The present disclosure describes heterocyclic compounds of Formula I or, its stereoisomers, pharmaceutically acceptable salts, complexes, hydrates, solvates, tautomers, polymorphs, racemic mixtures, optically active forms and pharmaceutically active derivatives thereof and pharmaceutical compositions containing them as the active ingredient. The present disclosure also describes the synthesis and characterization of aforementioned compounds to exhibit high anticancer activity. The compounds of the present disclosure are useful as medicaments and their use in the manufacture of medicaments for treatment, prevention, or suppression of diseases, and conditions mediated by one or more BET family of bromodomains.