Antitumor agents 290. Design, synthesis, and biological evaluation of new LNCaP and PC-3 cytotoxic curcumin analogs conjugated with anti-androgens

In our continuing study of curcumin analogs as potential anti-prostate cancer drug candidates, 15 new curcumin analogs were designed, synthesized and evaluated for cytotoxicity against two human prostate cancer cell lines, androgen-dependent LNCaP and androgen-independent PC-3. Twelve analogs (5-12, 15, 16, 19, and 20) are conjugates of curcumin (1) or methyl curcumin (2) with a flutamide- or bicalutamide-like moiety. Two compounds (22 and 23) are C4-mono- and difluoro-substituted analogs of dimethyl curcumin (DMC, 21). Among the newly synthesized conjugates compound 15, a conjugate of 2 with a partial bicalutamide moiety, was more potent than bicalutamide alone and essentially equipotent with 1 and 2 against both prostate tumor cell lines with IC(50) values of 41.8 μM (for LNCaP) and 39.1 μM (for PC-3). A cell morphology study revealed that the cytotoxicity of curcumin analogs or curcumin-anti-androgen conjugates detected from both prostate cancer cell lines might be due to the suppression of pseudopodia formation. A molecular intrinsic fluorescence experiment showed that 1 accumulated mainly in the nuclei, while conjugate 6 was distributed in the cytosol. At the tested conditions, anti-androgens suppressed pseudopodia formation in PC-3 cells, but not in LNCaP cells. The evidence suggests that distinguishable target proteins are involved, resulting in the different outcomes toward pseudopodia suppression.     

Antitumor agents 281. Design, synthesis, and biological activity of substituted 4-amino-7,8,9,10-tetrahydro-2H-benzo[h]chromen-2-one analogs (ATBO) as potent in vitro anticancer agents

In our exploration of new biologically active chemical entities, we designed and synthesized a novel class of antitumor agents, substituted 4-amino-7,8,9,10-tetrahydro-2H-benzo[h]chromen-2-one (ATBO) analogs. We evaluated their cytotoxic activity against seven human tumor cell lines from different tissues, and established preliminary structure-activity relationships (SAR). All analogs, except 8, 9, and 25-27, displayed potent tumor cell growth inhibitory activity. Especially, compounds 15 and 33 with a 4-methoxyphenyl group at position C-4 were extremely potent with ED(50) values of 0.008-0.064 and 0.035-0.32 μM, respectively. Compound 15 was the most potent analog compared with structurally related neo-tanshinlactone (e.g., 1) and 4-amino-2H-benzo[h]chromen-2-one (ABO, e.g., 4) analogs, and thus merits further exploration as an anti-cancer drug candidate.     

Design,synthesis, and biological evaluation of 1,9-diheteroarylnona-1,3,6,8-tetraen-5-ones as a new class of anti-prostate cancer agents

In search of more effective chemotherapeutics for the treatment of castration-resistant prostate cancer and inspired by curcumin analogues, twenty five (1E,3E,6E,8E)-1,9-diarylnona-1,3,6,8-tetraen-5-ones bearing two identical terminal heteroaromatic rings have been successfully synthesized through Wittig reaction followed by Horner–Wadsworth–Emmons reaction. Twenty-three of them are new compounds. The WST-1 cell proliferation assay was employed to assess their anti-proliferative effects toward both androgen-sensitive and androgen-insensitive human prostate cancer cell lines. Eighteen out of twenty-five synthesized compounds possess significantly improved potency as compared with curcumin. The optimal compound, 78, is 14- to 23-fold more potent than curcumin in inhibiting prostate cancer cell proliferation. It can be concluded from our data that 1,9-diarylnona-1,3,6,8-tetraen-5-one can serve as a new potential scaffold for the development of anti-prostate cancer agents and that pyridine-4-yls and quinolin-4-yl act as optimal heteroaromatic rings for the enhanced potency of this scaffold. Two of the most potent compounds, 68 and 75, effectively suppress PC-3 cell proliferation by activating cell apoptosis and by arresting cell cycle in the G₀/G₁ phase.     

