The purpose of this study is to determine whether pralatrexate, given with vitamin B12 and folic acid, is effective in the treatment of advanced or metastatic bladder cancer. The study will also investigate the safety of pralatrexate with vitamin B12 and folic acid in this patient population. Additionally, this study includes the collection of blood samples to investigate the pharmacokinetics (PK) of pralatrexate in this patient population (PK is the activity of a drug in the body over a period of time, including how the drug is absorbed, distributed in the body, localized in the tissues, and excreted from the body).