Translational Research
Targeting Protein Translation as a New Strategy for the Treatment of Multiple Myeloma
mRNA competition for translation initiation. The mRNA cap-binding eukaryote initiation factor 4E (eIF4E) is rate limiting for cap-dependent translation. The strong mRNAs, which are well translated even when the availability of eIF4E is limiting, and the weak mRNAs, which are translated only when eIF4E availability is increased, as in malignancy. The translational efficiency of mRNA with highly complex 5’-untranslated regions is especially dependent on eIF4E levels. An increase in eIF4E level or activity does not lead to increased rates of global translation, but instead results in increased translation of mRNAs with highly complex 5’-untranslated regions (Figure adapted with permission from De Benedetti A, Graff JR.Oncogene 2004;23:3189–3199)
The translation initiation factor eIF4E is critical for protein synthesis in general and induces a malignant phenotype by regulating oncogenic protein translation. Aberrant control of protein synthesis contributes to lymphomagenesis opening up possibilities of innovative therapeutics by targeting the translational machinery. Therefore, our laboratory focuses on the understanding of the mechanisms that control protein synthesis as an exciting new research area in multiple myeloma with significant potential for developing innovative therapies. Our data so far showed that the levels of free eIF4E are significantly elevated in multiple myeloma and knockdown of eIF4 in vitro and in vivo lead to complete inhibition of multiple myeloma cell growth and induction of apoptosis. We anticipate that our studies will increase the understanding of the role of eIF4E in multiple myeloma and evaluate whether translation controlling drugs can potentially be used as a new strategy for future therapy.
Development of Anti-Amyloid Fibril-Reactive Monoclonal Antibodies for Treatment of AL Amyloidosis
Amyloid light chain (AL) amyloidosis is an incurable rare monoclonal plasma cell dyscrasia closely related to multiple myeloma. The clonal plasma cells produce excessive misfolded monoclonal immunoglobulin light chains which form extracellular insoluble fibrils, destroy tissue architecture, cause functional damage in organs, and eventually lead to death. We are developing AL amyloid fibril specific monoclonal antibodies, which recruit macrophages to the fibril and resolve the deposition by phagocytosis.
AL Amyloidosis is characterized by the pathologic deposition of light chain fibrils in vital organs that lead to their eventual failure and, ultimately, result in death. All established therapies in amyloidosis focus on the destruction of plasma cells and subsequently the stop of the production of light chains forming the amyloid. Hence the new accumulation of amyloid will be prohibited, but unfortunately, existing amyloid will not be affected by the treatment resulting in continuous impairment of the organ function. Immunotherapy using monoclonal antibodies targeting directly the amyloid fibrils and subsequently destroying the existing amyloid is a very innovative and exciting approach. The amyloid fibril-reactive monoclonal antibody binds to a structure only present on human light-chain amyloid fibrils and initiates cell-mediated phagocytosis. Antibody-dependent phagocytosis is a major mechanism of action of many antibodies against cancer through the interaction between the Fc region on antibodies with its receptors on the macrophage surface. Macrophage and neutrophil-mediated phagocytosis is a critical step for amyloid elimination as confirmed by in vivo studies. Therefore our research focuses on the development of bispecific antibodies, which target well-identified macrophage/neutrophil cell surface markers as well as AL amyloid, to further enhance amyloid elimination. The use of antibody immunotherapy aiming at reversing fibril deposition will result in a more favorable outcome due to improved organ function, as compared to chemotherapy which only targets the amyloid-precursor producing plasma cell clone.
Targeting Multiple Myeloma Bone Disease
MM induced OCL fusion is mediated by the MMP-13/PD-1H axis. BM stromal cells express high IL-6 which further upregulates the MMP-13 secretion from myeloma cells. MMP-13 binds to PD-1H on OCL cell surface. The binding enhances RANKL triggered activation ERK1/2 mediated upregulation of NFATc1 and DC-STAMP and enhancing cell fusion.
Multiple myeloma is characterized by increased osteoclast (OCL) activity and reduced bone formation that results in bone destruction and purely lytic lesions in ~80% of the patients. Multiple myeloma cells secret osteoclastogenic factors causing dysregulation of the bone remodeling process that leads to excessive bone resorption mediated by activated OCLs. Our laboratory focuses on the identification of new pro-osteoclastogenic agents that could potentially serve as therapeutic targets capable of ameliorating bone disease. We found that myeloma cells express high levels of the matrix metalloproteinase, MMP-13. MMP-13 directly enhances osteoclast multinucleation and bone-resorptive activity by triggering up-regulation of the cell fusogen, DC-STAMP, independently of the enzyme’s proteolytic activity. Further, in mouse xenograft models, silencing MMP-13 expression in myeloma cells inhibits the development of osteolytic lesions. In patient cohorts, MMP-13 expression localizes to bone marrow-associated myeloma cells while elevated MMP-13 serum levels predict correctly the presence of active bone disease. Our data demonstrate that MMP-13 is critical for the development of osteolytic lesions in multiple myeloma, and that targeting the MMP-13 protein – rather than its catalytic activity – constitutes a novel approach ameliorating bone disease in affected patients.
Our current work focuses on delineating the effects of MMP-13 on osteoclasts as well as on the development of strategies to block MMP-13 for the treatment of MM bone disease.
Targeting GCK as a Novel and Selective Therapeutic Strategy Against RAS Mutated Multiple Myeloma
In RAS mutated MM, activating mutations in RAS proteins inhibit GTPase activity resulting in constitutive activation of RAS downstream effector pathways including GCK. The inhibition of GCK induces IKZF1 degradation independent of CRBN, then induced downregulation of IRF4 and c-MYC and associated MM cytotoxicity
MM is characterized by clonal evolution with a rising number of mutations. Around 43% of newly diagnosed and MM patients carry RAS mutations associated with a poorer prognosis. Unfortunately, so far there is no treatment targeting RAS mutations in MM. Our work demonstrated that K- or N-RAS mutated MM cells express elevated levels of Germinal Center Kinase (GCK) and are more sensitive to GCK inhibition than RAS wild-type (WT) MM. This led to the hypothesis that the inhibition of GCK will be especially effective not only in RAS mutated MM but also in other malignancies harboring K- or N-RAS mutations. In light of this, our research will present novel approaches for the treatment of RAS mutation-driven cancer. Moreover, we found that blocking GCK overcomes resistance to Immunomodulatory Derivatives (IMiDs) in MM by cereblon-independent degradation of transcriptions factors critical for MM. Therefore, blocking GCK based on RAS-mutational status holds significant therapeutic potential for the treatment of relapsed/refractory and especially multi-drug resistant MM.