Kalanchosides A-C, new cytotoxic bufadienolides from the aerial parts of Kalanchoe gracilis.

[Structure: see text] Three new compounds, kalanchosides A-C (1-3), as well as five known compounds, were isolated from the aerial parts of Kalanchoe gracilis. The compound structures were determined by spectroscopic methods. All eight isolated compounds showed significant cytotoxic activity against a panel of human tumor cell lines, with potency reaching the nanomolar range. However, only bryophyllin B (8) inhibited HIV replication in H9 lymphocyte cells.

New acridone inhibitors of human herpes virus replication.

Modern biomedicinal research with acridones began with plant secondary metabolites but the successful development of these alkaloids into drugs has yet to be realized. However, there are synthetic acridones unrelated to the natural products now emerging as promising bioactive compounds. The purpose of this mini-review is to highlight the renewed interest in acridones for antiviral drug research, with the emphasis placed on several derivatives in early stage development for treating herpes virus infection. Novel anti-herpes acridones developed using a ligand-based approach have much simpler structure and generally have higher selectivity than the corresponding alkaloids. Three sub-types are currently classified on the basis of activity against Herpes Simplex Virus (HSV) and, or Human Cytomegalovirus (HCMV) and all of them inhibit viral replication post-adsorption. In terms of mode/mechanism of action, this "second wave" of early generation lead molecules appears unique in comparison to the natural products and to drugs derived from more traditional templates. Inhibition of HSV replication by these agents is best understood and it occurs after viral DNA synthesis. The mechanism for one prototype inhibitor (5-chloro-1,3-dihydroxy acridone), involves a blockade of viral DNA maturation (cleavage/packaging) and viral capsids accumulate abnormally. Interestingly, the 7-Chloro regioisomer blocks a later stage of viral assembly. At this time it is unclear whether atypical target-interaction or unusual polypharmacology is responsible for the antiviral activities observed and this key issue will hamper future drug development until it is resolved.

Cell culture replication of herpes simplex virus and, or human cytomegalovirus is inhibited by 3,7-dialkoxylated, 1-hydroxyacridone derivatives.

The synthetic acridone compound, 5-chloro-1,3-dihydroxyacridone inhibits herpes simplex virus (HSV) replication by inducing the formation of defective viral (B-type) capsids [Antiviral Res. 53 (2002) 113]. In this report, synthetic elaboration of the 1-hydroxyacridone scaffold coupled with antiviral testing led to the identification of 3,7-dimethoxy-1-hydroxy-acridone (2) as an inhibitor of low multiplicity human cytomegalovirus (HCMV) infection (ED(50) value of 1.4 microM (0.5 microg/ml); greater than 35-fold selectivity). Compound 2 was inactive against HSV replication and the efficacy as an anti-HCMV agent at higher viral loads was only apparent if host cells were replicated in the presence of the compound prior to infection. Interestingly, the 3,5-dimethoxy regioisomer inhibited cell replication (mean CC(50) 33 microM) and was inactive as a selective anti-herpes agent. A limited parallel synthesis and testing of ten 3,7-dialkoxylated compounds closely related to compound 2 led to the discovery of the 3-ethoxy-, 3-propoxy-, 3-isopropoxy- and 3-allyloxy-derivatives as dual inhibitors of both HSV and HCMV (selectivity of the 3-allyloxy analog was greater than 10- and 36-fold, respectively). The 3-benzyloxy-derivative was active (ED(50) value of 6.9 microM) against HCMV only. Moreover, the corresponding C-7 variable alkoxylated parallel series were either weakly active or inactive antiviral agents suggesting an apparent requirement for a C-7 methoxy substituent in the active structure. Exploratory mode of action studies showed that dual inhibitors were most active against a low multiplicity HSV infection and potent inhibition of viral release likely contributed to this. Furthermore, suppression of late viral protein synthesis by dual inhibitors did not correlate with anti-HSV activity. On the basis of the present findings, the 1-hydroxyacridone scaffold is further expanded as a useful template for the discovery of investigational anti-herpes agents. As a group, the active 3,7-dialkoxylated compounds likely have diverse mechanisms of action, consequently they are of potential medicinal interest.

