The Effect of a Histone Deacetylase Inhibitor (AR-42) and Zoledronic Acid on Adult T-Cell Leukemia/Lymphoma Osteolytic Bone Tumors

Simple Summary

Adult T-cell leukemia (ATL) Leukemia is an aggressive, peripheral blood (T-cell) neoplasm associated with human T-cell leukemia virus type 1 (HTLV-1) infection. Recent studies have implicated dysregulated histone deacetylases in ATL pathogenesis. ATL modulates the bone microenvironment of patients and activates osteoclasts (bone resorbing cells) that cause severe bone loss. The objective of this study was to assess the individual and dual effects of AR-42 (HDACi) and zoledronic acid (Zol) on the growth of ATL cells in vitro and in vivo. AR-42 and Zol reduced the viability of ATL cells in vitro. Additionally, Zol and Zol/AR-42 decreased ATL tumor growth and halted osteolysis in bone tumor xenografts in immunodeficient mice in vivo. Our study suggests that dual targeting of ATL cells (using HDACi) and bone osteoclasts (using bisphosphonates) may be exploited as a valuable approach to reduce bone tumor burden and improve the life quality of ATL patients.

Abstract

Adult T-cell leukemia/lymphoma (ATL) is an intractable disease affecting nearly 4% of Human T-cell Leukemia Virus Type 1 (HTLV-1) carriers. Acute ATL has a unique interaction with bone characterized by aggressive bone invasion, osteolytic metastasis, and hypercalcemia. We hypothesized that dual tumor and bone-targeted therapies would decrease tumor burden in bone, the incidence of metastasis, and ATL-associated osteolysis. Our goal was to evaluate dual targeting of both ATL bone tumors and the bone microenvironment using an anti-tumor HDACi (AR-42) and an osteoclast inhibitor (zoledronic acid, Zol), alone and in combination. Our results showed that AR-42, Zol, and AR-42/Zol significantly decreased the viability of multiple ATL cancer cell lines in vitro. Zol and AR-42/Zol decreased tumor growth in vivo. Zol ± AR-42 significantly decreased ATL-associated bone resorption and promoted new bone formation. AR-42-treated ATL cells had increased mRNA levels of PTHrP, ENPP2 (autotaxin) and MIP-1α, and TAX viral gene expression. AR-42 alone had no significant effect on tumor growth or osteolysis in mice. These findings indicate that Zol adjuvant therapy has the potential to reduce growth of ATL in bone and its associated osteolysis.

Characterization of receptor tyrosine kinase activation and biological activity of toceranib phosphate in canine urothelial carcinoma cell lines

Background

Urothelial carcinoma (UC) accounts for > 90% of canine tumors occurring in the urinary bladder. Toceranib phosphate (TOC) is a multi-target receptor tyrosine kinase (RTK) inhibitor that exhibits activity against members of the split kinase family of RTKs. The purpose of this study was to evaluate primary UC tumors and UC cell lines for the expression and activation of VEGFR2, PDGFRα, PDGFRβ, and KIT to assess whether dysregulation of these RTKs may contribute to the observed biological activity of TOC.

Results

Transcript for VEGFR2, PDGFRα, PDGFRβ, and KIT was detected in all UC tissue samples and UC cell lines. The Proteome Profiler™ Human Phospho-RTK Array Kit (R & D Systems) provided a platform to assess phosphorylation of 42 different RTKs in primary UC tumors and UC cell lines. Evidence of PDGFRα and PDGFRβ phosphorylation was present in only 11% or 33% of UC tumors, respectively, and 25% of UC cell lines. Treatment of UC cell lines with TOC had no significant impact on cell proliferation, including UC cell lines with evidence of PDGFRβ phosphorylation.

Conclusions

Phosphorylation of several key RTKs targeted by TOC is present in a small subset of primary UC tumors and UC cell lines, suggesting that these RTKs do not exist in a state of continuous activation. These data suggest that activation of RTKs targeted by TOC is present in a small subset of UC tumors and UC cell lines and that treatment with TOC at physiologically relevant concentrations has no direct anti-proliferative effect on UC cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03027-0.

