The invention describes a potent, orally bioavailable small molecule isoQC inhibitor targeting the CD47-SIRP⍺ immune checkpoint signal. DBPR22998 effectively inhibits isoQC enzyme activity, reducing the binding of CD47 and SIRPα on the surface of tumor cells and the "don＇t eat me" signal. DBPR22998 is best used in combination with monoclonal antibody-targeted drugs or immune checkpoint antibodies to promote antibody-dependent cell phagocytosis and enhance tumor elimination.