The Role of the Androgen Receptor in Prostate Cancer-induced Platelet Aggregation and Invasion

• Author / Creator

  Jan K Rudzinski

• Background: Prostate cancer (PCa) is the most common visceral malignancy and third leading cause of cancer death among men in Canada. The 2018 Canadian Cancer Society estimates suggest that 21,300 men were diagnosed and 4,100 patients died of this disease. Metastatic prostate cancer (mPCa) is incurable. The 5-year overall survival of hormone sensitive androgen receptor expressing phenotype (AR+) is 30%. Upon disease progression, mPCa becomes refractory to AR signalling, assuming the AR independent subtype (AR-). In this hormone refractory phase, mPCa has a 3-year overall survival rate of 30%. Hence, there is a strong need to better understand and identify novel targets to halt progression to metastasis. Human platelets have been shown to contribute to epithelial cancer metastasis by the process of tumor cell induced platelet aggregation (TCIPA). In the circulation, TCIPA aids in the ability of the tumor cells to evade the immune system, arrest, extravasate, then grow and disseminate in the secondary sites. Given more aggressive nature of hormone insensitive tumors, my hypothesis is that PCa cell lines lacking AR expression will exhibit higher platelet aggregation potency compared to cell lines with intact AR signaling.

  Objective: To characterize the role of AR in PCa induced TCIPA and platelet-induced invasion.

  Methods: TCIPA experiments were performed with benign prostate cells (RWPE, AR+) and PCa cell lines: LNCaP (AR+), DU145 (AR-), and PC3 (AR-). A subset of LNCaP cells were exposed to the androgen receptor inhibitor bicalutamide for 24 hours (LNCaP+bic). Prostacyclin-washed platelets isolated from healthy human donors were used for TCIPA experiments. TCIPA (0.25x106 – 2.0x106 cells/mL) was investigated using light-transmittance aggregometry (Chrono-log Dual Channel Lumi-Aggregator). Western blot was performed to measure PCa prothrombin/thrombin in cellular lysates. Boyden chamber invasion assay and gelatin zymography were performed to assess the effects of platelets on PCa invasion and matrix metalloproteinase (MMP) expression, respectively. One-way, two-way ANOVA, and two tailed t-test were used to evaluate differences between groups.

  Results: Both AR+ cell lines, benign RWPE and LNCaPs, failed to induce platelet aggregation. However, AR- cell lines DU145 and PC3, and AR-inhibited LNCaP (LNCaP+bic) all induced platelet aggregation (64.06+0.88% vs. 26.34+11.78% vs. 43.73+8.62%, respectively). The direct thrombin inhibitor, dabigatran (0.8M), completely abolished DU145, PC3 and LNCaP+bic induced TCIPA. Western blot analysis of PCa lysates demonstrated approximately three-fold greater expression of prothrombin/thrombin in AR- DU145, PC3, and AR-inhibited LNCaP (LNCaP+bic) compared to AR+ RWPE and LNCaPs, p<0.05. Platelets enhanced DU145 and PC3, and AR-inhibited LNCaP (LNCaP+bic) invasion and MMP-2 and -9 expression, but not that of LNCaP.

  Conclusions: Inhibition or loss of AR signaling within PCa results in increased thrombogenicity due to upregulation of prothrombin/thrombin expression. Reciprocally, platelets enhance invasion of AR-negative PCa cells via increased MMP expression.

• Subjects / Keywords

  • prostate cancer
  • platelets
  • tumour cell induced platelet aggregation

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-f257-9849

• License

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