Zoledronic acid is unable to induce apoptosis, but slows tumor growth and prolongs survival for non-small-cell lung cancers.
BACKGROUND
Although zoledronic acid (ZOL), a third-generation nitrogen-containing bisphosphonate, has been identified as an attractive therapeutic agent against breast cancer, prostate cancer, multiple myeloma as well as small-cell lung cancer (SCLC), as best as we are aware, the anti-tumor effect of ZOL upon non-small-cell lung cancer (NSCLC) remains to be effectively investigated. This study examined the effects of ZOL upon the line-1 tumor cell, using a murine lung adenocarcinoma cell line similar to the behavior of human lung adenocarcinoma.


METHODS
We investigated the anti-tumor effects of ZOL (3-100 microM) on line-1 tumor cells in vitro, including cellular proliferation, by means of an MTT assay, cell-cycle analysis by flow cytometry and by assessing the level of apoptosis by annexin V/propidium iodide (PI) and 4'-6-diamidino-2-phenylindole (DAPI) staining. Further, we evaluated the growth and survival of line-1 tumor cells following ZOL treatment (1 microg/kg/week) using an animal model. We also examined the in vivo cell-cycle pattern using lacZ-expressing line-1 cells (line-1/lacZ).


RESULTS
ZOL significantly slowed the line-1 tumor growth in a dose-dependent manner in vitro. The treated line-1 tumor cells typically arrested at the S/G2/M-phase of the cell-cycle following ZOL exposure, but no apoptotic cells could be detected by either annexin V/PI or DAPI staining. When the ZOL was washed out, the drug-inhibited cells continued to proliferate again and the cell-cycle prolongation elicited earlier by the drug, then disappeared. Within 72-96 h following drug removal, the cell-cycle of the treated cells revealed a similar distribution to that of the untreated controls. In vivo studies demonstrated that ZOL significantly slowed the line-1 tumor growth. Indeed, mice lived significantly longer when they had been ZOL-treated than was the case for untreated mice (p<0.05). Using line-1/lacZ cells, the in vivo cell-cycle distribution of line-1 tumor cells subsequent to ZOL exposure revealed S/G2/M-phase arrest that was identical to the in vitro culture.


CONCLUSIONS
ZOL maintains the potential to reduce tumor burden and prolong survival for murine pulmonary adenocarcinoma. The flow cytometrical analysis of cell-cycle demonstrated that ZOL induces no apoptosis but is able to arrest line-1 tumor cells at the S/G2/M-phase. Although the clinical relevance of these results warrants verification for human lung cancer patients, ZOL combined with chemotherapy and/or radiotherapy appears to be a new therapeutic strategy for the effective treatment of NSCLC.
Li
Ying-Ying
YY
Division of Hemato-oncology, Department of Internal Medicine, Chang Gung Memorial Hospital, Keelung & Chang Gung University, College of Medicine, Keelung, Taiwan.
Chang
John W-C
JW
Chou
Wen-Chi
WC
Liaw
Chuang-Chi
CC
Wang
Hung-Ming
HM
Huang
Jen-Seng
JS
Wang
Cheng-Hsu
CH
Yeh
Kun-Yun
KY
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D050071:Bone Density Conservation Agents / Q000627:therapeutic use; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004164:Diphosphonates / Q000627:therapeutic use*; D018450:Disease Progression; D005434:Flow Cytometry; D007093:Imidazoles / Q000627:therapeutic use*; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008858:Microscopy, Phase-Contrast; D009374:Neoplasms, Experimental / Q000139:chemically induced / Q000473:pathology; D015996:Survival Rate; D016896:Treatment Outcome; D000077211:Zoledronic Acid
D050071:Bone Density Conservation Agents; D004164:Diphosphonates; D007093:Imidazoles; D000077211:Zoledronic Acid