MEK1/2 inhibition promotes Taxotere® lethality in mammary tumors in vivo

Abstract

KEY WORDSinhibitor, kinase, CI-1040, PD184352, Taxotere, Docetaxel, tumor, in vivo Taxol (paclitaxel) and Taxotere (docetaxel) are considered as two of the most important anti-cancer chemotherapy drugs. The cytotoxic action of these drugs has been linked to their ability to inhibit microtubule depolymerization, causing growth arrest and subsequent cell death. Studies by a number of laboratories have also linked suppression of MEK1/2 signaling to enhanced Taxol toxicity in vitro and in vivo. The present study examined the interactions of the semi-synthetic taxane Taxotere with MEK1/2 inhibitors in epithelial tumor cells. In vitro colony formation studies demonstrated that Taxotere and the MEK1/2 inhibitor PD184352 interacted in a sequence dependent fashion to synergistically kill human mammary carcinoma cells (MDA-MB-231, MCF7) as well as in other tumor cell types; e.g. prostate and renal cell carcinoma. Athymic mice were implanted in the rear flank with either MDA-MB-231 or MCF7 cells and tumors permitted to form to a volume of ~100 mm 3 prior to a two day exposure of either Vehicle, PD184352 (25 mg/kg), Taxotere (15 mg/kg) or the drug combination. Tumor volume was measured every other day and tumor growth determined over the following ~30 days. Transient exposure of MDA-MB-231 tumors or MCF7 tumors to PD184352 did not significantly alter tumor growth rate or the mean tumor volume in vivo ~15-30 days after drug administration. Transient Taxotere exposure of MDA-MB-231 or to a lesser extent MCF7, tumors modestly reduced the mean tumor volume in vivo ~15-30 days after drug administration. In contrast, combined treatment with PD184352 and Taxotere significantly reduced MDA-MB-231 and MCF7 tumor growth. The tumor control values for MDA-MB-231 cells and MCF7 cells were 0.43 and 0.71, respectively. Fractionated irradiation of MDA-MB-231 tumors during drug exposure or single dose irradiation prior to drug administration did not significantly further suppress tumor growth beyond that of cells exposed to Taxotere and MEK1/2 inhibitor. Single dose irradiation of tumors after drug exposure, however, caused a significant further suppression of tumor growth below that caused by drug exposure. These findings were also reflected in ex vivo colony formation analyses of isolated tumor cells. Collectively, these findings argue that Taxotere and MEK1/2 inhibitors have the potential to suppress mammary tumor growth in vivo which is enhanced by sequence-dependent exposure to ionizing radiation. Based on the cell lines used in these studies, our findings argue that the interaction of Taxotere and PD184352 is independent of p53 status, estrogen dependency, caspase 3 levels or oncogenic K-RAS expression.

Noninvasive molecular imaging of apoptosis in vivo using a modified firefly luciferase substrate, Z-DEVD-aminoluciferin

“…Docetaxel is a microtubule-disruptive apoptotic agent commonly used as chemotherapy medication to treat various cancer indications, and has previously been shown to be a potent activator of caspase-3/7 in human mammary (MDA-MB-231) and ovarian (SKOV3) adenocarcinoma cell lines. [22][23][24] To image docetaxelinduced apoptosis in vitro, 150 mM of Z-DEVD-aminoluciferin was added to luciferase-expressing derivatives of these cell lines treated with a range (1-4000 nM) of docetaxel concentrations for 48 h. Luminescent images were acquired using a Xenogen IVIS Spectrum imaging system (Caliper Life Sciences, Hopkinton, MA, USA), and activation of caspase-3/7 was quantified. Representative images for MDA-MB-231-luc-LN cells are shown in Figure 1a.…”

Microtubule-targeting-compound PBOX-15 radiosensitizes cancer cells in vitro

“…This phenomenon was enhanced by sequencedependent exposure to ionizing radiation. 41 Manipulation of the PI3K-AKT pathway by anti-HER2 antibodies trastuzumab was also proposed to potentiate the growth inhibitory activity of docetaxel by affecting cell cycle progression. 42 The potential interaction of PBOX-15 with these pathways may have resulted in increased HIF-1α protein levels in the present study.…”

Human chorionic gonadotropin (hCG) interacts with lovastatin and ionizing radiation to modulate prostate cancer cell viability in vivo

“…Other reagents were as described. [20][21][22][23][24][25][26] Methods. Culture and in vitro exposure of cells to drugs.…”

“…For apoptosis assays, cells were treated as described; cells were isolated, and either subjected to trypan blue cell viability assay by counting in a light microscope or as indicated fixed to slides, and stained using a commercially available TUNEL assay kit according to manufacture's instructions. [20][21][22][23][24][25][26] Cells for in vitro colony formation assays were plated at 250-4000 cells per well in sextupilcate as indicated. Ten-14 days after exposure or tumor isolation, plates were washed in PBS, fixed with methanol and stained with a filtered solution of crystal violet (5% w/v).…”

“…We generated previously noted recombinant adenoviruses to express dominant negative caspase 9 and BCL-XL . [20][21][22][23][24][25][26] Prostate cancer cells were infected with these adenoviruses at an approximate multiplicity of infection (m.o.i.) of 25.…”