Download Molecular Evolution Assays Reveal Novel Targets and Mechanisms

Molecular Evolution Assays Reveal Novel Targets and Mechanisms of Drug
Resistance
Adam Hermawan
Abstract
Important progress has been achieved for breast cancer treatment in recent years, however,
classical chemotherapy is still one the most frequently used in clinics, and therefore
chemoresistance is still a major challenge for successful breast cancer therapy. As a result of
intrinsic or acquired chemoresistance, tumors will progress or relapse with locally advanced
or metastatic breast cancer. Accordingly, research on drug resistance formation and solution
to overcome drug resistance is urgently needed to achieve better efficacy of
chemotherapeutic drugs. In this present study, clinical application of chemotherapy is
mimicked by an in vitro model called molecular evolution assay. Cells were sequentially
treated with the same dose of drugs (doxorubicin or salinomycin) for several cycles/rounds,
followed by a recovery time.
The discovery of salinomycin as anti-cancer stem cell drug provides progress in overcoming
chemoresistance. However, a study on whether long term application of salinomycin is able
to abolish drug resistance remained elusive. In this study, sequential treatment of
salinomycin was performed in MCF-7 and BT-474 epithelial breast cancer cells as well as
MDA-MB 231 and MDA-MB 436 mesenchymal cells and the gene expression of multiple
drug resistance (MDR) genes was further analyzed. Here, sequential treatment of
salinomycin generated resistance in all cell lines and increased the chemosensitivity towards
doxorubicin. Drug efflux pump gene expression and the pump activity of MDR1 and BCRP1
were downregulated in these cells. Moreover, intracellular drug accumulation was increased
compared to the respective parental cells. These findings suggest a novel treatment option
for multiple drug resistant tumors by sensitizing these tumors via salinomycin pretreatment.
The luminal subtype of breast cancer is the most common breast cancer cases, and due to
its dependency of estrogen signaling, inhibition of the signaling with tamoxifen is considered
as the firstline treatment. However, cells develop resistance to tamoxifen by activating ligand
independent signaling pathway. In this part of the thesis, sequential treatment of tamoxifen
on MCF-7 cells generated tamoxifen-resistant cells. Upregulation of efflux pumps and cancer
stem cell marker, but downregulation of ERα gene expression was observed in tamoxifen
resistant cells. Here, salinomycin circumvents tamoxifen resistance by inhibiting ligand
independent pathway. Therefore combinational treatment of tamoxifen and salinomycin is a
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novel strategy to improve clinical efficacy of tamoxifen.
Doxorubicin is the most commonly used chemotherapy in clinic, and therefore exploring
chemoresistance mechanism of doxorubicin is urgently needed to improve its clinical
outcome. Bone morphogenetic protein receptor type II (BMPR2) is a serine/threonine kinase
and receptor of TGF-ß family. BMPR2 can regulate bone, teeth, and vascular formation, as
well as kidney regulation and hypertension. In this part of the thesis, BMPR2 was identified
as a promising target of doxorubicin resistance. This study demonstrates that BMPR2
promotes doxorubicin chemoresistance in breast cancer cells via regulating cell proliferation
and cell cycle, DNA repair, and apoptosis. Furthermore, increased BMPR2 expression in
doxorubicin resistant breast cancer cells was confirmed in a xenograft mouse model. These
findings show a novel role of BMPR2 in breast cancer chemoresistance. Antagonizing
BMPR2 action might improve clinical outcome of breast cancer patients by sensitizing
resistant tumor cells to doxorubicin. In this thesis many options to circumvent
chemoresistance were found. Further studies are needed to validate these novel treatment
options.
E-mail :
[email protected]
Home institute address :
Laboratory of Biochemistry and Molecular Biology, Building IV, Faculty of Pharmacy,
Universitas Gadjah Mada.
Sekip Utara II, Yogyakarta 55281, Indonesia
Host institute address :
Pharmaceutical Biotechnology, Department of Pharmacy, Ludwig-Maximilians Universität
(University of Munich).
Butenandtstr. 5-13, Building D 3.041, 81377, München
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