A phase II study of temsirolimus and liposomal doxorubicin for patients with recurrent and refractory bone and soft tissue sarcomas

Mesenchymal Stem Cells-Derived Small Extracellular Vesicles and Their Validation as a Promising Treatment for Chondrosarcoma in a 3D Model in Vitro

Chondrosarcomas (CHS) constitute approximately 20% of all primary malignant bone tumors, characterized by a slow growth rate with initial manifestation of few signs and symptoms. These malignant cartilaginous neoplasms, particularly those with dedifferentiated histological subtypes, pose significant therapeutic challenges, as they exhibit high resistance to both radiation and chemotherapy. Ranging from relatively benign, low-grade tumors (grade I) to aggressive high-grade tumors with the potential for lung metastases and a grim prognosis, there is a critical need for innovative diagnostic and therapeutic approaches, particularly for patients with more aggressive forms. Herein, small extracellular vesicles (sEVs) derived from mesenchymal stem cells are presented as an efficient nanodelivery tool to enhance drug penetration in an in vitro 3D model of CHS. Employing high-pressure homogenization (HPH), we achieved unprecedented encapsulation efficiency of doxorubicin (DXR) in sEVs derived from mesenchymal stem cells (MSC-EVs). Subsequently, a comparative analysis between free DXR and MSC-EVs encapsulated with DXR (DXR-MSC-EVs) was conducted to assess their penetration and uptake efficacy in the 3D model. The results unveiled a higher incidence of necrotic cells and a more pronounced toxic effect with DXR-MSC-EVs compared to DXR alone. This underscores the remarkable ability of MSC-EVs to deliver drugs in complex environments, highlighting their potential application in the treatment of aggressive CHS.

Pegylated liposomal doxorubicin combined with cyclophosphamide and vincristine in pediatric patients with relapsed/refractory solid tumor: a single-arm, open-label, phase I study

Background

The combined vincristine, pegylated liposomal doxorubicin (PLD), and cyclophosphamide (VPC) regimen has never been studied in pediatric patients.

Methods

This open-label, single-center, single-arm phase I study utilizing a "3 + 3" design enrolled children with relapsed/refractory (R/R) solid tumors. Three dose levels of PLD (Duomeisu®) were studied (30, 40, or 50 mg/m2) in combination with cyclophosphamide (1500 mg/m2), mesna (1500 mg/m2), and vincristine (1.5 mg/m2, maximum 2 mg) once every 3 weeks. The primary endpoints included safety, the maximum tolerated dose (MTD) of PLD (Duomeisu®), and the recommended phase 2 dose (RP2D) of PLD (Duomeisu®) for further phase 2 investigation. The secondary endpoints were objective response rate (ORR) and disease control rate (DCR). This study is registered with ClinicalTrials.gov, NCT04213612.

Findings

Between January 7, 2020, and November 18, 2021, 34 patients were eligible and evaluable for toxicity, while 26 patients were evaluable for response. The MTD of PLD (Duomeisu®) was 30 mg/m2. The most common adverse event (AE) was grade 3 or 4 neutropenia (61.8%). The most common grade 1 or 2 non-hematologic AE and cardiotoxicity effects were vomiting (35.3%) and abnormal electrocardiogram T waves (20.6%), respectively. ORR and DCR to VPC regimen after two cycles were 50.0% and 92.3%, respectively. Targeted gene panel sequencing revealed the activation of TP53 mutation may be an adverse prognostic factor.

Interpretation

The VPC regimen showed a promising safety profile and had preliminary efficacy in children with R/R solid tumors. The RP2D for PLD (Duomeisu®) combined with cyclophosphamide and vincristine is 30 mg/m2 once every 3 weeks.

Funding

CSPC Ouyi Pharmaceutical Co., Ltd., Shijiazhuang, the National Key Research and Development Program of China [No. 2022YFC2705005], the National Natural Science Foundation of China [No. 82203303], and the Basic and Applied Basic Research Foundation of Guangdong Province [No. 2021A1515110234].

