Induction of cell death of human osteogenic sarcoma cells by zoledronic acid resembles anoikis

Inhibitory effects of a new bisphosphonate, minodronate, on proliferation and invasion of a variety of malignant bone tumor cells

Little is known about the biological effects of bisphosphonates on primary malignant bone tumors. The purpose of this study was to investigate the antitumor effects of newly developed minodronate (MIN) on a variety of human malignant bone tumors. We examined the effects of MIN and clinically relevant incadronate (INC) on the proliferation, apoptosis, and cell cycle of two osteosarcoma (Saos-2, MG-63), two chondrosarcoma (SW1353, OUMS27), and two Ewing's sarcoma (RD-ES, SK-ES-1) cell lines. Furthermore, we investigated the anti-invasion effects of MIN on sarcoma cells and the effects of MIN on tumor growth in nude mice. MIN inhibited the viability of all six cell lines in a dose-dependent manner with IC50 values of 2.7 to 5.0 microM, which were significantly lower than those of INC. Importantly, both bisphosphonates affected the viability of normal bone marrow stromal cells much less than sarcoma cells. Both bisphosphonates induced cell cycle perturbation in all sarcoma cells tested and apoptosis in Saos-2 and SW1353 cells, although they failed to induce apoptosis in RD-ES and SK-ES-1 cells. MIN significantly suppressed invasion, even at a low concentration of 1 microM (p < 0.01). Daily injection of 5 microg of MIN inhibited the growth of SK-ES-1 xenograft sarcoma in nude mice without loss of body weight. These findings suggest that MIN may have a beneficial adjuvant role in the treatment of patients with malignant bone tumors.

Anticancer effects of zoledronic acid against human osteosarcoma cells

Based on neoadjuvant chemotherapy, the prognosis of osteosarcoma patients has improved dramatically. However, due to therapy resistance in patient subgroups, the development of new treatment strategies is still of utmost importance. The aim of our study was to test the effects of the nitrogen-containing bisphosphonate zoledronic acid (ZOL) on osteosarcoma cell lines (N = 9). Exposure to ZOL at low micromolar concentrations induced a dose- and time-dependent block of DNA synthesis and cell cycle progression followed by microfilament breakdown and apoptosis induction. The ZOL-induced cell cycle accumulation in S phase was accompanied by significant changes in the expression of cyclins and cyclin-dependent kinase inhibitors with a prominent loss of cyclin E and D1. ZOL not only inhibited growth but also migration of osteosarcoma cells. The mevalonate pathway intermediary geranyl-geraniol (GGOH) but not farnesol (FOH) significantly inhibited the anticancer effects of ZOL against osteosarcoma cells. Correspondingly, ZOL sensitivity correlated with the blockade of protein geranylgeranylation indicated by unprenylated Rap1. Overexpression of even high levels of P-glycoprotein, as frequently present in therapy-resistant osteosarcomas, did not impair the anticancer activity of ZOL. Summarizing, our data suggest that ZOL, which selectively accumulates in the bone, represents a promising agent to improve osteosarcoma therapy.

Synthesis and study of the cancer cell growth inhibitory properties of α-, γ-tocopheryl and γ-tocotrienyl 2-phenylselenyl succinates

Vitamin E succinate selenium-conjugated molecules were synthesized and their apoptogenic properties were evaluated. 4-Methyl-2-phenylselenyl succinate (4) was prepared by the reaction of sodium benzeneselenolate with 2-bromosuccinic anhydrite in methanol solution. The methyl ester was converted to the acid (5) by hydrolysis with aqueous hydrochloric acid. Reaction of the 2-phenylselenyl succinic anhydrite (6) with alpha-tocopherol (1a), gamma-tocopherol (1c), and gamma-tocotrienol (2c) in acidic conditions gave the respective esters. The free radical scavenging properties of alpha-tocopheryl-2-phenylselenyl succinate (7), gamma-tocopheryl-2-phenylselenyl succinate (8), and gamma-tocotrienyl-2-phenylselenyl succinate (9) were evaluated in comparison with those of alpha-tocopheryl succinate (10), gamma-tocopheryl succinate (11), and gamma-tocotrienyl succinate (12), respectively, and the free tocopherols and gamma-tocotrienol. Compounds 7-9 induced a statistically significant decrease in prostate cancer cell viability compared to 10-12, respectively, or 5, exhibiting features of apoptotic cell death and associated with caspase-3 activation. These data show that structural modifications of vitamin E components by 5 enhance their apoptogenic properties in cancer cells.

