Bortezomib facilitates the TRAIL-mediated killing of resistant rhabdomyosarcoma by ErbB2/ Her2-targeted CAR-NK-92 cells via upregulation of DR5

Treatment resistance and immune escape are hallmarks of metastatic rhabdomyosarcoma (RMS), underscoring the urgent medical need for therapeutic agents against this disease entity as a key challenge in pediatric oncology. Chimeric antigen receptor (CAR)-based immunotherapies, such as the ErbB2 (Her2)-CAR-engineered natural killer (NK) cell line NK-92/5.28.z, provide antitumor cytotoxicity primarily through CAR-mediated cytotoxic granule release and thereafter - even in cases with low surface antigen expression or tumor escape - by triggering intrinsic NK cell-mediated apoptosis induction via additional ligand/receptors. In this study, we showed that bortezomib increased susceptibility towards apoptosis in clinically relevant RMS cell lines RH30 and RH41, and patient-derived RMS tumor organoid RMS335, by upregulation of the TRAIL receptor DR5 in these metastatic, relapsed/refractory (r/r) RMS tumors. Subsequent administration of NK-92/5.28.z cells significantly enhanced antitumor activity in vitro. Applying recombinant TRAIL instead of NK-92/5.28.z cells confirmed that the synergistic antitumor effects of the combination treatment were mediated via TRAIL. Western blot analyses indicated, that the combination treatment with bortezomib and NK-92/5.28.z cells increased apoptosis by interacting with the NF-κB, JNK and caspase pathways. Overall, bortezomib pretreatment can sensitize r/r RMS tumors to CAR- and by upregulating DR5, to TRAIL-mediated cytotoxicity of NK-92/5.28.z cells.