Synthesis and Biological Evaluation of Novel 3'-Difluorovinyl Taxoids.

A series of 3'-difluorovinyl taxoids with C10 modifications, as well as those with C2 and C10 modifications, were strategically designed to block the metabolism by cytochrome P-450 3A4 enzyme and synthesized. These novel difluorovinyl taxoids were evaluated for their cytotoxicity against drug-sensitive human breast (MCF7), multidrug-resistant (MDR) human ovarian (NCI/ADR), human colon (HT-29) and human pancreatic (PANC-1) cancer cell lines. 3'-Difluorovinyl taxoids exhibit several to 16 times better activity against MCF7, HT-29 and PANC-1 cell lines and up to three orders of magnitude higher potency against NCI/ADR cell line as compared to paclitaxel. Structure-activity relationship study shows the critical importance of the C2 modifications on the activity against MDR cancer cell line, while the C10 modifications have a rather minor effect on the potency with some exceptions. The effect of the C2 modifications on potency against MCF7 cell line increases in the following order: H < F < Cl

Design and synthesis of de novo cytotoxic alkaloids by mimicking the bioactive conformation of paclitaxel.

Novel paclitaxel-mimicking alkaloids were designed and synthesized based on a bioactive conformation of paclitaxel, that is, REDOR-Taxol. The alkaloid 2 bearing a 5-7-6 tricyclic scaffold mimics REDOR-Taxol best among the compounds designed and was found to be the most potent compound against several drug-sensitive and drug-resistant human cancer cell lines. MD simulation study on the paclitaxel mimics 1 and 2 as well as REDOR-Taxol bound to the 1JFF tubulin structure was quite informative to evaluate the level of mimicking. The MD simulation study clearly distinguishes the 5-6-6 and 5-7-6 tricyclic scaffolds, and also shows substantial difference in the conformational stability of the tubulin-bound structures between 2 and REDOR-Taxol. The latter may account for the large difference in potency, and provides critical information for possible improvement in the future design of paclitaxel mimics.

Use of an anti-vascular endothelial growth factor antibody in a pharmacokinetic strategy to increase the efficacy of intraperitoneal chemotherapy.

The efficacy of intraperitoneal chemotherapy for ovarian cancers is limited by poor penetration of drug into peritoneal tumors. Based on pharmacokinetic theory that suggests that penetration depth is primarily determined by the rate of drug removal via tumor capillaries, we have hypothesized that co-administration of antiangiogenic therapy will allow for decreased drug removal, increased drug concentrations in tumor, and increased efficacy of intraperitoneal chemotherapy. Pharmacokinetic modeling was conducted to simulate the effect of tumor blood flow on tumor concentrations of topotecan. Simulations predicted that tumor blood flow reductions, as potentially achieved by antiangiogenic therapy, would lead to substantial increases in tumor concentrations after intraperitoneal chemotherapy but would lead to a slight decrease after systemic chemotherapy. Pharmacokinetic studies performed using the A2780 xenograft tumor model showed that animals receiving combined intraperitoneal topotecan and an anti-vascular endothelial growth factor (VEGF) monoclonal antibody had approximately 6.5-fold higher (p = 0.0015) tumor topotecan concentrations compared with animals receiving intraperitoneal topotecan alone, whereas there was no significant (p = 0.16) difference for systemic topotecan. Therapeutic studies conducted with two different drugs, topotecan and cisplatin, showed that animals receiving combined intraperitoneal chemotherapy and anti-VEGF therapy displayed superior survival relative to animals treated with chemotherapy alone (i.e., cisplatin or topotecan), anti-VEGF alone, or intravenous chemotherapy with concomitant anti-VEGF therapy. Combined intraperitoneal topotecan and anti-VEGF resulted in the complete cure of four of 11 mice. The proposed combination of antiangiogenic therapy and intraperitoneal chemotherapy, which was predicted to be beneficial by pharmacokinetic simulations, may provide substantial benefit to patients with peritoneal malignancies.

Design, synthesis, and biological evaluation of new-generation taxoids.

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 potency against multidrug-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 paclitaxel-resistant ovarian cancer cell lines with mutations in beta-tubulin as well, wherein the drug resistance is mediated by the beta-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 four pancreatic cancer cell lines, expressing three to four 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.

Design, synthesis, and biological evaluation of novel C14-C3'BzN-linked macrocyclic taxoids.

