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Paul Workman

Publications and source records attributed to Paul Workman.

80 records · Page 5Linked to original sources
PubMed2002

Assays for the identification and evaluation of histone acetyltransferase inhibitors.

There is presently enormous interest in the function and regulatory roles of histone acetyltransferase enzymes. Along with deacetylases it is now evident that these enzymes play a key role in many cellular processes including chromatin remodeling and gene transcription. As such, effective small molecule enzyme inhibitors would be useful tools for molecular pharmacology and may also be suitable for further development into agents for the treatment of diseases such as cancer. A high-throughput assay based on the use of scintillating microplates (FlashPlates) suitable for screening libraries of compounds for inhibitors of acetylase activity is described here. Confirmation of activity of selected compounds is achieved with a conventional filter assay, the details of which are also described. In addition, an assay suitable for confirming that cellular protein acetylation has been altered by inhibition of acetylases or deacetylases is also presented. On the same plate, cells are grown, exposed to compound, fixed, and permeabilized, and protein acetylation is determined using standard ELISA methodology and a europium-labeled second antibody. This latter method provides a medium-throughput alternative to the use of immunoblotting for mechanistic studies.

Acetyltransferases↗
PubMed2002

Activation of the ATPase activity of hsp90 by the stress-regulated cochaperone aha1.

Client protein activation by Hsp90 involves a plethora of cochaperones whose roles are poorly defined. A ubiquitous family of stress-regulated proteins have been identified (Aha1, activator of Hsp90 ATPase) that bind directly to Hsp90 and are required for the in vivo Hsp90-dependent activation of clients such as v-Src, implicating them as cochaperones of the Hsp90 system. In vitro, Aha1 and its shorter homolog, Hch1, stimulate the inherent ATPase activity of yeast and human Hsp90. The identification of these Hsp90 cochaperone activators adds to the complex roles of cochaperones in regulating the ATPase-coupled conformational changes of the Hsp90 chaperone cycle.

Adenosine Triphosphatases↗
PubMed2002

HSP90 as a new therapeutic target for cancer therapy: the story unfolds.

Current anticancer drug development strategies involve identifying novel molecular targets which are crucial for tumourigenesis. The molecular chaperone heat shock protein (HSP) 90 is of interest as an anticancer drug target because of its importance in maintaining the conformation, stability and function of key oncogenic client proteins involved in signal transduction pathways leading to proliferation, cell cycle progression and apoptosis, as well as other features of the malignant phenotype such as invasion, angiogenesis and metastasis. The natural product HSP90 inhibitors geldanamycin and radicicol exert their antitumour effect by inhibiting the intrinsic ATPase activity of HSP90, resulting in degradation of HSP90 client proteins via the ubiquitin proteosome pathway. Anticancer selectivity may derive from the simultaneous combinatorial effects of HSP90 inhibitors on multiple cancer targets and pathways. 17-allylamino, 17-demethoxygeldanamycin (17AAG), a geldanamycin derivative, showed good activity and cancer selectivity in preclinical models and has now progressed to Phase I clinical trial in cancer patients with encouraging initial results. Phase II trials including combination studies with cytotoxic agents are now being planned and these should allow the therapeutic activity of 17AAG to be determined. Second generation HSP90 inhibitors may be designed to overcome some of the drawbacks of 17AAG, including limited oral bioavailability and solubility. They could also be engineered to target specific functions of HSP90, which may not only provide greater molecular selectivity and clinical benefit but may also increase understanding of the complex functions of this molecular chaperone. HSP90 inhibitors provide proof of concept for drugs directed at HSP90 and protein folding and this principle may be applicable to other medical conditions involving protein aggregation and stability.

Animals↗
PubMed2002

Establishment and characterization of acquired resistance to the farnesyl protein transferase inhibitor R115777 in a human colon cancer cell line.

R115777 (Zarnestra) is a farnesyl protein transferase inhibitor currently undergoing worldwide clinical trials. As acquired drug resistance may limit the efficacy of the drug, a model of acquired resistance has been established in vitro by continuous drug exposure of the human colon cancer cell line KM12. A stably resistant cell line possessing 13-fold resistance to R115777 was generated. The resistant cells showed cross-resistance to another, structurally different farnesyl transferase inhibitor-277, but not to GGTI-298. A lack of cross-resistance was observed to a variety of other agents, which included clinically used drugs, such as doxorubicin, etoposide, cisplatin, and paclitaxel, as well as signal transduction blockers, such as the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor UO126, the phosphatidylinositol 3'-kinase inhibitor LY294002, and the epidermal growth factor receptor tyrosine kinase inhibitor PD153035. Resistance did not appear to be related to differences in drug efflux pumps, such as P-glycoprotein or in drug accumulation. Total levels of farnesyl transferase protein subunits were similar in the parent and resistant cells, but, notably, the enzyme activity was markedly reduced in the resistant cell line compared with the parent cells. This was not because of a mutation in the enzyme or a difference in activation of the alpha-subunit of farnesyl transferase by phosphorylation. Hence, resistance to R115777 was generated; the mechanism of resistance in this model may be associated with the enzyme target of the inhibitor. The results suggest that the development of clinical resistance may occur with farnesyl protein transferase inhibitors.

