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Research Articles: Therapeutics, Targets, and Development

Differential effects of prostate cancer therapeutics on neuroendocrine transdifferentiation

Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina

Requests for reprints: Donald P. McDonnell, Department of Pharmacology and Cancer Biology, Duke University Medical Center, Box 3813, Durham, NC 27710. Phone: 919-684-6035; Fax: 919-681-7139. E-mail: donald.mcdonnell{at}duke.edu

Abstract

Androgen ablation therapy is widely used for the treatment of advanced prostate cancer. However, the effectiveness of this intervention strategy is generally short-lived as the disease ultimately progresses to a hormone-refractory state. In recent years, it has become clear that even in antiandrogen-resistant cancers the androgen receptor (AR) signaling axis is intact and is required for prostate cancer growth. Thus, there is a heightened interest in developing small molecules that function in part by down-regulating AR expression in tumors. Paradoxically, AR expression has been shown to be important in preventing the transdifferentiation of epithelial prostate cancer cells toward a neuroendocrine phenotype associated with tumor progression. Consequently, we have evaluated the relative effect of prostate cancer therapeutics that function in part by depleting AR levels on neuroendocrine differentiation in established cellular models of prostate cancer. These studies reveal that although histone deacetylase inhibitors can down-regulate AR expression they increase the expression of neuroendocrine markers and alter cellular morphology. Inhibition of AR signaling using classic AR antagonists or small interfering RNA–mediated AR ablation induces incomplete neuroendocrine differentiation. Importantly, the Hsp90 inhibitor geldanamycin effectively down-regulates AR expression while having no effect on neuroendocrine differentiation. Taken together, these data show that the phenotypic responses to pharmacologic agents used in the clinic to prevent the progression of prostate cancer are not equivalent, a finding of significant therapeutic importance. [Mol Cancer Ther 2008;7(3):659–69]

Grant support: NIH grants F32 DK072794 (D.E. Frigo) and R01 DK065251 (D.P. McDonnell).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Supplementary material for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).

² Daniel E. Frigo, Suzanne E. Wardell, and Noah M. Grom, unpublished data.

Received 7/17/07; revised 12/12/07; accepted 1/28/08.