PI3K Signaling Pathway Inhibitor Affects Myeloma Cells in a Culture-Dependent Manner.

Purpose: The survival and progression of multiple myeloma (MM) cells rely heavily on supportive factors and cells within the MM microenvironment, notably macrophages. The PI3K signaling pathway plays a crucial role in both myeloma cells survival and macrophage polarity, making it a potential target for altering the MM microenvironment dynamics.

Methods: In this study, the impact of LY294002, a PI3K signaling pathway inhibitor, on the viability of U266 myeloma cells in mono-culture and MM patient-derived bone marrow mononuclear cells (BM-MNCs) in co-culture was investigated. Additionally, the effect of treatments on the M1/M2 macrophage ratio was assessed. Cultures were conducted in both two-dimensional (2D) matrix-free and fibrin gel-based three-dimensional (3D) environments.

Results: The treatment significantly increased U266 cell death in 2D cultures, dose-dependently compared to control. However, this effect was not replicated in 3D cultures. In both 2D and 3D cultures, the percentages of cells in G0/G1 phase were dose-dependently increased, compared to the untreated control. However, the percentages of cells in S and G2/M phases in both 2D and 3D cultures were dose-dependently decreased, compared to control. Treatment of BM-MNCs with LY294002 showed patient- and culture-dependent patterns of CD138⁺ myeloma cell death and M1/M2 macrophage ratio, contrasting the observed consistent responses in U266 mono-culture.

Conclusion: LY294002 affected U266 cell viability and cell cycle in a dose-dependent manner in 2D mono-cultures. However, its impact varied in 3D cultures. Treatment of MNCs showed varied responses based on individuals and culture conditions, underscoring the need for more similar tumor microenvironment (TME) recapitulation for drug screening.