Biotech Stock Mailbag: Amicus, Celldex

Data from phase II studies have been mixed but more positive than not, with sufficient numbers of patients achieving 50% reductions in GL3 to be reasonably confident the phase III study will succeed. Is a positive outcome guaranteed? No, which is why Amicus' stock price isn't higher already.

Amicus and Glaxo will announce top-line results from Study 011 in December but details may be scant. Amicus has only committed to disclosing if the primary endpoint was reached with statistical significance or not, a company spokesman told me Wednesday. Details about the exact number of Fabry patients in each arm responding to Amigal or placebo may not be revealed until a presentation of the study data at a medical meeting next year.

A brief mention about the potential for Amigal-Fabrazyme combination therapy: Amicus and Glaxo's second phase III study is testing whether Fabry patients currently treated with Fabrazyme can benefit from the addition of Amigal. The thesis is that Amigal may further stabilize and boost the activity of the replacement enzyme, thereby making therapy more effective. Results from this phase III study are expected next year.

Combination therapy in Fabry disease is a larger commercial opportunity for Amicus. The challenge is demonstrating the cost-effectiveness of any added benefit. Fabrazyme therapy costs about $250,000 per year. Amigal pricing hasn't been determined but let's assume that it won't be cheap. That means the incremental benefit from Amigal will have to be substantial to justify the added expense. Insurance companies may put up a fight if the added benefit is minor.

Michael W. writes, "I'd like you to write about Celldex Therapeutics (CLDX) again since you haven't mentioned the stock since May. Do you think the new data will be as good this time as what we saw back then?"

Michael is referring to Celldex's targeted breast cancer drug CDX-011. Last May, Celldex released interim results from a phase II study demonstrating superior response rates in patients with advanced metastatic breast cancer compared to single-agent chemotherapy. CDX-011 worked best in a subset of patients with tumors containing high levels of a protein linked to more aggressive disease.

On Saturday, Dec. 8, Celldex will be presenting updated CDX-011 data from the same breast cancer study at the San Antonio Breast Cancer Symposium.

I'll review the May results in a moment but I'd be cautious about expecting radically different CDX-011 data in December. Response rates aren't likely to have changed significantly, if at all. Hopefully, we get updated and more specific progression-free survival results plus some survival data.

The updated CDX-011 data have been talked up as a significant catalyst for Celldex but I'm not so sure. It may be a big trading event but not much more. More important to Celldex will be the outcome of a planned meeting with FDA to discuss next steps for CDX-011.

Celldex will be seeking FDA sign-off to conduct a pivotal phase III study of CDX-011 in advanced breast cancer patients who overexpress the GPNMB protein and have triple-negative disease. Breast cancer is particularly aggressive in these patients and there are no approved therapies to treat them.

From the interim results in May, CDX-011 yielded a 36% partial response rate in the prospectively defined subset of triple negative/high GPNMB expression patients compared to 0% response rate for similar patients treated with "investigator's choice" therapy.

The confirmed partial response rate in this subset of patients was 9% for CDX-011 versus 0% for investigator's choice therapy.

Celldex bears (yes, I'm talking about the short sellers) point out the subgroup of triple negative/high GPNMB expression patients totaled just 14 in the phase II study. (11 randomized to CDX-011, 3 to placebo.) This means Celldex is basing its optimism for CDX-011's activity on four partial responders, or just a single partial responder if you only count the confirmed response data. Too flimsy to be believed, Celldex bears say.

CDX-011 is a monoclonal antibody drug conjugate. The antibody portion targets cancer cells that express the GPNMB protein, which has been shown to correlate with poorer outcomes in breast cancer patients. When the CDX-011 antibody attaches to GPNMB-expressing tumor cells, it releases a toxic chemotherapy payload. This "drug conjugate" was licensed from Seattle Genetics (SGEN) and is the same one used in the newly approved lymphoma drug Adcetris.

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