Actinomycin D Decreases Mcl-1 Expression and Acts Synergistically with ABT-737 against Small Cell Lung Cancer Cell Lines

• Published in: Clinical cancer research 2010-09, Vol.16 (17), p.4392-4400
• Main Authors: HAISHAN XU, KRYSTAL, Geoffrey W
• Format: Article
• Language: English
• Subjects: Antibiotics, Antineoplastic - pharmacology; Antineoplastic agents; Apoptosis - drug effects; Biological and medical sciences; Biphenyl Compounds - pharmacology; Blotting, Western; Cell Division - drug effects; Cell Line, Tumor; Cell Proliferation - drug effects; Cell Survival - drug effects; Dactinomycin - pharmacology; Dose-Response Relationship, Drug; Drug Synergism; Flow Cytometry; G2 Phase - drug effects; Humans; Lung Neoplasms - metabolism; Lung Neoplasms - pathology; Medical sciences; Myeloid Cell Leukemia Sequence 1 Protein; Nitrophenols - pharmacology; Pharmacology. Drug treatments; Piperazines - pharmacology; Pneumology; Poly(ADP-ribose) Polymerases - metabolism; Proto-Oncogene Proteins c-bcl-2 - metabolism; Small Cell Lung Carcinoma - metabolism; Small Cell Lung Carcinoma - pathology; Sulfonamides - pharmacology; Time Factors; Tumors of the respiratory system and mediastinum
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.CCR-10-0640

ABT-737, which blocks the function of Bcl-2 and Bcl-X(L) but not Mcl-1, has shown single-agent activity in preclinical models of small cell lung cancer (SCLC). Elevated expression of Mcl-1 induces resistance to ABT-737 in SCLC. Based on the short half-life of Mcl-1 mRNA and protein, we hypothesized that the actinomycin D could reverse Mcl-1-induced resistance to ABT-737. The dose-response of multiple SCLC cell lines to actinomycin D in the absence and presence of ABT-737 was followed by the assessment of Bcl-2 family expression and poly ADP ribose polymerase cleavage by Western blot, viability by tetrazolium dye reduction and clonogenic assay, and cell cycle kinetics by flow cytometry. Actinomycin D decreased Mcl-1 expression and resulted in a cell line-dependent increase in Noxa expression. Clinically relevant concentrations of actinomycin D from 0.4 to 4 ng/mL showed single-agent activity across a panel of SCLC cell lines. When combined with low micromolar doses of ABT-737, near complete loss of viability was seen with synergistic combination indices of 0.5 to 0.7. Exposure to 4 ng/mL actinomycin was only required for the first 24 hours of the combined incubation, mimicking a clinically achievable area under the curve, but the presence of ABT-737 was required for an additional 48 hours to obtain maximal effect. Clinically relevant concentrations of actinomycin D act synergistically with ABT-737 to induce SCLC apoptosis, which can be at least partially attributed to the actinomycin D-induced decrease in Mcl-1 and increase in Noxa expression. Taken together, these data suggest the feasibility of combining actinomycin D with BH3-mimetic drugs in the clinical setting.