P-glycoprotein expression: critical determinant in the response to osteosarcoma chemotherapy

P-glycoprotein (P-gp)-driven cancer drug resistance: biological profile, non-coding RNAs, drugs and nanomodulators

Drug resistance has compromised the efficacy of chemotherapy. The dysregulation of drug transporters including P-glycoprotein (P-gp) can mediate drug resistance through drug efflux. In this review, we highlight the role of P-gp in cancer drug resistance and the related molecular pathways, including phosphoinositide 3-kinase (PI3K)-Akt, phosphatase and tensin homolog (PTEN) and nuclear factor-κB (NF-κB), along with non-coding RNAs (ncRNAs). Extracellular vesicles secreted by the cells can transport ncRNAs and other proteins to change P-gp activity in cancer drug resistance. P-gp requires ATP to function, and the induction of mitochondrial dysfunction or inhibition of glutamine metabolism can impair P-gp function, thus increasing chemosensitivity. Phytochemicals, small molecules and nanoparticles have been introduced as P-gp inhibitors to increase drug sensitivity in human cancers.

CD44 Contributes to the Regulation of MDR1 Protein and Doxorubicin Chemoresistance in Osteosarcoma

Osteosarcoma is the most common type of pediatric bone tumor. Despite great advances in chemotherapy during the past decades, the survival rates of osteosarcoma patients remain unsatisfactory. Drug resistance is one of the main reasons, leading to treatment failure and poor prognosis. Previous reports correlated expression of cluster of differentiation 44 (CD44) with drug resistance and poor survival of osteosarcoma patients, however the underlying mechanisms are poorly defined. Here, we investigated the role of CD44 in the regulation of drug chemoresistance, using osteosarcoma cells isolated from mice carrying a mutation of the tumor suppressor neurofibromatosis type 2 (Nf2) gene. CD44 expression was knocked-down in the cells using CRISPR/Cas9 approach. Subsequently, CD44 isoforms and mutants were re-introduced to investigate CD44-dependent processes. Sensitivity to doxorubicin was analyzed in the osteosarcoma cells with modified CD44 expression by immunoblot, colony formation- and WST-1 assay. To dissect the molecular alterations induced by deletion of Cd44, RNA sequencing was performed on Cd44-positive and Cd44-negative primary osteosarcoma tissues isolated from Nf2-mutant mice. Subsequently, expression of candidate genes was evaluated by quantitative reverse transcription PCR (qRT-PCR). Our results indicate that CD44 increases the resistance of osteosarcoma cells to doxorubicin by up-regulating the levels of multidrug resistance (MDR) 1 protein expression, and suggest the role of proteolytically released CD44 intracellular domain, and hyaluronan interactions in this process. Moreover, high throughput sequencing analysis identified differential regulation of several apoptosis-related genes in Cd44-positive and -negative primary osteosarcomas, including p53 apoptosis effector related to PMP-22 (Perp). Deletion of Cd44 in osteosarcoma cells led to doxorubicin-dependent p53 activation and a profound increase in Perp mRNA expression. Overall, our results suggest that CD44 might be an important regulator of drug resistance and suggest that targeting CD44 can sensitize osteosarcoma to standard chemotherapy.

Impact of ABC Transporters in Osteosarcoma and Ewing's Sarcoma: Which Are Involved in Chemoresistance and Which Are Not?

The ATP-binding cassette (ABC) transporter superfamily consists of several proteins with a wide repertoire of functions. Under physiological conditions, ABC transporters are involved in cellular trafficking of hormones, lipids, ions, xenobiotics, and several other molecules, including a broad spectrum of chemical substrates and chemotherapeutic drugs. In cancers, ABC transporters have been intensely studied over the past decades, mostly for their involvement in the multidrug resistance (MDR) phenotype. This review provides an overview of ABC transporters, both related and unrelated to MDR, which have been studied in osteosarcoma and Ewing's sarcoma. Since different backbone drugs used in first-line or rescue chemotherapy for these two rare bone sarcomas are substrates of ABC transporters, this review particularly focused on studies that have provided findings that have been either translated to clinical practice or have indicated new candidate therapeutic targets; however, findings obtained from ABC transporters that were not directly involved in drug resistance were also discussed, in order to provide a more complete overview of the biological impacts of these molecules in osteosarcoma and Ewing's sarcoma. Finally, therapeutic strategies and agents aimed to circumvent ABC-mediated chemoresistance were discussed to provide future perspectives about possible treatment improvements of these neoplasms.

Drug Resistance in Osteosarcoma: Emerging Biomarkers, Therapeutic Targets and Treatment Strategies

Simple Summary

Despite the adoption of aggressive, multimodal treatment schedules, the cure rate of high-grade osteosarcoma (HGOS) has not significantly improved in the last 30 years. The most relevant problem preventing improvement in HGOS prognosis is drug resistance. Therefore, validated novel biomarkers that help to identify those patients who could benefit from innovative treatment options and the development of drugs enabling personalized therapeutic protocols are necessary. The aim of this review was to give an overview on the most relevant emerging drug resistance-related biomarkers, therapeutic targets and new agents or novel candidate treatment strategies, which have been highlighted and suggested for HGOS to improve the success rate of clinical trials.

Abstract

High-grade osteosarcoma (HGOS), the most common primary malignant tumor of bone, is a highly aggressive neoplasm with a cure rate of approximately 40–50% in unselected patient populations. The major clinical problems opposing the cure of HGOS are the presence of inherent or acquired drug resistance and the development of metastasis. Since the drugs used in first-line chemotherapy protocols for HGOS and clinical outcome have not significantly evolved in the past three decades, there is an urgent need for new therapeutic biomarkers and targeted treatment strategies, which may increase the currently available spectrum of cure modalities. Unresponsive or chemoresistant (refractory) HGOS patients usually encounter a dismal prognosis, mostly because therapeutic options and drugs effective for rescue treatments are scarce. Tailored treatments for different subgroups of HGOS patients stratified according to drug resistance-related biomarkers thus appear as an option that may improve this situation. This review explores drug resistance-related biomarkers, therapeutic targets and new candidate treatment strategies, which have emerged in HGOS. In addition to consolidated biomarkers, specific attention has been paid to the role of non-coding RNAs, tumor-derived extracellular vesicles, and cancer stem cells as contributors to drug resistance in HGOS, in order to highlight new candidate markers and therapeutic targets. The possible use of new non-conventional drugs to overcome the main mechanisms of drug resistance in HGOS are finally discussed.

Tumor-Associated Antigens (TAAs) for the Serological Diagnosis of Osteosarcoma

Osteosarcoma (OS) is the most common form of malignant bone tumor found in childhood and adolescence. Although its incidence rate is low among cancers, the prognosis of OS is usually poor. Although some biomarkers, such as p53, have been identified in OS, the association between the biomarkers and clinical outcome is not well understood. Thus, it is necessary to establish a method to identify patients diagnosed with OS at an early stage. It is becoming obvious that anti-tumor-associated antigens (TAAs) autoantibodies (TAAbs) in sera could be used as serological biomarkers in the detection of many different types of cancers. This notion indicates that TAAbs are considered as immunological “sentinels” associated with tumorigenesis underlying molecular events. It provides new insights into the molecular and cellular biology of the differential diagnosis of cancers. What’s more, it is reported that a customized TAA array could significantly increase the sensitivity/specificity. TAA arrays also have great application prospects in detecting cancer at an early stage, monitoring cancer progression, discovering new therapeutic targets, and designing personalized treatment. In this review, we provide an overview of the TAAs identified in OS as well as the possibility that TAAs and TAAbs system be used as biomarkers in the immunodiagnosis and prognosis of OS.

