Camptothecins (CPTs) are cytotoxic natural alkaloids that specifically target DNA topoisomerase I. Research on CPTs has undergone a significant evolution from the initial discovery of CPT in the late 1960s through the study of synthetic small molecule derivatives to investigation of macromolecular constructs and formulations. Over the past years, intensive medicinal chemistry efforts have generated numerous CPT derivatives. Three derivatives, topotecan, irinotecan, and belotecan, are currently prescribed as anticancer drugs, and several related compounds are now in clinical trials. Interest in other biological effects, besides anticancer activity, of CPTs is also growing exponentially, as indicated by the large number of publications on the subject during the last decades. Therefore, the main focus of the present review is to provide an ample but condensed overview on various biological activities of CPT derivatives, in addition to continued up-to-date coverage of anticancer effects.
Camptothecins; DNA topoisomerase I; biological activities; structure-activity relationship
Podophyllotoxin (PPT), as well as its congeners and derivatives, exhibits pronounced biological activities, especially antineoplastic effects. Its strong inhibitory effect on tumor cell growth led to the development of three of the most highly prescribed anticancer drugs in the world, etoposide, teniposide, and the water-soluble prodrug etoposide phosphate. Their clinical success as well as intriguing mechanism of action stimulated great interest in further modification of PPT for better antitumor activity. The C-4 position has been a major target for structural derivatization aimed at either producing more potent compounds or overcoming drug resistance. Accordingly, numerous PPT derivatives have been prepared via hemisynthesis and important structure–activity relationship (SAR) correlations have been identified. Several resulting compounds, including GL-331, TOP-53, and NK611, reached clinical trials. Some excellent reviews on the distribution, sources, applications, synthesis, and SAR of PPT have been published. This review focuses on a second generation of new etoposide-related drugs and provides detailed coverage of the current status and recent development of C-4-modified PPT analogs as anticancer clinical trial candidates.
podophyllotoxin; cytotoxic agents; C-4 position; reviews
novel 20-sulfonylamidine derivatives (9a–9l) of camptothecin (1) were synthesized via
a Cu-catalyzed three-component reaction. They showed similar or superior
cytotoxicity compared with that of irinotecan (3) against
A-549, DU-145, KB, and multidrug-resistant (MDR) KBvin tumor cell
lines. Compound 9a demonstrated better cytotoxicity against
MDR cells compared with that of 1 and 3.
Mechanistically, 9a induced significant DNA damage by
selectively inhibiting Topoisomerase (Topo) I and activating the ATM/Chk
related DNA damage-response pathway. In xenograft models, 9a demonstrated significant activity without overt adverse effects
at 5 and 10 mg/kg, comparable to 3 at 100 mg/kg. Notably, 9a at 300 mg/kg (i.p.) showed no overt toxicity in contrast
to 1 (LD50 56.2 mg/kg, i.p.) and 3 (LD50 177.5 mg/kg, i.p.). Intact 9a inhibited
Topo I activity in a cell-free assay in a manner similar to that of 1, confirming that 9a is a new class of Topo
I inhibitor. 20-Sulfonylamidine 1-derivative 9a merits development as an anticancer clinical trial candidate.
Nineteen new halogenated diarylpyridinamine (DAPA) analogues (6a-n and 8a-e) modified on the phenoxy C-ring were synthesized and evaluated for anti-HIV activity and certain drug-like properties. Ten compounds showed high anti-HIV activity (EC50 < 10 nM). Particularly, (E)-6-(2”-bromo-4”-cyanovinyl-6“-methoxy)phenoxy-N2-(4′-cyanophenyl)pyridin-2,3-diamine (8c) displayed low nanomolar antiviral potency (3–7 nM) against wild-type and resistant viral strains with E138K or K101E mutation, associated with resistance to rilvipirine (1b). Compound 8c exhibited much lower resistance fold changes (RFC 1.1–2.1) than 1b (RFC 11.8–13.0). Compound 8c also exhibited better metabolic stability (in vitro half-life) than 1b in human liver microsomes (HLM), possessed low lipophilicity (clog D: 3.29; measured log P: 3.31), and had desirable lipophilic efficiency indices (LE > 0.3, LLE >5, LELP <10). With balanced potency and drug-like properties, 8c merits further development as an anti-HIV drug candidate.
