To evaluate whether CD147 expression affects cancer cell proliferation, we used 3 human cancer cell lines with different CD147 expression levels. Using real-time PCR and Western blot assays, we confirmed that CD147 was relatively highly expressed in U-87 cells, moderately expressed in A-431 cells, and poorly expressed in SK-BR-3 cells at both the mRNA and protein levels (Figure 1A and 1B). Interestingly, using a WST-1 assay, we found that U-87 cells exhibited the highest proliferative activity. Within 24 hours, the level of proliferation by U-87 cells was 60%, that of A-431 cells was 40% and that of SK-BR-3 cells was 20%. Thus, there is a possibility that in these tumor cells, higher CD147 expression causes stronger proliferative activity (Figure 1C). To further test this finding, a parallel test was performed using two other lung cancer cell lines: NCI-H460 (460) and NCI-H1299 (1299). A previous study demonstrated that CD147 exhibits higher expression levels in 460 cells than in 1299 cells. Using WST-1 assays, we also verified that the viability of 460 cells was much greater than that of 1,299 cells under intervention with cisplatin, a broad-spectrum antineoplastic drug (Figure 1D). Furthermore, we altered the expression level of CD147 in each lung cancer cell line and compared proliferation (Figure 1E). As shown in Figure 1F and 1G, using the same drugs (cisplatin), we observed that proliferation was reduced in NCI-H460 cells, in which CD147 was knocked down (460 CD147-), but was increased in NCI-H1299 cells, where CD147 was overexpressed (1299 CD147+). In summary, we showed a positive correlation between CD147 expression and tumor cell proliferation.
Figure 1. Positive correlation between the level of CD147 expression and cancer cell viability. (A) Expression of CD147 in various cancer cell lines at the protein level; (B) Expression of CD147 in various cancer cell lines at the mRNA level. (C) Proliferation of cell lines as measured by WST-1 assays; (D) Inhibitory effects of antitumor drugs on cell viability in NCI-H460 and NCI-H1299 cells; (E) Changes in the expression level of CD147 in each lung cancer cell line; (F and G) Effect of drugs on cell viability with changes in the expression level of CD147 in each lung cancer cell line measured by aWST-1 assay. All the bars represent the mean of three measurements for each sample, and the error bars indicate ± SD. ***P < 0.001, **P < 0.01, Student’s t-test.
Our previous work identified a novel compound (AC-73) that could significantly inhibit cancer invasion in HCC by targeting CD147. However, AC-73 barely reduced cancer cell proliferation at certain concentrations. Therefore, we synthesized another compound, HA-08 (Figure 2A), based on the structure of AC-73. To evaluate whether HA-08 is more active than AC-3, a WST-1 assay was performed to assess their tumor inhibitory activity. HA-08 exhibited better anticancer properties than AC-73 on Huh-7 cells treated with the same concentration (Figure 2B). A Western blot assay was used to examine the effects of both compounds on the expression of proliferation- and apoptosis-related proteins in Huh-7 cells. As shown in Figure 2C, we observed that HA-08 had a greater effect on the expression of ERK1/2, Bcl-2, and Bak than AC-73. In fact, HA-08 also exerted greater cytotoxicity on other cancer cell lines (Figure 2D-2J). These results suggested that, compared with AC-73, the new compound, HA-08, was better in terms of tumor suppressor activity and promoting apoptosis.
Figure 2. HA-08 exhibits better antitumor activity than AC-73. (A) Substituent structure of HA-08; (B, D-J) Differences in cell viability under exposure to AC-73 and HA-08 measured by WST-1 assays; (C) Effects of both compounds on the expression of proliferation- and apoptosis-related proteins in cancer cells as measured by Western blot assays. All the bars represent the mean of three measurements of each sample, and the error bars indicate ± SD. ***P < 0.001, **P < 0.01, *P < 0.05, one-way ANOVA (H) for multiple comparisons.
