AstraZeneca, Stroke, NXY-059--the Saint-2 trial
Astrazeneca Stroke nxy-059
Oxygen? "I rarely use it myself, sir. It promotes rust." Robby the Robot, Forbidden Planet (1956)
1) The positive results in the Saint-1 trial likely reflect neuroprotectant activity.
2) The negative results in the Saint-2 trial show this neuroprotectant is not NXY-059.
3) The putative neuroprotectant is likely t-butylhydroxylamine (NtBHA) and/or its parent spintrap 2-methyl-2-nitrosopropane (MNP) produced by in vitro hydrolysis of NXY-059.
4) The trial methodology both detected an unexpected neuroprotectant and distinguished this from NXY-059.
Briefly. After very promising results in the first clinical trial (Saint-1) using NXY-059 for the treatment of stroke, the second NXY-059 trial (Saint-2) failed.
It is unlikely that a drug demonstrating significant neuroprotection in a stroke trial involving 1700 patients should so utterly fail in a second neuroprotection trial involving almost double that number. Moreover, a second parallel trial, looking at prevention of hemorrhagic stroke secondary to the use of the clot-buster tPA, showed even more striking results in Saint-1, with a p value less than 0.005. Further, this was on the basis of hard, dichotomous ("yes or no") radiological data and not a "soft" measure of function such as the Modified Rankin Scale.
The difference between Saint-1 and Saint-2 seems too large to be accounted for by variations in the experimental methodology or patient population. Arguably, there was some material difference in the drug formulations used in the two trials.
PBN derivatives such as NXY-059 (PBN-2,4,disulfonate) are somewhat unstable. During storage and in solution such nitrones spontaneously hydrolyze to produce the corresponding benzaldehyde derivative and N-t-butylhydroxylamine ("NtBHA" or "MNP-OH"). As an AstraZeneca patent notes in another context, NtBHA then readily "aerial oxidizes" to its parent spintrap, MNP or "2-methyl,2-nitroso propane"*.
In vivo, NtBHA scavenges radicals significantly better than PBN, forming more MNP. In addition to scavenging radicals itself, MNP is reduced by (say) vitamin-C back to NtBHA.
For some refs, go here, here, and here and follow to the citing papers.
Moreover, on exposure to light or in oxidizing conditions, MNP releases nitric oxide (NO). Thus, e.g., Lapchak et al, Lapchal and Araujo and a Swedish PhD dissertation (warning--large file). On Page 46, the dissertation author notes, "According to AstraZeneca representatives there is no evidence of any in vivo decomposition of S-PBN or NXY-059 (personal communication)...". Note the in vivo limitation.
NO is a natural messenger substance with antiplatelet, antioxidant, neuroprotective and blood-vessel-dialating properties. On paper at least, the NtHBA-MNP couple is a designer neuroprotectant, both scavenging radicals and, unlike other NO-donors, releasing NO specifically at sites of oxidative stress, but not much elsewhere. This may be what it takes to get an effective human neuroprotectant. Incidentally, this writer pointed out the connection between the spin traps and nitric oxide and the relationship this has to stroke.
Ignoring other products, these reactions are roughly as follows:
Such neuroprotective hydrolysis products might account for the apparent efficacy found in the Saint-I trial and their absence for the failure of the Saint-II trial. Something almost identical to Saint-1 and Saint-2 occurred in previous studies with PBN, in which it similarly proved impossible to replicate earlier results produced with "aged" PBN. This was later tracked down to NtBHA and MNP production during storage.
Among possible scenarios: By history, the Saint-1 trial was suspended pending more animal toxicity studies. Perhaps, as a result of this months-long delay, the Saint-1 trial was done with "Old" NXY-059 and Saint-2 with new. NtHBA and its air oxidation product MNP would be produced during storage.
Significantly, the '527 patent also states: "...it is apparent that one pathway for the decomposition involves hydrolysis of the nitrone functional group to yield the aldehyde (II) and N-tert-butylhydroxylamine as products. A second pathway involves an autoxidation process, possibly involving a free radical mediated degradation. In this pathway the same two products are formed initially but the N-tert-butylhydroxylamine subsequently undergoes further reactions to give other products..."
Arguably, application of the technology outlined in AZ's '527 patent to the Saint-2 trial may explain its failure. In this scenario, as the Saint-1 trial progressed, AZ researchers became aware of the "unacceptably short" storage life of NXY-059. Possibly, they then attempted to correct this before the Saint-2 trial, say, by flushing the material with nitrogen, keeping the pH well above 7, etc., as detailed in the '527 patent. Alternately, there was no change in the formulation and the many variables that modulate the rate of hydrolysis came into play.
Finally, because of the failure of previous trials for neuroprotective agents, extraordinary effort went into setting up the Saint-1 and Saint-2 trials. The failure of the Saint-2 trial in the face of the putative success of the Saint-1 trial has resulted in much unjustified "what did we do wrong?" gloom and despair on the part of the investigators.
In fact, their only likely error is not crediting what the cumulative Saint-2/Saint-2 trials demonstrate. This is that a neuroprotectant is present, though not the one expected. Further, the trial methodology is not only sufficient to demonstrate this neuroprotectant (whatever it may be), but to distinguish it from NXY-059. Whether or not this lead is followed up, this is a finding of much import for further research on neuroprotectants, since it shows the methodology works well.
Disclosure: I own patent claims covering nitrone and nitroso spin traps, including MNP and its reduction products.
Phone: 713-960-1616 or firstname.lastname@example.org
Peter H. Proctor, PhD, MD
Who am I and why can I say this
* MNP is also variously known as "2-methyl-2 nitrosopropane", "tert-nitrosobutane" or "t-NB".
** The Swedish version of the '527 patent (PCT/SE01/01164) lists AstraZeneca as the applicant.
Key words: NXY-059 astrazeneca stroke renovis saint organic semiconductors conductive polymers NXY-059 astrazeneca stroke renovis saint neuroprotection mnp tertiary-nitrosobutane 2-methyl,2-nitrosopropane n-tertiary-butylhydroxylamine NtBHA renovis centaur antioxidant in vitro Stair clinical trial preclinical subarachnoid in vivo t-hba N-thba neuroprotective vascular endothelium stroke AstraZeneca. Clot buster tpa cerebral hemorrhage STAIR committee neuroprotection saint-1 as well as saint-2 clinical trial failure cerovive. 2-methyl-2-nitrosopropane butylhydroxylamine NtBHA.
This link is irrelevant, at least at the moment. I leave it to provide links so the search engines don't get confused.