anti-HIV activity; antiviral agents; diarylpyridinamine; drug-like properties; lipophiliicity
Herein, we evaluated the anti-cancer effect and molecular mechanisms of a novel betulinic acid (BA) derivative, SYK023, by using two mouse models of lung cancer driven by KrasG12D or EGFRL858R. We found that SYK023 inhibits lung tumor proliferation, without side effects in vivo or cytotoxicity in primary lung cells in vitro. SYK023 triggered endoplasmic reticulum (ER) stress. Blockage of ER stress in SYK023-treated cells inhibited SYK023-induced apoptosis. In addition, we found that the expression of cell cycle-related genes, including cyclin A2, B1, D3, CDC25a, and CDC25b decreased but, while those of p15INK4b, p16INK4a, and p21CIP1 increased following SYK023 treatment. Finally, low doses of SYK023 significantly decreased lung cancer metastasis in vitro and in vivo. Expression of several genes related to cell migration, including synaptopodin, were downregulated by SYK023, thereby impairing F-actin polymerization and metastasis. Therefore, SYK023 may be a potentially therapeutic treatment for metastatic lung cancer.
SYK023; ER stress; metastasis; synaptopodin
The 6-methoxy-1,2,3,4-tetrahydroquinoline moiety in prior leads 2-chloro- and 2-methyl-4-(6-methoxy-3,4-dihydroquinolin-1(2H)-yl)quinazoline (1a and 1b) was modified to produce 4-(N-cycloamino)quinazolines (4a–c and 5a–m). The new compounds were evaluated in cytotoxicity and tubulin inhibition assays, resulting in the discovery of new tubulin-polymerization inhibitors. 7-Methoxy-4-(2-methylquinazolin-4-yl)-3,4-dihydroquinoxalin- 2(1H)-one (5f), the most potent compound, exhibited high in vitro cytotoxic activity (GI50 1.9–3.2 nM), significant potency against tubulin assembly (IC50 0.77 μM), and substantial inhibition of colchicine binding (99% at 5 μM). In mechanism studies, 5f caused cell arrest in G2/M phase, disrupted microtubule formation, and competed mostly at the colchicine site on tubulin. Compound 5f and N-methylated analogue 5g were evaluated in nude mouse MCF7 xenograft models to validate their antitumor activity. Compound 5g displayed significant in vivo activity (tumor inhibitory rate 51%) at a dose of 4 mg/kg without obvious toxicity, whereas 5f unexpectedly resulted in toxicity and death at the same dose.
6-methoxy-1,2,3,4-tetrahydroquinoline moiety in prior leads
2-chloro- and 2-methyl-4-(6-methoxy-3,4-dihydroquinolin-1(2H)-yl)quinazoline (1a and 1b)
was modified to produce 4-(N-cycloamino)quinazolines
(4a–c and 5a–m). The new compounds were evaluated in cytotoxicity and tubulin
inhibition assays, resulting in the discovery of new tubulin-polymerization
2(1H)-one (5f), the most potent compound,
exhibited high in vitro cytotoxic activity (GI50 1.9–3.2
nM), significant potency against tubulin assembly (IC50 0.77 μM), and substantial inhibition of colchicine binding
(99% at 5 μM). In mechanism studies, 5f caused
cell arrest in G2/M phase, disrupted microtubule formation, and competed
mostly at the colchicine site on tubulin. Compound 5f and N-methylated analogue 5g were evaluated in nude
mouse MCF7 xenograft models to validate their antitumor activity.
Compound 5g displayed significant in vivo activity (tumor
inhibitory rate 51%) at a dose of 4 mg/kg without obvious toxicity,
whereas 5f unexpectedly resulted in toxicity and death
at the same dose.