Zoledronic acid slows down rat primary chondrosarcoma development, recurrent tumor progression after intralesional curretage and increases overall survival

Chondrosarcoma is a difficult musculoskeletal tumor to treat. Surgical treatment leads to severe disability, with high rates of local recurrence and life threat. No adjuvant therapy is effective in differentiated chondrosarcomas. Bisphosphonates (BPs) are a class of molecules which is effective in malignant bone diseases. The aim of the present study was to determine the effects of zoledronic acid (ZOL) on chondrosarcoma tumor progression. ZOL was tested in vivo (s.c. 100 microg/kg, twice a week) in a rat chondrosarcoma model and in vitro (10(-7)-10(-4) M) on cells derived from this model. Two types of animal models were assessed, the first simulated development after intralesional curettage, the second nonoperative development of the tumor. Cell proliferation, caspase-1, -3 activities and cell cycle analysis were studied. The results revealed that ZOL slows down primary tumor development, tumor progression after intralesional curretage and increases overall survival. ZOL inhibits cell proliferation and increases cell death, with no significant variation of caspase-1 and -3 activities and cell cycle profiles. The present study demonstrates for the first time that in addition to surgery, the therapy of chondrosarcoma with BPs might be beneficial. Because of these first results, new therapeutic approaches of chondrosarcoma must be considered, mainly for low grade chondrosarcoma when disabling operation is planned and when only intralesional resection can be undertaken.

Enhanced tumor regression and tissue repair when zoledronic acid is combined with ifosfamide in rat osteosarcoma

The efficacy of zoledronic acid (ZOL), with or without the anticancer drug ifosfamide (IFO), was tested on primary bone tumor growth using a rat-transplantable model of osteosarcoma. The effects on bone remodeling and tumor growth were analyzed by radiography, micro-computed tomography (micro-CT), and histological staining. The in vitro effects of ZOL were studied by proliferation, apoptosis, and cell cycle analyses on the osteosarcoma cells OSRGA compared to rat primary osteoblasts. Treatment with ZOL was effective in preventing the formation of osteolytic lesions that developed in bone sites and in reducing the local tumor growth, as compared to the untreated rats. The combination of ZOL and IFO was more effective than each agent alone in preventing tumor recurrence, improving tissue repair, and increasing bone formation as revealed by the analysis of trabecular architecture. In vitro studies demonstrated that ZOL was more potent against the OSRGA cell line than osteoblasts (with a half-maximal inhibitory effect on proliferation seen at 0.2 and 20 microM, respectively), the ZOL-induced inhibition of OSRGA proliferation being due to cell cycle arrest in S-phase. No effect on OSRGA apoptosis could be observed in vitro, as assessed by Hoechst staining and caspase-1 and -3 activation. In situ cell death was determined by TUNEL staining on tumor tissue sections. No significant difference in TUNEL-positive cells could be observed between ZOL-treated and -untreated rats. This is the first report of the anti-bone resorption and antitumoral activities of zoledronic acid in a rat model of osteosarcoma, and its beneficial association with an antitumoral chemotherapeutic drug in preventing tumor recurrence.

