Standardised Uptake Values as Determined on PSMA PET/CT is associated with Oncological Outcomes in Prostate Cancer Patients

Objectives

To investigate the association between intraprostatic, intratumoral maximum standardised uptake values (SUV_max) on prostate‐specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) in patients with prostate cancer (PCa) prior to robot‐assisted radical prostatectomy (RARP) and pathology outcomes, including pathological International Society of Urological Pathology score (pISUP) and lymph node (LN) status (pN0/pN1).

Patients and Methods

A bi‐centric, secondary analysis of two previous, prospective cohort studies was performed in 318 patients with biopsy confirmed PCa and who were scheduled for RARP. Before surgery, patients received a PSMA PET/CT with either ⁶⁸Ga‐PSMA‐11 (59% of the patients) or ¹⁸F‐PSMA (DCFPyL; 41%) as radiotracer. PET/CT images were analysed both visually and semi‐quantitatively by measuring the SUV_max of the most intense suspect lesion in the prostate. The association between the SUV_max of the primary tumour and pre‐ and postoperative variables was analysed.

Results

The SUV_max was associated with clinical and biopsy preoperative variables, as well as with pISUP score and pathological tumour stage. Patients with a pISUP of ≤2 showed significantly lower SUV_max compared to patients with a pISUP of >2 for both tracers (SUV_max¹⁸F‐PSMA: median 5.1 vs 9.6, P = 0.002; SUV_max⁶⁸Ga‐PSMA‐11: 6.6 vs 8.6, P = 0.003). Moreover, patients with pN1 had significantly higher median SUV_max than those with pN0/pNx for both tracers (SUV_max¹⁸F‐PSMA: 7.9 vs 12.3, P = 0.04; SUV_max⁶⁸Ga‐PSMA‐11: 7.6 vs 12.0, P < 0.001). On multivariable logistic regression analysis, the intraprostatic SUV_max was an independent predictor of pN1 for both ⁶⁸Ga‐PSMA‐11 (per doubling: odds ratio [OR] 1.96, 95% confidence interval [CI] 1.27–3.01)) and ¹⁸F‐PSMA (per doubling: OR 1.79, 95% CI 1.06–3.03).

Conclusion

Intraprostatic, intratumoral PSMA intensity on PET/CT, as semi‐quantitatively expressed by SUV_max, may be a valuable innovative biomarker in patients with localised PCa, as it is highly associated with known conventional prognostic factors, such as pISUP and LN status.

Abstract 1085: Prostate cancer secreted microRNAs influence early steps in bone metastasis via osteoclast precursors

BACKGROUND: Bone metastasis is a complex process involving reciprocal interplay between cancer and bone cells. Metastatic prostate cancer (PCA) cells secrete extracellular vesicles (EVs), that contain microRNAs (miRNAs), and these can be found in blood. We hypothesize that precursor osteoclasts scavenge PCA EVs, leading to a manipulation of their behavior thereby driving metastasis.

METHODS: To test how EV-miRNAs affect metastasis, we stably overexpressed two metastasis-related miRNAs in PCA cells. Bone metastases were induced by inoculating miRNA overexpressing PCA cells into nude mice via intracardiac route with or without the presence of subcutaneous tumors. Tumor progression was monitored by F-luciferase signal (IVIS) while bones were analyzed by microCT ex vivo. miRNAs expression was analyzed by qRT-PCR on precursor osteoclasts isolated from mice blood. Osteoclast differentiation assays were performed using human peripheral mononucleated blood cells on bone chips together with RANKL and M-CSF to drive differentiation.

