Synthesis and biological evaluation of novel 9-functional heterocyclic coupled 7-deoxy-9-dihydropaclitaxel analogue

Novel 9-functional heterocyclic coupled 7-deoxy-9-dihydropaclitaxel analogues 17 and 22-24 synthesized from a natural taxoid 5-cinnamoyltriacetyltaxicin-I (3) and their biological evaluation in tubulin assembly activity and cytotoxicity in vitro against several human tumor cell lines are first presented. The biologically tested results show that 17, 22 and 23 are inactive in tubulin assembly assay and have no more remarkable cytotoxicities against human tumor cell lines SK-OV3, WIDR and MCF-7, though 22 and 23 exhibit more potent cytotoxicity against human liver cancer and human esophagus cancer cell lines (BEL-7402 and ECa-109) than paclitaxel.     

Synthesis and biological evaluation of novel 3'-N-tert-butylsulfonyl analogues of docetaxel

Novel 3′-N-tert-butylsulfonyl analogues 10a–c of docetaxel were synthesized and their biological evaluation in cytotoxicity in vitro against several human tumor cell lines were presented. The biologically tested results showed that N-oxide pyridyl substituted10b–c had potent cytotoxicities against human tumor cell lines Eca-109, SKOV3, SMMC-7721, HCT-8, PC3, MCF-7, HeLa and KB.     

Antitumor agents 210. Synthesis and evaluation of taxoid-epipodophyllotoxin conjugates as novel cytotoxic agents

Five compounds composed of a taxoid (paclitaxel or cephalomannine) and a 4'-O-demethyl epipodophyllotoxin derivative joined by an imine linkage were prepared and evaluated as cytotoxic agents and inhibitors of mammalian DNA topoisomerase II. Compounds 12 and 14-16 exhibited comparable or better activity than the unconjugated epipodophyllotoxin derivatives in most tumor cell lines, and 12, 15, and 16 also showed enhanced activity against paclitaxel-resistant cells. Compound 13, which contains an epipodophyllotoxin moiety at both the taxoid 2' and 7 positions, did not stimulate protein-DNA breaks, but was 2-fold more potent than 12 and 15 and comparable to GL-331 in the topo II inhibitory assay.     

Synthesis and biological evaluation of 4-deacetoxy-1,7-dideoxy azetidine paclitaxel analogues

Three novel 4-deacetoxy-1,7-dideoxy azetidine paclitaxel analogues were synthesized through a convenient route that employed hydroboration-amination and intramolecular S(N)2-type substitution reaction from a natural taxoid taxinine. All analogues have been tested for cytotoxicity against three human tumor cell lines. None of them showed remarkable cytotoxicity compared to paclitaxel against tested tumor cell lines.     

Cyclostreptin (FR182877), an antitumor tubulin-polymerizing agent deficient in enhancing tubulin assembly despite its high affinity for the taxoid site

Cyclostreptin (FR182877), a bacterial natural product, was reported to have weak paclitaxel-like activity with tubulin but antitumor activity in vivo. We used synthetic cyclostreptin in studies of its mechanism of action. Although less potent than paclitaxel in several human cancer cell lines, cyclostreptin was active against cells resistant to paclitaxel and epothilone A. At equitoxic concentrations with paclitaxel, cyclostreptin was more effective in arresting MCF-7 cells in mitosis and equivalent in bundling microtubules in PtK(2) cells. Tubulin assembly with paclitaxel occurs at low temperatures and in the absence of GTP or microtubule-associated proteins (MAPs). Brisk assembly with cyclostreptin required MAPs, GTP, and higher reaction temperatures. On the basis of turbidimetry, cyclostreptin-induced microtubules were more stable in the cold than the paclitaxel-induced polymer. Moreover, at 37 degrees C cyclostreptin was a strong competitive inhibitor of the binding of radiolabeled paclitaxel to tubulin polymer, with an apparent K(i) value of 88 nM. Competition studies versus a fluorescent taxoid across a temperature range, in comparison with paclitaxel and docetaxel, showed that only the binding of cyclostreptin to microtubules was markedly reduced at 4 degrees C versus temperatures over 30 degrees C. The binding of cyclostreptin to microtubules was characterized by a relatively greater endothermic and entropic profile as compared with those of the taxoid binding reactions, which are characterized more by exothermic and enthalpic interactions. Molecular modeling showed that cyclostreptin formed a pharmacophore with taxoids but formed hydrogen bonds only with the S9-S10 and M loops in the taxoid site. Initial studies also indicate that, relative to paclitaxel, cyclostreptin is more deficient in nucleation than elongation of polymer.     

