Screening of PCNA ubiquitylation inhibitors as novel synthetic lethality inducers in Homologous-Recombination-deficient cancer cells

QUIROGA, RODRIGO; VILLAFAÑEZ, FLORENCIA; VILLARREAL, MARCOS A.; VILLAFAÑEZ, FLORENCIA; VILLARREAL, MARCOS A.; GARCÍA, ALEJANDRA I.; SORIA, GASTÓN; GARCÍA, ALEJANDRA I.; SORIA, GASTÓN; QUIROGA, RODRIGO

Egmond aan Zee

Congreso; 31st International Association for Breast Cancer Research Conference; 2019

International Association for Breast Cancer Research

Translesion DNA Synthesis (TLS) and homologousrecombination (HR) cooperate during S-phase to safeguard replicationforks integrity. Thus, the inhibition of TLS becomes a promisingpoint of therapeutic intervention in HR-deficient cancers, where TLSimpairment might trigger synthetic lethality (SL). The mainlimitation to test this hypothesis is the current lack of selectivepharmacological inhibitors of TLS. In this work we show thedevelopment of two complementary screenings assays to identify smallmolecules that inhibit PCNA ubiquitylation, a key post-translationalmodification required for efficient TLS activation. First, we setup aminiaturized WB assay with dual antibodies for ubi-PCNA and totalPCNA coupled to infrared laser scanning. Second, we designed avirtual screening strategy to identify direct blockers ofPCNA-ubiquitylation using molecular modeling. Herein, we present theidentification of strong PCNA ubiquitylation inhibitors using bothstrategies. Moreover, using multiple experimental models we performedproof-of-concept experiments showing that the abolishment of PCNAubiquitylation triggers synthetic lethality in HR-deficient cellssubmitted to UV irradiation and Cisplatin treatment. Collectively,these findings set the ground for developing a first-in-class type oftherapeutic approach, where TLS inhibition can be achieved by thepharmacological inhibition of PCNA ubiquitylation. Given the vastincidence of HR deficiencies in multiple types of human cancers (i.e.Breast and Ovarian cancer), the pharmacological inhibition of TLScould become a niche for drug discovery as an alternative targetedtherapy to treat these malignancies.p { margin-bottom: 0.1in; direction: ltr; line-height: 120%; text-align: left; }a:link { }