Joshua S. Boger

Cellular and biochemical characterization of VX-710 as a chemosensitizer ; reversal of P-glycoprotein-mediated multidrug resistance in vitro

VX-710 or (S)-N[2-Oxo-2-(3,4,5-trimethoxyphenyl)acetyl]-piperidine-2-carboxylic acid 1,7-bis(3-pyridyl)-4-heptyl ester, a novel non-macrocyclic ligand of the FK506-binding protein FKBP12, was evaluated for its ability to reverse P-glycoprotein-mediated multidrug resistance in vitro. VX-710 at 0.5-5 microM restored sensitivity of a variety of multidrug resistant cells to the cytotoxic action of doxorubicin, vincristine, etoposide or paclitaxel, including drug-selected human myeloma and epithelial carcinoma cells, and human MDR1 cDNA-transfected mouse leukemia and fibroblast cells. Uptake experiments showed that VX-710 at 0.5-2.5 microM fully restored intracellular accumulation of [14C]doxorubicin in multidrug resistant cells, suggesting that VX-710 inhibits the drug efflux activity of P-glycoprotein. VX-710 effectively inhibited photoaffinity labeling of P-glycoprotein by [3H]azidopine or [125I]iodoaryl azidoprazosin with EC50 values of 0.75 and 0.55 microM. Moreover, P-glycoprotein was specifically labeled by a tritiated photoaffinity analog of VX-710 and unlabeled VX-710 inhibited analog binding with an EC50 of 0.75 microM. VX-710 also stimulated the vanadate-inhibitable P-glycoprotein ATPase activity 2- to 3-fold in a concentration-dependent manner with an apparent k(a) of 0.1 microM. These data indicate that a direct, high-affinity interaction of VX-710 with P-glycoprotein prevents efflux of cytotoxic drugs by the MDR1 gene product in multidrug resistant tumor cells.

Total synthesis of 1-156,602, a novel cyclic hexadepsipeptide antibiotic

Abstract The total synthesis of the naturally occurring cyclic hexadepsipeptide antibiotic L-156,602 ( 1 ) is described.

Degradative studies on the tricarbonyl containing macrolide rapamycin

Abstract The degradation of rapamycin, a tricarbonyl containing macrolide similar in structure to the potent immunosuppressant FK-506, is described. Three principal fragments are obtained in this process that should have utility in the semi-synthesis of FK-506 and rapamycin congeners.

Chapter 26. Renin Inhibition

Publisher Summary This chapter discusses the recent progress in the design of renin inhibitors, focusing on in vivo evaluation of these compounds. Renin of the plasma renin-angiotensin system (RAS) is synthesized in the juxtaglomerular cells of the kidney and released from storage granules into the bloodstream. Renin release is regulated by a variety of factors, including renal perfusion pressure, a β-adrenergic receptor mechanism, sodium balance etc. Human renin is a less specific enzyme than the other mammalian renins studied. Renin is inhibited weakly by many hydrophobic compounds. Several synthetic phospholipids have been prepared as renin inhibitors, but these have all been of only mM potency in vitro . Recently, peptides related to the prosegment of pro-renin have been synthesized as competitive renin inhibitors. The mechanisms responsible for the anti-hypertensive and other cardiovascular actions of angiotensin converting enzyme inhibitors (CEIs) are still controversial. However, if mechanisms unrelated to the inhibition of the RAS are involved in the anti-hypertensive effects of CEIs, then specific inhibitors of renin may not be medicinally useful. The RAS in the brain and its possible role in the control of blood pressure has been the subject of recent comprehensive reviews. In addition to the modulation of blood pressure, the brain RAS may be involved in control of sodium appetite and thirst. Despite the potential for greater specificity for renin inhibitors, no advantages of renin inhibition over angiotensin converting enzyme inhibition have been discussed in the chapter.

