Jack Burton

Identification of a novel receptor/signal transduction pathway for IL-15/T in mast cells

Interleukin-15/T(IL-15) is a growth factor that utilizes IL-2 receptor (IL-2R) components in addition to its private binding protein IL-15R(alpha) in T-cells. Here, we report that IL-15 induces mast cell proliferation in the absence of IL-2R alpha and beta. Using transfectants of these cells with a cytoplasmic-truncated mutant of gamma(c), we demonstrated that IL-15 signaling in mast cells does not involve gamma(c). Cross-linking of mast cells with [(125)I]IL-15 revealed a 60-65 kDa IL-15 binding protein that is distinct from known components of T-cell IL-15 receptors. Mast cell IL-15 receptors recruit JAK-2 and STAT-5, instead of JAK1/3 and STAT3/5 that are activated in T-cells. Thus IL-15 is a mast cell growth factor that utilizes a novel receptor and distinct signaling pathway.

Potential of Peroxisome Proliferator-Activated Receptor Gamma Antagonist Compounds as Therapeutic Agents for a Wide Range of Cancer Types

PPARγ is a therapeutic target that has been exploited for treatment of type II diabetes mellitus (T2DM) with agonist drugs. Since PPARγ is expressed by many hematopoietic, mesodermal and epithelial cancers, agonist drugs were tested and shown to have both preclinical and clinical anticancer activities. While preclinical activity has been observed in many cancer types, clinical activity has been observed only in pilot and phase II trials in liposarcoma and prostate cancer. Most studies address agonist compounds, with substantially fewer reports on anticancer effects of PPARγ antagonists. In cancer model systems, some effects of PPARγ agonists were not inhibited by PPARγ antagonists, suggesting noncanonical or PPARγ-independent mechanisms. In addition, PPARγ antagonists, such as T0070907 and GW9662, have exhibited antiproliferative effects on a broad range of hematopoietic and epithelial cell lines, usually with greater potency than agonists. Also, additive antiproliferative effects of combinations of agonist plus antagonist drugs were observed. Finally, there are preclinical in vivo data showing that antagonist compounds can be administered safely, with favorable metabolic effects as well as antitumor effects. Since PPARγ antagonists represent a new drug class that holds promise as a broadly applicable therapeutic approach for cancer treatment, it is the subject of this review.

Enhanced histone deacetylase enzyme activity in primary myelofibrosis

We measured histone deacetylase (HDAC) activity in 17 patients with primary myelofibrosis (PMF); 19 with other myeloproliferative neoplasm (MPN) and 16 normal volunteers. Significantly elevated HDAC levels were shown in patients with PMF compared with other MPN patients and normal volunteers (p < 0.05). Sixteen patients with PMF were also studied for correlation between JAK2 mutation status and HDAC levels; no significant correlation was found. We further correlated HDAC levels with clinical features in PMF: there was no correlation with WBC, platelet counts, Hb levels or degree of bone marrow fibrosis, but HDAC levels were correlated to the degree of splenomegaly. This suggests that HDAC may be recruited as essential thrombocythemia or polycythemia vera progresses into myelofibrosis or PMF progresses into more advanced stage. We then used the qRT-PCR cycle threshold (CT) method to study which HDACs were elevated in PMF. The results showed that, in general, Class 1 HDACs were elevated (HDAC1,2,8) except HDAC3, Class II HDACs were depressed (HDAC4,5) except HDAC6 and 10, and Class III HDACs were generally elevated. The current study may form the basis for using HDAC inhibitor in the treatment of patients with PMF and may implicate a possible role of HDAC in the association of pathogenesis of PMF.

Peroxisome proliferator-activated receptor-?? antagonists exhibit potent antiproliferative effects versus many hematopoietic and epithelial cancer cell lines

Peroxisome proliferator-activated receptor-&ggr; ligands have preclinical and clinical anticancer activity. Most studies in this area address agonists, with relatively few reports on anticancer effects of peroxisome proliferator-activated receptor-&ggr; antagonists. Thus, we evaluated the two pure peroxisome proliferator-activated receptor-&ggr; antagonists, T0070907 and GW9662, on a panel of hematopoietic and epithelial cell lines. The peroxisome proliferator-activated receptor-&ggr; antagonists and a reference agonist (pioglitazone) were tested in an in-vitro proliferation assay on a panel of seven hematopoietic and nine epithelial cancer cell lines, some of which are chemoresistant. Peroxisome proliferator-activated receptor-&ggr; expression was measured by immunoblotting, as was the effect of treatment with these agents on peroxisome proliferator-activated receptor-&ggr; levels. The effect of exogenous interleukin-6, an antiapoptotic cytokine, on growth inhibition was evaluated as well as the apoptotic effects of these drugs. The peroxisome proliferator-activated receptor-&ggr; antagonists showed significantly greater potency on all cell lines (IC50s of 3.2–29.7 versus 26.5–78.7 μmol/l for pioglitazone) and greater maximum growth inhibition. Peroxisome proliferator-activated receptor-&ggr; levels did not correlate with growth inhibition in this panel of cell lines. Combinations of peroxisome proliferator-activated receptor-&ggr; antagonists and the agonist actually showed schedule-dependent increases in growth inhibition. Exogenous interleukin-6 did not induce resistance to these agents. Both the antagonists and the agonist induced apoptosis, but only the former drugs showed caspase dependence. These two peroxisome proliferator-activated receptor-&ggr; antagonists have significantly more potent in-vitro antiproliferative effects versus hematopoietic and epithelial cancer cell lines. This effect does not correlate with peroxisome proliferator-activated receptor-&ggr; levels, suggesting alternative mechanisms or other targets of action. These findings support further translational studies to explore the mechanism of action and therapeutic potential of this class of agents.