Novel macrocyclic paclitaxel congeners were designed to mimic the bioactive conformation of paclitaxel. Computational analysis of the "REDOR-Taxol" structure revealed that this structure could be rigidified by connecting the C14 position of the baccatin moiety and the ortho position of C3'N-benzoyl group (C3'BzN), which are ca. 7.5 A apart, with a short linker (4-6 atoms). 7-TES-14beta-allyloxybaccatin III and (3R,4S)-1-(2-alkenylbenzoyl)-beta-lactams were selected as key components, and the Ojima-Holton coupling afforded the corresponding paclitaxel-dienes. The Ru-catalyzed ring-closing metathesis (RCM) of paclitaxel-dienes gave the designed 15- and 16-membered macrocyclic taxoids. However, the RCM reaction to form the designed 14-membered macrocyclic taxoid did not proceed as planned. Instead, the attempted RCM reaction led to the occurrence of an unprecedented novel Ru-catalyzed diene-coupling process, giving the corresponding 15-membered macrocyclic taxoid (SB-T-2054). The biological activities of the novel macrocyclic taxoids were evaluated by tumor cell growth inhibition (i.e., cytotoxicity) and tubulin-polymerization assays. Those assays revealed high sensitivity of cytotoxicity to subtle conformational changes. Among the novel macrocyclic taxoids evaluated, SB-T-2054 is the most active compound, which possesses virtually the same potency as that of paclitaxel. The result may also indicate that SB-T-2054 structure is an excellent mimic of the bioactive conformation of paclitaxel. Computational analysis for the observed structure-activity relationships is also performed and discussed.

Syntheses and Structure-Activity Relationships of Novel 3'-Difluoromethyl and 3'-Trifluoromethyl-Taxoids.

A series of novel 3'-difluoromethyl-taxoids and 3'-trifluoromethyl-taxoids with modifications at the C2 and C10 positions were synthesized and evaluated for their in vitro cytotoxicities against human breast carcinoma (MCF7-S, MCF7-R, LCC6-WT, LCC6-MDR), non-small cell lung carcinoma (H460) and colon adenocarcinoma (HT-29) cell lines. These second-generation fluoro-taxoids exhibited several times to more than 20 times better potency than paclitaxel against drug-sensitive cancer cell lines, MCF7-S, LCC6-WT, H460, and HT-29. These fluoro-taxoids also possess two orders of magnitude higher potency than paclitaxel against drug-resistant cancer cell lines, MCF7-R and LCC6-MDR. Structure-activity relationship study shows the importance of the C10 modification for increasing the activity against multidrug-resistant cancer cell lines. Effects of the C2-benzoate modifications on the potency in the 3-difluoromethyl-taxoid series are very clear (i.e., F < MeO < Cl < N(3)), while those in the 3-trifluoromethyl-taxoid series are less obvious. Also, different trends in the sensitivity to the C2-substitution are observed between drug-sensitive cell lines and drug-resistant cancer cell lines that overexpress efflux pumps.

Use of the tubulin bound paclitaxel conformation for structure-based rational drug design.

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.

High-resolution magnetic resonance imaging of the efficacy of the cytosine analogue 1-[2-C-cyano-2-deoxy-beta-D-arabino-pentofuranosyl]-N(4)-palmitoyl cytosine (CS-682) in a liver-metastasis athymic nude mouse model.

High-resolution magnetic resonance (MR) imaging techniques in a liver metastatic mouse model were used to assess CS-682, a novel 2'-deoxycytidine analogue of 1-[2-C-cyano-2-deoxy-beta-D-arabino-pentofuranosyl]-N(4)-palmitoyl cytosine. The efficacy of CS-682 was visualized in real time by MR imaging of initial seeding and subsequent growth of liver metastases. The relative therapeutic efficacies of CS-682 and two agents used clinically, gemcitabine [2'-deoxy-2',2'-difluorocytidine monohydrochloride (DFDC)] and 5-fluorouracil (5-FU), were compared in this model. CS-682 was found to exhibit superior efficacy by delaying the onset and inhibiting the growth of liver metastasis compared with gemcitabine, 5-FU, and control. The overall occurrence of metastases was decreased 62% by CS-682, 18% by DFDC, and 35% by 5-FU. CS-682 increased the life span of the treated animals significantly, by 28 days above the 29-day median survival without treatment, compared with 11 days by DFDC and 14 days by 5-FU. The increased survival in CS-682-treated animals correlated with the antimetastatic activity of this compound. These preclinical findings support the potential clinical utility of CS-682 in the treatment of liver metastasis.

