Use of an ABC transporter peptide inhibitor

Abstract

Disclosed herein is a use of an adenosine triphosphate (ATP) binding cassette (ABC) transporter peptide inhibitor HX-12C. This disclosure also discloses a method of treating a tumor with multidrug resistance mediated by the ABC transporter using a combination of the peptide HX-12C shown in SEQ ID NO: 1 and an ABC transporter substrate chemotherapeutic drug. Moreover, this disclosure also provides a composition for treating a tumor with multidrug resistance mediated by an ABC transporter, consisting of the peptide HX-12C shown in SEQ ID NO: 1 and an ABC transporter substrate chemotherapeutic drug.

Claims

1. A method of treating a tumor with multidrug resistance mediated by an ABC transporter in a subject in need thereof, comprising: administering a combination of 3 μM of a peptide HX-12C shown in SEQ ID NO: 1 and an ABC transporter substrate chemotherapeutic drug to the subject; wherein the ABC transporter is ABCC1.

2. The method of claim 1, wherein the ABC transporter substrate chemotherapeutic drug is selected from the group consisting of vinca alkaloids, anthracyclines, epipodophyllotoxins and tyrosine kinase inhibitors.

3. The method of claim 2, wherein the ABC transporter substrate chemotherapeutic drug is selected from the group consisting of anthracyclines, vinca alkaloids, epipodophyllotoxins, camptothecin, methotrexate, saquinavir, mitoxantrone, imatinib and a combination thereof.

4. A pharmaceutical composition for treating a tumor with multidrug resistance mediated by an ABC transporter, consisting of: 3 μM of a peptide HX-12C shown in SEQ ID NO: 1; and an ABC transporter substrate chemotherapeutic drug; wherein the ABC transporter is ABCC1, and the ABC transporter substrate chemotherapeutic drug is selected from the group consisting of a vinca alkaloid, an anthracycline, an epipodophyllotoxin and tyrosine kinase inhibitor.

5. The pharmaceutical composition of claim 4, wherein the ABC transporter substrate chemotherapeutic drug is selected from the group consisting of the anthracycline, the vinca alkaloid, the epipodophyllotoxin, camptothecin, methotrexate, saquinavir, mitoxantrone, imatinib and a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A schematically depicts a secondary structure of a peptide HX-12C;

(2) FIG. 1B is a circular dichroism analysis of the secondary structure of the peptide HX-12C;

(3) FIGS. 2A-2C show survival curves of a drug-selected ABCB1-overexpressing cell line (KB-C2) and its parental cell line (KB-3-1) versus concentration of a peptide, where 2A: peptide HX-12A; 2B: peptide HX-12B; and 2C: peptide HX-12C;

(4) FIGS. 3A-3B show an expression of ABCB1 in the ABCB1-overexpressing cell line detected by Western blotting method; FIG. 3A shows an expression of the ABCB1 protein after incubation with different concentrations of the peptide HX-12C for 72 h in KB-C2 cells; KB-3-1 cells without any treatment are used as a negative control of ABCB1 protein expression; GAPDH is used as a loading control; FIG. 3B shows a relative intensity of the expression of ABCB1 to the expression of GAPDH;

(5) FIGS. 4A-4B show an expression of ABCC1 in the ABCC1-overexpressing cell line detected by Western blotting method; FIG. 4A shows an expression of the ABCC1 protein after incubation with different concentrations of the peptide HX-12C for 72 h in KB-CV60 cells; KB-3-1 cells without any treatment are used as a negative control of ABCB1 protein expression; GAPDH is used as a loading control; FIG. 4B shows a relative intensity of the expression of ABCB1 to the expression of GAPDH;

(6) FIG. 5 shows an expression and cellular localization of ABCB1 protein in the KB-3-1 and KB-C2 cells after incubation with the peptide HX-12C;

(7) FIG. 6 shows an expression and cellular localization of ABCC1 protein in the KB-3-1 and KB-CV60 cells after incubation with the peptide HX-12C;

(8) FIGS. 7A-7B show an effect of the peptide HX-12C on intracellular accumulation and efflux of [.sup.3H]-paclitaxel in the KB-C2 and KB-3-1 cells; FIG. 7A shows an effect of the peptide HX-12C on the intracellular accumulation of [.sup.3H]-paclitaxel in the KB-C2 and KB-3-1 cells; FIG. 7B shows an effect of the peptide HX-12C on the efflux of [.sup.3H]-paclitaxel in the KB-C2 and KB-3-1 cells;

