Prolactin receptor antagonism reduces the clonogenic capacity of breast cancer cells and potentiates doxorubicin and paclitaxel cytotoxicity.
BACKGROUND
Exogenous prolactin is mitogenic and antiapoptotic in breast cancer cells, and overexpression of autocrine prolactin cDNA in breast cancer cell lines has been shown to stimulate their growth and to protect against chemotherapy-induced apoptosis. We examined the effects of the 'pure' prolactin receptor antagonist Delta1-9-G129R-hPrl (Delta1-9) on the breast cancer cell number and clonogenicity, alone and in combination with chemotherapy.


METHODS
The effects of doxorubicin, paclitaxel and Delta1-9 on the growth of breast cancer cell lines (MCF-7, T47D, MDA-MB-453, MDA-MB-468 and SK-BR-3) in monolayer culture were assessed by the sulphorhodamine B assay. Effects on clonogenicity were assessed by soft agar assay for the cell lines and by the mammosphere assay for disaggregated primary ductal carcinoma in situ samples. Dual-fluorescence immunocytochemistry was used to identify subpopulations of cells expressing the prolactin receptor and autocrine prolactin.


RESULTS
Delta1-9 as a single agent had no effect on the cell number in monolayer culture, but potentiated the cytotoxic effects of doxorubicin and paclitaxel. Doxorubicin accordingly induced expression of prolactin mRNA and protein in all five breast cancer cell lines tested. Delta1-9 alone inhibited the clonogenicity in soft agar of cell lines by ~90% and the mammosphere forming efficiency of six disaggregated primary ductal carcinoma in situ samples by a median of 56% (range 32% to 88%). Subpopulations of cells could be identified in the cell lines based on the prolactin receptor and prolactin expression.


CONCLUSIONS
Autocrine prolactin appears to act as an inducible survival factor in a clonogenic subpopulation of breast cancer cells. The rational combination of cytotoxics and Delta1-9 may therefore improve outcomes in breast cancer therapy by targeting this cell population.
Howell
Sacha J
SJ
Breast Biology Group, Paterson Institute for Cancer Research, University of Manchester, Wilmslow Road, Manchester M20 4BX, UK. SHowell@picr.man.ac.uk
Anderson
Elizabeth
E
Hunter
Tom
T
Farnie
Gillian
G
Clarke
Robert B
RB
D000362:Agar / Q000737:chemistry; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D018076:DNA, Complementary / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology*; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D017239:Paclitaxel / Q000494:pharmacology*; D011388:Prolactin / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011981:Receptors, Prolactin / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012235:Rhodamines / Q000494:pharmacology
D000970:Antineoplastic Agents; D018076:DNA, Complementary; D012333:RNA, Messenger; D011981:Receptors, Prolactin; D012235:Rhodamines; C022027:lissamine rhodamine B; D004317:Doxorubicin; D000362:Agar; D011388:Prolactin; D017239:Paclitaxel