Alkyl and Aryl Transferases↗
PubMed2002

Validation of the fluorinated 2-nitroimidazole SR-4554 as a noninvasive hypoxia marker detected by magnetic resonance spectroscopy.

PURPOSE: Tumor hypoxia is associated with poor prognosis and a more malignant tumor phenotype. SR-4554, a fluorinated 2-nitroimidazole, is selectively bioreduced and bound in hypoxic cells. We present validation studies of SR-4554 as a noninvasive hypoxia marker detected by fluorine-19 magnetic resonance spectroscopy ((19)F MRS) in the P22 carcinosarcoma, a tumor with clinically relevant hypoxia levels. EXPERIMENTAL DESIGN: Tumor-bearing female severe combined immunodeficient mice received SR-4554 at 180 mg/kg. Pharmacokinetic studies of parent SR-4554 in plasma and tumors were performed using high-performance liquid chromatography-UV. Total SR-4554 (parent SR-4554 and bioreduction products) was monitored in tumor by (19)F MRS using a 4.7 T spectrometer, with continuous acquisition for up to 5 h. A parameter of total SR-4554 retention, the 3-h (19)F retention index ((19)FRI) was determined. Tumor pO(2), assessed polarographically, was decreased (5 mg/kg hydralazine or 100 mg/kg combretastatin A-4 phosphate) or increased [1 l/min carbogen (5% CO(2), 95% O(2)) plus 500 mg/kg nicotinamide], and the corresponding (19)FRI was measured. RESULTS: Comparative HPLC-UV- and MRS-derived assessments of parent and total SR-4554, respectively, indicated that concentrations of total SR-4554 consistently exceeded parent SR-4554, the differential increasing with time. This indicates formation and retention of SR-4554 bioreduction products in tumor, confirming the presence of hypoxia. The (19)FRI was higher in hydralazine- and combretastatin-treated animals compared with unmodulated animals (P = 0.004 and 0.15, respectively) and animals receiving carbogen and nicotinamide (P = 0.0001 and 0.005, respectively). Significant correlations were demonstrated between mean (19)FRI and polarographic pO(2) parameters (P < 0.002). CONCLUSIONS: Retention of hypoxia-related SR-4554 bioreduction products can be detected in the clinically relevant P22 tumor by (19)F MRS, and the (19)FRI correlates with polarographically measured pO(2). These findings support the use of SR 4554 as a noninvasive hypoxia marker.

Animals↗
PubMedDate not supplied

ErbB2 overexpression in an ovarian cancer cell line confers sensitivity to the HSP90 inhibitor geldanamycin.

ErbB2 is overexpressed in 25-30% of breast and ovarian cancers, correlates with poor prognosis and lower survival and has also been associated with chemoresistance. We have established an isogenic pair of human ovarian cells that differ only in the expression of erbB2 protein in order to elucidate the role of the protein in determining cellular sensitivity to various drugs and agents. These included cisplatin and paclitaxel, the main drugs used in the treatment of ovarian cancer, and also various signal transduction inhibitors affecting the ras and P13K pathways. Transfection of erbB2 resulted in cells stably overexpressing the protein and showing increased motility compared to the empty vector control cells. In cells overexpressing erbB2, the most notable effect on chemosensitivity was that of significantly increased (5-fold) sensitivity to the heat shock protein 90 (HSP90) molecular chaperone inhibitor geldanamycin. In contrast, erbB2-overexpressing cells showed statistically significant resistance to cisplatin, the P13K inhibitor LY294002 and the tyrosine kinase inhibitor emodin. No significant difference in growth inhibition was observed after exposure to paclitaxel, two additional HSP90 inhibitors radicicol and 17AAG, the cyclin-dependent kinase inhibitor flavopiridol, the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor PD153035, the mek inhibitor U0126 or the famesyl transferase inhibitor R115777. Exposure of cells to geldanamycin, 17AAG, emodin, LY294002 and cisplatin led to depletion of erbB2 in the transfected cells. These data suggest that erbB2 status in ovarian cancr may contribute to chemosensitivity, in some cases leading to increased sensitivity (as with geldanamycin) but in other cases leading to resistance (as with cisplatin).

Antibiotics, Antineoplastic↗