GPC, Pharmion's phase III failure could raise eyebrows at Poniard

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The failure of GPC Biotech and Pharmion’s platinum compound satraplatin in a phase III prostate cancer trial could prompt concern at San Francisco-based Poniard Pharmaceuticals, which is testing a similar chemotherapy agent for the same cancer.

Important differences in the compounds and trials will more than likely mean a different outcome. But given that the studies represent the only two ongoing attempts to evaluate platinum compounds in prostate cancer, the failure of one trial will focus attention on the other.

Earlier today GPC and Pharmion announced that satraplatin failed to improve survival rates in a trial of 950 patients with hormone-refractory prostate cancer. The news effectively dashed any hopes of approval in the US, where GPC has marketing rights, causing the German company’s shares to lose almost two-thirds of their value, wiping €170m off its market cap. Most of the value in GPC was tied to satraplatin, which was forecast to generate annual sales of $393m in 2012.

Spectrum Pharmaceuticals, the owner of worldwide rights to Satraplatin, slumped 10%. Spectrum out-licensed rights to GPC in September 2002 and would have received royalties of 10-12%.

Pharmion, which owns marketing rights in Europe where a small chance for approval remains, was not initially affected. However, according to consensus net present value provided by EvaluatePharma the product is valued at $250m, equal to 14% of the group’s share price, so it could come under pressure if Europe decides it cannot proceed with the current filing.

Platinum compounds

Platinum-based agents have been a cornerstone of chemotherapy for some time, so the surprising result from GPC and Pharmion will not be put down to a class effect. The agents are already on the market in the form of Sanofi-Aventis’s Eloxatin for colorectal cancer, Bristol-Myers Squibb’s Paraplatin for ovarian cancer, and a handful of others used to treat a range of solid tumour cancers.

Numerous companies are conducting trials of the compounds in a range of indications, but only Poniard and GPC/Pharmion are studying prostate cancer. That could point to problems treating this particular cancer with platinum compounds. Bristol-Myers Squibb abandoned development of satraplatin in prostate, lung and ovarian cancer at phase II in 1999, stating a lack of potential to become a blockbuster product.

Perhaps more crucially, satraplatin is being developed as the first orally delivered platinum compound. Poniard’s candidate, like all approved products, is injected.

New generation

Poniard, which has been trading 2.5% lower since this news, has described its candidate, picoplatin, as a “new generation” platinum chemotherapy agent. It is designed to overcome platinum resistance, to prolong the time to relapse, whilst exhibiting an improved safety profile compared with existing platinum chemotherapeutics.

The US company is also taking a different approach to the indication. GPC/Pharmion evaluated satraplatin in combination with prednisone, as a second-line treatment in hormone-refractory prostate cancer. Picoplatin is in trials with docetaxel plus prednisone, as front-line therapy in the treatment of patients with metastatic hormone-refractory prostate cancer, who are newly diagnosed and have not received previous chemotherapy.

Poniard's trial is much earlier stage, only a phase II, so failure at this stage would not be as disappointing. Plus, the company’s biggest hope currently rests with the drug in small cell lung cancer, where a phase III trial is under way. The drug has been granted orphan status in both the US and Europe for the indication.

Still, if the failure of satraplatin is found to be a problem treating prostate cancer in particular, the company could face similarly disappointing results. The trial started at the end of July and aimed to recruit 30 people. With all of the company's research efforts focused on picoplatin, Poniard will be hoping for a more positive outcome.

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