Inhibition or Enhancement of Proliferation of Multiple Myeloma Cell Lines by CD137 Ligand Signaling?

Abstract 4998

Multiple myeloma is an plasma cell malignancy. Despite new adjuvant biotherapeutics (thalidomide-like immunomodulatory drugs and proteasome inhibitors) have improved prognosis and survival, MM is still incurable. So unraveling the intricate pathobiology and exploitation of novel therapy are needed. CD137 and its ligand are members of the Tumor Necrosis Factor (TNF) receptor and TNF superfamilies, respectively. Since CD137 ligand cross-linking enhances proliferation and survival of healthy B cells we wonder that it would also act as a growth stimulus for B cell cancers.

From the study, the constitutive expression of CD137 ligand on U266, RPMI 8226, LP1, MY5 and OPM2 MM cell lines were detected as 89. 2%, 90. 9%, 57. 9%, 77. 9% and 78. 7% by Flow cytometry. Then U266 cell and RPMI 8226 cell were selected to explore the biological effect of CD137L signaling and its underlying mechanism. Resultly, in vitro study showed the proliferation and survival of U266 is enhanced by stimulating- CD137L mAb (1F1) as 4. 2*10e5 cells/ml(1F1 group) compared to 3. 5*10e5 cells/ml(control group) by cell counting at incubation for 48h. On the other wise, RPMI 8226 was not susceptible to 1F1 and was inhibited proliferation and induced cell death, by cell counting as 4. 9*10e5 cells/ml(1F1 group) compared to 5. 4*10e5 cells/ml (control group) at 48h and by CFSE as 277 compared to 197 (X-Mean of FCM) at 48h assay demonstrated. The cell cycle analysis showed that CD137 ligand induces proliferation and increases in the number of cells in the S phase from 36. 1% to 42. 5% of U266, while, showing the opposite from 50% to41% of RPMI 8226. Intracellular cytokine staining showed that treatment of cells with 1F1 increased the production of IL-6 of two cell lines, 3. 8% to 63. 9% of U266 and 90pg/ml to 250pg/ml of RPMI 8226. Finally, the two cells were treated with bortezomib and the growth of cells is analyzed by WST assay. It demonstrated that bortezomib can inhibit the function of 1F1 at U266 cells but have synergistic effection of 1F1 at RPMI 8226 cells. Inhibition rate of bortezomib were 22%, 51% and 58% of U266 and 58%, 80% and 77% of RPMI 8226 at 24h, 48h and 72h. As the inhibition rate of the two cells treated with bortezomib and 1F1 were 22. 9%, 46. 7% and 58% of U266 and 56%. 85% and 79. 7% of RPMI 8226.

It is at first sight surprisingly that CD137 ligand acts in concert with 1F1 having two opposite effection in different MM cell lines. Even so, we think it needed to explain some mechanism regarding different pass ways in different cell lines(the experiment under way).