Macrophages Activation By ICAM1 Antibody Combined With Lenalidomide Has Enhanced Anti-Myeloma Activity In a Supportive Microenvironment In Vivo and In Vitro
Authors: Venkateshaiah Sathisha Upparahalli , Bam Rakesh , Li Xin , Sharmin Khan , Wen Ling , Shelton Randal S. , Teige Ingrid , Frendéus Björn , Barlogie Bart , Yaccoby Shmuel 
Published: October 2019

Abstract
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.

Disclosures:
Teige: BioInvent International: Employment. Frendéus:BioInvent International: Employment.