(PA-040) Overcoming Resistance in CD44-Overexpressing Myeloma through combination therapy with ATRA, Bortezomib, and NK Cells

CD44, a surface glycoprotein, is often highly expressed in patients with poor treatment response and advanced disease stages across numerous studies. This study aims to investigate the prognostic impact of CD44 overexpression in multiple myeloma (MM) patients, and investigates the therapeutic impact of combining NK cell therapy with all-trans retinoic acid (ATRA) and bortezomib in CD44-overexpressing myeloma cell lines.

Methods:   

Clinical data from the CoMMpass database were analyzed to assess survival outcomes associated with CD44 expression. NK cells were expanded from healthy donors using K562-OX40L-mbIL18/21 feeder cells and IL-2/IL-15. Functional assays were performed using CD44-high myeloma cell lines treated with ATRA and bortezomib, individually and in combination with NK cells. Changes in CD44 expression, β-catenin levels, and downstream effectors (NF-κB, MMP2/9) were examined via western blot and qPCR. NK cell activation markers and cytotoxicity were assessed by flow cytometry.

Results:   

CD44 overexpression was significantly associated with worse overall survival in MM patients (P < 0.0001), including those in R-ISS I and III stages. In addition, CD44 expression was associated with myeloma cell proliferation, migration and invasion, which is mediated through the downregulation of NF-ĸB, MMP2, and MMP9 in myeloma cell lines. In vitro, the combination of ATRA and bortezomib significantly downregulated CD44 and β-catenin levels, reduced MM cell proliferation, migration, and invasion, and enhanced susceptibility to NK cell-mediated lysis. This was accompanied by upregulation of activation ligands (MICA/B, FAS, TRAILR2) and adhesion molecules (ICAM1), suggesting improved NK-target cell interaction. NK cells alone not sufficient to kill myeloma cells overexpressing CD44; however, cytotoxicity was significantly increased when NK cells were combined with ATRA and bortezomib against CD44 overexpression myeloma cells at all E:T ratios.

Conclusions:   

Our findings highlight CD44 as a poor prognostic marker and a viable therapeutic target in MM. The combination of ATRA and bortezomib effectively sensitizes CD44 overexpression myeloma cells to NK cell-mediated cytotoxicity. This strategy may offer a novel approach to improving NK cell-based immunotherapy in high-risk MM patients.