Radioimmunotherapy of non-Hodgkin’s lymphoma: a critical appraisal

Radioimmunotherapy is a unique form of radiation therapy that uses antibodies to specifically target radionuclides for systemic cancer treatment. While chemotherapy remains the frontline treatment for non-Hodgkin’s lymphoma, two radioimmunotherapy agents are approved for use in certain follicular and transformed forms of recurrent non-Hodgkin’s lymphoma as a second- or third-line treatment option. However, there are number of clinical trials underway that will likely lead to a more expanded use of this treatment modality in the future. New agents and approaches for radioimmunotherapy are also being developed that could offer an even greater potential for this new form of therapy.

Human B lymphocytes express the p75 component of the interleukin 2 receptor

The nature of the interleukin 2 (IL-2) receptor on purified human B lymphocytes was examined. Both normal and malignant cells showed evidence of a 70-75,000 mol. wt (p75) IL-2 binding molecule as assessed by 125I-labeled IL-2 binding and receptor cross-linking. On normal, Tac-negative B lymphocytes the estimated number of p75 binding sites was 1100 per cell and the dissociation constant (Kd) was 1.7 nM. Consistent with this, cross-linking experiments demonstrated the presence of an IL-2 binding molecule of 70-75,000 mol. wt. Purified B cells from patients with hairy cell leukemia and chronic lymphocytic leukemia (CLL) also expressed the p75 IL-2 binding molecule. In the HCL samples, a small number of high-affinity IL-2 binding sites were detected (27-90) while the majority of binding sites (2100-10,800) were typical of low-affinity p55 Tac binding. IL-2 added to the purified normal and CLL B lymphocytes led to the induction of p55 Tac expression and the generation of high-affinity IL-2 receptors. This response to IL-2 was equivalent to the response observed when normal B lymphocytes were stimulated by Staphylococcus aureus Cowan I.

The interleukin-2 receptor: a target for immunotherapy.

Immune intervention began almost two centuries ago when Jenner introduced vaccination with cowpox as a means of protecting against smallpox. This form of immune intervention plays a dominant role in the prevention of human disease. Furthermore, immunological approaches including radioimmunoassays, enzyme-linked immunoassays, microfluorometry, and modern molecular immunogenetics are critical in clinical diagnosis.

A phase I/II trial of fixed-dose docetaxel plus irinotecan and escalating doses of estramustine phosphate for second-line or greater treatment of selected advanced solid tumors.

This phase I/II study evaluated the safety of the combination of irinotecan, docetaxel, and estramustine for selected advanced solid tumors and also obtained initial efficacy data. Twenty-two patients were enrolled in the study. The regimen consisted of docetaxel 30 mg/m2 and irinotecan 60 mg/m2 both given intravenously on days 1 and 8 every 21 days in combination with escalating doses of estramustine (500 mg/m2/day escalated to 750 mg/m2/day on days 0, 1, 2, 7, 8, and 9 given every 21 days) during phase I. Dose escalation was continued until the maximum planned dose level of estramustine (750 mg/m2/day) was reached. After the appropriate phase II dose of estramustine was found additional patients were enrolled. Twenty-one of the 22 patients were evaluable for toxicity and 17 for tumor response. The recommended phase II dose of estramustine was found to be 750 mg/m2/day orally on days 0, 1, 2, 7, 8, and 9 given every 21 days. Hematologic toxicity was fairly mild, with only one episode of grade 3 neutropenia. Diarrhea was the most common nonhematologic toxicity with grade 3 toxicity occurring in five of 21 patients. Only one episode of venous thrombosis was observed. Objective response rate was 15.8%, overall clinical benefit rate was 63%, and median time to progression was 15 weeks. Estramustine in combination with the doublet of docetaxel and irinotecan is a well-tolerated regimen with minimal hematologic toxicity, mild to moderate nonhematologic toxicity, and promising initial antitumor activity in previously treated patients with advanced solid tumors.