Reduced folate carrier protein expression in osteosarcoma: implications for the prediction of tumor chemosensitivity

The strategy and clinical relevance of in vitro models of MAP resistance in osteosarcoma: a systematic review

Over the last 40 years osteosarcoma (OS) survival has stagnated with patients commonly resistant to neoadjuvant MAP chemotherapy involving high dose methotrexate, adriamycin (doxorubicin) and platinum (cisplatin). Due to the rarity of OS, the generation of relevant cell models as tools for drug discovery is paramount to tackling this issue. Four literature databases were systematically searched using pre-determined search terms to identify MAP resistant OS cell lines and patients. Drug exposure strategies used to develop cell models of resistance and the impact of these on the differential expression of resistance associated genes, proteins and non-coding RNAs are reported. A comparison to clinical studies in relation to chemotherapy response, relapse and metastasis was then made. The search retrieved 1891 papers of which 52 were relevant. Commonly, cell lines were derived from Caucasian patients with epithelial or fibroblastic subtypes. The strategy for model development varied with most opting for continuous over pulsed chemotherapy exposure. A diverse resistance level was observed between models (2.2-338 fold) with 63% of models exceeding clinically reported resistance levels which may affect the expression of chemoresistance factors. In vitro p-glycoprotein overexpression is a key resistance mechanism; however, from the available literature to date this does not translate to innate resistance in patients. The selection of models with a lower fold resistance may better reflect the clinical situation. A comparison of standardised strategies in models and variants should be performed to determine their impact on resistance markers. Clinical studies are required to determine the impact of resistance markers identified in vitro in poor responders to MAP treatment, specifically with respect to innate and acquired resistance. A shift from seeking disputed and undruggable mechanisms to clinically relevant resistance mechanisms may identify key resistance markers that can be targeted for patient benefit after a 40-year wait.

Novel nanomedicines to overcome cancer multidrug resistance

Chemotherapy remains a powerful tool to eliminate malignant cells. However, the efficacy of chemotherapy is compromised by the frequent emergence of intrinsic and acquired multidrug resistance (MDR). These chemoresistance modalities are based on a multiplicity of molecular mechanisms of drug resistance, including : 1) Impaired drug uptake into cancer cells; 2) Increased expression of ATP-binding cassette efflux transporters; 3) Loss of function of pro-apoptotic factors; 4) Enhanced DNA repair capacity; 5) Qualitative or quantitative alterations of specific cellular targets; 6) Alterations that allow cancer cells to tolerate adverse or stressful conditions; 7) Increased biotransformation or metabolism of anticancer drugs to less active or completely inactive metabolites; and 8) Intracellular and intercellular drug sequestration in well-defined organelles away from the cellular target. Hence, one of the major aims of cancer research is to develop novel strategies to overcome cancer drug resistance. Over the last decades, nanomedicine, which focuses on targeted delivery of therapeutic drugs into tumor tissues using nano-sized formulations, has emerged as a promising tool for cancer treatment. Therefore, nanomedicine has been introduced as a reliable approach to improve treatment efficacy and minimize detrimental adverse effects as well as overcome cancer drug resistance. With rationally designed strategies including passively targeted delivery, actively targeted delivery, delivery of multidrug combinations, as well as multimodal combination therapy, nanomedicine paves the way towards efficacious cancer treatment and hold great promise in overcoming cancer drug resistance. Herein, we review the recent progress of nanomaterials used in medicine, including liposomal nanoparticles, polymeric nanoparticles, inorganic nanoparticles and hybrid nanoparticles, to surmount cancer multidrug resistance. Finally, the future perspectives of the application of nanomedicine to reverse cancer drug resistance will be addressed.

Mechanisms of Resistance to Conventional Therapies for Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor, mainly occurring in children and adolescents. Current standard therapy includes tumor resection associated with multidrug chemotherapy. However, patient survival has not evolved for the past decades. Since the 1970s, the 5-year survival rate is around 75% for patients with localized OS but dramatically drops to 20% for bad responders to chemotherapy or patients with metastases. Resistance is one of the biological processes at the origin of therapeutic failure. Therefore, it is necessary to better understand and decipher molecular mechanisms of resistance to conventional chemotherapy in order to develop new strategies and to adapt treatments for patients, thus improving the survival rate. This review will describe most of the molecular mechanisms involved in OS chemoresistance, such as a decrease in intracellular accumulation of drugs, inactivation of drugs, improved DNA repair, modulations of signaling pathways, resistance linked to autophagy, disruption in genes expression linked to the cell cycle, or even implication of the micro-environment. We will also give an overview of potential therapeutic strategies to circumvent resistance development.

Targeting Molecular Mechanisms Underlying Treatment Efficacy and Resistance in Osteosarcoma: A Review of Current and Future Strategies

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. Due to micrometastatic spread, radical surgery alone rarely results in cure. Introduction of combination chemotherapy in the 1970s, however, dramatically increased overall survival rates from 20% to approximately 70%. Unfortunately, large clinical trials aiming to intensify treatment in the past decades have failed to achieve higher cure rates. In this review, we revisit how the heterogenous nature of osteosarcoma as well as acquired and intrinsic resistance to chemotherapy can account for stagnation in therapy improvement. We summarise current osteosarcoma treatment strategies focusing on molecular determinants of treatment susceptibility and resistance. Understanding therapy susceptibility and resistance provides a basis for rational therapy betterment for both identifying patients that might be cured with less toxic interventions and targeting resistance mechanisms to sensitise resistant osteosarcoma to conventional therapies.