Copalic acid analogs down-regulate androgen receptor and inhibit small chaperone protein

Copalic acid, one of the diterpenoid acids in copaiba oil, inhibited the chaperone function of α-crystallin and heat shock protein 27 kD (HSP27). It also showed potent activity in decreasing an HSP27 client protein, androgen receptor (AR), which makes it useful in prostate cancer treatment or prevention. To develop potent drug candidates to decrease the AR level in prostate cancer cells, more copalic acid analogs were synthesized. Using the level of AR as the readout, 15 of the copalic acid analogs were screened and two compounds were much more potent than copalic acid. The compounds also dose-dependently inhibited AR positive prostate cancer cell growth. Furthermore, they inhibited the chaperone activity of α-crystallin as well.     

Free radical scavenging and antiproliferative properties of Biginelli adducts

A series of Biginelli adducts bearing different substituents at C-4 position were synthesized by using p-sulfonic acid calix[4]arene as a catalyst. The in vitro potential to scavenge reactive nitrogen/oxygen species (RNS and ROS) and the ability to inhibit cancer cells growth were then investigated. Four adducts were found to be potent scavengers of 2,2-diphenyl-1-picrylhydrazyl (RNS) and/or superoxide anion (ROS) radicals. The antiproliferative activity against cancer cells was disclosed for the first time for 16 monastrol analogs. The capacity of all compounds to inhibit cancer cells growth was dependent on the histological origin of cells, except for BA24, which was highly active against all cell lines. BA20 and BA33 were as potent as the reference drug doxorubicin against adriamycin-resistant ovarian and prostate cancer cells, respectively. These results highlight some monastrol analogs as lead compounds for the design of new free radical scavengers and anticancer agents.     

The natural product CCR5 antagonist anibamine and its analogs as anti-prostate cancer agents

Prostate cancer is a leading cause of death among males in the United States. As the chemokine receptor CCR5 is over-expressed in more aggressive forms of prostate cancer, and is also a critical receptor in inflammation, chemokine receptor CCR5 antagonists could potentially act as anti-prostate cancer agents. Anibamine, a natural product CCR5 antagonist, provides a unique molecular scaffold for the generation of novel analogs with possible anti-prostate cancer activity. A series of analogs of anibamine were designed, synthesized and tested against several prostate cancer cell lines. The analogs all acted as CCR5 antagonists at micromolar range affinity to the receptor while their anti-proliferative activity varied depending on the cell line type and their chemical structural properties. Further basal cytotoxicity characterization on these compounds indicated some of them may be suitable for in vivo studies.     

Antioxidation and tyrosinase inhibition of polyphenolic curcumin analogs

A series of polyphenolic curcumin analogs were synthesized and their inhibitory effects on mushroom tyrosinase and the inhibition of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical formation were evaluated. The results indictated that the analogs possessing m-diphenols and o-diphenols exhibited more potent inhibitory activity on tyrosinase than reference compound rojic acid, and that the analogs with o-diphenols exhibited more potent inhibitory activity of DPPH free-radical formation than reference compound vitamin C. The inhibition kinetics, analyzed by Lineweaver-Burk plots, revealed that compounds B(2) and C(2) bearing o-diphenols were non-competitive inhibitors, while compounds B(11) and C(11) bearing m-diphenols were competitive inhibitors. In particular, representative compounds C(2) and B(11) showed no side effects at a dose of 2,000 mg/kg in a preliminary evaluation of acute toxicity in mice. These results suggest that such polyphenolic curcumin analogs might serve as lead compounds for further design of new potential tyrosinase inhibitors.     

