17P - New therapeutic target in triple-negative breast cancer for enhancing PARP inhibitor efficacy and stimulating the anti-tumour immune response

Background

Triple negative (TNBC) is the most aggressive subtype of breast cancer, lacking effective targeted therapies. PARP inhibitors (PARPi) like olaparib, in combination with immune checkpoint inhibitors, stand out among the groundbreaking strategies to treat BRCA1/2 mutated TNBC but are often connected to resistance.

Methods

Western blot, coimmunoprecipitation, qPCR, immunofluorescence, proliferation and cytotoxicity assays.

Results

Our preclinical results unprecedentedly show that connexin43 (Cx43) upregulation in Cx43-null BRCA1 mutated TNBC cells, de novo resistant to PARPi olaparib, deeply resensitizes them, reducing their IC50 almost by half as well as their 2D and physiologically-appropriate 3D spheroid proliferation upon treatment with the drug. Consistent with this, olaparib therapy reduces global protein PARylation and induces significantly higher levels of DNA double-strand damage, PARP1 cleavage and caspase 3-mediated apoptosis in Cx43-restored cells, emphasizing their higher susceptibility to PARPi. Similar results were obtained under physiologically-relevant Anoikis conditions and in BRCA1 mutated ovarian cancer cells. Wild type but not Cx43-restituted cells accumulate RAD51 foci after drug treatment, denoting a potential underlying mechanism of resistance. In order to validate our proposal, an innovative extracellular vesicle-based approach was developed as an avant-garde translational strategy to efficiently deliver both Cx43 and PARPi drug to tumour cells. Combination of olaparib with Cx43-enriched vesicles distinctively enhanced olaparib efficacy against de novo resistant BRCA1 mutated TNBC cells versus the drug alone. In addition, in cocultures of patient-derived and EGFR-CAR(chimeric-antigen-receptor)-engineered natural killer (NK) cells with BRCA1 mutated TNBC cells, Cx43 restoration in tumour cells elicited a significantly higher cytotoxic NK antitumour response than wild type cells.

Conclusions

These results, protected by a EU patent, reveal Cx43 as a dual promising novel therapeutic target to increase the efficacy and to resensitize de novo resistant BRCA1 mutated TNBC to PARPi olaparib, as well as to boost NK cytotoxicity against TNBC.

Clinical trial identification

Editorial acknowledgement

N/A

Legal entity responsible for the study

The authors.

Funding

Ministerio de Universidades, European Molecular Biology Organization, Xunta de Galicia.

Disclosure

All authors have declared no conflicts of interest.