Raloxifene attenuation of 5-FU/methotrexate cytotoxicity in human breast cancer cells: the importance of sequence in combination chemotherapy.
BACKGROUND
The selective estrogen receptor modulator raloxifene (RAL), used to treat and prevent osteoporosis, is under investigation for its use in the treatment and prevention of breast cancer. RAL in combination with the antimetabolites methotrexate (MTX) and 5-fluorouracil (5-FU) has not been extensively studied. Because RAL and the antimetabolites target different phases of the cell cycle and exhibit different mechanisms of action and clinical toxicity, the effects of sequence of administration on the growth inhibition of MCF-7 human breast cancer cells were investigated.


METHODS
MCF-7 human breast cancer cells were exposed to vehicle alone, 10 microM MTX, 1 microM 5-FU, 10 microM RAL, 10 microM RAL 24 hours prior to 1 microM 5-FU followed 2 hours later by 10 microM MTX, and 1 microM 5-FU 2 hours prior to 10 microM MTX followed 24 hours later by 10 microM RAL. The cells were evaluated for viability and proliferation. The retinoblastoma (Rb) protein, a cell cycle regulator which when phosphorylated allows the progression of cells from G1- to S-phase, was used as a marker to determine the effects of early RAL and late RAL on cellular progression at the molecular level.


RESULTS
Early RAL administration exhibited a cell viability of 66.83 +/- 6.17% of the control. However, late RAL administration exhibited cell viability 39.40 +/- 17.03% of the control. Late RAL was a more cytotoxic combination than RAL alone or early RAL. These findings from manual cell counting were also supported by cell flow cytometric analysis and Western blot data.


CONCLUSIONS
Late RAL in combination with 5-FU and MTX, due to greater cytotoxicity, is a more desirable combination to treat breast cancer than RAL alone.
Fryar
Elizabeth B
EB
Department of Pharmacology, College of Medicine, Howard University, Washington, DC 20059, USA.
Das
Jharna R
JR
Davis
Jillian H
JH
Desoto
Joseph A
JA
Laniyan
Ibrahim
I
Southerland
William M
WM
Bowen
Donnell
D
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage* / Q000009:adverse effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004334:Drug Administration Schedule; D004347:Drug Interactions; D005434:Flow Cytometry; D005472:Fluorouracil / Q000008:administration & dosage / Q000009:adverse effects; D006801:Humans; D008727:Methotrexate / Q000008:administration & dosage / Q000009:adverse effects; D020849:Raloxifene Hydrochloride / Q000008:administration & dosage
D020849:Raloxifene Hydrochloride; D005472:Fluorouracil; D008727:Methotrexate