Rapamycin inhibits growth of premalignant and malignant mammary lesions in a mouse model of ductal carcinoma in situ.
OBJECTIVE
Rapamycin has been shown to have antitumor effects in various tumor models. To study the effect of rapamycin at different stages of breast cancer development, we used two unique mouse models of breast cancer with activated phosphatidylinositol 3-kinase (PI3K) pathway. Met-1 tumors are highly invasive and metastatic, and mammary intraepithelial neoplasia-outgrowths (MIN-O), a model for human ductal carcinoma in situ, are transplantable premalignant mammary lesions that develop invasive carcinoma with predictable latencies. Both of these models were derived from mammary lesions in Tg(MMTV-PyV-mT) mice.


METHODS
Met-1 tumors were used to study the effect of rapamycin treatment on invasive disease. Transplanted MIN-O model was used to study the effect of rapamycin on premalignant mammary lesions. Animals were in vivo micro-positron emission tomography imaged to follow the lesion growth and transformation to tumor during the treatment. Cell proliferation, angiogenesis, and apoptosis was assayed by immunohistochemistry.


RESULTS
Rapamycin inhibited in vitro tumor cell proliferation and in vivo Met-1 tumor growth. The growth inhibition was correlated with dephosphorylation of mammalian target of rapamycin (mTOR) targets. Rapamycin treatment significantly reduced the growth of the premalignant MIN-O lesion, as well as tumor incidence and tumor burden. Growth inhibition was associated with reduced cell proliferation and angiogenesis and increased apoptosis.


CONCLUSIONS
In PyV-mT mouse mammary models, rapamycin inhibits the growth of premalignant lesions and invasive tumors. Although the inhibitory effect of rapamycin was striking, rapamycin treatment did not completely obliterate the lesions.
Namba
Ruria
R
Department of Pathology and Laboratory Medicine, School of Medicine, University of California, Davis, Sacramento, CA 95817, USA.
Young
Lawrence J T
LJ
Abbey
Craig K
CK
Kim
Lisa
L
Damonte
Patrizia
P
Borowsky
Alexander D
AD
Qi
Jinyi
J
Tepper
Clifford G
CG
MacLeod
Carol L
CL
Cardiff
Robert D
RD
Gregg
Jeffrey P
JP
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000502:physiology; D017209:Apoptosis / Q000187:drug effects; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000235:genetics / Q000473:pathology / Q000517:prevention & control*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000473:pathology / Q000517:prevention & control*; D051379:Mice; D008822:Mice, Transgenic; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D049268:Positron-Emission Tomography; D011230:Precancerous Conditions / Q000098:blood supply / Q000473:pathology / Q000517:prevention & control*; D011494:Protein Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors
D000903:Antibiotics, Antineoplastic; D000952:Antigens, Polyomavirus Transforming; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse