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AGENCY USE ONLY (Leave blank)2. REPORT DATE
August 2002
TITLE AND SUBTITLE
Radiosensitization of Human Mammary Carcinoma Cells by Specific Inhibition of Signal Transduction Cascades
REPORT TYPE AND DATES COVEREDAnnual Summary (1 Aug 01 -
AUTHOR(S)Paul Dent, Ph.D.
PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Virginia Commonwealth University Richmond, Virginia 23298-0568 E-Mail: pdent@hsc.vcu.edu We investigated the impact of combined exposure to the check-point abrogator (UCN-01) in conjunction with MEK1/2 inhibitors upon survival of mammary carcinoma cells. Treatment of cells with UCN-01 resulted in prolonged activation of the MAPK pathway. Inhibition of MEK1/2 caused modest reductions in basal MAPK activity and suppressed UCN-01-stimulated MAPK activity below that of MEK1/2 inhibitor alone. Significantly, combined, but not individual, exposure of cells to UCN-01 and MEK1/2 inhibitors enhanced BAX association with mitochondria and triggered release of cytochrome c into the cytosol, accompanied by activation of effector pro-caspases, resulting in a synergistic potentiation of apoptosis within 18-24h. Radiation exposure of drug treated cells did not further enhance apoptosis. Treatment of cells with both caspase 9 and caspase 8 inhibitors was required to completely inhibit apoptosis in carcinoma cells. Over-expression of Bcl-x L blocked cytochrome c release and cell killing induced by the drug combination.
SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES)UColony forming assays demonstrated that cells exposed to both agents exhibited a substantial reduction in clonogenic survival compared to either drug alone; moreover, radiation further reduced clonogenic survival despite failing to promote additional apoptosis. [9]. It is thought that UCN-01 at physiologic concentrations promotes cell death via Cdk dephosphorylation rather than by inhibition of PKC enzymes [10].
SUBJECT TERMSThe ability of the "classical" mitogen activated protein kinase (MAPK) pathway to regulate proliferation versus differentiation and survival appears to depend upon the amplitude and duration of MAPK activation. A short activation of the MAPK cascade by growth factors has been correlated with enhanced progression through the Gl-S transition [11]. In contrast, prolonged elevation of MAPK activity has been demonstrated to inhibit DNA synthesis through s...