Recent advances in genomics and proteomics in multiple myeloma (MM) have allowed for advances in our understanding of disease pathogenesis, identified novel therapeutic targets, allowed for molecular classification, and provided the scientific rationale for combining targeted therapies to increase tumor cell cytotoxicity and abrogate drug resistance. Specifically, gene microarray profiling has shown major differences between normal plasma cells versus those from monoclonal gammopathy of unclear significance (MGUS) and multiple myeloma (MM), with further modulations within MM and progression to plasma cell leukemia.1 These studies identify genetic changes associated with progression of MGUS to MM, with great promise for prognostic or therapeutic application. Moreover, known genes likely represent only the tip of the iceberg, and ongoing efforts are integrating comparative genomic hybridization (aCGH), spectral karyotyping (SKY), and expression profiling data, followed by functional validation in cancer and MM models, to identify new therapeutic targets. Specifically aCGH analyses of 55 MM cell lines and 73 patient samples has identified 46 amplicons, containing 258 genes overexpressed by gene profiling. These putative oncogenes are being correlated with similar studies of lung, pancreatic, and colon cancers, as well as glioblastomas, in order to further select for common oncogenes. Functional validation in cancer and MM models will allow for identification of novel gene products critical in MM pathogenesis to be targeted with novel small molecule or antibody therapies. In a recent study, correlation of expression profiling for cyclin D, five recurrent IgH translocations, and specific trisomies has formed the basis for a new classification system in MM, with important prognostic and therapeutic implications.2 For example, clinical trials are ongoing with a specific tyrosine kinase inhibitor targeting fibroblast growth factor receptor 3 (FGFR3), which is expressed only in 15-20 percent of patients. It is also possible to profile individual newly-diagnosed patients in order to tailor specific targeted therapy.3 As in infectious diseases, it is likely that cocktails of targeted therapeutics will be needed to overcome resistance.
Recognition of the role of the bone marrow (BM) milieu in conferring growth, survival, and drug resistance in MM cells, both in laboratory and animal models, has allowed for the establishment of a new treatment paradigm targeting the tumor cell and its microenvironment to overcome drug resistance and improve patient outcome in MM4 , which now serves as a model for target identification, drug validation, and rapid translation from the laboratory to the clinic.5 Our studies both in vitro and in vivo in a SCID mouse human MM model have demonstrated modulations associated with binding of MM cells to BM, including upregulation of growth, survival, and drug resistance genes in MM cells; increased adhesion molecule expression on MM cells and BM stromal cells (SCs); and increased cytokine transcription and secretion in BMSCs. Thalidomide, the proteasome inhibitor Bortezomib, and the novel immunomodulatory drug lenalidomide maintain their cytotoxicity against MM cells even in the BM milieu by: directly inducing apoptosis of drug resistant MM cells; decreasing their adhesion to BMSCs and extracellular matrix proteins; downregulating transcription and secretion of cytokines in the BM milieu mediating tumor cell growth, survival, and migration; inhibiting angiogenesis; and stimulating host anti-MM immunity.4 Each of these drugs has first been shown to have anti-tumor activity in relapsed and refractory MM, both alone and when combined with Dexamethasone (Dex). Clinical trials have then rapidly evaluated their utility earlier in the disease course, including relapsed and newly-diagnosed patients. Both frequency and extent of response is markedly increased. For example, either Bortezomib or lenalidomide combined with Dex can achieve responses in the majority of patients with newly-diagnosed MM, including one-third complete or near complete responses6,7 These studies serve as a testament to the power of collaborations between academia, pharmaceutical companies, Food and Drug Administration (FDA), National Cancer Institute, and advocacy groups to rapidly identify therapeutic targets in the MM cell and its BM microenvironment, use laboratory and animal models of human MM to validate novel agents directed at these targets, and then design clinical trials evaluating these agents which ultimately lead to their rapid FDA approval.5
Finally, correlative gene profiling, proteomic, and signaling studies in tumor cell samples from patients treated on clinical trials of novel agents can: establish the in vivo mechanisms of sensitivity versus resistance to novel agents; provide the rationale for selection of patients most likely to respond; serve as the framework for the design of combination therapy strategies to enhance sensitivity and even overcome resistance in MM cells; and suggest strategies for the development of next generation more potent, selective, and less toxic novel targeted therapeutics. For example, gene profiling studies of MM cells after Bortezomib treatment showed induction of heat shock protein 90 (hsp 90); conversely, blockade of hsp 90 with 17 AAG enhances sensitivity and even overcomes resistance to Bortezomib in preclinical studies8 . Clinical trials already show efficacy of combined therapy in Bortezomib refractory MM. Recently, our laboratory has demonstrated the importance of the aggresome cascade for protein catabolism; identified histone deacetylase 6 (HDAC 6) to be essential in the chaperoning of ubiquinated proteins for aggresomal degradation; and validated the preclinical anti-MM activity of a newly synthesized HDAC 6 inhibitor tubacin9 . Most excitingly, dual inhibition of proteasomes and aggresomes with Bortezomib and tubacin, respectively, induces synergistic cytotoxicity, setting the stage again for clinical translation of a new class of cancer therapeutics. Finally, correlative science studies on patient samples showed upregulation of hsp 27 as a mechanism of Bortezomib resistance, setting the stage for preclinical and clinical studies of p38 MAPK inhibitors to downregulate hsp27 and thereby overcome Bortezomib resistance.10 These studies illustrate the use of oncogenomics to inform design of clinical protocols to enhance cytotoxicity, overcome drug resistance, and improve patient outcome.
In summary, a new paradigm for overcoming drug resistance and improving patient outcome in MM has great promise, not only to change the natural history of MM, but also to serve as a model for targeted therapeutics directed to improve outcome of patients with other hematologic malignancies and solid tumors as well.
