Expression of multidrug resistance-associated protein (MRP) in thyroid cancers

Utilizing Three-Dimensional Culture Methods to Improve High-Throughput Drug Screening in Anaplastic Thyroid Carcinoma

Anaplastic thyroid carcinoma (ATC) is the most aggressive endocrine neoplasm, with a median survival of just four to six months post-diagnosis. Even with surgical and chemotherapeutic interventions, the five-year survival rate is less than 5%. Although combination dabrafenib/trametinib therapy was recently approved for treatment of the ~25% of ATCs harboring BRAFV600E mutations, there are no approved, effective treatments for BRAF-wildtype disease. Herein, we perform a screen of 1525 drugs and evaluate therapeutic candidates using monolayer cell lines and four corresponding spheroid models of anaplastic thyroid carcinoma. We utilize three-dimensional culture methods, as they have been shown to more accurately recapitulate tumor responses in vivo. These three-dimensional cultures include four distinct ATC spheroid lines representing unique morphology and mutational drivers to provide drug prioritization that will be more readily translatable to the clinic. Using this screen, we identify three exceptionally potent compounds (bortezomib, cabazitaxel, and YM155) that have established safety profiles and could potentially be moved into clinical trial for the treatment of anaplastic thyroid carcinoma, a disease with few treatment options.

Exogenous bacterial DnaK increases protein kinases activity in human cancer cell lines

BACKGROUND

Studies of molecular mechanisms underlying tumor cell signaling highlighted a critical role for kinases in carcinogenesis and cancer progression. To this regard, protein kinases regulates a number of critical cellular pathways by adding phosphate groups to specific substrates. For this reason, their involvement in the complex interactions between the human microbiota and cancer cells to determine therapy and tumor progression outcome is becoming increasingly relevant. Mycoplasmas are components of the normal human microbiota, and several species have also been associated to human diseases, including certain cancers. It is also important to note that Mycoplasmas and their proteins are a component of the common tumor microenvironment. In addition, several epidemiological, in vivo and in vitro studies indicate a close involvement of Mycoplasmas in cellular transformation and cancer progression.

METHODS

In this study, we investigate the effect of exogenous Mycoplasma DnaK on kinases activity by treating in vitro four different eukaryotic cancer cell lines, namely lung and prostate cancer, colon adenocarcinoma, and neuroblastoma. Phosphorylation of kinases and specific substrates was measured at 20 and 60 min.

RESULTS

Kinome analysis of our data indicates that Mycoplasma DnaK promotes the dysregulation of the activity of specific kinases and their substrates, with a known involvement in carcinogenesis and cancer progression.

CONCLUSIONS

Given the similarity in structure and amino acid composition of this protein with other bacterial DnaKs we provide a novel mechanism whereby components of the human microbiota and present in the tumor microenvironment are able to deregulate phosphorylation events occurring during carcinogenesis and cancer progression.

The Possible Role of Cancer Stem Cells in the Resistance to Kinase Inhibitors of Advanced Thyroid Cancer

Target therapy with various kinase inhibitors (KIs) has been extended to patients with advanced thyroid cancer, but only a subset of these compounds has displayed efficacy in clinical use. However, after an initial response to KIs, dramatic disease progression occurs in most cases. With the discovery of cancer stem cells (CSCs), it is possible to postulate that thyroid cancer resistance to KI therapies, both intrinsic and acquired, may be sustained by this cell subtype. Indeed, CSCs have been considered as the main drivers of metastatic activity and therapeutic resistance, because of their ability to generate heterogeneous secondary cell populations and survive treatment by remaining in a quiescent state. Hence, despite the impressive progress in understanding of the molecular basis of thyroid tumorigenesis, drug resistance is still the major challenge in advanced thyroid cancer management. In this view, definition of the role of CSCs in thyroid cancer resistance may be crucial to identifying new therapeutic targets and preventing resistance to anti-cancer treatments and tumor relapse. The aim of this review is to elucidate the possible role of CSCs in the development of resistance of advanced thyroid cancer to current anti-cancer therapies and their potential implications in the management of these patients.

