George Tang

Soluble B-Cell Maturation Antigen Mediates Tumor-Induced Immune Deficiency in Multiple Myeloma

Purpose: Reduced uninvolved immunoglobulin (Ig) levels are a hallmark of multiple myeloma. We previously showed that B-cell maturation antigen (BCMA) is solubilized and at high levels in multiple myeloma patient serum. We hypothesize that soluble BCMA binds B-cell–activating factor (BAFF) preventing its function to stimulate late B cells, and would result in lower polyclonal antibody levels in these patients. Experimental Design: Mice were dosed with recombinant human BCMA (rhBCMA) and BCMA–BAFF complexes were analyzed in plasma, and its effects on antibody and Ig heavy chain mRNA levels determined. Using flow cytometry, BAFF binding to B cells was examined in the presence of rhBCMA and sera from multiple myeloma patients. In multiple myeloma sera, BCMA–BAFF complex formation and BCMA, IgA, IgG levels, and heavy–light chain isoform pair levels were determined. Results: rhBCMA–BAFF complexes formed in immune-competent and deficient mice. Mice with human multiple myeloma xenografts, which contain plasma hBCMA and hBCMA–BAFF complexes, showed reduced plasma-free BAFF levels. rhBCMA administered to immune competent mice markedly reduced plasma IgA, IgG, and IgM levels and splenic Ig heavy chain mRNA levels. In serum from multiple myeloma patients, BCMA–BAFF complexes were detected and BAFF levels were reduced. Multiple myeloma patient sera containing BCMA prevented binding of BAFF to B cells. There is an inverse correlation between serum BCMA and uninvolved polyclonal Ig level in multiple myeloma patients. Conclusions: Our results show that soluble BCMA sequesters circulating BAFF, thereby preventing it from performing its signaling to stimulate normal B-cell and plasma cell development, resulting in reduced polyclonal antibody levels in multiple myeloma patients. Clin Cancer Res; 22(13); 3383–97. ©2016 AACR.

Combined TRAF6 Targeting and Proteasome Blockade has Anti-tumor and Anti-bone Resorptive Effects

TNF receptor–associated factor 6 (TRAF6) has been implicated in polyubiquitin-mediated IL1R/TLR signaling through activation of IκB kinase (IKK) to regulate the NF-κB and JNK signaling pathways. Here, TRAF6 protein was determined to be overexpressed in bone marrow mononuclear cells (BMMC) from patients with multiple myeloma. TRAF6 expression in BMMCs from patients with progressive disease is significantly elevated as compared with individuals in complete remission, with monoclonal gammopathy of undetermined significance, or healthy subjects. Furthermore, TRAF6 dominant–negative (TRAF6dn) peptides were constructed which specifically reduced TRAF6 signaling and activation of IKK. TRAF6 not only reduced cellular growth but also increased the apoptosis of multiple myeloma tumor cells in a concentration-dependent fashion. Because TRAF6 activates IKK through polyubiquitination, independent of its proteasome activity, a TRAF6dn peptide was combined with the proteasome inhibitors bortezomib or carfilzomib to treat multiple myeloma. Importantly, targeting of TRAF6 in the presence of proteasome inhibition enhanced anti–multiple myeloma effects and also decreased TLR/TRAF6/NF-κB–related signaling. Finally, TRAF6dn dose dependently inhibited osteoclast cell formation from CD14+ monocytes, induced with RANKL and mCSF, and markedly reduced bone resorption in dentin pits. In all, these data demonstrate that blocking TRAF6 signaling has anti–multiple myeloma effects and reduces bone loss. Implications: The ability to target TRAF6 signaling and associated pathways in multiple myeloma suggests a promising new therapeutic approach. Mol Cancer Res; 15(5); 598–609. ©2017 AACR.

The Role of B-Cell Maturation Antigen in the Biology and Management of, and as a Potential Therapeutic Target in, Multiple Myeloma

B-cell maturation antigen (BCMA) was originally identified as a cell membrane receptor, expressed exclusively on late stage B-cells and plasma cells (PCs). Investigations of BCMA as a target for therapeutic intervention in multiple myeloma (MM) were initiated in 2007, using cSG1 as a naked antibody (Ab) as well as an Ab–drug conjugate (ADC) targeting BCMA, ultimately leading to ongoing clinical studies for previously treated MM patients. Since then, multiple companies have developed anti-BCMA-directed ADCs. Additionally, there are now three bispecific antibodies in development, which bind to both BCMA and CD3ε on T-cells. This latter binding results in T-cell recruitment and activation, causing target cell lysis. More recently, T-cells have been genetically engineered to recognize BCMA-expressing cells and, in 2013, the first report of anti-BCMA-chimeric antigen receptor T-cells showed that these killed MM cell lines and human MM xenografts in mice. BCMA is also solubilized in the blood (soluble BCMA [sBCMA]) and MM patients with progressive disease have significantly higher sBCMA levels than those responding to treatment. sBCMA circulating in the blood may limit the efficacy of these anti-BCMA-directed therapies. When sBCMA binds to B-cell activating factor (BAFF), BAFF is unable to perform its major biological function of inducing B-cell proliferation and differentiation into Ab-secreting PC. However, the use of γ-secretase inhibitors, which prevent shedding of BCMA from PCs, may improve the efficacy of these BCMA-directed therapies.