Combination Treatment with Liposomal Doxorubicin and Inductive Moderate Hyperthermia for Sarcoma Saos-2 Cells

Despite efforts in osteosarcoma (OS) research, the role of inductive moderate hyperthermia (IMH) in delivering and enhancing the antitumor effect of liposomal doxorubicin formulations (LDOX) remains unresolved. This study investigated the effect of a combination treatment with LDOX and IMH on Saos-2 human OS cells. We compared cell viability using a trypan blue assay, apoptosis and reactive oxygen species (ROS) measured by flow cytometry and pro-apoptotic Bax protein expression examined by immunocytochemistry in response to IMH (42 MHz frequency, 15 W power for 30 min), LDOX (0.4 μg/mL), and LDOX plus IMH. The lower IC50 value of LDOX at 72 h indicated increased accumulation of the drug in the OS cells. LDOX plus IMH resulted in a 61% lower cell viability compared to no treatment. Moreover, IMH potentiated the LDOX action on the Saos-2 cells by promoting ROS production at temperatures of <42 °C. There was a 12% increase in cell populations undergoing early apoptosis with a less heterogeneous distribution of Bax after combination treatment compared to those treated with LDOX (p < 0.05). Therefore, we determined that IMH could enhance LDOX delivery and its antitumor effect via altered membrane permeabilization, ROS generation, and a lower level of visualized Bax heterogeneity in the Saos-2 cells, suggesting the potential translation of these findings into in vivo studies.

Rhabdomyosarcoma: Current Therapy, Challenges, and Future Approaches to Treatment Strategies

Rhabdomyosarcoma is a rare cancer arising in skeletal muscle that typically impacts children and young adults. It is a worldwide challenge in child health as treatment outcomes for metastatic and recurrent disease still pose a major concern for both basic and clinical scientists. The treatment strategies for rhabdomyosarcoma include multi-agent chemotherapies after surgical resection with or without ionization radiotherapy. In this comprehensive review, we first provide a detailed clinical understanding of rhabdomyosarcoma including its classification and subtypes, diagnosis, and treatment strategies. Later, we focus on chemotherapy strategies for this childhood sarcoma and discuss the impact of three mechanisms that are involved in the chemotherapy response including apoptosis, macro-autophagy, and the unfolded protein response. Finally, we discuss in vivo mouse and zebrafish models and in vitro three-dimensional bioengineering models of rhabdomyosarcoma to screen future therapeutic approaches and promote muscle regeneration.

Targeting the MDM2-p53 pathway in dedifferentiated liposarcoma

Dedifferentiated liposarcoma (DDLPS) is an aggressive adipogenic cancer with poor prognosis. DDLPS tumors are only modestly sensitive to chemotherapy and radiation, and there is a need for more effective therapies. Genetically, DDLPS is characterized by a low tumor mutational burden and frequent chromosomal structural abnormalities including amplification of the 12q13-15 chromosomal region and the MDM2 gene, which are defining features of DDLPS. The MDM2 protein is an E3 ubiquitin ligase that targets the tumor suppressor, p53, for proteasomal degradation. MDM2 amplification or overexpression in human malignancies is associated with cell-cycle progression and worse prognosis. The MDM2-p53 interaction has thus garnered interest as a therapeutic target for DDLPS and other malignancies. MDM2 binds p53 via a hydrophobic protein interaction that is easily accessible with synthetic analogues. Multiple agents have been developed, including Nutlins such as RG7112 and small molecular inhibitors including SAR405838 and HDM201. Preclinical in vitro and animal models have shown promising results with MDM2 inhibition, resulting in robust p53 reactivation and cancer cell death. However, multiple early-phase clinical trials have failed to show a benefit with MDM2 pathway inhibition for DDLPS. Mechanisms of resistance are being elucidated, and novel inhibitors and combination therapies are currently under investigation. This review provides an overview of these strategies for targeting MDM2 in DDLPS.

