PARPi cytotoxicity is significantly higher when combined with X-rays in liver cells
HBx expression significantly lowered this survival, probably driven by SMC5/6 loss
HCC Tumor tissues had higher PARP mRNA levels than Peri-Tumor and control livers
Increased DNA damage levels are found during liver disease progression
A promising avenue for cancer treatment is exacerbating the deregulation of the DNA repair machinery that would normally protect the genome. To address the applicability of poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) combined with radiotherapy for the treatment of hepatocellular carcinoma (HCC) two approaches were used: firstly, the in vitro sensitivity to the PARPi Veliparib and Talazoparib +/- radiation exposure was determined in liver cell lines and the impact of the HBV X protein (HBx) that deregulates cellular DNA damage repair via SMC5/6 degradation was investigated. Secondly, PARP expression profiles and DNA damage levels using the surrogate marker gammaH2AX were assessed in a panel of control liver vs HCC tissues.
Cell cytotoxicity was measured by clonogenic survival or relative cell growth and the DNA damage response using immunological-based techniques in Hep3B, PLC/PRF/5, HepG2- and HepaRG-derived models. Transcriptome changes due to HBx expression vs SMC6 loss were assessed by RNA sequencing in HepaRG-derived models. PARP and PARG transcripts (qPCR) and PARP1, H2AX and gammaH2AX protein levels (RPPA) were compared in control liver vs HBV-, HCV-, alcohol- and non-alcoholic steatohepatitis-associated HCC (tumor/peritumor) tissues.
PARPi cytotoxicity was significantly enhanced when combined with X-rays (2Gy) with Talazoparib having a greater impact than Veliparib in most in vitro models. HBx expression significantly lowered survival, probably driven by SMC5/6 loss based on the transcriptome analysis and higher DNA damage levels. PARP1 and PARP2 transcript levels were significantly higher in tumor than peritumor and control tissues. The HBV/HCV/alcohol-associated tumor tissues studied had reduced H2AX but higher gammaH2AX protein levels compared to peritumor and control tissues providing evidence of increased DNA damage during liver disease progression.
These proof-of-concept experiments support PARPi alone or combined with radiotherapy for HCC treatment, particularly for HBV-associated tumors, that warrant further investigation.Le texte complet de cet article est disponible en PDF.
Abbreviations : HCC, RT, HBV, SBRT, PARP, PARPi, IR, SMC5/6, HR, DSBs, PARG, gammaH2AX, PT, T, HepaRG TR, HepaRG TRX, HepaRG TRX sh-scramble, HepaRG TRX sh-SMC6, HU, DAPI, AU, D37, RPPA, FPKM, DDR
Keywords : Liver cancer, Hepatitis B virus (HBV) X protein, gammaH2AX, DNA damage, SMC5/6, Talazoparib, Veliparib.