(9) FIGS. 8A-8B show an effect of the peptide HX-12C on intracellular accumulation and efflux of [.sup.3H]-vincristine in the KB-CV60 and KB-3-1 cells; FIG. 8A shows an effect of the peptide HX-12C on the intracellular accumulation of [.sup.3H]-vincristine in the KB-CV60 and KB-3-1 cells; FIG. 8B shows an effect of the peptide HX-12C on the efflux of [.sup.3H]-vincristine in the KB-CV60 and KB-3-1 cells;

(10) FIG. 9 shows effect of peptide HX-12C on an ATPase activity of the ABCB1 transporter;

(11) FIGS. 10A-10C schematically depict a molecular binding between the peptide HX-12C and the ABCB1 transporter; FIG. 10A schematically depicts domains and positions of the ABCB1 transporter binding with the peptide HX-12C; FIG. 10B schematically depicts a surface structure of a peptide HX-12C-ABCB1 complex; FIG. 10C schematically depicts a predicted binding mode of the peptide HX-12C with the ABCB1 transporter; and

(12) FIGS. 11A-11B schematically depict a molecular binding between the peptide HX-12C and the ABCC1 transporter; FIG. 11A schematically depicts domains and positions of the ABCC1 transporter binding with the peptide HX-12C; and FIG. 11B schematically depicts a surface structure of a peptide HX-12C-ABCC1 complex.

DETAILED DESCRIPTION OF EMBODIMENTS

(13) The disclosure will be further illustrated with reference to the accompanying drawings and embodiments. The experiments in the embodiments are all performed using conventional procedures unless otherwise specified. Materials, reagents and the like used in the following embodiments are commercially available unless otherwise specified. It should be understood that these embodiments are merely illustrative of the present disclosure, and are not intended to limit the scope of the present disclosure.

(14) The polypeptides described below are synthesized by solid phase synthesis. Optionally, the synthesis can also be entrusted to a commercial company.

Example 1 Prediction and Analysis of a Secondary Structure of Peptide HX-12C

(15) A secondary structure of an antimicrobial peptide HX-12C was predicted through secondary structure prediction service, and was analyzed through circular dichroism. As shown in FIG. 1, the predicted secondary structure of the peptide HX-12C showed a typical characteristic of an amphiphilic molecular that a hydrophobic surface and a hydrophilic of the peptide HX-12C were regularly distributed on both sides of the peptide helix. The prediction was verified by the circular dichroism analysis, in which the circular dichroism spectrum of the peptide HX-12C in aqueous phases (0.01 mol/L phosphate buffer) showed the peptide HX-12C had an irregular secondary structure, and the circular dichroism spectrum of the peptide HX-12C in membrane phases (30% trifluoroethanol (TFE) solution or 70% TEF solution) showed the peptide HX-12C had a typical α-helix secondary structure. An acidic environment was more conducive to a formation of the helix structure, which further explained an interaction between the peptide HX-12C and the cell membrane, especially for tumor cells.

Example 2 Effect of Peptide HX-12C on ABCB1-Overexpressing Cell Lines

(16) In order to determine an effect of the peptide HX-12C on the ABC transporter, a sensitivity of an ABCB1-overexpressing cell KB-C2 to the peptide HX-12C was tested. Cytotoxicity of the peptide HX-12C in different cell lines was determined by MTT ((3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay, in which 5000 cells/well were seeded in a 96-well microplate and incubated overnight. The cells were then added with the peptide HX-12C with a designated concentration gradient, and incubated for 68 h. Each well was added with 20 μL of a MTT solution (4 mg/mL), and incubated for another 4 h. After aspirating the culture medium, a formaldehyde crystal was dissolved using 100 μL of dimethyl sulfoxide (DMSO). An absorbance was determined at 570 nm using an ultraviolet-visible spectrophotometer. As shown in FIG. 2, half maximal inhibitory concentrations IC.sub.50 values of peptides HX-12A (FFRKVLKLIRKI, as shown in SEQ ID NO: 2), HX-12B (FFRKVLKLIRKIF, as shown in SEQ ID NO: 3) and HX-12C in ABCB1-overexpressing cancer cells (KB-C2) were 6.45 μM, 7.61 μM, and 6.06 μM, respectively. The IC.sub.50 values of these peptides in parental cells (KB-3-1) were 9.18 μM, 5.42 μM, and 7.53 μM, respectively (FIG. 2). These peptides would not produce significant cytotoxicity at a concentration lower than 3 μM, and were selected for the reversal study.