The antiviral agent 5-chloro-1,3-dihydroxyacridone interferes with assembly and maturation of herpes simplex virus.

Antiviral drug screening and exploratory mechanistic work identified 5-chloro-1,3-dihydroxyacridone as a lead inhibitor of herpes simplex virus (HSV) replication, one without a primary effect on either HSV DNA or late viral protein synthesis (Antivir. Res. 45 (2000) 123). In this report, drug effects on viral DNA cleavage and packaging, HSV capsid production and virion morphogenesis in infected Vero cells were studied systematically in order to better localize the sensitive stage of the replication cycle. Maturation of replicating HSV DNA and virion production at late times were inhibited in the same dose-dependent fashion, suggesting that the drug might directly inhibit the cleavage and packaging processes. Based on density centrifugation analysis however, this possibility appears unlikely because overproduction of neither A- or B-capsids occurred upon drug treatment. Interestingly, similar studies coupled with either Western immunoblot or ultrastructural analysis showed that B-capsids with apparent normal protein composition accumulated at reduced levels (maximally about two- to three-fold) in drug-treated cells. Limited attempts to isolate drug-resistant viral mutants using standard approaches proved unsuccessful. In summery, 5-chloro-1,3-dihydroxyacridone inhibits one or more steps of HSV assembly since treatment results in reduced levels of capsids (particularly B-type) and reduced levels of encapsidated DNA. The action of the acridone derivative is an unusual one, with distinctive features when compared to a recently reported class of HSV encapsidation inhibitor and to the late replication defects of relevant viral mutants.

Simple isoquinoline and benzylisoquinoline alkaloids as potential antimicrobial, antimalarial, cytotoxic, and anti-HIV agents.

Twenty-six simple isoquinolines and 21 benzylisoquinolines were tested for antimicrobial, antimalarial, cytotoxic, and anti-HIV activities. Some simple isoquinoline alkaloids were significantly active in each assay, and may be useful as lead compounds for developing potential chemotherapeutic agents. These compounds include 13 (antimicrobial), 25, 26, and 42 (antimalarial), 13 and 25 (cytotoxic), and 28 and 29 (anti-HIV). A quaternary nitrogen atom of isoquinolium or dihydroisoquinolinium type may contribute to enhanced potency in the first three types of activities. In contrast, anti-HIV activity was found with tetrahydroisoquinoline and 6,7-dihydroxyisoquinolium salts.

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, DNA cross-linking activity, and cytotoxicity of dimeric mitomycins.

Dimeric DNA cross-linking compounds have emerged as important new antitumor agents. We report the synthesis and biochemical evaluation of a select set of dimeric mitomycins in which the two mitomycin units are tethered at either the mitomycin C(7) amino or the aziridine N(1a) positions. Significantly, mitomycin C (1) itself is the prototypical bioreductive DNA cross-linking agent. DNA cross-linking experiments using a denaturing-gel-electrophoresis-based assay showed that the extent of DNA cross-linking for select dimeric mitomycins can exceed that of the parent compound, mitomycin C, and that the reaction proceeds, in part, at the two distal C(1) sites in the mitomycins. The efficiency of DNA cross-linking depended on the nature of the linker and the position of linker unit's attachment. When we compared the efficiency of DNA cross-linking for the dimeric mitomycins with their in vitro cytotoxicities in cultured human tumor cells, we observed a poor correlation. The mitomycins that gave the highest levels of DNA cross-linked adducts displayed the weakest cytotoxicities. These findings determined that the denaturing-gel-electrophoresis-based assay was a poor predictor of cytotoxic activity.

Cytotoxic pheophorbide-related compounds from Clerodendrum calamitosum and C. cyrtophyllum.

