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Germline mutations within the MEIS-interaction domain of HOXB13 have implicated a critical function for MEIS-HOX interactions in prostate cancer etiology and progression. The functional and predictive role of changes in MEIS expression within prostate tumor progression, however, remain largely unexplored. Here we utilize RNA expression datasets, annotated tissue microarrays, and cell-based functional assays to investigate the role of MEIS1 and MEIS2 in prostate cancer and metastatic progression. These analyses demonstrate a stepwise decrease in the expression of both MEIS1 and MEIS2 from benign epithelia, to primary tumor, to metastatic tissues. Positive expression of MEIS proteins in primary tumors, however, is associated with a lower hazard of clinical metastasis (HR = 0.28) after multivariable analysis. Pathway and gene set enrichment analyses identified MEIS-associated networks involved in cMYC signaling, cellular proliferation, motility, and local tumor environment. Depletion of MEIS1 and MEIS2 resulted in increased tumor growth over time , and decreased MEIS expression in both patient-derived tumors and MEIS-depleted cell lines was associated with increased expression of the protumorigenic genes cMYC and CD142, and decreased expression of AXIN2, FN1, ROCK1, SERPINE2, SNAI2, and TGFβ2. These data implicate a functional role for MEIS proteins in regulating cancer progression, and support a hypothesis whereby tumor expression of MEIS1 and MEIS2 expression confers a more indolent prostate cancer phenotype, with a decreased propensity for metastatic progression. .

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423 Background: Standard therapy for high-risk non-muscle invasive bladder cancer (NMIBC) is intravesical BCG. Despite its established efficacy, up to 50% of patients may recur. The development of predictive biomarkers for BCG immunotherapy would enhance treatment algorithms and potentially uncover mechanisms of resistance. Recent data have characterized the presence of a commensal urine microbiome, but its role in BCG-treated NMIBC patients remains unexplored. We assessed the composition of the urine microbiome in NMIBC patients and evaluated associations with response to therapy. Methods: Patients with a newly diagnosed bladder tumor were enrolled prior to TURBT on an institutional review board-approved study at a single institution. Adjuvant BCG instillation was administrated to high-risk patients according to the surgical histology. Urine samples for microbiome assessment were collected by catheterization to eliminate urethral contamination before the TURBT and up to 8 additional timepoints. 16S sequencing and analysis was performed on baseline specimens prior to BCG. Results: Among 31 patients enrolled, 10 (32%) recurred and 21 (68%) had no recurrence with a median follow up of 6 months. Median age was 69 years (range 46-87), and 9 (29%) patients were female and 22 patients (71%) were male. The most abundant phyla observed were Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria, and Tenericutes. Together these accounted for > 99% of the phyla detected in the cohort. Global analysis of distances by operational taxonomic units (OTUs) indicated a significant difference between patients with and without recurrence (Bonferroni-corrected P = 0.017). The abundance of Proteobacteria was higher in patients with recurrence (P = 0.035), with stronger differences observed for specific classes such as Gammaproteobacteria (P = 0.0025). Firmicutes such as Lactobacillales were more abundant in patients without recurrence (P = 0.049). Conclusions: In this study we detected variation in the composition of the urine microbiome in NMIBC patients, which may predict response to BCG immunotherapy. Further studies to confirm these results are ongoing.