Amine substituted reverse pyrimidine compounds and forms thereof that inhibit the function and reduce the level of B-cell specific Moloney murine leukemia virus integration site 1 (Bmi-1) protein and methods for their use to inhibit Bmi-1 function and reduce the level of Bmi-1 to treat a cancer mediated by Bmi-1 are described herein. 4,6-diamino-pyrimidine compounds of Formula (I) are described, wherein R1 is substituted 1H-benzimidazolyl, X is N, R2 is amino and the remaining substituents are as defined herein.