Management of Refractory Pediatric Sarcoma: Current Challenges and Future Prospects

Paediatric sarcomas are a heterogeneous group of disorders constituting bone sarcoma and various soft tissue sarcomas. Almost one-third of these presents with metastasis at baseline and another one-third recur after initial curative treatment. There is a huge unmet need in this cohort in terms of curative options and/or prolongation of survival. In this review, we have discussed the current treatment options, challenges and future strategies of managing relapsed/refractory paediatric sarcomas. Upfront risk-adapted treatment with multidisciplinary management remains the main strategy to prevent future recurrence or relapse of the disease. In the case of limited local and/or systemic relapse or late relapse, initial multimodality management can be administered. In treatment-refractory cases or where cure is not feasible, the treatment options are limited to novel therapeutics, immunotherapeutic approach, targeted therapies, and metronomic therapies. A better understanding of disease biology, mechanism of treatment refractoriness, identifications of driver mutation, the discovery of novel targeted therapies, cellular vaccine and adapted therapies should be explored in relapsed/refractory cases. Close national and international collaboration for translation research is needed to fulfil the unmet need.

Nanomedicine in osteosarcoma therapy: Micelleplexes for delivery of nucleic acids and drugs toward osteosarcoma-targeted therapies

Osteosarcoma(OS) represents the main cancer affecting bone tissue, and one of the most frequent in children. In this review we discuss the major pathological hallmarks of this pathology, its current therapeutics, new active biomolecules, as well as the nanotechnology outbreak applied to the development of innovative strategies for selective OS targeting. Small RNA molecules play a role as key-regulator molecules capable of orchestrate different responses in what concerns cancer initiation, proliferation, migration and invasiveness. Frequently associated with lung metastasis, new strategies are urgent to upgrade the therapeutic outcomes and the life-expectancy prospects. Hence, the prominent rise of micelleplexes as multifaceted and efficient structures for nucleic acid delivery and selective drug targeting is revisited here with special emphasis on ligand-mediated active targeting. Future landmarks toward the development of novel nanostrategies for both OS diagnosis and OS therapy improvements are also discussed.

Pharmacogenomics of genes involved in antifolate drug response and toxicity in osteosarcoma

INTRODUCTION

Antifolates are structural analogs of folates, which have been used as antitumor drugs for more than 60 years. The antifolate drug most commonly used for treating human tumors is methotrexate (MTX), which is utilized widely in first-line treatment protocols of high-grade osteosarcoma (HGOS). In addition to MTX, two other antifolates, trimetrexate and pemetrexed, have been tested in clinical settings for second-line treatment of recurrent HGOS with patients unfortunately showing modest activity. Areas covered: There is clinical evidence which suggsest that, like other chemotherapeutic agents, not all HGOS patients are equally responsive to antifolates and do not have the same susceptibility to experience adverse drug-related toxicities. Here, we summarize the pharmacogenomic information reported so far for genes involved in antifolate metabolism and transport and in MTX-related toxicity in HGOS patients. Expert opinion: Identification and validation of genetic biomarkers that significantly impact clinical antifolate treatment response and related toxicity may provide the basis for a future treatment modulation based on the pharmacogenetic and pharmacogenomic features of HGOS patients.

The pharmacogenomics of osteosarcoma

Osteosarcoma (OS), the most common malignant tumor of bone, is presently treated with multidrug neoadjuvant chemotherapy protocols, which allow to cure 60-65% of patients but also induce toxicity events that cannot be predicted or efficiently prevented. The identification and validation of pharmacogenomic biomarkers is, therefore, absolutely warranted to provide the bases for planning personalized treatments with the aim to increase the therapeutic benefits and to avoid or limit unnecessary toxicities. As several targeted therapies against molecular and immunological markers in OS are presently under clinical investigation, it may be speculated that some new agents for innovative treatments may emerge in the next years. However, the real improvement of therapeutic perspectives for OS is strictly connected to the identification of pharmacogenomic biomarkers that may stratify patients in responders or non-responders and identify those individuals with higher susceptibility to treatment-associated toxicity. This review provides an overview of the pharmacogenomic biomarkers identified so far in OS, which appear to be promising candidates for a translation to clinical practice, after further investigation and/or prospective validation.

Research progress on the multidrug resistance mechanisms of osteosarcoma chemotherapy and reversal

Osteosarcoma (OS) is the most common and aggressive primary malignant type of bone cancer in children and adolescents. Chemotherapy is one of the most important treatments for OS. Although cancer therapy has improved over the past few decades, survival outcomes for OS patients remain unsatisfactory. One of the primary reasons for the failure of current treatments is that patients with stage IV cancer often develop resistance to anticancer agents. This article will review multidrug resistance (MDR) mechanisms of OS and strategies for overcoming resistance.

Flavonostilbenes from Sophora alopecuroides L. as multidrug resistance associated protein 1 (MRP1) inhibitors

Flavonoids have always attracted much attention due to their reversal activity on multidrug resistance (MDR). Eight flavonoids isolated from traditional Chinese medicine Sophora alopecuroides L. were applied to test their effect on MDR associated protein 1 (MRP1) through the established predicting assay. Three flavonostilbenes (alopecurone A, B and D) were first found exhibiting potent inhibitory activity on MRP1. All of them dramatically increased 6-carboxyfluorescein diacetate and doxorubicin accumulation in MRP1-transfected U-2 OS cells. The compounds significantly increased the cytotoxicity and decreased the IC₅₀ value of doxorubicin on the MDR cells (12-, 5- and 8-fold, respectively) at a non-toxic concentration (20 μM). Besides, Q-PCR analysis reveals that the MRP1 mRNA level in U-2 OS/MRP1 was also markedly decreased by the three compounds. These findings indicate a new therapeutic role of the herb. The three flavonostilbenes may have the possibility for further development as novel therapeutic reversal agents against MDR.

Proximal tumor location and fluid-fluid levels on MRI predict resistance to chemotherapy in stage IIB osteosarcoma

BACKGROUND

Primary tumor growth during neoadjuvant chemotherapy is believed to be a sign of resistance to chemotherapy (chemoresistance), and often is associated with poor histologic response, local recurrence, and poorer survival. Currently there are no proven indicators to predict poor response to chemotherapy at the time of diagnosis.

QUESTIONS/PURPOSES

We asked (1) what clinicopathologic factors present at diagnosis predict primary tumor growth during neoadjuvant chemotherapy, (2) what factors at presentation predict survival, and (3) when the factors at presentation and the treatment-related factors are considered, what factors independently correlate with survival.

