Analysis of 7a Selectivity for Pgp. Pgp and MDRassociated protein 1 (MRP1 or ) are the primary proteins thought to be involved in MDR phenotypes, and all are
Figure 5. Effects of 7a on Pgp protein expression (A) and subcellular localization (B). Following treatment with 7a, Pgp levels in KBV cells were assessed via western blotting (A) and immunofluorescence (B) assay. Dapi (blue) indicates the nuclei. Scale bar: .
overexpressed by KBV cells. Notably, most known Pgp modulators have been found to inhibit to varying extents due to the similarities in both structure and function between Pgp and ABCC1. Thus, the selectivity of was examined by assessing its capacity to sensitize KBV cells to exporter-mediated anticancer agents. As shown in Tables 2 and 5, derivative 7a markedly sensitized MDR cells to the Pgp substrates adriamycin and Ptx, where it failed to sensitize KBV
Table 5. Assessment of the Selectivity of as an Inhibitor of ABC Transporters Overexpressed in KBV Cells
treatment
反转折叠
adriamycin
1.0
8.0
15.8
Vrp
13.2
cisplatin
1.0
1.0
1.0
MK571
3.6
Data are mean .
cells to cisplatin, a nonsubstrate of Pgp. However, MK571, a specific inhibitor, could robustly sensitize KBV cells to cisplatin (Table 5), consistent with the observation that ABCC1 is involved in cisplatin resistance. These data suggest that selectively inhibits Pgp efflux activity.
Cellular Thermal Shift Assay (CETSA). A CETSA approach was next used to assess the binding affinity of with in situ Pgp as this label-free method can enable efficient analyses of protein-compound interactions in physiological environments. Briefly, live KBV cells were incubated with followed by thermal denaturation at different temperatures. Cell lysate soluble fractions were then collected and evaluated following freeze-thaw cycles. The binding of a protein to a given compound can increase its overall resistance to denaturation such that it may remain stable in the soluble lysate fraction at a higher temperature relative to the unbound protein. Indeed, treatment with stabilized Pgp at higher temperatures compared with DMSO treatment, but not ABCC1 (Figures 6
Synthesis of Compounds . To a solution containing a given intermediate (1 or 2 ) , 1-ethyl-3-(3dimethylaminopropyl)carbodiimide hydrochloride (EDCI, , ), and -Boc-L-proline in dry , 4-dimethylaminopyridine (DMAP, ) was added under argon. The solution was stirred for at RT, and the reaction was then terminated via adding . The mixture was then extracted with , washed with brine, dried over , and purified by silica gel column chromatography to yield and .
TFA was added to 13 (or 15 at , and the mixture was stirred for at RT, after which it was concentrated to yield compounds 14 and 16 .
Cell Culture. KBV cells (from Dr. Xiaoguang Chen of the Institute of Materia Medica, Chinese Academy of Medical Sciences) were grown in DMEM supplemented with fetal bovine serum (FBS), penicillin, and streptomycin in a humidified incubator at . The drug-resistant properties of these cells were maintained by routinely treating them with Ptx .
MDR Reversal Assay. An MTT assay was utilized to assess cell viability as discussed previously. Briefly, following a incubation with test compounds of interest, cells were treated with an MTT solution for . Dark blue crystals were dissolved in DMSO (150 , and absorbance at was then evaluated to assess the rate of cell survival.
Molecular Docking Analyses. Potential modes of binding between the compounds and the dynamic models of human Pgp in an outward-facing conformation or the human Pgp structure (PDB: ) in inward-facing conformation were predicted using AutoDock 4.2.6. The protein structure was established by the protonation and the removal of ligands, water molecules, and other heteroatoms. Ligand docking was limited in a grid box centered on the putative allosteric site of Pgp points; grid point spacing: . The grid box centered on the drug-binding site of Pgp was set a dimension of 40 points with a grid point spacing of . One hundred replicates for each compound were calculated, with the docking programs being used to compute the lowest estimated binding energy to the protein. Structural figures were drawn using PyMOL and LigPlus.
ATPase Activity Assay. A Promega Pgp-Glo assay kit was employed to examine the impact of on the Pgp-ATPase activity as discussed previously. Briefly, Pgp was pretreated for with test compounds (25,500 or of and/or of and reacted for with at . The reaction was then terminated via the addition of the ATP Detection Reagent and incubated for at RT, and luminescence was then measured with a SpectraMax M5 multifunctional microplate reader.
