Macrophages Activation By ICAM1 Antibody Combined With Lenalidomide Has Enhanced Anti-Myeloma Activity In a Supportive Microenvironment In Vivo and In Vitro

Tumor associated macrophages are reportedly accumulated in myelomatous bones and support myeloma cell survival and growth. Myeloma cells from the majority of patients express ICAM1, a cell surface receptor associated with the interaction of myeloma cells with stromal cells. BI-505, a humanized IgG1 lambda antibody against ICAM1, has been recently reported to inhibit growth of ICAM1-expressing myeloma cells by specifically activating macrophages (Veitonmäki et al, Cancer Cell, 2013) while lenalidomide is a known clinical immunomodulatory agent. The aim of the study was to test the effect of combination treatment with BI-505 and lenalidomide on growth of myeloma cells in vivo and in vitro. ICAM1-expressing myeloma cells from 4 patients with progressive disease were engrafted in SCID-hu mice and treated with control antibody, BI-505 (10 mg/kg, weekly, i.p.), lenalidomide (2 mg/kg, daily, p.o.) or BI-505 and lenalidomide for 5-8 weeks (5-6 mice/group in each set of patient's cells). Myeloma growth was assessed by monitoring circulating human kappa light chain immunoglobulin or soluble syndecan-1 in the mice sera, or using live-animal imaging of myeloma cells infected with lentiviral particles containing EGFP/luciferase construct. Myeloma growth was inhibited by the two drugs in all experiments. At the end of each experiment, tumor burden in the BI-505, lenalidomide and drug combination groups was 13±4% (p<0.0001), 21±6% (p<0.0001) and 3±1% (p<0.0001) relative to control groups, respectively. Myeloma burden was also significantly lower in the drug combination group compared to BI-505 (p<0.03) or lenalidomide (p<0.008) groups. These data are well in concordance with results from experiments with myeloma cell lines RPMI8226 and U266 in immunodeficient mice where the combination of BI-505 and lenalidomide showed significantly more anti-tumor effect compared to either treatment alone. In vitro, we established a coculture system in which whole donor bone marrow (BM) cells were cultured for 7 days with serum pooled from myeloma patients, followed by coculture with CD138-selected myeloma cells for an additional 7 days (BM:myeloma cell ratio 4:1). Phenotypically, the cultured BM contained cells of various hematopoietic lineages including macrophages. Growth of myeloma cells was assessed by CD45/CD38 flow cytometry or bioluminescence analysis of luciferase-expressing myeloma cells in coculture. In this system, primary myeloma cells survived and propagated regardless of their molecular risk signature or subsets while BI-505 (1-5 μg/ml) inhibited growth of ICAM1-expressing myeloma cells by 54±6% (n=5, p<0.003) but had no effect on myeloma cells that do not express ICAM1. In the coculture setting, combination of BI-505 (2.5 μg/ml) and lenalidomide (0.5 μM) had higher anti-tumor efficacy than each of the agents alone. These data indicate that macrophages can be activated by BI-505 to induce anti-myeloma response and that the anybody activity is enhanced in combination with lenalidomide.