METHODS

We studied 567 patients with Stage IIB osteosarcomas. The factors assessed included age, sex, location, pattern on plain radiographs (radiodense, radiolucent, mixed), MRI findings, pathologic subtype, initial tumor volume determined by MRI, tumor volume change after chemotherapy, surgical margin, and histologic response to preoperative chemotherapy. Logistic modeling was used to identify risk factors.

RESULTS

Independent risk factors associated with primary tumor growth after neoadjuvant chemotherapy were proximal tumor location (p < 0.01; relative risk [RR], 2.41; 95% CI, 1.5-3.86) and fluid-fluid level on initial MRI (p < 0.01; RR, 5.56; 95% CI, 3.48-8.87). Among factors at presentation, large initial tumor volume (p < 0.01; RR, 1.58; 95% CI, 1.22-2.04), proximal tumor site (p < 0.01; RR, 1.61; 95% CI, 1.19-2.19), and presence of fluid-fluid level (p < 0.01; RR, 1.83; 95% CI, 1.37-2.5) independently predicted reduced event-free survival. When we consider the factors at presentation and treatment-related factors, large initial tumor volume (p < 0.01; RR, 1.54), tumor growth after neoadjuvant chemotherapy (p < 0.01; RR, 3.88), inadequate surgical margin (p < 0.01; RR, 2.42), and poor histologic response (p = 0.03; RR, 1.43) were independent poor prognostic factors of event-free survival.

CONCLUSIONS

Proximal tumor location and the presence of the fluid-fluid level on initial MRI were predictors of tumor progression and poor survival in patients presenting with Stage IIB osteosarcomas. If confirmed in other studies, patients with these risk factors should be considered for trials of other treatment strategy.

LEVEL OF EVIDENCE

Level III, prognostic study. See the Instructions for Authors for a complete description of levels of evidence.

Molecular mechanisms of chemoresistance in osteosarcoma (Review)

Due to the emergence of adjuvant and neoadjuvant chemotherapy, the survival rate has been greatly improved in osteosarcoma (OS) patients with localized disease. However, this survival rate has remained unchanged over the past 30 years, and the long-term survival rate for OS patients with metastatic or recurrent disease remains poor. To a certain extent, the reason behind this may be ascribed to the chemoresistance to anti-OS therapy. Chemoresistance in OS appears to be mediated by numerous mechanisms, which include decreased intracellular drug accumulation, drug inactivation, enhanced DNA repair, perturbations in signal transduction pathways, apoptosis- and autophagy-related chemoresistance, microRNA (miRNA) dysregulation and cancer stem cell (CSC)-mediated drug resistance. In addition, methods employed to circumvent these resistance mechanism have been shown to be effective in the treatment of OS. However, almost all the current studies on the mechanisms of chemoresistance in OS are in their infancy. Further studies are required to focus on the following aspects: i) Improving the delivery of efficacy through novel delivery patterns; ii) improving the understanding of the signal transduction pathways that regulate the proliferation and growth of OS cells; iii) elucidating the signaling pathways of autophagy and its association with apoptosis in OS cells; iv) utilizing high-throughput miRNA expression analysis to identify miRNAs associated with chemoresistance in OS; and v) identifying the role that CSCs play in tumor metastasis and in-depth study of the mechanism of chemoresistance in the CSCs of OS.

Targeted expression of human folylpolyglutamate synthase for selective enhancement of methotrexate chemotherapy in osteosarcoma cells

The antifolate methotrexate (MTX) is an important chemotherapeutic agent for treatment of osteosarcoma. This drug is converted intracellularly into polyglutamate derivates by the enzyme folylpolyglutamate synthase (FPGS). MTX polyglutamates show an enhanced and prolonged cytotoxicity in comparison to the monoglutamate. In the present study, we proved the hypothesis that transfer of the human fpgs gene into osteosarcoma cells may augment their MTX sensitivity. For this purpose, we employed the human osteocalcin (OC) promoter, which had shown marked osteosarcoma specificity in promoter studies using different luciferase assays in osteosarcoma and non-osteosarcoma cell lines. A recombinant lentiviral vector was generated with the OC promoter driving the expression of fpgs and the gene for enhanced green fluorescent protein (egfp), which was linked to fpgs by an internal ribosomal entry site (IRES). As the vector backbone contained only a self-inactivating viral LTR promoter, any interference of the OC promoter by unspecific promoter elements was excluded. We tested the expression of FPGS and enhanced green fluorescent protein (EGFP) after lentiviral transduction in various osteosarcoma cell lines (human MG-63 cells and TM 791 cells; rat osteosarcoma (ROS) 17/2.8 cells) and non-osteogenic tumor cell lines (293T human embryonic kidney cells, HeLa human cervix carcinoma cells). EGFP expression and MTX sensitivity were assessed in comparison with non-transduced controls. Whereas the OC promoter failed to enhance MTX sensitivity via FPGS expression in non-osteogenic tumor cell lines, the OC promoter mediated a markedly increased MTX cytotoxicity in all osteosarcoma cell lines after lentiviral transduction. The present chemotherapy-enhancing gene therapy system may have great potential to overcome in future MTX resistance in human osteosarcomas.

How can survival be improved in localized osteosarcoma?

Despite numerous chemotherapy trials and the introduction of novel agents, survival in localized osteosarcoma, which plateaued in the mid-1980s, has been recalcitrant to our best efforts. The authors considered that a review of previous and current strategies that target survival might provide a direction for research efforts. Here, the focus is placed mainly on the reappraisal of previous mass chemotherapy trials and prognostic factors, in the hope of contriving a strategy to overcome the current stasis.

Single agent and combination studies of pralatrexate and molecular correlates of sensitivity

Background:

Pralatrexate is a dihydrofolate reductase (DHFR) inhibitor with high affinity for reduced folate carrier 1 (RFC-1) and folylpolyglutamate synthetase (FPGS), resulting in extensive internalization and accumulation in tumour cells. Pralatrexate is approved in the US for the treatment of relapsed or refractory peripheral T-cell lymphoma and is being investigated in various malignancies. Here, we evaluated molecular correlates of sensitivity to pralatrexate and explored combinations with a variety of anticancer agents.

