The mechanisms of somatostatin induced enhanced chemosensitivity of gallbladder cancer cell line to doxorubicin: cell cycle modulation plus target enzyme up-regulation. Biomed Pharmacother. 2010;64:451-457. [PMID: 20359855 DOI: 10.1016/j.biopha.2010.01.010]

Update on Chemoresistance Mechanisms to First-Line Chemotherapy for Gallbladder Cancer and Potential Reversal Strategies

OBJECTIVE

Gallbladder cancer (GBC) mortality remains high and chemoresistance is increasing. This review consolidates what is known about the mechanisms of chemoresistance to inform and accelerate the development of novel GBC-specific chemotherapies.

METHODS

Studies related to GBC-related chemoresistance were systematically screened in PubMed using the advanced search function. Search terms included GBC, chemotherapy, and signaling pathway.

RESULTS

Analysis of existing studies showed that GBC has poor sensitivity to cisplatin, gemcitabine (GEM), and 5-fluorouracil. DNA damage repair-related proteins, including CHK1, V-SCR, and H2AX, are involved in tumor adaptation to drugs. GBC-specific chemoresistance is often accompanied by changes in the apoptosis and autophagy-related molecules, BCL-2, CRT, and GBCDRlnc1. CD44 + and CD133 + GBC cells are less resistant to GEM, indicating that tumor stem cells are also involved in chemoresistance. In addition, glucose metabolism, fat synthesis, and glutathione metabolism can influence the development of drug resistance. Finally, chemosensitizers such as lovastatin, tamoxifen, chloroquine, and verapamil are able improve the therapeutic effect of cisplatin or GEM in GBC.

CONCLUSIONS

This review summarizes recent experimental and clinical studies of the molecular mechanisms of chemoresistance, including autophagy, DNA damage, tumor stem cells, mitochondrial function, and metabolism, in GBC. Information on potential chemosensitizers is also discussed. The proposed strategies to reverse chemoresistance should inform the clinical use of chemosensitizers and gene-based targeted therapy for this disease.

Background autofluorescence induced by plant extracts in human lymphocytes: A flow cytometric analysis of a critical bias

The presence of background autofluorescence sources is considered as an important problem when performing fluorometric methods, due to the possible spectral overlap between it and the fluorescence emission of probes. Regarding that, we evaluated the presence of background autofluorescence in human lymphocytes after the treatment with extracts from three medicinal plants, including ethanolic extract from aerial parts of Ageratum fastigiatum, ethanolic extract from aerial parts of Eriosema campestre and the ethanolic extract from stem of Pseudobrickellia brasiliensis. Human peripheral blood mononuclear cells were treated with each extract in vitro during 24 h, followed by flow cytometric analysis. Additionally, the fluorescence emission of plant extracts was evaluated by fluorometry, using the same concentrations used in cell cultures. We identified that plant extracts treatment on lymphocytes induced background autofluorescence detectable in several wavelength ranges. Isolated extracts showed no expressive fluorescence emission in fluorometric analyses, suggesting that background autofluorescence was induced in lymphocytes by interactions between cellular components and extracts compounds. Here we discuss the importance to perform previous tests to evaluate a possible background autofluorescence induction after cell treatments with plant extracts or any other substance. In spite of being mandatory, background autofluorescence analysis of cells after treatments and stimulations is still underestimated on literature. In summary, following the precautions herein established should help to reduce the incidence of false positive results.

Effect of bixin on DNA damage and cell death induced by doxorubicin in HL60 cell line

Bixin is a natural red pigment extracted from annatto. Although it is widely used as a coloring agent in food, there are few studies about the effect of this carotenoid on DNA. This study aimed to investigate the effects of bixin on cytotoxicity and genotoxicity induced by doxorubicin in HL60 cells. At concentrations above 0.3 μg/mL, bixin demonstrated cytotoxic effects in HL60 cells. Furthermore, this carotenoid was neither mutagenic nor genotoxic to HL60 cells and reduced the DNA damage induced by doxorubicin. Bixin and doxorubicin showed no apoptotic effect in HL60 cells, but the simultaneous combined treatments showed an increase in the percentage of apoptotic cells. In conclusion, our results showed that bixin modulates the cytotoxicity of doxorubicin via induction of apoptosis. The results of this study provide more knowledge about the toxic effects of anticancer treatments and how the natural compounds can be useful on these therapeutic approaches.

Differential expression of somatostatin receptor subtypes in gastric cancer

AIM: To examine the expression of somatostatin receptor subtypes (SSTRs), including SSTR1, SSTR2, SSTR3, SSTR4 and SSTR5, in gastric cancer and to analyze their relationship with clinical and pathological characteristics.

METHODS: The expression of SSTRs in 58 gastric cancer specimens and adjacent normal stomach tissue specimens were examined by immunohistochemical staining. Correlations between SSTR expression and clinical and pathological parameters were analyzed by the chi-square test.

RESULTS: All five SSTR subtypes were expressed in gastric cancer tissues, with SSTR3 having the highest expression. SSTR5 expression increased significantly in gastric cancer compared with that in normal gastric tissue (P < 0.05). SSTR4 expression was significantly lower in gastric cancer with lymph node metastasis than in gastric cancer without lymph node metastasis (P < 0.05). SSTR3 expression in highly and moderately differentiated gastric cancer was significantly higher than that in poorly differentiated gastric cancer (P < 0.05). SSTR2 was lowly expressed in each group; SSTR1 expression was higher than SSTR5 expression in normal stomach tissue, but was lower in gastric cancer tissue.

