Synthesis and Quantitative Structure–Activity Relationships of Selective BCRP Inhibitors

The breast cancer resistance protein (BCRP/ABCG2) is a member of the ABC transporter superfamily. This protein has a number of physiological functions, including protection of the human body from xenobiotics. The overexpression of BCRP in certain tumor cell lines causes cross‐resistance against various drugs used in chemotherapeutic treatment. In a previous work we showed that a new class of compounds derived from XR9576 (tariquidar) selectively inhibits BCRP. In this work we synthesized more members of this class, with modification on the second and third aromatic rings. The inhibitory activities against BCRP and P‐gp were assayed using a Hoechst 33342 assay for BCRP and a calcein AM assay for P‐gp. Finally, quantitative structure–activity relationships for both aromatic rings were established. The results obtained show the importance of the electron density on the third aromatic ring, influenced by substituents, pointing to interactions with aromatic residues of the protein binding site. In the second aromatic ring the activity of compounds is influenced by the steric volume of the substituents.     

Synthesis and Structure–Activity Relationships of 1‐Benzyl‐4,5,6‐trimethoxyindoles as a Novel Class of Potent Antimitotic Agents

Combretastatin A‐4 derivatives : A series of combretastatin A‐4‐derived 1‐benzyl‐4,5,6‐trimethoxyindoles was designed and prepared as a novel class of potent antimitotic agents acting through the colchicine binding site on the microtubule.

     

Design,Synthesis and Structure–Activity Relationships Studies on the D Ring of the Natural Product Triptolide

Triptolide is a diterpene triepoxide natural product isolated from Tripterygium wilfordii Hook F, a traditional Chinese medicinal herb. Triptolide has previously been shown to possess antitumor, anti‐inflammatory, immunosuppressive, and antifertility activities. Earlier reports suggested that the five‐membered unsaturated lactone ring (D ring) is essential for potent cytotoxicity, however, to the best of our knowledge, systematic structure–activity relationship studies have not yet been reported. Here, four types of D ring‐modified triptolide analogues were designed, synthesized and evaluated against human ovarian (SKOV‐3) and prostate (PC‐3) carcinoma cell lines. The results suggest that the D ring is essential to potency, however it can be modified, for example to C18 hydrogen bond acceptor and/or donor furan ring analogues, without complete loss of cytotoxic activity. Interestingly, evaluation of the key series of C19 analogues showed that this site is exquisitely sensitive to polarity. Together, these results will guide further optimization of this natural product lead compound for the development of potent and potentially clinically useful triptolide analogues.     

Norcantharidin Analogues: Synthesis,Anticancer Activity and Protein Phosphatase 1 and 2A Inhibition

Cantharidin ( 1 ) and its derivatives are of significant interest as serine/threonine protein phosphatase 1 and 2A inhibitors. Additionally, compounds of this type have displayed growth inhibition of various tumour cell lines. To further explore both of these inhibition pathways, a number of amide–acid norcantharidin analogues ( 15 – 26 ) were prepared. Compounds 23 and 24 , containing two carboxylic acid residues, showed good PP1 and PP2A activity, with IC₅₀ values of ～15 and ～3 μm, respectively. Substituted aromatic amide analogues 45 , 48 , 49 , 52 , 53 , and 54 also displayed good PP1 and PP2A inhibition, with IC₅₀ values in the range of 15–10 μM (PP1) and 11–5 μM (PP2A). However, bulky ortho substituents on the aromatic ring caused the aromatic ring to be skewed from the NCO planarity, leading to a decrease in PP1 and PP2A inhibition. A number of analogues, 20 , 22, 25 and 46 , showed excellent tumour growth inhibition, with 46 in particular being more potent than the lead, norcantharidin 2 .     