Example 3 Effect of Peptide HX-12C on ABCC1-Overexpressing Cell Line

(17) In order to determine an effect of the peptide HX-12C on the ABC transporter, a sensitivity of an ABCC1-overexpressing cell KB-CV60 to the peptide HX-12C was tested. Cytotoxicity of the peptide HX-12C in different cell lines was determined by MTT ((3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay, in which 5000 cells/well were seeded in a 96-well microplate and incubated overnight. The cells were then added with the peptide HX-12C with a designated concentration gradient, and incubated for 68 h. Each well was added with 20 μL of a MTT solution (4 mg/mL), and incubated for another 4 h. After aspirating the culture medium, a formaldehyde crystal was dissolved using 100 μL of dimethyl sulfoxide (DMSO). An absorbance was determined at 570 nm using an ultraviolet-visible spectrophotometer. As shown in Table. 1, half maximal inhibitory concentrations IC.sub.50 values of peptides HX-12A (FFRKVLKLIRKI, as shown in SEQ ID NO: 2), HX-12B (FFRKVLKLIRKIF, as shown in SEQ ID NO: 3) and HX-12C in ABCC1-overexpressing cancer cells (KB-C2) were 24.95 μM, 7.41 μM, and 6.38 μM, respectively. The IC.sub.50 values of these peptides in parental cells KB-CV60 were 20.55 mM, 5.16 μM, and 6.26 μM, respectively. These peptides would not produce significant cytotoxicity at a concentration lower than 3 μM, and were selected for the reversal study.

(18) TABLE-US-00001 TABLE 1 Cytotoxicity of peptides IC.sub.50 (RM) Treatment KB-3-1 KB-CV60 HX-12A 20.55 24.95 HX-12B 5.16 7.41 HX-12C 6.26 6.38 Vincristine 0.095 16.06 Cisplatin 2.29 2.96

Example 4 Investigation on Reversal Effect of Peptide HX-12C on Drug Resistance of ABCB1-Overexpressing Cell Line

(19) To determine whether the peptide HX-12C can reverse multi-drug resistance (MDR) mediated by ABCB1 transporter, the sensitivity of drug-induced resistant tumor cell line (KB-C2), the transfected ABCB1-overexpressing cell lines (HEK293/ABCB1) (Shi Z, Tiwari A K, Shukla S, et al. Sildenafil Reverses ABCB1- and ABCG2-Mediated Chemotherapeutic Drug Resistance[J]. Cancer Research, 2011, 71(8):3029-3041.) and their parental cell lines (KB-3-1 and HEK293/pcDNA3.1) to the peptide HX-12C were tested. The test results were shown in Tables. 2-3. Compared to the parental cell lines (KB-3-1 and HEK293/pcDNA3.1), the peptide HX-12C reduced the IC.sub.50 values of ABCB1 overexpressing cell lines (KB-C2 and HEK293/ABCB1) to paclitaxel and doxorubicin. In addition, compared to the corresponding parental cell lines (KB-3-1 and HEK293/pc DNA3.1), the peptide HX-12C did not change IC.sub.50 values of cisplatin (a non-substrate of ABCB1) in ABCB1-overexpressing cell lines (KB-C2 and HEK293/ABCB1) (Table. 4). These results showed that the peptide HX-12C can reverse the MDR of cancer cells mediated by ABCB1 overexpression, whereas the peptide HX-12A and the peptide HX-12B had no reversal effect under the same condition, although the peptide HX-12A and the peptide HX-12B only had 1 to 2 amino acids different with the peptide HX-12C.

