Phase II study of the farnesyltransferase inhibitor R115777 in advanced melanoma: CALGB 500104

8014

Background: Ras-based signaling is thought to be critical in the genesis of melanoma. Farneslytransferase (FT) inhibitors (FTIs) have been developed as a pharmacologic strategy to inhibit Ras function. Additional farnesylated proteins are also important for the malignant process, and FTIs inhibit melanoma cell line proliferation in vitro. These considerations motivated the development of a phase II trial of the FTI R115777 in patients with melanoma. Farnesylated proteins are also important for T cell activation. The interest in future combinations of targeted agents and immunotherapeutics in this disease prompted analysis of T cell function ex vivo. Methods: A 3-stage design was pursued with a maximum of 40 patients planned and early stopping if there were no responders in the first 14, or fewer than 2 responders in the first 28 patients. Eligibility included intact organ function, PS≤1, no prior chemotherapy, at most 1 prior immunotherapy, no brain metastases, and presence of at least 2 cutaneous lesions amenable to excisional biopsy. R115777 (300 mg orally) was administered twice per day for 21 days of a 28-day cycle. Patients were evaluated every 2 cycles by RECIST criteria. Blood was obtained pre-treatment and during week 7 for analysis of HDJ-2 farnesylation and for T cell IFN-γ production in response to SEA. In addition, tumor biopsies were performed pre- and post-treatment when feasible to directly measure FT activity. Results: 14 patients were enrolled. 2 patients had grade 3 toxicities, which included myelosuppression, nausea/vomiting, elevated BUN, and anorexia. There were no clinical responses, and only 4 patients went on to a second course of treatment. All analyzed patients showed HDJ-2 gel shift in peripheral blood cells, as well as marked inhibition of FT activity (by 85–98%) in tumor tissue. T cell production of IFN-γ was also suppressed. Conclusions: Despite potent target inhibition, the FTI R115777 showed no evidence for clinical activity as a single agent in this cohort of 14 metastatic melanoma patients. Inhibition of T cell function has implications for future combination therapies and suggests the possibility for FTIs as candidate immunosuppressive agents. New therapeutic approaches for melanoma, or logically selected combination therapies, are needed.

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Natural phosphate doped with KI in HMDS: a mild and efficient reagent for alkylation and glycosylation of nucleobases

Several D-ribonucleosides are prepared from 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranoside and trimethylsilylated nucleobases under mild conditions by using natural phosphate doped with KI as catalyst.

Removal of lead from aqueous solutions by activated phosphate

The potential of using activated phosphate as a new adsorbent for the removal of Pb from aqueous solutions was investigated. The kinetic of lead adsorption and the adsorption process were compared for natural phosphate (NP) and activated phosphate (AP). The results indicate that equilibrium was established in about 1h for NP and 3 h for AP. The effect of the pH was examined in the range 2-6. The maximum removal obtained is between two and three for NP and between three and four for AP. The maximum adsorption capacities at 25 degrees C are 155.04 and 115.34 mg/g for AP and NP, respectively. The effect of temperature has been carried out at 25, 35 and 45 degrees C. The data obtained from adsorption isotherms of lead at different temperatures fit to linear form of Langmuir adsorption equation. The thermodynamic parameters such as enthalpy (DeltaH), free energy (DeltaG) and entropy (DeltaS) were calculated. They show that adsorption of lead on NP and AP is an endothermic process more effective at high temperatures. These results show that AP is a good adsorbent for heavy metals from aqueous solutions and could be used as a purifier for water and wastewater.

Removal of heavy metal ions from water by using calcined phosphate as a new adsorbent

Calcined phosphate (CP) has been employed in our laboratories as a heterogeneous catalyst in a variety of reactions. In this study, CP was evaluated as a new product for removal of heavy metals from aqueous solution. Removal of Pb2+, Cu2+, and Zn2+ on the CP was investigated in batch experiments. The kinetic of lead on CP adsorption efficiency and adsorption process were evaluated and analysed using the theories of Langmuir and Freundlich. The influence of pH was studied. The adsorption capacity obtained at pH 5 were 85.6, 29.8, and 20.6 mg g(-1) for Pb2+, Cu2+ and Zn2+, respectively. We hypothesize at pH 2 and 3, the dissolution of CP and precipitation of a fluoropyromorphite for lead and the formation of solid-solution type fluorapatite for copper. The results obtained show that CP is a good adsorbent for these toxic heavy metals. The abundance of natural phosphate, its low price and non-aggressive nature towards the environment are advantage for its utilisation in point of view of wastewater and wastes clean up.

Doped natural phosphate: a new and environmentally friendly catalyst in nucleoside synthesis

Doped natural phosphate is used as acidic or basic catalyst in nucleoside and acyclonucleoside synthesis. Some examples are given.

Building blocks for polyamide nucleic acids: facile synthesis using potassium fluoride doped natural phosphate as basic catalyst

Potassium fluoride doped natural phosphate, inexpensive and environmentally friendly catalyst, is shown to be an efficient basic catalyst for the N1/N9 alkylation of different nucleobases as synthons for PNAs.

