Expression of drug resistance-related genes in head and neck squamous cell carcinomas and normal mucosa

Dissecting multi drug resistance in head and neck cancer cells using multicellular tumor spheroids

One of the hallmarks of cancers is their ability to develop resistance against therapeutic agents. Therefore, developing effective in vitro strategies to identify drug resistance remains of paramount importance for successful treatment. One of the ways cancer cells achieve drug resistance is through the expression of efflux pumps that actively pump drugs out of the cells. To date, several studies have investigated the potential of using 3-dimensional (3D) multicellular tumor spheroids (MCSs) to assess drug resistance; however, a unified system that uses MCSs to differentiate between multi drug resistance (MDR) and non-MDR cells does not yet exist. In the present report we describe MCSs obtained from post-diagnosed, pre-treated patient-derived (PTPD) cell lines from head and neck squamous cancer cells (HNSCC) that often develop resistance to therapy. We employed an integrated approach combining response to clinical drugs and screening cytotoxicity, monitoring real-time drug uptake, and assessing transporter activity using flow cytometry in the presence and absence of their respective specific inhibitors. The report shows a comparative response to MDR, drug efflux capability and reactive oxygen species (ROS) activity to assess the resistance profile of PTPD MCSs and two-dimensional (2D) monolayer cultures of the same set of cell lines. We show that MCSs provide a robust and reliable in vitro model to evaluate clinical relevance. Our proposed strategy can also be clinically applicable for profiling drug resistance in cancers with unknown resistance profiles, which consequently can indicate benefit from downstream therapy.

MRP7/ABCC10 expression is a predictive biomarker for the resistance to paclitaxel in non-small cell lung cancer

We used the paclitaxel-resistant human small cell lung cancer subline PC-6/TAX1-1, selected from PC-6 cells by paclitaxel, to test whether MRP7/ABCC10 (ABCC10) confers paclitaxel resistance. We found that gene expression of both ABCB1/MDR1 (ABCB1) and ABCC10 was higher in PC-6/TAX1-1 cells than in PC-6 cells. The expression levels of ABCC10 showed a significant inverse correlation with paclitaxel sensitivity (r = 0.574; P < 0.05) in 17 non-small cell lung cancer (NSCLC) cells unlike the expression levels of ABCB1. Pretreatment with the ABCC10 inhibitor sulfinpyrazone altered the sensitivity to paclitaxel in ABCC10-expressing NSCLC cells, concomitant with increased intracellular paclitaxel accumulation. These findings suggest that expression of the ABCC10 gene is induced by paclitaxel and that ABCC10 confers paclitaxel resistance by enhancing the efflux for paclitaxel. To confirm this hypothesis, we tested the effect on paclitaxel cytotoxicity of decreasing the expression of ABCC10 by small interfering RNA and found that this enhanced paclitaxel cytotoxicity in NCI-H23 cells concomitant with increased intracellular paclitaxel accumulation. These data indicate that ABCC10 may be one of the biomarkers for paclitaxel resistance in NSCLC.

Role of ABCG2 as a biomarker for predicting resistance to CPT-11/SN-38 in lung cancer

To examine the mechanism of resistance to 7-ethyl-10-hydroxycamptothecin (SN-38) in lung cancer, we continuously exposed the non-small-cell lung cancer (NSCLC) cell line NCI-H23 to SN-38 and selected the SN-38-resistant clone H23/SN-38. After 2 months of culturing in SN-38-free conditions, H23/SN-38 cells recovered their sensitivity to SN-38 and were subsequently established as the revertant H23/SN-38REV cell line. Because H23/SN-38 cells show cross resistance to certain anticancer drugs, such as topotecan, etoposide, doxorubicin and mitoxantrone, we examined the gene and protein expression levels of drug efflux transporters of the ATP-binding cassette (ABC) family. We found that both gene and protein expression of ABCG2/BCRP (ABCG2) in H23/SN-38 cells was increased compared with that in NCI-H23 cells and H23/SN-38REV cells. The cellular accumulation of topotecan in H23/SN-38 cells was decreased compared with that in NCI-H23 and H23/SN-38REV cells, and treatment with reserpine (an inhibitor of ABCG2) increased the cellular accumulation of topotecan in H23/SN-38 cells. Furthermore, treatment with reserpine also altered the sensitivity of H23/SN-38 cells to SN-38. These results indicate that the upregulation of ABCG2 was functional, and related to the resistance of H23/SN-38 cells to SN-38. Moreover, we found that gene expression levels of ABCG2 were significantly correlated with the concentration of SN-38 for 50% cell survival in 13 NSCLC cells (r=0.592, P<0.05). The present results indicate that the induction of ABCG2 by SN-38 does confer acquired resistance to CPT-11/SN-38, but the induction of ABCG2 and subsequent drug resistance are reversible. However, the expression level of ABCG2 may be a useful indicator of CPT-11/SN-38 activity in lung cancer.