Methods:

Antiproliferative effects of pralatrexate were evaluated in 15 human-cancer cell lines using the MTT assay. Gene expression was evaluated using qRT–PCR.

Results:

Pralatrexate and methotrexate had a similar pattern of cytotoxicity, pralatrexate being more potent. Pralatrexate potentiated the effects of platinum drugs, antimetabolites and EGFR inhibitors. Dose- and time-dependent cytotoxicity of pralatrexate correlated with high mRNA expression of FPGS. Acquired resistance to pralatrexate was associated with decreased RFC-1 expression, whereas methotrexate resistance correlated with increased DHFR expression, suggesting different mechanisms of acquired resistance.

Conclusion:

Pralatrexate was more potent than methotrexate in a panel of solid tumour lines. Our findings support the further clinical development of pralatrexate in combination with certain cytotoxics and targeted therapies, and suggest that RFC-1, FPGS and DHFR may be potential biomarkers of outcome.

Emerging drugs for high-grade osteosarcoma

IMPORTANCE OF THE FIELD

Osteosarcoma (OS) is the most common primary malignant bone tumour in children and adolescents. This review focuses on the most promising therapeutic markers and drugs which may potentially be considered for innovative high-grade OS treatments.

AREAS COVERED IN THIS REVIEW

The list of drugs and compounds reviewed has been generated by taking into account those which target markers of potential clinical interest for high-grade OS and have been included in Phase I, II or III clinical trials. The literature search covers the last 40 years, starting from the first OS chemotherapy reports of the early 1970s. Particular relevance was given to reports and reviews on new targeted therapies of possible clinical usefulness for high-grade OS.

WHAT THE READER WILL GAIN

This review gives an updated overview of novel therapeutic approaches which have been or are going to be evaluated in Phase I/II/III clinical studies for high-grade OS.

TAKE HOME MESSAGE

On the basis of the information that has emerged so far, it can be predicted that in the next 5 - 10 years, new agents to be included in innovative treatment strategies for selected subgroups of high-grade OS patients may become available.

Using expression and genotype to predict drug response in yeast

Personalized, or genomic, medicine entails tailoring pharmacological therapies according to individual genetic variation at genomic loci encoding proteins in drug-response pathways. It has been previously shown that steady-state mRNA expression can be used to predict the drug response (i.e., sensitivity or resistance) of non-genotyped mammalian cancer cell lines to chemotherapeutic agents. In a real-world setting, clinicians would have access to both steady-state expression levels of patient tissue(s) and a patient's genotypic profile, and yet the predictive power of transcripts versus markers is not well understood. We have previously shown that a collection of genotyped and expression-profiled yeast strains can provide a model for personalized medicine. Here we compare the predictive power of 6,229 steady-state mRNA transcript levels and 2,894 genotyped markers using a pattern recognition algorithm. We were able to predict with over 70% accuracy the drug sensitivity of 104 individual genotyped yeast strains derived from a cross between a laboratory strain and a wild isolate. We observe that, independently of drug mechanism of action, both transcripts and markers can accurately predict drug response. Marker-based prediction is usually more accurate than transcript-based prediction, likely reflecting the genetic determination of gene expression in this cross.

Methotrexate in pediatric osteosarcoma: response and toxicity in relation to genetic polymorphisms and dihydrofolate reductase and reduced folate carrier 1 expression

OBJECTIVE

To determine the influence of the genotype and the level of expression of different enzymes involved in folate metabolism on the response to and toxicity of high-dose methotrexate treatment in pediatric osteosarcomas.

STUDY DESIGN

DHFR and Reduced folate carrier 1 (RFC1) semiquantitative expression was analyzed in 34 primary and metastatic osteosarcoma tissues by real-time polymerase chain reaction. The following polymorphisms were also analyzed in peripheral blood from 96 children with osteosarcoma and 110 control subjects: C677T, A1298C (MTHFR), G80A (RFC1), A2756G (MTR), C1420T (SHMT), the 28bp-repeat polymorphism, and 1494del6 of the TYMS gene. Treatment toxicity was scored after each cycle according to criteria from the World Health Organization.

RESULTS

DHFR and RFC1 expression was lower in initial osteosarcoma biopsy specimens than in metastases (P = .024 and P = .041, respectively). RFC1 expression was moderately decreased in samples with poor histologic response to preoperative treatment (P = .053). Patients with osteosarcoma with G3/G4 hematologic toxicity were more frequently TT than CT/CC for C677T/MTHFR (P = .023) and GG for A2756G/MTR (P = .048 and P = .057 for gastrointestinal and hematologic toxicity, respectively).

CONCLUSIONS

The role of C677T/MTHFR and A2756G/MTR on chemotherapy-induced toxicity should be further investigated in pediatric osteosarcomas receiving high-dose methotrexate. Altered expression of DHFR and RFC1 is a feasible mechanism by which osteosarcoma cells become resistant to methotrexate.

Selection for methotrexate resistance in mammalian cells bearing a Drosophila dihydrofolate reductase transgene: Methotrexate resistance in transgenic mammalian cells

Antifolates, such as methotrexate (MTX), are the treatment of choice for numerous cancers. MTX inhibits dihydrofolate reductase (DHFR), which is essential for cell growth and proliferation. Mammalian cells can acquire resistance to antifolate treatment through a variety of mechanisms but decreased antifolate titers due to changes in drug efflux or influx, or alternatively, the amplification of the DHFR gene are the most commonly acquired resistance mechanisms. In Drosophila, however, a resistant phenotype has only been observed to occur by mutation resulting in a MTX-resistant DHFR. It is unclear if differences in gene structure and/or genome organization between Drosophila and mammals contribute to the observed differences in acquired drug resistance. To investigate if gene structure is involved, Drosophila Dhfr cDNA was transfected into a line of CHO cells that do not express endogenous DHFR. These transgenic cells, together with wild-type CHO cells, were selected for 19 months for resistance to increasing concentrations of MTX, from 50- to 200-fold over the initial concentration. Since Drosophila Dhfr appears to have been amplified several fold in the selected transgenic mammalian cells, a difference in genome organization may contribute to the mechanism of MTX resistance.