Structural optimizations of the prior lead 1a led to the discovery of a series of N-aryl-6-methoxy-1,2,3,4-tetrahydroquinoline derivatives as a novel class of tubulin polymerization inhibitors targeted at the colchicine binding site. The most active compound 6d showed extremely high cytotoxicity against a human tumor cell line panel (A549, KB, KBvin, and DU145) with GI50 values ranging from 1.5 to 1.7 nM, significantly more potent than paclitaxel, especially against the drug-resistant KBvin cell line, in the same assays. Analogues 5f, 6b, 6c, and 6e were also quite potent, with a GI50 range of 0.011–0.19 μM. In further studies, active compounds 6b–6e and 5f significantly inhibited tubulin assembly, with IC50 values of 0.92 to 1.0 μM and strongly inhibited colchicine binding to tubulin, with inhibition rates of 75–99% (at 5 μM), comparable with or more potent than combretastatin A-4 (IC50 0.96 μM). Current studies included design, synthesis, and biological evaluations of 24 new compounds (series 3–6). Related SAR analysis, molecular modeling, and evaluation of essential drug-like properties, i.e. water solubility, log P, and in vitro metabolic stability, were also performed.
N-aryl-6-methoxy-1,2,3,4-tetrahydroquinolines; cytotoxicity; tubulin polymerization inhibitors; colchicine binding site
Five novel tigliane-type diterpenes, stelleracins A–E (3–7), a novel flavanone dimer, chamaeflavone A (8), and six known compounds were isolated from roots of Stellera chamaejasme. Their structures were elucidated by extensive spectroscopic analyses. The isolated compounds were evaluated for anti-HIV activity in MT4 cells. New compounds 3–5 showed potent anti-HIV activity (EC90 0.00056–0.0068 μM) and relatively low or no cytotoxicity (IC50 4.4–17.2 μM). These new compounds represent promising new leads for development into anti-AIDS clinical trial candidates.
Bevirimat (1, BVM) is an anti-HIV agent that blocks HIV-1 replication by interfering with HIV-1 Gag-SP1 processing at a late stage of viral maturation. However, clinical trials of 1 have revealed a high baseline drug resistance that is attributed to naturally-occurring polymorphisms in HIV-1 Gag. To overcome the drug resistance, 28 new derivatives of 1 were synthesized and tested against compound 1-resistant (BVM-R) HIV-1 variants. Among them, compound 6 exhibited much improved activity against several HIV-1 strains carrying BVM-R polymorphisms. Compound 6 was at least 20-fold more potent than 1 against the replication of NL4-3/V370A, which carries the most prevalent clinical BVM-R polymorphism in HIV-1 Gag-SP1. Thus, compound 6 merits further development as a potential anti-AIDS clinical trial candidate.
Betulinic acid; Bevirimat; HIV-1; Maturation inhibitors; Bevirimat-resistance
Accumulation of aberrant protein aggregates, such as
peptide (Aβ), due to decreased proteasome activities, might
contribute to the neurodegeneration in Alzheimer's disease. In this
study, lithocholic acid derivatives 3α-O-pimeloyl-lithocholic
acid methyl ester (2) and its isosteric isomer (6) were found to activate the chymotrypsin-like activity of
the proteasome at an EC50 of 7.8 and 4.3 μM, respectively.
Replacing the C24 methyl ester in 2 with methylamide
resulted in a complete devoid of proteasome activating activity. Epimerizing
the C3 substituent from an α to β orientation transformed
the activator into a proteasome inhibitor. Unlike the cellular proteasome
activator PA28, proteasome activated by 2 was not inhibited
by Aβ. Furthermore, 2 potently antagonized the
inhibitory effect of Aβ on the proteasome. In summary, compound 2 represents a novel class of small molecules that not only
activates the proteasome but also antagonizes the inhibitory effect
of Aβ on the proteasome.
proteasome activator; lithocholic acid; Alzheimer's
disease; amyloid β
In a continuing study of bevirimat (2), the anti-HIV-maturation clinical trials agent, 28 new betulinic acid (BA, 1) derivatives were designed and synthesized. Among these compounds, 17, with a C-28 MEM ester moiety, and 22, with a C-28 ethyl hexanoate, increased the anti-HIV replication activity compared with 2 by two-fold, while compounds 40–41 and 48–49, with C-28 piperazine or piperidine amide substitutions, increased the activity by three- to fifteen-fold. The best new compound 41 exhibited an anti-HIV IC50 value of 0.0059 μM, compared with 0.087 μM for 2. All of the active compounds showed only anti-maturation effects, as confirmed by TZM-bl assay, in blocking the HIV replication. The results suggest that proper C-28 substitutions can further enhance the anti-maturation activity of 2, without any anti-entry effects. Thus, 41 may serve as a promising new lead for development of anti-AIDS clinical trial candidates.