Antitumor agents. 256. Conjugation of paclitaxel with other antitumor agents: evaluation of novel conjugates as cytotoxic agents

Sixteen different taxoid conjugates were prepared by linking various anticancer compounds, including camptothecin (CPT), epipodophyllotoxin (EP), colchicine (COL), and glycyrrhetinic acid (GA), at the 2'- or 7-position on paclitaxel (TXL, 1) through an ester, imine, amine, or amide bond. Newly synthesized conjugates were evaluated for cytotoxic activity against replication of several human tumor cell lines. Among them, TXL-CPT conjugates, 8-10, were more potent than TXL itself against the human prostate carcinoma cell line PC-3 (ED(50)=14.8, 3.1, 19.4nM compared with 55.5nM), and conjugate 10 was also 8-fold more active than TXL against the LN-CAP prostate cancer cell line. These compounds also possessed anti-angiogenesis ability as well as lower inhibitory effects against a normal cell line (MRC-5). Thus, conjugates 8-10 are possible antitumor drug candidates, particularly for prostate cancer.     

Synthesis and evaluation of water-soluble docetaxel prodrugs-docetaxel esters of malic acid

The synthesis of docetaxel esters of malic acid is described. These compounds were found to have greatly improved water solubility and are stable in solution at neutral pH. The C2' modified compounds 2a-c and 3a-c behave as prodrugs, that is, docetaxel is generated upon exposure to human plasma, whereas the C7 and C2',7,10- l modified derivatives do not. 2'-dl-Malyl docetaxel sodium salt demonstrated enhanced antitumor activity in vitro when compared to docetaxel and showed the inhibitory effect on tumor growth in vivo.     

Synthesis and biological evaluation of imidazol-2-one derivatives as potential antitumor agents

A new series of aryl substituted imidazol-2-one derivatives structurally related to combretastatin A-4 (CA-4) were synthesized and evaluated for their cytotoxic activities in vitro against various human cancer cell lines including MDR cell line. The cytotoxic effects of compounds 7b and 7i proved to be similar to or greater than that of docetaxel. The highly active compound 7b also exhibited excellent inhibitory activity on tumor growth in vivo.     

Synthesis and hypoxic-cytotoxic activity of some 3-amino-1,2,4-benzotriazine-1,4-dioxide derivatives

A series of 3-amino-1,2,4-benzotriazine-1,4-dioxide derivatives 1 have been synthesized and evaluated for their cytotoxic activity in vitro against human leukemia cell lines: Molt-4, K562, HL60, human liver cancer cell Hep-G2, human prostate cancer cell PC-3 in hypoxia. Most of the compounds showed more potent activity than TPZ. Compounds 1i and 1m displayed encouraging superior activity against Molt-4 and HL-60 cell lines. Three potential derivatives received the test of the activity in hypoxia and in normoxia against Molt-4 and HL-60 cell lines and showed obvious hypoxia selectivity. Further mechanism study revealed that the cytotoxic activities of compounds 1i and 1k in Molt-4 cells might be mediated by modulation of p53 protein expression and mitochondrial membrane potential (DeltaPsi(m)).     