(20) TABLE-US-00002 TABLE 2 Reversal effects of peptides on drug-induced ABCB1-overexpressing cancer cell lines IC50.sup.1 (μm) (RF.sup.2) Treatment KB-3-1 KB-C2 Paclitaxel  0.002 ± 0.0007 (1.00) 1.430 ± 0.241 (715.00) + HX-12A (3 μM)  0.005 ± 0.0004 (2.50) 1.389 ± 0.356 (694.50) + HX-12B (3 μM)  0.001 ± 0.0006 (1.50) 0.542 ± 0.097 (271.00) + HX-12C (3 μM)  0.003 ± 0.0007 (1.50) 0.031 ± 0.002*** (15.50) + Verapamil (3 μM)  0.001 ± 0.0002 (0.50) 0.030 ± 0.004*** (15.00) Doxorubicin 1.186 ± 0.279 (1.00) 69.79 ± 4.637 (58.84) + HX-12A (3 μM) 1.099 ± 0.169 (0.93) 65.41 ± 0.281 (55.15) + HX-12B (3 μM) 1.042 ± 0.211 (0.88) 40.21 ± 0.206 (33.90) + HX-12C (3 μM) 1.012 ± 0.060 (0.85) 1.454 ± 0.015*** (1.23) + Verapamil (3 μM) 0.897 ± 0.143 (0.76) 0.734 ± 0.165*** (0.62) Cisplatin 1.793 ± 0.476 (1.00) 2.025 ± 0.428 (1.13) + HX-12A (3 μM) 1.687 ± 0.398 (0.94) 2.503 ± 0.336 (1.40) + HX-12B (3 μM) 1.593 ± 0.512 (0.89) 2.096 ± 0.389 (1.17) + HX-12C (3 μM) 1.693 ± 0.452 (0.94) 2.087 ± 0.233 (1.16) + Verapamil (3 μM) 1.676 ± 0.478 (0.93) 2.107 ± 0.361 (1.18)

(21) TABLE-US-00003 TABLE 3 Reversal effects of peptides on transfected ABCB1-overexpressing cancer cell lines IC50.sup.1 (μm) (RF.sup.2) Treatment HEK293/pcDNA3.1 HEK293/ABCB1 Paclitaxel 1.449 ± 0.121 (1.00) 30.924 ± 4.665 (21.34) + HX-12A (3 μM) 1.405 ± 0.285 (0.97) 22.117 ± 1.199 (15.26) + HX-12B (3 μM) 1.302 ± 0.255 (0.90) 20.190 ± 1.047 (13.93) + HX-12C (3 μM) 1.446 ± 0.462 (1.00)   1.501 ± 0.342*** (1.04) + Verapamil (3 μM) 1.486 ± 0.377 (1.03)   1.708 ± 0.147*** (1.18) Doxorubicin 1.235 ± 0.571 (1.01) 31.233 ± 5.406 (25.29) + HX-12A (3 μM) 1.206 ± 0.405 (0.98) 25.327 ± 4.318 (20.51) + HX-12B (3 μM) 1.221 ± 0.488 (0.99) 22.374 ± 3.774 (18.12) + HX-12C (3 μM) 1.420 ± 0.453 (1.15)   1.182 ± 0.253*** (0.96) + Verapamil (3 μM) 1.271 ± 0.358 (1.03)   1.245 ± 0.265*** (1.00) Cisplatin 2.214 ± 0.541 (1.00) 2.665 ± 0.208 (1.20) + HX-12A (3 μM) 2.337 ± 0.438 (1.06) 2.525 ± 0.284 (1.14) + HX-12B (3 μM) 2.403 ± 0.389 (1.09) 2.692 ± 0.176 (1.22) + HX-12C (3 μM) 2.464 ± 0.144 (1.11) 2.184 ± 0.317 (0.99) + Verapamil (3 μM) 2.128 ± 0.238 (0.96) 2.287 ± 0.138 (1.03)

Example 5 Investigation on Reversal Effect of Peptide HX-12C on Drug Resistance of ABCC1-Overexpressing Cell Line

(22) To determine whether the peptide HX-12C can reverse multi-drug resistance (MDR) mediated by ABCC1 transporter, the sensitivity of drug-induced resistant tumor cell line (KB-CV60), the transfected ABCC1-overexpressing cell lines (HEK293/ABCC1) (Shi Z, Tiwari A K, Shukla S, et al. Sildenafil Reverses ABCB1- and ABCG2-Mediated Chemotherapeutic Drug Resistance[J]. Cancer Research, 2011, 71(8):3029-3041.) and their parental cell lines (KB-3-1 and HEK293/pcDNA3.1) to the peptide HX-12C were tested. The test results were shown in Tables. 4-5. Compared to the parental cell lines (KB-3-1 and HEK293/pcDNA3.1), the peptide HX-12C reduced the IC.sub.50 values of ABCB1 overexpressing cell lines (KB-CV60 and HEK293/ABCC1) to vincristine. In addition, compared to the corresponding parental cell lines (KB-3-1 and HEK293/pc DNA3.1), the peptide HX-12C did not change IC.sub.50 values of cisplatin (a non-substrate of ABCC1) in ABCC1-overexpressing cell lines (KB-CV60 and HEK293/ABCC1)(Table. 4). These results showed that the peptide HX-12C can reverse the MDR of cancer cells mediated by ABCC1 overexpression.

