induced by lack of blood flow, to prevent femoral head deformity and long-term negative effects as well as positively impact Quality of Life.