Design, synthesis and structure-activity relationships of novel taxane-based multidrug resistance reversal agents.

A series of novel taxane-based multidrug resistance (MDR) reversal agents (TRAs) has been designed and synthesized. Structure-activity relationship (SAR) study clearly indicates that modification of the C-7 position with hydrophobic arenecarbonylcinnamoyl groups brings about high potency against drug efflux mediated by P-glycoprotein (P-gp). Six TRAs exhibit ability to modulate a wide range of ATP-binding cassette (ABC) transporters, such as P-gp, multidrug resistance-associated protein 1 (MRP1), and breast cancer resistance protein (BCRP), which may serve as novel broad-spectrum modulators of ABC transporters.

Taxane-based reversal agents modulate drug resistance mediated by P-glycoprotein, multidrug resistance protein, and breast cancer resistance protein.

Overexpression of ATP-binding cassette transport proteins, including P-glycoprotein (Pgp), multidrug resistance (MDR) protein (MRP-1), and breast cancer resistance protein (BCRP), is a well-characterized mechanism of MDR in tumor cells. Although the cytotoxic taxanes paclitaxel and docetaxel are substrates for Pgp-mediated efflux, the semisynthetic taxane analogue ortataxel inhibits drug efflux mediated by Pgp as well as, as we recently demonstrated, MRP-1 and BCRP. Nevertheless, ortataxel is not optimal for development as a clinical MDR modulator because of its cytotoxicity [corrected]. We sought to identify noncytotoxic taxane-based broad-spectrum modulators from a library of noncytotoxic taxane-based reversal agents (tRAs) designed by eliminating the C-13 side chain of the taxane molecule, which inhibits microtubule depolymerization. Twenty tRAs, selected based on modulation of paclitaxel cytotoxicity in Pgp-overexpressing MDA435/LCC6(mdr1) cells, were studied for modulation of retention and cytotoxicity of substrates of MRP-1 and BCRP as well as Pgp in established cell lines overexpressing each of these transporters. Four tRAs modulated MRP-1 and 17 modulated BCRP in addition to Pgp. The four broad-spectrum tRAs strongly modulated daunorubicin and mitoxantrone efflux and enhanced their cytotoxicity in cell lines overexpressing the three MDRs, decreasing IC(50) values by as much as 97% [corrected]. These tRAs, especially tRA 98006, have promise for development as clinical broad-spectrum MDR modulators and warrant more preclinical analysis to determine pharmacokinetic interactions and efficacy.

Synthesis and biological evaluation of 2'-methyl taxoids derived from baccatin III and 14beta-OH-baccatin III 1,14-carbonate.

A series of 2'-methyl taxoids were synthesized and essayed for growth inhibition experiments conducted in human ovarian cancer cell line A2780wt and its counterparts A2780cis, A2780tax, and A2780adr, resistant to cisplatin, paclitaxel, and doxorubicin, respectively, to test the effect of this substituent on the antitumor activity. Additional experiments were performed on MCF-7 human breast cancer cell line and MCF7-R resistant to doxorubicin. In several cases these taxoids were more active than paclitaxel showing subnanomolar IC(50) values.

Broad-spectrum modulation of ATP-binding cassette transport proteins by the taxane derivatives ortataxel (IDN-5109, BAY 59-8862) and tRA96023.

PURPOSE: The taxanes paclitaxel and docetaxel are substrates for P-glycoprotein (Pgp), an ATP-binding cassette (ABC) transport protein associated with multidrug resistance (MDR). In contrast, the synthetic taxane ortataxel (BAY 59-8862, IDN-5109) is effective against Pgp-expressing cells by virtue of modulation of Pgp-mediated transport. The synthetic taxane tRA96023 also modulates Pgp and is noncytotoxic due to removal of the tubulin-binding side chain at the C-13 position of the taxane backbone. We studied the effects of ortataxel and tRA96023 on the other MDR-associated ABC transport proteins, multidrug resistance protein (MRP-1) and breast cancer resistance protein (BCRP, MXR, ABCG2). METHODS: Modulation of mitoxantrone, daunorubicin and doxorubicin retention and cytotoxicity by ortataxel and tRA96023 was studied in established cell lines overexpressing Pgp, MRP-1 and wild type (BCRP(R482)) and mutant (BCRP(R482T)) BCRP, and was compared with modulation by the established Pgp-, MRP-1- and BCRP-specific modulators PSC-833, probenecid and fumitremorgin C, respectively. RESULTS: Ortataxel effectively modulated drug retention and cytotoxicity in cell lines overexpressing MRP-1 and BCRP(R482), in addition to Pgp. tRA96023 modulated drug retention and cytotoxicity in cell lines overexpressing BCRP(R482) and Pgp, but not those overexpressing MRP-1. Neither ortataxel nor tRA96023 modulated BCRP(R482T). CONCLUSIONS: The synthetic taxane derivatives ortataxel and tRA96023 are broad-spectrum ABC protein modulators. Further studies will seek to identify a noncytotoxic synthetic taxane that modulates Pgp, MRP-1 and BCRP.