This article reviews the antitumor and anti-HIV activities of naturally occurring triterpenoids, including the lupane, ursane, oleanane, lanostane, dammarane, and miscellaneous scaffolds. Structure–activity relationships of selected natural compounds and their synthetic derivatives are also discussed.
This review discusses recent progress in the development of anti-HIV agents targeting the viral entry process. The three main classes (attachment inhibitors, co-receptor binding inhibitors, and fusion inhibitors) are further broken down by specific mechanism of action and structure. Many of these inhibitors are in advanced clinical trials, including the HIV maturation inhibitor bevirimat, from the authors’ laboratories. In addition, the CCR5 inhibitor maraviroc has recently been FDA-approved. Possible roles for these agents in anti-HIV therapy, including treatment of virus resistant to current drugs, are also discussed.
HIV entry inhibitors; attachment inhibitors; co-receptor binding inhibitors; fusion inhibitors; maraviroc (MVC; UK-427, 857); enfuvirtide (T20;fuzeon); bevirimat (DSB;PA-457)
Twenty-one new 4-substituted diarylaniline compounds (DAANs) (Scheme 2, series 13, 14, and 15) were designed, synthesized, and evaluated against wild-type and drug resistant HIV-1 viral strains. As a result, approximately a dozen new DAANs showed high potency with low nano- to sub-nanomolar EC50 values ranging from 0.2 to 10 nM. The three most promising compounds 14e, 14h, and 15h exhibited high potency against wild-type and drug-resistant viral strains with EC50 values at the sub-nanomolar level (0.29–0.87 nM), and were comparable to or more potent than the new NNRTI drug riplivirine (2) in the same assays. Drug-like physicochemical property assessments revealed that the most active DAANs (EC50 <10 nM) have better aqueous solubility (>1–90 μg/mL at pH 7.4 and pH 2) and metabolic stability in vitro than 2, as well as desirable log P values (<5) and polar surface area (PSA) (<140 Å2). These promising results warrant further development of this novel compound class as potential potent anti-AIDS clinical trial candidates.
Betulinic acid derivatives modified at the C28 position are HIV-1entry inhibitors such as compound A43D; however, modified at the C3 position instead of C28 give HIV-1 maturation inhibitor such as bevirimat. Bevirimat exhibited promising pharmacokinetic profiles in clinical trials, but its effectiveness was compromised by the high baseline drug resistance of HIV-1 variants with polymorphism in the putative drug binding site. In an effort to determine whether the viruses with bevirimat resistant polymorphism also altered their sensitivities to the betulinic acid derivatives that inhibit HIV-1 entry, a series of new betulinic acid entry inhibitors were synthesized and tested for their activities against HIV-1 NL4-3 and NL4-3 variants resistant to bevirimat. The results show that the bevirimat resistant viruses were approximately 5- to10-fold more sensitive to three new glutamine ester derivatives (13, 15 and 38) and A43D in an HIV-1 multi-cycle replication assay. In contrast, the wild type NL4-3 and the bevirimat resistant variants were equally sensitive to the HIV-1 RT inhibitor AZT. In addition, these three new compounds markedly improved microsomal stability compared to A43D.
