Abstract LB-44: Effect of modulation of I kappa B kinases (IKKs) in prostate cancer cell growth and apoptosis
Authors: Sophia Hatziieremia , Mackenzie Lewis , Seywright M , Mackay Simon , Mackay Simon , Paul Andy , Edwards Joanne 
Published: February 2011

Prostate cancer is the most common cancer in men. Although a wide variety of treatments such as surgery, radiation and hormone therapy exist, patients diagnosed with locally advanced or metastatic disease eventually progress to a castrate resistant state [1]. Understanding the mechanism by which castrate resistant prostate cancer (CRPC) develops remains a major issue. Elevated nuclear factor kappa B (NFkB) activity has been observed in many tumors including prostate cancer [2]. In this study, we employed patient samples in combination with in vitro methods to examine the role of NFkB and IKKs in prostate cancer growth and apoptosis.

Tissue microarray technology was employed to assess NFkB p65 protein expression in 255 prostate cancer specimens obtained at diagnosis. Immunohistochemistry was performed using an antibody to p65 and expression assessed using the weighted histoscore method. IKKα and/or IKKβ were down regulated in PC3 cells by electroporation with specific siRNA. The effects of IKKα and/or IKKβ silencing on cell growth, cell cycle markers and apoptosis were examined.

Full clinical follow-up was available for the patient cohort, mean follow-up was 8.05 years, 129 patients died of their disease and 56 patients had metastases at diagnosis. Gleason sum (p=0.001), presence of metastasis (p=0.001), stage (p=0.016) and androgen receptor status (p=0.002) significantly correlated with decreased disease specific survival. NFkB p65 expression was observed in both the tumor cell cytoplasm and nucleus (location when activated). Cytoplasmic p65 expression was not associated with any known clinical parameters, however high (supra medium) nuclear p65 expression was associated with decrease in disease specific survival (p=0.005) and this was independent when combined with Gleason sum, presence of metastasis stage and androgen receptor status on multivariate analysis (p=0.004, hazard ratio 4.5 (1.6-12.8)). We further designed a series of experiments to assess the effect of inhibiting NFkB activation on prostate cancer cells via knocking down IKKα and/or IKKβ expression. When IKKα and IKKβ alone or combined were silenced, p65 expression in PC3 cells was observed only in the cell cytoplasm and not in the nucleus, suggesting NFkB activation had been inhibited. However, no significant effect on cell proliferation (as measured by WST-1) or apoptosis (Annexin V/ ViaProbe) was observed. Furthermore, no significant change was observed in protein levels of cyclin D1, A, B1 or E as measured by western blotting, however an inhibition of Wee 1, a known G2 checkpoint regulator, was observed following IKKβ silencing revealing a novel cell cycle target for IKKs.

In conclusion, NFkB p65 nuclear expression is a negative prognostic marker for prostate cancer at diagnosis and modification of IKKα and IKKβ alone or combined may offer a potential therapeutic target by modifying the functions of cell cycle regulators.

References

1. Chen et al., 2009 Lancet Oncol. 10:981-91.

2. Ross et al., 2004 Clin Cancer Res. 10:2466-72.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-44.