Genomics in multiple myeloma: biology and clinical implications

Aberrant hyperediting of the myeloma transcriptome by ADAR1 confers oncogenicity and is a marker of poor prognosis

The integrity of the MM transcriptome is compromised by ADAR1 overexpression, conferring oncogenic events in an editing-dependent manner. NEIL1 is an important ADAR1 editing target, and its recoded protein has a defective functional capacity and gain-of-function properties.

Biological and Clinical Implications of Clonal Heterogeneity and Clonal Evolution in Multiple Myeloma

Clonal heterogeneity and clonal evolution have emerged as critical concepts in the field of oncology over the past four decades, largely thanks to the implementation of novel technologies such as comparative genomic hybridization, whole genome/exome sequencing and epigenetic analysis. Along with the identification of cancer stem cells in the majority of neoplasia, the recognition of intertumor and intratumor variability has provided a novel perspective to understand the mechanisms behind tumor evolution and its implication in terms of treatment failure and cancer relapse or recurrence. First hypothesized over two decades ago, clonal heterogeneity and clonal evolution have been confirmed in multiple myeloma (MM), an incurable cancer of plasma cells, almost universally preceded by a pre-malignant conditioned named monoclonal gammopathy of undetermined significance (MGUS). The genetic events and molecular mechanisms underlying such evolution have been difficult to dissect. Moreover, while a role for the bone marrow microenvironment in supporting MM cell survival, proliferation and drug-resistance has been well established, whether it is directly involved in driving evolution from MGUS to MM is at present unclear. We present in this review a historical excursus on the concepts of clonal heterogeneity and clonal evolution in MM with a special emphasis on their role in the progression from MGUS to MM; the contribution of the microenvironment; and the clinical implications in terms of resistance to treatment and disease relapse/recurrence.

CD147 regulates the expression of MCT1 and lactate export in multiple myeloma cells

Increased use of the glycolytic pathway, even in the presence of oxygen, has recently been recognized as a key characteristic of malignant cells. However, the glycolytic phenotype results in increased lactic acid production and, in order to prevent cellular acidosis, tumor cells must increase proton efflux via upregulation of pH regulators such as proton-pumps, sodium-proton exchangers, and/or monocarboxylate transporters (MCT) (e.g., MCT1, MCT4). Interestingly, expression of MCT1 and MCT4 has been previously shown to be dependent upon expression of the transmembrane glycoprotein CD147. Recently, we demonstrated that primary patient multiple myeloma (MM) cells and human MM cell lines (HMCLs) overexpress CD147. Therefore, the goal of the current study was to specifically determine if MCT1 and MCT4 were also overexpressed in MM cells. RT-PCR analysis demonstrated both primary patient MM cells and HMCLs overexpress MCT1 and MCT4 mRNA. Notably, primary MM cells or HMCLs were found to express variable levels of MCT1 and/or MCT4 at the protein level despite CD147 expression. In those HMCLs positive for MCT1 and/or MCT4 protein expression, MCT1 and/or MCT4 were found to be associated with CD147. Specific siRNA-mediated downregulation of MCT1 but not MCT4 resulted in decreased HMCL proliferation, decreased lactate export, and increased cellular media pH. However, western blot analysis revealed that downregulation of MCT1 also downregulated CD147 and vice versa despite no effect on mRNA levels. Taken together, these data demonstrate the association between MCT1 and CD147 proteins in MM cells and importance of their association for lactate export and proliferation in MM cells.

Correlation between eight-gene expression profiling and response to therapy of newly diagnosed multiple myeloma patients treated with thalidomide-dexamethasone incorporated into double autologous transplantation

We performed a molecular study aimed at identifying a gene expression profile (GEP) signature predictive of attainment of at least near complete response (CR) to thalidomide-dexamethasone (TD) as induction regimen in preparation for double autologous stem cell transplantation in 112 younger patients with newly diagnosed multiple myeloma. A GEP supervised analysis was performed on a training set of 32 patients, allowing to identify 157 probe sets differentially expressed in patients with CR versus those failing CR to TD. We then generated an eight-gene GEP signature whose performance was subsequently validated in a training set of 80 patients. A correct prediction of response to TD was found in 71 % of the cases analyzed. The eight genes were downregulated in patients who achieved CR to TD. Comparisons between post-autotransplantation outcomes of the 44 non-CR-predicted patients and of the 36 CR-predicted patients showed that this latter subgroup had a statistically significant benefit in terms of higher rate of CR after autotransplant(s) and longer time to progression, event-free survival, and overall survival. These results can be an important first step to identify at diagnosis those patients who will respond more favourably to a particular treatment strategy.

Proteomics: addressing the challenges of multiple myeloma

Multiple myeloma (MM) is a malignancy of terminally differentiated B-lymphocytes that accounts for ~13% of all hematologic cancers. Despite a wealth of knowledge describing the molecular biology of MM as well as significant advances in therapeutics, this disease remains incurable. Since proteins govern the cellular structure and biological function, a wide selection of proteomic approaches holds great promise for increasing our understanding of this disease, such as by investigating the dynamic nature of protein expression, cellular and subcellular distribution, post-translational modifications, and interactions at both the cellular and subcellular levels. The aims of this review are to introduce the available and emerging proteomic technologies that have potential applications in the study of MM and to highlight the current status of proteomic studies of MM. To date, although there have been a limited number of proteomic studies in MM, those performed have provided valuable information with regard to MM diagnosis and therapy. The potential future application of proteomic technologies is expected to provide new avenues in MM diagnostics, individualized therapy design and therapy response surveillance for the clinician.

Oncology: Treatment of Multiple Myeloma in the Targeted Therapy Era

Objective:

To review the clinical trials that have impacted treatment standards of multiple myeloma (MM).

Data Source:

A PubMed search (1980–June 2008) restricted to English-language publications was conducted using the key words multiple myeloma, clinical trials, targeted therapy, thalidomide, lenalidomide, bortezomib, dexamethasone, melphalan, autologous stem-cell transplantation, and tumor biology. Abstracts emanating from the meetings of the American Society of Clinical Oncology and American Society of Hematology from June 2002 to June 2008 were also reviewed.

Data Synthesis:

Although hematopoietic stem-cell transplantation has improved the response rate and duration of overall survival, MM remains an incurable disease. However, focused research aimed at the molecular basis of the disease has led to a number of new treatment strategies. Evidence from clinical trials indicates that each of the 3 novel agents, thalidomide, lenalidomide, and bortezomib, is remarkably effective as first-line therapy. The data also suggest that clinicians may need to reevaluate the role of stem-cell transplantation in the disease.

Conclusions:

Thalidomide, lenalidomide, or bortezomib in combination with dexamethasone have replaced traditional chemotherapy such as melphalan, doxorubicin, and vincristine as initial therapy of patients with MM who are eligible for stem-cell transplantation. Furthermore, these novel drugs can be incorporated into regimens used to treat transplant-ineligible patients or those with relapsing disease.

Multiple myeloma: biology, standard therapy, and transplant therapy

The understanding of the pathogenesis of multiple myeloma has undergone a major transformation over the past eight years. New insights into the microenvironment of the plasma cell as well as elucidation of signaling pathways that prevent plasma cell apoptosis are leading to rapid new drug development. The introduction of novel agents has led to a significant increase in survival. Combinations of novel agents are expected to provide higher complete response rate with anticipated prolongation of relapse free and overall survival. Autologous and allogeneic stem cell transplantation remains an integral part of therapy further improving the outcomes following induction with novel agents.