Bisphosphonates (BPs) are effective inhibitors of tumor-induced bone resorption. Recent studies have demonstrated that BPs inhibit growth, attachment and invasion of cancer cells in culture and promote apoptosis. The mechanisms responsible for the observed anti-tumor effects of BPs are beginning to be elucidated. Recently, we reported that nitrogen-containing bisphosphonates (N-BPs) induce formation of a novel ATP analog (ApppI) as a consequence of the inhibition of farnesyl diphosphate synthase in the mevalonate pathway. Similar to AppCp-type metabolites of non-N-BPs, ApppI is able to induce apoptosis. This study investigated BP-induced ATP analog formation and its effect on cancer cell growth. To evaluate zoledronic acid (a N-BP)-induced ApppI accumulation, inhibition of protein prenylation and clodronate (a non-N-BP) metabolism to AppCCl2p, MCF-7 and MDA-MB-436 breast cancer cells, MCF-10A nonmalignant breast cells, PC-3 prostate cancer cells, MG-63 osteosarcoma cells, RPMI-8226, and NCI-H929 myeloma cells were treated with 25 micromol/l zoledronic acid or 500 micromol/l clodronate for 24 h. The inhibition of cell growth by zoledronic acid and clodronate was studied in MCF-7, MDA-MB-436, and RPMI-8226 cells by exposing the cells with 1-100 micromol/l zoledronic acid or 10-2000 micromol/l clodronate for 72 h. Marked differences in zoledronic acid-induced ApppI formation and clodronate metabolism between the cancer cell lines were observed. The production of cytotoxic ATP analogs in tumor cells after BP treatment is likely to depend on the activity of enzymes, such as farnesyl diphosphate synthase or aminoacyl-tRNA synthetases, responsible for ATP analog formation. Additionally, the potency of clodronate to inhibit cancer cell growth corresponds to ATP analog formation.

IntroductionThe majority of deaths from breast cancer are a result of metastases; however, little is understood about the genetic alterations underlying their onset. Genetic profiling has identified the adhesion molecule plakoglobin as being three-fold reduced in expression in primary breast tumors that have metastasized compared with nonmetastatic tumors. In this study, we demonstrate a functional role for plakoglobin in the shedding of tumor cells from the primary site into the circulation.MethodsWe investigated the effects of plakoglobin knockdown on breast cancer cell proliferation, migration, adhesion, and invasion in vitro and on tumor growth and intravasation in vivo. MCF7 and T47D cells were stably transfected with miRNA sequences targeting the plakoglobin gene, or scramble vector. Gene and protein expression was monitored by quantitative polymerase chain reaction (qPCR) and Western blot. Cell proliferation, adhesion, migration, and invasion were measured by cell counting, flow cytometry, and scratch and Boyden Chamber assays. For in vivo experiments, plakoglobin knockdown and control cells were inoculated into mammary fat pads of mice, and tumor growth, shedding of tumor cells into the bloodstream, and evidence of metastatic bone lesions were monitored with caliper measurement, flow cytometry, and microcomputed tomography (μCT), respectively.ResultsPlakoglobin and γ-catenin expression were reduced by more than 80% in all knockdown cell lines used but were unaltered after transfection with the scrambled sequence. Reduced plakoglobin resulted in significantly increased in MCF7 and T47D cell proliferation in vitro and in vivo, compared with control, with significantly more tumor cells being shed into the bloodstream of mice bearing plakoglobin knockdown tumors. In addition, plakoglobin knockdown cells showed a >250% increase in invasion through basement membrane and exhibited reduced cell-to-cell adhesion compared with control cells.ConclusionDecreased plakoglobin expression increases the invasive behavior of breast cancer cells. This is the first demonstration of a functional role for plakoglobin/γ-catenin in the metastatic process, indicating that this molecule may represent a target for antimetastatic therapies.

