CurePSP asked me to write up something on ASOs for their website (www.curepsp.org). Thought I’d give my loyal blog readers a sneak peak:
Probably the single biggest story in the world of PSP right now is NIO752. That’s an antisense oligonucleotide (ASO) being tested for safety and tolerability in people with PSP.
ASOs interrupt the process by which a specific gene’s DNA is transcribed into RNA, thereby reducing the production of the encoded offending protein. The ASO itself is a short stretch of RNA whose genetic code is a mirror-image of part of the DNA whose translation is to be suppressed. The ASO’s genetic sequence and that of the offending DNA recognize each other and stick together, preventing the corresponding protein from being produced. In this case, the targeted DNA is the MAPT gene, which encodes the tau protein. Other ASOs operate by targeting slightly different stages of the transcription/translation process.
In the US, the FDA has approved several kinds of ASO, the best-known being nusinersin (brand name “Spinraza”) for spinal muscular atrophy, a progressive and usually fatal condition that typically starts in infancy but in mild forms can start at any age. In the pivotal trial of nusinersen, 21 of 51 infants receiving the drug were improved after 6 months, while that was true for none of the 27 infants receiving sham treatment. If we can achieve similar results for NIO752, it would be by far the best news ever for PSP.
ASO molecules are too large to cross the blood-brain barrier, which means that for a brain disease, they must be administered by injection directly into the spinal fluid. This is performed as for a diagnostic spinal tap. In the current trial, NIO752 is given once monthly over a period of 3 months and the participants are examined periodically for an additional 9 months. The 64 participants are at 4 sites in the US (La Jolla, CA; Boca Raton, FL; Rochester, MN and Nashville TN), 2 in Canada (both in Montreal), 5 in Germany and 1 in the UK. This safety and tolerability trial is expected to end in May 2024. Its sponsor is Novartis Pharmaceuticals, co-headquartered in Basel, Switzerland and Cambridge, MA. For more information: 1-888-669-6682 or firstname.lastname@example.org
A trial can detect important safety issues with only 64 participants but detecting actual benefit requires more. The standard “primary outcome measure” for clinical treatment trials in PSP is the PSP Rating Scale. Assuming that is still the case in 2024, when a treatment trial would begin, and half of the participants receive placebo, the minimum number of participants needed would be 276. That number also assumes that the study is designed to detect at least a 30% difference between the two groups’ rates of progression. Detecting less of a difference would require more participants and detecting a greater difference would require fewer. A new outcome measure with less variability than the PSPRS would reduce the number of participants required.
From the standpoint of those with PSP and their families hoping to enter a trial of NIO752, the most important number isn’t a number, but a date: A trial starting in mid-2024 would probably end in 2027. Another important number is the eventual price of the drug. NIO752 would have to be injected every month, lifelong. Nusinersen’s price is $125,000 per injection. So, if the price of NIO752 is anything like that, the cost to Medicare, Medicaid and private insurors would present an impossible situation. CurePSP estimates that about 20,000 people in the US have PSP at any given time. If even half of them received a $125,000-per-month drug, the total annual cost would be $15 billion plus the doctors’ fees for the monthly injection procedure. Clearly, something would have to give.
But first, let’s hope that NIO752 actually works.