Role of sorafenib and sunitinib in the induction of expressions of NKG2D ligands in nasopharyngeal carcinoma with high expression of ABCG2.

BACKGROUND: Sorafenib and sunitinib are novel small molecule tyrosine kinase inhibitors with multiple targets on tumor cells, which have been demonstrated to be beneficial in the treatment of several carcinomas. Combining the usage of molecular targeted agents and adoptive cellular immunotherapy (ACI) against drug-resistant relapse nasopharyngeal carcinoma which had no standard therapeutic regimen was investigated by our research in order to study whether synergistic effects exist and related mechanisms.
METHODS: Human multidrug-resistant nasopharyngeal carcinoma cell line CNE2/DDP with high and low expressions of ABCG(2) (abbreviated to ABCG (2) (High) CNE2/DDP and ABCG (2) (Low) CNE2/DDP) cells and NK cells were isolated by magnetic activated cell sorting, and the purity of isolated cells was detected by flow cytometry. mRNA expressions of drug-resistant gene ABCG(2), Bcl-2, MDR1, MRP and MGMT in ABCG (2) (High) CNE2/DDP and ABCG (2) (Low) CNE2/DDP cells were detected by reverse transcription polymerase chain reaction (RT-PCR). Drug sensitivity of two kinds of cells to fluorouracil, cisplatin, vincristine, carboplatin, epirubicin, daunorubicin, paclitaxel, mitomycin, sorafenib, and sunitinib were detected by MTT assay. FCM was used to evaluate the expressions of NKG2D ligands (NKG2DLs,) on target cells before and after incubated with sorafenib and sunitinib. Subsequently, the cytotoxic sensitivity of incubated and un-incubated ABCG (2) (High) CNE2/DDP and ABCG (2) (Low) CNE2/DDP cells to NK cells was measured by CytoTox 96(®) Non-Radioactive Cytotoxicity Assay.
RESULTS: The results revealed that target cells' cytotoxic sensitivity to natural killer (NK) cells increased in association with up-regulation of NKG2DLs on tumor cells after incubation with sorafenib and sunitinib. Furthermore, up-regulation in sunitinib group was much higher than in sorafenib group when it came to the expressions of NKG2DLs on tumor cells. For another, ABCG (2) (High) CNE2/DDP was much more sensitive to the regulation than ABCG (2) (Low) CNE2/DDP.
CONCLUSIONS: Our research revealed for the first time that sorafenib and sunitinib could up-regulate NKG2DLs on tumor cells resulting in markedly increased tumor cells cytotoxic sensitivity to NK cells, which suggested that combining usage of molecular targeted agents and ACI may result in great benefits in clinical practice for the therapy-resistant cases and drug-resistant relapse.