Monoclonal antibody to parathyroid hormone-related protein induces differentiation and apoptosis of chondrosarcoma cells

Roles of Parathyroid Hormone-Related Protein (PTHrP) and Its Receptor (PTHR1) in Normal and Tumor Tissues: Focus on Their Roles in Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor and originates from bone forming mesenchymal cells and primarily affects children and adolescents. The 5-year survival rate for OS is 60 to 65%, with little improvement in prognosis during the last four decades. Studies have demonstrated the evolving roles of parathyroid hormone-related protein (PTHrP) and its receptor (PTHR1) in bone formation, bone remodeling, regulation of calcium transport from blood to milk, regulation of maternal calcium transport to the fetus and reabsorption of calcium in kidneys. These two molecules also play critical roles in the development, progression and metastasis of several tumors such as breast cancer, lung carcinoma, chondrosarcoma, squamous cell carcinoma, melanoma and OS. The protein expression of both PTHrP and PTHR1 have been demonstrated in OS, and their functions and proposed signaling pathways have been investigated yet their roles in OS have not been fully elucidated. This review aims to discuss the latest research with PTHrP and PTHR1 in OS tumorigenesis and possible mechanistic pathways.

This review is dedicated to Professor Michael Day who died in May 2020 and was a very generous collaborator.

Chondrosarcoma of bone

Chondrosarcoma is a cartilage forming neoplasm, which is the second most common primary malignancy of bone. Clinicians who treat chondrosarcoma patients must determine the grade of the tumor, and must ascertain the likelihood of metastasis. Acral lesions are unlikely to metastasize, regardless of grade, whereas axial, or more proximal lesions are much more likely to metastasize than tumors found in the distal extremities with equivalent histology. Chondrosarcoma is resistant to both chemotherapy and radiation, making wide local excision the only treatment. Local recurrence is frequently seen after intralesional excision, thus wide local excision is sometimes employed despite significant morbidity, even in low-grade lesions. Chondrosarcoma is difficult to treat. The surgeon must balance the risk of significant morbidity with the ability to minimize the chance of local recurrence and maximize the likelihood of long-term survival.

Chondrosarcomas revisited

Chondrosarcomas are malignant bone tumors with pure hyaline cartilage differentiation; myxoid changes, calcification, or ossification may be present. Several subtypes of chondrosarcomas exist. Behavior patterns vary, ranging from slow-growing nonmetastasizing lesions to aggressive metastasizing sarcomas. Symptoms are usually mild, with duration ranging from several months to years, and usually consist of persistent, dull, aching pain or palpable masses. Radiographic findings include bone expansion with cortical thickening, radiolucent areas with variably distributed punctate or ring-like matrix calcifications, cortical erosion or destruction, endosteal scalloping, and scant or absent periosteal reaction; extension into the soft tissue may be present. Histological differential diagnosis from benign cartilaginous lesions can be achieved by increased cellularity, enlarged plump nuclei, binucleated cells, hyperchromatic nuclear pleomorphism, and permeation of cortical or medullary bone. Atypia is usually mild to moderate; necrosis and mitoses can be seen, particularly in high-grade lesions. Adequate surgery is the mainstay of treatment. High-grade and pelvic chondrosarcomas are best managed with wide resection. Because of the low metastatic potential and low local recurrence rate noted with intralesional surgery, low-grade chondrosarcomas can be treated with curettage (with or without treatment of the defect cavity) with a local adjuvant, such as phenol or cryotherapy. Adjuvant chemotherapy may be considered for mesenchymal and dedifferentiated chondrosarcomas. Radiation therapy can be considered after incomplete resection or if resection is not feasible or would cause unacceptable morbidity.

Review of therapeutic strategies for osteosarcoma, chondrosarcoma, and Ewing's sarcoma

The most prevalent forms of bone cancer are osteosarcoma, chondrosarcoma, and Ewing’s sarcoma. Although chemotherapy and radiotherapy have replaced traditional surgical treatments, survival rates have undergone only marginal improvements. Current knowledge of the molecular pathways involved in each type of cancer has led to better approaches in cancer treatment. A number of cell signaling molecules are involved in tumorigenesis, and specific targets have been identified based on these signal transducers. This review highlights some of the important cellular pathways and potential therapeutic targets, tumor site-specific irradiation techniques, and novel drug delivery systems used to administer these drugs.

