Abstract
The aim of this study was to elucidate the carryover effect of olaparib to subsequent chemotherapy and its underlying mechanisms. We generated olaparib-resistant SNU-484, SNU-601, SNU-668, and KATO-III gastric cancer cell lines and confirmed their resistance by cell viability and colony forming assays. Notably, olaparib-resistant cell lines displayed cross-resistance to cisplatin except for KATO-III. Inversely, olaparib-resistant SNU-484, SNU-668, and KATO-III were more sensitive to irinotecan than their parental cells. However, sensitivity to paclitaxel remained unaltered. There were compensatory changes in the ATM/ATR axis and p-Chk1/2 protein expression. ERCC1 was also induced in olaparib-resistant SNU-484, SNU-601, and SNU-668, which showed cross-resistance to cisplatin. Olaparib-resistant cells showed tyrosyl-DNA phosphodiesterase 1 (TDP1) downregulation with higher topoisomerase 1 (TOP1) activity, which is a target of irinotecan. These changes of TOP1 and TDP1 in olaparib-resistant cells was confirmed as the underlying mechanism for increased irinotecan sensitivity through manipulated gene expression of TOP1 and TDP1 by specific plasmid transfection and siRNA. The patient-derived xenograft model established from the patient who acquired resistance to olaparib with BRCA2 mutation showed increased sensitivity in irinotecan. In conclusion, the carryover effects of olaparib to improve antitumor effect of subsequent irinotecan were demonstrated. These effects should be considered when determining the subsequent therapy with olaparib.
Highlights
Olaparib is an oral poly(ADP-ribose) polymerase (PARP) inhibitor that traps inactivated PARP onto single-strand DNA breaks (SSBs), leading to double-strand DNA breaks that induce cell death [1,2].Olaparib showed antitumor effect alone or in combination with chemotherapy in tumors with deficiencies at the repair of double-strand breaks caused by BRCA1/2 mutations, ATM dysfunction, and RAD51C deficiency [3,4,5,6]
Except for KATO-III, all olaparib-resistant cell lines became resistant to cisplatin
Through manipulating gene expressions, increased sensitivity to irinotecan in olaparib-resistant cells was confirmed to be attributed to topoisomerase 1 (TOP1) upregulation and tyrosyl-DNA phosphodiesterase 1 (TDP1) downregulation, which was shown in olaparib-resistant cells
Summary
Olaparib is an oral poly(ADP-ribose) polymerase (PARP) inhibitor that traps inactivated PARP onto single-strand DNA breaks (SSBs), leading to double-strand DNA breaks that induce cell death [1,2]. Olaparib showed antitumor effect alone or in combination with chemotherapy in tumors with deficiencies at the repair of double-strand breaks caused by BRCA1/2 mutations, ATM dysfunction, and RAD51C deficiency [3,4,5,6]. In germline BRCA-mutated advanced ovarian cancer patients who have been treated with three or more prior lines of chemotherapy, olaparib showed clinical efficacy and has been approved by U.S Food and Drug Administration [4]. We found that RAD51C depletion led to hypersensitivity to olaparib in gastric cancer cells [6].
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