We next assessed the effect of HA-08 on cell viability in human cancer cell lines other than HCC. As shown in Table 1, ten cancer cell lines in total were treated with HA-08 for 48 h and then subjected to a WST-1 assay. The anticancer activity of HA-08 was quantified by determining the IC50 values, which were found to be in the micromolar range. In general, HA-08 could effectively reduce the viability of many types of human cancer cells (breast cancer cell lines, non-small cell lung cancer (NSCLC) cell lines, pancreatic cancer cell lines and colorectal cancer cell lines), but not Chinese hamster ovary (CHO) cells. Specifically, MDA-MB-231, NCI-H460, and A549 cells appeared to have relatively high sensitivity to HA-08, with IC50 values below 30 μmol/L. Huh-7, NCI-H1299, NCI-H292, and MIA-PaCa-2 cells had relatively moderate sensitivity to HA-08, with IC50 values between 30 μmol/L and 50 μmol/L. MCF-7 and HCT-8 cells had relatively low sensitivity to HA-08, with IC50 values from 60 μmol/L to 100 μmol/L. Finally, the CHO cell line was essentially resistant to HA-08 (IC50 > 100 μmol/L). From these results, we can conclude that compared to AC-73, HA-08 is more cytotoxic to human malignant cell lines but less cytotoxic to normal cells.
Characteristics Cell lines Cell type IC50 (μmol/L) 95% confidence intervals Relatively high sensitivity
(IC50 < 30 μmol/L)
MDA-MB-231 Breast, metastatic-pleural,invasive ductal carcinoma 26.47 ± 1.04 NCI-H460 Large cell lung cancer 21.08 ± 1.06 A549 Non-small cell lung cancer 29.57 ± 1.1 Relatively Moderate sensitivity
(30 < IC50 < 50 μmol/L)
Huh7 Hepatocellular carcinoma 36.19 ± 1.05 NCI-H1299 Non-small cell lung cancer 37.62 ± 1.04 NCI-H292 Non-small cell lung cancer 42.13 ± 1.04 MIA PaCa-2 Pancreatic carcinoma 42.43 ± 1.02 Relatively Low sensitivity
(60 < IC50 < 100 μmol/L)
MCF7 Breast, metastatic-pleural, invasive ductal carcinoma 60.50 ± 2.31 HCT116 Colorectal carcinoma 67.57 ± 0.33 Resistant
(IC50 > 100 μmol/L)
CHO Cells from the ovaries of Chinese hamsters > 100
Table 1. Characteristics of cell lines screened by HA-08
To determine whether HA-08 induces malignant cell death, we chose two cancer cell lines, MDA-MB-231 and NCI-H1299, which exhibited relatively high sensitivity and moderate sensitivity to HA-08, respectively. The number of apoptotic cells after treatment with HA-08 was determined by positive annexin V staining, marks phosphatidylserines on the surface of apoptotic cells (Figure 3A-3D). We observed that both cancer cell lines underwent apoptosis after exposure to HA-08 in a dose-dependent manner, although higher concentrations were required for NCI-H1299 cells than for MDA-MB-231 cells. To determine whether caspases are involved in HA-08-induced apoptosis, we measured the level of apoptosis with or without the caspase inhibitor Z-VAD-FMK (ZVAD) in A549 cells, which have relatively high sensitivity to HA-08. The results indicated that ZVAD significantly reduced the degree of HA-08-induced apoptosis (Figure 3E and 3F), suggesting that HA-08 induces apoptosis mainly through a caspase-dependent pathway. However, some contribution by a caspase-independent pathway cannot be excluded.
Figure 3. Effects of HA-08 on apoptosis determined by FACS analysis. Cells were left untreated or were treated with HA-08, and apoptosis was evaluated by FACS analysis after double cell labeling with propidium iodide (PI) and annexin V-FITC. (A) HA-08 (0, 15, 30 μmol/L) induces apoptosis in MDA-MB-231 cells; (B) Quantitative analysis of % annexin V-positive cells; (C) HA-08 (0, 40, 60 μmol/L) induces apoptosis in NCI-H1299 cells; (D) Quantitative analysis of % annexin V-positive cells; (E) Effect of HA-08 and ZVAD on apoptosis in A549 cells; (F) Quantitative analysis of % annexin V-positive cells. All the bars represent the mean of three measurements of each sample, and the error bars indicate ± SD. ***P < 0.001, **P < 0.01, *P < 0.05, one-way ANOVA (H) for multiple comparisons (B, D, and E).
