Author ORCID Identifier
Date of Graduation
Doctor of Philosophy (PhD)
Eugenie S. Kleinerman
The purpose of this study was to investigate the effect of the HDAC inhibitor entinostat on the efficacy of NK cell therapy for OS lung metastasis. The Lung is the most common site of OS metastatic spread in OS and pulmonary metastasis is the main cause of mortality. We have previously demonstrated that NK cell therapy has minimal efficacy against OS metastasis. We wished to determine whether we could augment the killing of OS cells in vitro and improve the efficacy of NK cell therapy in vivo by adding oral administration of entinostat. We elected to use our nude mouse human OS lung metastasis model for this purpose. In vitro, entinostat increased NK cell ligands on OS cells (MIC A/B, ULBP1, ULBP2/5/6, and CD155) and enhanced the NK cell-mediated cytotoxicity. Entinostat oral administration also increased MICA/B expression on lung tumors. Entinostat (≤ 2 μM) did not have any adverse effect on NK cell viability, receptor expression, or function within the 24 h treatment.
We demonstrated two potential mechanisms by which entinostat enhanced expression of MICA and MICB. Our data showed that entinostat increased the acetylation of histone 4 on the MICA and MICB gene promoters which enhanced MICA and MICB gene transcription. We also showed that entinostat decreased the expression of mir-20a, mir-93, and mir-106b, microRNAs that up-regulate both MICA and MICB.
Although our findings showed that entinostat augmented NK cell-mediated cytotoxicity against OS cells in vitro, the in vivo studies failed to show enhanced efficacy of the combination therapy. This may be explained by our finding that while NK cells infiltrated into the lungs and were at the tumor periphery, we were unable to detect the presence of NK cells inside lung tumors. This suggests that adding a cytokine such as IL-2 and IL-21 may enhance the NK cells trafficking into the lung nodules and improve the NK cell therapy efficacy. Entinostat up-regulated the immune inhibitory molecule PD-L1 on OS cells. Therefore, blocking PD/PDL1 interaction by PD-L1 monoclonal antibody may increase the anti-tumor effect of entinostat+ NK cells. Further investigations are necessary to define the specific mechanism of resistance.
Osteosarcoma, NK cell, Entinostat