Biotech Strategy Blog

Commentary on Science, Innovation & New Products with a focus on Oncology, Hematology & Cancer Immunotherapy

Posts tagged ‘fracture-risk’

Following on from my recent blog post on emerging treatments in osteoporosis, one of new approaches in development is the inhibition of cathepsin-K.

Cathepsin-K inhibition is a novel approach to osteoporosis treatment and Merck’s odanacatib is leading the way in this new class of drugs. It is currently in phase III development, with 16,716 subjects enrolled (NCT00529373).

Cathepsins are lysosomal proteases. Cathepsin K (Cat-K) is a cysteine protease that plays an important role in the function of osteoclasts (the cells responsible for bone destruction). Cat-K acts to degrade bone collagen. By inhibiting it, the removal of bone matrix proteins by osteoclasts is reduced.

However, Cat-K inhibitors such as odanacatib do not kill off the osteoclast, but allow it to still produce chemokines and growth factors such as WNT that are responsible for the effective function of osteoblasts (the cells responsible for bone formation).

The net result is that Cat-K inhibitors reduce bone resorption.

Phase II clinical trial results for odanacatib presented at the American Society of Bone and Mineral Research (ASBMR) annual meeting last year (abstract #1247),  showed an increase in spine and hip bone mineral density (BMD) after four years of follow-up, suggesting that odanacatib use leads to increased bone strength. As reported by Merck in their press release:

In postmenopausal women who received odanacatib 50 mg weekly for four years (N=13), an increase in BMD of 2.8 percent at the lumbar, and 2.7 percent at the hip were demonstrated between years three and four of treatment. Over four years of treatment, these women had increases in lumbar spine (10.7 percent) and hip (8.3 percent) BMD from baseline.

If you are looking for further information on the science, the February 2011 issue of “The Journal of Bone and Mineral Research” has several papers on odanacatib, osteocytes and cathepsin K inhibitors.

Merck has 16,716 subjects enrolled in their phase III trial for odanacatib, and July 2012 is indicated as the date when data will be available for the primary end-point of reduction in fracture risk over the three year treatment period.  We can expect the phase III results shortly after that, and if positive, an FDA approval could be expected in 2013.

The development of odanacatib by Merck is clearly a strategy to combat generic alendronate, which has eroded Merck’s market share and profits for Fosamax.  Both odanacatib and generic alendronate, are once weekly doses. The timeline for a product launch for odanacatib appears to be in the late 2013/2014 period, and I am sure further clarity on this will appear from Merck nearer the time.

The challenge for odanacatib is that by 2015, analysts estimate that Amgen’s RANKL inhibitor denosumab will be a blockbuster (more than $1 billion in sales) and sales of parathyroid hormone analogues will have tripled to $1.4 billion.

Although the market opportunity in osteoporosis is likely to grow given the aging population around the world, it remains to be seen how the cost/benefit of odanacatib will stack up against the competition, and whether Merck can capitalize on this.

The February 2011 issue of Nature Reviews Drug Discovery has an interesting review by Kawai, Mödder and colleagues on “Emerging therapeutic opportunities for skeletal restoration.”

Some of the new products they discuss include:

  1. Parathyroid Hormone-Related protein (PTHRP)
  2. Cathepsin K Inhibitors: odanacatib
  3. Wnt-ß-catenin pathway targets: sclerostin, DKK1 antagonists, lithium.

The market opportunity for osteoporosis remains significant, affecting 44 million people in the United States over the age of 50, resulting in healthcare costs in excess of $15 billion a year; numbers that are set to increase with the ageing population of baby boomers.  The low bone mineral density (BMD) associated with osteoporosis results in increased risk of hip fracture, from which the mortality rate is 20-30% in the first year.

The current competitive landscape for osteoporosis includes antiresorptive agents such as the bisphosponates (alendronate, risedronate, ibandronate, zoledronic acid) that inhibit bone resorption.  These compounds reduce fracture-risk by 20-30%, but long-term safety issues remain a concern.  High doses of zoledronic acid (Zometa) has been linked to osteonecrosis of the jaw (see previous blog post).

Amgen’s new monoclonal antibody, denosumab, binds to RANK-L, thereby inhibiting its action, with the result that osteoclasts (the cells responsible for bone resorption) cannot form, function or survive.  The result of this mechanism of action is a reduction in bone loss and bone destruction.

Like zoledronic acid, denosumab also has a risk of osteonecrosis of the jaw developing.  However, one additional long-term safety issue for denosumab is the fact it suppresses TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) that is not only produced by osteoblasts (the cells responsible for bone formation), but also by immune cells.  This raises the possibility of skin and immune adverse events, which were seen in the clinical trial data.

Kawai & Mödder in their review article conclude that:

“There is still a need for therapies that reduce fracture risk beyond the level achievable with bone-resorbing agents, particularly as virtually all of the currently available drugs do not eliminate the possibility of future fractures.”

However in addition to having a market opportunity and scientific rationale, any biotechnology company looking at osteoporosis as part of their marketing strategy, must face up to the increasing ethical concerns over placebo-controlled clinical trials.  This topic was highlighted last year in the New England Journal of Medicine.

In the future there is likely to be increased pressure not to recruit subjects at high-risk of osteoporosis (T score less than -2.5) into placebo-controlled trials, thus increasing the costs, number of patients and time to bring new products to market.  In addition, the regulatory barriers to entry are becoming higher, given that regulatory agencies require a reduction in fractures over 3 years to establish the efficacy of a new drug.  This ultimately results in the need for large, expensive, and long phase III clinical trials.

In forthcoming posts, I will discuss the opportunities for market entry by new osteoporosis drugs targeting the Wnt- ß-catenin pathway, Cathepsin K inhibitors and Parathyroid hormone-related protein.

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