Geldanamycin-induced PCNA degradation in isolated Hsp90 complex from cancer cells

Hsp90 is a molecular chaperone involved in the folding and proteolytic turnover of many regulatory proteins associated with it. Some of the Hsp90 client proteins are known to be involved in tumorigenesis. An Hsp90-specific inhibitor, geldanamycin, is shown to bind to the ATP binding site of the chaperone to induce degradation of many client proteins, and results in antitumor activities. However, the mechanism of geldanamycin-induced client protein degradation is not fully understood. A large-scale immunoaffinity purification with anti-Hsp90 antibodies identified many Hsp90 client proteins from colon cancer cell line, HCT-116. One of the identified proteins, PCNA, was confirmed to be associated with Hsp90 in two additional cancer cell lines. After geldanamycin treatment, both PCNA and Hsp90 were shown to be degraded. More interestingly, this study demonstrated that in two different cancer cell lines, the degradation occurred in the isolated Hsp90 complex in vitro. This result indicated that the components responsible for the PCNA degradation are also associated with Hsp90. This finding provided a new mechanism for the Hsp90-mediated protein degradation induced by Hsp90-specific inhibitors.

Synergy between celecoxib and radiotherapy results from inhibition of cyclooxygenase-2-derived prostaglandin E2, a survival factor for tumor and associated vasculature

Previous work has demonstrated that selective cyclooxygenase-2 (COX-2) inhibitors can act synergistically with radiotherapy to improve tumor debulking and control in preclinical models. The underlying mechanism of this remarkable activity has not yet been determined. Here, we report that radiation can elevate intratumoral levels of COX-2 protein and its products, particularly prostaglandin E(2) (PGE(2)). Furthermore, inhibition of COX-2 activity or neutralization of PGE(2) activity enhances radiotherapy even in tumors where COX-2 expression is restricted to the tumor neovasculature. Direct assessment of vascular function by direct contrast enhancement-magnetic resonance imaging showed that the combination of radiation and celecoxib lead to enhanced vascular permeability. These observations suggest that an important mechanism of celecoxib-induced radiosensitization involves inhibition of COX-2-derived PGE(2), thus removing a survival factor for the tumor and its vasculature.

Inhibition of cyclooxygenase-2 by celecoxib reverses tumor-induced wasting

There have been a number of reports suggesting inhibition of prostaglandin production may impact tumor-mediated wasting and levels of associated humoral factors such as hypercalcemia. These reductions were achieved using traditional nonsteroidal anti-inflammatory drugs (NSAIDs), which are often contraindicated in cancer patients. This is especially true during chemotherapeutic regimens due to concerns of bleeding from gastrointestinal and hematopoietic toxicities associated with inhibition of the housekeeping cyclooxygenase enzyme COX-1. Here, we report that celecoxib, one of the new class of selective COX-2 inhibitors, has the potential to reverse tumor-mediated wasting and associated humoral factors such as interleukin (IL)-6 and hypercalcemia in preclinical models of cachexia. Tumor bearing mice in late stage cachexia regained weight within days of the start of celecoxib treatment. Two models were tested. The first was the Colon 26 (Col26) syngeneic murine model that induces high levels of circulating IL-6 and hypercalcemia. The second was the human head and neck 1483 HNSCC xenograft model, which is less inflammatory and produces less prostaglandin than Col26. Despite the observation that no significant impact on tumor growth was observed between vehicle and celecoxib-treated animals over the course of the studies, celecoxib rapidly reversed weight loss in both cachectic models. With the added safety of celecoxib over traditional NSAIDs, these results suggest a possible therapeutic use for celecoxib for treating tumor-mediated wasting.

Chiral N,N-disubstituted trifluoro-3-amino-2-propanols are potent inhibitors of cholesteryl ester transfer protein

