CT analysis of tumour bearing bones showed significantly inc

μCT analysis of tumour bearing bones showed significantly increased bone density in animals receiving zoledronic acid, alone or in combination with doxorubicin, compared to PBS control. Our results confirmed that a single dose of zoledronic your list caused sustained bone effects throughout the experiment (until day 23). Despite this, the effects on bone cell numbers in the tumour-bearing environment were less prominent than those detected in the tumour-free bones, possibly due to the strong influence the tumour cells have on bone turnover at the metastatic site. No reduction in osteoclast number was detected on day 15 although μCT analysis clearly showed a dramatic increase in bone volume. In agreement with our previous study using a 6-week regimen in established, intratibial MDA-MB-436 tumours [14], zoledronic acid, as well as combination therapy, caused a decrease in osteoclast numbers compared to PBS control on day 23. Zoledronic acid could not only cause a reduction in the number of osteoclasts, but more importantly reduce their activity. We suggest that the morphological changes observed in osteoclasts from the zoledronic acid treated animals reflect this, as was shown by scoring of mean osteoclast area. The presence of “giant” osteoclasts has also been reported after long-term alendronate treatment in an osteoporotic setting [33]. The authors proposed that aminobisphosphonates effectively inhibited osteoclast activity and prolonged the lifespan of the cells, ultimately leading to an increase in cell size due to continuous fusion of the osteoclast with mononuclear precursors. In addition, apoptosis was detected in about 30% of the “giant” cells [34]. The data therefore suggest that bisphosphonate therapy decreases osteoclast activity and induces changes cell morphology before reducing viability. Prolonged/repeated treatment may not be required to generate this effect, as we have consistently noted larger osteoclasts in samples from zoledronic acid treated animals compared to control. A direct link between osteoclast size and anti-resorptive activity could not be established in the present study, as serum CTX levels did not reflect the treatment-induced changes in bone structure. This was most likely due to the 2–3 week time gap between treatment and the collection of serum. In summary, we have shown that administration of a single round of combination therapy significantly reduces tumour burden and preserves bone integrity, but is not sufficient to eliminate tumour growth in bone. Our results are in agreement with the established clinical effects of zoledronic acid in the advanced cancer setting, showing a dampening of disease rather than elimination of bone metastasis [35]. Our data show that although zoledronic acid modifies the bone microenvironment through effects on both osteoblasts and osteoclasts, this does not result in a significant anti-tumour effect in the absence of doxorubicin. As indicated by the recently published data from the AZURE trial [7], additional components of the bone microenvironment linked to menopausal status may be the key to the development of tumour growth in bone and response to combination therapy.
Acknowledgements This study was supported by the Weston Park Hospital Cancer Charity, Sheffield UK and the Breast Cancer Campaign, UK. Zoledronic acid used in this study was a kind gift from Novartis Pharma.
Introduction Following the results of several large randomised trials of endocrine treatment strategies, adjuvant treatment with an aromatase inhibitor (AI) has become part of standard care for most post-menopausal patients with oestrogen receptor positive (ER+) breast cancer [1–5]. Whilst the side effect profile of AIs is generally favourable in comparison to tamoxifen, with fewer thrombo-embolic and gynaecological adverse events, musculoskeletal side effects including accelerated bone loss and arthralgias are more frequent with the AIs. In the ATAC trial bone sub-protocol, patients treated with anastrozole lost on average 2.3%, 4.0% and 6.1% bone mineral density (BMD) at the lumbar spine (LS) and 1.5%, 3.9% and 7.2% at the hip (TH) after 1, 2 and 5 years respectively (p<0.001) [6]. This degree of bone loss is much higher than the normal rate of decline in postmenopausal women of 0.6–1.0% per year [7]. Similar effects have been seen with letrozole [8] and exemestane [9]. Additionally, the effects of AIs on bone turnover and the associated increased bone loss results in a 40–50% increase in on treatment fracture rate compared to the use of tamoxifen [10]. In order to prevent clinically important adverse bone events, a number of guidelines have been developed providing advice on how to monitor patients, assess the risk of fragility fractures and treat at risk patients with bone targeted drugs to prevent bone loss [11–14].