STING agonist-3 trihydrochloride, extracted from patent WO2017175147A1 (example 10), is a selective and non-nucleotide small-molecule STING agonist with a pEC50 and pEC50 of 7.5 and 9.5, respectively. STING agonist-3 trihydrochloride has durable anti-tumor effect and tremendous potential to improve treatment of cancer.