Circulating biomarkers of cell death after treatment with the BH-3 mimetic ABT-737 in a preclinical model of small-cell lung cancer.
OBJECTIVE
This study evaluated epithelial cell death ELISAs that measure circulating cytokeratin 18 in mice bearing small-cell lung cancer xenografts treated with a proapoptotic dose of the BH-3 mimetic ABT-737.


METHODS
H146 tumor-bearing and non-H146 tumor-bearing severe combined immunodeficient (SCID)/bg mice were treated with ABT-737 or vehicle control. Plasma collected before and 2 to 360 hours after treatment was analyzed by M30 (caspase-cleaved cytokeratin 18) and M65 (intact and cleaved cytokeratin 18) ELISA. In parallel, tumors were interrogated for cleaved caspase-3 and cleaved cytokeratin 18 as biomarkers of apoptosis.


RESULTS
ABT-737-treated tumors regressed by 48 hours (P < 0.01) compared with controls, correlating with increased cleaved cytokeratin 18 (P < 0.01; 6 and 24 hours) and increased intact cytokeratin 18 (P < 0.01; 24 hours). Cleaved cytokeratin 18 levels decreased below baseline between 72 and 360 hours for ABT-737-treated and control mice whereas intact cytokeratin 18 decreased below the level of detection at 8 and 15 days in ABT-737-treated mice only. Apoptosis in tumors reflected changes in circulating cytokeratin 18 (cleaved caspase-3, P < 0.05 at 2 hours and P < 0.001 at 6, 12, and 24 hours; caspase-cleaved cytokeratin 18, P < 0.05 at 15 days, for drug treated versus controls).


CONCLUSIONS
ABT-737 caused tumor regression by apoptosis in H146 xenografts that mapped to a drug-specific, early increase in circulating cleaved cytokeratin 18 that subsequently declined. Circulating, intact cytokeratin 18 levels correlated with tumor burden. Cleaved caspase-3 and caspase-cleaved cytokeratin 18 in tumor correlated with treatment (P < 0.05, 2 hours; P < 0.001, 6, 12, and 24 hours; cleaved caspase-3, P < 0.05, 15 days; caspase-cleaved cytokeratin 18), indicating that events in plasma were tumor derived. These circulating biomarker data will be translated to clinical trials wherein serial tumor biopsies are rarely obtained.
Micha
Dimitra
D
Clinical and Experimental Pharmacology Group, Paterson Institute for Cancer Research, University of Manchester, Manchester, United Kingdom.
Cummings
Jeff
J
Shoemaker
Alex
A
Elmore
Steven
S
Foster
Kelly
K
Greaves
Martin
M
Ward
Tim
T
Rosenberg
Saul
S
Dive
Caroline
C
Simpson
Kathryn
K
D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D014408:Biomarkers, Tumor / Q000097:blood*; D040761:Biomimetic Materials / Q000627:therapeutic use; D001713:Biphenyl Compounds / Q000627:therapeutic use*; D002084:Butylated Hydroxytoluene / Q000031:analogs & derivatives / Q000737:chemistry; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007150:Immunohistochemistry; D053538:Keratin-18 / Q000097:blood / Q000378:metabolism; D008175:Lung Neoplasms / Q000097:blood* / Q000188:drug therapy; D051379:Mice; D009596:Nitrophenols / Q000627:therapeutic use*; D010879:Piperazines / Q000627:therapeutic use; D055752:Small Cell Lung Carcinoma / Q000097:blood* / Q000188:drug therapy; D013449:Sulfonamides / Q000627:therapeutic use*; D023041:Xenograft Model Antitumor Assays
C501332:ABT-737; D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D001713:Biphenyl Compounds; D053538:Keratin-18; D009596:Nitrophenols; D010879:Piperazines; D013449:Sulfonamides; D002084:Butylated Hydroxytoluene; C006008:BH 3; D053148:Caspase 3