update 2013-01-31: this post has been deprecated; please see The rise and fall of pentosan polysulfate in prion disease for a more complete treatment of the subject.
Another potential therapeutic which has been studied, of which we learned only recently, is pentosan polysulfate, originally approved for treating interstitial cystitis of the bladder. This garnered a lot of attention in the early 2000s and made it further than anything besides quinacrine and doxycycline have done– it was administered to 11 patients in Japan and at least 7 in the UK, and has led to some patients living quite a long time– BBC reports on one person living with vCJD for at least three years under treatment with pentosan polysulfate. Though there was never a clinical trial, this drug wound up being the subject of a rather extensive study by Dr. Ian Bone, who seems to have concluded that the drug is not necessarily effective, results in some surgical complications, and did not merit much further study: “There are currently no prospective open dose-finding and efficacy (phase I/II) follow-up studies planned.” Re: the surgical complications, the drug doesn’t cross the blood-brain barrier, so it was administered using an intraventricular catheter, meaning a hole was drilled in the patient’s skull and the drug was dripped in continuously. Predictably this seems to have resulted in a lot of serious infections.
In spite of all this, the UK’s MRC Prion Unit till lists pentosan polysulfate as one of its potential drug treatments for prion disease, and bene pharmaChem, which owns the drug, still promotes prion disease as a potential application for the drug. The most recent paper I could find [Honda 2011], published in Neuropathology, dissects brains of patients treated with the drug and did not seem to find any clear signs of what the drug had achieved.