Risk stratification based on the clinical factors at diagnosis is closely related to the survival of localized osteosarcoma

BACKGROUND

Survival of osteosarcoma patients has reached a plateau with the addition of chemotherapy and in part predicted based on histologic response. Risk-adapted therapy might be an alternative approach. We aimed to identify risk groups using clinical variables available at time of diagnosis in order to better predict outcomes and form the basis for risk-adapted therapy.

METHODS

This retrospective study analyzed 288 patients with high-grade osteosarcoma of their extremities. Clinicopathologic variables were analyzed to identify factors relevant to risk stratification.

RESULTS

A risk assessment system was developed using age, maximal tumor length (MTL) and tumor location. Index scores were based on the sum total of factor scores, for each of the following: Age (years); "1" for >or=40 or 12-14 (female) or 13-15 (male), "0" for other ages; MTL (cm); "2" for >or=8, "1" for 6-8, "0" for <or=6; Tumor location; "1" for humerus, "0" for elsewhere. Index score 0 or 1 was assigned as low-risk, 2 as intermediate-risk, and 3 or 4 as high-risk. Of the 288 patients, 98 (34.0%) were designated as low-risk, 128 (44.4%) as intermediate-risk and 62 (21.6%) as high-risk. Risk group was related to histologic response and survival. While 63.3% of low-risk patients were good responders, only 43.0% and 33.9% of intermediate- and high-risk patients were good responders. Ten-year event-free survival (EFS) was 81.6 +/- 3.9% for low-risk group, but 31.6 +/- 6.0% for high-risk group.

CONCLUSION

We defined three risk groups that could be used as basis of risk-adapted therapy for osteosarcoma.

Therapy for osteosarcoma: where do we go from here?

Osteosarcoma is the most common malignant primary bone tumor in children and adolescents. Current optimal treatment for osteosarcoma consists of multi-agent chemotherapy and aggressive surgical resection of all sites of disease involvement. The current national and international cooperative trial for patients with newly diagnosed osteosarcoma builds upon the backbone of cisplatin, doxorubicin, and methotrexate. This protocol is designed to clarify whether (i) the addition of ifosfamide and etoposide to postoperative chemotherapy with cisplatin, doxorubicin, and methotrexate improves the event-free survival and overall survival for patients with resectable osteosarcoma and a poor histologic response to 10 weeks of preoperative chemotherapy; and (ii) the addition of pegylated interferon-alpha-2b as maintenance therapy after postoperative chemotherapy with cisplatin, doxorubicin, and methotrexate improves the event-free survival and overall survival for patients with resectable osteosarcoma and a good histologic response to 10 weeks of preoperative chemotherapy. However, the optimal treatment strategy (or strategies) for patients with relapsed or metastatic disease has yet to be defined. This remains one of the persistent challenges in the treatment of osteosarcoma. Recent therapeutic advances have focused on circumventing chemotherapy resistance mechanisms, incorporation of non-classical agents into upfront therapy, targeting of the tumor micro-environment, and investigating the role of novel delivery mechanisms. In patients with localized disease the 5-year survival rate is at least 70%; patients with metastatic or recurrent disease have <20% chance of long-term survival despite aggressive therapies. These figures have changed little in the past 2 decades. This review focuses on the current therapy for osteosarcoma, and highlights emerging strategies that will hopefully change the outlook for patients with this disease.

Farnesyl diphosphate synthase is involved in the resistance to zoledronic acid of osteosarcoma cells

We recently demonstrated original anti-tumor effects of zoledronic acid (Zol) on osteosarcoma cell lines independently of their p53 and Rb status. The present study investigated the potential Zol-resistance acquired by osteosarcoma cells after prolonged treatment. After 12 weeks of culture in the presence of 1 μm Zol, the effects of high doses of Zol (10–100 μm) were compared between the untreated rat (OSRGA, ROS) and human (MG63, SAOS2) osteosarcoma cells and Zol-pretreated cells in terms of cell proliferation, cell cycle analysis, migration assay and cytoskeleton organization. Long-term treatment with 1 μm Zol reduced the sensitivity of osteosarcoma cells to high concentrations of Zol. Furthermore, the Zol-resistant cells were sensitive to conventional anti-cancer agents demonstrating that this resistance process is independent of the multidrug resistance phenotype. However, as similar experiments performed in the presence of clodronate and pamidronate evidenced that this drug resistance was restricted to the nitrogen-containing bisphosphonates, we then hypothesized that this resistance could be associated with a differential expression of farnesyl diphos-phate synthase (FPPS) also observed in human osteosarcoma samples. The transfection of Zol-resistant cells with FPPS siRNA strongly increased their sensitivity to Zol. This study demonstrates for the first time the induction of metabolic resistance after prolonged Zol treatment of osteosarcoma cells confirming the therapeutic potential of Zol for the treatment of bone malignant pathologies, but points out the importance of the treatment regimen may be important in terms of duration and dose to avoid the development of drug metabolic resistance.

Global protein-expression analysis of bone and soft tissue sarcomas

Analysis of global protein expression, an approach known as expression proteomics, can offer important clues for understanding tumor biology that cannot be obtained by other approaches (e.g., genome or transcriptome analysis). Using two-dimensional difference gel electrophoresis (2D-DIGE) and mass spectrometry, we performed global protein expression studies of bone and soft tissue sarcomas to develop novel diagnostic and therapeutic biomarkers and allow molecular classification of the tumors. Among 1500 protein variants identified in the two-dimensional gel, 67 proteins correctly distinguished the eight subtypes of 99 histologically classified soft tissue sarcomas. Hierarchical clustering demonstrated leiomyosarcoma and MFH shared a similar protein expression profile, and clear cell sarcoma, synovial sarcoma, and MPNST could be grouped according to their protein expression patterns. Pleomorphic leiomyosarcoma and MFH showed similar tropomyosin isoform expression patterns. Patients with gastrointestinal stromal tumors expressing pfetin protein had better survival than those whose tumors lacked it. We identified 10 protein spots associated with the chemosensitivity of osteosarcoma to preoperative chemotherapy. These 10 spots could be new diagnostic and prognostic markers for osteosarcoma and new therapeutic targets for the disease. Proteomic analysis using 2D-DIGE provides novel information on the biology of bone and soft tissue sarcomas that could be used to diagnosis and treat these tumors.

