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2017 ; 8
(7
): 11302-11315
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Secretion modification region-derived peptide blocks exosome release and mediates
cell cycle arrest in breast cancer cells
#MMPMID28076321
Huang MB
; Gonzalez RR
; Lillard J
; Bond VC
Oncotarget
2017[Feb]; 8
(7
): 11302-11315
PMID28076321
show ga
PURPOSE: Discovery and development of a novel anticancer PEG-SMR-Clu peptide to
prevent breast cancer metastasis. How breast cancer cells and primary mammary
epithelial cells interact and communicate with each other to promote
tumorigenesis and how to prevent tumor metastasis has long been a concern of
researchers. Cancer cells secrete exosomes containing proteins and RNA. These
factors can influence tumor development by directly targeting cancer cells and
tumor stroma. In this study, we determined the effects of a peptide as an
inhibitor of exosome secretion on breast tumors. We developed a peptide derived
from the Secretion Modification Region (SMR) of HIV-1 Nef protein that was
modified with PEG on the N-terminus and with a Clusterin (Clu)-binding peptide on
the C-terminus. Attachment of PEG to the SMR peptide, termed PEGylation, offers
improved water solubility and stability as well as reduced clearance through the
kidneys, leading to a longer circulation time. The 12-mer Clu-binding peptide
plays multiple roles in tumor development and metastasis. The Clu peptide can be
detected by antibody in vivo, thus it has the potential to be used to monitor
tumor status and treatment efficacy in animal studies and eventually in cancer
patients. RESULTS: PEG-SMRwt-Clu and PEG-SMRwt peptides inhibited the growth of
both of MCF-7 (estrogen responsive, ER+) and MDA-MD-231 (estrogen non-responsive,
ER-) human breast cancer cells in a dose and time-dependent manner, without
inducing cytotoxic effects. The SMRwt peptide, combined with paclitaxel, induced
G2/M phase cell cycle arrest on MCF-7 and MDA-MB-231 cells but did not promote
apoptosis. PEG-SMRwt-Clu peptide treatment blocked exosome release from both
MCF-7 and MDA-MB-231 cells. This effect was blocked by knockdown of the chaperone
protein mortalin by either antibody or siRNA. MATERIALS AND METHODS: MCF-7 and
MDA-MB-231 breast tumor cells were treated with PEG-SMR-Clu peptide alone and in
combination with paclitaxel and cisplatin. Cell proliferation and viabilty were
determined via cell cycle analysis using Cellometer imaging cytometry, Annexin V
and MTT assays. The effects of the PEG-SMR-Clu peptide on tumor exosome release
were determined by testing isolated exosome fractions, for (i) expression of CD63
and Alix proteins by Western blotting, (ii) NanoSight nanoparticle tracking
analysis (NTA 10) to measure exosomes size and concentration, and (iii)
measurement of acetylcholinesterase (AchE) for exosome specific enzyme activity.
CONCLUSIONS: PEG-SMRwt-CLU peptides inhibited the growth of human breast cancer
cells and blocked tumor exosome release in vitro. The peptide alone did not cause
increased cytotoxicity or apoptosis induction, but did cause cell cycle G2/M
phase arrest in both estrogen responsive and non-responsive breast cancer cells.
These data suggest a potential therapeutic value of SMR to prevent breast cancer
metastasis and as an adjuvant for the chemotherapeutic treatment of human breast
cancer.