Intracellular Accumulation of Pyxinol Derivatives. Approximately or cells were treated with pyxinol or pyxinol derivatives for . The cells were collected, washed in phosphate-buffered saline (PBS), and lysed in of PBS by sonication. Intracellular pyxinol and pyxinol derivatives were extracted by EtOAc . Supernatants were collected after centrifugation , dried under gas, and redissolved in . The samples were analyzed on an Agilent 1290 Infinity (Agilent column, SB-C18, ) coupled with an AB SCIEX mass spectrometer (QTRAP 5500) by ultraperformance liquid chromatography coupled with mass spectrometry (UPLC-MS) analysis (the mobile phases: A, ammonium acetate aqueous; B, in ; isocratic A for 6 min with a flow rate of ; mass conditions: positive mode; ion spray voltage ; temperature ; declustering potential, for pyxinol and for and 11f). The following precursors and fragments were used:
Pyxinol：母离子477.4，碎片离子303.4。
Y30：母离子689.5，碎片离子553.5。
7a：母离子573.5，碎片离子143.1。
11 C：母离子747.5，碎片离子591.4。
11F：母离子795.6，碎片离子695.5。
Assessment of Intracellular Rh123 Accumulation. The impact of 7a on Rh123 accumulation was assessed via flow cytometry assay as published previously. Briefly, KBV cells were treated for with test compounds and with for . The cells were then collected, rinsed with PBS, and evaluated with a BD flow cytometer, with mean fluorescence intensity of 8000 being calculated.
Fluorescence Imaging. Fluorescence imaging was used to assess the accumulation of Ptx-C (fluorescent analogue of Ptx conjugated with coumarin). After planting in the glass-bottom dish, the cells were treated with Ptx-C in the absence or presence of ) for and then imaged by a Zeiss confocal microscope (LSM800) or quantified by a microplate reader.
Western Blotting. Western blotting was used to assess protein levels in KBV cells as per our previous protocols. Briefly, following treatment, KBV cells were lysed using radioimmunoprecipitation assay (RIPA) buffer, and proteins in the resultant lysates were separated via sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDSPAGE) and transferred to poly(vinylidene fluoride) (PVDF) membranes, which were then probed with antibodies against glyceraldehyde 3-phosphate dehydrogenase (GAPDH, AG019, Beyotime), ABCC1 (AF7503, Beyotime), or Pgp (ab3366, Abcam), and then with an HRP-conjugated secondary antibody (Beyotime). Chemiluminescent detection was then performed with an ECL reagent (Beyotime).
Immunofluorescence Assay. KBV cells were plated in the glassbottom plates and incubated with for . The cells were then fixed with formaldehyde (4%) for , permeabilized with Triton X-100 (0.1%) for , blocked with bovine serum albumin (BSA, 5%) for , and treated with the anti-Pgp antibody (ab3366, Abcam) at overnight. The cells were subsequently incubated with an Alexa Fluor 488-conjugated secondary antibody (A0428, Beyotime) for , counterstained with DAPI for , and imaged using a Zeiss confocal microscope (LSM800).
Cellular Thermal Shift Assay. KBV cells were pretreated for with or DMSO as a solvent control at , after which they were treated for an additional with or DMSO at 37 prior to separation into eight PCR tubes. The cells were then heated for to the indicated temperatures before being allowed to cool to RT. The samples were then lysed through six freeze-thaw cycles performed using liquid nitrogen, after which the samples were centrifuged at and supernatants were assessed via Western blotting.
Cell Cycle Distribution Assay. Cell cycle progression was assessed via flow cytometry as previously described. Briefly, KBV cells were cultured for in six-well plates with appropriate test compounds, after which they were collected and fixed overnight at in ethanol. Samples were then stained for with PI and RNaseA in PBS, after which they were analyzed with a BD flow cytometer.
Xenograft Studies. Nude male BALB/c mice ( weeks old) were employed to establish a xenograft model based on our previous study. Briefly, KBV cells were subcutaneously implanted on the back of each mouse. When tumors were in size, the animals were randomized into four groups: the control, Ptx , and Ptx groups. Ptx was administered intraperitoneally to appropriate mice once every three days, while was administered once per day. Tumor growth was assessed every three days over the treatment period. After treatment, the mice were euthanized and the tumors were weighed. The Animal Experimentation Ethics Committee of Yantai University approved the present study (protocol number 20180407), which was consistent with the guidelines for ethical conduct in the care and use of animals.
Statistical analysis. Data are presented as mean and were compared with Student's -test. **: .
Coordinates of modeled structures in PDB format: 7a in complex with Pgp (the dynamic model of human Pgp in an outward-facing conformation ) (PDB)
作者信息
通讯作者
Gangqiang Yang - School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Yantai University, Yantai 264005, China; (1) orcid.org/0000-0001-6030-3570; Phone: +86535-6706095; Email: oceanygq@ytu.edu.cn
Hongbo Wang - School of Pharmacy, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Yantai University, Yantai 264005, China; (1) orcid.org/0000-0001-5055-4261;
G.Y., S.L., and C.Z. contributed equally. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
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