Three pheophorbide-related compounds (1-3) were isolated from the leaves and stems of Clerodendrum calamitosum. The methyl ester of 3 (6) and the known (10S)-hydroxypheophytin a (7) also were isolated from leaves of the related plant Clerodendrum cyrtophyllum. Compounds 1 and 6 were isolated for the first time as naturally occurring products from a plant source. All structures were elucidated by detailed spectroscopic analysis. Biological evaluation showed that 1 and 2 exhibited strong cytotoxicity against human lung carcinoma (A549), ileocecal carcinoma (HCT-8), kidney carcinoma (CAKI-1), breast adenocarcinoma (MCF-7), malignant melanoma (SK-MEL-2), ovarian carcinoma (1A9), and epidermoid carcinoma of the nasopharynx (KB), and its etoposide- (KB-7d), vincristine- (KB-VCR), and camptothecin-resistant (KB-CPT) subclones. Compound 3 was less cytotoxic than 1 and 2. Compounds 4-6, the methyl esters of 1-3, showed strongly increased cytotoxicity compared with the parent acids. Interestingly, 6 was the most active derivative among these compounds. Compound 7 was inactive.

Anti-HIV and cytotoxic activities of Ru(II)/Ru(III) polypyridyl complexes containing 2,6-(2'-benzimidazolyl)-pyridine/chalcone as co-ligand.

Ru(II)/Ru(III) polypyridyl complexes containing 2,6-(2'-benzimidazolyl)-pyridine or chalcone as co-ligands were synthesized and characterized previously (Mishra, L.; Sinha, R. Indian J. Chem., Sec. A 2001, in press. Mishra, L.; Sinha, R. Indian J. Chem., Sec. A, 39A, 2000, 1131). Their interaction with aqueous buffered calf thymus DNA was measured. (Novakova, O.; Kasparkova, J.; Vrana, O.; van Vliet, P. M., Reedijk, J.; Brabec, V., Biochem. 34, 1995, 12369 and these results prompted additional screening for anti-HIV (human immunodeficiency virus) activity against DNA replication in H9 lymphocytes and cytotoxic activity against eight tumor cell lines. The most active compounds were 17 in the former assay (EC(50) < 0.1 microg/mL and TI > 23.1) and 3, 8, 10, and 14 in the latter assay, especially selectively against the 1A9 ovarian cancer cell line (IC(50) = 4.1, 3.8, 3.6, and 2.5 microg/mL, respectively).

Antitumor agents. Part 204: synthesis and biological evaluation of substituted 2-aryl quinazolinones.

A series of 2',3',4',6,7-substituted 2-aryl quinazolinones were synthesized and evaluated for biological activity. Among them, 17 displayed significant growth inhibitory action against a panel of tumor cell lines. Compound 17 was also a potent inhibitor of tubulin polymerization. Compounds 8-10 displayed selective activity against P-gp-expressing epidermoid carcinoma of the asopharynx.

Antitumor agents. 207. Design, synthesis, and biological testing of 4beta-anilino-2-fluoro-4'-demethylpodophyllotoxin analogues as cytotoxic and antiviral agents.

2-Fluoropodophyllotoxin (11) and several 4beta-anilino-2-fluoro-4'-O-demethyl analogues were synthesized and evaluated in both antineoplastic and antiviral assays. These compounds were moderately active against some cancer cell lines, but they were less active than the corresponding nonfluorinated analogues. Compound 11 exhibited the best activity against KB carcinoma with a GI(50) of approximately 30 nM. Most compounds exhibited moderate activity against HCMV with ID(50) and ID(90) values in the range of 1 microM and 4 microM, respectively. Both 9 and 11 showed an unusual 10-fold selectivity for HSV-2 compared to HSV-1.

Novel mechanism of cellular DNA topoisomerase II inhibition by the pyranonaphthoquinone derivatives alpha-lapachone and beta-lapachone.

