Tubacin is a highly potent and selective, reversible, cell-permeable HDAC6 inhibitor with an IC50 of 4 nM, approximately 350-fold selectivity over HDAC1.

HDAC2:6.27 μM, HDAC8:1.27 μM, HDAC5:3.35 μM, HDAC3:1.27 μM, HDAC10:3.71 μM, HDAC9:4.31 μM, HDAC11:3.79 μM, HDAC1:1.40 μM, HDAC6 (cell-free assay):4nM, HDAC4:17.30 μM, HDAC7:9.70 μM

Tubacin, without directly stabilizing microtubules, induces an increase in α-tubulin acetylation with EC50 of 2.5 μM in A549 cells. Tubacin inhibits HDAC6-mediated α-tubulin deacetylation, and inhibits the migration of both wild-type and HDAC6-overexpressing cells. Tubacin, in combination with paclitaxel, synergistically enhances tubulin acetylation. Tubacin significantly inhibits both drug-sensitive and drug–resistant MM cell growth with IC50 of 5–20 μM, and induces cell apoptosis by activation of caspases.

In chick embryos, inhibition of HDAC6 activity by Tubacin reduces the formation of new blood vessels in matrigel/nylon mesh. In angioreactors implanted in mice, Tubacin also impairs the formation of new blood vessels.

Enzyme Inhibition Assay:Enzyme inhibition assays are performed using the Reaction Biology HDAC Spectrum platform. The HDAC1, 2, 4, 5, 6, 7, 8, 9, 10, and 11 assays used isolated recombinant human protein; HDAC3/NcoR2 complex is used for the HDAC3 assay. Substrate for HDAC1, 2, 3, 6, 10, and 11 assays is a fluorogenic peptide from p53 residues 379-382 (RHKKAc); substrate for HDAC8 is fluorogenic diacyl peptide based on residues 379-382 of p53 (RHKAcKAc). Acetyl-Lys(trifluoroacetyl)-AMC substrate is used for HDAC4, 5, 7, and 9 assays. Compounds are dissolved in DMSO and tested in 10-dose IC50 mode with 3-fold serial dilution starting at 30 μM. Control Compound Trichostatin A (TSA) is tested in a 10-dose IC50 with 3-fold serial dilution starting at 5 μM. IC50 values are extracted by curve-fitting the dose/response slopes.

Cell lines: Drug-sensitive (MM.1S,U266,INA-6,and RPMI8226) and drug-resistant (RPMI-LR5 and RPMI-Dox40) MM cell lines. Concentrations: ~20 μM. Incubation Time: 72 hours. Method:The inhibitory effect of bortezomib and/or tubacin on MM cell growth is assessed by measuring 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) dye absorbance.All experiments are performed in quadruplicate.

Animal Models: Athymic nude mice implanted with angioreactorsFormulation: DMSODosages: --Administration: Tubacin is filled in semiclosed angioreactors, and then implanted into the mice.