LEE011-d6 is the isotope analog of LEE011(L321000). LEE011 is an orally bioavailable and highly specific CDK4/6 (cyclin-dependent kinase 4/6) inhibitor. LEE011 in combination with LGX818 (a V600E BRAF specific inhibitor) or BYL719 (a PIK3CA specific inhibitor) leads to robust anti-tumor activity in melanoma and breast cancer tumor models.