Eric Davis

Targeting B-cell receptor signaling: changing the paradigm

It is well known that signals emanating from the B-cell receptor (BCR) activate downstream pathways to regulate the development and survival of normal B cells. In B-cell malignancies, it is increasingly understood that similar pathways are activated through both tonic and chronic active BCR signaling to promote tumor viability and resistance to therapy. Recently, several active and oral agents have emerged that target key proximal kinases in the BCR pathway, including Bruton tyrosine kinase, PI3K, and spleen tyrosine kinase. In early clinical studies, these agents have shown significant activity across a broad range of B-cell lymphomas and chronic lymphocytic leukemia. Especially impressive responses have been reported in mantle cell lymphoma and chronic lymphocytic leukemia, and many patients remain on treatment with continued disease control. Toxicity profiles have been mild in the majority of early studies, without significant myelosuppression over prolonged dosing. Due to these attractive attributes, several agents targeting the BCR pathway are now entering early combination studies with traditional chemotherapeutics and/or other novel agents. It is clear that agents targeting the BCR pathway will significantly affect the design of future therapeutic regimens for B-cell malignancies. Future research will focus on understanding potential mechanisms of resistance, identifying biomarkers of response, and defining optimal combination regimens.

C-reactive protein promotes bone destruction in human myeloma through the CD32–p38 MAPK–Twist axis

Liver-secreted C-reactive protein is not just a biomarker of myeloma, it promotes myeloma-associated bone loss in patients. Liver protein instructs bone loss in myeloma Bone loss is common in patients with multiple myeloma (MM). MM cells activate osteoclasts, cells that degrade bone. The sera of MM patients typically have increased amounts of C-reactive protein (CRP), which is secreted by the liver in response to cytokines associated with tissue inflammation and physiological stress, including those secreted by MM. Using samples from patients, as well as human cell lines and mice bearing human bone grafts and MM cells, Yang et al. found that CRP is not merely a diagnostic marker for MM but that rather it feeds back on MM cells to stimulate the expression and secretion of osteoclast-activating cytokines from MM cells, thereby driving bone loss in patients. These findings suggest that targeting the cyclical CRP signaling axis may reduce or prevent MM-associated bone loss. Bone destruction is a hallmark of myeloma and affects 80% of patients. Myeloma cells promote bone destruction by activating osteoclasts. In investigating the underlying mechanism, we found that C-reactive protein (CRP), a protein secreted in increased amounts by hepatocytes in response to myeloma-derived cytokines, activated myeloma cells to promote osteoclastogenesis and bone destruction in vivo. In mice bearing human bone grafts and injected with multiple myeloma cells, CRP bound to surface CD32 (also known as FcγRII) on myeloma cells, which activated a pathway mediated by the kinase p38 MAPK and the transcription factor Twist that enhanced the cells’ secretion of osteolytic cytokines. Furthermore, analysis of clinical samples from newly diagnosed myeloma patients revealed a positive correlation between the amount of serum CRP and the number of osteolytic bone lesions. These findings establish a mechanism by which myeloma cells are activated to promote bone destruction and suggest that CRP may be targeted to prevent or treat myeloma-associated bone disease in patients.

The role of transcription factor Runx2 in tumor infiltrating T cells

Adoptive T cell therapy (ACT) is a promising treatment for melanoma patients with a clinical response rate of about 50%. However, half of patients treated do not respond to this therapy, underlining the need for improvement . One of the limitations of ACT is the poor effector function of transferred T cells influenced by the immunosuppressive tumor microenvironment. In order to identify pathways which may contribute to this observation, we used a murine ACT model in which mice bearing established B16 tumors were treated with Pmel T cells which recognize the melanoma antigen gp100 in the context of H-2Db. Pmel T cells were recovered on day 6 and 13, after transfer, from the tumor and spleen of treated mice and their gene expression patterns were compared. We found that 720 genes were differentially expressed by T cells recovered from the tumor site compared to those recovered from the spleen. Amongst the differentially expressed genes were several transcription factors, including Runx2, Rora, E2F1 and Tcf7. After an initial in vivo screen, Runx2 overexpressing Pmels conferred a worse antitumor effect when compared to the control Pmels (median tumor size 30.7 vs 20.7 mm 2 respectively on day 7 after T cell transfer, p<0.05). We also found fewer numbers of circulating Pmels in mice that received Runx2 overexpressing Pmels when compared to mice that received control Pmels. In addition, there was decreased accumulation of Runx2 overexpressing Pmels at the tumor site when compared to the control Pmel (Median luciferase output of 2.0X10 7 vs 9.0X10 7 photons/s/cm 2 /sr, respectively on day 6 after T cell transfer, p value =0.042). To further interrogate the role of Runx2 in T cells, we assessed the production of IFN-g after stimulation in vitro with either plate bound anti-CD3 or gp100 expressing tumor cells. We found that IFN-g production was comparable between Runx2 overexpressing Pmels and control Pmels after anti-CD3 stimulation. However, IFN-g production was impaired in Runx2 overexpressing Pmels upon stimulation with tumor cells. Furthermore, in vitro characterization also revealed that Runx2 overexpressing Pmels have decreased proliferation and display an apoptotic phenotype. Taken together, our studies suggest that Runx2 regulates apoptosis, proliferation and IFN-g production in tumor reactive T cells. Further studies to mechanistically understand these findings are ongoing.