Enhancing the safety of ovarian cortex autotransplantation: cancer cells are purged completely from human ovarian tissue fragments by pharmacological inhibition of YAP/TAZ oncoproteins.

STUDY QUESTION: Is it possible to eliminate metastasized cancer cells from ovarian cortex fragments prior to autotransplantation without compromising the ovarian tissue or follicles?

SUMMARY ANSWER: Ex vivo pharmacological inhibition of YAP/TAZ by Verteporfin enabled us to efficiently eradicate experimentally induced small tumours, derived from leukaemia and rhabdomyosarcoma, from human ovarian tissue fragments.

WHAT IS KNOWN ALREADY: Autotransplantation of ovarian tissue fragments that contain metastasized tumour cells may reintroduce the malignancy to the recipient. In order to enhance safety for the patient there is a strong need for protocols that effectively purges the ovarian tissue from malignant cells ex vivo prior to transplantation, without compromising ovarian tissue integrity.

STUDY DESIGN, SIZE, DURATION: Tumour foci were experimentally induced in human ovarian cortex tissue fragments derived from at least three patients by micro-injection of cancer cell lines. Next, the tissue fragments were cultured to allow formation of metastasis-like structures followed by a 24 h ex vivo treatment with the YAP/TAZ inhibitor Verteporfin to eradicate the cancer cells. A control treatment was included in all experiments. The purged ovarian cortex fragments were cultured for an additional 6 days to allow any possibly surviving cancer cells to establish new metastatic foci.

PARTICIPANTS/MATERIALS, SETTING, METHODS: Human ovarian tissue was obtained after female-to-male sex reassignment surgery. Human rhabdomyosarcoma, leukeamia, breast cancer and Ewing's sarcoma cell lines were utilized for the induction of tumour foci. Tumour specific (immuno)histochemistry and RT-PCR were used for the detection of residual cancer cells after ex vivo treatment. Ovarian tissue and follicle integrity after exposure to Verteporfin was evaluated by histology, a follicular viability assay and a glucose uptake assay.

MAIN RESULTS AND THE ROLE OF CHANCE: Metastasized rhabdomyosarcoma and leukaemia cells could be effectively purged from ovarian cortex tissue by a 24 h ex vivo treatment with Verteporfin, while breast cancer and Ewing's sarcoma did not respond to this treatment. Ovarian tissue integrity was not affected by purging, as no statistically significant difference (P > 0.05) was observed in the percentage of morphologically normal follicles, percentage of follicles with apoptotic cells, follicular viability or glucose uptake between the control treated ovarian cortex and Verteporfin treated ovarian cortex.

LIMITATIONS, REASONS FOR CAUTION: Our tumour model is based on growth of human cancer cell lines. It is unclear whether these cells reflect the behaviour of malignant cells that have metastasized to the ovary during natural disease progression. Furthermore, the functionality of the ovarian tissue after ex vivo treatment requires further investigation in vivo.

WIDER IMPLICATIONS OF THE FINDINGS: The results indicate that ex-vivo tumour cell purging of human ovarian cortex fragments intended for fertility preservation purposes is feasible by short-term pharmacological treatment. Effective purging of the ovarian cortex tissue enhances safety of ovarian cortex autotransplantation for the patient. This increases the likelihood that this form of fertility restoration may become an option for patients with malignancies for which ovarian cortex transplantation is currently considered unsafe.

STUDY FUNDING/COMPETING INTEREST(S): Unconditional funding was received from Merck B.V. The Netherlands (Number 2016-FERT-1) and the foundation 'Radboud Oncologie Fonds' (Number KUN 00007682). The authors have no conflicts of interest.

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