Synthesis and biological evaluation of novel 3-benzylcoumarin-imidazolium salts

A series of novel 3-benzylcoumarin-imidazolium salts were prepared and evaluated in vitro against a panel of human tumor cell lines. The results showed that the existence of 5,6-dimethyl-benzimidazole ring and substitution of the imidazolyl-3-position with a naphthylacyl group were vital for modulating cytotoxic activity. Notably, compound 38 was found to be the most potent derivative with IC₅₀ values of 2.04–4.51 μM against five human tumor cell lines, while compound 34 were more selective to SW-480 cell lines with IC₅₀ value 40.0-fold lower than DDP. Mechanism of action studies indicated that compound 38 can cause the G0/G1 phase cell cycle arrest and apoptosis in SMMC-7721 cell lines.     

Synthesis and anticancer activity of 5'-chloromethylphosphonates of 3'-azido-3'-deoxythymidine (AZT)

A series of novel N-alkyl 5'-chloromethylphosphonates of 3'-azido-3'-deoxythymidine (6-15) was synthesized by means of phosphonylation of 3'-azido-3'-deoxythymidine (4) with P-chloromethylphosphonic ditriazolide (3) followed by a reaction with the appropriate amine. The synthesized phosphonamidates 6-15 were evaluated for their cytotoxic activity in two human cancer cell lines: oral (KB) and breast (MCF-7) using the sulforhodamine B (SRB) assay. The highest activity in KB human cancer cells was displayed by phosphonamidate 8 (IC(50)=5.8 μg/mL), however, this compound was less potent than the parent AZT (IC(50)=3.1 μg/mL). Phosphonamidate 10 showed only moderate activity (IC(50)=12.1 μg/mL) whereas the other phosphonamidates proved inactive. Similarly, the highest activity in MCF-7 human cancer cells was displayed by phosphonamidate 8 (IC(50)=3.7 μg/mL) but it proved somewhat less active than AZT (IC(50)=2.6 μg/mL). Some activity was also displayed by phosphonamidate 10 (IC(50)=12.8 μg/mL) but the other phosphonamidates were found inactive. Hydrolysis studies indicate that the synthesized phosphonamidates are likely to act as prodrugs of the parent nucleoside (AZT). Transport measurements showed that the most active phosphonamidates (8 and 10) were able to permeate across the intestinal epithelium in vitro. The apparent permeability coefficients determined in Caco-2 cell monolayers indicated that these compounds could be moderately absorbed in humans.     

Nitroarylmethylcarbamate prodrugs of doxorubicin for use with nitroreductase gene-directed enzyme prodrug therapy

A series of nitrobenzyl- and nitroimidazolylmethyl carbamate prodrugs of doxorubicin were prepared and evaluated for their potential use in nitroreductase (NTR) mediated gene-directed enzyme prodrug therapy (GDEPT). The carbamate prodrugs and doxorubicin were tested in a cell line panel comprising parental and NTR transfected human (SKOV3/SKOV3-NTR(neo), WiDr/WiDr-NTR(neo)), Chinese hamster (V79/V79-NTR(puro)) and murine (EMT6/EMT6-NTR(puro)) cell line pairs, and were compared with the established NTR substrates CB 1954 (an aziridinyl dinitrobenzamide) and the analogous dibromomustard SN 29427. The low solubility of the prodrugs (from 3 to 39 microM) precluded the determination of IC(50) values against the parent cell lines in some instances. All of the prodrugs were unstable in culture medium with 5% added fetal calf serum over a 24h period, although release of doxorubicin was not observed. The prodrugs were 20- to >336-fold less toxic than doxorubicin in the human cells lines SKOV3 and WiDr, with overall less deactivation seen in the V79 cell line (11- to >286-fold) and EMT6 cell line (1.8- to >178-fold). Prodrugs with the nitrobenzyl unit directly conjugated to doxorubicin showed modest selectivity for NTR across the cell line panel (1- to 5.9-fold) but this was increased to between >10- and >370-fold with the interpolation of an 4-aminobenzyl spacer unit between the bioreductive unit and doxorubicin. A 2-nitroimidazolylmethyl carbamate provided deactivation of doxorubicin (8- to 124-fold) but showed only modest selectivity for NTR (2- to 14-fold) across the panel. The interpolation of a 4-aminobenzyl spacer gave slightly lower deactivation (3- to 64-fold) and similar selectivity for NTR (>1.2- to >12-fold) for 2- and 5-nitroimidazolylmethyl prodrugs. The activity of two nitrobenzyl prodrugs containing an aminobenzyl spacer, providing excellent selectivity for NTR+ve cells in culture, was evaluated against EMT6 tumours comprising ca. 10% NTR+ve cells, but neither showed statistically significant levels of killing even of NTR+ve cells. This lack of activity in tumours, despite potent and selective activity in culture, indicates that pharmacokinetic optimization is needed to achieve in vivo efficacy against solid tumours with this new class of NTR prodrugs.     

