Cytotoxic activity of the third-generation bisphosphonate zoledronic acid in acute myeloid leukemia

Zoledronic acid inhibits the growth of leukemic MLL-AF9 transformed hematopoietic cells

A leukemic in vitro model produced by transducing Cord Blood derived-hematopoietic CD34⁺ cells with the MLL-AF9 translocation resulting in the oncogenic fusion protein, is used to assess for sensitivity to Zoledronic acid. These cells are practically immortalized and are of myeloid origin. Proliferation, clonogenic and stromal co-culture assays showed that the MLL-AF9 cells were considerably more sensitive to Zoledronic acid than normal hematopoietic CD34⁺ cells or MS-5 stromal cells. The MLL-AF9 cells were notably more inhibited by Zoledronic acid when cultured as colonies in 3 dimensions, requiring cell-cell contacts compared to suspension expansion cultures. This is coherent with the mechanism of action of Zoledronic acid inhibiting farnesyl diphosphate synthase which results in a block in prenylation of GTPases such that their role in the membrane is compromised for cell-cell contacts. Zoledronic acid can be proposed to target the MLL-AF9 leukemic stem cells before they emerge from the hematopoietic niche, which being in proximity to bone osteoclasts where Zoledronic acid is sequestered can be predicted to result in sufficient levels to result in an anti-leukemic action.

Zoledronic acid overcomes adriamycin resistance in acute myeloid leukemia cells by promoting apoptosis

Zoledronic acid (ZOL), a nitrogen‑containing bisphosphonate, is widely used in metastatic bone disease. Previous studies indicate that ZOL has marked anti‑leukemia activity, however, the underlying mechanism of action remains to be elucidated. The present study aimed to explore the mechanism of the anti‑leukemia effect of ZOL in leukemia cells. It was observed that ZOL inhibited the proliferation of HL‑60 and adriamycin‑resistant HL‑60 (HL‑60/A) cells using a WST‑8 assay. An Annexin V‑propidium iodide indicated that ZOL induced apoptosis of the two cell types in a dose‑ and time‑dependent manner. Hoechst 33342 staining was also used to verify the levels of apoptosis. The colony formation assay demonstrated that ZOL significantly inhibited colony formation capacity in acute myeloid leukemia (AML) cells. This was achieved by the induction of S‑phase cell cycle arrest, downregulation of B‑cell lymphoma 2 (Bcl‑2) and upregulation of Bcl‑2 associated X protein and cleaved poly (ADP‑ribose) polymerase. The results indicate that ZOL inhibited cell proliferation by inducing apoptosis via the mitochondrial apoptotic pathway and this anti‑leukemic activity appeared notably enhanced in HL‑60/A cells. As ZOL is already available for clinical use, these results indicate that it may be an effective addition to the chemotherapeutic strategies for AML.

Pilot study on the use of zoledronic acid to prevent bone loss in allo-SCT recipients

Bone loss is recognized as worsening the quality of life in long-term survivors of Allo-SCT. This study evaluated the risk factors associated with bone loss and the role of zoledronic acid in preventing bone loss in allogeneic recipients. Fifty-three patients who underwent HLA-matched Allo-SCT were evaluated for their bone mineral density (BMD) in the lumbar spine and femoral neck at regular intervals. Zoledronic acid (4 mg) was given i.v. to 18 patients (ZA patients) at 2 months after SCT and then every 3 months until 2 years. Grade 2-4 acute GVHD was associated with bone loss (odds ratio (OR)=4.90, 95% confidence interval (CI)=1.41-16.99; P=0.012) at 1 year after SCT, whereas extensive chronic GVHD and steroid use were both unfavorable prognostic factors (OR=9.00 and 7.22, 95% CI=1.52-53.40 and 1.44-36.22; P=0.016, respectively) in terms of osteopenia/osteoporosis at 2 years after transplantation. The use of zoledronic acid significantly prevented bone loss in the femoral neck as well as the spine (OR=0.18, 95% CI=0.05-0.69, P=0.012). Therefore, BMD measurements and the use of zoledronic acid are recommended in cases of GVHD or long-term steroid use after Allo-SCT to prevent bone loss and threatening skeletal events.

Erufosine, a novel alkylphosphocholine, in acute myeloid leukemia: single activity and combination with other antileukemic drugs

PURPOSE

Alkylphosphocholines represent a new class of cytostatic drugs with a novel mode of action. Erufosine (ErPC3), the first compound of this class that can be administered intravenously, has recently been shown to be active against human tumor and leukemic cell lines.

METHODS

In order to evaluate the antileukemic potential of ErPC3 in acute myeloid leukemia (AML) the lethal concentration 50% (LC 50) was determined using WST-1 assay. For analysis of cell death, staining for Annexin V and activated caspase 3 was performed. An interaction analysis was performed by calculation of combination index and construction of isobolograms.

RESULTS

The LC 50 was 7.4 microg/ml after 24 h and 3.2 microg/ml after 72 h in HL 60 cells and 30.1 and 8.6 microg/ml, respectively, in 19 fresh samples from patients with AML. ErPC3 was found to be cytotoxic in HL60 cells with distinct activation of caspase 3. ErPC3 was not cross-resistant with cytarabine, idarubicine and etoposide as shown by the linear relation of respective LC 50s. The latter agents, however, exerted an additive cytotoxicity in combination with ErPC3 as revealed by isobologram analysis and combination index, although results are uneven for idarubicine.

CONCLUSION

Based on these data ErPC3 appears as a novel antileukemic candidate drug, which needs to be explored further in the treatment of AML.