Structure-activity analysis of taxane-based broad-spectrum multidrug resistance modulators.

BACKGROUND: Clinical drug resistance is frequently associated with overexpression of the multidrug resistance (MDR) proteins P-glycoprotein (Pgp), multidrug resistance protein (MRP-1) and breast cancer resistance protein (BCRP). Taxanes are substrates for Pgp and MRP-1, but not BCRP. Taxane-based reversal agents (tRAs) are non-cytotoxic MDR modulators previously examined for broad-spectrum modulation of Pgp, MRP-1 and BCRP. MATERIALS AND METHODS: Modulation by tRAs was studied by flow cytometry and resistance to taxanes was studied in cytotoxicity assays in the parental HL60/wt, 8226/wt and MCF7/S, and the resistant HL60/ADR, 8226/Dox6, 8226/MR20 and MCF7 AdVp3000 cell lines. Amino acid sequence (BLAST) alignments were performed using ClustalW. RESULTS: Structure-activity analysis demonstrated greatest alignment of BCRP with the transmembrane 7-12 region of Pgp and identified tRA side groups that contributed or were detrimental to modulation. CONCLUSION: Identification of tRA side groups contributing to modulation of Pgp, MRP-1 and BCRP will allow the design of a next generation of tRAs and will optimize their potential clinical applicability.

Evaluation of combined bevacizumab and intraperitoneal carboplatin or paclitaxel therapy in a mouse model of ovarian cancer.

PURPOSE: To evaluate the pharmacokinetics of bevacizumab following IP and IV administration, and to investigate combined bevacizumab therapy (IP or IV) with IP paclitaxel or carboplatin in a mouse model of ovarian cancer. METHODS: Bevacizumab pharmacokinetics were investigated following IV or IP dosing, and mice bearing peritoneal A2780 xenografts were treated with vehicle, IV or IP bevacizumab, IP paclitaxel, IP paclitaxel with co-administration of IV or IP bevacizumab, IP carboplatin, and IP carboplatin with co-administration of IV or IP bevacizumab. Survival time was defined as the time to death or the time to reach 120% of baseline body weight. RESULTS: Following IP administration, bevacizumab was rapidly absorbed and bioavailability was 92.8%. Median survival time, which was 33 days for control mice, was increased by 24% with IP paclitaxel. IP carboplatin failed to increase survival time when administered alone. IV and IP bevacizumab increased survival time by 42 and 33%. Combined bevacizumab and IP paclitaxel was superior to paclitaxel alone (P = 0.01 for IV and P = 0.04 for IP bevacizumab), and combined bevacizumab and IP carboplatin was superior to carboplatin alone (P = 0.002 for IV and P = 0.02 for IP bevacizumab). There were no significant differences in survival between groups receiving bevacizumab IV or IP, either alone (P = 0.586), in combination with paclitaxel (P = 0.467), or in combination with carboplatin (P = 0.149). CONCLUSIONS: Following IP administration to mice, bevacizumab demonstrates rapid and near complete absorption. Bevacizumab therapy, initiated prior to IP carboplatin or paclitaxel administration, increased survival time significantly in mice, and results were not dependent on the route of bevacizumab administration (IV vs. IP).

Modeling the combination of amphotericin B, micafungin, and nikkomycin Z against Aspergillus fumigatus in vitro using a novel response surface paradigm.