LEVEL OF EVIDENCE

Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Clinical impact of the methotrexate resistance-associated genes C-MYC and dihydrofolate reductase (DHFR) in high-grade osteosarcoma

BACKGROUND

Aims of this study were the validation of C-MYC involvement in methotrexate (MTX) resistance and the assessment of clinical impact of C-MYC and dihydrofolate reductase (DHFR) in osteosarcoma (OS).

MATERIALS AND METHODS

The involvement of C-MYC in MTX resistance was validated with an antisense approach. C-MYC and DHFR protein levels at diagnosis were assessed by immunohistochemistry on series of patients treated with either a MTX-based protocol (IOR/OS-1; 72 patients) or with a standard four-drug regimen (ISG/SSG 1; 61 patients).

RESULTS

Down-regulation of C-MYC significantly decreased the MTX resistance level of OS cells, demonstrating its causal involvement in this phenomenon. In clinical samples, a worse outcome was associated with increased levels of DHFR and C-MYC at diagnosis in the IOR/OS-1 patients and of C-MYC in the ISG/SSG 1 patients.

CONCLUSIONS

Meanwhile the adverse clinical impact of DHFR overexpression appeared to be closely related to the relevance of MTX in the chemotherapeutic protocol, that of C-MYC overexpression was more general and not strictly MTX related. The assessment of C-MYC and DHFR at diagnosis, together with that of other known prognostic markers, can be considered for an early identification of subgroups of OS patients with higher risk of adverse outcome.

Resistance to chemotherapy in cancer: a complex and integrated cellular response

Inherent and acquired resistance pathways account for the high rate of failure in cancer chemotherapy. The mechanisms or pathways mediating resistance may be classified as pharmacokinetic (i.e. alter intratumour drug exposue) or pharmacodynamic (i.e. failure to elicit cytotoxicity). More often than not, the resistant phenotype is characterised by alterations in multiple pathways. Consequently, the pathways may act synergistically or generate a broad spectrum of resistance to anticancer drugs. There has been a great deal of systematic characterisation of drug resistance in vitro. However, translating this greater understanding into clinical efficacy has rarely been achieved. This review explores the phenomenon of drug resistance in cancer and highlights the gap between in vitro and in vivo observations. This gap presents a major obstacle in overcoming drug resistance and restoring sensitivity to chemotherapy.

Polymorphisms in Folate, Pyrimidine, and Purine Metabolism Are Associated with Efficacy and Toxicity of Methotrexate in Psoriasis

Methotrexate is the gold standard therapy for moderate to severe psoriasis, but there is marked interpersonal variation in its efficacy and toxicity. We hypothesized that in psoriasis patients, specific common polymorphisms in folate, pyrimidine, and purine metabolic enzymes are associated with methotrexate efficacy and/or toxicity. DNA from 203 retrospectively recruited psoriasis patients treated with methotrexate was collected and genotyped by restriction endonuclease digestion or length polymorphism assays. The reduced folate carrier (RFC) 80A allele and the thymidylate synthase (TS) 3'-untranslated region (3'-UTR) 6 bp deletion were associated with methotrexate-induced toxicity (P=0.025 and P=0.025, respectively). RFC 80A and 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (ATIC) 347G were associated with methotrexate discontinuation (P=0.048 and P=0.038). The TS 5'-UTR 28 bp 3R polymorphism correlated with poor clinical outcome (P=0.029), however, this was not the case when patients with palmoplantar pustular psoriasis were not included in the analysis. Stronger associations between specific polymorphisms and methotrexate-induced toxicity and discontinuation were found in a subanalysis of patients on methotrexate not receiving folic acid supplementation. We have demonstrated preliminary evidence that specific polymorphisms of enzymes involved in folate, pyrimidine, and purine metabolism could be useful in predicting clinical response to methotrexate in patients with psoriasis.

Human reduced folate carrier: translation of basic biology to cancer etiology and therapy

This review attempts to provide a comprehensive overview of the biology of the physiologically and pharmacologically important transport system termed the "reduced folate carrier" (RFC). The ubiquitously expressed RFC has unequivocally established itself as the major transport system in mammalian cells and tissues for a group of compounds including folate cofactors and classical antifolate therapeutics. Loss of RFC expression or function may have potentially profound pathophysiologic consequences including cancer. For chemotherapeutic antifolates used for cancer such as methotrexate or pemetrexed, synthesis of mutant RFCs or loss of RFC transcripts and proteins results in antifolate resistance due to incomplete inhibition of cellular enzyme targets and insufficient substrate for polyglutamate synthesis. Since RFC was first cloned in 1994, tremendous advances have been made in understanding the complex transcriptional and posttranscriptional regulation of RFC, in identifying structurally and functionally important domains and amino acids in the RFC molecule as a prelude to establishing the mechanism of transport, and in characterizing the molecular defects in RFC associated with loss of transport in antifolate resistant cell line models. Many of the insights gained from laboratory models of RFC portend opportunities for modulating carrier expression in drug resistant tumors, and for designing a new generation of agents with improved transport by RFC or substantially enhanced transport by other folate transporters over RFC. Many of the advances in the basic biology of RFC in cell line models are now being directly applied to human cancers in the clinical setting, most notably pediatric acute lymphoblastic leukemia and osteogenic sarcoma.

