A series of new 3'-(2-methyl-1-propenyl) and 3'-(2-methylpropyl) taxoids with modifications at C-10 was synthesized by means of the beta-lactam synthon method using 10-modified 7-(triethylsilyl)-10-deacetylbaccatin III derivatives. The new taxoids thus synthesized show excellent cytotoxicity against human ovarian (A121), non-small-cell lung (A549), colon (HT-29), and breast (MCF-7) cancer cell lines. All but one of these new taxoids possess better activity than paclitaxel and docetaxel in the same assay, i.e., the IC50 values of almost all the taxoids are in the subnanomolar level. It is found that a variety of modifications at C-10 is tolerated for the activity against normal cancer cell lines, but the activity against a drug-resistant human breast cancer cell line expressing MDR phenotype (MCF7-R) is highly dependent on the structure of the C-10 modifier. A number of the new taxoids exhibit remarkable activity (IC50 = 2.1-9.1 nM) against MCF7-R. Among these, three new taxoids, SB-T-1213 (4a), SB-T-1214 (4b), and SB-T-1102 (5a), are found to be exceptionally potent, possessing 2 orders of magnitude better activity than paclitaxel and docetaxel. The observed exceptional activity of these taxoids may well be ascribed to an effective inhibition of P-glycoprotein binding by the modified C-10 moieties. The new taxoid SB-T-1213 (4a) shows an excellent activity (T/C = 0% at 12.4 and 7.7 mg/kg/dose, log10 cell kill = 2.3 and 2.0, respectively) against B16 melanoma in B6D2F1 mice via intravenous administration.

Novel second-generation taxoids with systematic modifications at the C2, C10, and C3'N positions were synthesized and their structure-activity relationships studied. A number of these taxoids exhibited exceptionally high potentency against multidrug drug-resistant cell lines, and several taxoids exhibited virtually no difference in potency against the drug-sensitive and drug-resistant cell lines. These exceptionally potent taxoids were termed "third-generation taxoids". 19 (SB-T-1214), 14g (SB-T-121303), and 14i (SB-T-1213031), exhibited excellent activity against paclitaxelresistant ovarian cancer cell lines as well, wherein the drug-resistance is mediated by β-tubulin mutation. These taxoids were found to possess exceptional activity in promoting tubulin assembly, forming numerous very short microtubules similar to those formed by discodermolide. Taxoids 19 and 14g also showed excellent cytotoxicity against 4 pancreatic cancer cell lines, expressing 3-4 multidrug resistant genes. Moreover, taxoid 19 exhibited excellent in vivo efficacy against highly drug-resistant CFPAC-1 pancreatic as well as DLD-1 human colon tumor xenografts in mice.

Survivin is a novel anti-apoptotic protein that is highly expressed in cancer but is undetectable in most normal adult tissues. It was reported that taxol-mediated mitotic arrest of cancer cells is associated with survivin induction, which preserves a survival pathway and results in resistance to taxol. In this study, we provide new evidence that induction of survivin by taxol is an early event and is independent of taxol-mediated G 2 /M arrest. Taxol

A new computational docking protocol has been developed and used in combination with conformational information inferred from REDOR-NMR experiments on microtubule bound 2-(p-fluorobenzoyl)paclitaxel to delineate a unique tubulin binding structure of paclitaxel. A conformationally constrained macrocyclic taxoid bearing a linker between the C-14 and C-3'N positions has been designed and synthesized to enforce this "REDOR-taxol" conformation. The novel taxoid SB-T-2053 inhibits the growth of MCF-7 and LCC-6 human breast cancer cells (wild-type and drug resistant) on the same order of magnitude as paclitaxel. Moreover, SB-T-2053 induces in vitro tubulin polymerization at least as well as paclitaxel, which directly validates our drug design process. These results open a new avenue for drug design of next generation taxoids and other microtubule-stabilizing agents based on the refined structural information of drug-tubulin complexes, in accordance with typical enzyme-inhibitor medicinal chemistry precepts.