A novel series of substituted N-benzyl-N-phenyl-trifluoro-3-amino-2-propanols are described that reversibly inhibit cholesteryl ester transfer protein (CETP). Starting with screening lead 22, various structural features were explored with respect to inhibition of the CETP-mediated transfer of [(3)H]cholesterol from high-density cholesterol donor particles to low-density cholesterol acceptor particles. The free hydroxyl group of the propanol was required for high potency, since acylation or alkylation reduced activity. High inhibitory potency was also associated with 3-ether moieties in the aniline ring, and the highest potencies were exhibited by 3-phenoxyaniline analogues. Activity was substantially reduced by oxidation or substitution in the methylene of the benzylic group, implying that the benzyl ring orientation was important for activity. In the benzylic group, substitution at the 3-position was preferred over either the 2- or the 4-positions. Highest potencies were observed with inhibitors in which the 3-benzylic substituent had the potential to adopt an out of plane orientation with respect to the phenyl ring. The best 3-benzylic substituents were OCF(2)CF(2)H (42, IC(50) 0.14 microM in buffer, 5.6 microM in human serum), cyclopentyl (39), 3-iso-propoxy (27), SCF(3) (67), and C(CF(3))(2)OH (36). Separation of 42 into its enantiomers unexpectedly showed that the minor R(+) enantiomer 1a was 40-fold more potent (IC(50) 0.02 microM in buffer, 0.6 microM in human serum) than the major S(-) enantiomer 1b, demonstrating that the R-chirality at the propanol 2-position is key to high potency in this series. The R(+) enantiomer 1a represents the first reported acyclic CETP inhibitor with submicromolar potency in plasma. A chiral synthesis of 1a is reported.

Large-scale purification of myeloperoxidase from HL60 promyelocytic cells: characterization and comparison to human neutrophil myeloperoxidase

A large-scale purification procedure was developed for the isolation of myeloperoxidase from HL60 promyelocytic cells in culture. Initial studies showed the bulk of peroxidase-positive myeloperoxidase activity to be located in the cetyltrimethylammonium bromide solubilized particulate fraction of cell homogenates. The myeloperoxidase was then chromatographically purified using concanavalin A followed by gel filtration. SDS-PAGE analysis of the final preparation showed the presence of only two proteins with molecular masses of approximately 55 and 15 kDa, corresponding to the large and small subunits of myeloperoxidase. These data, along with Reinheit Zahl (RZ) values (A(430)/A(280)) of greater than or equal to 0.72, indicate that the myeloperoxidase prepared by this method is apparently homogeneous. Preparations routinely yielded 12-20 mg of pure myeloperoxidase per 10 ml of cell pellet. The HL60 myeloperoxidase was shown to be indistinguishable from purified human neutrophil myeloperoxidase by size exclusion chromatography, analytical ultracentrifugation, SDS-PAGE, Western blot, and NH(2)-terminal sequence analysis. The activities of the two myeloperoxidase samples, as measured using either the tetramethylbenzidine or the taurine chloramine assay, were indistinguishable. Finally, both enzymes responded identically to dapsone and aminobenzoic acid hydrazide, known inhibitors of myeloperoxidase. A protocol is presented here for the rapid, large-scale purification of myeloperoxidase from cultured HL60 cells, as well as evidence for the interchangeability of this myeloperoxidase and that purified from human neutrophils.

Tumor vascular permeability factor stimulates endothelial cell growth and angiogenesis

Vascular permeability factor (VPF) is an Mr 40-kD protein that has been purified from the conditioned medium of guinea pig line 10 tumor cells grown in vitro, and increases fluid permeability from blood vessels when injected intradermally. Addition of VPF to cultures of vascular endothelial cells in vitro unexpectedly stimulated cellular proliferation. VPF promoted the growth of new blood vessels when administered into healing rabbit bone grafts or rat corneas. The identity of the growth factor activity with VPF was established in four ways: (a) the molecular weight of the activity in preparative SDS-PAGE was the same as VPF (Mr approximately 40 kD); (b) multiple isoforms (pI greater than or equal to 8) for both VPF and the growth-promoting activity were observed; (c) a single, unique NH2-terminal amino acid sequence was obtained; (d) both growth factor and permeability-enhancing activities were immunoadsorbed using antipeptide IgG that recognized the amino terminus of VPF. Furthermore, 125I-VPF was shown to bind specifically and with high affinity to endothelial cells in vitro and could be chemically cross-linked to a high-molecular weight cell surface receptor, thus demonstrating a mechanism whereby VPF can interact directly with endothelial cells. Unlike other endothelial cell growth factors, VPF did not stimulate [3H]thymidine incorporation or promote growth of other cell types including mouse 3T3 fibroblasts or bovine smooth muscle cells. VPF, therefore, appears to be unique in its ability to specifically promote increased vascular permeability, endothelial cell growth, and angio-genesis.