HIV-1; Entry inhibitor; Maturation inhibitor; Betulinic acid; Berivimat; Berivimat-resistance
Accumulation of aberrant protein aggregates, such as amyloid beta peptide (Aβ), due to decreased proteasome activities might contribute to the neurodegeneration in Alzheimer's disease. In this study, lithocholic acid derivatives 3α-O-pimeloyl-lithocholic acid methyl ester (2) and its isosteric isomer (6) were found to activate the chymotrypsin-like activity of the proteasome at an EC50 of 7.8 and 4.3 μM, respectively. Replacing the C24 methyl ester in 2 with methylamide resulted in a complete devoid of proteasome activating activity. Epimerizing the C3 substituent from an alpha to beta orientation transformed the activator into a proteasome inhibitor. Unlike the cellular proteasome activator PA28, proteasome activated by 2 was not inhibited by Aβ. Furthermore, 2 potently antagonized the inhibitory effect of Aβ on the proteasome. In summary, compound 2 represents a novel class of small molecules that not only activates the proteasome but also antagonizes the inhibitory effect of Aβ on the proteasome.
proteasome activator; lithocholic acid; Alzheimer's disease; amyloid beta
3-Hydroxymethyl-4-methyl-DCK (3, HMDCK) was discovered previously as a potent HIV non-nucleoside reverse transcriptase inhibitor (NNRTIs) (EC50: 0.004 μM, TI: 6225) with a novel mechanism of action. It exerts anti-HIV activity by inhibiting the production of HIV-1 double-stranded viral DNA from a single-stranded DNA intermediate, rather than blocking the generation of single-stranded DNA from a RNA template, which is the mechanism of action of current HIV-1 RT inhibitors. However, the insufficient metabolic stability of 3 limits its further clinical development. In the current study, a series of ester prodrugs of 3 was designed and synthesized to explore the new drug candidates as NNRTIs. The l-alanine ester prodrug 10 exhibited desirable pharmacokinetic properties in vitro and in vivo and showed improved oral bioavailability of 26% in rat, and would be a potential clinical candidate as a new anti-AIDS drug.
3-Hydroxymethyl-4-methyl-DCK; Synthesis; Pharmacokinetic; Prodrug
In the present study, a new strategy to link AZT with betulin/betulinic acid (BA) by click chemistry was designed and achieved. This conjugation via a triazole linkage offers a new direction for modification of anti-HIV triterpenes. Click chemistry provides an easy and productive way for linking two molecules, even when one of them is a large natural product. Among the newly synthesized conjugates, compounds 15 and 16 showed potent anti-HIV activity with EC50 values of 0.067 and 0.10 µM, respectively, which are comparable to that of AZT (EC50: 0.10 µM) in the same assay.
Betulin; Betulinic acid; AZT; Anti-HIV; Click chemistry
The current optimization of 2,4-diarylaniline analogs (DAANs) on the central phenyl ring provided a series of new active DAAN derivatives 9a–9e, indicating an accessible modification approach that could improve anti-HIV potency against wild-type and resistant strains, aqueous solubility, and metabolic stability. A new compound 9e not only exhibited extremely high potency against wild-type virus (EC50 0.53 nM) and several resistant viral strains (EC50 0.36 – 3.9 nM), but also showed desirable aqueous solubility and metabolic stability, which were comparable or better than those of the anti-HIV-1 drug TMC278 (2). Thus, new compound 9e might be a potential drug candidate for further development of novel next-generation NNRTIs.
Diarylaniline; NNRTIs; lead optimization; anti-HIV agents
Six 3′R,4′R-di-O-(S)-camphanoyl-2′,2′-dimethyldihydropyrano[2,3-f]chromone (DCP) and two 3′R,4′R-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) derivatives were designed, synthesized, and evaluated for inhibition of HIV-1NL4-3 replication in TZM-bl cells. 2-Ethyl-2′-monomethyl-1′-oxa- and -1′-thia-DCP (5a, 6a), as well as 2-ethyl-1′-thia-DCP (7a) exhibited potent anti-HIV activity with EC50 values of 30, 38 and 54 nM and therapeutic indexes of 152.6, 48.0 and 100.0, respectively, which were better than or comparable to those of the lead compound 2-ethyl-DCP in the same assay. 4-Methyl-1′-thia-DCK (8a) also showed significant inhibitory activity with an EC50 of 128 nM and TI of 237.9.