QSAR for anti-HIV activity of HEPT derivatives

QSARs were derived for 103 analogues of 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT), a potent inhibitor of the HIV-1 reverse transcriptase (RT). The activity of these compounds was investigated by means of multiple linear regression (MLR) and artificial neural network (ANN) techniques. Considering the relevant descriptors obtained from the MLR, a correlation coefficient of 0.92 (n = 95) was obtained with a 4-5-1 ANN model. The contribution of each descriptor to the structure-activity relationships was evaluated. The results showed that the anti-HIV activity of HEPT derivatives was strongly dependent on hydrophobic character and also steric factors of substituents.

Phosphotyrosyl peptides block Stat3-mediated DNA binding activity, gene regulation, and cell transformation

Signal transducers and activators of transcription (STATs) comprise a family of cytoplasmic signaling proteins that participates in normal cellular responses to cytokines and growth factors. Frequently, however, constitutive activation of certain STAT family members, particularly Stat3, has accompanied a wide variety of human malignancies. To identify small molecule inhibitors of Stat3, we investigated the ability of the Stat3 SH2 domain-binding peptide, PY*LKTK (where Y* represents phosphotyrosine), to disrupt Stat3 activity in vitro. The presence of PY*LKTK, but not PYLKTK or PFLKTK, in nuclear extracts results in significant reduction in the levels of DNA binding activities of Stat3, to a lesser extent of Stat1, and with no effect on that of Stat5. Analyses of alanine scanning mutagenesis and deletion derivatives of PY*LKTK reveal that the Leu residue at the Y+1 position and a substituent at the Y-1 position (but not necessarily Pro) are essential for the disruption of active Stat3, thereby mapping the minimum active sequence to the tripeptide, XY*L. Studies involving bead-coupled PY*LKTK peptide demonstrate that this phosphopeptide directly complexes with Stat3 monomers in vitro, suggesting that PY*LKTK disrupts Stat3:Stat3 dimers. As evidence for the functional importance of peptide-directed inhibition of Stat3, PY*LKTK-mts (mts, membrane translocating sequence) selectively inhibits constitutive and ligand-induced Stat3 activation in vivo. Furthermore, PY*LKTK-mts suppresses transformation by the Src oncoprotein, which has been shown previously to require constitutive Stat3 activation. Altogether, we have identified a minimal peptide that inhibits Stat3 signaling and provides the conceptual basis for use of this peptide as a lead for novel peptidomimetic drug design.

v-Src transformation is mediated through farnesylated proteins

Src is an oncoprotein which has been implicated in a number of human malignancies in which it has been shown to be overexpressed and highly activated. The precise mechanism of Src transformation, however, is still poorly understood. We hypothesized that Ras and other farnesylated proteins may mediate Src transformation. To test this hypothesis, v-Src-transfected rat fibroblasts (3Y1) were treated every 72 h with a 15 microM concentration of a farnesyl-transferase inhibitor (FTI). At 2 weeks, a focus formation assay was performed to assess transformation potential. Untreated and FTI-treated v-Src-transfected 3Y1 cells formed a mean of 39 (+/-2.6) and 29.8 (+/-2.9) foci per well, respectively. This 24% decrease was judged to be statistically significant (P = 0.02). Moreover, foci (>90%) in the FTI-treated wells were also consistently smaller than foci in the untreated wells. Western blots with antibody directed toward H-Ras confirmed complete inhibition of Ras farnesylation in the treated cell lines. The specificity of this inhibition was verified by Western blot using antibody specific for Rap1A. The transforming potential of v-Src is inhibited, but not eliminated by FTI treatment. This suggests that v-Src transformation is mediated in part by farnesylated proteins, one of which may be Ras.

Retinoblastoma protein activation of interleukin 8 expression inhibits tumor cell survival in nude mice

Loss of retinoblastoma protein (Rb) has been implicated in the formation of a variety of human malignancies. Restoration of Rb expression in the cell lines representing these tumors eliminates or significantly reduces tumorigenicity in nude mice, but the mechanism for this Rb effect is unknown. Results from this study indicated that Rb expression reduced tumor cell survival in nude mice by dramatically enhancing interleukin 8 (IL-8) secretion. IL-8 secreted by the Rb-transformed cells attracted neutrophils in vitro and tumor-infiltrating neutrophils in vivo, which is consistent with the Rb-mediated tumor regression being dependent on IL-8. The apparent, contradictory roles of IL-8 as a protumorigenic and antitumorigenic cytokine are discussed.

