Ben Van Camp

Evidence that the clonogenic cell in multiple myeloma originates from a pre‐switched but somatically mutated B cell

Summary. There is still much controversy about the precursor cell type in multiple myeloma (MM). Some authors claim that it is a pre‐B cell, others state that it is a memory B cell or plasmablast. We have recently shown that the VDJ region of the MM immunoglobulin heavy chain gene is somatically hypermutated and antigen selected, without intraclonal variation or evolution in time. By using a patient‐specific PCR approach we have now obtained evidence that the premyeloma cell can be situated in the pre‐switched B‐cell compartment and that heavy chain switching can occur without further somatic mutation. Based on the MM immunoglobulin sequences derived from the bone marrow, patient‐specific CDR2 and CDR3 oligonucleotides were designed. B lymphocytes were separated from plasma cells based on the expression of CD19 and HLA class II or surface bound IgM using immunomagnetic beads. The expressed Ig sequences were amplified by RT‐PCR using patient specific CDR2 primers and isotype specific primers (Cμ, Cγ and Cα). Myeloma‐specific Ig sequences were detected by a myeloma‐specific CDR 3 probe and sequenced. In one out of five cases we found in the peripheral blood clonally related IgM and IgA sequences with the same somatic mutations as the MM‐IgG sequence. In another case of an IgG MM we found in the bone marrow clonally related IgA sequences with the same somatic mutations. These findings, together with the fact that myeloma‐Ig genes contain somatic mutations without intraclonal variation, suggest that the clonogenic cell in multiple myeloma can originate from a pre‐switched but somatically mutated B cell.

Multiple myeloma biology: lessons from the 5TMM models

Summary:  Multiple myeloma (MM) is a B cell neoplasm characterized by the monoclonal proliferation of plasma cells in the bone marrow, the development of osteolytic lesions and the induction of angiogenesis. These different processes require three‐dimensional interactions, with both humoral and cellular contacts. The 5TMM models are suitable models to study these interactions. These murine models originate from spontaneously developed myeloma in elderly mice, which are propagated by in vivo transfer of the myeloma cells into young syngeneic mice.

Targeting the multiple myeloma hypoxic niche with TH-302, a hypoxia-activated prodrug

Hypoxia is associated with increased metastatic potential and poor prognosis in solid tumors. In this study, we demonstrated in the murine 5T33MM model that multiple myeloma (MM) cells localize in an extensively hypoxic niche compared with the naive bone marrow. Next, we investigated whether hypoxia could be used as a treatment target for MM by evaluating the effects of a new hypoxia-activated prodrug TH-302 in vitro and in vivo. In severely hypoxic conditions, TH-302 induces G(0)/G(1) cell-cycle arrest by down-regulating cyclinD1/2/3, CDK4/6, p21(cip-1), p27(kip-1), and pRb expression, and triggers apoptosis in MM cells by up-regulating the cleaved proapoptotic caspase-3, -8, and -9 and poly ADP-ribose polymerase while having no significant effects under normoxic conditions. In vivo treatment of 5T33MM mice induces apoptosis of the MM cells within the bone marrow microenvironment and decreases paraprotein secretion. Our data support that hypoxia-activated treatment with TH-302 provides a potential new treatment option for MM.

Role of CCR1 and CCR5 in homing and growth of multiple myeloma and in the development of osteolytic lesions: a study in the 5TMM model

Multiple myeloma (MM) is a plasma cell malignancy, characterized by the localization of the MM cells in the bone marrow (BM), where they proliferate and induce osteolysis. The MM cells first need to home or migrate to the BM to receive necessary survival signals. In this work, we studied the role of CCR1 and CCR5, two known chemokine receptors, in both chemotaxis and osteolysis in the experimental 5TMM mouse model. A CCR1–specific (BX471) and a CCR5–specific (TAK779) antagonist were used to identify the function of both receptors. We could detect by RT-PCR and flow cytometric analyses the expression of both CCR1 and CCR5 on the cells and their major ligand, macrophage inflammatory protein 1α (MIP1α) could be detected by ELISA. In vitro migration assays showed that MIP1α induced a 2-fold increase in migration of 5TMM cells, which could only be blocked by TAK779. In vivo homing kinetics showed a 30% inhibition in BM homing when 5TMM cells were pre-treated with TAK779. We found, in vitro, that both inhibitors were able to reduce osteoclastogenesis and osteoclastic resorption. In vivo end-term treatment of 5T2MM mice with BX471 resulted in a reduction of the osteolytic lesions by 40%; while TAK779 treatment led to a 20% decrease in lesions. Furthermore, assessment of the microvessel density demonstrated a role for both receptors in MM induced angiogenesis. These data demonstrate the differential role of CCR1 and CCR5 in MM chemotaxis and MM associated osteolysis and angiogenesis.