Role of ABCB1 in mediating chemoresistance of triple-negative breast cancers

Triple-negative breast cancer (TNBC) is a group of breast cancers which neither express hormonal receptors nor human epidermal growth factor receptor. Hence, there is a lack of currently known targeted therapies and the only available line of systemic treatment option is chemotherapy or more recently immune therapy. However, in patients with relapsed disease after adjuvant or neoadjuvant therapy, resistance to chemotherapeutic agents has often developed, which results in poor treatment response. Multidrug resistance (MDR) has emerged as an important mechanism by which TNBCs mediate drug resistance and occurs primarily due to overexpression of ATP-binding cassette (ABC) transporter proteins such as P-glycoprotein (Pgp). Pgp overexpression had been linked to poor outcome, reduced survival rates and chemoresistance in patients. The aim of this mini-review is to provide a topical overview of the recent studies and to generate further interest in this critical research area, with the aim to develop an effective and safe approach for overcoming Pgp-mediated chemoresistance in TNBC.

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.

Selenium-doped calcium phosphate biomineral reverses multidrug resistance to enhance bone tumor chemotherapy

The construction of a functional drug delivery system to reverse the multidrug resistance (MDR) of bone tumors in cases of failed chemotherapy remains a challenge. Herein, we demonstrate a selenium-doped calcium phosphate (Se-CaP) biomineral with high biocompatibility, biodegradability and pH-sensitive drug release properties. Se-CaP may not only serve as an effective drug-carrier to enhance the uptake of doxorubicin (DOX), but may also synchronously induce caspases-mediated apoptosis of osteosarcoma by generating intracellular reactive oxygen species (ROS). Furthermore, in vitro and in vivo studies obviously demonstrate that Se-CaP can reverse the MDR of osteosarcoma by down-regulating the expression of MDR-related ABC (ATP binding cassette) transporters proteins (ABCB1 and ABCC1). Finally, DOX-loaded Se-CaP can significantly inhibit DOX-resistant MG63 (MG63/DXR) tumor growth in nude mice. Considering its biomimetic chemical properties, the Se-CaP biomineral, with the multiple functions mentioned above, could be a promising candidate for treating bone tumors with MDR characteristics.

Circular RNA hsa_circ_0001649 suppresses the growth of osteosarcoma cells via sponging multiple miRNAs

Osteosarcoma (OS) is a serious bone malignancy commonly occurred in childhood and adolescence. Circular RNA (circRNA) is a novel endogenous RNA that may be considered as a new biomarker for diseases' diagnosis or prognosis. This study explored the roles and mechanism of circ_0001649 in OS. The qRT-PCR was performed to test circ_0001649 expression in OS tissues and cells. Luciferase was used to confirm the binding of circ_0001649 with miR-338-5p, miR-647 and miR-942. OS cells were stably transfected with pEX-circ_0001649 or miRNAs mimic, CCK-8 kit, colony formation, apoptosis and western blot analysis were used to detect the roles of circ_0001649. Circ_0001649 was low-expressed in OS tissues and cell lines. Circ_0001649 overexpression suppressed U2OS and HOS cell viability and survival fraction, and induced apoptosis presented as the increasing levels of Apaf-1, cleaved-caspase-3 and cleaved-caspase-9. Further, circ_0001649 worked as a sponge to absorb miR-338-5p, miR-647 and miR-942 to suppress cell proliferation, induce apoptosis and inhibit STAT pathway. Circ_0001649 suppressed OS cell proliferation and STAT pathway and induced apoptosis through sponging miR-338-5p, miR-647 and miR-942.

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.

Role of ATP-binding cassette transporters in cancer initiation and progression

ATP Binding Cassette (ABC) transporters, widely studied in cancer for their role in drug resistance, have been more recently also considered for their contribution to cancer cell biology. To date, many data provide evidences for their potential role in all the phases of cancer development from cancer susceptibility, tumor initiation, tumor progression and metastasis. Although many evidences are based on correlative analyses, data describing a direct or indirect role of ABC transporters in cancer biology are increasing. Overall, current available information suggests a relevant molecular effector role of some ABC transporters in cancer invasion and metastasis as reported in experimental tumor models. From a therapeutic point of view, due to the physiological relevant roles that ABC transporters play in the organism, the capability to selectively inhibit the function or the expression of ABC transporters in cancer stem cells or other tumor cells, represents the main challenge for researcher scientists. A detailed and updated description of the current knowledge on the role of ABC transporters in cancer biology is provided.

GLUL Ablation Can Confer Drug Resistance to Cancer Cells via a Malate-Aspartate Shuttle-Mediated Mechanism

Glutamate-ammonia ligase (GLUL) is important for acid-base homeostasis, ammonia detoxification, cell signaling, and proliferation. Here, we reported that GLUL ablation conferred resistance to several anticancer drugs in specific cancer cell lines while leaving other cell lines non-resistant to the same drugs. To understand the biochemical mechanics supporting this drug resistance, we compared drug-resistant GLUL knockout (KO) A549 non-small-cell lung carcinoma (NSCLC) cells with non-resistant GLUL KO H1299 NSCLC cells and found that the resistant A549 cells, to a larger extent, depended on exogenous glucose for proliferation. As GLUL activity is linked to the tricarboxylic acid (TCA) cycle via reversed glutaminolysis, we probed carbon flux through both glycolysis and TCA pathways by means of ¹³C5 glutamine, ¹³C5 glutamate, and ¹³C6 glucose tracing. We observed increased labeling of malate and aspartate in A549 GLUL KO cells, whereas the non-resistant GLUL KO H1299 cells displayed decreased ¹³C-labeling. The malate and aspartate shuttle supported cellular NADH production and was associated with cellular metabolic fitness. Inhibition of the malate-aspartate shuttle with aminooxyacetic acid significantly impacted upon cell viability with an IC₅₀ of 11.5 μM in resistant GLUL KO A549 cells compared to 28 μM in control A549 cells, linking resistance to the malate-aspartate shuttle. Additionally, rescuing GLUL expression in A549 KO cells increased drug sensitivity. We proposed a novel metabolic mechanism in cancer drug resistance where the increased capacity of the malate-aspartate shuttle increased metabolic fitness, thereby facilitating cancer cells to escape drug pressure.

MT2A is an early predictive biomarker of response to chemotherapy and a potential therapeutic target in osteosarcoma

Osteosarcoma is the most prevalent primary bone malignancy in children and young adults. Resistance to chemotherapy remains a key challenge for effective treatment of patients with osteosarcoma. The aim of the present study was to investigate the preventive role of metallothionein-2A (MT2A) in response to cytotoxic effects of chemotherapy. A panel of human and murine osteosarcoma cell lines, modified for MT2A were evaluated for cell viability, and motility (wound healing assay). Cell-derived xenograft models were established in mice. FFPE tumour samples were assessed by IHC. In vitro experiments indicated a positive correlation between half-maximal inhibitory concentration (IC50) for drugs in clinical practice, and MT2A mRNA level. This reinforced our previously reported correlation between MT2A mRNA level in tumour samples at diagnosis and overall survival in patients with osteosarcoma. In addition, MT2A/MT2 silencing using shRNA strategy led to a marked reduction of IC50 values and to enhanced cytotoxic effect of chemotherapy on primary tumour. Our results show that MT2A level could be used as a predictive biomarker of resistance to chemotherapy, and provide with preclinical rational for MT2A targeting as a therapeutic strategy for enhancing anti-tumour treatment of innate chemo-resistant osteosarcoma cells.