PURPOSE: The mechanisms of intracellular topoisomerase II inhibition by the pyranonaphthoquinone derivatives alpha-lapachone and beta-lapachone were studied. METHODS: Cell-based mechanistic studies were designed based on the in vitro mechanisms [17] and primarily involved the use of cultured KB (nasopharyngeal tumor cells) cells and the etoposide-resistant sub-line KB-7d. RESULTS: The KB-7d cells exhibited collateral sensitivity to alpha-lapachone; this supports the possibility of catalytic inhibition of topoisomerase II in the cells. Interestingly, both compounds induced an increase (two- to threefold) in reversible double-stranded DNA breaks in cell lines with a reduced expression of topoisomerase II. However, these drug-induced DNA breaks became irreversible at treatment times greater than 1 h. Studies showed that DNA breaks in KB-7d cells were not caused by endonucleases. Use of antioxidants abolished the appearance of cellular DNA breaks; this suggests involvement of the oxidation-reduction cycle of pyranonaphthoquinones in topoisomerase II inhibition; however, irreversible DNA breaks were not a result of drug-induced oxidative stress. CONCLUSIONS: On the basis of the findings, it is proposed that the compounds, on longer incubation with cells, induce abortive dissociation of topoisomerase II from the DNA, leading to an irreversible accumulation of high molecular weight DNA fragments. In addition to establishing topoisomerase II as an intracellular target of alpha-lapachone, the results suggest that both compounds can be classified as neither typical poisons nor as typical catalytic inhibitors of the enzyme. In summary, both compounds are members of a new inhibitor class, and alpha-lapachone, in particular, can be considered a potential lead for the development of drugs to treat multidrug-resistant cell lines with lower expression of topoisomerase II.

Novel mechanisms of DNA topoisomerase II inhibition by pyranonaphthoquinone derivatives-eleutherin, alpha lapachone, and beta lapachone.

Pyranonaphthoquinones have diverse biological activities against Gram-positive bacteria, fungi, and mycoplasms, and, recently, there has also been an increasing interest in their anti-cancer activity. This study includes three derivatives: eleutherin (compound 1), beta lapachone (compound 2), and its structural isomer, alpha lapachone (compound 3). The mechanism of topoisomerase II inhibition by the three derivatives was examined systematically with respect to the steps of the catalytic cycle of the enzyme. Etoposide, the prototypical enzyme poison, was used as a control and in combination with compounds 1-3 to localize their mechanism of action. The study revealed that eleutherin (1) and beta lapachone (2) inhibited topoisomerase II by inducing religation and dissociation of the enzyme from DNA in the presence of ATP. Whereas compound 2 was an "irreversible" inhibitor of topoisomerase II, compound 1 merely slowed the catalytic cycle of the enzyme. alpha Lapachone (3), on the other hand, inhibited initial non-covalent binding of topoisomerase II to DNA and, in addition, induced religation of DNA breaks (even in pre-established ternary complexes) before dissociating the enzyme from DNA. Compound 3 was an "irreversible" inhibitor of topoisomerase II. The diverse and unique mechanisms of topoisomerase II inhibition by pyranonaphthoquinone derivatives reveal novel ways to target the enzyme with potential for anti-cancer drug design.

Antitumor agents. 203. Carbazole alkaloid murrayaquinone A and related synthetic carbazolequinones as cytotoxic agents.

Murrayaquinone A (1) and murrayafoline A (3), isolated from the root bark of Murraya euchrestifolia, were identified as cytotoxic compounds. Murrayaquinone A (1) demonstrated significant cytotoxicity against SK-MEL-5 and Colo-205 cells, with ED(50) values of 2.58 and 3.85 microg/mL, respectively. In contrast, murrayafoline A (3) exhibited marginal or weak cytotoxicity against SK-MEL-5, Colo-205, HCT-8, KB, and A-549 tumor cell lines, with ED(50) values ranging from 5.31 to 7.52 microg/mL. In total, 20 carbazole alkaloids (1-20), isolated previously by Furukawa et al. from various plant sources were also evaluated for their cytotoxic profiles in the NCI's human disease-oriented, 60-cell line, in vitro antitumor screening protocol. Compounds 3 and 15 showed potent cell-line selective cytotoxicity against MOLT-4 cells, with log GI(50) values of -8.60 and -8.49 M, respectively, while 12 demonstrated better selectivity against the colon cancer subpanel. Moreover, synthetic 2-methyl- or 3-methyl-carbazolequinone derivatives with various substituents in the A-ring were evaluated against KB, SK-MEL-5, Colo-205, and HCT-8 tumor cells. 6-Methoxy- (21), 6-methyl- (22), and 6-chloro- (24) 3-methyl-carbazolequinones demonstrated significant cytotoxicity against SK-MEL-5 cells, with ED(50) values of 0.55, 0.66, and 0.83 microg/mL, respectively. Compounds 21 and 22 were also significantly cytotoxic toward KB cells, with ED(50) values of 0.76 and 0.92 microg/mL, respectively, and 21 displayed a similar level of toxicity against Colo-205 cells (ED(50) 0.87 microg/mL).

