Osteoporosis represents one of the paradoxes of modern drug development, where a huge market and the success of current treatments provides few incentives for novel approaches, even though the relatively small number of therapeutic alternatives suffer side effects ranging from the merely inconvenient to the fairly serious.
Indeed, the bisphosphonates, which block bone resorption, have now surpassed $5 billion in annual sales. But they are associated with burdensome compliance requirements as well as GI problems and osteonecrosis of the jaw.
On the other side of the coin, there is Forteo teriparatide, the only agent approved to stimulate new bone growth. The recombinant parathyroid hormone (PTH 1-34) from Eli Lilly and Co. (LLY, Indianapolis, Ind.) posted $594.3 million in sales last year, which was up 53% from $389.3 million in 2005. But daily injections and the risk of hypercalcemia associated with Forteo may limit its market penetration.
Given the obvious potential for improved treatments, along with an aging population that is likely to drive continued market growth, osteoporosis remains an active field for drug development. However, with a few notable exceptions, industry is primarily focused on improving current treatments, while academic groups have taken the lead in identifying new targets that might play roles in disease pathogenesis, which results in decreased bone density and increased risk of fracture.
Indeed, over the last few months, a number of academic groups have published studies elucidating proteins and pathways that may have utility as targets in the complex system of signals that exists between bone resorption by osteoclasts and bone formation by osteoblasts (see "Bone Remodeling Targets").
Mitchell Steiner, CEO of men's health company GTx Inc. (GTXI, Memphis, Tenn.), said osteoporosis research is similar to other disease areas in that "basic research is very expensive, laborious, and time-consuming. Rather than turning over one rock at a time looking for a snake, in academia, thousands of labs are turning over rocks looking for a snake. A company just has to wait for the snake to be discovered by an academic lab."
According to Steiner, it is no surprise that many companies choose to focus on next-generation or improved versions of approved drugs rather than address novel targets. It is "very low risk to 'reuse' well-validated targets, especially with existing bone mineral density data that can be compared to the bone mineral density data of the new generation and improved agents," he said.
Brian MacDonald, CEO of