Pterostilbene downregulates BCR/ABL and induces apoptosis of T315I-mutated BCR/ABL-positive leukemic cells.

In this study, we examined the antileukemic effects of pterostilbene, a natural methylated polyphenol analog of resveratrol that is predominantly found in berries and nuts, using various human and murine leukemic cells, as well as bone marrow samples obtained from patients with leukemia. Pterostilbene administration significantly induced apoptosis of leukemic cells, but not of non-malignant hematopoietic stem/progenitor cells. Interestingly, pterostilbene was highly effective in inducing apoptosis of leukemic cells harboring the BCR/ABL fusion gene, including ABL tyrosine kinase inhibitor (TKI)-resistant cells with the T315I mutation. In BCR/ABL+ leukemic cells, pterostilbene decreased the BCR/ABL fusion protein levels and suppressed AKT and NF-κB activation. We further demonstrated that pterostilbene along with U0126, an inhibitor of the MEK/ERK signaling pathway, synergistically induced apoptosis of BCR/ABL+ cells. Our results further suggest that pterostilbene-promoted downregulation of BCR/ABL involves caspase activation triggered by proteasome inhibition-induced endoplasmic reticulum stress. Moreover, oral administration of pterostilbene significantly suppressed tumor growth in mice transplanted with BCR/ABL+ leukemic cells. Taken together, these results suggest that pterostilbene may hold potential for the treatment of BCR/ABL+ leukemia, in particular for those showing ABL-dependent TKI resistance.

Iron removal enhances vitamin C-induced apoptosis and growth inhibition of K-562 leukemic cells.

Although vitamin C (VC) has recently garnered interest as an alternative cancer therapy, its clinical effects remain controversial. It was recently reported using in vitro prostate cancer cell lines that excess extracellular iron (EEI) diminishes anti-cancer effects of VC, promoting the decomposition of hydrogen peroxide (H2O2) generated by VC. Here we demonstrated that EEI diminished the inhibitory effect of VC on the survival of K562 human leukemic cells in vitro, by reducing the amount of H2O2 and abrogating the apoptosis pathways induced by VC. In vivo, in the presence of EEI, the growth inhibitory effect of VC on K562 cells was completely abrogated; in fact, VC enhanced K562 cell growth. Reduction of EEI restored the apoptosis-inducing effect of VC in vitro and enhanced the growth inhibitory effect of VC in vivo. Further studies are warranted to investigate whether the combination of VC and iron depletion has similar effects in various other leukemic or cancer cells against which VC has been effective in previous experimental studies.

Functional analysis of the SEPT9-ABL1 chimeric fusion gene derived from T-prolymphocytic leukemia.

We analyzed the function of a SEPT9-ABL1 fusion identified in a case of T-prolymphocytic leukemia with tyrosine kinase inhibitor (TKI) resistance. Five isoforms with different N-termini, including SEPT9a-ABL1, SEPT9b-ABL1, SEPT9d-ABL1, SEPT9e-ABL1 and SEPT9f-ABL1, were detected in the leukemic cells. All isoforms except SEPT9d-ABL1 are localized in the cytoplasm, undergo autophosphorylation and phosphorylate the downstream targets, STAT-5 and Crkl, and provided IL-3-independence and in vivo invasiveness to 32D cells. Additionally, these SEPT9-ABL1 isoforms were resistant to TKIs in vitro and in vivo, in comparison to BCR-ABL1. These findings demonstrated that SEPT9-ABL1 had oncogenic activity and conferred resistance to TKIs.

Phase I Clinical Trial of Intravenous L-ascorbic Acid Following Salvage Chemotherapy for Relapsed B-cell non-Hodgkin's Lymphoma.

PURPOSE: To determine the safety and the appropriate dose of intravenous l-ascorbic acid (AA) in conjunction with chemotherapy for patients with relapsed lymphoma. PATIENTS AND METHODS: Patients with relapsed CD20-positive B-cell non-Hodgkin's lymphoma, who were going to receive the CHASER regimen as salvage therapy, were enrolled and treated with escalating doses of AA administered by drip infusion after the 2nd course of the CHASER regimen. The target plasma concentration immediately after AA administration was >15 mM (264 mg/dl). RESULTS: A serum AA concentration of >15 mM was achieved in 3 sequentially registered patients, all of whom had received a 75 g whole body dose. No obvious adverse drug reaction was observed in the patients. The trial was therefore successfully completed. CONCLUSION: Intravenous AA at a whole body dose of 75 g appears to be safe and sufficient to achieve an effective serum concentration. A phase II trial to evaluate the efficacy of intravenous AA in relapsed/refractory lymphoma patients will now be initiated.

High concentrations of L-ascorbic acid specifically inhibit the growth of human leukemic cells via downregulation of HIF-1α transcription.

We examined the antileukemic effects of high concentrations of L-ascorbic acid (high AA) on human leukemic cells. In vitro, high AA markedly induced apoptosis in various leukemic cell lines by generating hydrogen peroxide (H2O2) but not in normal hematopoietic stem/progenitor cells. High AA significantly repressed leukemic cell proliferation as well as neoangiogenesis in immunodeficient mice. We then noted that in leukemic cells, HIF-1α transcription was strongly suppressed by high AA and correlated with the transcription of VEGF. Our data indicate that exposure to high AA markedly increased the intracellular AA content of leukemic cells and inhibited the nuclear translocation of NF-κB, which mediates expression of HIF-1α. We next generated K562 cells that overexpressed HIF-1α (K562-HIF1α cells) and assessed the mechanistic relationship between inhibition of HIF-1α transcription and the antileukemic effect of high AA. The ability of high AA to induce apoptosis was significantly lower in K562-HIF1α cells than in K562 cells in vitro. We found that expression of HIF-1α-regulated antiapoptotic proteins of the Bcl-2 family, such as Mcl-1, Bcl-xL, and Bcl-2, was significantly suppressed by high AA in K562 cells, but was sustained at higher levels in K562-HIF1α cells, regardless of high AA exposure. Moreover, repression of cell proliferation and neoangiogenesis by high AA was completely abrogated in mice receiving transplants of K562-HIF1α cells. These results indicate that, along with H2O2 generation, downregulation of HIF-1α transcription plays a crucial role in growth inhibition of human leukemic cells by high AA.