Synergistic lethality between PARP-trapping and alantolactone-induced oxidative DNA damage in homologous recombination-proficient cancer cells

Abstract

PARP1 and PARP2 play critical roles in regulating DNA repair and PARP inhibitors have been approved for the treatment of BRCA1/2-mutated ovarian and breast cancers. It has long been known that PARP inhibition sensitizes cancer cells to DNAdamaging cytotoxic agents independent of BRCA status, however, clinical use of PARP inhibitors in combination with DNAdamaging chemotherapy is limited by the more-than-additive cytotoxicity. The natural compound alantolactone (ATL) inhibits the thioredoxin reductase to induce ROS accumulation and oxidative DNA damage selectively in cancer cells. Here, we showed that nontoxic doses of ATL markedly synergized with the PARP inhibitor olaparib to result in synthetic lethality irrespective of homologous recombination status. Synergistic cytotoxicity was seen in cancer but not noncancerous cells and was reduced by the ROS inhibitor NAC or knockdown of OGG1, demonstrating that the cytotoxicity resulted from the repair of ATL-induced oxidative DNA damage. PARP1 knockdown suppressed the synergistic lethality and olaparib was much more toxic than veliparib when combined with ATL, suggesting PARP-trapping as the primary inducer of cytotoxicity. Consistently, combined use of ATL and olaparib caused intense signs of replication stress and formation of double strand DNA breaks, leading to S and G 2 arrest followed by apoptosis. In vivo, the combination effectively induced regression of tumor xenografts, while either agent alone had no effect. Hence, PARP trapping combined with specific pro-oxidative agents may provide safe and effective ways to broaden the therapeutic potential of PARP inhibitors.

Recent advancements in PARP inhibitors-based targeted cancer therapy

“…Alantolactone, a ROS inducer, is shown to synergize with olaparib and induce lethality irrespective of HR status. 20 …”

Frequency and prognostic value of mutations associated with the homologous recombination DNA repair pathway in a large pan cancer cohort

“…Hence, it is not clear how many patients identified in this study will in fact have HRD or would benefit from PARP inhibition. Additionally, clinical response to PARP inhibition is not solely driven by HRD, involving several other factors including replication, oxidative, and ER stress [65][66][67][68][69] . www.nature.com/scientificreports/ www.nature.com/scientificreports/ Therefore, specific alterations to these and other genes warrant further investigation prior to any being proposed as a reliable surrogate for HRD, particularly in the setting of other cellular processes.…”

Regulation of DNA Damage Response and Homologous Recombination Repair by microRNA in Human Cells Exposed to Ionizing Radiation

“…Due to the fact that the DNA repair system by homologous recombination is active only in the cell division phase, when the correct chromatid is needed for effective repair, the search for potential tumor sensitizing targets on radiotherapy in this DNA repair pathway is particularly well-founded. The concept of synthetic lethality involving homologous biologists [17][18][19][20][21][22][23][24] MicroRNAs (miRNAs) are single-stranded short noncoding RNAs of 20-25 nt in length involved in the regulation of gene expression by repressing translation or cleaving target mRNA. More than 1000 miRNA transcription units have been identified in human genomes.…”

“…Due to the fact that the DNA repair system by homologous recombination is active only in the cell division phase, when the correct chromatid is needed for effective repair, the search for potential tumor sensitizing targets on radiotherapy in this DNA repair pathway is particularly well-founded. The concept of synthetic lethality involving homologous biologists [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]…”