Synthesis and biological evaluation of novel curcumin analogs as anti-cancer and anti-angiogenesis agents

A series of novel curcumin analogs were synthesized and screened for anti-cancer and anti-angiogenesis activities at Emory University and at the National Cancer Institute (NCI). These compounds are symmetrical alpha,beta-unsaturated and saturated ketones. The majority of the analogs demonstrated a moderate degree of anti-cancer activity. Compounds 10, 11, and 14 exhibited a high degree of cytotoxicity in the NCI in vitro anti-cancer cell line screen. In addition, this screen revealed that these compounds inhibit tumor cell growth with a higher potency than the commonly used chemotherapeutic drug, cisplatin. In independent in vitro screens conducted at Emory, the same compounds plus 4, 5, 8, 9, and 13 exhibited a high degree of cytotoxicity to tumor cells. Analogs that were effective in the anti-cancer screens were also effective in in vitro anti-angiogenesis assays. Compounds 4, 9, 11, and 14 were most effective in the anti-angiogenesis assays run at Emory. In the assays conducted by the NCI, compound 14 was almost as potent as the anti-angiogenic drug TNP-470, which has undergone clinical trials. Based on the favorable in vitro anti-cancer and anti-angiogenesis results with 14, further in vivo tests were conducted. This compound effectively reduced the size of human breast tumors grown in female athymic nude mice and showed little toxicity. This data, coupled with the remarkable in vitro data, suggests that compound 14 may potentially be an effective chemotherapeutic agent. As a follow-up, a 3D quantitative structure relationship based on 14 has been developed. It shows a cross-validated r2(q2) and a predictive r2(p2) = 0.71. COMPARE analysis suggests the compound to be a possible RNA/DNA antimetabolite, but also implies that the compound's cytotoxicity may arise from a presently unknown mechanism.     

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.     

Novel analogs of D-e-MAPP and B13. Part 1: synthesis and evaluation as potential anticancer agents

A series of novel isosteric analogs of the ceramidase inhibitors, (1S,2R)-N-myristoylamino-phenylpropanol-1 (d-e-MAPP) and (1R,2R)-N-myristoylamino-4'-nitro-phenylpropandiol-1,3 (B13), with modified targeting and physicochemical properties were designed, synthesized, and evaluated as potential anticancer agents. When MCF7 cells were treated with the analogs, results indicated that the new analogs were of equal or greater potency compared to the parent compounds. Their activity was predominantly defined by the nature of the modification of the N-acyl hydrophobic interfaces: N-acyl analogs (class A), urea analogs (class B), N-alkyl analogs (class C, lysosomotropic agents), and omega-cationic-N-acyl analogs (class D, mitochondriotropic agents). The most potent compounds belonged to either class D, the aromatic ceramidoids, or to class C, the aromatic N-alkylaminoalcohols. Representative analogs selected from this study were also evaluated by the National Cancer Institute In Vitro Anticancer Drug Discovery Screen. Again, results showed a similar class-dependent activity. In general, the active analogs were non-selectively broad spectrum and had promising activity against all cancer cell lines. However, some active analogs of the d-e-MAPP family were selective against different types of cancer. Compounds LCL85, LCL120, LCL385, LCL284, and LCL204 were identified to be promising lead compounds for therapeutic development.     

Synthesis and activity evaluation of phenylurea derivatives as potent antitumor agents

We have discovered several tubulin-active compounds in our previous studies. In the establishment of a compound library of small molecule weight tubulin ligands, 14 new N-3-haloacylaminophenyl-N′-(alkyl/aryl) urea analogs were designed and synthesized. The structure–activity relationship (SAR) analysis revealed that (i) the order of anticancer potency for the 3-haloacylamino chain was following –CH₂Br > –CHBrCH₃; (ii) the N′-substituent moiety was not essential for the anticancer activity, and a proper alkyl substitution might enhance the anticancer activity. Among these analogs, the compounds 16j bearing bromoacetyl at the N′-end exhibited a potent activity against eight human tumor cell lines, including CEM (leukemia), Daudi (lymphoma), MCF-7 (breast cancer), Bel-7402 (hepatoma), DU-145 (prostate cancer), DND-1A (melanoma), LOVO (colon cancer) and MIA Paca (pancreatic cancer), with the IC₅₀ values between 0.38 and 4.07 μM. Interestingly, compound 16j killed cancer cells with a mechanism independent of the tubulin-based mechanism, indicating a significant change of the action mode after the structure modification.     

