pep005 and Leukemia

Members of the protein kinase C (PKC) family of serine-threonine kinases are important regulators of immune cell survival. Ingenol 3-angelate (PEP005) activates a broad range of PKC isoforms and induces apoptosis in acute myeloid leukemia cells by activating the PKC isoform PKCdelta. We show here that, in contrast to its effect on leukemic cells, PEP005 provides a strong survival signal to resting and activated human T cells. The antiapoptotic effect depends upon the activation of PKC. This PKC isoform is expressed in T cells but is absent in myeloid cells. Further studies of the mechanism involved in this process showed that PEP005 inhibited activated CD8(+) T cell apoptosis through the activation of NFkappaB downstream of PKC, leading to increased expression of the antiapoptotic proteins Mcl-1 and Bcl-x(L). Transfection of CD8(+) T cells with dominant-negative PKC diminished the prosurvival effect of PEP005 significantly. Ectopic expression of PKC in the acute myeloid leukemia cell line NB4 turned their response to PEP005 from an increased to decreased rate of apoptosis. Therefore, in contrast to myeloid leukemia cells, PEP005 provides a strong survival signal to T cells, and the expression of functional PKC influences whether PKC activation leads to an anti- or proapoptotic outcome in the cell types tested.

Topics: Antineoplastic Agents; Apoptosis; Caspase 3; CD8-Positive T-Lymphocytes; Cell Line, Tumor; Diterpenes; Drug Screening Assays, Antitumor; Enzyme Activation; Gene Expression Regulation, Leukemic; Humans; Isoenzymes; Leukemia; Protein Isoforms; Protein Kinase C; Protein Kinase C-theta; T-Lymphocytes; Transcription Factor RelA

The sap of Euphorbia peplus, commonly know as 'petty spurge', 'radium weed' or 'milkweed' has been used for centuries as a traditional treatment for skin conditions, including warts, corns and cancers of the skin. Documentation of its use by medical professionals to treat basal cell carcinoma (BCC) dates from the early 19 century. Individuals who participated in a 1988 survey of home treatments for cancer indicated the sap of E. peplus was an effective cure for actinic lesions leading the investigators to suggest that this potential utility should be further explored in controlled clinical trials. The fractionation of the sap E. peplus using solvents of varying polarity yielded several macrocyclic diterpenes, many of which were found to have cytotoxic activity or the ability to influence cellular differentiation. Ultimately, ingenol 3-angelate (I3A) of PEP005, emerged as a promising potential new anti-cancer treatment. Here we report the proceedings from the First International Conference on PEP005, covering the exciting potential of PEP005 as the therapeutic agent for the treatment of skin cancer, leukemia and bladder cancer.

Topics: Administration, Topical; Animals; Antineoplastic Agents, Phytogenic; Diterpenes; Esters; Humans; Leukemia; Melanoma; Mice; Neoplasms; Skin Neoplasms; Urinary Bladder Neoplasms

Ingenol 3-angelate (PEP005) is a selective small molecule activator of protein kinase C (PKC) extracted from the plant Euphorbia peplus, whose sap has been used as a traditional medicine for the treatment of skin conditions including warts and cancer. We report here that PEP005 also has potent antileukemic effects, inducing apoptosis in myeloid leukemia cell lines and primary acute myeloid leukemia (AML) cells at nanomolar concentrations. Of importance, PEP005 did not induce apoptosis in normal CD34+ cord blood myeloblasts at up to 2-log concentrations higher than those required to induce cell death in primary AML cells. The effects of PEP005 were PKC dependent, and PEP005 efficacy correlated with expression of PKC-delta. The delta isoform of PKC plays a key role in apoptosis and is therefore a rational potential target for antileukemic therapies. Transfection of KG1a leukemia cells, which did not express PKC-delta or respond to PEP005, with enhanced green fluorescent protein (EGFP)-PKC-delta restored sensitivity to induction of apoptosis by PEP005. Our data therefore suggest that activation of PKC-delta provides a novel approach for treatment of acute myeloid leukemia and that screening for PKC-delta expression may identify patients for potential responsiveness to PEP005.

Topics: Apoptosis; Diterpenes; Enzyme Inhibitors; Esters; Humans; Leukemia; Leukemia, Myeloid; Prognosis; Protein Kinase C; Protein Kinase C-delta; Transfection; Tumor Cells, Cultured