Next, we morphologically characterized apoptotic cells in two lung cancer cell lines using Hoechst 33258 staining. A549 and NCI-H1299 cells were treated with or without HA-08 and their nuclei were stained with Hoechst 33258 to detect apoptotic morphology. In the control groups, the nuclei of both cell types had regular, round contours. In contrast, the nuclei of cells treated with HA-08 appeared to undergo chromatin condensation and nuclear fragmentation in a dose-dependent manner, both of which are typical hallmarks of apoptosis (Figure 4A). In addition, changes in the mitochondrial membrane potential of three different malignant cell lines were detected using JC-1 staining. JC-1 molecules localize to the mitochondrial matrix in the cytosol and form J-aggregates in nonapoptotic cells, which emit orange fluorescence. In apoptotic cells, JC-1 molecules exist in a monomeric form, and the cytosol emits green fluorescence. In Figure 4B, we observed that with JC-1 staining, the cytosolic emission transitioned from orange to green with increasing concentrations of HA-08. Interestingly, the three cell lines did not show a significantly different sensitivity to HA-08, and HCT-8 cells showed relatively low sensitivity to HA-08-induced inhibition of cell viability. This indicated that HA-08 increases cancer cell apoptosis by destroying the permeability of mitochondrial membranes and altering their potential.
Figure 4. Effects of HA-08 on apoptosis based on morphological and molecular expression changes. (A) Morphological changes in the nuclei (typical of apoptosis) of lung cancer cell lines treated with HA-08 at various concentrations and stained with Hoechst 33258. Selected fields exhibiting condensed chromatin (yellow arrowhead) indicating the occurrence of cell apoptosis are shown. Each inset shows images at 100× magnification, scale bars: 100 μm; (B) Collapse of the mitochondrial membrane potential of three cancer cell lines treated with 0, 15, or 30 μmol/L HA-08 and stained with JC-1. Selected fields containing the corresponding live cells (orange-red) and apoptotic cells (green). Each inset shows images obtained at 100× magnification, scale bars: 100 μm; (C) Western blot to determine the expression of apoptosis-related proteins in two lung cancer cell lines treated with different concentrations of HA-08.
Next, we determined the expression levels of apoptosis-regulating proteins in both A549 and NCI-H460 cells after exposure to HA-08 (0, 10, 20, or 30 μmol/L). These results showed that HA-08 significantly reduces expression of Bcl-2 and Bcl-xL, which are antiapoptotic molecules. Moreover, the expression of BAK, which is part of a family of proapoptotic factors, was increased after HA-08 treatment. Furthermore, we found that poly (ADP-ribose) polymerase (CLE-PARP) cleavage was activated by HA-08 in a dose-dependent manner, which is a sign of cell apoptosis (Figure 4C). Taken together, our results suggested that HA-08 plays a vital role in promoting cancer cell apoptosis.
In addition to results from in vitro assays, we examined whether HA-08 could inhibit tumor growth in xenografts in nude mice. A549 cells were prepared and injected into the right back side of nude mice. After cell injection, the mice were randomly divided into 5 groups and given different concentrations of HA-08. The weight of the mice was continuously monitored for 4 weeks; the mice were then sacrificed, and the subcutaneous transplanted tumors appeared to be striped, as shown in Figure 5A and 5B. We observed that HA-08 not only prevented tumor growth but also induced tumor death in a dose-dependent manner, based on calculations of tumor size, especially when the concentration of HA-08 reached 60 mg/kg (Figure 5C, 5D, and 5F). We found that over 4 weeks, the HA-08-treated groups generally exhibited a good condition, with a weight loss of less than 10% that of the control group, even in the final group, which consisted of normal nude mice without xenografts treated with 60 mg/kg HA-08 (Figure 5E). This indicated that the HA-08 treatment resulted in no major toxicity or harm to the animals. Therefore, we suggest that HA-08 has potential therapeutic effects on the prevention of tumor growth.
Figure 5. HA-08 inhibits A549 cell tumorigenesis in a xenograft model. Tumor-bearing mice were treated intravenously with the vehicle or HA-08 (10, 40, and 60 mg/kg). (A and B) Gross anatomy of nude mice and exfoliated tumor tissue; (C and D) Tumor size; (E) Body weight; (F) Tumor weight. Data are presented as the mean ± SD.