Molecular basis of antifolate resistance

Folates play a key role in one-carbon metabolism essential for the biosynthesis of purines, thymidylate and hence DNA replication. The antifolate methotrexate has been rationally-designed nearly 60 years ago to potently block the folate-dependent enzyme dihydrofolate reductase (DHFR) thereby achieving temporary remissions in childhood acute leukemia. Recently, the novel antifolates raltitrexed and pemetrexed that target thymidylate synthase (TS) and glycineamide ribonucleotide transformylase (GARTF) were introduced for the treatment of colorectal cancer and malignant pleural mesothelioma. (Anti)folates are divalent anions which predominantly use the reduced folate carrier (RFC) for their cellular uptake. (Anti)folates are retained intracellularly via polyglutamylation catalyzed by folylpoly-gamma-glutamate synthetase (FPGS). As the intracellular concentration of antifolates is critical for their pharmacologic activity, polyglutamylation is a key determinant of antifolate cytotoxicity. However, anticancer drug resistance phenomena pose major obstacles towards curative cancer chemotherapy. Pre-clinical and clinical studies have identified a plethora of mechanisms of antifolate-resistance; these are frequently associated with qualitative and/or quantitative alterations in influx and/or efflux transporters of (anti)folates as well as in folate-dependent enzymes. These include inactivating mutations and/or down-regulation of the RFC and various alterations in the target enzymes DHFR, TS and FPGS. Furthermore, it has been recently shown that members of the ATP-binding cassette (ABC) superfamily including multidrug resistance proteins (MRP/ABCC) and breast cancer resistance protein (BCRP/ABCG2) are low affinity, high capacity ATP-driven (anti)folate efflux transporters. This transport activity is in addition to their established facility to extrude multiple cytotoxic agents. Hence, by actively extruding antifolates, overexpressed MRPs and/or BCRP confer antifolate resistance. Moreover, down-regulation of MRPs and/or BCRP results in decreased folate efflux thereby leading to expansion of the intracellular folate pool and antifolate resistance. This chapter reviews and discusses the panoply of molecular modalities of antifolate-resistance in pre-clinical tumor cell systems in vitro and in vivo as well as in cancer patients. Currently emerging novel strategies for the overcoming of antifolate-resistance are presented. Finally, experimental evidence is provided that the identification and characterization of the molecular mechanisms of antifolate-resistance may prove instrumental in the future development of rationally-based novel antifolates and strategies that could conceivably overcome drug-resistance phenomena.

Chemotherapy resistance in osteosarcoma: current challenges and future directions

For patients with osteosarcoma, the use of chemotherapy has improved survival from 11% with surgical resection alone in the 1960s, to 70% by the mid-1980s. However, survival has since plateaued, despite advances in anticancer therapy. Elucidation of the mechanisms of chemoresistance and implementation of strategies to overcome chemoresistance will likely be pivotal to improving survival. In this review, the focus is on the current understanding of the mechanisms of resistance to the most commonly used agents in the treatment of osteosarcoma and the methods employed to overcome chemotherapy resistance.

Sarcomas and pharmacogenetics

Sarcomas are a heterogeneous group of tumors, requiring different chemotherapeutic approaches. Recently, several regimens for metastatic tumors were evaluated with respect to the different responses to conventional chemotherapy of the various histologic subtypes of sarcomas. The impact of pharmacogenetics in the progress of chemotherapy appears to be crucial in defining the clinical response to many drugs, such as anthracycline or alkylating agents, that are widely used in treatment regimens for soft tissue sarcomas (STS) or sarcomas of the bone. Polymorphisms of metabolizing enzymes (e.g., cytochrome P450 and glutathione-S-transferase), transporter proteins (reduced folate carrier and P-glycoprotein) or target proteins (thymidylate synthase, methylenetetrahydrofolate reductase, dihydrofolate reductase, and c-KIT) may be responsible for an altered clinical outcome, in terms of both response and toxicity. The administration of new chemotherapeutic agents, such as imatinib for gastrointestinal tumors (GIST), requires the study of genetic polymorphisms possibly affecting the integrity of the target (c-KIT), which may provide valid information regarding possible developments of therapy. For STS and sarcoma of the bone, the genetic markers, which could be unambiguously predictive of the phenotypic profile of patients, are as yet undetermined.

Microbubble-enhanced ultrasound exposure promotes uptake of methotrexate into synovial cells and enhanced antiinflammatory effects in the knees of rabbits with antigen-induced arthritis

OBJECTIVE

To evaluate whether microbubble-enhanced ultrasound (US) treatment promotes the delivery of methotrexate (MTX) into synovial cells and the enhanced antiinflammatory effects of intraarticular MTX therapy in a rabbit arthritis model.

METHODS

Arthritis was induced in both knees of 53 rabbits by immunization with ovalbumin. MTX including a microbubble agent was then injected into the left and right knee joints, and the right knees were exposed to US (MTX+/US+ group), while the left knees were not (MTX+/US- group). The knee joints were evaluated histologically in 7 rabbits at 5 time points up to day 56. Quantitative gene expression of interleukin-1beta (IL-1beta) in synovial tissue was measured on days 7 and 28. Eight rabbits were used for the measurement of MTX concentration in synovial tissue 12 hours after treatment. To evaluate the effect of microbubble-enhanced US treatment in the absence of MTX, only the microbubble agent was injected into the left and right knee joints of 10 rabbits with or without US exposure, and these animals were evaluated histologically on days 7 and 28.

RESULTS

The MTX concentration in synovial tissue was significantly higher in the MTX+/US+ group than in the MTX+/US- group. Synovial inflammation was less prominent in the MTX+/US+ group compared with the MTX+/US- group, judging from the results of the histologic evaluation and the gene expression levels of IL-1beta in synovial tissue. It also appeared that microbubble-enhanced US exposure itself did not affect inflammation.

CONCLUSION

Microbubble-enhanced US exposure promoted the uptake of MTX into synovial cells, which resulted in enhancement of the antiinflammatory effects of the intraarticular MTX injection. These results suggest that application of this technique may have clinical benefit.

