The PARP inhibitor olaparib enhances the sensitivity of Ewing sarcoma to trabectedin

Abstract

Recent preclinical evidence has suggested that Ewing Sarcoma (ES) bearing EWSR1-ETS fusions could be particularly sensitive to PARP inhibitors (PARPinh) in combination with DNA damage repair (DDR) agents. Trabectedin is an antitumoral agent that modulates EWSR1-FLI1 transcriptional functions, causing DNA damage. Interestingly, PARP1 is also a transcriptional regulator of EWSR1-FLI1, and PARPinh disrupts the DDR machinery. Thus, given the impact and apparent specificity of both agents with regard to the DNA damage/DDR system and EWSR1-FLI1 activity in ES, we decided to explore the activity of combining PARPinh and Trabectedin in in vitro and in vivo experiments. The combination of Olaparib and Trabectedin was found to be highly synergistic, inhibiting cell proliferation, inducing apoptosis, and the accumulation of G2/M. The drug combination also enhanced γH2AX intranuclear accumulation as a result of DNA damage induction, DNA fragmentation and global DDR deregulation, while EWSR1-FLI1 target expression remained unaffected. The effect of the drug combination was corroborated in a mouse xenograft model of ES and, more importantly, in two ES patient-derived xenograft (PDX) models in which the tumors showed complete regression. In conclusion, the combination of the two agents leads to a biologically significant deregulation of the DDR machinery that elicits relevant antitumor activity in preclinical models and might represent a promising therapeutic tool that should be further explored for translation to the clinical setting.

PARP1 expression drives the synergistic antitumor activity of trabectedin and PARP1 inhibitors in sarcoma preclinical models

“…Our result reflects the fact that veliparib is a pure catalytic inhibitor of PARP1 activation, whereas olaparib is a poisoning drug that blocks activated PARP1 enzyme at the site of damage (PARP1-trapping activity) impeding the subsequent recruitment of repairing machinery [11, 52, 55]. We studied the synergism of PARP1 inhibitors and trabectedin in a large set of different tumor cell lines and in in vivo models, demonstrating that PARP1 inhibition improved the antitumor activity of trabectedin in a cell-line dependent intensity, as previously shown in breast cancer and in Ewing’s sarcoma cell lines [44, 55]. Among the tested BSTS histotypes, Ewing’s sarcoma cells were the most sensitive to the combination, a result that might be explained by the known exquisite sensitivity of the pathognomonic fusion protein EWS/FLI1-expressing cells to both trabectedin and PARP1 inhibition [10, 56–59].…”

Vincristine, Ifosfamide, and Doxorubicin for Initial Treatment of Ewing Sarcoma in Adults

“…In spite of these results, to date none of these agents have achieved approval for use in ES. Transcription factor‐targeting drugs such as trabectedin or lurbinectedin and YK‐4‐279 have also demonstrated promising preclinical activity, and clinical trials have just recently been initiated to assess their antineoplastic activity in ES patients. Some of the drugs in development have been shown to synergize with vinca‐alkaloids , and the addition of new drugs may further abrogate the number of cytotoxics needed.…”

Etv6/Runx1 Fusion Gene Abrogation Decreases The Oncogenic Potencial Of Tumour Cells In A Preclinical Model Of Acute Lymphoblastic Leukaemia

“…Excised tumours were sampled just after sacrifice and representative areas were a) formalin-fixed (24 hours) (Merck Millipore) and paraffin-embedded and (b) snap-frozen in OCT and stored at 80ºC as previously described. 19 Tissue sections 2μM thick were stained with hematoxilin & eosin (H&E) and prepared for immunohistochemistry (IHC). IHC was performed as previously described 19 using the anti-Ki67primary antibody (Merck Millipore).…”

“…19 Tissue sections 2μM thick were stained with hematoxilin & eosin (H&E) and prepared for immunohistochemistry (IHC). IHC was performed as previously described 19 using the anti-Ki67primary antibody (Merck Millipore). The number of mitotic figures were counted in 6 high-power field.…”