Direct tumor lysis by NK cells uses a Ras-independent mitogen-activated protein kinase signal pathway

Destruction of tumor cells is a key function of lymphocytes, but the molecular processes driving it are unclear. Analysis of signal molecules indicated that mitogen-activated protein kinase (MAPK)/extracellular regulated kinase 2 critically controlled lytic function in human NK cells. We now have evidence to indicate that target ligation triggers a Ras-independent MAPK pathway that is required for lysis of the ligated tumor cell. Target engagement caused NK cells to rapidly activate MAPK within 5 min, and PD098059 effectively blocked both MAPK activation and tumoricidal function in NK cells. Target engagement also rapidly activated Ras, detected as active Ras-GTP bound to GST-Raf-RBD, a GST fusion protein linked to the Raf protein fragment containing the Ras-GTP binding domain. However, Ras inactivation by pharmacological disruption with the farnesyl transferase inhibitor, FTI-277, had no adverse effect on the ability of NK cells to lyse tumor cells or to express MAPK activation upon target conjugation. Notably, MAPK inactivation with PD098059, but not Ras inactivation with FTI-277, could interfere with perforin and granzyme B polarization within NK cells toward the contacted target cell. Using vaccinia delivery of N17 Ras into NK cells, we demonstrated that IL-2 activated a Ras-dependent MAPK pathway, while target ligation used a Ras-independent MAPK pathway to trigger lysis in NK cells.

Protein geranylgeranylation is required for osteoclast formation, function, and survival: inhibition by bisphosphonates and GGTI-298

Bisphosphonates are the important class of antiresorptive drugs used in the treatment of metabolic bone diseases. Although their molecular mechanism of action has not been fully elucidated, recent studies have shown that the nitrogen-containing bisphosphonates can inhibit protein prenylation in macrophages in vitro. In this study, we show that the nitrogen-containing bisphosphonates risedronate, zoledronate, ibandronate, alendronate, and pamidronate (but not the non nitrogen-containing bisphosphonates clodronate, etidronate, and tiludronate) prevent the incorporation of [14C]mevalonate into prenylated (farnesylated and geranylgeranylated) proteins in purified rabbit osteoclasts. The inhibitory effect of nitrogen-containing bisphosphonates on bone resorption is likely to result largely from the loss of geranylgeranylated proteins rather than loss of farnesylated proteins in osteoclasts, because concentrations of GGTI-298 (a specific inhibitor of geranylgeranyl transferase I) that inhibited protein geranylgeranylation in purified rabbit osteoclasts prevented osteoclast formation in murine bone marrow cultures, disrupted the osteoclast cytoskeleton, inhibited bone resorption, and induced apoptosis in isolated chick and rabbit osteoclasts in vitro. By contrast, concentrations of FTI-277 (a specific inhibitor of farnesyl transferase) that prevented protein farnesylation in purified rabbit osteoclasts had little effect on osteoclast morphology or apoptosis and did not inhibit bone resorption. These results therefore show the molecular mechanism of action of nitrogen-containing bisphosphonate drugs in osteoclasts and highlight the fundamental importance of geranylgeranylated proteins in osteoclast formation and function.

Requirement for Ras/Rac1-mediated p38 and c-Jun N-terminal kinase signaling in Stat3 transcriptional activity induced by the Src oncoprotein

Signal transducers and activators of transcription (STATs) are transcription factors that mediate normal biologic responses to cytokines and growth factors. However, abnormal activation of certain STAT family members, including Stat3, is increasingly associated with oncogenesis. In fibroblasts expressing the Src oncoprotein, activation of Stat3 induces specific gene expression and is required for cell transformation. Although the Src tyrosine kinase induces constitutive Stat3 phosphorylation on tyrosine, activation of Stat3-mediated gene regulation requires both tyrosine and serine phosphorylation of Stat3. We investigated the signaling pathways underlying the constitutive Stat3 activation in Src oncogenesis. Expression of Ras or Rac1 dominant negative protein blocks Stat3-mediated gene regulation induced by Src in a manner consistent with dependence on p38 and c-Jun N-terminal kinase (JNK). Both of these serine/threonine kinases and Stat3 serine phosphorylation are constitutively induced in Src-transformed fibroblasts. Furthermore, inhibition of p38 and JNK activities suppresses constitutive Stat3 serine phosphorylation and Stat3-mediated gene regulation. In vitro kinase assays with purified full-length Stat3 as the substrate show that both JNK and p38 can phosphorylate Stat3 on serine. Moreover, inhibition of p38 activity and thus of Stat3 serine phosphorylation results in suppression of transformation by v-Src but not v-Ras, consistent with a requirement for Stat3 serine phosphorylation in Src transformation. Our results demonstrate that Ras- and Rac1-mediated p38 and JNK signals are required for Stat3 transcriptional activity induced by the Src oncoprotein. These findings delineate a network of tyrosine and serine/threonine kinase signaling pathways that converge on Stat3 in the context of oncogenesis.

Inhibitors of prenyl transferases

Because farnesylation of Ras is required for its cancer-causing activity, several classes of farnesyl transferase inhibitors have recently been developed as potential anticancer drugs. During the last 12 months, important advances have been made in this field. In this review, we focus on three topics: targets of farnesyl transferase inhibitors other than Ras, alternative prenylation of K-Ras by the closely related prenyl transferase, geranyl geranyl transferase I, and the effects of geranyl geranyl transferase I inhibitors on cell cycle, apoptosis, and human tumor growth.