Parathyroid Hormone-Related Protein (PTHrP): A Key Regulator of Life/Death Decisions by Tumor Cells with Potential Clinical Applications

Parathyroid hormone-related protein (PTHrP), classically regarded as the mediator of the humoral hypercalcemia of malignancy syndrome, is a polyhormone that undergoes proteolytic processing into smaller bioactive forms. These bioactive forms comprise an N-terminal- as well as midregion- and C-terminal peptides, which have been shown to regulate various biological events, such as survival, proliferation and differentiation, in diverse cell model systems, both normal and pathological. A number of experimental data have demonstrated that PTHrP is also able to modulate tumor-relevant phenotypic expressions, thereby playing a role in early and advanced tumorigenesis, and in the response to treatment. In particular, interest has mainly been focused on the effects of PTHrP on cell proliferation/apoptosis, migration and invasion, which are the main roles involved in cancer development in vivo. The objective of this review is to discuss collectively the literature data on the molecular and biochemical basis of the mechanisms underlying the different, and sometimes opposite, effects exerted by PTHrP on various neoplastic cytotypes, with some final comments on both present and potential utilization of PTHrP as a target for anti-cancer therapy.

Therapeutic molecular targets in human chondrosarcoma

Chondrosarcomas are malignant cartilage tumours. They are poorly responsive to chemotherapy and radiotherapy. Treatment is usually limited to surgical resection; however, survival of patients with high-grade chondrosarcoma is poor, even with wide surgical resection. Induction of apoptosis in chondrosarcoma cells, either directly or by enhancement of the response to chemotherapeutic drugs and radiation, may be a route by which outcome can be improved. In this article, we review potential molecular targets that regulate chondrocyte apoptosis and discuss the experimental evidence for their utility.

Cartilage tumours and bone development: molecular pathology and possible therapeutic targets

As a group, cartilage tumours are the most common primary bone lesions. They range from benign lesions, such as enchondromas and osteochondromas, to malignant chondrosarcoma. The benign lesions result from the deregulation of the hedgehog signalling pathway, which is involved in normal bone development. These lesions can be the precursors of malignant chondrosarcomas, which are notoriously resistant to conventional chemotherapy and radiotherapy. Cytogenetic studies and mouse models are beginning to identify genes and signalling pathways that have roles in tumour progression, such as hedgehog, p53, insulin-like growth factor, cyclin-dependent kinase 4, hypoxia-inducible factor, matrix metalloproteinases, SRC and AKT, suggesting potential new therapeutic approaches.

Molecular pathology of chondroid neoplasms: part 2, malignant lesions

This is the second part of a two-part review presenting an overview of the molecular findings associated with both benign and malignant chondroid neoplasms. The first part presented a brief review of modern methods in molecular pathology, along with a review of the cytogenetic and molecular genetic findings in benign chondroid neoplasms. This second part reviews the cytogenetic and molecular genetic findings in malignant chondroid neoplasms. Clinical aspects of the various lesions are briefly discussed, and each tumor is illustrated with representative radiographic and pathologic images.

Pathology of primary malignant bone and cartilage tumours

Bone- and cartilage-forming tumours (osteosarcomas and chondrosarcomas) are rare malignant neoplasms. These tumours are clinically aggressive and often need extensive local and/or systemic treatment. Whereas no other treatment but surgery is currently available for chondrosarcomas, osteosarcomas show an approximately 50-80% response rate to adjuvant chemotherapy. Surgical removal of these tumours is currently mostly performed with limb salvage, but amputation may be required in some cases. In addition, the tumours have a risk of local recurrences adversely affecting the prognosis compared to the primary tumour. In this report we will mainly focus on two of the most prevalent malignant bone tumours, conventional osteosarcoma and conventional chondrosarcoma, and use these to illustrate the problems with the diagnosis of bone sarcomas in general.

Recent advances in the basic science of chondrosarcoma

Chondrosarcoma are a heterogeneous group of tumors whose treatment is limited to surgical removal. Molecular genetic analysis of these tumors has revealed some of the abnormalities responsible for the traits of the malignant phenotype.

Effects of Parathyroid Hormone Like Hormone (PTHLH) Antagonist, PTHLH7–34, on Fetoplacental Development and Growth During Midgestation in Rats1

Parathyroid hormone-like hormone (PTHLH) secretion has been reported in human amnion, chorion, decidual cytotrophoblast, syncytiotrophoblast, endometrium, and myometrium; however, the functions of PTHLH during pregnancy, particularly during placenta formation and fetal development, are not well understood. We examined whether neutralization of PTHLH action using PTHLH antagonist, PTHLH(7-34), in rats during early gestation affects fetal and placental growth. Rats received s.c. a daily dose of either 0, 4, 12, or 36 microg of PTHLH(7-34) infused continuously through mini-osmotic pumps from Day 8 through Day 15 of pregnancy. Fetal weights measured on Day 15 were significantly decreased in rats treated with all the doses of PTHLH(7-34) compared to controls, and decreases in placental weights were significant at the 12-microg dose. TUNEL assay demonstrated an increased number of apoptotic cells in placenta of treated rats, including rats treated with the 4-microg dose. Cleaved caspase 3 (CASP3), caspase 9 (CASP9) (P < 0.05) and poly-ADP-ribose polymerase (PARP1) (P < 0.01) expression was increased and BCL2 (P < 0.01) expression was decreased in rats treated with 4 microg PTHLH(7-34) compared to that in control. Placental cytochrome c expression was increased (P < 0.01) in cytosolic and decreased (P < 0.01) in mitochondrial fraction in PTHLH(7-34)-treated rats. Caspase 8 expression was not affected by the treatment. Immunohistochemical analysis of platelet endothelial cell adhesion molecule (PECAM1) showed higher staining intensity in control than in treated rats. In conclusion, these results suggests that PTHLH plays a role in early pregnancy, and that antagonization of PTHLH action causes fetoplacental growth restriction through activation of mitochondrial pathway of apoptosis in the placenta and through decreased expression of PECAM1.