Response surface methods for the study of multiple-agent interaction allow one to model all of the information present in full concentration-effect data sets and to visualize and quantify local regions of synergy, additivity, and antagonism. In randomized wells of 96-well plates, Aspergillus fumigatus was exposed to various combinations of amphotericin B, micafungin, and nikkomycin Z. The experimental design was comprised of 91 different fixed-ratio mixtures, all performed in quintuplicate. After 24 h of drug exposure, drug effect on fungal viability was assessed using the tetrazolium salt 2,3-bis {2-methoxy-4-nitro-5-[(sulfenylamino) carbonyl]-2H-tetrazolium-hydroxide} (XTT) assay. First, we modeled each fixed-ratio combination alone using the four-parameter Hill concentration-effect model. Then, we modeled each parameter, including the 50% inhibitory concentration (IC(50)) effect, versus the proportion of each agent using constrained polynomials. Finally, we modeled the three-agent response surface overall. The overall four-dimensional response surface was complex, but it can be explained in detail both analytically and graphically. The grand model that fit the best included complex polynomial equations for the slope parameter m and the combination index (equivalent to the IC(50) for a fixed-ratio concentration, but with concentrations normalized by the respective IC(50)s of the drugs alone). There was a large region of synergy, mostly at the nikkomycin Z/micafungin edge of the ternary plots for equal normalized proportions of each drug and extending into the center of the plots. Applying this response surface method to a huge data set for a three-antifungal-agent combination is novel. This new paradigm has the potential to significantly advance the field of combination antifungal pharmacology.

The 4'-O-benzylated doxorubicin analog WP744 overcomes resistance mediated by P-glycoprotein, multidrug resistance protein and breast cancer resistance protein in cell lines and acute myeloid leukemia cells.

BACKGROUND: The synthetic 4'-O-benzylated doxorubicin analog WP744 was designed to abrogate transport by the multidrug resistance (MDR)-associated ATP-binding cassette (ABC) proteins P-glycoprotein (Pgp) and multidrug resistance protein (MRP-1). We compared its uptake and cytotoxicity with those of doxorubicin and daunorubicin in cell lines overexpressing Pgp, MRP-1 or breast cancer resistance protein (BCRP) and in acute myeloid leukemia (AML) cells. METHODS: Cellular uptake was studied by flow cytometry and cytotoxicity in 96-h 96-well cultures in cell lines overexpressing Pgp, MRP-1 or wild type (BCRP(R482)) or mutant (BCRP(R482T), BCRP(R482G)) BCRP and in pre-treatment AML marrow cells. RESULTS: Uptake and cytotoxicity of WP744 were consistently greater than those of doxorubicin and daunorubicin at equimolar concentrations in all cell lines studied and in AML cells. CONCLUSION: WP744 overcomes transport by Pgp, MRP-1 and BCRP in cell lines and AML cells and is a promising agent for clinical development in AML and other malignancies with broad-spectrum multidrug resistance.

Syntheses and evaluation of novel fatty acid-second-generation taxoid conjugates as promising anticancer agents.

Polyunsaturated fatty acids such as docosahexaenoic acid (DHA), linolenic acid, and linoleic acid were linked to the C-2' position of the second-generation taxoids that could overcome MDR caused by overexpressed ABC transporters. The new conjugates, tested in vivo, exhibited strong activity against drug-resistant colon cancer and drug-sensitive ovarian cancer xenografts in mice. Two of the new conjugates, DHA-SB-T-1214 and DHA-SB-T-1213, were found to achieve the total regression of drug-resistant and drug-sensitive tumors, respectively, in the animal models with substantially reduced systemic toxicity.

Effect of amphotericin B and micafungin combination on survival, histopathology, and fungal burden in experimental aspergillosis in the p47phox-/- mouse model of chronic granulomatous disease.

Chronic granulomatous disease (CGD) is an inherited disorder of the NADPH oxidase characterized by recurrent life-threatening bacterial and fungal infections. We characterized the effects of single and combination antifungal therapy on survival, histopathology, and laboratory markers of fungal burden in experimental aspergillosis in the p47phox-/- knockout mouse model of CGD. CGD mice were highly susceptible to intratracheal Aspergillus fumigatus challenge, whereas wild-type mice were resistant. CGD mice were challenged intratracheally with a lethal inoculum (1.25 x 10(4) CFU/mouse) of A. fumigatus and received one of the following regimens daily from day 0 to 4 after challenge (n = 19 to 20 per treatment group): (i) vehicle, (ii) amphotericin B (intraperitoneal; 1 mg/kg of body weight), (iii) micafungin (intravenous; 10 mg/kg), or (iv) amphotericin B plus micafungin. The rank order of therapeutic efficacy based on prolonged survival, from highest to lowest, was as follows: amphotericin B plus micafungin, amphotericin B alone, micafungin alone, and the vehicle. Lung histology showed pyogranulomatous lesions and invasive hyphae, but without hyphal angioinvasion or coagulative necrosis. Treatment with micafungin alone or combined with amphotericin B produced swelling of invasive hyphae that was not present in mice treated with the vehicle or amphotericin B alone. Assessment of lung fungal burden by quantitative PCR showed no significant difference between treatment groups. Serum galactomannan levels were at background despite documentation of invasive aspergillosis by histology. Our findings showed the superior efficacy of the amphotericin B and micafungin combination compared to either agent alone after A. fumigatus challenge and also demonstrated unique features of CGD mice as a model for experimental aspergillosis.

