In vitro study of CI-994, a histone deacetylase inhibitor, in non-small cell lung cancer cell lines

CI-994 (N-acetyldinaline) is a novel oral compound with a wide spectrum of antitumor activity in preclinical models, in vitro and in vivo. The mechanism of action may involve inhibition of histone deacetylation and cell cycle arrest. We studied the action of CI-994 on two non-small cell lung cancer (NSCLC) cell lines: A-549 (adenocarcinoma) and LX-1 (squamous cell carcinoma). Different drug concentrations were tested, ranging from 0.01 to 160 μM at 24, 48, and 72 h of treatment, with MTT assay. A concentration-dependent cell survival inhibition was observed, with an IC₅₀ at 80 μM. The effect of CI-994, as demonstrated by recovery experiments, was cytostatic and seemed to be superimposable in both cell lines. Cytofluorimetric analysis to assess cell cycle perturbation and apoptosis was performed after 24 h of treatment, indicating a cell block with concomitant increase at G₀G₁ phase, a reduction at S phase level at 20, 40, 80, and 160 μM, and apoptosis at the higher concentration (160 μM). When CI-994 was combined with antineoplastic agents commonly used in NSCLC management, a marked synergism of action (R = 1.8, R = 1.5) was observed between CI-994 (40 μM) and gemcitabine (0.01 μM) at 48 and 72 h of treatment. The same result was obtained with docetaxel (0.001 μM) combination (R = 1.4, R = 1.2), but no synergism of action was noted with paclitaxel. CI-994 showed no radiopotentiating effects, when combined with 100, 200, or 400 cGy irradiation. In conclusion, our experiments indicate that CI-994 is a promising novel cytostatic for the treatment of NSCLC. Its use in combination with standard anticancer agents, such as gemcitabine and docetaxel, is warranted.