Estrogen Signaling Is Active in Cartilaginous Tumors: Implications for Antiestrogen Therapy as Treatment Option of Metastasized or Irresectable Chondrosarcoma

PURPOSE

Chondrosarcoma is a malignant cartilaginous matrix-producing tumor that can be lethal in 10% to 50% of the patients. Surgery is the only effective treatment known as these tumors are notorious refractory to all types of conventional chemotherapy or radiotherapy. To identify a target for therapy, we want to determine whether estrogen signaling is active in chondrosarcoma because estrogen is important in the regulation of longitudinal growth that is initiated by chondrocyte proliferation and differentiation in the epiphyseal growth plate of long bones.

EXPERIMENTAL DESIGN

We studied protein expression of the estrogen receptor in 35 cartilaginous tumors as well as mRNA levels for the estrogen receptor and for aromatase, an enzyme for estrogen synthesis and another potential therapeutic target. Furthermore, the activity of aromatase was determined in vitro by the tritiated water release assay. Dose-response experiments with chondrosarcoma cultured cells were done with estrogen, androstenedione, and exemestane.

RESULTS

All chondrosarcomas tested showed mRNA and nuclear protein expression of the estrogen receptor. Also, aromatase mRNA was detected. The aromatase activity assay showed a functional aromatase enzyme in primary chondrosarcoma cultures and in a cell line. Growth of chondrosarcoma cell cultures can be stimulated by adding estrogen or androstenedione, which can be inhibited by exemestane.

CONCLUSIONS

These results show, on the RNA, protein, and cell biological levels, that the ligand and the receptor are active in estrogen-mediated signal transduction. This observation implicates potential use of targeted drugs that interfere with estrogen signaling, such as those applied for treating breast cancer.

Emerging pathways in the development of chondrosarcoma of bone and implications for targeted treatment

Chondrosarcoma is a malignant cartilage-forming tumour of bone, of which distinct clinicopathological subtypes are known. Conventional chondrosarcoma is notorious for its locally aggressive behaviour as well as for its resistance to chemotherapy and radiotherapy; so far surgery is the only effective therapeutic option. During the past 10 years, substantial new insights have been gained about molecular cell biology, molecular cytogenetics, and immunopathology, leading to better understanding of chondrosarcoma development at the molecular level, which will ultimately lead to better clinical understanding and possibly to the development of targeted treatment.

Genetics of chondrosarcoma and related tumors

PURPOSE OF REVIEW

The burgeoning body of information on the genetic changes present in and underlying the development and biology of human cancers has carried implications regarding the possible genetic events that are responsible for not only the genesis of these cancers but also the hope of the cure for these cancers. Chondrosarcomas are a group of tumors that fall into this category. The purpose of this review is to summarize the genetic findings in these tumors.

RECENT FINDINGS

The histopathologic variability of chondrosarcomas is reflected in the complexity and lack of specificity of their cytogenetic and molecular genetic findings, except for extraskeletal myxoid chondrosarcomas. These are characterized in the preponderant number of cases by a translocation, t(9;22)(q22;q12), and in a small number of cases by variant translocations t(9;17)(q22;q11) and t(9;15)(q22;q21). These translocations lead to the formation of abnormal fusion genes and gene products (proteins). In each of these translocations, the CHN gene is involved, resulting in the chimeric fusion genes EWS/CHN, RBP56/CHN, and TCF12/CHN, respectively. The specific translocations and their associated molecular genetic changes are diagnostic of extraskeletal myxoid chondrosarcomas. The abnormal proteins resulting from these fusion genes aberrantly affect gene transcription and cellular signaling pathways thought to be responsible for initiating sarcoma formation. In skeletal (central) chondrosarcomas of varying histopathologic types, the cytogenetic and molecular genetic findings are variable, complex, and apparently lacking in specificity. These changes may reflect a stepwise process (or processes) of oncogenesis involving an array of genes.

SUMMARY

Although some cartilaginous tumors are characterized by specific or recurrent chromosome alterations and molecular genetic changes, much is yet to be learned about the nature and sequence of these genetics events and about their unique role in the stepwise process involved in the development and biology of each tumor type, both malignant and nonmalignant. Until such time, some of the genetic changes, particularly the presence of specific translocations, can be of definite diagnostic value.