** Shares of drug developer Tectonic Therapeutic TECX.O fall 37.6% to $15.49 premarket

** AstraZeneca AZN.L has discontinued AZD3427, its relaxin-based drug for a type of heart-related disease, citing efficacy concerns

** Tectonic is testing TX45, another relaxin-based therapy targeting similar heart conditions

** Despite the setback, Mizuho analyst Uy Ear believes "TX45 may still have a chance," even though investors might view AZD3427's failure as a negative signal for similar drugs

** Independent Data Monitoring Committee (IDMC) recently advised TX45's mid-stage study continue unchanged, analyst notes

** In an early-stage study, TX45 showed improved blood flow and reduced pressure in lungs and heart

** Last year, Eli Lilly LLY.N also discontinued its own relaxin drug volenrelaxin, after disappointing mid-stage trial data

** TECX fell 54% in 2025

(Reporting by Kamal Choudhury in Bengaluru)

((Kamal.Choudhury@thomsonreuters.com;))