Molecular mechanisms restoring olaparib efficacy through ATR/CHK1 pathway inhibition in olaparib-resistant BRCA1/2(MUT) ovarian cancer models.

Resistance to olaparib inevitably develops in ovarian cancer (OC) patients, highlighting the necessity for effective strategies to improve its efficacy. Here, we established a novel olaparib-resistant patient-derived xenograft model of high-grade serous OC with BRCA1/2 mutations and examined the molecular characteristics of acquired resistance and resensitization to olaparib in treatment-naïve tumors in vivo. Olaparib-resistant xenografts were treated with olaparib, ATR inhibitor (ATRi, ceralasertib), CHK1 inhibitor (CHK1i, MK-8776) or their combinations. Proliferation, apoptosis, ATR/CHK1 activity, PARP signaling, DNA damage response (DDR), epithelial-to-mesenchymal transition (EMT), and MDR1 expression, were examined via RT-qPCR, western blot, and immunohistochemistry. Resistant tumors exhibited defects in PARP and ATR/CHK1 signaling, accompanied by altered expression of proteins involved in DDR and EMT. Olaparib rechallenge combined with ATR/CHK1 inhibitors showed promising synergistic effects on tumor growth inhibition. Mechanistically, combined treatments suppressed tumor proliferation without increasing apoptosis or necrosis, while inducing tumor cell vacuolization indicative of cell death. ATRi combined with olaparib induced or augmented downregulation of ATR, CHK1, PARP1, PARG, BRCA1, γH2AX, and PARylated protein expression, while reversing olaparib-induced upregulation of vimentin, BRCA2, and 53BP1. Our collective findings indicate that ATR/CHK1 pathway inhibition restores the olaparib efficacy in resistant BRCA1/2MUT high-grade serous OC, highlighting promising approach for olaparib rechallenge of non-responsive patients. Uncovered mechanisms might improve our understanding of acquisition and overcoming resistance to olaparib in ovarian cancer.

Biegała Ł ，Statkiewicz M ，Gajek A ，Szymczak-Pajor I ，Rusetska N ，Śliwińska A ，Marczak A ，Mikula M ，Rogalska A ... -  《-》

LCP1 promotes ovarian cancer cell resistance to olaparib by activating the JAK2/STAT3 signalling pathway.

Gai M ，Zhao L ，Li H ，Jin G ，Li W ，Wang F ，Liu M ... -  《-》

Poly (ADP-Ribose) Polymerase Inhibitor Olaparib-Resistant BRCA1-Mutant Ovarian Cancer Cells Demonstrate Differential Sensitivity to PARP Inhibitor Rechallenge.

Shih CT ，Huang TT ，Nair JR ，Ibanez KR ，Lee JM ... -  《Cells》

Targeted inhibition of the ATR/CHK1 pathway overcomes resistance to olaparib and dysregulates DNA damage response protein expression in BRCA2(MUT) ovarian cancer cells.

Biegała Ł ，Gajek A ，Szymczak-Pajor I ，Marczak A ，Śliwińska A ，Rogalska A ... -  《Scientific Reports》

Targeting the ATR/CHK1 Axis with PARP Inhibition Results in Tumor Regression in BRCA-Mutant Ovarian Cancer Models.

Purpose: PARP inhibition (PARPi) has modest clinical activity in recurrent BRCA-mutant (BRCAMUT) high-grade serous ovarian cancers (HGSOC). We hypothesized that PARPi increases dependence on ATR/CHK1 such that combination PARPi with ATR/CHK1 blockade results in increased cell death and tumor regression.Experimental Design: Effects of PARPi (olaparib), CHK1 inhibition (CHK1i;MK8776), or ATR inhibition (ATRi;AZD6738) alone or in combination on survival, colony formation, cell cycle, genome instability, and apoptosis were evaluated in BRCA1/2MUT HGSOC cells. Tumor growth in vivo was evaluated using a BRCA2MUT patient-derived xenograft (PDX) model.Results: PARPi monotherapy resulted in a decrease in BRCAMUT cell survival, colony formation and suppressed but did not eliminate tumor growth at the maximum tolerated dose (MTD) in a BRCA2MUT PDX. PARPi treatment increased pATR and pCHK1, indicating activation of the ATR-CHK1 fork protection pathway is relied upon for genome stability under PARPi. Indeed, combination of ATRi or CHK1i with PARPi synergistically decreased survival and colony formation compared with single-agent treatments in BRCAMUT cells. Notably, PARPi led to G2 phase accumulation, and the addition of ATRi or CHK1i released cells from G2 causing premature mitotic entry with increased chromosomal aberrations and apoptosis. Moreover, the combinations of PARPi with ATRi or CHK1i were synergistic in causing tumor suppression in a BRCA2MUT PDX with the PARPi-ATRi combination inducing tumor regression and in most cases, complete remission.Conclusions: PARPi causes increased reliance on ATR/CHK1 for genome stability, and combination PARPi with ATR/CHK1i is more effective than PARPi alone in reducing tumor burden in BRCAMUT models. Clin Cancer Res; 23(12); 3097-108. ©2016 AACR.

Kim H ，George E ，Ragland R ，Rafail S ，Zhang R ，Krepler C ，Morgan M ，Herlyn M ，Brown E ，Simpkins F ... -  《-》