Hyaluronated liposomes containing H2S-releasing doxorubicin are effective against P-glycoprotein-positive/doxorubicin-resistant osteosarcoma cells and xenografts

Doxorubicin (dox) is one of the first-line drug in osteosarcoma treatment but its effectiveness is limited by the efflux pump P-glycoprotein (Pgp) and by the onset of cardiotoxicity. We previously demonstrated that synthetic doxs conjugated with a H₂S-releasing moiety (Sdox) were less cardiotoxic and more effective than dox against Pgp-overexpressing osteosarcoma cells. In order to increase the active delivery to tumor cells, we produced hyaluronic acid (HA)-conjugated liposomes containing Sdox (HA-Lsdox), exploiting the abundance of the HA receptor CD44 in osteosarcoma. HA-Lsdox showed favorable drug-release profile and higher toxicity in vitro and in vivo than dox or the FDA-approved liposomal dox Caelyx^® against Pgp-overexpressing osteosarcoma, displaying the same cardiotoxicity profile of Caelyx^®. Differently from dox, HA-Lsdox delivered the drug within the endoplasmic reticulum (ER), inducing protein sulfhydration and ubiquitination, and activating a ER stress pro-apoptotic response mediated by CHOP. HA-Lsdox also sulfhydrated the nascent Pgp in the ER, reducing its activity. We propose HA-Lsdox as an innovative tool noteworthy to be tested in Pgp-overexpressing patients, who are frequently less responsive to standard treatments in which dox is one of the most important drugs.

Mapping discontinuous epitopes for MRK-16, UIC2 and 4E3 antibodies to extracellular loops 1 and 4 of human P-glycoprotein

P-glycoprotein (P-gp), an ATP-dependent efflux pump, is associated with the development of multidrug resistance in cancer cells. Antibody-mediated blockade of human P-gp activity has been shown to overcome drug resistance by re-sensitizing resistant cancer cells to anticancer drugs. Despite the potential clinical application of this finding, the epitopes of the three human P-gp-specific monoclonal antibodies MRK-16, UIC2 and 4E3, which bind to the extracellular loops (ECLs) have not yet been mapped. By generating human-mouse P-gp chimeras, we mapped the epitopes of these antibodies to ECLs 1 and 4. We then identified key amino acids in these regions by replacing mouse residues with homologous human P-gp residues to recover binding of antibodies to the mouse P-gp. We found that changing a total of ten residues, five each in ECL1 and ECL4, was sufficient to recover binding of both MRK-16 and 4E3 antibodies, suggesting a common epitope. However, recovery of the conformation-sensitive UIC2 epitope required replacement of thirteen residues in ECL1 and the same five residues replaced in the ECL4 for MRK-16 and 4E3 binding. These results demonstrate that discontinuous epitopes for MRK-16, UIC2 and 4E3 are located in the same regions of ECL1 and 4 of the multidrug transporter.

Cancer stem cells and hypoxia-inducible factors (Review)

Cancer stem cells (CSCs), also known as tumor-initiating cells, are a subpopulation of tumor cells that exhibit properties similar to those of normal stem cells. Oxygen is an important regulator of cellular metabolism; hypoxia-inducible factors (HIFs) mediate metabolic switches in cells in hypoxic environments. Hypoxia clearly has the potential to exert a significant effect on the maintenance and evolution of CSCs. Both HIF‑1α and HIF‑2α may contribute to the regulation of cellular adaptation to hypoxia and resistance to cancer therapies. This review provides an overview of the roles of HIFs in CSCs. HIF‑1α and HIF‑2α have significant prognostic and predictive value in the clinic and the concept of personalized medicine should be applied in designing clinical trials for HIF inhibitors.

Targeting ABCB1 (MDR1) in multi-drug resistant osteosarcoma cells using the CRISPR-Cas9 system to reverse drug resistance

Background

Multi-drug resistance (MDR) remains a significant obstacle to successful chemotherapy treatment for osteosarcoma patients. One of the central causes of MDR is the overexpression of the membrane bound drug transporter protein P-glycoprotein (P-gp), which is the protein product of the MDR gene ABCB1. Though several methods have been reported to reverse MDR in vitro and in vivo when combined with anticancer drugs, they have yet to be proven useful in the clinical setting.

Results

The meta-analysis demonstrated that a high level of P-gp may predict poor survival in patients with osteosarcoma. The expression of P-gp can be efficiently blocked by the clustered regularly interspaced short palindromic repeats (CRISPR)-associated Cas9 system (CRISPR-Cas9). Inhibition of ABCB1 was associated with reversing drug resistance in osteosarcoma MDR cell lines (KHOSR2 and U-2OSR2) to doxorubicin.

Materials and Methods

We performed a meta-analysis to investigate the relationship between P-gp expression and survival in patients with osteosarcoma. Then we adopted the CRISPR-Cas9, a robust and highly efficient novel genome editing tool, to determine its effect on reversing drug resistance by targeting endogenous ABCB1 gene at the DNA level in osteosarcoma MDR cell lines.

Conclusion

These results suggest that the CRISPR-Cas9 system is a useful tool for the modification of ABCB1 gene, and may be useful in extending the long-term efficacy of chemotherapy by overcoming P-gp-mediated MDR in the clinical setting.

Therapeutic potential of the metabolic modulator Metformin on osteosarcoma cancer stem-like cells

PURPOSE

Osteosarcoma is the most common primary bone tumour appearing in children and adolescents. Recent studies demonstrate that osteosarcoma possesses a stem-like cell subset, so-called cancer stem-like cells, refractory to conventional chemotherapeutics and pointed out as responsible for relapses frequently observed in osteosarcoma patients. Here, we explored the therapeutic potential of Metformin on osteosarcoma stem-like cells, alone and as a chemosensitizer of doxorubicin.

METHODS

Stem-like cells were isolated from human osteosarcoma cell lines, MNNG/HOS and MG-63, using the sphere-forming assay. Metformin cytotoxicity alone and combined with doxorubicin were evaluated using MTT/BrdU assays. Protein levels of AMPK and AKT were evaluated by Western Blot. Cellular metabolic status was assessed based on [¹⁸F]-FDG uptake and lactate production measurements. Sphere-forming efficiency and expression of pluripotency transcription factors analysed by qRT-PCR were tested as readout of Metformin effects on stemness features.

RESULTS

Metformin induced a concentration-dependent decrease in the metabolic activity and proliferation of sphere-forming cells and improved doxorubicin-induced cytotoxicity. This drug also down-regulated the expression of master regulators of pluripotency (OCT4, SOX2, NANOG), and decreased spheres' self-renewal ability. Metformin effects on mitochondria led to the activation and phosphorylation of the energetic sensor AMPK along with an upregulation of the pro-survival AKT pathway in both cell populations. Furthermore, Metformin-induced mitochondrial stress increased [¹⁸F]-FDG uptake and lactate production in parental cells but not in the quiescent stem-like cells, suggesting the inability of the latter to cope with the energy crisis induced by metformin.