Immunohistochemical study of DNA topoisomerase I, DNA topoisomerase II alpha, p53, and Ki-67 in oral preneoplastic lesions and oral squamous cell carcinomas

Human DNA topoisomerase I (topo I) is the molecular target of the camptothecin group of anticancer drugs. Laboratory studies have shown that the cellular response to topo I-targeted drugs depends on the topo I expression and DNA replication rate and the apoptotic pathway activity. In this study, we tested potential indicators of the sensitivity of topo I-targeted drugs in 36 cases of oral squamous cell carcinoma (OSCC). Formalin-fixed, paraffin-embedded tissue sections were immunostained with monoclonal antibodies against Ki-67, p53, and topo I, and with polyclonal antibodies against DNA topoisomerase II-alpha (topo II-alpha). These markers were also tested in 18 epithelial hyperplastic lesions and 18 mild dysplasias. Immunostaining was quantified by the percentage of stained nuclei in each sample (the labeling index); 200 immunoreactive epithelial nuclei were counted per case for each antibody. The results support the possibility of using topo II-alpha staining for assessing the proliferative activity. High expression of topo II-alpha and topo I in OSCCs suggests that they may serve as potential indicators of sensitivity to topo I inhibitors. However, the apoptotic pathway assessed by p53 immunostaining was found to be uninformative. Analysis of the relationship between immunohistochemical results and clinical and pathologic parameters (the T and N stages and differentiation) showed that only the differentiation parameter correlated with the topo I expression rate. Thus, significant increase in the topo I expression in the poorly differentiated OSCCs suggests their higher sensitivity to drug treatment.

Quantitative analysis of multidrug-resistance mdr1 gene expression in head and neck cancer by real-time RT-PCR

Progression of head and neck cancer is always associated with changes of gene expression profile. In this study, we characterized the expression of multidrug-resistance mdr1 gene, which may play a role in tumorigenesis and multidrug resistance in head and neck cancer. A TaqMan one-step RT-PCR with a linear range for quantification across at least a 5 log scale of concentration of mdr1 mRNA was designed to determine the level of mdr1 expression in 50 pairs of normal vs. malignant head and neck tissues. Both the absolute level of mdr1 mRNA in tumor (T) and the relative mdr1 expression between tumor and its normal counterpart (T/N) were measured and their associations with several clinical variables were analyzed. Among the clinical variables analyzed, only the clinical stage of tumor was found to be associated with mdr1 expression. The distribution of clinical stages differed significantly (P<0.01) among the 27 specimens that had a T/N>1, with 59.3%, 22.2%, 14.8% and 3.7% in stage IV, III, II, and I, respectively. In addition, 76% of stage IV and 75% of stage III tumors had a T/N>1 compared to 25% of stage II and 20% of stage I tumors (P=0.004). Multivariate logistic regression analysis also indicated a significant difference of mdr1 expression between the early (I and II) and advanced (III and IV) stages tumors. The adjusted odds ratios (95% confidence intervals) were 1.477 (1.084 - 2.012) and 1.001 (1.000-1.002) for T/N (P<0.05) and T (P<0.05) treated as continuous variables, and 15.521 (3.414-70.550) and 5.074 (1.154-22.311) for T/N (P<0.001) and T (P<0.05) treated as binary variables, respectively. Taken together, the data presented here indicated that real-time RT-PCR provides a quantitative way to monitor mdr1 gene expression. The differential expression of mdr1 between early and advanced stages of head and neck cancer may shed light on the process of tumorigenicity and offer clues to the planning of new treatments.