The PARP-1 inhibitor Olaparib suppresses BRCA1 protein levels, increases apoptosis and causes radiation hypersensitivity in BRCA1^+/- lymphoblastoid cells

Abstract

The use of polyADPribose polymerase inhibitors in cancer treatment provides a unique opportunity to target DNA repair processes in cancer cells while leaving normal tissue intact. The PARP-1 enzyme repairs DNA single strand breaks (SSB). Therefore PARP-1 inhibition in BRCA1 negative cancers results in the formation of cytotoxic DNA double strand breaks (DSB) causing synthetic lethality. The use of PARP1 inhibitors is gaining momentum in the treatment of a variety of tumours with BRCA1 involvement including breast, ovarian, pancreatic and prostate cancer.Our previous work showed that the PARP-1 inhibitor Olaparib causes both hypersensitivity of BRCA1+/- cells following exposure to gamma radiation due to the persistence of DNA strand breaks in cells, measured by the DNA damage biomarker γ-H2AX. Therefore dual treatment of cancers with radiotherapy and PARP1 inhibition may lead to cases of increased normal tissue toxicity in cancer patients.In this study we exposed two normal lymphoblastoid cell lines and three heterozygous BRCA1 lymphoblastoid cell lines to the PARP-1 inhibitor Olaparib and gamma radiation and after measured BRCA1 protein expression and apoptosis levels following treatment. BRCA1 protein foci analysis was performed on cells exposed to 2 Gy radiation in the presence or absence of 5 μM Olaparib. Using immunofluorescence and imaging flow cytometry, foci were measured in untreated cells and at 0.5, 3, 5 and 24 hours post-irradiation. Exposing normal and BRCA1+/- cells to Olaparib followed by gamma radiation results in a dramatic change in BRCA1 protein foci expression, with a significant reduction in BRCA1 protein expression observed in the heterozygote cells, together with an increase in apoptosis levels in these cells.In conclusion, combining PARP1 inhibitors with radiotherapy in treating of BRCA1-related cancers has clinical relevance, however this study and our previous publications serve to highlight the potential problems of increased side effects in these scenarios.

MiR-200c sensitizes Olaparib-resistant ovarian cancer cells by targeting Neuropilin 1

“…As expected, we observed that treatment with Olaparib is capable of inducing DNA damage and G2/M phase cell-cycle arrest in all the OC cell lines, but such alterations lead to activation of apoptotic pathways only in sensitive UWB cells, maybe due to the persistence of DNA strand breaks, which are restored at 144 h in UWB-BRCA and SKOV3 cells, with subsequent no apoptosis induction following Olaparib treatment. In agreement with our data, lymphoblastoid cells with mono-allelic mutations of BRCA1 showed a persistent DNA damage upon Olaparib treatment, which rendered them hypersensitive to gamma radiation [61]. However, our results pointed out a partial reduction of clonogenic ability induced by Olaparib in UWB-BRCA cells.…”

The PARP inhibitor olaparib potentiates the effect of the DNA damaging agent doxorubicin in osteosarcoma

“…In addition, anti-cancer therapy which combine PARP inhibition and genotoxic chemotherapeutic agents according to the expression of PARP1, γH2AX, BRCA1, and BRCA2 has been suggested for breast carcinomas [ 37 ] and Ewing sarcomas [ 38 , 40 ]. Olaparib suppressed BRCA1 protein level and induced hypersensitivity to radiation in lymphoblastoid cells [ 41 ]. In addition, it has recently been reported that PARP inhibitors are effective for the treatment of BRCA1/2-mutated Ewing sarcoma [ 38 ].…”

Patients Resistant Against PSMA-Targeting α-Radiation Therapy Often Harbor Mutations in DNA Damage-Repair–Associated Genes

“…Encouraging clinical results have also been demonstrated for combination of 177 Lu-PSMA-617 with radio-sensitizers (38). In addition to their specific anti-tumor activity in ATM and BRCA1/2 mutated patients, PARP-inhibitors also act as unspecific radio-sensitizers (13,14,39). Thus, regardless whether the observed coincidence of DRMs and resistance to PSMA-TAT despite PSMA-positivity reflects tumor biology or other selection biases, it seems reasonable to speculate that the combination of PSMA-TAT with immunotherapy or PARP-inhibitors may act complementary.…”

“…Loss of such DNA-damage "recognition and signaling" genes have often been described to promote radio-resistance (10)(11)(12)31,32). In contrast, the protein product of the BRCA2 gene plays a key role in the effector downstream of DNA-repair and deficiency at this point of the cascade commonly translates into increased radio-sensitivity (12,13,33,34).…”

“…Obviously, in addition to quantitative tumortargeting, accessory factors are influencing response to PSMA-TAT. Preclinical and early clinical studies reported that particular DNA-damage repair associated genemutations (DRMs) can either increase or decrease the radio-sensitivity of prostate cancers (8)(9)(10)(11)(12)(13)(14) and thus might represent one of these cofactors.…”