Ewing Sarcoma Meets Epigenetics, Immunology and Nanomedicine: Moving Forward into Novel Therapeutic Strategies

Ewing Sarcoma (EWS) is an aggressive bone and soft tissue tumor that mainly affects children, adolescents, and young adults. The standard therapy, including chemotherapy, surgery, and radiotherapy, has substantially improved the survival of EWS patients with localized disease. Unfortunately, this multimodal treatment remains elusive in clinics for those patients with recurrent or metastatic disease who have an unfavorable prognosis. Consistently, there is an urgent need to find new strategies for patients that fail to respond to standard therapies. In this regard, in the last decade, treatments targeting epigenetic dependencies in tumor cells and the immune system have emerged into the clinical scenario. Additionally, recent advances in nanomedicine provide novel delivery drug systems, which may address challenges such as side effects and toxicity. Therefore, therapeutic strategies stemming from epigenetics, immunology, and nanomedicine yield promising alternatives for treating these patients. In this review, we highlight the most relevant EWS preclinical and clinical studies in epigenetics, immunotherapy, and nanotherapy conducted in the last five years.

Inhibition of mTOR by temsirolimus overcomes radio-resistance in nasopharyngeal carcinoma

Radio-resistance is a leading cause of nasopharyngeal carcinoma (NPC) treatment failure and identification of sensitizing therapeutic target is an unmet need to enhance clinical management. Given that the mammalian target of rapamycin (mTOR) signaling confers resistance to cancer therapy, we investigated whether mTOR contributes to radio-resistance in NPC and pharmacological inhibition of mTOR can overcome radio-resistance. We found that mTOR mRNA and protein levels, and phosphorylation of its downstream effector were increased in radio-resistant NPC compared with parental cells. mTOR inhibitor temsirolimus inhibits proliferation and induces apoptosis in a panel of NPC cell lines. Importantly, temsirolimus acts synergistically with radiation and is effective against radio-resistant cells. Using radio-resistant xenograft mouse model, we validated the efficacy of temsirolimus in preventing tumor formation and inhibiting tumor growth. Temsirolimus overcome radio-resistance in NPC via inhibiting mTOR signaling. Our work provides the pre-clinical evidence that the combination of radiation and mTOR inhibitor may be a therapeutic strategy in NPC. Our findings might accelerate the initiation of clinical trials on radio-resistant NPC patients using temsirolimus. This article is protected by copyright. All rights reserved.

Interrogating the Genomic Landscape of Uterine Leiomyosarcoma: A Potential for Patient Benefit

Uterine leiomyosarcoma (uLMS) is a rare and aggressive gynaecological malignancy. Surgical removal and chemotherapy are commonly used to treat uLMS, but recurrence rates are high. Over the last few decades, clarification of the genomic landscape of uLMS has revealed a number of recurring mutations, including TP53, RB1, ATRX, PTEN, and MED12. Such genomic aberrations are difficult to target therapeutically or are actively targeted in other malignancies, and their potential as targets for the treatment of uLMS remains largely unexplored. Recent identification of deficiencies in homologous recombination in a minority of these tumours, however, has provided a rationale for investigation of PARP inhibitors in this sub-set. Here, we review these mutations and the evidence for therapeutic avenues that may be applied in uLMS. We also provide a comprehensive background on diagnosis and current therapeutic strategies as well as reviewing preclinical models of uLMS, which may be employed not only in testing emerging therapies but also in understanding this challenging and deadly disease.

Systemic Treatment of Ewing Sarcoma: Current Options and Future Perspectives

Ewing sarcoma (ES) is an uncommon malignant neoplasm, mostly affecting young adults and adolescents. Surgical excision, irradiation, and combinations of multiple chemotherapeutic agents are currently used as a multimodal strategy for the treatment of local and oligometastatic disease. Although ES usually responds to the primary treatment, relapsed and primarily refractory disease remains a difficult therapeutic challenge. The growing understanding of cancer biology and the subsequent development of new therapeutic strategies have been put at the service of research in recurrent and refractory ES, generating a great number of ongoing studies with compounds that could find superior clinical outcomes in the years to come. This review gathers the current available information on the treatment and clinical investigation of ES and aims to be a point of support for future research.

Irinotecan Plus Doxorubicin Hydrochloride Liposomes for Relapsed or Refractory Wilms Tumor

Purpose

The prognosis of relapsed or refractory pediatric Wilms tumor (WT) is dismal, and new salvage therapies are needed. This study aimed to evaluate the efficacy of the combination of irinotecan and a doxorubicin hydrochloride liposome regimen for relapsed or refractory pediatric WT.