Anti-angiogenic and anti-multiple myeloma effects of oprozomib (OPZ) alone and in combination with pomalidomide (Pom) and/or dexamethasone (Dex)

Oprozomib (OPZ or ONYX 0912) is an irreversible, orally administered proteasome inhibitor (PI) and an analog of carfilzomib. We set out to determine the anti-angiogenic effect of OPZ using the choriollantoic membrane/feather bud (CAM/FB) model and its anti-MM effects using MM xenograft models (LAGκ-1A, LAGλ-1). OPZ significantly reduced blood vessel formation, endothelial gene and protein expression using the CAM/FB assay. In vivo, we determined the anti-MM effects of OPZ, dexamethasone (Dex) and pomalidomide (Pom) and showed that the combinations of two drugs (OPZ+Dex or OPZ+Pom) showed marked anti-MM effects when compared to monotherapy. Pom+Dex and the triplicate combination (OPZ+Pom+Dex) showed more anti-MM effects when compared to the doublets of either OPZ+Dex or OPZ+Pom; continued treatment with all three drugs (OPZ+Pom+Dex) was superior when compared to Pom+Dex, in both MM xenograft models tested. These studies show that OPZ has anti-angiogenic effects, and that the combination of OPZ, Dex and Pom produces greater anti-MM effects in vivo when compared to any of the doublet combinations. These studies provide further support for clinical trials evaluating OPZ in combination with Pom and Dex.

The clinical significance of B-cell maturation antigen as a therapeutic target and biomarker

ABSTRACT Introduction: B-cell maturation antigen (BCMA) is a cell membrane bound tumor necrosis factor receptor family member that is expressed exclusively on late stage normal and malignant B-cells and plasma cells. Addition of two of its ligands, B-cell activating factor and a proliferation inducting ligand, to normal B-cells cause B-cell proliferation and antibody production. Serum BCMA is elevated among patients with multiple myeloma (MM) and chronic lymphocytic leukemia (CLL), and is a prognostic and monitoring tool for these patients. The first anti-BCMA antibody (Ab) was developed in 2007. Recently, biotech and pharmaceutical companies have created various forms of BCMA-directed Abs (naked Abs, Ab drug conjugates, and bispecific Abs) and cellular therapies (chimeric antigen receptor T-cells) with promising clinical results. Areas covered: This BCMA review encompasses full-text publications of original research articles and abstracts presented at hematology/oncology meetings. Expert commentary: The limited preclinical and ongoing clinical studies published to date evaluating BCMA-directed therapies have shown great promise. It has also been demonstrated that BCMA is solubilized and elevated in the blood of MM, Waldenstrom’s macroglobulinemia and CLL patients, and is also responsible for the immune deficiency in MM. Reducing circulating levels may improve the efficacy of these treatments.

TNFRSF17 (tumor necrosis factor receptor superfamily, member 17)

B Cell Maturation Antigen (BCMA) is a transmembrane signaling protein preferentially expressed on plasma cells. Its ligands include BCell Activating Factor (BAFF) and A Proliferation Inducing Ligand (APRIL). BCMA is involved in JNK and NF-kB activation pathways that induce Bcell development and autoimmune responses. BCMA has been implicated in autoimmune disorders as well as B-lymphocyte malignancies.

Abstract 1339: Effects of INCB052793, a selective JAK1 inhibitor, in combination with standard of care agents in human multiple myeloma (MM) cell lines and xenograft models

Several studies have demonstrated constitutive activation of the JAK-STAT pathway in MM through dysregulated signaling of cytokines such as IL-6. In addition to its crucial role in promoting the growth, proliferation and survival of myeloma cells, IL-6 is also a potent stimulator of osteoclastogenesis and influences the tumor microenvironment in the bone marrow of myeloma patients by promoting an immunosuppressive milieu. Since JAK1 has been shown to be important for IL-6 signaling, studies to assess the effect of JAK1 inhibition alone and in combination with other anti-MM agents were undertaken. The human MM cell lines, RPMI8226 or U266, were cultured in the presence of the JAK1 selective inhibitor INCB052793 plus a panel of anti-MM agents including the alkylating agents, cyclophosphamide (CY), melphalan (MEL), and bendamustine, the proteasome inhibitor, carfilzomib, the corticosteroid, dexamethasone (DEX) or the immunomodulatory agents lenalidomide (LEN) and pomalidomide (POM). After 48 hours, cell viability was assessed. Combinations of INCB052793 plus the three alkylating agents or carfilzomib synergistically inhibited the viability of both cell lines in vitro. INCB052793 plus CY or MEL also significantly decreased the viability of the MM1S MM cell line. In vivo, mice bearing the human patient derived MM tumor LAGκ-1A had significantly smaller tumors when treated with INCB052793 alone when compared to vehicle control at Day 35 post implantation. This was in contrast to mice treated with single agent DEX, LEN or POM. Although the combination of INCB052793 with DEX, LEN or POM did not synergistically inhibit MM cell line growth in vitro, mice receiving the doublets of INCB052793 and DEX, LEN or POM demonstrated an effect on tumor growth that was superior to the doublets of DEX with LEN or POM. Mice receiving the triple combination of INCB052793 + DEX with LEN or POM demonstrated the most significant effect on tumor growth compared to all other combinations tested. The inhibition of tumor growth with these combinations was observed throughout the study (through Day 70) and all combinations were well tolerated. Concomitant with effects on tumor growth, a significant reduction in serum human IgG levels was also observed. Studies to further understand the mechanistic effects of these combinations on myeloma signaling and the tumor microenvironment are ongoing. In conclusion, these in vitro and in vivo studies demonstrate that the combination of INCB052793 with a broad spectrum of anti-MM agents is effective, and provide further support for the clinical evaluation of these drug combinations in MM patients. Citation Format: Eric Sanchez, Mingjie Li, Cathy Wang, Puja Mehta, George Tang, Haiming Chen, James R. Berenson. Effects of INCB052793, a selective JAK1 inhibitor, in combination with standard of care agents in human multiple myeloma (MM) cell lines and xenograft models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1339.