Synthesis and biological evaluation of quinoline derivatives as potential anti-prostate cancer agents and Pim-1 kinase inhibitors

In this work, a series of quinoline derivatives were designed and synthesized as antitumor agents. Most quinolines showed potent anti-proliferative activity against human prostatic cancer PC-3 cell line. Among which, 9d, 9f and 9g were the most effective compounds with GI₅₀ values of 2.60, 2.81 and 1.29 μM, respectively. Structure–activity relationship analysis indicated that the secondary amine linked quinoline and pyridine ring played an important role in the anti-proliferative effects. Mechanistic studies revealed that 9g was a potential Pim-1 kinase inhibitor with abilities of cell cycle arrest and apoptosis induction. Considering of the increased activity of Pim-1 in prostate cancer, such compounds have potential to be developed as anti-prostate cancer agents.     

Structure–activity relationship studies of curcumin analogues

Two series of curcumin analogues, a total of twenty-four compounds, were synthesized and evaluated. The most potent compound, compound 23, showed potent growth inhibitory activities on both prostate and breast cancer lines with IC₅₀ values in sub-micromolar range, fifty times more potent than curcumin. Curcumin analogues might be potential anti-tumor agents for breast and prostate cancers.     

4-Bromo-4’-chloro pyrazoline analog of curcumin augmented anticancer activity against human cervical cancer,HeLa cells: in silico-guided analysis,synthesis, and in vitro cytotoxicity

Abstract

Inspired by the synergistic effects of hetero-aromatic scaffolds on curcumin, a novel array of pyrazoline substituted curcumin analogs was designed. Multi-scale computational studies were carried out to target the proposed analogs on human kinase β (IKK-β), a potential anti-cancer target. In molecular docking analysis, all the eleven molecules were observed to bind the target site and 4-bromo-4’-chloro analog displayed three hydrogen bond interactions with a docking score of –11.534?kcal/mol higher than parent molecule, curcumin (docking score = –7.12?kcal/mol) as the propellant shaped of analogs aided in proper binding with Kinase Domain binding pocket. The molecular dynamics and simulations studies revealed that the stable complexes of lead molecule were developed as the minimal deviations per residue of protein found within the range of 0.11 to 0.92?Å. The proposed compounds were synthesized, characterized and biologically evaluated against human cervical cancer cell line, HeLa, using standard MTT cell assay. Bio-evaluation studies exhibited superior cytotoxic profile for many analogs as Chloro bromo analog with IC₅₀ value (8.7?µg/mL) exhibited fivefolds improvement in the potency in comparison to curcumin (IC₅₀ = 42.4?µg/mL) but was less potent than the standard drug, paclitaxel (IC₅₀ = 0.008µg/mL). The apoptotic effect was evaluated in the terms of caspase-3 enzyme cleavage and exhibited 70.5% of apoptosis significantly (p?<?0.05) higher than 19.9% induced by curcumin. In short, 4-bromo-4’-chloro analog was the potent cytotoxic agent in this structural class and must be evaluated further under a set of stringent parameters for transforming in to a clinically viable therapeutic molecule.

Communicated by Ramaswamy H. Sarma     

Antitumor agents. 258. Syntheses and evaluation of dietary antioxidant--taxoid conjugates as novel cytotoxic agents

Various dietary antioxidants, including vitamins, flavonoids, curcumin, and a coumarin, were conjugated with paclitaxel (1) through an ester linkage. The newly synthesized compounds were evaluated for cytotoxic activity against several human tumor cell lines as well as the corresponding normal cell lines. Interestingly, most tested conjugates selectively inhibited the growth of 1A9 (ovarian) and KB (nasopharyngeal) tumor cells without activity against other cell lines. Particularly, conjugates 16 and 20 were highly active against 1A9 (ED(50) value of 0.005 microg/mL) as well as KB (ED(50) values of 0.005 and 0.14 microg/mL, respectively) cells. Compound 22b, the glycinate ester salt of vitamin E conjugated with 1, appears to be a promising lead for further development as a clinical trial candidate as it exhibited strong inhibitory activity against Panc-1 (pancreatic cancer) with less effect on the related E6E7 (normal) cell line.     

