Biotech Strategy Blog

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Posts tagged ‘Osteoporosis’

Targeting Sclerostin in Osteoporosis

Continuing my previous post about emerging drugs for osteoporosis, one of the new classes in development are those that target sclerostin.

Sclerostin is a protein produced by osteocytes within bone that inhibits bone formation. It is thought to pass through the surface of bone where it acts on osteoblasts (cells responsible for bone formation).  There it binds to low-density lipoprotein receptors and inhibits the Wnt/beta-catenin signaling involved in bone mass regulation.

There is some uncertainty in the scientific literature as to the precise method by which sclerostin acts on bone. However, the Wnt/beta-catenin osteocytic signaling does play a role in bone homeostasis.

Preclinical animal work using an antibody to sclerostin led to increased bone formation, bone mineral density and bone mineral strength. This supports the concept that inhibition of sclerostin has potential as a treatment for osteoporosis.

Interest in sclerostin has grown enormously, with over 50 abstracts presented on its measurement at the 2010 American Society of Bone and Mineral Research (ASBMR) annual meeting.  Also last year, Biomedica and its distribution partner ALPCO Diagnostics launched the first commercial immunoassay kit for the measurement of circulating sclerostin.

Not surprisingly companies have started to look at sclerostin inhibition as a drug development target.  The leader in the pack is Amgen with AMG 785, a sclerostin monoclonal antibody.

The phase 1 trial results published by Padhi et al in the January issue of the Journal of Bone and Mineral Research (JBMR) show that it was well tolerated in 72 healthy subjects that received AMG 785 or placebo.

AMG 785 is now in phase 2 clinical trials that will look more closely at dosing and efficacy.  A 330 patient study to assess fracture healing is currently recruiting (NCT01081678).  The study will look at three doses of AMG 785 (70mg, 140mg, 210mg ) given by injection subcutaneously (under the skin).

The study hypothesis is that giving AMG 785 to those with a new hip fracture will increase their healing. The functional healing will be measured using the timed-up-and-go (TUG) test i.e. the time to stand up on one’s own, walk three meters, turn around, walk back and sit down.

The estimated primary completion date for this trial is December 2012, so I don’t expect we will see some data till 2013 at the earliest.

Amgen already has a major osteoporosis franchise with denosumab, it’s RANKL inhibitor for postmenopausal women at high risk for fracture. It’s a smart new products strategy to build on this, although its too early to tell whether AMG 785 will make it to market.

One unknown challenge for those targeting sclerostin’s action is whether disruption of Wnt/beta-catenin signaling in bone could lead to the stimulation of cancers elsewhere in the body, since this pathway is also involved in a wide range of cellular signaling in the body, including cancer.

While this may not be a problem in healthy individuals, it could raise the issue of the use of sclerostin inhibitors in those patients with low bone mineral density (BMD) or fractures who are being treated for cancer at the same time. Since skeletal related events (SRE) are seen in many advanced breast and prostate cancer patients, this may be a cause for concern.

Further information on Pharma Strategy Blog where Sally Church has written an excellent post on “Wnt Signaling and Cancer.”

Update Jan 2, 2014 Phase 2 Data for Romosozumab published in NEJM

New Year’s day is not when you might expect the New England Journal of Medicine to publish an online first article. However, that’s what happened yesterday when the phase 2 trial data for romosozumab (AMG 785) in postmenopausal women with osteoporosis was published. The joy of Twitter is that interesting news is rapidly shared:

The trial data published in the NEJM by McClung et al shows that romosozumab, a sclerostin inhibitor being developed by Amgen/UCB Pharma provides increased bone mineral density and bone formation:

“All dose levels of romosozumab were associated with significant increases in bone mineral density at the lumbar spine, including an increase of 11.3% with the 210-mg monthly dose, as compared with a decrease of 0.1% with placebo and increases of 4.1% with alendronate and 7.1% with teriparatide”

In the accompanying NEJM editorial, Carolyn B. Becker MD from Brigham and Women’s Hospital in Boston describes the results as “impressive” and outlines many of the questions that remain unanswered that hopefully the results of the phase 3 trial under way (NCT01631214) will provide.

Whether it is a potential blockbuster as some on Twitter questioned yesterday evening, I think we will have to wait and see what the phase 3 trial data shows in a larger study.

However, based on the phase 2 data published in the NEJM it looks like romosozumab will be a future addition to Amgen’s osteoporosis franchise unless something untoward is seen in the phase 3 trial results.

References

ResearchBlogging.orgPadhi, D., Jang, G., Stouch, B., Fang, L., & Posvar, E. (2011). Single-dose, placebo-controlled, randomized study of AMG 785, a sclerostin monoclonal antibody Journal of Bone and Mineral Research, 26 (1), 19-26 DOI: 10.1002/jbmr.173

Merck’s cathepsin-K inhibitor odanacatib in osteoporosis

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.

Emerging drugs in development for Osteoporosis

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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