Synthesis and conformational analysis of (E)-9,10-dehydroepothilone B: a suggestive link between the chemistry and biology of epothilones.
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Animals↗
Biomedical subjects
Ting-Chao Chou
Publications and source records attributed to Ting-Chao Chou.
Complex target-oriented total synthesis in the drug discovery process: the discovery of a highly promising family of second generation epothilones.
The total synthesis of a family of (E)-9,10-dehydro derivatives of epothilone D (i.e., 12,13-desoxyepothilone B) is described. The route is particularly concise and amenable to production of new congeners. Furthermore, the chemistry described herein constitutes a major simplification in the total synthesis of EpoD, which is in human clinical trials. This new family of epothilones shows major advantages in terms of their potency and pharmacostability relative to the wild-type saturated analogues in the D series. From the perspective of compound availability through synthesis, potency, and pharmacokinetic properties, these compounds could well warrant advancement to clinical evaluation in humans.
Antineoplastic Agents↗
Design of antineoplastic agents based on the '2-phenylnaphthalene-type' structural pattern--synthesis and biological activity studies of 11H-indolo[3.2-c]quinoline derivatives.
Designed as a new group of planar molecule containing the proposed 2-phenylnaphthalene-type structure, a number of 11H-indolo[3.2-c]quinoline derivatives were synthesized and evaluated biologically. Several compounds were found to possess cytotoxic activity against the growth of human promyelocytic leukemia cells (HL-60), against the small cell lung cancer (SCLC), and showed good response in the National Cancer Institute preclinical antitumor drug discovery 60-cell line panel.
Antineoplastic Agents↗
Primary African HIV clade A and D isolates: effective cross-clade neutralization with a quadruple combination of human monoclonal antibodies raised against clade B.
We investigated the ability of several human neutralizing monoclonal antibodies (nmAbs), originally raised against human immunodeficiency virus (HIV) clade B isolates, to neutralize primary clade A and D isolates as single agents and in combinations. All four primary HIV clade A isolates and five primary HIV clade D isolates tested were neutralized >99% by the quadruple combination of nmAbs IgG1b12, 2G12, 2F5, and 4E10. These mAbs recognize conserved epitopes on HIV-1 envelope (Env), resulting in strong cross-clade neutralization. Previously, we showed synergistic neutralization of primary HIV-1 clade C isolates in vitro by the same nMAb combination. We and others also showed neutralization of primary HIV clade B strains. Together, our data show that the quadruple combination of mAbs effectively neutralized primary HIV clade A, B, C, and D isolates.
Africa↗
Synergistic growth inhibitory effects of interferon-alpha and lovastatin on bcr-abl positive leukemic cells.
The chimeric bcr-abl tyrosine kinase is of crucial pathogenic importance in chronic myeloid leukemia (CML). As shown, bcr-abl activates the ras pathway by phosphorylation of adapter proteins such as Grb-2 and Crkl. Functional inhibition of p21ras might partially inhibit the mitogenic signaling by bcr-abl. By depletion of cellular mevalonate pools, p21ras proteins can be rendered non-functional as a result of deficient post-translational protein farnesylation. We investigated the pharmacologic effect of mevalonate depletion by lovastatin in conjunction with interferon-alpha 2b (INF-alpha 2b) in bcr-abl positive K562 cells. At various concentrations, both drugs synergistically reduced cell proliferation of CML line K562 in a liquid culture system as well as clonal growth of colony forming units in a patient with newly diagnosed CML. Lovastatin and IFN-alpha 2b in combination led to cell cycle arrest and resulted in significant reduction of phosphorylation on tyrosine, serine, and threonine protein residues. IFN-alpha 2b alone showed little effect on protein phosphorylation but strongly enhanced lovastatin driven loss of phosphorylation. Subsequently, DNA fragmentation occurred in 50% of cells. In conclusion, exposure to IFN-alpha 2b and lovastatin synergistically inhibited proliferation of bcr-abl positive cells and resulted in loss of protein phosphorylation and subsequent apoptosis in K562 cells. Our in vitro model suggests further investigations are required of the potential value of HMG-CoA reductase inhibitors as adjunct to therapy of CML with interferon.
