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Role of drug induced nuclear CTSL (nCTSL) in DNA damage response in cancer- therapeutic implications
Abstract:
In our efforts to enhance sensitivity to PARP inhibitors, we identified clofarabine (CLF) as a potential therapy for drug-resistant ovarian cancer and nuclear trafficking of Cathepsin L (CTSL) as a treatment- responsive biomarker. Using PARP inhibitor-sensitive and -resistant OC cell lines, ex vivo cultures of patient-derived ovarian ascites (OVA), primary ovarian tumors, and xenografts (PDX), we found that CLF monotherapy induces nuclear CTSL (nCTSL) in CLF-responsive cells (CLF-r) and sensitizes them to PARP inhibitors olaparib and rucaparib. In CLF non-responsive cells (CLF-nr), a combination of CLF with olaparib is necessary for nCTSL trafficking and synergy. CLF+olaparib synergy was observed in 47% of CLF-r and 24% of CLF-nr OVA samples. Drug-induced nCTSL is crucial for DNA damage response, including cell cycle arrest and apoptosis. Knockdown of CTSL in both CLF-r and CLF-nr cells conferred resistance to the CLF+olaparib combination, emphasizing nCTSL's role in the DNA damage response pathway (DDR). Mechanistically, CLF facilitates CTSL nuclear import via KPNB1 in CLF-r cells. In CLF-nr cells, both olaparib and CLF are needed to facilitate CTSL nuclear import. Additionally, CLF downregulates the nuclear export protein CRM1 (XPO1) in both cohorts. Interestingly, CLF does not downregulate CRM1 in a subset of OVAs (29%), and they were classified as CLF-resistant (CLF- Res). In these samples, inhibiting CRM1 with KPT8602 restored synergy between CLF and PARP inhibitors. In vivo, CLF-r and CLF-nr PDX models exhibited enhanced DDR, reduced tumor burden, and prolonged survival with the CLF+olaparib combination. These findings suggest the CLF+olaparib combination is a promising therapeutic strategy for drug-resistant OC by inducing DDR through CTSL nuclear localization.
Insights
Clofarabine (CLF) combined with PARP inhibitors shows promise for drug-resistant ovarian cancer. This combination induces nuclear Cathepsin L (CTSL), enhancing DNA damage response and improving treatment outcomes.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Therapeutics
Background:
- Ovarian cancer (OC) often develops resistance to PARP inhibitors, necessitating novel therapeutic strategies.
- Cathepsin L (CTSL) nuclear trafficking is a potential biomarker for treatment response in drug-resistant OC.
- Clofarabine (CLF) is investigated for its potential to overcome PARP inhibitor resistance.
Purpose of the Study:
- To evaluate clofarabine (CLF) as a therapy for drug-resistant ovarian cancer (OC).
- To investigate the role of nuclear Cathepsin L (CTSL) trafficking as a biomarker for CLF and PARP inhibitor response.
- To determine the synergistic effects of CLF in combination with PARP inhibitors (olaparib, rucaparib) in OC models.
Main Methods:
- Utilized PARP inhibitor-sensitive and -resistant OC cell lines, patient-derived ascites (OVA), primary tumors, and xenografts (PDX).
- Assessed CLF monotherapy and combination therapy with olaparib, evaluating CTSL nuclear localization (nCTSL) and DNA damage response (DDR).
- Investigated mechanisms including KPNB1-mediated nuclear import, CRM1 (XPO1) downregulation, and in vivo efficacy in PDX models.
Main Results:
- CLF monotherapy induced nCTSL in CLF-responsive (CLF-r) cells, sensitizing them to PARP inhibitors.
- Combination of CLF and olaparib was required for nCTSL trafficking and synergy in CLF non-responsive (CLF-nr) cells.
- CLF+olaparib synergy was observed in 47% of CLF-r and 24% of CLF-nr OVA samples; nCTSL was crucial for DDR, and CRM1 inhibition restored synergy in resistant cases.
Conclusions:
- The CLF+olaparib combination represents a promising strategy for overcoming drug resistance in ovarian cancer.
- CLF induces DDR by promoting CTSL nuclear localization, offering a novel therapeutic approach.
- CTSL nuclear trafficking serves as a predictive biomarker for response to CLF and PARP inhibitor combinations.
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