Patients and Methods

The present study enrolled relapsed or refractory pediatric WT patients who were treated with the AI regimen (doxorubicin hydrochloride liposomes 40 mg/m² per day, day 1, and irinotecan 50 mg/m² per day with 90-min infusion, days 1–5; this regimen was repeated every 3 weeks) at Sun Yat-sen University Cancer Center from July 2018 to September 2020. The response was defined as the best-observed response after at least two cycles according to the Response Evaluation Criteria of Solid Tumors (RECIST 1.1), and toxicity was evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE 4.03).

Results

A total of 16 patients (male:female, 8:8) with a median age of 4.2 years (0.5–11 years) with relapsed or refractory disease were enrolled in this study, including 14 patients with relapsed disease and two patients with refractory disease. These patients received 1–8 courses (median, 3 courses) of the AI regimen. Fourteen patients were assessable for response: two with complete response (CR), five with partial response (PR), two with stable disease (SD), and five with progressive disease (PD). The objective response rate was 50% (two CR, five PR), and the disease control rate was 64% (two CR, five PR, and two SD). Seven out of 14 patients (50%) were alive at the last follow-up, ranging from 2.6 to 32.4 months. The median progression-free survival and median overall survival were 3.5 months (range 0.5–12 months) and 8 months (range 1–28 months), respectively. Sixteen patients were assessable for toxicity, with the most common grade 3 or 4 adverse events being alopecia (62%), leukopenia (40%), abdominal pain (38%), diarrhea (23%), and mucositis (16%), etc. No fatal adverse events have been observed, and modest adverse effects can be administered.

Conclusion

Irinotecan and doxorubicin hydrochloride liposome regimens have positive efficacy on relapsed or refractory pediatric WT with well-tolerated toxicity. A prospective clinical trial is warranted.

223-Radium for metastatic osteosarcoma: combination therapy with other agents and external beam radiotherapy

Background

Bone-seeking radiopharmaceuticals can deposit radiation selectively to some osteosarcoma tumours because of the bone-forming nature of this cancer.

Objectives

This is the first report of using 223-radium, an alpha-emitting calcium analogue with a high therapeutic index, in combination therapy with other agents in 15 patients with metastatic osteoblastic osteosarcoma.

Methods

Candidates for alpha-radiotherapy if ^99mTc-MDP bone scan had avid bone-forming lesions and no therapy of higher priority (eg, definitive surgery). Monthly 223-radium infusions (1.49 μCi/kg or 55.13 kBq/kg) were given.

Results

The median infusion number was three and the average time to progression was 4.3 months for this cohort receiving 223-radium+other agents. Agents provided during 223-radium included (1) drugs to reduce skeletal complications: monthly denosumab (n=13) or zolendronate (n=1); (2) agents with antivascular endothelial growth factor activity, pazopanib (n=8) or sorafenib (n=1), (3) alkylating agents: oral cyclophosphamide (n=1) or ifosfamide, given as a 14-day continuous infusion (n=1, two cycles), (4) high-dose methotrexate (n=1), pegylated liposomal doxorubicin (n=1); and (5) two other combinations: nivolumab and everolimus (n=1) and rapamycin and auranofin (n=1). Radiation therapy, including stereotactic body radiotherapy (SBRT), was also given to 11 patients concurrently with 223-radium (n=2), after 223-radium completion (n=3), or both concurrently and then sequentially for other sites (n=6). After 223-radium infusions, patients without RT had a median overall survival of 4.3 months compared with those with SBRT and/or RT, who had a median overall survival of 13.5 months.