CONCLUSIONS

This preclinical study suggests that Metformin may be a potentially useful therapeutic agent and chemosensitizer of osteosarcoma stem-like cells to doxorubicin.

Anticancer efficacy of the hypoxia-activated prodrug evofosfamide is enhanced in combination with proapoptotic receptor agonists against osteosarcoma

Tumor hypoxia is a major cause of treatment failure for a variety of malignancies. However, hypoxia also leads to treatment opportunities as demonstrated by the development of compounds that target regions of hypoxia within tumors. Evofosfamide is a hypoxia‐activated prodrug that is created by linking the hypoxia‐seeking 2‐nitroimidazole moiety to the cytotoxic bromo‐isophosphoramide mustard (Br‐IPM). When evofosfamide is delivered to hypoxic regions of tumors, the DNA cross‐linking toxin, Br‐IPM, is released leading to cell death. This study assessed the anticancer efficacy of evofosfamide in combination with the Proapoptotic Receptor Agonists (PARAs) dulanermin and drozitumab against human osteosarcoma in vitro and in an intratibial murine model of osteosarcoma. Under hypoxic conditions in vitro, evofosfamide cooperated with dulanermin and drozitumab, resulting in the potentiation of cytotoxicity to osteosarcoma cells. In contrast, under the same conditions, primary human osteoblasts were resistant to treatment. Animals transplanted with osteosarcoma cells directly into their tibiae developed mixed osteosclerotic/osteolytic bone lesions and consequently developed lung metastases 3 weeks post cancer cell transplantation. Tumor burden in the bone was reduced by evofosfamide treatment alone and in combination with drozitumab and prevented osteosarcoma‐induced bone destruction while also reducing the growth of pulmonary metastases. These results suggest that evofosfamide may be an attractive therapeutic agent, with strong anticancer activity alone or in combination with either drozitumab or dulanermin against osteosarcoma.

P-glycoprotein attenuates DNA repair activity in multidrug-resistant cells by acting through the Cbp-Csk-Src cascade

Recent studies have demonstrated that P-glycoprotein (P-gp) expression impairs DNA interstrand cross-linking agent-induced DNA repair efficiency in multidrug-resistant (MDR) cells. To date, the detailed molecular mechanisms underlying how P-gp interferes with Src activation and subsequent DNA repair activity remain unclear. In this study, we determined that the C-terminal Src kinase-binding protein (Cbp) signaling pathway involved in the negative control of Src activation is enhanced in MDR cells. We also demonstrated that cells that ectopically express P-gp exhibit reduced activation of DNA damage response regulators, such as ATM, Chk2, Braca1 and Nbs1 and hence attenuated DNA double-strand break repair capacity and become more susceptible than vector control cells to DNA interstrand cross-linking (ICL) agents. Moreover, we demonstrated that P-gp can not only interact with Cbp and Src but also enhance the formation of inhibitory C-terminal Src kinase (Csk)-Cbp complexes that reduce phosphorylation of the Src activation residue Y416 and increase phosphorylation of the Src negative regulatory residue Y527. Notably, suppression of Cbp expression in MDR cells restores cisplatin-induced Src activation, improves DNA repair capacity, and increases resistance to ICL agents. Ectopic expression of Cbp attenuates cisplatin-induced Src activation and increases the susceptibility of cells to ICL agents. Together, the current results indicate that P-gp inhibits DNA repair activity by modulating Src activation via Cbp-Csk-Src cascade. These results suggest that DNA ICL agents are likely to have therapeutic potential against MDR cells with P-gp-overexpression.

Genome Analysis of Osteosarcoma Progression Samples Identifies FGFR1 Overexpression as a Potential Treatment Target and CHM as a Candidate Tumor Suppressor Gene

Osteosarcoma (OS) is the most common primary malignant tumor of bone, showing complex chromosomal rearrangements but with few known consistent changes. Deeper biological understanding is crucial to find new therapies to improve patient survival. We have sequenced the whole exome of two primary tumors (before and after chemotherapy), one metastatic tumor and a matched normal sample from two OS patients, to identify mutations involved in cancer biology. The metastatic samples were also RNA sequenced. By RNA sequencing we identified dysregulated expression levels of drug resistance- and apoptosis-related genes. Two fusion transcripts were identified in one patient (OS111); the first resulted in p53 inactivation by fusing the first exon of TP53 to the fifth exon of FAM45A. The second fusion joined the two first exons of FGFR1 to the second exon of ZNF343. Furthermore, FGFR1 was amplified and highly expressed, representing a potential treatment target in this patient. Whole exome sequencing revealed large intertumor heterogeneity, with surprisingly few shared mutations. Careful evaluation and validation of the data sets revealed a number of artefacts, but one recurrent mutation was validated, a nonsense mutation in CHM (patient OS106), which also was the mutation with the highest expression frequency (53%). The second patient (OS111) had wild-type CHM, but a downregulated expression level. In a panel of 71 clinical samples, we confirmed significant low expression of CHM compared to the controls (p = 0.003). Furthermore, by analyzing public datasets, we identified a significant association between low expression and poor survival in two other cancer types. Together, these results suggest CHM as a candidate tumor suppressor gene that warrants further investigation.

Evaluation of P-glycoprotein (Pgp) expression in human osteosarcoma by high-throughput tissue microarray

Survival of osteosarcoma patients is currently limited by the development of metastases and multidrug resistance (MDR). A well-established cause of MDR involves overexpression of P-glycoprotein (Pgp) in tumor cells. However, some discrepancies still exist as to the clinical significance of Pgp in osteosarcoma. We sought to elucidate further whether the Pgp expression correlated with clinical behavior in a series of patients with osteosarcoma via high-throughput tissue microarray (TMA) analysis. Immunohistochemical analysis of Pgp expression in a TMA of 114 specimens with a retrospective review of 70 osteosarcoma patients admitted to the Massachusetts General Hospital (MGH) was performed. High Pgp expression was correlated with metastasis development and poor response to pre-operative chemotherapy in osteosarcoma patients. Eighteen of the fifty-seven patients initially admitted with primary osteosarcoma showed high Pgp expression. Among these 18 patients with high Pgp expression, 13 of 18 (72%) patients eventually developed metastases. There was no significant clinical relevance between Pgp expression and osteosarcoma survival. These results support that high expression of Pgp is important, but cannot be assigned as, an individual predictor in the development of human osteosarcoma. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1606-1612, 2016.

Cisplatin-resistant osteosarcoma cells possess cancer stem cell properties in a mouse model

Osteosarcoma is the most common malignancy of the bones, and although advances in chemotherapy and surgery had been achieved in recent years, the long-term survival rate has reached a plateau. The main reason for this is the aggressive malignant potential and poor response of the disease to chemotherapy. However, several studies have found that tumor resistance is associated with cancer stem cells (CSCs). To address this issue, in the present study, osteosarcoma cells were treated with specially designated concentrations of cisplatin (CDDP) in a mouse model. Hematoxylin and eosin staining analyses were performed to assess tissue structure, in vivo passaging and CDDP treatment. Drug resistance genes and well-established stemness genes were detected by quantitative polymerase chain reaction. A serum-starved sphere formation assay was adopted to evaluate the ability to generate spherical clones and flow cytometry as used to test the expression of the cluster of differentiation 117 and Stro-1 surface markers, known as markers of CSCs. It was found that CDDP could induce an effect of resistance in the osteosarcoma cells, which possessed cancer stem CSC properties, as shown by the elevated expression of CSC marker genes and the higher expression of the cluster of differentiation 117 and Stro-1 surface markers. Moreover, the cells that dissociated from the tumor tissues exhibited an increased ability to form sarcospheres. The results of this study provided a significant correlation between resistance and CSCs, and revealed a clue indicating that osteosarcoma recurrence is likely to be associated with CSCs.