RESULTS: In vivo, intracardiac injection of PC3 cells that overexpress selected miRNAs accelerated the formation of bone metastases (0-85%) compared to control PC3 cells (43%). To determine whether EVs secreted by PCA cells affect osteoclasts, human monocytes were allowed to differentiate to osteoclasts while exposing them to PCA EVs. EVs secreted by control PCA cell lines increased osteoclast differentiation by 22.5% (p&lt;0.01), compared to EVs secreted by RWPE1 noncancerous prostate cells. Exposure to EVs secreted by the miRNA overexpressing PCA cells further enhanced osteoclast formation by an additional 10% (p&lt;0.05). To test whether pro-metastatic miRNAs enhance metastases when mouse osteoclast precursors are pre-stimulated (via EVs or soluble factors), subcutaneous tumours of pro-metastatic cells were grown for 2 weeks. In circulating osteoclast precursors of mice that were pre-stimulated with PCA factors that were secreted by subcutaneous tumors (2 weeks), the miRNA levels were increased by 1.5 - 4 fold (p&lt;0.05), demonstrating that these cells scavenge the secreted tumor miRNAs. Subsequently, mice received an intracardiac injection with matching cells to induce metastases. Trabecular bone volume of &gt;15% was used as indicator for metastasis induced bone loss. Mice that grew both a subcutaneous tumor and also received an intracardiac injection to drive metastasis formation led to an ~30% increased number of mice with &gt;15% bone loss (p&lt;0.01). This indicates that osteoclasts may be manipulated by the cancer cell-secreted factors to form a pro-metastatic niche.

CONCLUSION: PCA miRNAs secreted via EVs stimulate osteoclast formation, potentially increasing the formation of overt metastases. Further investigation is needed to unravel novel pathways that can be targeted to prevent bone metastasis.

Citation Format: L. Ayse Erozenci, Ning Wang, Albert A. Geldof, Jorn Mulder, Connie R. Jimenez, R. Jeroen van Moorselaar, Allison Gartland, Teun J. de Vries, Irene V. Bijnsdorp. Prostate cancer secreted microRNAs influence early steps in bone metastasis via osteoclast precursors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1085.

Feasibility of urinary extracellular vesicle proteome profiling using a robust and simple, clinically applicable isolation method

Extracellular vesicles (EVs) secreted by prostate cancer (PCa) cells contain specific biomarkers and can be isolated from urine. Collection of urine is not invasive, and therefore urinary EVs represent a liquid biopsy for diagnostic and prognostic testing for PCa. In this study, we optimised urinary EV isolation using a method based on heat shock proteins and compared it to gold-standard ultracentrifugation. The urinary EV isolation protocol using the Vn96-peptide is easier, time convenient (≈1.5 h) and no special equipment is needed, in contrast to ultracentrifugation protocol (>3.5 h), making this protocol clinically feasible. We compared the isolated vesicles of both ultracentrifugation and Vn96-peptide by proteome profiling using mass spectrometry-based proteomics (n = 4 per method). We reached a depth of >3000 proteins, with 2400 proteins that were commonly detected in urinary EVs from different donors. We show a large overlap (>85%) between proteins identified in EVs isolated by ultracentrifugation and Vn96-peptide. Addition of the detergent NP40 to Vn96-peptide EV isolations reduced levels of background proteins and highly increased the levels of the EV-markers TSG101 and PDCD6IP, indicative of an increased EV yield. Thus, the Vn96-peptide-based EV isolation procedure is clinically feasibly and allows large-scale protein profiling of urinary EV biomarkers.

Protein Complexes in Urine Interfere with Extracellular Vesicle Biomarker Studies

Urine exosomes (extracellular vesicles; EVs) contain (micro)RNA (miRNA) and protein biomarkers that are useful for the non-invasive diagnosis of various urological diseases. However, the urinary Tamm-Horsfall protein (THP) complex, which forms at reduced temperatures, may affect EV isolation and may also lead to contamination by other molecules including microRNAs (miRNAs). Therefore, we compared the levels of three miRNAs within the purified EV fraction and THP- protein-network. Urine was collected from healthy donors and EVs were isolated by ultracentrifugation (UC), two commercial kits or sepharose size-exclusion chromatography (SEC). SEC enables the separation of EVs from protein-complexes in urine. After UC, the isolation of EV-miRNA was compared with two commercial kits. The EV isolation efficiency was evaluated by measuring the EV protein markers, Alix and TSG101, CD63 by Western blotting, or miR-375, miR-204 and miR-21 by RT-qPCR. By using commercial kits, EV isolation resulted in either low yields or dissimilar miRNA levels. Via SEC, the EVs were separated from the protein-complex fraction. Importantly, a different ratio was observed between the three miRNAs in the protein fraction compared to the EV fraction. Thus, protein-complexes within urine may influence EV-biomarker studies. Therefore, the characterization of the isolated EV fraction is important to obtain reproducible results.