Antineoplastic Agents↗
Sequence-dependent synergistic cytotoxicity of ecteinascidin-743 and paclitaxel in human breast cancer cell lines in vitro and in vivo.
Ecteinascidin 743 (ET-743) is a potent antitumor agent from the Caribbean tunicate Ecteinascidia turbinata and is presently in clinical trials for human cancers. The aim of this study was to assess the nature of the interaction between ET-743 and other antineoplastic agents using the combination index method of Chou and Talalay to better understand how ET-743 might be used clinically. We examined the cytotoxic effect of ET-743 combined with six other antineoplastic agents on human breast cancer cell lines, MX-1, MCF7, and P-glycoprotein overexpressing MCF7/DXR to different schedules. Pretreatment with paclitaxel for 24 h before ET-743 was the most effective combination regimen in all three breast cancer cell lines. Furthermore, sequential treatment with paclitaxel followed by ET-743 increased the antitumor effects in nude mice bearing MX-1 mammary carcinoma xenografts without increasing toxicity. These results suggest that the combination of ET-743 and paclitaxel should be assessed in clinical trials for the treatment of breast cancer.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
On the introduction of a trifluoromethyl substituent in the epothilone setting: chemical issues related to ring forming olefin metathesis and earliest biological findings.
The disclosure herein describes the synthesis of 10,11-dehydro-13,14-desoxy-27-trifluoro-[17]epothilone B via a stereoselective ring-closing metathesis and provides early biological evaluation data pertinent to this compound. [reaction: see text]
Alkenes↗
Probing the SAR of dEpoB via chemical synthesis: a total synthesis evaluation of C26-(1,3-dioxolanyl)-12,13-desoxyepothilone B.
A practical total synthesis of 26-(1,3-dioxolanyl)-12,13-desoxyepothilone B (26-dioxolanyl dEpoB) was accomplished in a highly convergent manner. A novel sequence was developed to produce the vinyl iodide segment 17 in high enantiomeric excess, which was used in a key B-alkyl Suzuki merger. Subsequently, a Yamaguchi macrocyclization formed the core lactone, while a selective oxidation and a late stage Noyori acetalization incorporated the dioxolane functionality. Sufficient amounts of synthetic 26-dioxolane dEpoB were produced using this sequence for an in vivo analysis in mice containing xenograft CCRF-CEM tumors.
Animals↗
Total syntheses of [17]- and [18]dehydrodesoxyepothilones B via a concise ring-closing metathesis-based strategy: correlation of ring size with biological activity in the epothilone series.
A convergent ring-closing metathesis strategy has been employed for the highly concise syntheses of 10,11-dehydro-13,14-[17]desoxyepothilone B ([17]ddEpoB) and 10,11-dehydro-14,15-[18]desoxyepothilone B ([18]ddEpoB), which are 17- and 18-membered ring homologues of 10,11-dehydro-12,13-desoxyepothilone B ([16]ddEpoB or epothilone 490). We have demonstrated that the ring-closing metathesis (RCM) provides [17]ddEpoB or [18]ddEpoB with a high level of stereocontrol in the generation of the desired olefin in the products. These analogues were evaluated for antitumor activity. The results from the in vitro assays revealed that the [17]ddEpoB analogue is highly active against various tumor cell lines with a potency comparable to that of [16]ddEpoB. This is the first example of a 17-membered ring macrolactone epothilone that has retained its antitumor activity. In contrast, the biological data revealed that [18]ddEpoB is significantly less active than either [17]ddEpoB or the parent [16]ddEpoB.
Antineoplastic Agents↗
Antitumor AHMA linked to DNA minor groove binding agents: synthesis and biological evaluation.