Post‐transplantation tumour load in bone marrow, as assessed by quantitative ASO‐PCR, is a prognostic parameter in multiple myeloma

High‐dose therapy (HDT) and autologous transplantation prolongs remission duration and survival in multiple myeloma (MM), but relapse still occurs at a median of 2 years post‐HDT. In order to investigate whether the number of residual tumour cells in the bone marrow (BM) after transplantation can predict the duration of response, a quantitative allele‐specific oligonucleotide polymerase chain reaction (qASO‐PCR) assay was used to measure tumour load in BM at 3–6 months post‐HDT in 67 patients. The method of maximally selected log‐rank statistics was used to test for the existence of a cut‐off value in the BM tumour load data set. A cut‐off value with respect to progression‐free survival (PFS) was identified (P = 0·001). The estimated threshold for placing patients into a ‘good’ or ‘bad’ prognostic group was 0·015% (n = 22 and 38 respectively) with a median PFS of 64 months vs. 16. Multivariate analysis showed grouping by PCR result to be an independent prognostic factor for PFS (estimated hazard ratio after shrinkage, 3·91). This study identifies for the first time a threshold of the post‐HDT tumour load with prognostic significance for PFS in MM. Quantitative molecular assessment thus may help to identify those patients who are in need of further treatment early after autologous transplantation.

Detection of monoclonal B lymphocytes in bone marrow and peripheral blood of multiple myeloma patients by immunoglobulin gene rearrangement studies

To investigate whether B lymphocytes are involved in the malignant cell clone of multiple myeloma (MM), we performed immunoglobulin gene rearrangement analysis of mononuclear cells and separated B lymphocytes, isolated from bone marrow and peripheral blood of MM patients. The B lymphocytes were separated by immunomagnetic beads, coated with an HLA class II specific antibody. Southern blot analysis with a JH probe revealed in the bone marrow of three out of seven patients identical immunoglobulin gene rearrangements in the B lymphocytes when compared to the plasma cells. Out of 10 patients, two patients with a high tumour burden were found to have monoclonal B lymphocytes in the peripheral blood. These results suggest that B lymphocytes in the bone marrow are part of the myeloma clone and that they can circulate in the peripheral blood. Although previous studies indicated that the ratio of K to λ bearing lymphocytes in the peripheral blood can provide evidence for B cell monoclonality, we did not find a correlation between the results of K/λ analysis and immunoglobulin gene rearrangement.

Targeting the IGF-1R using picropodophyllin in the therapeutical 5T2MM mouse model of multiple myeloma: beneficial effects on tumor growth, angiogenesis, bone disease and survival.

During the last decade, a central role for insulin‐like growth factor 1 (IGF‐1) in the pathophysiology of multiple myeloma (MM) has been well established. IGF‐I provided by the tumor–microenvironment interaction may directly and indirectly facilitate the migration, survival and expansion of the MM cells in the bone marrow (BM). The inhibition of the IGF‐1R‐mediated signaling pathway has recently been suggested to be a possible new therapeutic principle in MM. Using the mouse 5T2MM model, we now demonstrate that targeting the IGF‐1R using picropodophyllin (PPP) in a therapeutical setting not only has strong antitumor activity on the established MM tumor but also influences the BM microenvironment by inhibiting angiogenesis and bone disease, having a profound effect on the survival of the mice. At therapeutically achievable concentrations of PPP, the average survival was 180 days for the PPP‐treated mice as compared to 100 days for vehicle‐treated mice. PPP used as single drug treatment in the 5T2MM model resulted in a decrease of tumor burden by 65% while the paraprotein concentrations were reduced by 75%. This decrease was associated with a significant inhibition of tumor‐associated angiogenesis and osteolysis. The present studies on the biological effects of PPP in the 5T2MM model constitute an important experimental platform for future therapeutic implementation.