(23) TABLE-US-00004 TABLE 4 Reversal effects of peptides on drug-induced ABCC1-overexpressing cancer cell lines IC50 (μm) (RF.sup.1) Treatment KB-3-1 KB-CV60 Vincristine 0.095 (1.00) 16.06 (169.05) + HX-12C (3 μM) 0.168 (1.77) 0.254*** (2.67) + MK571 (5 μM) 0.164 (1.73) 0.232*** (2.27) Cisplatin 1.793 (1.00) 2.233 (1.25) + HX-12C (3 μM) 1.693 (0.94) 1.942 (1.08) + MK571(5 μM) 1.496 (0.83) 1.725 0.96)

(24) TABLE-US-00005 TABLE 5 Reversal effects of peptides on transfected ABCC1-overexpressing cancer cell lines IC.sub.50 (μm) (RF.sup.1) Treatment HEK293/pcDNA3.1 HEK293/ABCC1 Vincristine 0.137 (1.00) 2.710 (19.79) + HX-12C(3 μM) 0.143 (1.04) 0.149*** (1.09) + MK571 (5 μM) 0.140 (1.02) 0.138*** (1.01) Cisplatin 2.214 (1.00) 2.235(1.01) + HX-12C (3 μM) 2.464 (1.11) 2.176 (0.98) + MK571(5 μM) 2.201 (0.99) 2.456(1.11)

Example 6 Effect of Peptide HX-12C on Expression of ABCB1 Transporter

(25) Western blotting analysis was performed to determine whether the peptide HX-12C affected the expression of ABCB1 transporter. The KB-C2 and non-treated KB-3-1 cells were treated with 0, 1, 3 and 6 μM of the peptide HX-12C for 72 h, and then incubated with a lysis buffer (containing 2.5% 1M Tris, 0.15% EDTA, 1% sodium deoxycholate, 0.1% sodium dodecyl sulfate (SDS), 0.88% NaCl, 1% Triton-X and a protease inhibitor) on ice for 20 min, and centrifuged at 4° C. to collect a supernatant. A protein concentration of the supernatant was determined by bicinchoninic acid (BCA)-based protein assay. Each protein sample was loaded and separated by SDS-polyacrylamide gel electrophoresis. After that, the gel was transferred to a polyvinylidene fluoride (PVDF) membrane followed by blocking with 5% milk for 2 h. The PVDF membrane was then incubated with a primary antibody (1:1000 dilution for both anti-P-glycoprotein and anti-GAPDH antibodies) at 4° C. overnight. Then the PVDF membrane was washed with TBST (Tris buffer, 0.1% Tween 20) buffer, and incubated with secondary horseradish peroxidase (HRP)-labeled antibodies ((1:1000 dilution for an anti-mouse antibody). The signal was detected by enhanced chemiluminescence, and the protein expression was quantified by a software. As shown in FIGS. 3A and 3B, different concentrations (0, 1, 3, 6 μM) of the peptide HX-12C treatment had no significant effect on the expression of ABCB1 protein (172 kDa) in the over-expressing KB-C2 cell lines.

Example 7 Effect of Peptide HX-12C on Expression of ABCC1 Transporter

(26) Western blotting analysis was performed to determine whether the peptide HX-12C affected the expression of ABCC1 transporter. The KB-C2 and non-treated KB-CV60 cells were treated with 0, 1, 3 and 6 μM of the peptide HX-12C for 72 h, and then incubated with a lysis buffer (containing 2.5% 1M Tris, 0.15% EDTA, 1% sodium deoxycholate, 0.1% sodium dodecyl sulfate (SDS), 0.88% NaCl, 1% Triton-X and a protease inhibitor) on ice for 20 min, and centrifuged at 4° C. to collect a supernatant. A protein concentration of the supernatant was determined by bicinchoninic acid (BCA)-based protein assay. Each protein sample was loaded and separated by SDS-polyacrylamide gel electrophoresis. After that, the gel was transferred to a polyvinylidene fluoride (PVDF) membrane followed by blocking with 5% milk for 2 h. The PVDF membrane was then incubated with a primary antibody (1:1000 dilution for both anti-P-glycoprotein and anti-GAPDH antibodies) at 4° C. overnight. Then the PVDF membrane was washed with TBST (Tris buffer, 0.1% Tween 20) buffer, and incubated with secondary horseradish peroxidase (HRP)-labeled antibodies ((1:1000 dilution for an anti-mouse antibody). The signal was detected by enhanced chemiluminescence, and the protein expression was quantified by a software. As shown in FIGS. 4A and 4B, different concentrations (0, 1, 3, 6 μM) of the peptide HX-12C treatment had no significant effect on the expression of ABCC1 protein (190 kDa) in the over-expressing KB-CV60 cell lines.