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Constitutive E-selectin expression on dermal microvascular endothelial cells plays a critical role in mediating rolling adhesive interactions of human skin-homing T cells and in pathologic accumulation of lymphocytes in skin. The major E-selectin ligand on human skin-homing T cells is cutaneous lymphocyte-associated antigen (CLA), a specialized glycoform of P-selectin glycoprotein ligand-1 (PSGL-1) defined by monoclonal antibody HECA-452. Since HECA-452 reactivity, and not PSGL-1 polypeptide itself, confers the specificity of human T cells to enter dermal tissue, inhibition of HECA-452 expression is a potential strategy for modulating lymphocyte migration to skin. In this study, we examined the efficacy of several well-characterized metabolic inhibi- IntroductionTissue-specific migration of lymphocytes in neoplastic and inflammatory processes is critically dependent on the expression of cell membrane adhesion molecules that regulate adhesive interactions with target tissue endothelium. Skin disorders, including cutaneous T-cell lymphomas, cutaneous graft-versus-host disease (GVHD), and other inflammatory diseases (eg, psoriasis), are mediated by infiltrations of skin-homing T cells that express cutaneous lymphocyte-associated antigen (CLA). [1][2][3][4][5][6][7][8][9][10] CLA is a sialyl Lewis X-like carbohydrate epitope displayed on the mucinlike molecule Pselectin glycoprotein ligand-1 (PSGL-1) recognized by the rat monoclonal antibody HECA-452. 2,11,12 CLA functions as the P-selectin ligand and the principal E-and L-selectin ligand on human skin-homing T cells; specifically, the presence of HECA-452 epitopes on PSGL-1 directly correlates with the capacity of skin-homing memory T cells (including skin-disease-related lymphocytes) to bind E-selectin, which is constitutively expressed on dermal microvasculature. 2,11,13 CLA-E-selectin binding interactions mediate lymphocyte trafficking to skin, and therefore, posttranslational glycosylations on skin-homing leukocytes represent a potential therapeutic target for controlling cutaneous tropism.The ␣2,3 sialyltransferase, ST3Gal IV, and ␣1,3 fucosyltransferases, FucTIV and FucTVII, expressed in human skin-homing lymphocytes are responsible for synthesizing terminal sialofucosylations, recognized by HECA-452, that serve as E-selectinbinding determinants on PSGL-1. 14-23 These terminal sialyl Lewis X structures are expressed on poly-N-acetyllactosamines [(Gal␤1,4GlcNAc␤1,3) n ] found on core 2 serine/threonine (O)-linked glycans and asparagine (N)-linked glycans displayed by PSGL-1. [24][25][26][27][28][29][30] Although the majority of sialyl Lewis X epitopes appear to reside on PSGL-1 O-glycans, there are 3 potential sites for N-glycosylation and sialyl Lewis X decoration. 30 Consequently, interfering with the synthesis of O-glycans or N-glycans or of poly-N-acetyllactosamine structures on either O-or N-glycans (or both) would prevent the synthesis of HECA-452 epitopes and could dampen the E-selectin-binding function of PSGL-1 (CLA) on skin-homing leukocytes. The pu...

Although the current clinical formulation of paclitaxel (Taxolt) is an important new anti-cancer agent, it has significant side effects, some of which are related to its formulation in Cremophor/ethanol. Paclitaxel is difficult to formulate for i.v. administration because of its poor aqueous solubility. Here, we report the therapeutic effects of 2 liposome formulations of paclitaxel against human ovarian A121 tumor growing as an s.c. xenograft in athymic nude mice. The liposome formulations used were ETL and TTL, which have 1 or 3 lipid components, respectively. TTL was used as a reconstituted lyophilate or as a stable aqueous suspension. ETL was used as a reconstituted lyophilate only. Both pacli-taxel-liposome formulations were much better tolerated than Taxolt after i.v. or i.p. administration. The acute reactions seen after Taxolt administration did not occur when paclitaxel-liposome formulations were administered. All ETL and TTL preparations significantly delayed A121 tumor growth similarly to Taxol at equivalent doses and schedules. Based on pharmacokinetic data, it is possible that paclitaxel rapidly dissociates from ETL or TTL after i.v. administration and distributes in a manner similarly to Taxol. ETL and TTL formulations may be useful clinically not only for eliminating toxic effects of the Cremophor/ethanol vehicle but also for allowing alterations in route and schedule of drug administration. Int. Paclitaxel is a hydrophobic molecule solubilized for clinical use as an anti-neoplastic agent in Cremophore EL (polyethoxylated castor oil) containing 50% dehydrated ethanol, Taxolt (Bristol Myers Squibb, Princeton, NJ). This formulation has shown significant activity against a broad range of human cancers, including refractory human ovarian and breast cancers, non-small-cell lung carcinoma, head and neck carcinoma and melanoma (Huizing et al., 1995; Rowinsky and Donehower, 1995; Rowinsky et al., 1992). However, Cremophor EL, the excipient used in the Taxol formulation , has been shown to cause serious hypersensitivity reactions in humans (Weiss et al., 1990). To reduce the incidence and intensity of hypersensitivity, pre-medication with corticosteroids (dexametha-sone) and anti-histamines is being used. Although the pre-medication regimen has reduced the incidence of serious hypersen-sitivity reactions to less than 5%, milder reactions still occur in approximately 30% of patients (Weiss et al., 1990; Runowicz et al., 1993). Furthermore, it has been shown that Cremophor EL is mainly responsible for the non-linear pharmacokinetic behavior of paclitaxel in mice, and this may also be the case in humans since the plasma Cremophor concentrations at which non-linearity occurs in mice are in the therapeutic range achieved in humans (Sparreboom et al., 1996). Therefore, there is a strong rationale for reformulating taxanes using a safer and better-tolerated vehicle than Cremophor. Since plain liposomes have little toxicity, formulation of pacli-taxel in liposomes may offer advantages over the cremophor-based form...

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