Biological evaluation of new antitumor taxoids: Alteration of substitution at the C-7 and C-10 of docetaxel

A series of new docetaxol analogues have been designed and synthesized. And their cytotoxicities against cancer cells have been evaluated by MTT method. Most of these compounds showed selective inhibitions on human cancer cell lines. Among them, compound 8 exhibited higher inhibitory activity than Paclitaxel (Taxol) against several cancer cell lines. This work indicated that appropriate modification at C-7 and C-10 of docetaxel might be a promising approach for this unique class of anticancer compounds.     

Synthesis and cytotoxic activities of novel hybrid 2-phenyl-3-alkylbenzofuran and imidazole/triazole compounds

A series of novel hybrid compounds of 2-phenyl-3-alkylbenzofuran and imidazole or triazole were prepared and evaluated in vitro against a panel of human tumor cell lines. The results suggest that the 2-ethyl-imidazole ring, and substitution of the imidazolyl-3-position with a 2-bromobenzyl or naphthylacyl group, were vital for modulating inhibitory activity. In particular, hybrid compound 31 was found to be the most potent derivative with IC₅₀ values of 0.08–0.55 μM against five strains human tumor cell lines and was found to be more selective against breast carcinoma (MCF-7) and colon carcinoma (SW480) (IC₅₀ values 40.8-fold and 40.1-fold lower than cisplatin (DDP)).     

Synthesis and preclinical characterization of a paclitaxel prodrug with improved antitumor activity and water solubility

The development of novel chemotherapy strategies based on prodrugs remains a major challenge for effective treatment of malignancies. We tested the hypothesis that this can be achieved by a prodrug of paclitaxel where one biologically active center, represented by the C7 hydroxyl group, was blocked by a dihydroxypropyl side chain which can be hydrolytically cleaved by a pH-dependent, slow-release mechanism. The prodrug was synthesized by condensation of solketal chloroformate with the C7 hydroxyl group of paclitaxel followed by a ring-opening reaction to the dihydroxyl derivative. The cytotoxicity of the prodrug was similar to paclitaxel, when tested in vitro against a variety of human tumor cell lines. In vitro cell cycle analysis indicated that concentrations within the micromolar range of both drug and prodrug are required to induce sufficient G2M arrest. The hydrophilic paclitaxel prodrug proved to be more than 50-fold more water soluble than the parental drug and effectively converted to paclitaxel by pH dependent hydrolysis. Importantly, the prodrug could be used at a 3-fold higher maximum tolerated dose (MTD) and revealed a markedly improved antitumor activity in mice compared to paclitaxel. Taken together, our results demonstrate, that a hydrolytically activated paclitaxel prodrug exhibits greater water solubility and superior antitumor activity than the parental drug.     