CONCLUSION: Our results indicated that SSRT5, SSTR3 and SSTR4 may play important roles in the development of gastric cancer.

Trypan blue exclusion assay by flow cytometry

Dye exclusion tests are used to determine the number of live and dead cells. These assays are based on the principle that intact plasma membranes in live cells exclude specific dyes, whereas dead cells do not. Although widely used, the trypan blue (TB) exclusion assay has limitations. The dye can be incorporated by live cells after a short exposure time, and personal reliability, related to the expertise of the analyst, can affect the results. We propose an alternative assay for evaluating cell viability that combines the TB exclusion test and the high sensitivity of the flow cytometry technique. Previous studies have demonstrated the ability of TB to emit fluorescence when complexed with proteins. According to our results, TB/bovine serum albumin and TB/cytoplasmic protein complexes emit fluorescence at 660 nm, which is detectable by flow cytometry using a 650-nm low-pass band filter. TB at 0.002% (w/v) was defined as the optimum concentration for distinguishing unstained living cells from fluorescent dead cells, and fluorescence emission was stable for 30 min after cell treatment. Although previous studies have shown that TB promotes green fluorescence quenching, TB at 0.002% did not interfere with green fluorescence in human live T-cells stained with anti-CD3/fluorescein isothiocyanate (FITC) monoclonal antibody. We observed a high correlation between the percentage of propidium iodide+CD3/FITC⁺ and TB+CD3/FITC⁺ cells, as well as similar double-stained cell profiles in flow cytometry dot-plot graphs. Taken together, the results indicate that a TB exclusion assay by flow cytometry can be employed as an alternative tool for quick and reliable cell viability analysis.

Somatostatin receptors 3, 4 and 5 play important roles in gallbladder cancer

Expression changes of somatostatin receptor subtypes (SSTRs) including SSTR1, SSTR2, SSTR3, SSTR4 and SSTR5 in the development of gallbladder cancer were assessed with attention to relationships with clinical pathological characteristics. SSTRs in 29 gallbladder cancer and 25 normal gallbladder tissue specimens were examined by immunohistochemical staining. Differences between SSTRs expressions and clinical pathological parameters were analyzed by chi-square test. The five subtypes of SSTR were all expressed in gallbladder cancer tissues and SSTR3 presented the highest expression. SSTR5 expression was increased significantly in gallbladder cancer (P<0.05) compared with that in normal gallbladder tissue. SSTR3 expression in highly and moderately differentiated gallbladder cancer was significantly higher than that in poorly differentiated lesions (P<0.05). SSTR4 expression was lower in gallbladder cancer with lymph node metastasis than that in gallbladder cancer without lymph node metastasis (P<0.05). Therfore, these results indicated that SSRT5, SSTR3 and SSTR4 may play important roles in the formation and development of gallbladder cancer.

Mechanisms of verapamil-enhanced chemosensitivity of gallbladder cancer cells to platinum drugs: glutathione reduction and MRP1 downregulation

Gallbladder cancer (GBC) is highly malignant with a low response rate after chemotherapy and platinum drugs are currently prominent in the treatment of biliary tract cancers. Therefore, the development of novel strategies to enhance the sensitivity of GBC to platinum drugs is required. In the present study, we examined the effects of verapamil, a classic chemosensitizer whose reported mechanisms of action include inhibiting the transport function of P-glycoprotein (MDR1) or stimulating glutathione (GSH) transport by multidrug resistance-related protein 1 (MRP1), in combination with cisplatin (CDDP), carboplatin (CBP) or oxaliplatin on the GBC cell lines, SGC996 and GBC-SD. Our results demonstrated that the co-treatment with verapamil markedly enhanced the chemosensitivity of GBC cells in comparison with platinum drug treatment alone. The mechanisms involved included GSH reduction and MRP1 downregulation. Verapamil/CDDP co-treatment inhibited tumor xenograft growth via the downregulation of MRP1 expression. MRP1 was highly expressed in human GBC tissue compared to non-tumorous gallbladder tissue. Our data demonstrate that verapamil may be used as a safe chemosensitizer for platinum drugs in the treatment of GBC. It functions by ROS and ATP-binding cassette transporter-related mechanisms.

Molecularly targeted therapy of gallbladder carcinoma

Gallbladder cancer (GBC) represents the most common and aggressive type of biliary tree cancers (BTCs). Complete surgical resection offers the only chance for cure; however, only 10% of patients with GBC present with early-stage disease and are considered surgical candidates. Among those patients who do undergo "curative" resection, recurrence rates are high. There are no established adjuvant treatments in this setting. Patients with unresectable or metastatic GBC have a poor prognosis. Molecularly targeted therapy offers a promising approach for the treatment of unresectable or metastatic GBC. Molecules involved in carcinogenesis or pathogenesis of GBC are target candidates. Molecularly targeted agents that inhibit angiogenesis and epidermal growth factor receptor (EGFR) pathways are entering clinical trials. Further understanding of the molecular mechanism of carcinogenesis coupled with more extensive genetic profiling of GBC patients will help assess the therapeutic relevance of targeting a specific pathway.