Downregulation of Mcl-1 by Panobinostat Potentiates Proton Beam Therapy in Hepatocellular Carcinoma Cells

Abstract

Epigenetic modulation by histone deacetylase (HDAC) inhibitors is an attractive anti-cancer strategy for diverse hematological and solid cancers. Herein, we explored the relative effectiveness of the pan-HDAC inhibitor panobinostat in combination with proton over X-ray irradiation in HCC cells. Clonogenic survival assays revealed that radiosensitization of Huh7 and Hep3B cells by panobinostat was more evident when combined with protons than X-rays. Panobinostat increased G2/M arrest and production of intracellular reactive oxygen species, which was further enhanced by proton irradiation. Immunofluorescence staining of γH2AX showed that panobinostat enhanced proton-induced DNA damage. Panobinostat dose-dependently decreased expression of an anti-apoptotic protein, Mcl-1, concomitant with increasing acetylation of histone H4. The combination of panobinostat with proton irradiation enhanced apoptotic cell death to a greater extent than that with X-ray irradiation. Depletion of Mcl-1 by RNA interference enhanced proton-induced apoptosis and proton radiosensitization, suggesting a potential role of Mcl-1 in determining proton sensitivity. Together, our findings suggest that panobinostat may be a promising combination agent for proton beam therapy in HCC treatment.

Roles and regulation of histone acetylation in hepatocellular carcinoma

“…Accumulating evidence indicates that apoptotic genes can be regulated by epigenetic mechanisms ( Zhou et al, 2019 ). Some HDAC inhibitors such as panobinostat ( Choi et al, 2021 ), SAHA analogues ( Srinivas et al, 2016 ), and traditional Chinese medicine galangin ( Li et al, 2016 ) have been recently reported to regulate apoptosis in HCC through controlling the expression of pro- and anti-apoptotic genes ( Buurman et al, 2016 ; Li and Seto, 2016 ). In general, administrations of HDACI can either directly prompt apoptosis through the extrinsic (death receptor)/intrinsic (mitochondria) pathway, or induce the susceptibility of tumor cells to apoptosis ( Li and Seto, 2016 ).…”

Does particle radiation have superior radiobiological advantages for prostate cancer cells? A systematic review of in vitro studies

“…The pattern of DNA methylation in cells that survive being exposed to charged particles or X-rays seems to be very different [ 83 ]. In addition, histone deacetylase inhibitors appear to promote cell death more efficiently following proton or carbon ion irradiation than following X-ray exposure [ 81 , 82 ]. All of this evidence seems to indicate that the radiation-induced epigenetic profile is influenced by radiation quality rather than LET alone.…”

“…Epigenetic regulation of DNA repair may also be reliant on radiation quality in addition to proteins directly engaged in DNA DSB rejoining [75][76][77]. Numerous studies have suggested that ubiquitination, methylation, and acetylation in DNA repair are important epigenetic pathways for targeting in particle therapy [78][79][80][81][82]. A previous study indicated that histone H2B ubiquitylation improves the repair of clustered DNA lesions, resulting in increased survival following exposure to high-LET radiation [79].…”

Particle radiotherapy and molecular therapies: mechanisms and strategies towards clinical applications

“…74), but it has been recently shown that histone deacetylase inhibitors seem to enhance cell death more effectively after proton (Ref. 75) or carbon ion (Ref. 76) irradiation than after X-rays.…”