An expression signature classifies chemotherapy-resistant pediatric osteosarcoma

Osteosarcoma is the most common malignant bone tumor in children. Osteosarcoma patients who respond poorly to chemotherapy are at a higher risk of relapse and adverse outcome. Therefore, it was the aim of this study to identify prognostic factors at the time of diagnosis to characterize the genes predictive of poor survival outcome and to identify potential novel therapeutic targets. Expression profiling of 30 osteosarcoma diagnostic biopsy samples, 15 with inferior necrosis following induction chemotherapy (Huvos I/II) and 15 with superior necrosis following induction chemotherapy (Huvos III/IV), was conducted using Affymetrix U95Av2 oligonucleotide microarrays. One hundred and four genes were found to be statistically significant and highly differentially expressed between Huvos I/II and III/IV patients. Statistically significant genes were validated on a small independent cohort comprised of osteosarcoma xenograft tumor samples. Markers of Huvos I/II response predominantly were gene products involved in extracellular matrix (ECM) microenvironment remodeling and osteoclast differentiation. A striking finding was the significant decrease in osteoprotegerin, an osteoclastogenesis inhibitory factor. Additional genes involved in osteoclastogenesis and bone resorption, which were statistically different, include annexin 2, SMAD, PLA2G2A, and TGFbeta1. ECM remodeling genes include desmoplakin, SPARCL1, biglycan, and PECAM. Gene expression of select genes involved in tumor progression, ECM remodeling, and osteoclastogenesis were validated via quantitative reverse transcription-PCR in an independent cohort. We propose that osteosarcoma tumor-driven changes in the bone microenvironment contribute to the chemotherapy-resistant phenotype and offer testable hypotheses to potentially enhance therapeutic response.

Zoledronic acid suppresses lung metastases and prolongs overall survival of osteosarcoma-bearing mice

BACKGROUND

Although there is no doubt that bisphosphonates (BPs), specific inhibitors of osteoclasts, are beneficial for the treatment of bone metastases, their effects on visceral metastases are unclear. The effect of zoledronic acid (ZOL) was examined in vivo on lung metastasis progression and animal survival, and in vitro on the cellular mechanisms involved.

METHODS

An animal model of lung metastasis was developed in C3H/He mice inoculated intravenously with a spontaneous murine osteosarcoma POS-1 cell line. Lung metastasis was determined at the time of autopsy. ZOL was assessed in vitro on POS-1 cell proliferation, cell cycle progression, and caspase-1 and -3 activities.

RESULTS

The overall survival in five independent experiments (two series treated with ZOL 0.1 mg/kg twice a week, and three series with 0.1 mg/kg five times a week) showed a significant increase of the actuarial survival: 0.422 +/- 0.07 in ZOL-treated animals versus 0.167 +/- 0.07 in controls (P = 0.036). Lung metastases were absent in all ZOL-treated mice that survived more than 21 days postinjection as revealed by macroscopic and histologic analysis. In vitro, a 48-hour incubation with 10 microM ZOL inhibited POS-1 cell line proliferation associated with cell cycle arrest in S-phase. In addition, ZOL induced a weak increase of caspase-3 activity, but not caspase-1.

CONCLUSION

We demonstrate that ZOL exerts a direct antitumor effect on POS-1 cells in vitro, significantly diminishes osteosarcoma-induced lung metastasis in vivo, thereby prolonging survival of POS-1-inoculated animals.

Sequence- and schedule-dependent enhancement of zoledronic acid induced apoptosis by doxorubicin in breast and prostate cancer cells

We investigated whether the combination of zoledronic acid and doxorubicin induced apoptosis of breast and prostate cancer cell lines, and if synergistic interaction was present. We investigated whether the levels of cell death altered depending on the sequence in which the drugs were administered and the possible mechanism of action responsible for the increased cell death following combined treatments. Breast and prostate cancer cells were treated with zoledronic acid alone, doxorubicin alone, or drugs in sequence (doxorubicin before, after, or with zoledronic acid), and the levels of apoptotic death were determined by evaluation of nuclear morphology. We found that clinically relevant concentrations of doxorubicin and zoledronic acid induced sequence- and schedule-dependent apoptosis of breast and prostate cancer cells. For maximal apoptosis, cells had to be pretreated for 24 hr with doxorubicin before immediate treatment with zoledronic acid for 1 hr. This observation is a characteristic feature of cell cycle phase-specific synergistic effect. Replacing zoledronic acid with the nonnitrogen-containing bisphosphonate clodronate did not induce increased apoptosis. Induction of apoptosis was mainly via inhibition of the mevalonate (MVA) pathway, as addition of the MVA pathway intermediary geranylgeraniol inhibited the induction of apoptosis by doxorubicin followed by zoledronic acid. In conclusion, combined treatment of breast and prostate cancer cell lines with clinically relevant doses of doxorubicin and zoledronic acid induces apoptosis in a synergistic fashion. These findings may have relevance for the clinical setting, particularly breast cancer patients receiving these drugs in the adjuvant setting.