Chapter 18. Immunomodulatory Approaches to the Treatment of Inflammation

Publisher Summary The propensity of the inflammatory process to cross over from protection to pathology, as exhibited in autoimmune diseases, such as rheumatoid arthritis, glomerulonephritis, systemic lupus erythematosus, insulin-dependent diabetes, thyroiditis, and multiple sclerosis, makes inflammation a focus of medicinal research. Control of these immunopathological diseases might be achieved by modulation of the signals controlling the activation and proliferation of the cells of chronic inflammation. This chapter discusses the possible roles of interleukins 1-6, tissue necrosis factor (TNF), and the interferons (particularly gamma-interferon) in inflammation and to the possible rational strategies available for modulation of their actions. Recent advances toward definition of these factors at the molecular level have allowed recognition that many reported disparate activities reside in a relatively few molecules. A strong link has been proposed between interleukin-1 (IL-1) and rheumatoid arthritis (RA), with high level of IL-1 found in synovial joint fluid. Monocytes from RA patients with recent onset or exacerbation of disease had enhanced spontaneous IL-1 secretion, whereas patients with stable disease had normal levels, suggesting that enhanced IL-1 activity might be a primary factor in the early stages of the disease. Recombinant TNFα stimulates resorption and inhibits synthesis of proteoglycan in explants of cartilage and stimulates the metogenesis of fibroblasts, minimizing the action of IL-1. There is abundant evidence suggesting that inappropriate production of lymphokines and monokines plays a significant role in different inflammatory diseases, but definitive proof awaits the development of potent and specific medicinal agents applicable to clinical situations.

Synthetic studies on the immunosuppressive agent FK-506: Enantioselective synthesis of a C22C34 fragment

Abstract The C28C32 cyclohexyl group of the natural product, FK-506, was prepared enantioselectively from the iodolactone by replacement of iodide with retention of configuration . The C27C28 trisubstituted olefin was introduced stereoselectively via a classical aldol/elimination sequence employing titanium enolate methodology. Elaboration of this chemistry has led to a synthesis of a C22C34 fragment of the natural product.

Synthetic studies on the immunosuppressive agent FK-506: Construction of the polycarbonyl region

Abstract The C10C17 fragment of the natural product, FK-506, has been stereoselectively synthesized from L-gulose. Methods for elaboration to the C1C17 fragment and installation of the C9 carbonyl group are described.

The inhibition of C5a receptor binding by analogs of L-156,602, a cyclic hexadepsipeptide antibiotic

Abstract The cyclic hexadepsipeptide antibiotic L-156,602 ( 1 ) was found to be an inhibitor of anaphylatoxin C5a binding to its receptor (IC 50 =1.7 μg/mL). This compound also caused nonspecific degranulation of neutrophils, but not through interactions with the C5a or other receptors. The effects of chemical modification of the structure of 1 on C5a receptor inhibition and nonspecific actions are reported.

Dipeptide analogues. Synthesis of a potent renin inhibitor

The synthesis of a potent renin inhibitor containing a dipeptide analogue and the amino acid statine is described.

Interaction of Mouse Submaxillary Gland Renin with a Statine-Containing Subnanomolar, Competitive Inhibitor

The interaction between mouse submaxillary gland renin and a statine-containing, iodinated substrate analog inhibitor was studied. The compound, 1 (Boc-His-Pro-Phe-(4-iodo)-Phe-Sta-Leu-Phe-NH2, Sta = (3S,4S)-4-amino-3-hydroxy-6-methyl-heptanoic acid), a statine-containing analog of the renin substrate octapeptide, was a competitive inhibitor of cleavage of synthetic tetradecapeptide renin substrate by mouse submaxillary gland renin, with a Ki of 6.2 x 10(-10) M (pH 7.2, 37 degrees C). Titration of the partial quenching of the tryptophan fluorescence of the enzyme by 1 revealed tight binding with a dissociation constant less than 3 nM and a binding stoichiometry of one mole 1 per mole enzyme. The time course of tight binding of 1 to mouse renin appeared to be fast, with kON greater than or equal to 1.3 x 10(6) s-1 M-1. The UV difference spectrum generated upon binding of 1 to mouse renin had two prominent features: a strong, broad band that had a minimum at 242 nm with delta epsilon (242) = -19,500 cm-1 M-1, and a triplet of enhanced bands centered at 286 nm with delta epsilon (286) about +1100 cm-1 M-1. The strong, broad, negative band was similar to the difference between the UV absorbance of 1 in methanol and in 0.1 M citrate phosphate pH 7.2. A structure-activity correlation for analogs of 1 showed some moieties of 1 that are important for potent inhibition of mouse renin. The inhibition data for these compounds versus human kidney renin suggested that the solution of the crystal structure of 1 bound to mouse renin will provide useful information for the design of inhibitors of human kidney renin.