The bisphosphonate, zoledronic acid, induces apoptosis of breast cancer cells: evidence for synergy with paclitaxel

Abstract

SummaryBisphosphonates are well established in the management of breast-cancer-induced bone disease. Recent studies have suggested that these compounds are effective in preventing the development of bone metastases. However, it is unclear whether this reflects an indirect effect via an inhibition of bone resorption or a direct anti-tumour effect. The breast cancer cell lines, MCF-7 and MDA-MB-231 cells were treated with increasing concentrations of the bisphosphonate, zoledronic acid, for varying time periods, in the presence or absence of paclitaxel. The effects of zoledronic acid were determined by assessing cell number and rate of apoptosis by evaluating changes in nuclear morphology and using a fluorescence nick translation assay. Zoledronic acid caused a dose-and time-dependent decrease in cell number (P < 0.001) and a concomitant increase in tumour cell apoptosis (P < 0.005). Short-term exposure to zoledronic acid was sufficient to cause a significant reduction in cell number and increase in apoptosis (P < 0.05). These effects could be prevented by incubation with geranyl geraniol, suggesting that zoledronic acid-induced apoptosis is mediated by inhibiting the mevalonate pathway. Treatment with zoledronic acid and clinically achievable concentrations of paclitaxel resulted in a 4-5-fold increase in tumour cell apoptosis (P < 0.02). Isobologram analysis revealed synergistic effects on tumour cell number and apoptosis when zoledronic acid and paclitaxel were combined. Short-term treatment with zoledronic acid, which closely resembles the clinical setting, has a clear anti-tumour effect on breast cancer cells. Importantly, the commonly used antineoplastic agent, paclitaxel, potentiates the anti-tumour effects of zoledronic acid. These data suggest that, in addition to inhibiting bone resorption, zoledronic acid has a direct anti-tumour activity on breast cancer cells in vitro.

Bisphosphonates antagonise bone growth factors' effects on human breast cancer cells survival

“…We showed here that this relatively low concentration was able to block growth factors' effects, and to inhibit the 'protective' effect of growth factors on breast cancer cell survival. The effects of bisphosphonates that we observed were thus obtained with relatively low concentrations of bisphosphonates, in contrast to earlier works that reported the requirement for higher concentrations, between 20 and 1000 mM, to exhibit antitumour effects (Senaratne et al, 2000;Lee et al, 2001;Jagdev et al, 2001a).…”

“…Indeed, clodronate and pamidronate are bisphosphonates of first/second generations. In contrast, ibandronate and zoledronic acid are last generation bisphosphonates that represent the two most potent compounds (Hiraga et al, 2001;Jagdev et al, 2001a;Rosen et al, 2001;Body, 2003;Lipton, 2003). Despite their marked differences in potency to inhibit bone resorption in vitro or in vivo, we did not observe major differences between the potency of these four compounds in our in vitro experiments.…”

“…No significant effect was detected even at the highest concentration (10 À4 M; data not shown). Recent data go along the same line (Jagdev et al, 2001a) and led us to discard the possibility that the observed effects are due to simple cation chelation by the bisphosphonates.…”

“…Bisphosphonates can also decrease the number of bone metastases (Hall and Stoica, 1994;Powles et al, 2002). Moreover, we and others recently demonstrated that, in vitro, bisphosphonates irreversibly reduce breast cancer cell viability by inducing cell death, either by apoptosis or by direct cell necrosis (Fromigue et al, 2000;Senaratne et al, 2000;Jagdev et al, 2001a). The exact mechanism of action of bisphosphonates is unknown.…”

New insights into the actions of bisphosphonate zoledronic acid in breast cancer cells by dual RhoA-dependent and -independent effects

“…A recent study using an in vitro model of cell invasion has also suggested that BPs may inhibit the early event in the formation of bone metastases (Boissier et al, 2000). Furthermore, several investigations have reported the inhibition of cell growth and cell survival by BPs on breast cancer cells (Fromigue et al, 2000;Senaratne et al, 2000;Hiraga et al, 2001;Jagdev et al, 2001).…”