Cytotoxity of non-alkaloidal taxane diterpenes from Taxus chinensis against a paclitaxel-resistant cell line.

Seven taxane diterpenes were isolated from the EtOH extract of the aerial parts of Taxus chinensis, and evaluated for cytotoxicity against nine human cell lines, including a beta-tublin mutant resistant to paclitaxel. Compound 2, a non-alkaloid-type taxane diterpene, showed significant cytotoxicity in most cell lines, and notably, equipotent against both parental and beta-tublin mutant tumor cell lines.

1,3-Dihydroxyacridone derivatives as inhibitors of herpes virus replication.

The nuclear enzyme DNA topoisomerase II is a candidate pharmacological target for treating herpes virus infections and the novel catalytic inhibitors, 7-chloro-1,3-dihydroxyacridone (compound 1), and 1,3,7-trihydroxyacridone (2) are potential lead compounds [Bastow, K.F., Itoigawa, M., Furukawa, H., Kashiwada, Y., Bori, I.D., Ballas, L.M., Lee, K.-H., 1994. Antiproliferative actions of 7-substituted 1,3-dihydroxyacridones; possible involvement of DNA topoisomerase II and protein kinase C as biochemical targets. Bioorg. Med. Chem. 2, 1403-1411; Vance, J.R., Bastow, K.F., 1999. Inhibition of DNA topoisomerase II catalytic activity by the antiviral agents 7-chloro,1,3-dihydroxyacridone and 1,3,7-trihydroxyacridone. Biochem. Pharmacol. 58, 703-708]. In this report, four new 1,3-dihydroxyacridone analogs with functional groups at either the 5-, 6- or 8-positions (compounds 3-6) were synthesized. Target compounds, three other analogs including compounds 1 and 2 and three anticancer drugs that inhibit DNA topoisomerase II (etoposide, amsacrine and aclarubicin) were then evaluated as selective inhibitors of herpes simplex virus (HSV) replication in cell culture and as enzyme inhibitors in vitro. Etoposide and amsacrine inhibited HSV but acted non-selectively. In general, the activities of 1,3-dihydroxyacridone derivatives as selective anti-HSV agents and as enzyme inhibitors varied inversely suggesting that DNA topoisomerase II probably is not the critical antiviral target. The 5-Cl congener (compound 3) was the most selective agent (about 26-fold under a stringent assay condition) but was not an enzyme inhibitor. Results of exploratory mechanistic studies with compounds 1 and 3 show that HSV replication was blocked at a stage after DNA and late protein synthesis. The acridone derivatives were also tested against human cytomegalovirus (HCMV) replication but none of them were active.

Antitumor agents. Part 202: novel 2'-amino chalcones: design, synthesis and biological evaluation.

New 4',5',2,3,4-substituted 2'-amino chalcones were synthesized and evaluated for cytotoxicity against a panel of human tumor cell lines. Several compounds displayed significant cytotoxicity. The most promising lead molecule (10) also had high activity toward multi-drug resistant KB-VIN, and ovarian 1A9 cell lines. 2'-Amino chalcones demonstrated significantly increased antitumor activity compared with the corresponding chalcones, while, the epoxide derivatives generally showed greatly reduced activity.

Characterization of human lung cancer cells resistant to 4'-O-demethyl-4beta-(2"-nitro-4"-fluoroanilino)-4-desoxypodophyllotoxin , a unique compound in the epipodophyllotoxin antitumor class.