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.

Risk-Based Therapy for Localized Osteosarcoma

BACKGROUND

The outcome of localized osteosarcoma has remained constant over the past 30 years. Histological response to preoperative chemotherapy is the best predictor of outcome. Strategies to alter treatment based on histological response have not resulted in increased survival.

PROCEDURE

Patients with localized osteosarcoma received preoperative chemotherapy with cisplatin, doxorubicin, and methotrexate. Patients whose tumors had a good histological response (≥90% necrosis) continued with the same treatment postoperatively. Patients with poor histological response (<90% necrosis) received three courses of melphalan 100 mg/m(2) on day -4, cyclophosphamide 2,000 mg/m(2) on days -3, and -2 followed by stem cell infusion.

RESULTS

Fifty-two patients were enrolled. Median age was 14 years, and 56% of patients were male. The femur was the most common site. Forty patients underwent limb salvage surgery and amputation was performed in six patients. Forty-eight percent of tumors showed good histological response. Forty patients were evaluable for outcome; 18 patients with poor histologic response received high-dose chemotherapy. The 5-year event-free survival (EFS) and overall survival (OS) for patients treated on the high-dose chemotherapy arm were 28% (95% confidence interval [CI], 10-49) and 48% (95% CI, 23-69), respectively. The 5-year EFS and OS for patients treated on the standard chemotherapy arm were 62% (95% CI, 36-80) and 74% (95% CI, 44-90), respectively. All patients who received high-dose chemotherapy developed grade 3 or higher hematological toxicity. There were no treatment-related deaths.

CONCLUSIONS

Postoperative alkylator intensification with high-dose cyclophosphamide and melphalan in patients with localized osteosarcoma with poor histological response failed to improve survival.

Advances in emerging drugs for osteosarcoma

INTRODUCTION

Osteosarcoma (OS), the most common primary malignant bone tumor, is currently treated with pre- and postoperative chemotherapy in association with the surgical removal of the tumor. Conventional treatments allow to cure about 60 - 65% of patients with primary tumors and only 20 - 25% of patients with recurrent disease. New treatment approaches and drugs are therefore highly warranted to improve prognosis.

AREAS COVERED

This review focuses on the therapeutic approaches that are under development or clinical evaluation in OS. Information was obtained from different and continuously updated data bases, as well as from literature searches, in which particular relevance was given to reports and reviews on new targeted therapies under clinical investigation in high-grade OS.

EXPERT OPINION

OS is a heterogeneous tumor, with a great variability in treatment response between patients. It is therefore unlikely that a single therapeutic tool will be uniformly successful for all OS patients. This claims for the validation of new treatment approaches together with biologic/(pharmaco)genetic markers, which may select the most appropriate subgroup of patients for each treatment approach. Since some promising novel agents and treatment strategies are currently tested in Phase I/II/III clinical trials, we may hope that new therapies with superior efficacy and safety profiles will be identified in the next few years.

Hypoxia-activated pro-drug TH-302 exhibits potent tumor suppressive activity and cooperates with chemotherapy against osteosarcoma

Tumor hypoxia is a major cause of treatment failure for a variety of malignancies. However, tumor hypoxia also offers treatment opportunities, exemplified by the development compounds that target hypoxic regions within tumors. TH-302 is a pro-drug created by the conjugation of 2-nitroimidazole to bromo-isophosphoramide (Br-IPM). When TH-302 is delivered to regions of hypoxia, Br-IPM, the DNA cross linking toxin, is released. In this study we assessed the cytotoxic activity of TH-302 against osteosarcoma cells in vitro and evaluated its anticancer efficacy as a single agent, and in combination with doxorubicin, in an orthotopic mouse model of human osteosarcoma (OS). In vitro, TH-302 was potently cytotoxic to osteosarcoma cells selectively under hypoxic conditions, whereas primary normal human osteoblasts were protected. Animals transplanted with OS cells directly into their tibiae and left untreated developed mixed osteolytic/osteosclerotic bone lesions and subsequently developed lung metastases. TH-302 reduced tumor burden in bone and cooperated with doxorubicin to protect bone from osteosarcoma induced bone destruction, while it also reduced lung metastases. TH-302 may therefore be an attractive therapeutic agent with strong activity as a single agent and in combination with chemotherapy against OS.

Transferrin-targeted polymeric micelles co-loaded with curcumin and paclitaxel: efficient killing of paclitaxel-resistant cancer cells

PURPOSE

The ability to successfully treat advanced forms of cancer remains a challenge due to chemotherapy resistance. Numerous studies indicate that NF-κB, a protein complex that controls the expression of numerous genes, as being a key factor in producing chemo-resistant tumors. In this study, the therapeutic potential of transferrin (TF)-targeted mixed micelles, made of PEG-PE and vitamin E co-loaded with curcumin (CUR), a potent NF-κB inhibitor, and paclitaxel (PCL), was examined.

METHODS

The cytotoxicity of non-targeted and TF-targeted CUR and PCL micelles as a single agent or in combination was investigated against SK-OV-3 human ovarian adenocarcinoma along with its multi-drug resistant (MDR) version SK-OV-3-PCL-resistant (SK-OV-3TR) cells in vitro.

RESULTS

Our results indicated that the TF-targeted combination micelles were able to improve the net cytotoxic effect of CUR and PCL to clear synergistic one against the SK-OV-3 cells. In addition, even though the non-targeted combination treatment demonstrated a synergistic effect against the SK-OV-3TR cells, the addition of the TF-targeting moiety significantly increased this cytotoxic effect. While keeping CUR constant at 5 and 10 μM and varying the PCL concentration, the PCL IC50 decreased from ~1.78 to 0.68 μM for the non-targeted formulations to ~0.74 and 0.1 μM for the TF-targeted ones, respectively.

CONCLUSION

Our results indicate that such co-loaded targeted mixed micelles could have significant clinical advantages for the treatment of resistant ovarian cancer and provide a clear rational for further in vivo investigation.

Review of the molecular pathogenesis of osteosarcoma

Treating the osteosarcoma (OSA) remains a challenge. Current strategies focus on the primary tumor and have limited efficacy for metastatic OSA. A better understanding of the OSA pathogenesis may provide a rational basis for innovative treatment strategies especially for metastases. The aim of this review is to give an overview of the molecular mechanisms of OSA tumorigenesis, OSA cell proliferation, apoptosis, migration, and chemotherapy resistance, and how improved understanding might contribute to designing a better treatment target for OSA.

Reversal of ATP-binding cassette drug transporter activity to modulate chemoresistance: why has it failed to provide clinical benefit?