2′-Monomethyl-1′-oxa-DCP; 2′-Monomethyl-1′-thia-DCP; 2-Ethyl-1′-thia-DCP; 4-Methyl-1′-thia-DCK; Anti-HIV activity
In this study, 22 new betulinic acid (BA) derivatives were synthesized and tested for their inhibition of the chymotrypsin-like activity of 20S proteasome. From the SAR study, we concluded that the C-3 and C-30 positions are the pharmacophores for increasing the proteasome inhibition effects, and larger lipophilic or aromatic side chains are favored at these positions. Among the BA derivatives tested, compounds 13, 20, and 21 showed the best proteasome inhibition activity with IC50 values of 1.42, 1.56, and 1.80 µM, respectively, which are three- to four-fold more potent than the proteasome inhibition controls LLM-F and lactacystin.
In a continuing study of novel anti-HIV agents with drug-like structures and properties, 30 1′-O-, 1′-S-, 4′-O- and 4′-substituted-2′,3′-seco-3′-nor DCP and DCK analogues (8–37) were designed and synthesized. All newly synthesized seco-compounds were screened against HIV-1NL4-3 and a multiple reverse transcriptase (RT) inhibitor-resistant (RTMDR) strain in the TZM-bl cell line, using seco-DCK (7) and 2-ethyl-DCP (4) as controls. Several compounds (14, 18, 19, 22–24, and 32) exhibited potent anti-HIV activity with EC50 values ranging from 0.93 to 1.93 μM and therapeutic index (TI) values ranging from 20 to 39. 1′-O-Isopropoxy-2′,3′-seco-3′-nor-DCP (12) showed the greatest potency among the newly synthesized compounds with EC50 values of 0.47 and 0.88 μM, and TI of 96 and 51, respectively, against HIV-1NL4-3 and RTMDR strains. The seco-compounds exhibited better chemical stability in acidic conditions compared with DCP and DCK compounds. Overall, the results suggested that seco-DCP analogues with simplified structures may be more favorable for development as novel anti-HIV candidates.
2′, 3′-Seco-3′-nor-DCPs; Anti-HIV activity; Structure–activity relationship (SAR)
We prepared 1-(4′-azido-2′-deoxy-2′-fluoro-β -D-arabinofuranosyl)cytosine (10) and its hydrochloride salt (11) as potential antiviral agents based on the favorable antiviral profiles of 4′-substituted nucleosides. Compounds 10 and 11 were synthesized from 1,3,5-O-tribenzoyl-2-deoxy-2-fluoro-D-arabinofuranoside in multiple steps, and their structures were unequivocally established by IR, 1H NMR, 13C NMR, and 19F NMR spectroscopy, HRMS, and X-ray crystallography. Compounds 10 and 11 exhibited potent anti-HIV-1 activity (EC50: 0.3 and 0.13 nM, respectively) without significant cytotoxicity in concentrations up to 100 μM. Compound 11 exhibited extremely potent anti-HIV activity against NL4-3 (wild-type), NL4-3 (K101E), and RTMDR viral strains, with EC50 values of 0.086, 0.15, and 0.11 nM, respectively. Due to the high potency of 11, it was also screened against an NIH Reagent Program NRTI-resistant virus panel containing eleven mutated viral strains and for cytotoxicity against six different human cell lines. The results of this screening indicated that 11 is a novel NRTI that could be developed as an anti-AIDS clinical trial candidate to overcome drug-resistance issues.
4′-Azido-2′-deoxy-2′-fluoro nucleosides; Anti-HIV activity; Nucleoside reverse transcriptase inhibitor (NRTI); Drug resistance
Three novel 1-alkyldaphnane-type diterpenes, stelleralides A–C (4–6), and five known compounds were isolated from the roots of Stellera chamaejasme L. The structures of 4–6 were elucidated by extensive spectroscopic analyses. Several isolated compounds showed potent anti-HIV activity. Compound 4 showed extremely potent anti-HIV activity (EC90 0.40 nM) with the lowest cytotoxicity (IC50 4.3 μM), and appears to be a promising compound for development into anti-AIDS clinical trial candidates.