The Role of ATP-Binding Cassette Transporters in the Chemoresistance of Anaplastic Thyroid Cancer: A Systematic Review

Anaplastic thyroid cancer (ATC) is an aggressive type of thyroid cancer with a high mortality rate. Cytotoxic drugs are among the treatment modalities usually used for ATC treatment. However, systemic chemotherapies for ATC have not been shown to have remarkable efficacy. ATP-binding cassette (ABC) transporters have been suggested as a possible mechanism in ATC resistance to chemotherapy. This systematic review was aimed to define the possible roles of ABC transporters in ATC resistance to chemotherapy. Numerous databases, including Scopus, Web of Science, PubMed, Cochrane Library, Ovid, ProQuest, and EBSCO, were searched for papers published since 1990, with predefined keywords. The literature searches were updated twice, in 2015 and 2017. All identified articles were reviewed, and 14 papers that met the inclusion criteria were selected. In the eligible studies, the roles of 10 out of 49 ABC transporters were evaluated; among them, three pumps (ABCB1, ABCC1, and ABCG2) were the most studied transporters in ATC samples. ABCC1 and ABCG2 had the highest expression rates in ATC, and ABCB1 ranked second among the inspected transporters. In conclusion, ABC transporters are the major determinants of ATC resistance to chemotherapy. By identifying these transporters, we can tailor the best treatment approach for patients with ATC. Additional studies are needed to define the exact role of each ABC transporter and other mechanisms in ATC drug resistance.

The PLK1 inhibitor GSK461364A is effective in poorly differentiated and anaplastic thyroid carcinoma cells, independent of the nature of their driver mutations

BACKGROUND

Poorly differentiated thyroid carcinoma (PDTC) and anaplastic thyroid carcinoma (ATC) are the most aggressive forms of thyroid cancer. Despite their low incidence, they account for a disproportionate number of thyroid cancer-related deaths because of their resistance to most therapeutic approaches. We have generated mouse models that develop ATC ([Pten, p53](thyr-/-) mice) and follicular thyroid cancer with areas of poor differentiation (Pten(thyr-/-),Kras(G12D) mice). Comparative gene expression profiling of human and mouse ATCs reveals a common "mitotic signature" in which mitotic kinases, including Polo-like kinase-1 (PLK1), are found deregulated in both species. Most genes from this signature are also upregulated in poorly differentiated tumors developing in Pten(thyr-/-),Kras(G12D) mice. PLK1 is a crucial driving force for normal mitotic spindle formation, centrosome maturation, and separation, and its overexpression has been demonstrated in a wide range of tumors.

METHODS

Human and mouse ATC and PDTC cell lines were treated with the PLK1 inhibitor GSK461364A, and proliferation, apoptosis, and mitotic spindle alterations were analyzed. Furthermore, immunocompetent mice were injected in the flank with mouse ATC cells, and treated with placebo or GSK461364A.

RESULTS

We show that the PLK1 inhibitor GSK461364A inhibits cell proliferation and induces cell death in both mouse ATC- and PDTC-derived cell lines and in several human ATC cell lines carrying different driver mutations. Dose-dependent changes in chromosome alignment and spindle assembly during mitosis are observed after treatment, together with changes in the mitotic index. FACS analysis reveals a G2/M phase arrest, followed by apoptosis, and mitotic slippage in cells with PI3K activation. GSK461364A is also effective in vivo, in an allograft model of ATC.

CONCLUSIONS

Taken together, these data suggest that PLK1 targeting is a promising and effective therapeutic approach against PDTC cells and undifferentiated thyroid carcinoma cells.

Anti-apoptotic effects of protein kinase C-delta and c-fos in cisplatin-treated thyroid cells

BACKGROUND AND PURPOSE

We showed previously that cisplatin inititates a signalling pathway mediated by PKC-delta/extracellular signal-regulated kinase (ERK), important for maintaining viability in PC Cl3 thyroid cells. The studies described herein examined whether c-fos was associated with cisplatin resistance and the signalling link between c-fos and PKC-delta/ERK.

EXPERIMENTAL APPROACH

Cells were treated with various pharmacological inhibitors of PKCs and ERK, or were depleted of c-fos, PKC-delta, PKC-epsilon and caspase-3 by small interfering RNA (siRNA), then incubated with cisplatin and cytotoxicity assessed.

