You mean the same way that Sigma-1 Pridopidine failed for Teva after early success?
When I look at a potential drug I try to find reasons it might fail, that's why I'm so informed about several of these drugs. It doesn't take long to find S-1 or M-1 problems as research advances.
Or this failure in Japan? "A Japanese drug company, Toyama Chemical, is developing an Alzheimer's drug with the same sigma-1 receptor mechanism of action as Anavex's Anavex 2-73. Two years ago, Toyama reported results from a randomized, placebo-controlled phase IIa study enrolling 370 Alzheimer's patients.
Certainly not simple, that's why AVXL failed in combo with another Sig-1 binder donepezil. Failed PR and the only US granted patent AVXL has for 273 for AD that I can see.