The anti-tumor agent sagopilone shows antiresorptive effects both in vitro and in vivo

Sagopilone, a fully synthetic epothilone and very potent anti-tumor agent, has proved to be efficient in inhibiting bone destruction and tumor burden in a mouse model of breast cancer bone metastasis. In addition to its antiproliferative effects, this study shows direct effects of sagopilone on bone resorption and osteoclast activity.

INTRODUCTION

Sagopilone, a novel fully synthetic third-generation epothilone, has proved to be efficient in inhibiting bone destruction and tumor burden in a mouse model of breast cancer bone metastasis. The aim of this study was to investigate whether the effect was primarily due to sagopilone's antiproliferative effect and consequent inhibition of tumor cell growth, or if sagopilone exerts direct effects on bone resorption and osteoclast activity.

METHODS

Sagopilone was studied and compared to paclitaxel in vitro in human osteoclast differentiation and activity cultures. For studying the potential of sagopilone for inhibiting bone resorption in vivo, a mouse model of ovariectomy (ovx)-induced osteoporosis was utilized.

RESULTS

Sagopilone inhibited osteoclast differentiation and activity more efficiently than paclitaxel and showed less cytotoxicity. Whereas sagopilone showed inhibitory effects on human osteoclast differentiation and activity already at 5 and 15 nM, respectively, paclitaxel started to show effects only at 20 and 100 nM concentrations, respectively. Sagopilone treatment increased BMD In the mouse ovx model even though a non-optimized dose was used which is effective in tumor-bearing mice.

CONCLUSION

This is the first study to evaluate sagopilone's effects on bone resorption in non-cancerous situation. The evidence that sagopilone is beneficial for bone will strengthen the status of sagopilone as an anti-cancer compound compared to other microtubule stabilizing agents.

Characterization of a new renal cell carcinoma bone metastasis mouse model

Metastatic bone disease caused by renal cell carcinoma (RCC) occurs frequently and becomes more and more prevalent presumably because survival times among patients with disseminated cancers are increasing. Patients with bone metastases from renal cell carcinoma suffer from severe pain, nerve compression syndromes and pathologic fractures. Very little is known about the mechanisms of skeletal metastases of RCC. Thus, to better understand the molecular mechanism of renal cell cancer (RCC) bone metastasis, it is crucial to develop new animal models. We have established a new animal model of RCC metastasis to bone by inoculation of human 786-O/luciferase cells into the left cardiac ventricle of athymic nude mice. The animals developed aggressive osteolytic bone destruction as monitored by radiography and micro-CT-scans with the mean endpoint at 62 +/- 8 days. The extensive bone destruction observed was comparable to the clinical setting and mainly occurred in hind limbs, forelimbs and the spine. The tumors were primarily located within the bone and resulted in destruction of cortical bone. No soft tissue metastases were detected by BLI or histomorphometry. To increase the bone-metastatic potential of the 786-O cell line, an in vivo selection was done yielding a subpopulation causing osteolytic lesions with the mean endpoint of 47 +/- 3 days. The selected subline secreted more proangiogenic factors VEGF and bFGF in vitro compared to the parental cell line suggesting that these tumors are highly vascular. This model provides a reliable reproduction of the clinical situation and therefore, is suitable for designing and evaluating more effective treatments for RCC bone metastasis.

Abstract LB-144: In vivo detection of bone metastases in a mouse model by positron emission tomography (PET) with [F-18]-labeled tyrosine derivative (D-FMT)

Objective: Detection and localization of metastatic lesions in advanced stages of cancer is still a difficult obstacle for diagnosis and subsequent treatment decisions for an optimized cancer patient management and therapy control. Whole body molecular imaging applying positron emission tomography (PET) allows the sensitive detection of radioactive labeled molecules, which specifically accumulate in tumor tissue. This offers a promising tool to assess the stage of the disease comprehensively. At present [F-18]-fluorodeoxyglucose (FDG) is the mostly used PET-tracer in oncology. However, FDG has the disadvantageof limited specificity by accumulating also in inflammatory cells due to their increased glucose metabolism. To overcome this problem, amino acids have been radiolabeled to study their potential imaging characteristics. D-[F-18]-fluoromethyl tyrosine (D-FMT, (R)-2-amino-3-(4-[F-18]fluoromethoxy-phenyl)-propionic acid) has shown good uptake into HeLa tumors in nude mice with no accumulation in sterile induced inflammation sites. The aim of this study was to investigate if D-FMT can also be used to image bone metastases besides primary soft tissue tumors.

Methods: Human 786-O/luciferase renal cell adenocarcinoma cells were injected intracardially, which gave rise to the formation of several bone metastases. The radiosynthesis of D-FMT was carried out using an indirect labeling method via the [F-18]-fluoromethyl bromide synthon. Micro-PET imaging was performed 51 and 65 days after tumor cell inoculation.

