While xenograft models based on established cancer cell lines representing different stages of cancer progression can be useful for identifying mechanisms underlying metastasis, they do not adequately mimic clinical disease. Efforts have therefore focused on use of patients�� prostate cancer tissues. However, the typical heterogeneity of such tissues, consisting of both non-metastatic and potentially metastatic subpopulations, makes it difficult to identify factors such as genes that underlie the development of metastasis. Moreover, it is difficult to obtain metastatic prostate cancer tissues from patients for experimental purposes, since they are not routinely or feasibly biopsied or resected from patients, and rapid autopsy programs are extremely expensive and difficult to manage. To overcome the above hurdles, we developed next generation patient-derived prostate cancer xenograft models, that more closely resemble the clinical situation, by using subrenal capsule grafting of patients�� cancer tissue into immuno-deficient mice. This methodology favors retention of the properties of the original cancers. Furthermore, it has been possible to establish transplantable, metastatic and non-metastatic prostate cancer sublines from heterogeneous xenografts. Use of metastatic and nonmetastatic xenografts has already been effective in the identification of prostate cancer metastasis-associated genes. Illumina��s massively parallel DNA sequencing by synthesis technology is a widely-adopted next-generation sequencing platform. It supports parallel sequencing using a proprietary reversible terminator-based method that enables detection of single bases as they are incorporated into growing DNA strands. A fluorescently-labeled terminator is imaged as each dNTP is added and then cleaved to allow incorporation of the next base. Since all four reversible terminator-bound dNTPs are present during each sequencing cycle, natural competition minimizes incorporation bias, leading to true base-by-base sequencing. In the present study, Illumina next generation sequencing technology was utilized to compare the miRNA profiles of a transplantable metastatic versus a non-metastatic prostate cancer xenograft line, both derived via subrenal capsule grafting from one patient��s primary cancer tissue. Differentially expressed known and novel miRNAs were found that may have specific roles in the metastasis of prostate cancer.NOD/SCID mice used for xenografting were bred and maintained at the British Columbia Cancer Research Centre Animal Facility. All experimental protocols were approved by the University of British Columbia Animal Care Committee. A prostate cancer biopsy specimen was obtained at the BC Cancer Agency with the patient��s written MLN4924 informed consent. PF-4217903 Ethical approval was provided by the University of British Columbia – British Columbia Cancer Agency Research Ethics Board. The establishment of transplantable prostate cancer tissue xenograft lines via subrenal capsule grafting has been described previously. In the present study, a recently prepared metastatic prostate cancer xenograft line, LTL-313H, and a nonmetastatic counterpart, LTL-313B, were used that had been derived from different loci of one patient��s prostate cancer biopsy sample. Both lines were PSA- and AR-positive as shown via immunohistochemistry. They were routinely maintained under renal capsules of male NOD/SCID mice supplemented with testosterone, as previously described. The LTL-313H xenografts showed invasion of the mouse host kidney and cancer cells were detected in the lungs of the hosts after 3 months of grafting. In contrast, the LTL-313B xenografts showed no obvious invasion of the mouse kidney and did not show any distant metastases. MicroRNAs have been implicated in the regulation of gene expression at the post-transcriptional level in almost every biological event, and there is an increasing body of evidence that altered expressions of specific miRNAs are involved in the development and progression of cancers.