A multicenter, non-randomized, open-label, dose-exploration study evaluating two new formulations of oprozomib plus pomalidomide and dexamethasone in patients with relapsed refractory multiple myeloma. The study will be conducted in two parts. Part 1 will evaluate the formulations of oprozomib in combination with dexamethasone only. Part 2 will evaluate the formulations of oprozomib administered at increasing dose levels (dose escalation) in combination with pomalidomide and dexamethasone.