Example 8 Effect of Peptide HX-12C on Expression Level and Cell Localization OF ABCB1

(27) In order to further confirm whether the peptide HX-12C affected the expression and cell localization of the ABCB1 protein, immunofluorescence staining was performed after treating the cells after different incubation times of the peptide HX-12C. The KB-3-1 and KB-C2 cells were seeded in 24-well plates (1×10.sup.4 cells/well), and incubated at 37° C. for 24 h. The cells were then incubated with 3 μM of the peptide HX-12C for 0, 24, 48 and 72 h, respectively, washed twice with a cold phosphate buffer saline (PBS) solution, fixed in 4% formaldehyde for 15 min and permeablized with 0.25% Triton X-100 for 15 min. After being incubated with BSA (6% in PBS) for 1 h, the cells were incubated with monoclonal anti-Pglycoprotein Clone F4 primary antibody with a dilution of 1:1000 at 4° C. overnight, and then further incubated with Alexa Fluor 488 conjugated rabbit anti-mouse IgG secondary antibody with dilution of 1:1000 for 1 h in the dark. The nuclei were counterstained with 4′,6-diamidino-2-phenylindole (DAPI) and observed with a fluorescence microscope. As shown in FIG. 5, compared to the parental cells KB-3-1, the ABCB1 protein was significantly expressed on the membrane of KB-C2 cells. The fluorescent intensity of ABCB1 protein in KB-C2 remained unchanged after the treatment of peptide HX-12C, which was consistent with the result of Western blot analysis. In addition, the peptide HX-12C had no significant effect on the subcellular distribution pattern of ABCB1 protein on the membrane of KB-C2 cells. These results showed that the reversal of MDR by the peptide HX-12C was not caused by decreasing the protein expression or change the protein location.

Example 9 Effect of Peptide HX-12C on Expression Level and Cellular Localization ABCC1

(28) In order to further confirm whether the peptide HX-12C affected the expression and cell localization of the ABCC1 protein, immunofluorescence staining was performed after treating the cells after different incubation times of the peptide HX-12C. The KB-CV60 and KB-C2 cells were seeded in 24-well plates (1×10.sup.4 cells/well), and incubated at 37° C. for 24 h. The cells were then incubated with 3 μM of the peptide HX-12C for 0, 24, 48 and 72 h, respectively, washed twice with a cold phosphate buffer saline (PBS) solution, fixed in 4% formaldehyde for 15 min and permeablized with 0.25% Triton X-100 for 15 min. After being incubated with BSA (6% in PBS) for 1 h, the cells were incubated with monoclonal anti-Pglycoprotein Clone F4 primary antibody with a dilution of 1:1000 at 4° C. overnight, and then further incubated with Alexa Fluor 488 conjugated rabbit anti-mouse IgG secondary antibody with dilution of 1:1000 for 1 h in the dark. The nuclei were counterstained with 4′,6-diamidino-2-phenylindole (DAPI) and observed with a fluorescence microscope. As shown in FIG. 6, compared to the parental cells KB-3-1, the ABCC1 protein was significantly expressed on the membrane of KB-C2 cells. The fluorescent intensity of ABCC1 protein in KB-CV60 remained unchanged after the treatment of peptide HX-12C, which was consistent with the result of Western blot analysis. In addition, the peptide HX-12C had no significant effect on the subcellular distribution pattern of ABCC1 protein on the membrane of KB-CV60 cells. These results showed that the reversal of MDR by the peptide HX-12C was not caused by decreasing the protein expression or change the protein location.