KEY RESULTS

Cisplatin provokes the induction of c-fos and the activation of conventional PKC-beta, and novel PKC-delta and -epsilon. The cisplatin-provoked c-fos induction was decreased by Gö6976, a PKC-beta inhibitor; by siRNA for PKC-delta- but not that for PKC-epsilon or by PD98059, a mitogen-activated protein kinase/ERK kinase inhibitor. Expression of c-fos was abolished by GF109203X, an inhibitor of all PKC isoforms, or by PD98059 plus Gö6976 or by PKC-delta-siRNA plus Gö6976. When c-fos expression was blocked by siRNA, cisplatin cytotoxicity was strongly enhanced with increased caspase-3 activation. In PKC-delta-depleted cells treated with cisplatin, caspase-3 activation was increased and cell viability decreased. In these PKC-delta-depleted cells, PD98059 did not affect caspase-3 activation.

CONCLUSIONS AND IMPLICATIONS

In PC Cl3 cells, in the cell signalling pathways that lead to cisplatin resistance, PKC-delta controls ERK activity and, together with PKC-beta, also the induction of c-fos. Hence, the protective role of c-fos in thyroid cells has the potential to provide new opportunities for therapeutic intervention.

Effect of sodium butyrate on doxorubicin resistance and expression of multidrug resistance genes in thyroid carcinoma cells

ATP-binding cassette (ABC) transporters [P-glycoprotein and multidrug resistance (MDR)-associated proteins (MRPs)] confer MDR to tumor cells. In this work, we investigated doxorubicin resistance in three thyroid carcinoma cell lines. The effects of sodium butyrate (NaB) on doxorubicin-induced cytotoxicity and on transcription of three MDR genes were also studied. Thyroid cell lines established from anaplastic (8505C) and two poorly differentiated follicular (FTC 238 and FTC 133) cancers were cultured for 24 or 48 h in the presence of NaB (0, 0.25, 0.5 and 1 mM) alone or combined with increased doses of doxorubicin. Cytotoxicity was assessed using the MTT test. MDR1, MRP1 and MRP2 mRNA expression was studied by RT-PCR. After a 24- or 48-h incubation, doxorubicin alone induced cytotoxicity in the three cell lines. NaB significantly (p<0.0001) increased the doxorubicin-induced cytotoxicity. MRP1 transcripts were expressed in the three non-treated cell lines. MDR1 and MRP2 mRNAs were both present in 8505C, but absent in FTC 133 or FTC 238 cell lines, respectively. Treatment with NaB for 24 or 48 h induced no change in MRP1 and MRP2 levels, but increased MDR1 expression in 8505C and FTC 238 cell lines comparably to alkaline phosphatase activity. In conclusion, MRP1 and sometimes MDR1 and MRP2 are expressed in the tested cell lines. NaB potentiates doxorubicin-induced cytotoxicity independently of the ABC transporters. The combination of doxorubicin and NaB might have clinical implications for thyroid cancer therapy.

Y-box binding protein expression in thyroid neoplasms: its linkage with anaplastic transformation

Recent studies have demonstrated that Y-box binding protein (YB-1) regulates the transcription of genes linked to carcinoma progression. In this study, we investigated the expression of this protein in thyroid neoplasms to elucidate its significance. The expression of YB-1 was immunohistochemically investigated using the monoclonal antibody for various thyroid neoplasms. Normal follicles did not overexpress YB-1, and only moderate overexpression of YB-1 was observed in some follicular tumors and papillary carcinoma, especially those of a larger size. In contrast, 92.9% of anaplastic carcinoma strongly overexpressed YB-1. YB-1 immunoreactivity was seen in both cytoplasms and cell nuclei, but the former was more predominant. These findings suggest that YB-1 plays a role in regulating the transcription as well as translation of genes contributing to the anaplastic transformation of thyroid carcinoma.

The expression of P-glycoprotein and multidrug resistance proteins 1 and 2 (MRP1 and MRP2) in human malignant mesothelioma

BACKGROUND

Malignant mesothelioma is a malignancy with a primary resistance to chemo- and radiotherapies for reasons which are still unclear. Multidrug resistance proteins might explain the observed resistance, but no studies have assessed their expression in mesothelioma.

PATIENTS AND METHODS

Immunohistochemical expression of P-glycoprotein (P-gp), and the multidrug resistance proteins 1 and 2 (MRP1 and MRP2) were investigated in 36 cases of malignant mesothelioma and in samples from normal mesothelium.

