Retinoblastoma tumor suppressor gene expression determines the response to sequential flavopiridol and doxorubicin treatment in small-cell lung carcinoma.
OBJECTIVE
Small-cell lung cancers (SCLC) are defective in many regulatory mechanisms that control cell cycle progression, i.e., functional retinoblastoma protein (pRb). Flavopiridol inhibits proliferation and induces apoptosis in SCLC cell lines. We hypothesized that the sequence flavopiridol followed by doxorubicin would be synergistic in pRb-deficient SCLC cells.


METHODS
A H69 pRb-deficient SCLC cell line, H865, with functional pRb and H865 pRb small interfering RNA (siRNA) knockdown cells were used for in vitro and in vivo experiments. The in vivo efficiencies of various sequential combinations were tested using nude/nude athymic mice and human SCLC xenograft models.


RESULTS
Flavopiridol then doxorubicin sequential treatment was synergistic in the pRB-negative H69 cell line. By knocking down pRb with specific siRNA, H865 clones with complete pRb knockdown became sensitive to flavopiridol and doxorubicin combinations. pRb-deficient SCLC cell lines were highly sensitive to flavopiridol-induced apoptosis. pRb-positive H865 cells arrested in G0-G1 with flavopiridol exposure, whereas doxorubicin and all flavopiridol/doxorubicin combinations caused a G2-M block. In contrast, pRb-negative SCLC cells did not arrest in G0-G1 with flavopiridol exposure. Flavopiridol treatment alone did not have an in vivo antitumor effect, but sequential flavopiridol followed by doxorubicin treatment provided tumor growth control and a survival advantage in Rb-negative xenograft models, compared with the other sequential treatments.


CONCLUSIONS
Flavopiridol and doxorubicin sequential treatment induces potent in vitro and in vivo synergism in pRb-negative SCLC cells and should be clinically tested in tumors lacking functional pRB.
Budak-Alpdogan
Tulin
T
Department of Medicine, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Cancer Institute of New Jersey, New Brunswick, NJ 08903, USA. budaktu@umdnj.edu
Chen
Bobin
B
Warrier
Anjali
A
Medina
Daniel J
DJ
Moore
Dirk
D
Bertino
Joseph R
JR
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D018288:Carcinoma, Small Cell / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000008:administration & dosage*; D005419:Flavonoids / Q000008:administration & dosage*; D016161:Genes, Retinoblastoma / Q000502:physiology*; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D008297:Male; D051379:Mice; D010880:Piperidines / Q000008:administration & dosage*; D034741:RNA, Small Interfering / Q000235:genetics; D023041:Xenograft Model Antitumor Assays
D005419:Flavonoids; D010880:Piperidines; D034741:RNA, Small Interfering; C077990:alvocidib; D004317:Doxorubicin