Both "East of Eden" and "Paradise Lost" are significantly influenced by the Biblical stories of the Garden of Eden (Genesis chapter 2), the disobedience of Adam and Eve resulting in their expulsion from the Garden of Eden (Genesis chapter 3), and the relationship between their sons Cain and Abel (Genesis chapter 4).  "Paradise Lost" addresses the downfall of humanity as a result of disobedience of the word of God and the consequences of that action.  Adam and Eve are sent out and God sets guards at the east side of the garden to prevent any access.  "East of Eden" is an allegory, a retelling of the story of the conflict between the two siblings and its results.