** Shares of biotech firm Definium Therapeutics DFTX.O rise 19% to $25.02 premarket

** Co says DT120, an experimental oral drug for major depressive disorder, a common mental health condition causing persistent low mood, met main goal in late-stage study

** Says patients showed 8.1-point greater improvement in depression scores vs placebo after six weeks

** DFTX says benefit seen within one week and remained significant at 12 weeks

** Says DT120, based on lysergide (LSD), was generally well tolerated with no serious safety concerns

** Co plans to advance DT120 toward regulatory review; also testing in anxiety and PTSD

** As of last close, stock up ~83% YTD