Bone Marrow-Derived Mesenchymal Stromal Cells Are Attracted by Multiple Myeloma Cell-Produced Chemokine CCL25 and Favor Myeloma Cell Growth In Vitro and In Vivo

Multiple myeloma (MM) is a malignancy of terminally differentiated plasma cells that are predominantly localized in the bone marrow (BM). Mesenchymal stromal cells (MSCs) give rise to most BM stromal cells that interact with MM cells. However, the direct involvement of MSCs in the pathophysiology of MM has not been well addressed. In this study, in vitro and in vivo migration assays revealed that MSCs have tropism toward MM cells, and CCL25 was identified as a major MM cell‐produced chemoattractant for MSCs. By coculture experiments, we found that MSCs favor the proliferation of stroma‐dependent MM cells through soluble factors and cell to cell contact, which was confirmed by intrafemoral coengraftment experiments. We also demonstrated that MSCs protected MM cells against spontaneous and Bortezomib‐induced apoptosis. The tumor‐promoting effect of MSCs correlated with their capacity to enhance AKT and ERK activities in MM cells, accompanied with increased expression of CyclinD2, CDK4, and Bcl‐XL and decreased cleaved caspase‐3 and poly(ADP‐ribose) polymerase expression. In turn, MM cells upregulated interleukin‐6 (IL‐6), IL‐10, insulin growth factor‐1, vascular endothelial growth factor, and dickkopf homolog 1 expression in MSCs. Finally, infusion of in vitro‐expanded murine MSCs in 5T33MM mice resulted in a significantly shorter survival. MSC infusion is a promising way to support hematopoietic recovery and to control graft versus host disease in patients after allogeneic hematopoietic stem cell transplantation. However, our data suggest that MSC‐based cytotherapy has a potential risk for MM disease progression or relapse and should be considered with caution in MM patients. STEM CELLS 2012; 30:266–279.

Bortezomib Alone or in Combination with the Histone Deacetylase Inhibitor JNJ-26481585: Effect on Myeloma Bone Disease in the 5T2MM Murine Model of Myeloma

The proteasome inhibitor bortezomib (Velcade) is currently approved as second-line treatment of multiple myeloma (MM). MM-related bone disease is one of the most debilitating complications of MM. Besides supportive care with biphosphonates, which have proven efficacy in reducing and delaying skeletal-related events, there is no specific treatment of lytic bone lesions. The present study investigated the effect of bortezomib alone or in combination with a hydroxamate-based histone deacetylase inhibitor, JNJ-26481585 on tumor burden, and MM bone disease in the 5T2MM model. Injection of 5T2MM cells into C57Bl/KaLwRij mice resulted in MM bone disease, characterized by an increase in the percentage osteoclasts, a decrease in osteoblasts, trabecular bone volume, trabecular number, and the development of bone lesions. Treatment of 5T2MM-bearing mice with bortezomib significantly reduced tumor burden, angiogenesis, and MM bone disease. More importantly, the combination of bortezomib with JNJ-26481585 resulted in a more pronounced reduction of osteoclasts and increase of osteoblasts, trabecular bone volume, and trabecular number compared with bortezomib as single agent. These data suggest that bortezomib has bone remodeling properties that can be improved in combination with low dose JNJ-26481585. The study indicates that this combination therapy could be a useful strategy for the treatment of MM patients, especially in those patients with skeletal complications.

The Involvement of Adhesion Molecules in the Biology of Multiple Myeloma

Multiple myeloma represents a B cell malignancy characterized by a monoclonal proliferation of plasma cells. A striking feature of the disease is the tendency of the malignant plasma cells to affect mainly the bone marrow environment and to invade the peripheral blood only in the terminal stage. The growth of myeloma plasma cells is believed to be regulated by a functional interplay between the tumor cells and the bone marrow stroma, involving the action of various cytokines. This growth control is most probably mediated by close cellular contact of the myeloma cells and marrow stromal components. Therefore it can be assumed that myeloma plasma cells possess the ability to interact with the bone marrow stroma. Until now the adhesive mechanisms that may underlie this interaction, remain undetermined. We investigated the expression of several adhesion molecules on bone marrow plasma cells in myeloma patients and normal controls. Normal as well as malignant plasma cells were found to be strongly positive for...