In vitro activity: CI-994 (< 160 mM) shows cytostatic effect with concomitant increase at G0/G1 phase, a reduction at S phase level and increased apoptosis in A-549 and LX-1 cells. CI-994 inhibits growth of LNCaP cell with IC50 of 7.4 μM. CI-994 exerts activity against several tumor cell lines with greater cytotoxicity against the solid tumors relative to both the leukemia and normal fibroblast cell lines. CI-994 inhibits growth of rat leukemia BCLO cells with IC50 of 2.5 μM.

Kinase Assay: Tacedinaline (N-acetyldinaline) is an inhibitor of the histone deacetylase (HDAC) with IC50s of 0.9, 0.9, 1.2 μM for recombinant HDAC 1, 2 and 3 respectively.

Cell Assay: LNCaP cell lines are maintained in RPMI 1640 medium containing 10% fetal bovine serum, 1% penicillin and streptomycin, as the complete culture medium. Cells (2×104) are seeded in 24-well plates and incubated in a 5% CO2 incubator at 37 °C for 1 day. Cultures are treated with CI-994, alone and in combination on day 2 and 4. Cells are washed on day 2 and 4 and media are changed. Mitochondrial metabolism is measured as a marker for cell growth by adding 100 μL/well MTT (5 mg/mL in medium) with 2 hours incubation at 37 °C on Day 6. Crystals formed are dissolved in 500 μL of DMSO. The absorbance is determined using a microplate reader at 560 nm. The absorbance data are converted into cell proliferation percentage. Each assay is performed in triplicate.