Enhanced drug extrusion from cells due to the overexpression of the ATP-binding cassette (ABC) drug transporters inhibits the cytotoxic effects of structurally diverse and mechanistically unrelated anticancer agents and is a major cause of multidrug resistance (MDR) of human malignancies. Multiple compounds can suppress the activity of these efflux transporters and sensitize resistant tumor cells, but despite promising preclinical and early clinical data, they have yet to find a role in oncologic practice. Based on the knowledge of the structure, function, and distribution of MDR-related ABC transporters and the results of their preclinical and clinical evaluation, we discuss probable reasons why these inhibitors have not improved the outcome of therapy for cancer patients. We also outline new MDR-reversing strategies that directly target ABC transporters or circumvent relevant signaling pathways.

Array comparative genomic hybridization in osteosarcoma

Osteosarcoma, the most frequent primary bone tumor, is a malignant mesenchymal sarcoma with a peak incidence in young children and adolescents. Left untreated, it progresses relentlessly to local and systemic disease, ultimately leading to death within months. Genomically, osteosarcomas are aneuploid with chaotic karyotypes, lacking the pathognomonic genetic rearrangements characteristic of most sarcomas. The familial genetics of osteosarcoma helped in elucidating some of the etiological molecular disruptions, such as the tumor suppressor genes RB1 in retinoblastoma and TP53 in Li-Fraumeni, and RECQL4 involved in DNA repair/replication in Rothmund-Thomson syndrome. Genomic profiling approaches such as array comparative genomic hybridization (aCGH) have provided additional insights concerning the mechanisms responsible for generating complex osteosarcoma genomes. This chapter provides a brief introduction to the clinical features of conventional osteosarcoma, the predominant subtypes, and a general overview of materials and analytical methods of osteosarcoma aCGH, followed by a more detailed literature overview of aCGH studies and a discussion of emerging genes, molecular mechanisms, and their clinical implications, as well as more recent application of integrative genomics in osteosarcoma. aCHG is helping elucidate genomic events leading to tumor development and evolution as well as identification of prognostic markers and therapeutic targets in osteosarcoma.

P-glycoprotein binds to ezrin at amino acid residues 149-242 in the FERM domain and plays a key role in the multidrug resistance of human osteosarcoma

Overexpression of the mdr1 gene encoding P-glycoprotein (Pgp) exerts a major role in reducing the effectiveness of cytotoxic therapy in osteosarcoma. The interaction between actin and Pgp has been shown to be instrumental in the establishment of multidrug resistance (MDR) in human tumor cells. The cytoskeleton linker ezrin exerts a pivotal role in maintaining the functional connection between actin and Pgp. We investigated the role of ezrin in a human multidrug-resistant osteosarcoma cell line overexpressing Pgp and compared it to its counterpart that overexpresses an ezrin deletion mutant. The results showed that Pgp binds at amino acid residues 149-242 of the N-terminal domain of ezrin. The interaction between ezrin and Pgp occurs in the plasma membrane of MDR cells, where they also co-localize with the ganglioside G(M1) located in lipid rafts. The overexpression of the ezrin deletion mutant entirely restored drug susceptibility of osteosarcoma cells, consistent with Pgp dislocation to cytoplasmic compartments and abrogation of G(M1) /Pgp co-localization at the plasma membrane. Our study provides evidence that ezrin exerts a key role in MDR of human osteosarcoma cells through a Pgp-ezrin-actin connection that is instrumental for the permanence of Pgp into plasma membrane lipid rafts. We also show for the first time that Pgp-binding site is localized to amino acid residues 149-242 of the ezrin Band 4.1, Ezrin/Radixin/Moesin (FERM) domain, thus proposing a specific target for future molecular therapy aimed at counteracting MDR in osteosarcoma patients.

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.

Zoledronic acid protects against osteosarcoma-induced bone destruction but lacks efficacy against pulmonary metastases in a syngeneic rat model

Osteosarcoma (OS) is the most common primary malignant tumor of bone in children and adolescents. In spite of successful control of the primary tumor, death from lung metastasis occurs in more than a third of patients. To investigate the efficacy of zoledronic acid (ZOL) on the development, progression and metastatic spread of OS, we used a rat model of OS, with features of the disease similar to human patients, including spontaneous metastasis to lungs. Rat OS cells were inoculated into the tibial marrow cavity of syngeneic rats. OS development was associated with osteolysis mixed with new bone formation, adjacent to the periosteum and extended into the surrounding soft tissue. Metastatic foci in the lungs formed 3-4 weeks postcancer cell transplantation. Treatment with a clinically relevant dose of ZOL was initiated 1 week after tumors were established and continued once weekly or as a single dose. ZOL preserved the integrity of both trabecular and cortical bone and reduced tumor-induced bone formation. However, the overall tumor burden at the primary site was not reduced because of the persistent growth of cancer cells in the extramedullary space, which was not affected by ZOL treatment. ZOL treatment failed to prevent the metastatic spread of OS to the lungs. These findings suggest that ZOL as a single agent protects against OS-induced bone destruction but lacks efficacy against pulmonary metastases in this rat model. ZOL may have potential value as an adjuvant therapy in patients with established OS.

Generating inhibitors of P-glycoprotein: where to, now?

The prominent role for the drug efflux pump ABCB1 (P-glycoprotein) in mediating resistance to chemotherapy was first suggested in 1976 and sparked an incredible drive to restore the efficacy of anticancer drugs. Achieving this goal seemed inevitable in 1982 when a series of calcium channel blockers were demonstrated to restore the efficacy of chemotherapy agents. A large number of other compounds have since been demonstrated to restore chemotherapeutic sensitivity in cancer cells or tissues. Where do we stand almost three decades since the first reports of ABCB1 inhibition? Unfortunately, in the aftermath of extensive fundamental and clinical research efforts the situation remains gloomy. Only a small handful of compounds have reached late stage clinical trials and none are in routine clinical usage to circumvent chemoresistance. Why has the translation process been so ineffective? One factor is the multifactorial nature of drug resistance inherent to cancer tissues; ABCB1 is not the sole factor. However, expression of ABCB1 remains a significant negative prognostic indicator and is closely associated with poor response to chemotherapy in many cancer types. The main difficulties with restoration of sensitivity to chemotherapy reside with poor properties of the ABCB1 inhibitors: (1) low selectivity to ABCB1, (2) poor potency to inhibit ABCB1, (3) inherent toxicity and/or (4) adverse pharmacokinetic interactions with anticancer drugs. Despite these difficulties, there is a clear requirement for effective inhibitors and to date the strategies for generating such compounds have involved serendipity or simple chemical syntheses. This chapter outlines more sophisticated approaches making use of bioinformatics, combinatorial chemistry and structure informed drug design. Generating a new arsenal of potent and selective ABCB1 inhibitors offers the promise of restoring the efficacy of a key weapon in cancer treatment--chemotherapy.

Osteosarcoma treatment: state of the art

Osteosarcoma (OS) is a class of cancer originating from bone, mainly afflicting children or young adults. It is the second highest cause of cancer-related death in these age groups, mainly due to development of often fatal metastasis, usually in the lungs. Survival for these patients is poor despite the aggressive use of surgery, chemotherapy, and/or radiotherapy. Thus, new effective drugs and other forms of therapy are needed. This article reviews the biology and the state of the art management of OS. New experimental drugs and potential therapies targeting molecular pathways of OS are also discussed.