Example 10 Effect of Peptide HX-12C on Accumulation and Efflux of [.SUP.3.H]-Paclitaxel

(29) The effect of the peptide HX-12C on accumulation and efflux of [.sup.3H]-paclitaxel in the ABCB1-overexpressing cells was determined by comparing the concentrations of [.sup.3H]-paclitaxel in the KB-3-1 cells and the KB-C2 cells. The KB-3-1 and KB-C2 cells were seeded in a 24-well plate (1×10.sup.4 cells/well) and incubated at 37° C. for 24 h. The cells were incubated for 72 h in the presence or absence of the peptide HX-12C and the positive reversal agent verapamil, and the medium was then replaced by a medium containing 5 μM of [.sup.3H]-paclitaxel and the peptide HX-12C or the positive reversal agent. After a 2-hour incubation, the medium was removed, and the cells were washed with ice-cold PBS three times and transferred to a scintillation fluid after lysis. A drug efflux analysis was performed, the operation was similar to the cumulative analysis. After discarding the medium containing [.sup.3H]-paclitaxel, the cells were washed with ice-cold PBS and incubated with a medium containing the peptide HX-12C or the positive reversal agent. Samples were taken at 30, 60, and 120 minutes. The cells were washed three times followed by lysis, and then transferred to the scintillation fluid. The radioactivity was measured with a liquid scintillation analyzer. The results were shown in FIG. 7A. After the 2-h incubation, the intracellular [.sup.3H]-paclitaxel in in ABCB1-overexpressing cells KB-C2 was about 100 times that of the parent cells KB-3-1. Compared with the control group, the intracellular concentration of [.sup.3H]-paclitaxel in the KB-C2 cells was significantly increased with the peptide HX-12C (3 μM) treatment, and the effect of the peptide HX-12C (3 μM) on the accumulation of [.sup.3H]-paclitaxel was comparable to that of the ABCB1 inhibitor verapamil (3 In addition, the effect of peptide HX-12C on the efflux of [.sup.3H]-paclitaxel in ABCB1-overexpressing KB-C2 cells was evaluated, and the results were shown in FIG. 7B. After the 2-hour incubation, the intracellular [.sup.3H]-paclitaxel level in KB-3-1 cells did not change significantly, and the inhibitor verapamil did not change the efflux function of KB-3-1 cells. However, the level of intracellular [.sup.3H]-paclitaxel in KB-C2 cells without inhibitor treatment was significantly decreased by about 50%. It was demonstrated that the peptide HX-12C (3 μM) can effectively inhibit the efflux function of KB-C2 cells.

Example 11 Effect of Peptide HX-12C on the Accumulation and Efflux of [.SUP.3.H]-Vincristine

(30) The effect of the peptide HX-12C on accumulation and efflux of [.sup.3H]-vincristine in the ABCC1-overexpressing cells was determined by comparing the concentrations of [.sup.3H]-vincristine in the KB-3-1 cells and the KB-CV60 cells. The KB-3-1 and KB-CV60 cells were seeded in a 24-well plate (1×10.sup.4 cells/well) and incubated at 37° C. for 24 h. The cells were incubated for 72 h in the presence or absence of the peptide HX-12C and the positive reversal agent MK571, and the medium was then replaced by a medium containing 5 μM of [.sup.3H]-vincristine and the peptide HX-12C or the positive reversal agent. After a 2-hour incubation, the medium was removed, and the cells were washed with ice-cold PBS three times and transferred to a scintillation fluid after lysis. A drug efflux analysis was performed, the operation was similar to the cumulative analysis. After discarding the medium containing [.sup.3H]-vincristine, the cells were washed with ice-cold PBS and incubated with a medium containing the peptide HX-12C or the positive reversal agent. Samples were taken at 30, 60, and 120 minutes. The cells were washed three times followed by lysis, and then transferred to the scintillation fluid. The radioactivity was measured with a liquid scintillation analyzer. The results were shown in FIG. 8A. After the 2-h incubation, the intracellular [.sup.3H]-vincristine in in ABCC1-overexpressing cells KB-CV60 was about seven times that of the parent cells KB-3-1. Compared with the control group, the intracellular concentration of [.sup.3H]-vincristine in the KB-CV60 cells was significantly increased with the peptide HX-12C (3 μM) treatment, and the effect of the peptide HX-12C (3 μM) on the accumulation of [.sup.3H]-vincristine was comparable to that of the ABCC1 inhibitor MK571 (5 In addition, the effect of peptide HX-12C on the efflux of [.sup.3H]-vincristine in ABCC1-overexpressing KB-CV60 cells was evaluated, and the results were shown in FIG. 8B. After the 2-hour incubation, the intracellular [.sup.3H]-vincristine level in KB-3-1 cells decreased by 25%, and the intracellular [.sup.3H]-vincristine level in KB-CV60 cells without inhibitor treatment was significantly decreased by about 70%. The intracellular [.sup.3H]-vincristine level in KB-CV60 cells treated with the peptide HX-12C (3 μM) decreased by 58%, which was equivalent to the effect of the inhibitor MK571. It was demonstrated that the peptide HX-12C (3 μM) can effectively inhibit the efflux function of KB-CV60 cells.