Conclusion Although only 1/15 of patients with osteoblastic osteosarcoma still remain alive after 223-radium, overall survival

Osteosarcoma, chondrosarcoma and Ewing sarcoma: Clinical aspects, biomarker discovery and liquid biopsy

Bone sarcomas, although rare, are associated with significant morbidity and mortality. The most frequent primary bone cancers include osteosarcoma, chondrosarcoma and Ewing sarcoma. The treatment approaches are heterogeneous and mainly chosen based on precise tumour staging. Unfortunately, clinical outcome has not changed significantly in over 30 years and tumour grade is still the best prognosticator of metastatic disease and survival. An option to improve this scenario is to identify molecular biomarkers in the early stage of the disease, or even before the disease onset. Blood-based liquid biopsies are a promising, non-invasive way to achieve this goal and there are an increasing number of studies which investigate their potential application in bone cancer diagnosis, prognosis and personalised therapy. This review summarises the interplay between clinical and molecular aspects of the three main bone sarcomas, alongside biomarker discovery and promising applications of liquid biopsy in each tumour context.

The Controversial Role of Autophagy in Ewing Sarcoma Pathogenesis-Current Treatment Options

Ewing Sarcoma (ES) is a rare, aggressive, and highly metastasizing cancer in children and young adults. Most ES cases carry the fusion of the Ewing Sarcoma Breakpoint Region 1 (EWSR1) and FLI1 (Friend leukemia virus integration site 1) genes, leading to an EWS-FLI1 fused protein, which is associated with autophagy, a homeostatic and catabolic mechanism under normal and pathological conditions. Following such interesting and controversial data regarding autophagy in ES, many clinical trials using modulators of autophagy are now underway in this field. In the present review, we summarize current data and clinical trials that associate autophagy with ES. In vitro studies highlight the controversial role of autophagy as a tumor promoter or a tumor suppressor mechanism in ES. Clinical and in vitro studies on ES, together with the autophagy modulators, suggest that caution should be adopted in the application of autophagy as a therapeutic target. Monitoring and targeting autophagy in every ES patient could eliminate the need for targeting multiple pathways in order to achieve the maximum beneficial effect. Future studies are required to focus on which ES patients are affected by autophagy modulators in order to provide novel and more efficient therapeutic protocols for patients with ES based on the current autophagy status of the tumors.

Selection of Effective Therapies Using Three-Dimensional in vitro Modeling of Chondrosarcoma

Purpose: Chondrosarcomas are a group of cartilaginous malignant neoplasms characterized by the deposition of chondrogenic extracellular matrix. Surgical resection is currently the only curative treatment option, due to their high resistance to conventional chemotherapy and radiotherapy. Novel therapeutic treatment options may improve outcome. Predominantly used cell line monolayer in vitro models lack in vivo complexity, such as the presence of extracellular matrix, and differing oxygen access. Hence, we aimed to improve pre-clinical chondrosarcoma research by developing an alginate-based 3D cell culture model.

Method: An alginate scaffold was applied to generate spheroids of three chondrosarcoma cell lines (CH2879, JJ012, SW1353). Morphological, histological and immunohistochemical assessment of the spheroids were used to characterize the chondrosarcoma model. Presto blue assay, morphological and immunohistochemical assessment were applied to assess spheroid response to a panel of chemotherapeutics and targeted therapies, which was compared to conventional 2D monolayer models. Synergistic effect of doxorubicin and ABT-737 (Bcl-2 inhibitor) was compared between monolayer and spheroid models using excess over Bliss. A 3D colony formation assay was developed for assessment of radiotherapy response.

Results: Chondrosarcoma spheroids produced chondrogenic matrix and remained proliferative after 2 weeks of culture. When treated with chemotherapeutics, the spheroids were more resistant than their monolayer counterparts, in line with animal models and clinical data. Moreover, for sapanisertib (mTOR inhibitor) treatment, a recovery in chondrosarcoma growth, previously observed in mice models, was also observed using long-term treatment. Morphological assessment was useful in the case of YM-155 (survivin inhibitor) treatment where a fraction of the spheroids underwent cell death, however a large fraction remained proliferative and unaffected. Synergy was less pronounced in 3D compared to 2D. A 3D clonogenic assay confirmed increased resistance to radiotherapy in 3D chondrosarcoma spheroids.

Conclusion: We demonstrate that the chondrosarcoma alginate spheroid model is more representative of chondrosarcoma in vivo and should be used instead of the monolayer model for therapy testing. Improved selection at in vitro stage of therapeutic testing will increase the amount of information available for experimental design of in vivo animal testing and later, clinical stages. This can potentially lead to increased likelihood of approval and success at clinical trials.