Functional analysis of altered reduced folate carrier sequence changes identified in osteosarcomas

Osteosarcomas are common primary malignant bone tumors that do not respond to conventional low-dose treatments of methotrexate (Mtx), suggesting an intrinsic resistance to this drug. Previous work has shown that cDNAs generated from osteosarcoma mRNA from a fraction of patients contain sequence changes in the reduced folate carrier (RFC), the membrane protein transporter for Mtx. In this study, the functionality of the altered RFC proteins was assessed by fusing the green fluorescent protein (GFP) to the C-terminal, and examining the ability of the transfected constructs to complement a hamster cell line null for the carrier. Confocal microscopy and cell surface biotinylation indicated that all altered proteins were properly localized at the cell membrane. Only one of those examined, Leu291Pro, was unable to complement the null carrier line, but did bind Mtx at the cell surface. Thus, this alteration confers drug resistance since the carrier is unable to translocate the substrate across the cell membrane. Three alterations, Ser46Asn, Ser4Pro and Gly259Trp, while able to complement the carrier null line, conferred some degree of resistance to Mtx via a decreased rate of transport (Vmax). Another set of alterations, Glu21Lys, Ala7Val, and the combined changes Thr222Ile, Met254Thr, complemented the carrier null line and did not confer resistance to Mtx. Thus, some, but not all of these identified alterations in the RFC may contribute to the lack of responsiveness of osteosarcomas to Mtx treatment.

Human osteosarcoma xenografts and their sensitivity to chemotherapy

Despite the increased survival rates of osteosarcoma patients attributed to adjuvant chemotherapy, at least one third of the patients still die due to their disease. Further improvements in the management of osteosarcoma may rely on a more individualised treatment strategy, as well as on the introduction of new drugs. To aid in the preclinical evaluation of new candidate substances against osteosarcoma, we have established 11 human osteosarcoma xenograft lines and characterised them with regard to response to five different reference drugs. Doxorubicin, cisplatin methotrexate, ifosfamide and lomustine were effective in 3/11, 3/11, 1/10, 5/11 and 4/11 of the xenografts, respectively. Five xenografts were resistant to all compounds tested. We also assessed the mRNA expression levels of the xenografts for the O(6)-Methylguanine DNA Methyltransferase (MGMT), DNA topoisomerase II- (Topo II)-alpha, Gluthathione-S-transferase (GST)-pi, Multidrug-resistance related protein (MRP) 1 and Multidrug-resistance (MDR) 1 genes. There was an inverse correlation between the transcript levels of GST-pi and doxorubicin growth inhibition (r=-0.66; p<0.05), and between the transcript levels of MGMT and the effect of lomustine (r=-0.72; p<0.01), whereas the expression of MRP1 and cisplatin growth inhibition was positively correlated (r=0.82; p<0.005). This panel of xenografts should constitute a good tool for pharmacological and molecular studies in osteosarcoma.

Reduced folate carrier mutations are not the mechanism underlying methotrexate resistance in childhood acute lymphoblastic leukemia

BACKGROUND

Although the majority of children with acute lymphoblastic leukemia (ALL) are cured with combination chemotherapy containing methotrexate (MTX), drug resistance contributes to treatment failure for a substantial fraction of patients. The primary transporter for folates and MTX is the reduced folate carrier (RFC). Impaired drug transport is a documented mechanism of MTX resistance in patients with ALL; however, to the authors' knowledge it is not known whether inactivating RFC mutations are a contributing factor.

METHODS

The authors devised a genomic polymerase chain reaction-single strand conformational polymorphism assay followed by sequencing and screened the entire RFC coding region for sequence alterations in DNA from 246 leukemia specimens from patients with diverse ethnic variation, 24 at the time of recurrence and the rest at the time of diagnosis. This cohort was comprised of 203 B-precursor ALL specimens (82.5%), 32 T-lineage ALL specimens (13%), and 11 acute myeloblastic leukemia specimens (4.5%).

RESULTS

Of 246 DNA samples, only 3 diagnosis B-precursor ALL specimens (1.2%) were found to harbor alterations in the RFC gene, including heterozygous single nucleotide changes resulting in D56H and D522N substitutions in the first extracellular loop and the C-terminus of this transporter, respectively. The third sample had a sequence alteration in exon 3 that could not be identified because of the lack of availability of DNA.

CONCLUSIONS

Whereas inactivating RFC mutations are a frequent mechanism of MTX resistance in human leukemia cell lines and in patients with osteosarcoma, they are not common and do not appear to play any significant role in intrinsic or acquired resistance to MTX in childhood leukemia. This is the first study of RFC mutations in multiple pediatric leukemia specimens.

Reduced folate carrier gene silencing in multiple antifolate-resistant tumor cell lines is due to a simultaneous loss of function of multiple transcription factors but not promoter methylation

The human reduced folate carrier (hRFC) is the major uptake route for antifolates used in cancer chemotherapy. Here we explored the molecular basis for the decrease or loss of hRFC gene expression in seventeen tumor cell lines with resistance to multiple antifolates due to impaired antifolate transport. We studied the role of various cis-acting elements including CRE/AP-1-like element and GC-box in hRFC promoters A and B, respectively, as well as AP-2, Mzf-1 and E-box that are contained within or near four tandemly repeated sequences upstream of promoter A. Decreased or abolished binding either to [32P]GC-box, Mzf-1, AP-1, E-box, or CRE oligonucleotides was detected in approximately 50-80% of antifolate-resistant cell lines. Strikingly, approximately 80% of the cell lines displayed a simultaneously decreased binding to three or more of these hRFC promoter elements, whereas normal AP-2 binding was retained. The possible contribution of promoter methylation to hRFC gene silencing was also explored. None of the antifolate-resistant cell lines, except for MDA-MB-231 cells, showed hRFC promoter methylation; consistently, MDA-MB-231 was the only cell line that retained binding to all six cis-acting elements. Western blot analysis demonstrated decreased expression of transcriptional activators (pCREB-1, pATF-1, USF-1, c-Fos, c-Jun, Sp1, and Sp3) and/or increased expression of repressors (short Sp3 isoforms), whereas normal AP2alpha levels were retained. Transient expression of the relevant transcription factors restored, at least partially, both promoter binding and hRFC gene expression. This is the first report that transcriptional silencing of the hRFC gene in multiple tumor cell lines with resistance to various novel antifolates is a result of a simultaneous loss of function of multiple transcription factors but not promoter methylation.