Synthesis and Biological Evaluation of N‐Substituted Noscapine Analogues

Noscapine is a phthalideisoquinoline alkaloid isolated from the opium poppy Papaver somniferum. It has long been used as an antitussive agent, but has more recently been found to possess microtubule‐modulating properties and anticancer activity. Herein we report the synthesis and pharmacological evaluation of a series of 6′‐substituted noscapine derivatives. To underpin this structure–activity study, an efficient synthesis of N‐nornoscapine and its subsequent reduction to the cyclic ether derivative of N‐nornoscapine was developed. Reaction of the latter with a range of alkyl halides, acid chlorides, isocyanates, thioisocyanates, and chloroformate reagents resulted in the formation of the corresponding N‐alkyl, N‐acyl, N‐carbamoyl, N‐thiocarbamoyl, and N‐carbamate derivatives, respectively. The ability of these compounds to inhibit cell proliferation was assessed in cell‐cycle cytotoxicity assays using prostate cancer (PC3), breast cancer (MCF‐7), and colon cancer (Caco‐2) cell lines. Compounds that showed activity in the cell‐cycle assay were further evaluated in cell viability assays using PC3 and MCF‐7 cells.     

Cytotoxicities and Structure–Activity Relationships of Natural and Unnatural Lamellarins toward Cancer Cell Lines

Shedding light on the lamellarins : Structural determinants for potent cytotoxic activity toward various cancer cell lines were systematically investigated to establish SARs for the marine alkaloids in the lamellarin family. The C5?C6 double bond ensures not only the planarity of the D‐ring, but also proper alignment of the substituents on the E‐ring with their respective moieties of the target. The importance of the C7 OH group is also revealed for the first time.

     

Synthesis, biological evaluation, and molecular modeling studies of rebeccamycin analogues modified in the carbohydrate moiety

A new series of indolocarbazole glycosides containing disaccharides were synthesized and their in vitro antiproliferative activity was evaluated against three human cancer cell lines (A2780, H460, and GLC4). Cytotoxicity appeared to be remarkably affected by the regio- and stereochemical features of the disaccharide moiety. In vivo antitumor activity of the compounds studied, two of which having IC(50)<100 nm, was determined using ovarian cancer cell line A2780 xenografted on nude mice. One compound showed an efficacy similar to that of the reference compound edotecarin, though with a lower long-lasting activity. The topoisomerase I inhibitory properties of some compounds were also examined. Molecular dynamics simulations of the ternary topoisomerase I-DNA-ligand complexes were performed to analyze the structural features of topoisomerase I poisoning with this class of indolocarbazoles. A plausible explanation of their biological behavior was provided. These theoretical results were compared with the recently published crystal structure of an indolocarbazole monosaccharide bound to the covalent human topoisomerase I-DNA complex.     

Structural Design,Synthesis and Structure–Activity Relationships of Thiazolidinones with Enhanced Anti‐Trypanosoma cruzi Activity

Pharmacological treatment of Chagas disease is based on benznidazole, which displays poor efficacy when administered during the chronic phase of infection. Therefore, the development of new therapeutic options is needed. This study reports on the structural design and synthesis of a new class of anti‐Trypanosoma cruzi thiazolidinones ( 4 a – p ). (2‐[2‐Phenoxy‐1‐(4‐bromophenyl)ethylidene)hydrazono]‐5‐ethylthiazolidin‐4‐one ( 4 h ) and (2‐[2‐phenoxy‐1‐(4‐phenylphenyl)ethylidene)hydrazono]‐5‐ethylthiazolidin‐4‐one ( 4 l ) were the most potent compounds, resulting in reduced epimastigote proliferation and were toxic for trypomastigotes at concentrations below 10 μM , while they did not display host cell toxicity up to 200 μM . Thiazolidinone 4 h was able to reduce the in vitro parasite burden and the blood parasitemia in mice with similar potency to benznidazole. More importantly, T. cruzi infection reduction was achieved without exhibiting mouse toxicity. Regarding the molecular mechanism of action, these thiazolidinones did not inhibit cruzain activity, which is the major trypanosomal protease. However, investigating the cellular mechanism of action, thiazolidinones altered Golgi complex and endoplasmic reticulum (ER) morphology, produced atypical cytosolic vacuoles, as well as induced necrotic parasite death. This structural design employed for the new anti‐T. cruzi thiazolidinones ( 4 a – p ) led to the identification of compounds with enhanced potency and selectivity compared to first‐generation thiazolidinones. These compounds did not inhibit cruzain activity, but exhibited strong antiparasitic activity by acting as parasiticidal agents and inducing a necrotic parasite cell death.     