The selective inhibitor of nuclear export (SINE) verdinexor exhibits biologic activity against canine osteosarcoma cell lines

Verdinexor (KPT-335) is a novel orally bioavailable selective inhibitor of nuclear export (SINE) compound that inhibits the function of the nuclear export protein Exportin 1 (XPO1/CRM1). In the present study, we sought to characterize the expression of XPO1 in primary canine osteosarcoma (OS) tumour samples, OS cell lines and normal osteoblasts and evaluate the in vitro activity of verdinexor alone or in combination with doxorubicin. Canine OS cell lines and a subset of primary OS tumours showed increased XPO1 transcript and protein expression as compared with normal canine osteoblast cells. All canine OS cell lines exhibited dose-dependent growth inhibition and increased caspase 3,7 activity in response to low nanomolar concentrations of verdinexor (IC₅₀ concentrations ranging from 21 to 74 nM). Notably, growth inhibition of normal canine osteoblast cell lines treated with verdinexor was observed at high micromolar concentrations (IC₅₀  = 21 μM). The combination of verdinexor and doxorubicin resulted in potent inhibition of cell viability and demonstrated synergetic activity in three canine OS cell lines. Concordantly, OS cell lines showed increased γH2A.X foci following treatment with doxorubicin and recovery in verdinexor compared with cells treated with doxorubicin and recovered in normal media for 24 hours. These findings demonstrate that verdinexor has biologic activity against canine OS cell lines at physiologically relevant doses and suggest that XPO1 inhibition in combination with standard doxorubicin treatment offers promising potential for chemotherapeutic intervention in canine OS.

Parathyroid hormone-related protein promotes bone loss in T-cell leukemia as well as in solid tumors

Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) are important factors that increase bone resorption and hypercalcemia in adult T-cell leukemia (ATL). We investigated the role of PTHrP and MIP-1α in the development of local osteolytic lesions in T-cell leukemia through overexpression in Jurkat T-cells. Injections of Jurkat-PTHrP and Jurkat-MIP-1α into the tibia and the left ventricle of NSG mice were performed to evaluate tumor growth and metastasis in vivo. Jurkat-pcDNA tibial neoplasms grew at a significantly greater rate and total tibial tumor burden was significantly greater than Jurkat-PTHrP neoplasms. Despite the lower tibial tumor burden, Jurkat-PTHrP bone neoplasms had significantly greater osteolysis than Jurkat-pcDNA and Jurkat-MIP-1α neoplasms. Jurkat-PTHrP and Jurkat-pcDNA cells preferentially metastasized to bone following intracardiac injection, though the overall metastatic burden was lower in Jurkat-PTHrP mice. These findings demonstrate that PTHrP induced pathologic osteolysis in T-cell leukemia but did not increase the incidence of skeletal metastasis.

Animal Models of Cancer-Associated Hypercalcemia

Cancer-associated hypercalcemia (CAH) is a frequently-occurring paraneoplastic syndrome that contributes to substantial patient morbidity and occurs in both humans and animals. Patients with CAH are often characterized by markedly elevated serum calcium concentrations that result in a range of clinical symptoms involving the nervous, gastrointestinal and urinary systems. CAH is caused by two principle mechanisms; humorally-mediated and/or through local osteolytic bone metastasis resulting in excessive calcium release from resorbed bone. Humoral hypercalcemia of malignancy (HHM) is the most common mechanism and is due to the production and release of tumor-associated cytokines and humoral factors, such as parathyroid hormone-related protein (PTHrP), that act at distant sites to increase serum calcium concentrations. Local osteolytic hypercalcemia (LOH) occurs when primary or metastatic bone tumors act locally by releasing factors that stimulate osteoclast activity and bone resorption. LOH is a less frequent cause of CAH and in some cases can induce hypercalcemia in concert with HHM. Rarely, ectopic production of parathyroid hormone has been described. PTHrP-mediated hypercalcemia is the most common mechanism of CAH in human and canine malignancies and is recognized in other domestic species. Spontaneous and experimentally-induced animal models have been developed to study the mechanisms of CAH. These models have been essential for the evaluation of novel approaches and adjuvant therapies to manage CAH. This review will highlight the comparative aspects of CAH in humans and animals with a discussion of the available animal models used to study the pathogenesis of this important clinical syndrome.