Actinomycin D decreases Mcl-1 expression and acts synergistically with ABT-737 against small cell lung cancer cell lines.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Xu
Haishan
H
Department of Medicine, Virginia Commonwealth University, Richmond, VA, USA.
Krystal
Geoffrey W
GW
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001713:Biphenyl Compounds / Q000494:pharmacology*; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003609:Dactinomycin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005434:Flow Cytometry; D016195:G2 Phase / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D055752:Small Cell Lung Carcinoma / Q000378:metabolism / Q000473:pathology; D013449:Sulfonamides / Q000494:pharmacology*; D013997:Time Factors
C501332:ABT-737; D000903:Antibiotics, Antineoplastic; D001713:Biphenyl Compounds; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols; C498702:PMAIP1 protein, human; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D003609:Dactinomycin; D011065:Poly(ADP-ribose) Polymerases