Using fresh prostate tissue to determine tumour responses to therapeutic agents: development of an explant model of prostate cancer

Using fresh prostate tissue to determine tumour responses to therapeutic agents: Development of an explant culture model of prostate cancer

Prostate tumour explants provide predictive drug response data in the context of an intact tumour microenvironment. An adjunct to traditional cell and animal models, explants expand the repertoire of ex vivo prostate cancer culture systems available for drug development. These individualised models offer opportunities for patient stratification and precision medicine. Varying methods of organotypic culture have been described, each attempting to better retain patient-specific morphology and increase longevity. However, there is currently no standardised successful approach. This study aimed to characterise and further develop explant establishment techniques, prior to evaluation of tumour responses to anti-androgens in an optimised culture system. Required access to fresh patient tissue restricts many research groups from carrying out ex vivo assays. As such, xenograft-derived explants were also established and utilised to examine the effects of histone deacetylase (HDAC) inhibitor Entinostat on human PCa tumour cells.

Surgical biopsies were obtained from patients undergoing radical prostatectomy and channel trans-urethral resection of the prostate. Tumours were dissected into 1-2mm3 patient-derived explants (PDEs) or precision-cut to generate 300μm-thick tissue slice cultures (TSCs). The effects of differing culture conditions and androgen stimulation on explants were assessed via automated immunostaining. Digital tissue segmentation and scoring enabled quantification of proliferation, apoptosis and AR protein levels. Tumour responses to anti-androgen enzalutamide were examined. In addition, xenograft-derived explants (XDEs) and TSCs were established from C4-2B and PC3 cell lines implanted in mouse models to compare 2D and 3D ex vivo tumour cell responses to anti-androgens alone and in combination with HDAC inhibition.

Basal cell hyperplasia and luminal cell loss were common in sponge-cultured tumour fragments. Hypoxia increased in 1-2mm3 PDEs and proliferation was limited to benign cells. Insert-cultured 300μm TSCs successfully preserved patient-specific tumour morphology. Exogenous androgen treatment enabled explants to retain AR signalling for six days, whilst continuous movement of TSCs increased tumour cell proliferation. Enzalutamide increased apoptosis and decreased proliferation in individual TSCs. Immunofluorescent imaging revealed HDAC inhibitor Entinostat reduced nuclear AR protein levels and increased acetylation of histone proteins in human PCa cells.

Whilst short-lived, tumour explants can be rapidly established from both patient and mouse tissue and utilised as a clinically relevant 3D drug efficacy assay. Precision-cut tumour slices are the most reproducible culture method and best recapitulate the tumour of origin.