Ferdinand Frauscher MD, Presenter: Nothing to Disclose

Iris Eder PhD, Abstract Co-Author: Nothing to Disclose

Andrea Klauser MD, Abstract Co-Author: Nothing to Disclose

Jonathan R Lindner, Abstract Co-Author: Nothing to Disclose

Alexander Klibanov PhD, Abstract Co-Author: Nothing to Disclose

Dieter Zur Nedden, Abstract Co-Author: Nothing to Disclose

Georg Bartsch MD, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

The androgen receptor (AR) is a key regulatory element involved both in androgen-dependent and androgen-independent growth of prostate cancer. Downregulation of the AR with specific antisense compounds was recently shown to significantly inhibit prostate tumor growth in vitro as well as in vivo. With regard to a clinical application, we now established an improved strategy to deliver antisense AR molecules into prostate cancer cells by means of ultrasound (US)-mediated destruction of microbubble contrast agents.

A small interference RNA (siRNA) molecule directed against the human AR (siRNA_AR) was designed, which was bound to positively charged perfluorocarbon gas-filled microbubbles. LNCaP prostate cancer cells were grown on Opticell culture chambers , which were immersed vertically in a water bath, equipped with a 4C1 US transducer (Acuson, MountainView, Cal.) mounted in parallel. siRNA-loaded microbubbles were added to the medium and triggered by US to release siRNAs into the cells. Transfection efficiency was evaluated by detecting AR expression with Western blot and induction of apoptosis with a M30 Apoptosense ELISA.

Maximum AR downregulation was achieved by loading 50 pMol siRNA_AR to 1x107 novel cationic microbubbles, which were effectively destroyed with a color Doppler US frequency of 1.75 MHz and a mechanical index of 1.9 over 9 minutes. This treatment resulted in a significant downregulation of the AR accompanied by 3-fold higher levels of apoptosis as compared with untreated controls. US treatment in combination with the siRNA alone had only a moderate effect on AR expression and induction of apoptosis (1.3-fold), respectively. A control siRNA molecule directed against the luciferase reporter gene (siRNA_luc) had no effects on the cells, emphasizing that induction of apoptosis in antisense AR-treated cells results from AR downregulation.

Our results show that siRNA molecules against the AR can be bound to cationic gas-filled microbubble contrast agents and directed into prostate cancer cells through US-mediated destruction. This noninvasive delivery system therefore represents a potential new tool to treat prostate cancer in the future.

Frauscher, F, Eder, I, Klauser, A, Lindner, J, Klibanov, A, Zur Nedden, D, Bartsch, G, et al, , Ultrasound Mediated Microbubble Destruction to Direct Antisense Molecules into Prostate Cancer Cells: An in Vitro Study.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4405843.html