Exatecan is a water soluble topoisomerase I inhibitor, with an IC50 of 2.2 μM (0.975 μg/mL)

Exatecan is a potent topoisomerase I inhibitor, with an IC₅₀ of 0.975 μg/mL. Exatecan Mesylate (DX-8951f) significantly inhibits the proliferation of several cancer cell lines, with mean GI₅₀s of 2.02 ng/mL, 2.92 ng/mL, 1.53 ng/mL, and 0.877 ng/mL for breast cancer cells, colon cancer cells, stomach cancer cells and lung cancer cells, respectively^[1]. Exatecan Mesylate (DX-8951f) displays cytotoxic activities against PC-6, PC-6/SN2-5 cells, with mean GI₅₀s of 0.186 and 0.395 ng/mL, respctively. Exatecan Mesylate (34 nM) stabilizes DNA-TopoI complexes in PC-6 and PC-6/SN2-5 cells

^{Exatecan Mesylate (DX-8951f, 3.325-50 mg/kg, i.v.) exhibits antitumor activities in the mice model bearing tumor cells, without toxic death[1]. Exatecan Mesylate (15, 25 mg/kg, i.v.) hightly inhibits MIA-PaCa, BxPC-3 primary tumor growth in the MIA-PaCa-2 early-stage model and early-stage model of BxPC-3. Exatecan Mesylate (15, 25 mg/kg, i.v.) also significantly suppresses BxPC-3 lymphatic metastasis and completely eliminates lung metastasis in the BxPC-3 late-stage cancer model.}

sup>[3]Cells (5×10⁶) are lysed with SDS buffer (10 mM HEPES, 2 mM orthovanadate, 10 mM NaF, 10 mM pyrophosphate, 1 mMPMSF, 10 µg/mL leupeptin, 10% 2-mercaptoethanol, 10% glycerol,8% SDS, 42 mM Tris-HCl, 0.002% bromophenol blue, pH 7.4). Protein in the whole cell lysates is separated in 7.5% polyacryl-amide gel and blotted onto nitrocellulose membrane. The membrane is treated with anti-Topo I human antibody and subsequently, with horseradish peroxidase-conjugated protein A. The Topo I-specific band is detected with ECL reagents. To obtain a nuclear extract, cells (5×10⁷) are washed with ice-cold buffer (2 mM K₂HPO₄, 5 mM MgCl₂, 150 mM NaCl, 1 mM EGTA, 0.1 mM dithiothreitol), resuspended in buffer containing 0.35% Triton-X100 and PMSF and then incubated on ice for 10 min. The resulting lysates are centrifuged, and precipitates are then incubated with buffer containing 0.35 M NaCl for 1 hr at 4°C. After centrifugation (18,000g, 10 min), the protein concentration of the supernatant (nuclear extract) is determined by Bradford’s method using a protein assay kit. The same amount of nuclear protein is analyzed by Western blotting analysis using anti-Topo I antibody^[3].