+ Site Statistics
+ Search Articles
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ PDF Full Text
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Translate
+ Recently Requested

Treosulfan Potently Induces Apoptosis in Human Acute Myeloid Leukemia Cells by a Protein Kinase C Dependent Mechanism, Which Can Be Markedly Augmented by the PKC-Activator Bryostatin-1

Treosulfan Potently Induces Apoptosis in Human Acute Myeloid Leukemia Cells by a Protein Kinase C Dependent Mechanism, Which Can Be Markedly Augmented by the PKC-Activator Bryostatin-1

Blood 100(11): Abstract No 4595, November 16

OBJECTIVES: Despite recent advances in the understanding of the underlying biology of acute myeloid leukemia (AML), the drugs employed have not changed over the past three decades. Primarily, cytosine arabinoside (ara-C) and anthracycline analogs are used in most chemotherapeutic regimens. Although dose-intensification with stem cell rescue and optimized supportive care improved response rates and overall survival, the disease remains incurable in the majority of patients. Thus, alternative or new cytotoxic compounds are warranted. METHODS: We performed chemosensitivity experiments with the alkylating agent treosulfan using AML cell lines (U937, TUR, HL-60, THP-1) and primary leukemia cells from five consecutive patients. Viability, cell cycle distribution, sub-G1-fraction, mitochondrial transmembrane potential and number of annexin V-positive, apoptotic cells were determined. To further evaluate the mechanism of treosulfan-induced apoptosis, we tested for alterations in the levels of pro- and antiapoptotic proteins by immunoblotting. Furthermore, as protein kinase C (PKC) is known to regulate diverse cellular functions, several PKC modulators were tested in conjunction with treosulfan. RESULTS: Treosulfan potently induces cell death in all four cell lines and primary leukemia cells with a LC90 of approximately 100muM, which is severalfold below the clinically achievable plasma levels. Whereas immunoblotting experiments did not reveal significant changes in the intracellular expression levels of common pro- and antiapoptotic proteins (e.g. BCL-2 family, inhibitors of apoptosis IAPs), treosulfan-induced cell death was associated with cellular events indicating apoptosis such as breakdown of the mitochondrial transmembrane potential, the proteolytic activation of caspases-9 and -3 as well as the appearance of a sub-G1 DNA peak. Treosulfan-induced apoptosis was significantly reduced by coincubation with the PKC-inhibitor GF109203X. In contrast, activation of PKC isozymes by TPA (12-O-tetradecanoylphorbol-13-acetate) or bryostatin-1 showed synergistic antileukemic effects with treosulfan in AML cell lines and primary leukemia cells. Since activation of PKCs is followed by proteolytic down-regulation of the kinases, we performed time-course experiments to determine the optimal sequence of PKC activation and treosulfan exposure. Whereas a 72 h preincubation with bryostatin-1 reduced the percentage of apoptotic cells by 61%, short-term preincubation (24 h or less) enhanced the cytotoxic effect of treosulfan exposure by 72%. CONCLUSION: Treosulfan, a drug related to busulfan, potently induces apoptosis in AML cell lines and primary leukemia cells from patients at clinically achievable doses. Thus, our results support the use of treosulfan as cytotoxic conditioning agent for autologous or allogeneic stem cell transplantation in the therapy of AML. Furthermore, bryostatin-1, which has been shown to be applicable in several clinical trials, demonstrates synergistic antileukemic effects with treosulfan when administered in close temporal proximity. Taken together, these data provide a rationale to evaluate treosulfan in combination with bryostatin-1 in the treatment of AML.

(PDF emailed within 1 workday: $29.90)

Accession: 035985731

Download citation: RISBibTeXText

Related references

Treosulfan-induced apoptosis in acute myeloid leukemia cells is accompanied by translocation of protein kinase C delta and enhanced by bryostatin-1. Experimental Hematology 32(1): 76-86, 2004

Potentiation of ara-C-induced apoptosis by the protein kinase C activator bryostatin 1 in human leukemia cells (HL-60) involves a process dependent upon c-Myc. Biochemical Pharmacology 54(5): 563-573, 1997

Protein kinase C-dependent activation of the tumor necrosis factor receptor-mediated extrinsic cell death pathway underlies enhanced apoptosis in human myeloid leukemia cells exposed to bryostatin 1 and flavopiridol. Molecular Cancer Therapeutics 2(1): 83-93, 2003

Modulation of protein kinase C activity and calcium-sensitive isoform expression in human myeloid leukemia cells by bryostatin 1: relationship to differentiation and ara-C-induced apoptosis. Experimental Cell Research 228(1): 65-75, 1996

Bryostatin, an activator of the calcium phospholipid-dependent protein kinase, blocks phorbol ester-induced differentiation of human promyelocytic leukemia cells HL-60. Proceedings of the National Academy of Sciences of the United States of America 83(5): 1334-1338, 1986

BMS-214662 potently induces apoptosis of chronic myeloid leukemia stem and progenitor cells and synergizes with tyrosine kinase inhibitors. Blood 111(5): 2843-2853, 2007

Microinjected catalytic subunit of cAMP-dependent protein kinase induces apoptosis in myeloid leukemia (IPC-81) cells. Experimental Cell Research 206(1): 157-161, 1993

The novel triterpenoid 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid induces apoptosis of human myeloid leukemia cells by a caspase-8-dependent mechanism. Cell Growth and Differentiation 11(5): 261-267, 2000

Melanoma differentiation associated gene-7/interleukin-24 potently induces apoptosis in human myeloid leukemia cells through a process regulated by endoplasmic reticulum stress. Molecular Pharmacology 78(6): 1096-1104, 2010

A celecoxib derivative inhibits focal adhesion signaling and induces caspase-8-dependent apoptosis in human acute myeloid leukemia cells. International Journal of Cancer 123(1): 217-226, 2008

Overexpression of protein kinase C isoform epsilon but not delta suppresses apoptosis and induces bcl-2 expression in human IL-3 dependent myeloid cells. Blood 90(10 SUPPL 1 PART 1): 167A, Nov 15, 1997

Inhibition of Bcl-2 antiapoptotic members by obatoclax potently enhances sorafenib-induced apoptosis in human myeloid leukemia cells through a Bim-dependent process. Blood 119(25): 6089-6098, 2012

The novel Akt inhibitor, perifosine, induces caspase-dependent apoptosis and downregulates P-glycoprotein expression in multidrug-resistant human T-acute leukemia cells by a JNK-dependent mechanism. Leukemia 22(6): 1106-1116, 2008

cis-Diamminedichloroplatinum(II) induces c-jun expression in human myeloid leukemia cells: potential involvement of a protein kinase C-dependent signaling pathway. Cancer Research 52(4): 878-882, 1992

Bryostatin 1 induces apoptosis in LNCaP human prostate cancer cells overexpressing protein kinase C alpha or PKC epsilon. Proceedings of the American Association for Cancer Research Annual Meeting 38(0): 543, 1997