Example 12 Effect of Peptide HX-12C on ABCB1 Transporter ATPase Activity

(31) The hydrolysis of ATP mediated by ABCB1 in the presence of different concentrations (0-40 μM) of the peptide HX-12C was measured to evaluate the effect of peptide HX-12C on ABCB1 ATPase activity. Membrane vesicles (10 μg of protein) were incubated in ATPase buffer at 37° C. for 5 min with or without 0.3 mM of vanadate, and then added with the peptide HX-12C at a concentration of 0 to 40 μM and the buffer and incubated at 37° C. for 3 min. After adding 5 mM of Mg-ATP with a total volume of 0.1 mL, an ATPase reaction was initiated until stopped by adding 100 μL of 5% SDS solution after incubation at 37° C. for 20 min. The ATPase activity of ABCB1 was calculated according to the amount of released inorganic phosphorus (IP) detected at 800 nm using a spectrophotometer. The results were shown in FIG. 9. The peptide HX-12C stimulated the ATPase activity of ABCB1 in a concentration-dependent manner, and the maximum stimulation amount is 4.7 times the basic activity. The concentration of peptide HX-12C required for 50% stimulation of ATPase activity of ABCB1 was 0.65 μM, which was much lower than the cytotoxic concentration. These results showed that the peptide HX-12C may interact with drug-substrate binding sites and affect the ATPase activity of ABCB1.

Example 13 Analysis of Peptide HX-12C-ABCB1 Binding by Molecular Docking

(32) Molecular docking was performed to obtain a potential binding mode and rationalize the observation effect of the peptide HX-12C. The peptide HX-12C was depicted using Sybyl/Sketch module (Tripos Inc., USA), and optimized by the Powell method. The convergence parameter was set at 0.05 kcal/(Amol), and assigned by the Gasteiger-Hsckel method. The crystal structure of ABCB1 was obtained from the RCSB Protein Data Bank protein database (PDB-ID: 4M2T). The peptide HX-12C was docked into the active site of ABCB1. Tripos force field and Pullman charge was used to remove the ligand, and add hydrogen and minimize the hydrogen. Other docking parameters remained default values. The results were shown in FIG. 10. The peptide HX-12C tightly bonded to the active site (substrate binding site) of ABCB1. The peptide HX-12C formed eight hydrogen bonds with residues E180, A225, L335, G342, G985, Q986 and S989 in ABCB1, which may improve the binding affinity of the peptide HX-12C to ABCB1. It should be noted that the salt bridge containing arginine in the peptide HX-12C and E180 in ABCB1 may help to improve the binding affinity. In addition, the peptide HX-12C was in hydrophobic contact with residues such as F299, F990, L232 and 1302 in ABCB1.

Example 14 Analysis of Peptide HX-12C-ABCC1 Binding by Molecular Docking

(33) Molecular docking was performed to obtain a potential binding mode and rationalize the observation effect of the peptide HX-12C. The peptide HX-12C was depicted using Sybyl/Sketch module (Tripos Inc., USA), and optimized by the Powell method. The convergence parameter was set at 0.05 kcal/(Amol), and assigned by the Gasteiger-Hsckel method. The crystal structure of ABCC1 was obtained from the RCSB Protein Data Bank protein database (PDB-ID: 4M2T). The peptide HX-12C was docked into the active site of ABCC1. Tripos force field and Pullman charge was used to remove the ligand, and add hydrogen and minimize the hydrogen. Other docking parameters remained default values. The results were shown in FIG. 11. The peptide HX-12C bonded tightly to the nucleotide-binding domains (NBD) region of ABCC1. The peptide HX-12C can form hydrogen bonds with QS656, D657, T660 and E694. Phenylalanine in the structure was also an important part for maintaining the binding force that the phenylalanine hydrophobically interacted with the surrounding Y710, P712 and W716, and formed π-π stacking due to an overlap with the pyrrole ring in W716. In addition, the arginine can form a hydrogen bond with D657 and a salt bridge, greatly enhancing the binding affinity.