Targeting Na-H exchanger 1 overcomes nuclear factor kappa B-mediated tumor resistance to radiotherapy.

Intrinsic or acquired radioresistance often limits the efficacy of radiation therapy (RT), thereby leading to local control failure. Cancerous cells have abnormal pH dynamics due to high metabolic demands, but it is unclear how pH dynamics contribute to radioresistance. In this study, we investigated the role of Na-H exchange 1 (NHE1), the major intracellular pH (pHi) regulator, in RT response. We observed that RT increased NHE1 expression and modulated pHi in MDA-MB-231 human breast cancer cells. When combined with RT, pharmacological NHE1 inhibition by 5-(N-Ethyl-N-isopropyl)amiloride (EIPA) reduced pHi and clonogenic survival. EIPA attenuated radiation-damaged DNA repair, increasing G2/M cell cycle arrest. The combination of EIPA and RT increased apoptotic cell death while decreasing phosphorylation of NF-κB p65. Similarly, the knockdown of NHE1 increased radiosensitivity with lower pHi and increased apoptosis. Consistent with in vitro data, the EIPA plus RT inhibited the growth of MDA-MB-231 xenograft tumors in mice to a greater extent than either EIPA or RT alone. EIPA abrogated the RT-induced increase in NHE1 and phospho-NF-κB p65 expression in tumor tissues. Such coincidence of increased NHE1 level, pHi, and NF-κB activation was also found in radioresistant MDA-MB-231 cells, which were reversed by EIPA treatment. Bioinformatics analysis of RNA sequencing data revealed that inhibiting NHE1 reversed three core gene networks that were up-regulated in radioresistant cells and correlated with high NHE1 expression in patient samples: NF-κB, senescence, and extracellular matrix. Taken together, our findings suggest that NHE1 contributes to RT resistance via NF-κB-mediated signaling networks, and NHE1 may be a promising target for improving RT outcomes.

Manganese Ferrite Nanoparticles Enhance the Sensitivity of Hepa1-6 Hepatocellular Carcinoma to Radiation by Remodeling Tumor Microenvironments.

We evaluated the effect of manganese ferrite nanoparticles (MFN) on radiosensitization and immunologic responses using the murine hepatoma cell line Hepa1-6 and the syngeneic mouse model. The clonogenic survival of Hepa1-6 cells was increased by hypoxia, while being restricted by ionizing radiation (IR) and/or MFN. Although MFN suppressed HIF-1α under hypoxia, the combination of IR and MFN enhanced apoptosis and DNA damage in Hepa1-6 cells. In the Hepa1-6 syngeneic mouse model, the combination of IR and MFN notably limited the tumor growth compared to the single treatment with IR or MFN, and also triggered more frequent apoptosis in tumor tissues than that observed under other conditions. Increased expression of PD-L1 after IR was not observed with MFN alone or the combination of IR and MFN in vitro and in vivo, and the percentage of tumor-infiltrating T cells and cytotoxic T cells increased with MFN, regardless of IR, in the Hepa1-6 syngeneic mouse model, while IR alone led to T cell depletion. MFN might have the potential to overcome radioresistance by alleviating hypoxia and strengthening antitumor immunity in the tumor microenvironment.