RESULTS

P-gp immunopositivity was found in 61%, MRP1 immunopositivity in 58% and MRP2 positivity in 33% of the cases. Normal mesothelium did not express these multidrug-resistant proteins. There was a significant association between P-gp and MRP2 (P = 0.022) expression. No or weak P-gp, MRP1 or MRP2 immunostaining was significantly more frequent in sarcomatoid mesothelimas than in epithelial or biphasic mesotheliomas (P = 0.031, P = 0.034 and P = 0.024, respectively). There was no significant association between patient survival and expression of the multidrug-resistant proteins.

CONCLUSIONS

The results show that P-gp, MRP1 and MRP2 are induced and expressed in malignant mesothelial cells. Regardless of their expression no association with survival of the patients was seen, suggesting that the primary resistance of malignant mesotheliomas is not solely dependent on their expression or function.

Expression of multidrug resistance-associated protein in endometrial carcinomas: correlation with clinicopathology and prognosis

The objective of the study reported here was to investigate the expression of multidrug resistance-associated protein (MRP) in endometrial carcinomas and to evaluate the relationship between its expression and clinical data. Using immunohistochemistry, we examined MRP expression in 15 normal endometria, 10 cases of endometrial hyperplasia, and 64 cases of endometrial carcinoma. The normal endometrial glands were weakly immunopositive throughout the menstrual cycle. In addition, we found a progressive increase in the MRP expression of the endometrial hyperplasias. Of the 64 cases of endometrial carcinoma, 62 (97%) expressed MRP. Of these 62 cases, 34 (55%) showed strong immunostaining (>/=50%) and 28 (45%) showed weak immunostaining (<50%). In particular, the intensity of the immunostaining was very strong in 25 (71%) of the 35 grade 1 carcinomas. There was a significant difference in MRP expression between the grade 1 carcinomas and the more poorly differentiated carcinomas (grade 2 or grade 3) (P <.01), especially at stages 1a and 1b (P <.001). However, beyond stage 1c, there was no significant difference in MRP immunoreactivity between the histologic differentiations. Furthermore, beyond stage 1c, those patients with strongly MRP-positive carcinomas had a relatively poorer survival rate than those with weakly MRP-positive carcinomas (P <.05). We concluded that MRP immunoreactivity was already present in normal endometrium and showed a progressive increase from endometrial hyperplasia to well-differentiated carcinoma. Beyond stage 1c, strongly MRP-positive carcinoma indicated a poorer survival rate.

Expression of multidrug resistance-associated protein (MRP) in head and neck squamous cell carcinoma

We investigated the expression of multidrug resistance-associated protein (MRP) in 115 cases of head and neck squamous cell carcinoma (H&NSCC) by immunohistochemistry and examined the relationship between MRP expression and clinical factors. Thirty-four (30%) of 115 cases of H&NSCC had expression of MRP. The clinical stage was inversely associated with the expression of MRP (P = 0.0090), but not with age, sex, tumor size, metastasis, recurrence, death from disease or overall survival rate for 5 years. In vitro chemosensitivity to five chemotherapeutic agents (cis-diamminedichloroplatinum, 5-fluorouracil, peplomycin, mitomycin C and Adriamycin) was tested by ATP assay and no correlation between the sensitivity of tumor cells to the cytotoxicity of any drug and MRP expression was found. These results suggest that the resistance to anticancer drugs is not dependent only on the expression of MRP in H&NSCC.

Lack of a point mutation of human DNA topoisomerase II in multidrug-resistant anaplastic thyroid carcinoma cell lines

DNA topoisomerases are major defined targets for a large variety of clinically important anticancer agents, including etoposide, adriamycin, and mitoxantrone. Mutations at amino acids 439, 450 and 803 of DNA topoisomerase II were examined in multiple anticancer drug-resistant anaplastic thyroid carcinomas (ten cell lines and three cancerous tissues) by reverse transcriptase-polymerase chain reaction (RT-PCR) and subsequent DNA sequencing. No mutation was found in these cell lines and tissues, but mdr1, mrp and/or lrp mRNA were expressed to a varying degree, and there was no significant difference in DNA topoisomerase IIalpha content among the cell lines and tissues as evaluated by Western blotting. Our experimental data indicate that overexpression of multidrug resistance-related mRNA is sufficient to confer drug resistance.