Results: The formation of metastases was monitored using bioluminescence imaging indicating the presence of tumor cells in the regions of hind limbs, forelimbs, spine and skull. A bone scan with [F-18]-fluoride confirmed skeletal metabolic activity at sites of osteolytic bone metastases. The i.v. application of [F-18]-D-FMT showed a very specific accumulation of the amino acid tracer in these bone metastases and, together with the low background, allowed very good imaging of these lesions. Based on the PET scan of [F-18]-D-FMT, sites of accumulation were excised. All imaged metastases could be verified histologically.

Conclusion: These data suggest D-FMT as a new potential imaging tracer for the detection of primary tumors as well as bone metastases. In addition, the sensitivity of this tracer suggests the possibility for substantial benefit in detecting soft tissue metastases as well.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-144.

Luminescent imaging technology as an opportunity to reduce and refine animal experiments: Light at the end of the tunnel?

In vivo luminescent imaging technology was introduced in experimental life science research several years ago and has rapidly gained wide acceptance. By making use of this technology substantially more information can be gained from animal experiments than was previously possible. The concept of the 3Rs describes the aim to Refine, Reduce and Replace animal models in research. The goal of the present paper is to systematically investigate the impact of luminescent imaging on the 3Rs. In particular, three examples of applications are explained in detail so as to be accessible to the reader unfamiliar with the procedure. The examples are subsequently analysed for and categorised according to their concrete effect on animal welfare as defined by the 3Rs.

Analysis of hypertrophic thyrotrophs in pituitaries of athyroid Pax8-/- mice

Thyroid hormone is important for pituitary development and maintenance. We previously reported that in the Pax8(-/-) mouse model of congenital hypothyroidism, lactotrophs are almost undetectable, whereas the thyrotrophs exhibit hyperplasia and hypertrophy. Because the latter might be caused by an overstimulation of thyrotrophs with TRH, we analyzed TRH-R1(-/-)Pax8(-/-) double-knockout mice, which miss a functional thyroid gland and the TRH transducing receptor-1 at pituitary target sites. Interestingly, in these double mutants, the hypertrophy and hyperplasia of the thyrotrophs still persist, suggesting that the phenotype is rather a direct consequence of the athyroidism of the animals. The increased expression of TSH in the Pax8(-/-) mice was paralleled by a strongly up-regulated expression of deiodinase type 2 (Dio2) in thyrotrophic cells. Moreover, coexpression of TSH and Dio2 could also be demonstrated in the pituitary of wild-type mice, underlining the important role of this enzyme in the negative feedback regulation of TSH by thyroid hormone. As another consequence of the athyroidism in the mutant mice, tyrosine hydroxylase mRNA expression was found to be also highly up-regulated in thyrotrophic cells of the pituitaries from Pax8(-/-) mice, whereas the transcript levels in the hypothalamus were not affected. Accordingly, tyrosine hydroxylase protein levels, enzyme activities, and ultimately dopamine concentrations were found to be strongly increased in the pituitaries of Pax8(-/-) mice compared with wild-type animals. These findings may explain in part the reduced number of lactotrophs found in the pituitary of athyroid Pax8(-/-) mice and suggest a novel paracrine regulatory mechanism of lactotroph activity.

Sagopilone inhibits breast cancer bone metastasis and bone destruction due to simultaneous inhibition of both tumor growth and bone resorption

PURPOSE

Bone metastases have a considerable impact on quality of life in patients with breast and other cancers. Tumors produce osteoclast-activating factors, whereas bone resorption promotes the growth of tumor cells, thus leading to a "vicious cycle" of bone metastasis. Sagopilone, a novel, fully synthetic epothilone, inhibits the growth of breast cancer cells in vitro and in vivo, and here we report its activity in the MDA-MB-231(SA) breast cancer bone metastasis mouse model.

EXPERIMENTAL DESIGN

The potency of sagopilone was determined in treatment models simulating the adjuvant (preventive) and metastatic (therapeutic) settings in the clinic.

RESULTS

We showed that sagopilone inhibited tumor burden and bone destruction, in addition to reducing tumor-induced cachexia and paraplegia. The reduction in osteolytic lesions, tumor growth in bone, and weight loss was statistically significant in the preventive model compared with the vehicle group. In the therapeutic model, sagopilone treatment significantly lowered the number of activated osteoclasts and significantly reduced the osteolytic lesion area, bone volume loss, and bone resorption compared with vehicle treatment while simultaneously inhibiting tumor burden. An in vitro assay confirmed that sagopilone inhibited osteoclast activation without cytotoxic effects, whereas paclitaxel resulted in lower inhibition and high levels of cytotoxicity.

CONCLUSIONS

Sagopilone seems to inhibit the vicious cycle at both the tumor growth and bone resorption stages, suggesting the possibility for substantial benefit in the treatment of patients with breast cancer at risk from bone metastases or with bone lesions already present. Phase II clinical trials with sagopilone in patients with breast cancer are ongoing.