Evaluation of small molecule drug uptake in patient-derived prostate cancer explants by mass spectrometry

Patient-derived explant (PDE) culture of solid tumors is increasingly being applied to preclinical evaluation of novel therapeutics and for biomarker discovery. In this technique, treatments are added to culture medium and penetrate the tissue via a gelatin sponge scaffold. However, the penetration profile and final concentrations of small molecule drugs achieved have not been determined to date. Here, we determined the extent of absorption of the clinical androgen receptor antagonist, enzalutamide, into prostate PDEs, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and matrix-assisted laser/desorption ionisation (MALDI) mass spectrometry imaging (MSI). In a cohort of 11 PDE tissues from eight individual patients, LC-MS/MS quantification of PDE homogenates confirmed enzalutamide (10 µM) uptake by all PDEs, which reached maximal average tissue concentration of 0.24-0.50 ng/µg protein after 48 h culture. Time dependent uptake of enzalutamide (50 µM) in PDEs was visualized using MALDI MSI over 24-48 h, with complete penetration throughout tissues evident by 6 h of culture. Drug signal intensity was not homogeneous throughout the tissues but had areas of markedly high signal that corresponded to drug target (androgen receptor)-rich epithelial regions of tissue. In conclusion, application of MS-based drug quantification and visualization in PDEs, and potentially other 3-dimensional model systems, can provide a more robust basis for experimental study design and interpretation of pharmacodynamic data.Shadrack M. Mutuku, Paul J. Trim, Bala K. Prabhala, Swati Irani, Kayla L. Bremert, Jessica M. Logan, Douglas A. Brooks, Jürgen Stahl, Margaret M. Centenera, Marten F. Snel, Lisa M. Butle

Patient-derived prostate cancer explants: a clinically relevant model to assess siRNA-based nanomedicines

Over the last thirty years, research in nanomedicine has widely been focused on applications in cancer therapeutics. However, despite the plethora of reported nanoscale drug delivery systems that can successfully eradicate solid tumor xenografts in vivo, many of these formulations have not yet achieved clinical translation. This issue particularly pertains to the delivery of small interfering RNA (siRNA), a highly attractive tool for selective gene targeting. One of the likely reasons behind the lack of translation is that current in vivo models fail to recapitulate critical elements of clinical solid tumors that may influence drug response, such as cellular heterogeneity in the tumor microenvironment. This study incorporates a more clinically relevant model for assessing siRNA delivery systems; ex vivo culture of prostate cancer harvested from patients who have undergone radical prostatectomy, denoted patient-derived explants (PDE). The model retains native human tissue architecture, microenvironment, and cell signaling pathways. Porous silicon nanoparticles (pSiNPs) behavior in this model is investigated and compared with commonly used 3D cancer cell spheroids for their efficacy in the delivery of siRNA directed against the androgen receptor (AR), a key driver of prostate cancer.Terence Tieu, Swati Irani, Kayla L. Bremert, Natalie K. Ryan, Marcin Wojnilowicz, Madison Helm, Helmut Thissen, Nicolas H. Voelcker, Lisa M. Butler, and Anna Cifuentes-Riu