A Multi-Objective Approach for Anti-Osteosarcoma Cancer Agents Discovery through Drug Repurposing

Osteosarcoma is the most common type of primary malignant bone tumor. Although nowadays 5-year survival rates can reach up to 60–70%, acute complications and late effects of osteosarcoma therapy are two of the limiting factors in treatments. We developed a multi-objective algorithm for the repurposing of new anti-osteosarcoma drugs, based on the modeling of molecules with described activity for HOS, MG63, SAOS2, and U2OS cell lines in the ChEMBL database. Several predictive models were obtained for each cell line and those with accuracy greater than 0.8 were integrated into a desirability function for the final multi-objective model. An exhaustive exploration of model combinations was carried out to obtain the best multi-objective model in virtual screening. For the top 1% of the screened list, the final model showed a BEDROC = 0.562, EF = 27.6, and AUC = 0.653. The repositioning was performed on 2218 molecules described in DrugBank. Within the top-ranked drugs, we found: temsirolimus, paclitaxel, sirolimus, everolimus, and cabazitaxel, which are antineoplastic drugs described in clinical trials for cancer in general. Interestingly, we found several broad-spectrum antibiotics and antiretroviral agents. This powerful model predicts several drugs that should be studied in depth to find new chemotherapy regimens and to propose new strategies for osteosarcoma treatment.

mTOR Inhibition Ablates Cisplatin-Resistant Salivary Gland Cancer Stem Cells

Patients with advanced salivary gland mucoepidermoid carcinoma (MEC) are treated with surgery and radiotherapy, as current systemic therapies are largely ineffective. As such, current treatment frequently leads to poor long-term survival due to locoregional recurrence or metastases. We have shown that salivary gland cancer stem cells (CSCs) are resistant to platinum-based chemotherapy and drive tumor progression. The purpose of this study was to investigate the effect of therapeutic inhibition of mTOR (mechanistic target of rapamycin) on resistance of CSCs to cisplatin, a prototypic platinum-based chemotherapeutic agent. Viability assays determined the effect of several inhibitors of PI3k/mTOR signaling (e.g., temsirolimus, BKM120, AZD8055, PF4708671) and/or cisplatin on survival of human MEC cells. The impact of mTOR inhibitors and/or cisplatin on MEC stemness was examined with salisphere assays, flow cytometry for ALDH/CD44 (CSC markers for MEC), and Western blots for Bmi-1 expression (marker of stem cell self-renewal). Salivary gland MEC patient-derived xenografts were used to examine the effect of cisplatin and/or temsirolimus on CSCs in vivo. We observed that cisplatin induced mTOR and S6K1 phosphorylation, increased the number and size of MEC salispheres, and induced Bmi-1 expression and the fraction of CSCs in MEC models in vitro. Cisplatin also increased the fraction of CSCs in vivo. In contrast, mTOR inhibition (e.g., temsirolimus) blocked cisplatin-induced Bmi-1 expression and salisphere formation in vitro. Remarkably, temsirolimus slowed down tumor growth and decreased the fraction of CSCs (P < 0.05) even in presence of cisplatin in a short-term in vivo experiment. Collectively, these results demonstrate that therapeutic inhibition of mTOR ablates cytotoxic-resistant CSCs, and they suggest that a combination of an mTOR inhibitor and platinum-based chemotherapy might be beneficial to patients with salivary gland mucoepidermoid carcinoma.

Cancer Stem Cells in Soft-Tissue Sarcomas

Soft tissue sarcomas (STS) are a rare group of mesenchymal solid tumors with heterogeneous genetic profiles and clinical features. Systemic chemotherapy is the backbone treatment for advanced STS; however, STS frequently acquire resistance to standard therapies, which highlights the need to improve treatments and identify novel therapeutic targets. Increases in the knowledge of the molecular pathways that drive sarcomas have brought to light different molecular alterations that cause tumor initiation and progression. These findings have triggered a breakthrough of targeted therapies that are being assessed in clinical trials. Cancer stem cells (CSCs) exhibit mesenchymal stem cell (MSC) features and represent a subpopulation of tumor cells that play an important role in tumor progression, chemotherapy resistance, recurrence and metastasis. In fact, CSCs phenotypes have been identified in sarcomas, allied to drug resistance and tumorigenesis. Herein, we will review the published evidence of CSCs in STS, discussing the molecular characteristic of CSCs, the commonly used isolation techniques and the new possibilities of targeting CSCs as a way to improve STS treatment and consequently patient outcome.