Design, synthesis, biological evaluation and molecular modeling of 1,3,4-oxadiazoline analogs of combretastatin-A4 as novel antitubulin agents

A total of 20 novel 1,3,4-oxadiazoline analogs (6a-6t) of combretastatin A-4 with naphthalene ring were designed, synthesized, and evaluated for biological activities as potential tubulin polymerization inhibitors. Among these compounds, 6n showed the most potent antiproliferative activities against multiple cancer cell lines and retained the microtubule disrupting effects. Docking simulation was performed to insert compound 6n into the crystal structure of tubulin to determine the probable binding model. These results indicated oxadiazoline compounds bearing the naphthyl moiety are promising tubulin inhibitors.     

Synthesis and antiproliferative activity of 2-aryl-4-oxo-thiazolidin-3-yl-amides for prostate cancer

We have previously described serine amide phosphates (SAPs) as a novel class of cytotoxic agents for prostate cancer. Several of them showed potent cytotoxicity against human prostate cancer cell lines, but were not selective in non-tumor cells. To improve the selectivity and further enhance the potency, we designed a new series of 2-aryl-4-oxo-thiazolidin-3-yl amides. The current work describes synthesis, SAR, and biological evaluation of these compounds for their ability to inhibit the growth of prostate cancer cells. The antiproliferative effects of synthesized compounds were examined in five human prostate cancer cell lines (DU-145, PC-3, LNCaP, PPC-1, and TSU), and in RH7777 cells (negative controls). From this study, three potent compounds (8, 20, and 21) have been detected, which are effective in killing prostate cancer cells with improved selectivity compared to SAPs.     

Synthesis and antiproliferative activity of novel 2-aryl-4-benzoyl-imidazole derivatives targeting tubulin polymerization

We previously reported the discovery of 2-aryl-4-benzoyl-imidazoles (ABI-I) as potent antiproliferative agents for melanoma. To further understand the structural requirements for the potency of ABI analogs, gain insight in the structure-activity relationships (SAR), and investigate metabolic stability for these compounds, we report extensive SAR studies on the ABI-I scaffold. Compared with the previous set of ABI-I analogs, the newly synthesized ABI-II analogs have lower potency in general, but some of the new analogs have comparable potency to the most active compounds in the previous set when tested in two melanoma and four prostate cancer cell lines. These SAR studies indicated that the antiproliferative activity was very sensitive to subtle changes in the ligand. Tested compounds 3ab and 8a are equally active against highly paclitaxel resistant cancer cell lines and their parental cell lines, indicating that drugs developed based on ABI-I analogs may have therapeutic advantages over paclitaxel in treating resistant tumors. Metabolic stability studies of compound 3ab revealed that N-methyl imidazole failed to extend stability as literature reported because de-methylation was found as the major metabolic pathway in rat and mouse liver microsomes. However, this sheds light on the possibility for many modifications on imidazole ring for further lead optimization since the modification on imidazole, such as compound 3ab, did not impact the potency.     

New substituted 4H-chromenes as anticancer agents

As a continuation of our efforts to discover and develop small molecules as anticancer agents, we identified GRI-394837 as an initial hit from similarity search on RGD and its analogs. Based on GRI-394837, we designed and synthesized a focused set of novel chromenes (4a-e) in a single step using microwave method. All five compounds showed activity in the nanomolar range (IC(50): 7.4-640 nM) in two melanoma, three prostate and four glioma cancer cell lines. The chromene 4e is active against all the cell lines and particularly against the A172 human glioma cell line (IC(50): 7.4 nM). Interestingly, in vitro tubulin polymerization assay shows 4e to be a weak tubulin polymerization inhibitor but it shows very strong cytotoxicity in cellular assays, therefore there must be additional unknown mechanism(s) for the anticancer activity. Additionally, the strong antiproliferative activity was verified by one of the selected chromene (4a) by the NCI 60 cell line screen. These results strongly suggest that the novel chromenes could be further developed as a potential therapeutic agent for a variety of aggressive cancers.