Rapid activation of epithelial-mesenchymal transition drives PARP inhibitor resistance in Brca2-mutant mammary tumours

Abstract

Tumours defective in the DNA homologous recombination repair pathway can be effectively treated with poly (ADP-ribose) polymerase (PARP) inhibitors; these have proven effective in clinical trials in patients with BRCA gene function-defective cancers. However, resistance observed in both pre-clinical and clinical studies is likely to impact on this treatment strategy. Over-expression of phosphoglycoprotein (P-gp) has been previously suggested as a mechanism of resistance to the PARP inhibitor olaparib in mouse models of Brca1/2 -mutant breast cancer. Here, we report that in a Brca2 model treated with olaparib, P-gp upregulation is observed but is not sufficient to confer resistance. Furthermore, resistant/relapsed tumours do not show substantial changes in PK/PD of olaparib, do not downregulate PARP1 or re-establish double stranded DNA break repair by homologous recombination, all previously suggested as mechanisms of resistance. However, resistance is strongly associated with epithelial-mesenchymal transition (EMT) and treatment-naïve tumours given a single dose of olaparib upregulate EMT markers within one hour. Therefore, in this model, olaparib resistance is likely a product of an as-yet unidentified mechanism associated with rapid transition to the mesenchymal phenotype.

Identifying and Overcoming Mechanisms of PARP Inhibitor Resistance in Homologous Recombination Repair-Deficient and Repair-Proficient High Grade Serous Ovarian Cancer Cells

“…Low EZH2 levels prevent MUS81 recruitment and so stabilize the fork, resulting in resistance to PARPi [35]. Activation of epithelial-mesenchymal transition in a mouse model of BRCA2-deficient breast cancer has also been found to trigger olaparib resistance [36].…”

“…To investigate the mechanism of olaparib resistance in our HRR-proficient and -deficient HGSOC clones, protein lysates were Western blotted for proteins previously found to be involved in PARPi resistance mechanisms in HRR-deficient cells [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Lysates were made from resistant clones grown under olaparib selection, while parental cell lysates were made from cells in ordinary medium.…”

“…While PARP inhibitors have greatly improved treatment options for HRR-deficient HGSOC, development of PARP inhibitor resistance in some patients limits the clinical outcome [21]. In vitro and in vivo models suggest that PARPi resistance can occur by a variety of independent mechanisms [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. The aim of this study is to compare mechanisms of resistance to PARP inhibitor olaparib in HRR-proficient and -deficient HGSOC cells and then use the resistant cells to test a method to overcome olaparib resistance considered particularly appropriate for HGSOC.…”

Recent advancements in PARP inhibitors-based targeted cancer therapy

“…Defining both molecular features and elucidating underlying mechanisms of PARPi resistance stand at the foundation of overcoming resistance to PARP treatments. While activation of epithelial-mesenchymal transition (EMT) 78 , 79 and induction of P-glycoprotein expression 12 , 80 have been observed in PARPi-resistant biopsies, they are not sufficient to confer resistance. 78 Recent research supports the notion that the primary mechanisms for PARPi resistance are HR restoration and replication fork protection.…”

Development of a 3D functional assay and identification of biomarkers, predictive for response of high-grade serous ovarian cancer (HGSOC) patients to poly-ADP ribose polymerase inhibitors (PARPis): targeted therapy

“…Since epithelial to mesenchymal transition (EMT) has been strongly involved in mechanisms of resistance to EOC therapy [44], including PARPis resistance [45], we examined the expression of the two major EMT markers, E-cadherin and N-cadherin, in a panel of PARPisresistant and PARPis-sensitive AsPCs (based on their response to treatment in 3D (spheroid) cultures). Both Western blot (see Additional file 4A) and immunofluorescence (see Additional file 4B) analyses were indicative of significantly higher N-cadherin protein expression levels in PARPis-resistant AsPCs compared to their sensitive counterparts, while no significant differences were observed when examining E-cadherin protein expression levels in both sensitive and resistant AsPCs.…”