The effect of a bromide leaving group on the properties of nitro analogs of the duocarmycins as hypoxia-activated prodrugs and phosphate pre-prodrugs for antitumor therapy

Nitro seco analogs (nitroCBIs) of the antitumor antibiotic duocarmycins are a new class of hypoxia activated prodrugs. These compounds undergo hypoxia-selective metabolism to form potent DNA alkylating agents. A series of four nitroCBI alcohol prodrugs containing a bromide rather than chloride or sulfonate leaving group was synthesized. In assays for in vitro hypoxia-selective cytotoxicity against human tumor cell lines the two bromides with DNA minor groove binding basic side chains displayed hypoxic cytotoxicity ratios (HCRs) of 52-286 in HT29 cells and 41-43 in SiHa cells. These values compare well with a related previously reported chloride analog. The corresponding more water soluble phosphate pre-prodrugs of the bromides were synthesized and evaluated for in vivo antitumor activity against SiHa human tumor xenografts. All four phosphates, with both neutral and basic side chains, demonstrated activity providing statistically significant hypoxic log(10) cell kills of 0.87-2.80 at non-toxic doses, matching or proving superior to those of their chloride analogs.     

Synthesis and antitumor activity of water-soluble duocarmycin B1 prodrugs

The water-soluble duocarmycin B1 prodrugs such as glycoside 3, phosphate 4 and carbamate 5 were synthesized for improving biological and pharmaceutical profiles of duocarmycin. Among these prodrugs, N-methylpiperazinylcarbamoyl derivative 5 exhibited potent antitumor activity against several human tumors in vivo.     

Design,Synthesis and In Vitro Activity of Anticancer Styrylquinolines. The p53 Independent Mechanism of Action

A group of styrylquinolines were synthesized and tested for their anti-proliferative activity. Anti-proliferative activity was evaluated against the human colon carcinoma cell lines that had a normal expression of the p53 protein (HCT116 p53^+/+) and mutants with a disabled TP53 gene (HCT116 p53^-/-) and against the GM 07492 normal human fibroblast cell line. A SAR study revealed the importance of Cl and OH as substituents in the styryl moiety. Several of the compounds that were tested were found to have a marked anti-proliferative activity that was similar to or better than doxorubicin and were more active against the p53 null than the wild type cells. The cellular localization tests and caspase activity assays suggest a mechanism of action through the mitochondrial pathway of apoptosis in a p53-independent manner. The activity of the styrylquinoline compounds may be associated with their DNA intercalating ability.     

Antiproliferative activity of flavonoids on several cancer cell lines.

Twenty-seven Citrus flavonoids were examined for their antiproliferative activities against several tumor and normal human cell lines. As a result, 7 flavonoids were judged to be active against the tumor cell lines, while they had weak antiproliferative activity against the normal human cell lines. The rank order of potency was luteolin, natsudaidain, quercetin, tangeretin, eriodictyol, nobiletin, and 3,3',4',5,6,7,8-heptamethoxyflavone. The structure-activity relationship established from comparison among these flavones and flavanones showed that the ortho-catechol moiety in ring B and a C2-C3 double bond were important for the antiproliferative activity. As to polymethoxylated flavones, C-3 hydroxyl and C-8 methoxyl groups were essential for high activity.     

Synthesis,in vitro and in vivo evaluation of 3-arylisoquinolinamines as potent antitumor agents

In the search for potent water-soluble 3-arylisoquinolines, several 3-arylisoquinolinamines were designed and synthesized. Various substituted 3-arylisoquinolinamines exhibited strong cytotoxic activity against eight different human cancer cell lines. In particular, C-6 or C-7 dimethylamino-substituted 3-arylisoquinolinamines displayed stronger potency than the lead compound 7a. Interestingly, compounds 7b and 7c showed more effective activity against paclitaxel-resistant HCT-15 human colorectal cancer cell lines when compared to the original cytotoxic cancer drug, paclitaxel. We analyzed the cell cycle dynamics by flow cytometry and found that treatment of human HCT-15 cells with 3-arylisoquinolinamine 7b blocked or delayed the progression of cells from G0/G1 phase into S phase, and induced cell death. Treatment with compound 7b also significantly inhibited the growth of tumors and enhanced tumor regression in a paclitaxel-resistant HCT-15 xenograft model.