Radiopharmaceuticals for Treatment of Osteosarcoma

Although trace amounts of radioactivity are routinely used to detect osteosarcoma, the use of larger therapeutic amounts of radiation is often an unrecognized opportunity to treat metastatic osteosarcoma. This chapter will review a number of approaches to use ionizing radiation in the form of injectable radiopharmaceuticals. Since bone metastases are a common pattern of metastatic spread of cancer in general, a number of bone-seeking radiopharmaceuticals have been developed and FDA approved for treatment of bone metastases. Although osteosarcoma, a bone-forming cancer, would seem ideally suited to be treated with bone seekers, patterns of relapse involving non-ossifying metastases remain a major problem to be overcome. Thus, this review will not only describe experience using a number of bone-seeking radiopharmaceuticals such as 153-samarium-EDTMP, 153-samarium-DOTMP, and 223-radium against osteosarcoma, but also approaches to identify patients who may benefit as well as some means to the improve overall efficacy including combination therapy with routine agents and using nuclear imaging to develop best strategy for use. These include imaging with not only ^99mTc-MDP standard bone scans, but also ^99mTc-MDP bone scans with SPECT CT, bone-specific sodium fluoride PET-CT (Na¹⁸F), and ¹⁸FDG-PET-CT. Accurate knowledge of oligometastatic active disease can facilitate more effective use of combination therapy, including radiosensitizers and local control measures, for example, stereotactic body radiotherapy (SBRT) and/or cryoablation to reduce disease burden as well as manage and prevent micrometastatic disease from growing and metastasizing. Finally, a new tumor-specific radiopharmaceutical, CLR 131, may also provide another radiopharmaceutical to treat both osteoblastic and non-ossifying areas of osteosarcoma.

Targeting mTOR and Metabolism in Cancer: Lessons and Innovations

Cancer cells support their growth and proliferation by reprogramming their metabolism in order to gain access to nutrients. Despite the heterogeneity in genetic mutations that lead to tumorigenesis, a common alteration in tumors occurs in pathways that upregulate nutrient acquisition. A central signaling pathway that controls metabolic processes is the mTOR pathway. The elucidation of the regulation and functions of mTOR can be traced to the discovery of the natural compound, rapamycin. Studies using rapamycin have unraveled the role of mTOR in the control of cell growth and metabolism. By sensing the intracellular nutrient status, mTOR orchestrates metabolic reprogramming by controlling nutrient uptake and flux through various metabolic pathways. The central role of mTOR in metabolic rewiring makes it a promising target for cancer therapy. Numerous clinical trials are ongoing to evaluate the efficacy of mTOR inhibition for cancer treatment. Rapamycin analogs have been approved to treat specific types of cancer. Since rapamycin does not fully inhibit mTOR activity, new compounds have been engineered to inhibit the catalytic activity of mTOR to more potently block its functions. Despite highly promising pre-clinical studies, early clinical trial results of these second generation mTOR inhibitors revealed increased toxicity and modest antitumor activity. The plasticity of metabolic processes and seemingly enormous capacity of malignant cells to salvage nutrients through various mechanisms make cancer therapy extremely challenging. Therefore, identifying metabolic vulnerabilities in different types of tumors would present opportunities for rational therapeutic strategies. Understanding how the different sources of nutrients are metabolized not just by the growing tumor but also by other cells from the microenvironment, in particular, immune cells, will also facilitate the design of more sophisticated and effective therapeutic regimen. In this review, we discuss the functions of mTOR in cancer metabolism that have been illuminated from pre-clinical studies. We then review key findings from clinical trials that target mTOR and the lessons we have learned from both pre-clinical and clinical studies that could provide insights on innovative therapeutic strategies, including immunotherapy to target mTOR signaling and the metabolic network in cancer.