A new semi-synthetic podophyllotoxin derivative, 4'-O-demethyl-4beta-2"-nitro-4"-fluoroanilino)-4-desoxypo dophyllotoxin (compound 1), an analog of GL-331 (compound 2), is a potent and broad-spectrum inhibitor of cultured human cancer and drug-resistant cell growth. In general, 4'-demethylepipodophyllotoxin analogs, including 2, exert anti-tumor activity by targeting the nuclear enzyme DNA topoisomerase II, but 1 is not an enzyme inhibitor. Unlike the cytotoxic activity of compound 2, cell killing by 1 is dose-limiting and a significant fraction of cells (30-40%) survive treatment. As an approach to investigate mechanism of action, 1-resistant A549 (human lung cancer) sub-lines were selected and characterized. Results of the work show that 1-resistant cells: (i) are moderately cross-resistant (2- to 3-fold) to various cytotoxic drugs via a P-glycoprotein-independent mechanism, (ii) have an altered growth habit, (iii) are deficient in normal attachment on plastic and collagen substrata, and (iv) have an altered plasma membrane protein composition including several proteins in the 140->200 kDa molecular mass range and a doublet of phosphoserine-containing proteins of about 135 kDa. Since 1 treatment of cells affects neither cellular attachment or membrane-protein phosphorylation, the changes observed in 1-resistant cells are interpreted as a survival response to drug action.

Unique biochemical, cytotoxic, and antitumor activity of camptothecin and 4beta-amino-4'-O-demethylepipodophyllotoxin conjugates.

Two compounds having a camptothecin (CPT) analog conjugated to the 4beta-amino-4'-O-demethylepipodophyllotoxin analog were evaluated for their biochemical and biological activities. W1[camptothecin-(para)-4beta-amino-4'-O-demethylepipodophyllotoxin] had no activity against topoisomerase II (TOP II), but inhibited topoisomerase I (TOP I) with an IC(50) value 2-fold higher than CPT. W2 [camptothecin-(ortho)-4beta-amino-4'-O-demethylepipodophyllotoxin] had inhibitory activity against TOP I and TOP II with IC(50) values 1.5-fold higher than either CPT or etoposide (VP-16). Both conjugates had similar cytotoxicity against the KB cell line, although the protein-linked DNA breaks (PLDBs) generated by W2 in KB cells were about 4-fold more than those of W1. No cross-resistance with the two conjugates was seen in a VP-16-resistant KB subline, which showed down-regulation of TOP II and overexpression of the multiple drug resistance-associated protein, or in a vincristine-resistant KB subline with overexpression of gp-170/mdr-1. The CPT-resistant KB variant (KB CPT 100), which has a reduction in TOP I content and another mechanism that occurs post-PLDB formation, was partially resistant to both compounds. W1 was not affected by this post-PLDB resistance mechanism. Cell cycle analysis demonstrated that W1 and W1 had similar cell cycle effects on KB and KB CPT 100 cells, which accumulated in S-phase upon drug treatment. These results suggested that W1 and W2 exerted their cytotoxicity through TOP I. In CPT-resistant cells, however, an unidentified target also may be involved in the cytotoxic action of W1 and TOP II may still be a target for W1. In vivo, W1 was more effective against the growth of human prostate cancer cells in nude mice than VP-16, CPT, or W2. Given its antitumor activity and unique biochemical mechanism of action, W1 warrants exploration as an antitumor compound.

Anti-HIV agents 45(1) and antitumor agents 205.(2) two new sesquiterpenes, leitneridanins A and B, and the cytotoxic and anti-HIV principles from Leitneria floridana.

Two new sesquiterpenes, leitneridanin A (1) and leitneridanin B (2), and seven known compounds, lirioresinol B, (-)-pinoresinal, (+)-lariciresinol, quassimarin (3), simalikalactone D (4), 1-methoxycanthinone (5), and 5-methoxycanthinone (6), were isolated from Leitneria floridana. Their structures were identified on the basis of spectral data. In vitro biological evaluation showed that 5 is a potent anti-HIV agent (EC(50) 0.26 g/mL; TI >39) and that 3-6 suppressed the growth of a panel of human tumor cell lines (KB, A-549, HCT-8, CAKI-1, MCF-7, and SK-MEL-2). Compounds 3 and 4 were significantly active, with ED(50) values in the range of 0.26-0.012 g/mL.