P-426 In vitro and in vivo toxicity of carboplatin and paclitaxel regimen on BRCA-mutated ovarian tissue fragments
Authors: Dias Nunes J , Ntemou E , Van den Steen G , Diaz Vidal P , Devos M , Demeestere I 
Published: June 2023

Abstract

Study question
Does carboplatin and paclitaxel regimen have a toxic cumulative impact on the ovarian reserve of young breast cancer patients with germline Breast Cancer (BRCA) mutation?

Summary answer
Based on follicle classification and survival through apoptosis and DNA repair mechanism recruitment analyses, gonadotoxic but no cumulative effect was observed in BRCA-mutated ovarian tissue.

What is known already
Ovarian function recovery and fertility issues remain major concerns for young patients diagnosed with cancer. Breast cancer is the first cancer diagnosed among women under 40 years and around 10% of them are BRCA germline mutation carriers. Beside their predisposition to breast and ovarian cancers, BRCA carriers might be more sensitive to chemotherapy-induced gonadotoxicity due to the role of BRCA in DNA repair mechanism. Current therapies for BRCA-mutated breast cancer patients often include carboplatin and paclitaxel, drugs that are both considered as moderately gonadotoxic. However, the effect of combined therapy in BRCA-mutated ovarian tissue is unknown.

Study design, size, duration
Ovarian tissue cryopreserved for fertility preservation before chemotherapy and donated for research by breast cancer patients with or without BRCA1/2 mutation (&lt; 35 years at diagnosis) were used in this study. Two models were investigated: 3 days in vitro culture with carboplatin (10 µg/mL) and/or paclitaxel (1 µM) and ovarian tissue xenograft into mice followed by 3 weeks injections of carboplatin (50mg/kg/week) and paclitaxel (10mg/kg every 3 days). Control conditions were performed for each model.

Participants/materials, setting, methods
Ovarian tissue from 3 BRCA-mutated and 3 non-mutated patients were thawed and exposed in vitro and in vivo to chemotherapy. Follicle density (number of follicles/mm²) as well as ratios of quiescent/activated and healthy/atretic follicles were evaluated following haematoxylin-eosin staining. Apoptosis and DNA repair mechanisms were analysed using TUNEL/GDF9 co-staining and phosphorylated H2A histone family member X (γH2AX)/ZP-3 co-staining, respectively. Genes expression level will be evaluated on isolated follicles to assess the activation process.

Main results and the role of chance
First, the impact of in vitro culture and in vivo xenotransplantation was evaluated by follicle counting and classification. A decrease of follicular density (5 to 95% irrespective of patient, model, nor condition) and an increase of activated and atretic follicles was observed after both in vitro and in vivo experiments in all conditions. However, a slight increase of quiescent follicle pool was observed in the in vitro control condition, with no difference between mutated and non-mutated fragments. Then, immunofluorescence staining was performed to evaluate follicle damage. For quantification, 30 to 150 follicles per patient were counted within each condition and classified as positive if at least one cell was stained. Apoptosis was assessed with TUNEL/GDF9 co-staining. In both models, the ratio of positive follicles was higher in fragments treated with chemotherapy (40-60%) compared to control conditions (15-20%). Recruitment of DNA repair complex was analysed using γH2AX/ZP3 co-staining. In both models, an increase in positive follicles ratio was observed in treated fragments (15-40%) compared to control conditions (5-10%). Interestingly, the positive follicles ratio was lower in BRCA-mutated (15-18%) than in non-mutated fragments (25-40%) after 3-days in vitro culture, irrespective of the treatment used.

Limitations, reasons for caution
Reasons of caution include the high inter-variations between patients as well as intra-variations in one patient regarding follicular density within ovarian tissue. Moreover, BRCA-mutated patients included (27.67 ± 2.08) are younger than control ones (33.67 ± 1.53). Ongoing experiments with additional patients should support the results already obtained.

Wider implications of the findings
Carboplatin and paclitaxel combined exposure in vitro or in vivo does not seem to have a cumulative deleterious impact on ovarian reserve. Ovarian tissue with BRCA-mutation did not appear to be more sensitive to chemotherapy exposure. Further investigations focusing on DNA repair mechanisms will be performed in both models.

Trial registration number
Not applicable