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Research Articles: Therapeutics, Targets, and Development

Transient exposure of carcinoma cells to RAS/MEK inhibitors and UCN-01 causes cell death in vitro and in vivo

Departments of ¹ Biochemistry, ² Medicine, ³ Radiation Oncology, and ⁴ Anatomy and Neurobiology, Virginia Commonwealth University, Richmond, Virginia

Requests for reprints: Paul Dent, Department of Biochemistry, Virginia Commonwealth University, Box 980035, Richmond VA 23298-0035. Phone: 804-628-0861; Fax: 804-828-6042. E-mail: pdent{at}hsc.vcu.edu

Abstract

The present studies were initiated to determine in greater molecular detail how MEK1/2 inhibitors [PD184352 and AZD6244 (ARRY-142886)] interact with UCN-01 (7-hydroxystaurosporine) to kill mammary carcinoma cells in vitro and radiosensitize mammary tumors in vitro and in vivo and whether farnesyl transferase inhibitors interact with UCN-01 to kill mammary carcinoma cells in vitro and in vivo. Expression of constitutively activated MEK1 EE or molecular suppression of JNK and p38 pathway signaling blocked MEK1/2 inhibitor and UCN-01 lethality, effects dependent on the expression of BAX, BAK, and, to a lesser extent, BIM and BID. In vitro colony formation studies showed that UCN-01 interacted synergistically with the MEK1/2 inhibitors PD184352 or AZD6244 and the farnesyl transferase inhibitors FTI277 and R115,777 to kill human mammary carcinoma cells. Athymic mice carrying 100 mm³ MDA-MB-231 cell tumors were subjected to a 2-day exposure of either vehicle, R115,777 (100 mg/kg), the MEK1/2 inhibitor PD184352 (25 mg/kg), UCN-01 (0.2 mg/kg), or either of the drugs in combination with UCN-01. Transient exposure of tumors to R115,777, PD184352, or UCN-01 did not significantly alter tumor growth rate or the mean tumor volume in vivo 15 to 30 days after drug administration. In contrast, combined treatment with R115,777 and UCN-01 or with PD184352 and UCN-01 significantly reduced tumor growth. Tumor cells isolated after combined drug exposure exhibited a significantly greater reduction in plating efficiency using ex vivo colony formation assays than tumor cells that were exposed to either drug individually. Irradiation of mammary tumors after drug treatment, but not before or during treatment, significantly enhanced the lethal effects of UCN-01 and MEK1/2 inhibitor treatment. These findings argue that UCN-01 and multiple inhibitors of the RAS-MEK pathway have the potential to suppress mammary tumor growth, and to interact with radiation, in vitro and in vivo. [Mol Cancer Ther 2008;7(3):616–29]

Grant support: USPHS grants R01-DK52825 and Department of Defense Award DAMD17-03-1-0262 (P. Dent); USPHS grants R01-CA100866, CA63753-06, and CA93738 (S. Grant); and The Jim Valvano "Jimmy V" Foundation. P. Dent is the holder of the Universal Inc. Professorship in Signal Transduction Research and S. Grant is the holder of the Olsen Distinguished Professorship.

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.

Note: H. Hamed, W. Hawkins, and C. Mitchell contributed equally to this work.

⁵ Supplementary material for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).

Received 12/ 6/07; revised 1/12/08; accepted 1/18/08.