Evaluation of (64)Cu(DO3A-xy-TPEP) as a potential PET radiotracer for monitoring tumor multidrug resistance

In this study, we evaluated the potential of (64)Cu(DO3A-xy-TPEP) (DO3A-xy-TPEP = (2-(diphenylphosphoryl)ethyl)diphenyl(4-((4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)benzyl)phosphonium) as a PET (positron emission tomography) radiotracer for noninvasive monitoring of multidrug resistance (MDR) transport function in several xenografted tumor models (MDR-negative: U87MG; MDR-positive: MDA-MB-435, MDA-MB-231, KB-3-1, and KB-v-1). It was found that (64)Cu(DO3A-xy-TPEP) has a high initial tumor uptake (5.27 +/- 1.2%ID/g at 5 min p.i.) and shows a steady uptake increase between 30 and 120 min p.i. (2.09 +/- 0.53 and 3.35 +/- 1.27%ID/g at 30 and 120 min p.i., respectively) in the MDR-negative U87MG glioma tumors. (64)Cu(DO3A-xy-TPEP) has a greater uptake difference between U87MG glioma and MDR-positive tumors (MDA-MB-231: 1.57 +/- 0.04, 1.00 +/- 0.17, and 0.93 +/- 0.15; MDA-MB-435: 1.15 +/- 0.19, 1.12 +/- 0.20, and 0.81 +/- 0.11; KB-3-1: 1.45 +/- 0.31, 1.43 +/- 0.16, and 1.08 +/- 0.19; and KB-v-1: 1.63 +/- 0.47, 1.81 +/- 0.31, and 1.14 +/- 0.22%ID/g at 30, 60, and 120 min p.i., respectively) than (99m)Tc-Sestamibi. Regardless of the source of MDR, the overall net effect is the rapid efflux of (64)Cu(DO3A-xy-TPEP) from tumor cells, which leads to a significant reduction of its tumor uptake. It was concluded that (64)Cu(DO3A-xy-TPEP) is more efficient than (99m)Tc-Sestamibi as the substrate for MDR P-glycoproteins (MDR Pgps) and multidrug resistance-associated proteins (MRPs), and might be a more efficient radiotracer for noninvasive monitoring of the tumor MDR transport function. (64)Cu(DO3A-xy-TPEP) and (99m)Tc-Sestamibi share almost identical subcellular distribution patterns in U87MG glioma tumors. Thus, it is reasonable to believe that (64)Cu(DO3A-xy-TPEP), like (99m)Tc-Sestamibi, is able to localize in mitochondria due to the increased plasma and mitochondrial transmembrane potentials in tumor cells.

Zoledronic acid inhibits both the osteolytic and osteoblastic components of osteosarcoma lesions in a mouse model

PURPOSE

To evaluate the efficacy of zoledronic acid (ZOL) against osteosarcoma (OS) growth, progression, and metastatic spread using an animal model of human OS that closely resembles the human disease.

EXPERIMENTAL DESIGN

Human K-HOS or KRIB OS cells, tagged or untagged with a luciferase reporter construct, were transplanted directly into the tibial cavity of nude mice. ZOL was given as weekly, or a single dose of 100 microg/kg body weight, equivalent to the 4 mg i.v. dose used clinically. Tumor growth at the primary site and as pulmonary metastases was monitored by bioluminescence imaging and histology, and OS-induced bone destruction was measured using high-resolution micro-computed tomography.

RESULTS

Mice transplanted with OS cells exhibited aberrant bone remodeling in the area of cancer cell transplantation, with areas of osteolysis mixed with extensive new bone formation extending from the cortex. ZOL administration prevented osteolysis and significantly reduced the amount of OS-induced bone formation. However, ZOL had no effect on tumor burden at the primary site. Importantly, ZOL failed to reduce lung metastasis and in some cases was associated with larger and more numerous metastatic lesions.

CONCLUSIONS

Our data show that clinically relevant doses of ZOL, while protecting the bone from OS-induced bone destruction, do not inhibit primary tumor growth. Moreover, lung metastases were not reduced and may even have been promoted by this treatment, indicating that caution is required when the clinical application of the bisphosphonate class of antiresorptives is considered in OS.

Immunohistochemical Estimates of Angiogenesis, Proliferative Activity, p53 Expression, and Multiple Drug Resistance Have No Prognostic Impact in Osteosarcoma: A Comparative Clinicopathological Investigation

Purpose. To investigate angiogenesis, multiple drug resistance (MDR) and proliferative activity as prognostic variables in patients suffering from osteosarcoma. Methods. Histologic biopsies from 117 patients treated in the period from 1972 through 1999 were immunohistologically investigated regarding angiogenesis (CD34), proliferative activity (MIB-1), and the expression of p53 and MDR (P-glycoprotein (Pgp); clones JSB-1, C494, and MRK16). Quantitative and semiquantitative scores of immunoreactive cells were analyzed statistically along with retrospectively obtained clinicopathologic variables. Results. Chemotherapy reduced the rate of amputations (P = .00002). The Pgp was overexpressed (score ≥2) in 48% of the primary, diagnostic biopsies, and high Pgp correlated with high Pgp in postsurgical specimens (P = .003). In contrast, no such associations were disclosed for estimates of angiogenesis (P = .64) and p53 (P > .32), whereas the MIB-1 index was reduced in the post-chemotherapy specimens (P = .02). The overall, disease-specific survival was 47%, increasing to 54% in patients receiving pre-operative chemotherapy. Statistical analyses showed prognostic impact exclusively by patient age and type of osteosarcoma. Discussion. The studied series of patients documented already prior to the chemotherapy era, a rather excellent survival and estimates of angiogenesis, proliferation, p53, and Pgp expressions, did not demonstrate sufficient power to serve as predictors of treatment response or survival.

Prognostic factors in localized extremity osteosarcoma: a systematic review

AIM

Finding reliable prognostic factors for osteosarcoma remains problematic. A systematic review [Davis AM, Bell RS, Goodwin PJ. Prognostic factors in osteosarcoma: a critical review. Journal of Clinical Oncology 1994; 12(2): 423-431.] showed chemotherapy response as only independent factor. We tried to identify evidence-based prognostic factors in the literature since 1992 and to establish pooled relative risks of factors.

METHODS

MEDLINE and Embase search (1992-August 2006). Two reviewers independently selected papers addressing prognostic factors in localized extremity osteosarcoma, which were studied for methodological quality, and valuable new factors. An attempt was made to pool results.

RESULTS

Of 1777 "hits", 93 papers were studied in depth. Several "new" prognostic factors were found. Only 7 papers were of sufficient quality to analyze. Chemotherapy response, tumor size and site, alkaline phosphatase level and p-glycoprotein expression seemed to be independent factors. Some new factors looked promising.

CONCLUSIONS

Although the literature is abundant, it is disappointing that only few papers are of sufficient quality to allow hard conclusions. Because of heterogeneity of the studies pooling results is hardly possible. There is a need for standardization of studies and reports.

