Introduction
High grade serous ovarian cancer (HGSOC) survival rate remains dismal, especially for those resistant to first-line treatment. We have identified the Wnt receptor ROR1 as a therapeutic target in treating HGSOC. Antibody-drug conjugates (ADCs), are a promising new type of therapy which link a target specific antibody to a cytotoxic therapy allowing targeted drug delivery to antigen expressing cells. The humanized anti-ROR1 ADC, huXBR1-402-G5-PNU (Boehringer Ingelheim), has been developed to induce killing of ROR1 expressing tumour cells.
Objectives
This study aimed to explore the anti-proliferative effect of the anti-ROR1 ADC (huXBR1-402-G5-PNU) alone and in combination with commonly used gynaecological cancer therapies in HGSOC cell lines including platinum sensitive/resistant and homologous recombination (HR) proficient/deficient models.
Methods
HGSOC cell lines OVCAR4, Kuramochi, PEO1, PEO4 and four patient ascites derived primary cell lines (OC012, OC017, OC018 and OC023) were selected for this study. The cell surface expression level of ROR1was analysed with BD Quantibrite Beads using flow cytometry. Dose-effect analyses of carboplatin, paclitaxel, olaparib, huXBR1-402-G5-PNU alone and in combination were performed using the IncuCyte S3 over 120h. DNA damage following 5µg/ml huXBR1-402-G5-PNU treatment was investigated via Western blot. SynergyFinder 2.0 was applied to analyse and visualise the combination effect. The Bliss independence model was applied to estimate the summary synergy scores.
Results and Conclusions
Compared to the commercial cell lines, ascites derived primary cell lines showed higher ROR1 protein and surface antigen levels. Among all the cell lines analysed, PEO1 was the most sensitive to single carboplatin or olaparib treatment. The IC50 of the HGSOC cell lines to huXBR1-402-G5-PNU ranged from 0.5 to 5.9 µg/ml, with primary cell lines higher than commercial cell lines (4.12 ± 1.53 compared to 1.89 ± 0.99 µg/ml). Combining huXBR1-402-G5-PNU with adjuvant chemotherapies showed an overall additive effect (synergy score between -10 to 10) in the HGSOC cell lines. Synergistic interaction was observed in PEO4 and OC023 cells treated with huXBR1-402-G5-PNU and carboplatin (23.27 and 10.35 respectively) as well as PEO1 treated with huXBR1-402-G5-PNU and olaparib (18.84). DNA damage markers including cleaved PARP, cleaved Caspase 7 and Caspase 3 were increased following the huXBR1-402-G5-PNU treatment. This study showed the potential of a ROR1 targeting ADC (huXBR1-402-G5-PNU) in inducing HGSOC cell apoptosis in vitro, potentially synergising with carboplatin. Further studies are required to determine if this combination can be progressed into human clinical trials.