Treatment of HER-2/neu overexpressing breast cancer xenograft models with trastuzumab (Herceptin) and gefitinib (ZD1839): drug combination effects on tumor growth, HER-2/neu and epidermal growth factor receptor expression, and viable hypoxic cell fraction.
OBJECTIVE
The purpose of this research was to assess the effects of single agent and combination treatment with trastuzumab and gefitinib on tumor growth and tumor microenvironment in two HER-2/neu overexpressing breast xenograft models, MDA-MB-435/LCC6(HER-2) (LCC6(HER-2); estrogen receptor negative) and MCF-7(HER-2) (estrogen receptor positive).


METHODS
LCC6(HER-2) and MCF-7(HER-2) cells, both in tissue culture and xenografts grown in SCID-Rag 2M mice, were treated with trastuzumab and gefitinib, alone or in combination. The rate of tumor growth was determined. In addition, tumor HER-2/neu and epidermal growth factor receptor expression, cell viability, cell cycle distribution, and proportion of viable hypoxic cells were determined by flow cytometric analyses of single tumor cell suspensions.


RESULTS
Both tumor models were very sensitive to trastuzumab and moderately sensitive to gefitinib in vivo. The combination resulted in therapeutic effects, as judged by inhibition of tumor growth, which was greater (albeit not statistically significant) than that observed with trastuzumab administered as a single agent. Trastuzumab was effective in down-regulating HER-2/neu, and gefitinib mediated a reduction in epidermal growth factor receptor expression on tumor cells. In LCC6(HER-2) tumors, trastuzumab significantly reduced tumor cell viability, which was not improved by the addition of gefitinib. Gefitinib dramatically reduced the proportion of viable hypoxic cells in LCC6(HER-2) and MCF-7(HER-2) tumors. This effect was abrogated by the addition of trastuzumab.


CONCLUSIONS
Although in vivo efficacy studies in two HER-2/neu overexpressing breast xenograft models showed that the combination of trastuzumab and gefitinib was effective, analyses of various cellular parameters failed to reveal beneficial effects and argue that this drug combination may not be favorable.
Warburton
Corinna
C
Department of Advanced Therapeutics, British Columbia Cancer Agency, Vancouver, Canada.
Dragowska
Wieslawa H
WH
Gelmon
Karen
K
Chia
Stephen
S
Yan
Hong
H
Masin
Dana
D
Denyssevych
Tetyana
T
Wallis
Anne E
AE
Bally
Marcel B
MB
D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D000971:Antineoplastic Combined Chemotherapy Protocols; D001943:Breast Neoplasms / Q000378:metabolism*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002470:Cell Survival; D004396:Coloring Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D066246:ErbB Receptors / Q000096:biosynthesis; D005260:Female; D005434:Flow Cytometry; D000077156:Gefitinib; D006801:Humans; D000860:Hypoxia; D015674:Mammary Neoplasms, Animal / Q000188:drug therapy*; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D010766:Phosphorylation; D011799:Quinazolines / Q000627:therapeutic use*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis*; D013347:Subcellular Fractions / Q000378:metabolism; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013997:Time Factors; D000068878:Trastuzumab
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D004396:Coloring Agents; D066246:ErbB Receptors; D000077156:Gefitinib; D011799:Quinazolines; D018719:Erb-b2 Receptor Tyrosine Kinases; D013778:Tetrazolium Salts; D013844:Thiazoles; D000068878:Trastuzumab; C022616:thiazolyl blue