Biomarkers in Osteosarcoma

Osteosarcoma is the most common primary tumor of bone and accounts for approximately 19% of all malignant tumors of bone. It is the third most common malignant tumor in teenagers. More than twenty years ago, the advent of a multidisciplinary approach that combined multi-agent chemotherapy and limb-sparing surgery greatly improved the survival rate of patients with osteosarcoma. Unfortunately, since that time, survival rates have not dramatically improved. To date, the most powerful predictors of outcome have remained the ability to detect metastatic disease at diagnosis and the histopathologic response of the tumor to preoperative chemotherapy. Presently, 80% of patients who do not have distant metastases at initial diagnosis will become long-term survivors. Unfortunately, this means that approximately 20% of patients who do not present with metastases at diagnosis will not survive. This group of patients appears to be resistant to current treatment as attempts to intensify therapy after surgery for patients with a poor histopathologic response has not significantly improved survival rates. It is these patients that are in the greatest need of additional clinically relevant markers for prognosis and who can be most helped by molecular analysis. While steady progress has been made in the identification of genetic alterations in osteosarcoma, no individual molecular marker has thus far been demonstrated to have a better prognostic significance in the treatment of osteosarcomas than the current clinical markers. Thus there is clearly a need to employ new comprehensive analysis technologies to develop significantly more informative classification systems and to identify new therapeutic targets.

Expression and activity of taxane-metabolizing enzymes in ovarian tumors

OBJECTIVE

Current firstline chemotherapy for ovarian cancer consists of carboplatin combined with either paclitaxel or docetaxel. Disposition of carboplatin is determined by renal clearance, while the taxanes are metabolized by cytochrome P450 (CYP450) enzymes. Although the majority of taxane metabolism occurs in the liver, recent data have shown that some solid tumors express CYP450 enzymes in the tumors themselves. The objective of this study was to determine whether ovarian tumors express genes regulating cellular efflux and subsequent metabolism, and whether any clinico-pathologic features correlated with expression.

METHODS

Gene expression of CYP2C8, CYP3A4/A5 and the ABC transporter ABCB1 was determined in 56 primary epithelial ovarian tumors. Cells were grown from seven different tumors and exposed ex vivo to paclitaxel (PAC) and docetaxel (DOC) for up to 24 h. PAC and DOC concentrations were measured in the media by an LC-MS assay.

RESULTS

Results from this analysis demonstrate that ovarian cancer cells do express functional taxane-metabolizing enzymes. Such expression appeared to enhance the ability of cancer cells to metabolize DOC. Specifically, the PK of DOC was correlated with the ratio of CYP4A5 to ABCB1 gene expression, thus representing a novel mechanism of chemotherapy resistance. There was no relationship between PAC PK parameters and gene expression.

CONCLUSIONS

Knowledge of inter-individual variation in CYP450 enzyme and ABC transporter tumor expression and activity may influence the individualization of chemotherapy, by avoiding agents that are rapidly metabolized and selecting agents that are not.

Functional imaging of multidrug resistance in an orthotopic model of osteosarcoma using 99mTc-sestamibi

PURPOSE

The purpose of this work was the development of an orthotopic model of osteosarcoma based on luciferase-expressing tumour cells for the in vivo imaging of multidrug resistance (MDR) with (99m)Tc-sestamibi.

METHODS

Doxorubicin-sensitive (143B-luc(+)) and resistant (MNNG/HOS-luc(+)) osteosarcoma cell lines expressing different levels of P-glycoprotein and carrying a luciferase reporter gene were inoculated into the tibia of nude mice. Local tumour growth was monitored weekly by bioluminescence imaging and X-ray. After tumour growth, a (99m)Tc-sestamibi dynamic study was performed. A subset of animals was pre-treated with an MDR inhibitor (PSC833). Images were analysed for calculation of (99m)Tc-sestamibi washout half-life (t (1/2)), percentage washout rate (%WR) and tumour/non-tumour (T/NT) ratio.

RESULTS

A progressively increasing bioluminescent signal was detected in the proximal tibia after 2 weeks. The t (1/2) of (99m)Tc-sestamibi was significantly shorter (p < 0.05) in drug-resistant MNNG/HOS-luc(+) tumours (t (1/2) = 87.3 +/- 15.7 min) than in drug-sensitive 143B-luc(+) tumours (t (1/2) = 161.0 +/- 47.4 min) and decreased significantly with PSC833 (t (1/2) = 173.0 +/- 24.5 min, p < 0.05). No significant effects of PSC833 were observed in 143B-luc(+) tumours. The T/NT ratio was significantly lower (p < 0.05) in MNNG/HOS-luc(+) tumours than in 143B-luc(+) tumours at early (1.55 +/- 0.22 vs 2.14 +/- 0.36) and delayed times (1.12 +/- 0.11 vs 1.62 +/- 0.33). PSC833 had no significant effects on the T/NT ratios of either tumour.

CONCLUSION

The orthotopic injection of tumour cells provides an animal model suitable for functional imaging of MDR. In vivo bioluminescence imaging allows the non-invasive monitoring of tumour growth. The kinetic analysis of (99m)Tc-sestamibi washout provides information on the functional activity of MDR related to P-glycoprotein expression and its pharmacological inhibition in osteosarcoma.

A review of clinical and molecular prognostic factors in osteosarcoma

Traditional prognostic determinants in osteosarcoma have included demographics (age, sex), tumour size, site, stage, and the response to chemotherapy. Many of these are determined using varying techniques and units of measurement, which can make comparison between studies difficult. The absence of survival difference between limb sparing surgery and amputation has been repeatedly demonstrated in primary disease, and even in the setting of pathological fracture. On the other hand, there is still some controversy over the existence of increased local recurrence for limb-sparing surgery, and the implications of this. Commonly used prognostic determinants such as metastases, and response to chemotherapy enable a high degree of prognostic accuracy but usually at a late stage in the course of disease. Leading on from this, there is a need to uncover molecular pathways with specific influence over osteosarcoma progression to facilitate earlier treatment changes. Some important pathways are already being defined, for example the association of CXCR4 with metastases on presentation, the likelihood of doxorubicin resistance with positive P-glycoprotein, and the reduced survival prediction of over expressed survivin. It is anticipated that the future of osteosarcoma treatment will involve treatment tailored to the molecular profile of tumours at diagnosis, adjuvant therapy directed towards dysfunctional molecular pathways rather than the use of cytotoxics, and a more standardised approach to the measurement of clinical prognostic factors.

Caveolin-1 reduces osteosarcoma metastases by inhibiting c-Src activity and met signaling

Caveolin-1 (Cav-1) is highly expressed in normal osteoblasts. This article reports that Cav-1 down-regulation is part of osteoblast transformation and osteosarcoma progression and validates its role as oncosuppressor in human osteosarcoma. A survey of 6-year follow-up indicates a better overall survival for osteosarcoma expressing a level of Cav-1 similar to osteoblasts. However, the majority of primary osteosarcoma shows significantly lower levels of Cav-1 than normal osteoblasts. Accordingly, Met-induced osteoblast transformation is associated with Cav-1 down-regulation. In vitro, osteosarcoma cell lines forced to overexpress Cav-1 show reduced malignancy with inhibited anchorage-independent growth, migration, and invasion. In vivo, Cav-1 overexpression abrogates the metastatic ability of osteosarcoma cells. c-Src and c-Met tyrosine kinases, which are activated in osteosarcoma, colocalize with Cav-1 and are inhibited on Cav-1 overexpression. Thus, Cav-1 behaves as an oncosuppressor in osteosarcoma. Altogether, data suggest that Cav-1 down-modulation might function as a permissive mechanism, which, by unleashing c-Src and Met signaling, enables osteosarcoma cells to invade neighboring tissues. These data strengthen the rationale to target c-Src family kinases and/or Met receptor to improve the extremely poor prognosis of metastatic osteosarcoma.