The present invention relates to new compounds of Formulas (I) and (II), their tautomers, stereoisomers and polymorphs, and pharmaceutically acceptable salts, esters, metabolites or prodrugs thereof, compositions of the new compounds together with pharmaceutically acceptable carriers, and uses of the new compounds, either alone or in combination with at least one additional therapeutic agent, in the inhibition of Pirn kinase activity and/or the prophylaxis or treatment of cancer.