Preliminary evaluation of Chidamide in combination with novel [177Lu]Lu-DOTAGA-rituximab in rituximab-resistant Raji cells.

PURPOSE: Rituximab resistance in B-cell non-Hodgkin lymphoma (RR B-NHL) involves decreased CD20 expression, limiting the efficacy of CD20-targeting radioimmunotherapy (RIT). Since the histone deacetylase inhibitor Chidamide enhances CD20 expression, we investigated its potential to improve the effectiveness of rituximab and a novel rituximab-based RIT in RR Raji cells.

METHODS

RR Raji cells were generated via one-week rituximab exposure, then treated with Chidamide for 24 h to upregulate CD20. Cell death was measured following exposure to a rituximab-serum mixture. Additionally, a radioimmunoconjugate was synthesized using DOTAGA-anhydride and lutetium-177 (177Lu) for in vitro RIT on these cells.

RESULTS

Chidamide modestly increased CD20 expression (p = 0.655) but significantly enhanced cell death with the rituximab-serum mixture (p = 0.000), improving cytotoxicity. The synthesized [177Lu]Lu-DOTAGA-rituximab achieved clinical-grade quality (>98% radiochemical purity; >96% stability at 144 h). RIT using this conjugate caused significantly higher cell death in Chidamide-treated RR Raji cells compared to the control (without Chidamide) groups (p < 0.0001).

CONCLUSIONS

This in vitro proof-of-concept study demonstrates that Chidamide may enhance the cytotoxic effect of a novel [¹⁷⁷Lu]Lu-DOTAGA-rituximab in RR Raji cells. Despite limitations (a single cell line and an exploratory design), this finding supports the biological plausibility and feasibility of this combination therapy, warranting further in vivo validation.