DNA minor groove binder hybrid molecules, netropsin derivatives such as N-[2-(dimethylamino)ethyl]-1-methyl-4-aminopyrrolo-2-carboxamide (MePy) or its derivatives containing two units of N-methylpyrrolecarboxamide (diMePy) and bisbenzimidazole (Ho33258), were linked to the NH(2) function of AHMA or to the CH(2)OH group of AHMA-ethylcarbamate to form AHMA-N-netropsins (13-16) and AHMA-ethylcarbamate-O-netropsins (19-22), and AHMA-bisbenzimidazole (AHMA-Ho33258, 25), respectively. These conjugates' in vitro antitumor activity, inhibition of a variety of human tumor cell growth, revealed that AHMA-ethylcarbamate-O-netropsin derivatives were more cytotoxic than AHMA-N-netropsin compounds. In the same studies, all compounds bearing MePy were more potent than those compounds linked with diMePy. Moreover, AHMA-netropsin derivatives bearing a succinyl chain as the linking spacer were more potent than those compounds having a glutaryl bridge. Among these hybrid molecules, AHMA-ethylcarbamate-O-succinyl-MePy (19) was 2- to 6-fold more cytotoxic than the parent compound AHMA (5) in various cell lines, whereas compound 25 had very poor solubility and was inactive. Studies on the inhibitory effect against topoisomerase II (Topo II) and DNA interaction of these conjugates showed no correlation between the potency of DNA binding and inhibitory activity against Topo II.
Acridines↗
Highly concise routes to epothilones: the total synthesis and evaluation of epothilone 490.
A concise modular laboratory construction of the epothilone class of promising antitumor agents has been accomplished. For the first time in the epothilone area, the new synthesis exploits the power of ring-closing olefin metathesis (RCM) in a stereospecific way. Previous attempts at applying RCM to epothilone syntheses have been repeatedly plagued by complete lack of stereocontrol in the generation of the desired 12,13-olefin geometry in the products. The isolation of epothilone 490 (3) prompted us to reevaluate the utility of the RCM procedure for fashioning the 10,11-olefin, with the Z-12,13-olefin geometry already in place. Olefin metathesis of the triene substrate 12 afforded the product diene macrolide in stereoselective fashion. For purposes of greater synthetic convergency, the C3-(S)-alcohol was fashioned late in the synthesis, using chiral titanium-mediated aldol conditions with the entire O-alkyl fragment as a C15 acetate as the enolate component. Examination of the effects of protecting groups on the RCM process showed that deprotection of the C7 alcohol has a beneficial effect on the reaction yield. Performing the RCM as the last synthetic step in the sequence afforded a 64% yield of only the desired E-olefin. Selective diimide reduction of the new 10,11-olefin yielded 12,13-desoxyepothilone B, our current clinical candidate, demonstrating the utility of this new RCM-reduction protocol in efficiently generating the epothilone framework. Furthermore, the new olefin was selectively funtionalized to demonstrate the advantage conferred by this route for the construction of new analogues for SAR studies, in cytoxicity and microtubule affinity screens. Also described is the surprisingly poor in vivo performance of epothilone 490 in xenografts in the light of very promising in vitro data. This disappointing outcome was traced to unfavorable pharmacokinetic features of the drug in murine plasma. By the pharmacokinetic criteria, the prognosis for the effectiveness of 3 in humans is, in principle, much more promising.
Animals↗
Anti-human immunodeficiency virus interactions of SCH-C (SCH 351125), a CCR5 antagonist, with other antiretroviral agents in vitro.
