In vitro activity: BIBR 1532 exhibits an non-competitive inhibitory effect on telomerase activity. In JVM13 leukemia cell line, BIBR 1532 shows an antiproliferative effect in a dose-dependent range with IC50 of 52 μM, and similar results are also observed in other leukemia cell lines including Nalm-1, HL-60, and Jurkat. In addition, BIBR 1532 results in a direct antiproliferative effect on acute myeloid leukemia (AML) with IC50 of 56 μM without affecting the proliferative capacity of normal hematopoietic progenitor cells. BIBR 1532 (2.5 μM) reduces colony-forming ability, and induces telomere length shortening as well as chemotherapeutic sensitization by inhibiting telomerase activity in MCF-7/WT and melphalan-resistant MCF-7/MlnR cell lines. In T-cell prolymphocytic leukemia (T-PLL), BIBR 1532 shows selective cytotoxic effects in a dose-dependent manner and BIBR 1532-treated cells also demonstrates nuclear condensation and formation of apoptotic bodies morphologically compatible with apoptosis. A recent study shows that combination treatment of BIBR 1532 and chemotherapeutic agents carboplatin results in a potential synergy for eliminateing ovarian cancer spheroid-forming cells in ES2, SKOV3, and TOV112D cell lines.

Kinase Assay: For the direct telomerase assay with the endogenous telomerase, 10 μL of telomerase-enriched extract is mixed with different concentrations of BIBR1532 in a final volume of 20 μL. After 15-minute preincubation on ice, 20 μL of the reaction mixture is added, and the reaction is initiated by transferring the tubes to 37 °C. The final concentrations in the reaction mixture are 25 mM Tris-Cl (pH 8.3), 1 mM MgCl2, 1 mM EGTA, 1 mM dATP, 1 mM dTTP, 6.3 μM cold dGTP, 15 μCi [α-32P]dGTP (3000 Ci/mmol; NEN), 1.25 mM spermidine, 10 units of RNasin, 5 mM 2-mercaptoethanol, and 2.5 μM TS-primer (5'-AATCCGTCGAGCAGAGTT). For the recombinant enzyme, 1–7 μL of affinity-purified telomerase (containing less than 0.025 μm hTERT) are assayed in a final volume of 40 μL containing 50 mM Tris acetate (pH 8.5), 50 mM KCl, 1 mM MgCl2, 1 mM spermidine, 5 mM 2-mercaptoethanol, 1 mM dATP, 1 mM dTTP, 2.5 μM dGTP, 15 μCi of [α-32P]dGTP (3000 Ci/mmol) and 2.5 μm (TTAGGG)3. The reaction is initiated by incubation at 37 °C for 2 hours and stopped by addition of 50 μL of RNase mix (0.1 mg/mL RNaseA-100 u/mL RNaseT1 in 10 mM Tris-Cl (pH 8.3) and 20 mm EDTA) and incubation for 20 min at 37 °C. Samples are deproteinated by adding 50 μL of 0.3 mg/m proteinase K in 10 mM Tris-Cl (pH 8.3) and 0.5% w/v SDS, for a 30-minute incubation at 37 °C. DNA is recovered by phenol extraction and ethanol precipitation, and the extension products are analyzed on an 8% (endogenous telomerase) or 12% (recombinant telomerase) polyacrylamide-urea gel. Dried gels are exposed to a Kodak phosphorimager screen, and the results are analyzed.

Cell Assay: Cells are plated as triplicates in complete RPMI 1640 medium with various concentrations of BIBR1532. After 24 to 72 hours, water-soluble tetrazolium (WST-1) is added, which is transformed into formazan by mitochondrial reductase systems. The increase in the number of viable cells results in an increase of activity of mitochondrial dehydrogenases, leading to an increase of formazan dye formed, which is quantified by ELISA reader after 2, 3, and 4 hours of incubation.

J Biol Chem. 2002 May 3;277(18):15566-72; Blood. 2005 Feb 15;105(4):1742-9.