Abstract LB158: Synergistic cytotoxicity of histone deacetylase and poly-ADP ribose polymerase inhibitors and decitabine in pancreatic cancer cells: implications for novel therapy
Authors: Tsimberidou Apostolia M. , Valdez Benigno C. , Yuan Bin , Nieto Yago , Baysal Mehmet , Chakraborty Abhijit , Andersson Borje S. 
Published: April 2024

Abstract
Histone deacetylase inhibitors (HDACi) can modulate the acetylation status of proteins, influencing the genomic instability exhibited by cancer cells. Poly (ADP ribose) polymerase (PARP) inhibitors (PARPi) have a direct effect on protein poly (ADP-ribosyl)ation, which is important for DNA repair. Decitabine is a nucleoside cytidine analogue, which when phosphorylated gets incorporated into the growing DNA strand, inhibiting methylation and inducing DNA damage by inactivating and trapping DNA methyltransferase on the DNA, thereby activating transcriptionally silenced DNA loci. We explored various combinations of HDACi and PARPi +/- decitabine (hypomethylating agent) in pancreatic cancer cell lines BxPC-3 and PL45 (wild-type BRCA1 and BRCA2) and Capan-1 (mutated BRCA2). Colony formation and drug-mediated inhibition of cell proliferation in pancreatic cancer cell lines and comparison of the effects of each drug combination with the effect of the individual drugs are shown in Table. The combination of HDACi (panobinostat or vorinostat) with PARPi (talazoparib or olaparib) resulted in synergistic cytotoxicity in all cell lines tested. The addition of decitabine further increased the synergistic cytotoxicity noted with HDACi and PARPi, triggering apoptosis (evidenced by increased cleavage of caspase 3 and PARP1). The 3-drug combination treatments (vorinostat, talazoparib, and decitabine; vorinostat, olaparib, and decitabine; panobinostat, talazoparib, and decitabine; panobinostat, olaparib, and decitabine) induced more DNA damage (increased phosphorylation of histone 2AX) than the individual drugs and impaired the DNA repair pathways (decreased levels of ATM, BRCA1, and ATRX proteins). The 3-drug combinations also altered the epigenetic regulation of gene expression (NuRD complex subunits, reduced levels). This is the first study to demonstrate synergistic interactions between the aforementioned agents in pancreatic cancer cell lines and provides preclinical data to design individualized therapeutic approaches with the potential to improve pancreatic cancer treatment outcomes.
Table. Colony formation and drug-mediated inhibition of cell proliferation in pancreatic cancer cell lines. Comparison of the effects of each drug combination with the effect of the individual drugs (Table shows the p-values for each comparison.) Colony formation BxPC-3 PL45 Capan-1 Pano SAHA TLZ Ola DAC Pano SAHA TLZ Ola DAC Pano SAHA TLZ Ola DAC Pano+TLZ 0.00048 0.0052 2.40E-06 2.70E-06 0.0051 0.021 Pano+Ola 0.0035 0.078 0.0011 0.00094 0.0016 0.022 SAHA+TLZ 1.80E-05 0.17 0.0029 0.012 0.0014 0.019 SAHA+Ola 0.00018 0.014 0.0016 0.0068 0.0066 0.029 Pano+TLZ+DAC 4.20E-05 0.00026 0.0015 1.70E-05 1.20E-05 2.70E-06 0.00052 0.00088 0.0064 Pano+Ola+DAC 3.40E-05 0.00049 0.0013 7.10E-07 1.70E-06 2.20E-06 0.00068 0.0028 0.0053 SAHA+TLZ+DAC 0.00016 0.00016 0.0011 1.90E-05 3.70E-06 9.30E-07 0.00018 0.00017 0.011 SAHA+Ola+DAC 4.90E-07 0.00035 0.001 0.00022 0.00026 0.00084 0.00016 0.0016 0.0035 Drug-mediated inhibition of cell proliferation Pano+TLZ+DAC 3.57E-05 3.89E-07 1.30E-07 2.91E-05 3.76E-06 1.80E-08 0.0239 ND 0.0092 Pano+Ola+DAC 7.76E-05 1.43E-07 2.52E-07 6.59E-07 1.03E-08 2.22E-07 0.0013 0.21 0.0034 SAHA+TLZ+DAC 3.04E-06 0.00034 1.17E-05 4.91E-08 4.45E-06 1.74E-07 0.0013 1.75E-01 0.007 SAHA+Ola+DAC 0.00012 0.0032 0.000068 9.64E-09 1.53E-08 9.35E-07 0.0007 0.18 0.0054 Abbreviations: DAC: decitabine; ND: not determined; Ola: olaparib; Pano: panobinostat; SAHA: vorinostat; TLZ: talazoparib P ≤ 0.05 is considered statistically significant.
Citation Format: Apostolia M. Tsimberidou, Benigno C. Valdez, Bin Yuan, Yago Nieto, Mehmet Baysal, Abhijit Chakraborty, Borje S. Andersson. Synergistic cytotoxicity of histone deacetylase and poly-ADP ribose polymerase inhibitors and decitabine in pancreatic cancer cells: implications for novel therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB158.