Drug targets and resistance mechanisms in multiple myeloma

Multiple myeloma (MM), a malignancy of plasma cells, is the second most prevalent blood cancer (10%). A PubMed search has been conducted for English research papers and reviews published until January 2018. Numerous drugs are used in treatment of MM. These include the antineoplastic alkylating agents cyclophosphamide, busulfan and melphalan, immunomodulators such as lenalidomide and thalidomide, corticosteroids including dexamethasone, microtubule-targeting agents, such as paclitaxel and vinca alkaloids, as well as the proteasome inhibitors bortezomib and carfilzomib. Despite the considerable number of treatment options, MM is still difficult to treat, which is mirrored by the poor 10-year survival rate of 3%. Resistance to chemotherapy is often the cause for therapy failure. These resistances can be due to the overexpression of efflux pumps, genetic and epigenetic aberrations and the microenvironment of MM. With the gain of knowledge regarding genetic and molecular changes, many molecular targeted therapies including cell signaling targeted therapies are being developed against relapsed/refractory MM. Additionally, epigenetic aberrations such as DNA methylation and histone modifications steered MM management in new directions. Amongst these novel targeted therapies, inhibitors of histone deacetylase, Aurora kinase, inhibitors of the PI3K/AKT/mTOR pathway and cyclin dependent kinases are promising.