In the final part of this study, we explored possible molecular signaling mechanisms of HA-08. As a candidate compound, HA-08 was first evaluated to be a protein-protein interaction inhibitor. Using a co-ip assay, we detected whether HA-08 could affect the interaction of CD147-HOOK1, CD147-RAP2, CD147-MCT4, and CD147-CD44, pairs of membrane proteins have been reported to clearly interact, initiating downstream signaling pathways, and are involved various biological process of cancer[21-24]. The results showed that HA-08 barely affected the interaction of CD147-HOOK1, CD147-RAP2, and CD147-MCT4. However, HA-08 did disrupt the interaction of CD147 and CD44 in a dose dependent manner (Figure 6A and 6B). To further verify how HA-08 affects the interaction between the two proteins, immunofluorescence staining was performed. As shown in Figure 6C, we noticed that co-localization of CD147 and CD44 on cancer cell membrane was significantly disrupted with the exposure of HA-08 (10 μmol/L) compared to the control group (HA-08 0 μmol/L). Based on the above, we speculated that HA-08 inhibited the downstream signal pathways activated by the interaction between CD147 and CD44 through affecting their co-localization on the cancer cell membrane, thereby preventing their interaction. Next, we wondered which downstream signaling pathway of CD147-CD44 was mainly affected by HA-08. Our previous results indicated that HA-08 could be involved cancer apoptosis, including changing the expression of apoptosis-related molecules, such as the Bcl family (Bcl-2, Bcl-xl). It has also been reported that CD147, interacting with CD44s, plays a critical role in the development of cancer, with high co-expression of CD147-CD44 being associated with grave apoptosis resistance and poor patient survival[24,25]. In addition, as an important transcription factor in cancer cells, STAT3, a downstream molecule of CD147-CD44, is known to participate in tumor cell apoptosis, when activated under the regulation of JAK. Therefore, we hypothesized that HA-08 induced cancer apoptosis by disrupting CD147-CD44 interaction and reducing downstream JAK/STAT3/Bcl-2 signaling. Using western blot assays, we detected the expression of signaling molecules in A549 cells with or without HA-08 (Figure 6D and 6E). HA-08 was found not to change the protein expression of JAK and STAT3. However, the phosphorylation of JAK and STAT3 was suppressed in a dose dependent manner after treatment with HA-08 for 6 hrs. Further, through examination of tissue pathology in original orthotopic tumors, we found that HA-08 inhibited Bcl-2 expression through down-regulating the phosphorylation of JAK and STAT3 in a dose dependent manner (Figure 6F and 6G), suggesting that HA-08 suppresses the JAK/STAT3/Bcl-2 pathway in vivo. To sum up, HA-08 induced cancer apoptosis mainly by disrupting CD147-CD44 interaction and reducing downstream JAK/STAT3/Bcl-2 signaling.
Figure 6. Molecular mechanism of action of HA-08 in cancer cells. (A) Representative image of Co-IP analysis between CD147 and related proteins. HA-08 blocks CD147-CD44 interaction. (B) Quantification of protein expression by densitometry analysis. (C) Co-localization of CD147 and CD44 in A549 cells. Cells (5 × 105) were grown on coverslips for 24 h, fixed, and stained with Dylight488-conjugated goat-anti-mouse antibodies (CD147, green) and Dylight594-conjugated goat-anti-rabbit antibodies (CD44, red; Pearson’s coefficients are indicated as numerical data to the right of each panel, n = 3). Bar, 20 μm. (D, E) Bcl-2, Bcl-xl, JAK, and STAT3 activities and total JAK and STAT3 expression in A549 cells treated with different concentrations of HA-08. (F, G) Phosphorylation of JAK and STAT3 in total lysates of original orthotopic tumors from each group. The histogram shows quantification of the gray scale analysis from western blotting. All the Histograms show quantification of the gray scale analysis from western blotting. The bars represent the mean of each sample measured in triplicate and the error bars indicate ± SD. (***P < 0.001, **P < 0.01), one-way ANOVA (H) for multiple comparisons.
Synthesis and Evaluation of a Novel Small-molecule Compound as an Anticancer Inhibitor of CD147
- Received Date: 2019-06-04
- Accepted Date: 2019-07-25
|Citation:||FU Zhi Guang, WANG Yan, WANG Shuang, SHAO Dan, TIAN Li, LI Yun Xia, JIANG Jian Li, CHEN Zhi Nan, WEN Ning. Synthesis and Evaluation of a Novel Small-molecule Compound as an Anticancer Inhibitor of CD147[J]. Biomedical and Environmental Sciences, 2019, 32(9): 673-686. doi: 10.3967/bes2019.086|