Partial circumvention of P-glycoprotein-mediated multidrug resistance by doxorubicin-14-O-hemiadipate.

Previously, we have reported partial circumvention of P-glycoprotein (Pgp)-associated resistance to doxorubicin (Dox) in MCF7/R human breast carcinoma and P388/R murine leukemia cell lines by doxorubicin-14-O-hemiadipate (H-Dox) [Povarov L.S. et al. (1995) Russian J. Bioorganic Chemistry 21: 797-803]. We felt that these changes were due to alterations in the cellular pharmacokinetics of the analog in multidrug (MDR) resistant cells, as compared to that of Dox. To address this hypothesis, we performed comparative studies of the accumulation, retention and intracellular localization of H-Dox and Dox in Dox-sensitive murine leukemia cell line P388/S and its Dox-selected. Pgp-positive drug resistant P388/R subline. These studies were performed in the presence or absence of cyclosporin A (CsA), a competitive inhibitor of Pgp. Flow cytometric analysis revealed significant differences in Dox and H-Dox accumulation in P388/R cells when compared to P388/S cells. In P388/R versus P388/S cells, there was a 38-fold decrease in Dox accumulation, but only a 5-fold decrease in H-Dox accumulation, indicating over a 7-fold increase in H-Dox buildup in resistant cells. CsA did not affect uptake or retention of either drug by sensitive cells. However, coincubation with CsA resulted in a 54-fold increase in Dox accumulation and only a 5-fold increase in H-Dox uptake in P388/R cells, restoring anthracycline levels in P388/R to 100% of that found in P388/S cells. Once internalized by the resistant cells, H-Dox was retained better than Dox regardless of presence or absence of CsA. Confocal microscopic analysis revealed the presence of H-Dox but no Dox in cellular nuclei of P388/R cells. Thus, increased activity of H-Dox toward P388/R cells was correlated with its enhanced ability to enter and be retained in these cells, and also with redistribution of H-Dox into the nuclei of the resistant cells as compared to Dox. Overall, our findings support our initial hypothesis and provide evidence that H-Dox, a 14-O-hemiadipate of doxorubicin, is affected by Pgp-mediated MDR to a lesser extent than parental Dox due to changes iin the cellular pharmacokinetics of the analog.

Glycosylation-dependent inhibition of cutaneous lymphocyte-associated antigen expression: implications in modulating lymphocyte migration to skin.

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 inhibitors of glycosylation and of a novel fluorinated analog of N-acetylglucosamine (2-acetamido-1,3,6-tri-O-acetyl-4-deoxy-4-fluoro-D-glucopyranose [4-F-GlcNAc]) to alter HECA-452 expression on human CLA(+) T cells and prevent cell tethering and rolling on selectins under shear stress. At concentrations that did not affect PSGL-1 expression, we found that swainsonine (inhibitor of complex-type N-glycan synthesis) had no effect on HECA-452 expression or selectin ligand activity, whereas benzyl-O-N-acetylgalactosamide (BAG; inhibitor of O-glycan biosynthesis) ablated HECA-452 expression on PSGL-1 and significantly lowered selectin ligand activity. We found that 4-F-GlcNAc (putative inhibitor of poly-N-acetyllactosamine biosynthesis) was more potent than BAG at lowering HECA-452 expression and selectin binding. In addition, we show that 4-F-GlcNAc was directly incorporated into native CLA expressed on T cells, indicating direct inhibition on poly-N-acetyllactosamine elongation and selectin-binding determinants on PSGL-1 O-glycans. These observations establish a potential treatment approach for targeting pathologic lymphocyte trafficking to skin and indicate that 4-F-GlcNAc may be a promising agent for treatment of dermal tropism associated with malignancies and inflammatory disorders.