Background/Aims: The cytotoxic agent paclitaxel and the anti-resorptive drug zoledronic acid are used in the early and advanced breast cancer setting, respectively. Both agents have been demonstrated to have anti-tumour and anti-endothelial actions. Combining paclitaxel with zoledronic acid induces a synergistic increase in apoptotic breast cancer cell death in vitro, suggesting an increased anti-tumour effect in vivo, but any specific effects on the normal microvasculature and potential side-effects of this combination remain to be established. Methods: The effects of zoledronic acid and paclitaxel were investigated, alone and in combination, on human microvascular endothelial cells in vitro, using functional assays including proliferation, migration, tubule formation and apoptosis. The in vivo effect of the drugs on the normal microvasculature was determined using the dorsal microcirculation chamber model. Results/Conclusion: Zoledronic acid reduced human dermal microvascular endothelial cell (HuDMEC) proliferation, caused accumulation of cells in S phase, and inhibited migration, tube formation and Rap1a prenylation. Paclitaxel significantly inhibited tube formation and proliferation, and increased endothelial necrosis; the combination induced HuDMEC apoptosis and further enhanced the inhibition of tube formation and migration. The combination caused minimal effects on the normal microvasculature in vivo, suggesting that this potential therapeutic strategy is not associated with deleterious microvascular side-effects.

A series of novel aminodiol inhibitors of HIV protease based on the lead compound 1 with structural modifications at P1' were synthesized in order to reduce the cytotoxicity of 1. We have observed a high degree of correlation between the lipophilicity and cytotoxicity of this series of inhibitors. It was found that appropriate substitution at the para position of the P1' phenyl group of 1 resulted in the identification of equipotent (both against the enzyme and in cell culture) compounds (10l, 10m, 10n, and 15c) which possess significantly decreased cytotoxicity.

Background: Pre-clinical studies have demonstrated sequence-dependent synergistic anti-tumour effects of chemotherapy (CT) and zoledronic acid (Z) in bone and soft tissue tumours. We have also reported that the addition of Z to neoadjuvant CT appears to improve pathological response in the surgical resection specimen. The ANZAC study aimed to investigate the short-term anti-tumour effects of neoadjuvant CT +/− Z in patients with invasive breast cancer, evaluating biological end-points including apoptosis, proliferation and angiogenesis. Methods: Forty patients were randomised to receive a single 4mg infusion of Z 24 hours after the first cycle of FE100C chemotherapy, as per the most effective schedule demonstrated pre-clinically, or CT alone (CT n=20, CT+Z n=20). Randomisation was stratified for tumour (T) stage, ER, HER2 status and menopausal status to minimise biological differences in the two treatment groups that may influence chemosensitivity. All patients had repeat breast core biopsy at Day 5 (D5) +/− Day 21 (D21). Apoptotic index (AI) and proliferation were measured on core biopsy specimens using TUNEL and Ki67 immunohistochemistry, counting a total of 2000 and 1000 tumour cells respectively. Serum VEGF was also measured at baseline prior to CT +/− Z, and on D5 and D21. Differences between the groups in change from baseline to subsequent timepoints were investigated using the Mann-Whitney U test. Results: Baseline clinico-pathological characteristics were well balanced between the two groups. For the different biological end-points, percentage change from baseline to D5 and from baseline to D21 are shown in Table 1. At D5, a greater reduction in serum VEGF occurred in patients treated with CT+Z compared to CT: median percentage change -23.8% (IQR -32.9, -15.8) vs. -8.4% (IQR -27.3, +8.9); p=0.02), but these effetcs were lost by D21. Cell turnover index fell at D5 in both groups (increased apoptosis and reduced proliferation) but recovered much more rapidly with CT+Z than CT alone by D21 to levels above baseline (p=0.006). Conclusions: No definite evidence of a direct anti-tumour effect of the addition of Z to CT was observed, but potentially relevant biological effects were seen in this small study. The clinical relevance of recovery of cell turnover by D21 with CT+Z is unclear. Studies with more frequent dosing of Z are warranted to exploit any potential anti-angiogenic effect of Z. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-11-01.

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