Expression of the Multidrug Resistance-Associated Protein Gene in Refractory Lymphoma: Quantitation by a Validated Polymerase Chain Reaction Assay

Previous work investigating the role of MDR-1 overexpression in relapsed and refractory lymphoma led us to investigate a possible role for multidrug resistance-associated protein (MRP) as a cause of resistance in patients who did not overexpress MDR-1. A quantitative polymerase chain reaction (PCR) method for measuring MRP expression was validated. Immunoblot analysis suggested that no major discrepancy was present between mRNA expression and protein levels. MRP levels were found to be independent of sample tumor content by immunophenotyping, suggesting that the presence of normal cells had no significant impact on measurements of MRP expression. We evaluated MRP in 55 biopsy samples from 40 patients with refractory lymphoma enrolled on a trial of infusional chemotherapy (EPOCH). Pre- and post-EPOCH samples were available from 15 patients. MRP levels were also evaluated in 16 newly diagnosed, untreated lymphoma patient samples. No significant difference in MRP mRNA expression was noted between pre- and post-EPOCH groups. Also, MRP levels in the newly diagnosed patient samples were not significantly different from either pre- or post-EPOCH groups. Two of 15 paired pre- and post-EPOCH patient samples exhibited overexpression of MRP after EPOCH chemotherapy, with measured increases of 10-fold and 18-fold. We conclude that MRP overexpression is not responsible for non–P-glycoprotein (Pgp)–mediated drug resistance in the majority of these patients, although it may be important in a subset of patients. Defining this subset prospectively could aid in the development of clinical trials of MRP modulation in drug-resistant lymphoma.

Expression of the Multidrug Resistance-Associated Protein Gene in Refractory Lymphoma: Quantitation by a Validated Polymerase Chain Reaction Assay

Previous work investigating the role of MDR-1 overexpression in relapsed and refractory lymphoma led us to investigate a possible role for multidrug resistance-associated protein (MRP) as a cause of resistance in patients who did not overexpress MDR-1. A quantitative polymerase chain reaction (PCR) method for measuring MRP expression was validated. Immunoblot analysis suggested that no major discrepancy was present between mRNA expression and protein levels. MRP levels were found to be independent of sample tumor content by immunophenotyping, suggesting that the presence of normal cells had no significant impact on measurements of MRP expression. We evaluated MRP in 55 biopsy samples from 40 patients with refractory lymphoma enrolled on a trial of infusional chemotherapy (EPOCH). Pre- and post-EPOCH samples were available from 15 patients. MRP levels were also evaluated in 16 newly diagnosed, untreated lymphoma patient samples. No significant difference in MRP mRNA expression was noted between pre- and post-EPOCH groups. Also, MRP levels in the newly diagnosed patient samples were not significantly different from either pre- or post-EPOCH groups. Two of 15 paired pre- and post-EPOCH patient samples exhibited overexpression of MRP after EPOCH chemotherapy, with measured increases of 10-fold and 18-fold. We conclude that MRP overexpression is not responsible for non–P-glycoprotein (Pgp)–mediated drug resistance in the majority of these patients, although it may be important in a subset of patients. Defining this subset prospectively could aid in the development of clinical trials of MRP modulation in drug-resistant lymphoma.

Primary structure of a novel ABC transporter with a chromosomal localization on the band encoding the multidrug resistance-associated protein

Complementary DNA clones encoding a novel protein, ABC-C, with the typical structural features of the ABC transporter family were identified in a human medullary thyroid carcinoma cell line. The transporter consists of 1704 amino acid residues with two homologous repeats, each harboring six putative transmembrane helices and an ATP-binding cassette motif. The mRNA is expressed highest in normal lung, but also in varying amounts in other tissues and in C-cell carcinoma. The ABC-C gene is mapped on chromosome 16p13.3, in close physical proximity to another ABC transporter, the multidrug resistance-associated protein. This related protein is assumed to confer resistance to chemotherapeutic drugs in small cell lung carcinoma. The genomic clustering of both transporters, typical also for other members of the ABC family, supports the notion that ABC-C may be involved in development of resistance to xenobiotics.

MDR1 and multidrug resistance-associated protein (MRP) gene expression in epithelial ovarian tumors

Clinical drug resistance poses a major problem in the successful treatment of ovarian cancer. Two genes, MDR1 and MRP, have been found to play a role in the multidrug resistance phenotype of a number of human tumors. Using a sensitive semiquantitative PCR assay we examined 53 primary untreated ovarian tumors for expression of both MDR1 and MRP genes. Approximately one-third of the tumors expressed MDR1 while all the tumors expressed varying levels of the MRP gene.