SCH-C (SCH 351125) is a small-molecule antagonist of the human immunodeficiency virus type 1(HIV-1) coreceptor CCR5. It has in vitro activity against R5 viruses with 50% inhibitory concentrations ranging from 1.0 to 30.9 nM. We have studied anti-HIV-1 interactions of SCH-C with other antiretroviral agents in vitro. Synergistic interactions were seen with nucleoside reverse transcriptase inhibitors (zidovudine and lamivudine), nonnucleoside reverse transcriptase inhibitors (efavirenz), and protease inhibitors (indinavir) at all inhibitory concentrations evaluated. We have also studied antiviral interactions between the HIV-1 fusion inhibitor T-20 and SCH-C against a panel of R5 HIV-1 isolates. We found synergistic interactions against all the viruses tested, some of which harbored resistance mutations to reverse transcriptase and protease inhibitors. Anti-HIV-1 synergy was also observed between SCH-C and another R5 virus inhibitor, aminooxypentane-RANTES. These findings suggest that SCH-C may be a useful anti-HIV drug in combination regimens and that a combination of chemokine coreceptor/fusion inhibitors may be useful in the treatment of multidrug-resistant viruses.
Anti-HIV Agents↗
Synergy determination issues.
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Drug Synergism↗
Pharmacokinetic interactions augment toxicities of sirolimus/cyclosporine combinations.
This study correlated the dynamic effects of sirolimus (rapamycin; RAPA) and cyclosporine (CsA) alone versus in combination to produce renal dysfunction, myelosuppression, or hyperlipidemia, with their corresponding blood and tissue concentrations. After salt-depleted rats were treated with RAPA (0.4 to 6.4 mg/kg per d) and/or CsA (2.5 to 20.0 mg/kg per d) for 14 d, the GFR, lipid levels, bone marrow cellularity, and CsA/RAPA concentrations in whole blood versus liver or renal tissues were measured, and the median effect model was used to discern the type of drug interactions. Compared with vehicle controls (1.98 +/- 0.34 ml/min), GFR values were reduced only by large doses of drug monotherapy, namely RAPA (3.2 mg/kg per d = 1.2 +/- 0.02 ml/min or 6.4 mg/kg per d = 1.3 +/- 0.2 ml/min; both P < 0.01) or CsA (10.0 mg/kg per d = 1.2 +/- 0.1 ml/min or 20.0 mg/kg per d = 0.8 +/- 0.4 ml/min; both P < 0.01). In contrast, hosts that were treated with smaller doses of CsA/RAPA combinations showed more pronounced effects in reduction of GFR values: 2.5/0.4 mg/kg per d, modestly (1.5 +/- 0.5 ml/min; P < 0.01); 5.0/0.8 mg/kg per d, moderately (0.23 +/- 0.01 ml/min; P < 0.001); and higher-dose groups, markedly. The exacerbation of renal dysfunction seemed to be due to a pharmacokinetic interaction of RAPA to greatly increase CsA concentrations in whole blood and, particularly, in kidney tissue. In contrast, the pharmacodynamic effects of CsA to potentiate two RAPA-mediated toxicities-myelosuppression and increased serum cholesterol/low-density lipoprotein cholesterol-occurred independently of pharmacokinetic interactions. RAPA aggravates CsA-induced renal dysfunction owing to a pharmacokinetic interaction, whereas CsA produces a pharmacodynamic effect that augments RAPA-induced myelosuppression and hyperlipidemia.
Animals↗
Enhanced hydrolytic stability and water solubility of an aromatic nitrogen mustard by conjugation with molecular umbrellas.
Chlorambucil, an aromatic nitrogen mustard, has been conjugated to putrescine- and spermidine-based scaffolds bearing one, two, and four persulfated cholic acid units. Those conjugates bearing two or four sterols show improved hydrolytic stability and water solubility relative to chlorambucil. A similar conjugate that contained only one sterol unit shows negligible improvement in hydrolytic stability but a significant increase in water solubility. Qualitatively, the hydrolytic stability within this series of conjugates parallels the shielding effects that have previously been found for related conjugates bearing a pendant, hydrophobic fluorescent probe. In vitro studies indicate that these conjugates possess modest to moderate activity against certain human lymphoblastic leukemia and human colon carcinoma cells.
Cell Line, Tumor↗