Design,Synthesis, and Biological Evaluation of Pyrazoline‐Based Hydroxamic Acid Derivatives as Aminopeptidase N (APN) Inhibitors

Aminopeptidase N (APN) has been recognized as a target for anticancer treatment due to its overexpression on diverse malignant tumor cells and association with cancer invasion, metastasis and angiogenesis. Herein we describe the synthesis, biological evaluation, and structure–activity relationship study of two new series of pyrazoline analogues as APN inhibitors. Among these compounds, 5‐(2‐(2‐(hydroxyamino)‐2‐oxoethoxy)phenyl)‐3‐phenyl‐4,5‐dihydro‐1H‐pyrazole‐1‐carboxamide (compound 13 e ) showed the best APN inhibition with an IC₅₀ value of 0.16±0.02 μm , which is more than one order of magnitude lower than that of bestatin (IC₅₀=9.4±0.5 μm ). Moreover, compound 13 e was found to inhibit the proliferation of diverse carcinoma cells and to show potent anti‐angiogenesis activity. At the same concentration, compound 13 e presents significantly higher anti‐angiogenesis activity than bestatin in human umbilical vein endothelial cells (HUVECs) capillary tube formation assays. The putative binding mode of 13 e in the active site of APN is also discussed.     

Organofluorine Isoselenocyanate Analogues of Sulforaphane: Synthesis and Anticancer Activity

A series of previously unknown sulforaphane analogues with organofluorine substituents bonded to the sulfinyl sulfur atom, an isoselenocyanate moiety in place of the isothiocyanate group, the central sulfur atom in various oxidation states, and different numbers of methylene groups in the central alkyl chain were synthesized and fully characterized. All new compounds were tested for their biological properties in vitro and demonstrated much higher anticancer activity against two breast cancer cell lines than that shown by native sulforaphane; at the same time, the compounds were less toxic for normal cells. The influence of the particular structural changes in the molecules on the cytotoxicity is discussed.     

Structure–Activity Relationships of Glucosamine‐Derived Glycerolipids: the Role of the Anomeric Linkage,the Cationic Charge and the Glycero Moiety on the Antitumor Activity

The potent antitumor activity of 1‐O‐hexadecyl‐2‐O‐methyl‐3‐O‐(2′‐amino‐2′‐deoxy‐β‐D ‐glucopyranosyl)‐sn‐glycerol ( 1 ) was previously shown to arise through an apoptosis‐independent pathway. Here, a systematic structure–activity study in which the effects of the anomeric linkage, the cationic charge and the glycero moiety on the antitumor activity is described. Eight analogues of 1 were synthesized, and their antitumor activity against breast (JIMT1 and BT549), pancreas (MiaPaCa2) and prostate (DU145, PC3) cancer was determined. 1‐O‐Hexadecyl‐2‐O‐methyl‐3‐O‐(2′‐amino‐2′‐deoxy‐α‐D ‐glucopyranosyl)‐sn‐glycerol ( 2 ) consistently displayed the most potent activity against all five cell lines with CC₅₀ values in the range of 6–10 μM . However, replacement of the O‐glycosidic linkage by a thioglycosidic linkage or replacement of the amino group by an azide or guanidino group leads to a threefold or greater decrease in potency. The glycero moiety also contributes to the overall activity of 1 and 2 but its effects are of lesser importance. Investigation into the mode of action of this class of compounds revealed that, in agreement with previous findings, the cytotoxic effects arise through induction of large acid vacuoles.     

Synthesis and Biological Studies of Pyrazolyl‐Diamine PtII Complexes Containing Polyaromatic DNA‐Binding Groups

New [PtCl(pz*NN)]ⁿ⁺ complexes anchored by pyrazolyl‐diamine (pz*NN) ligands incorporating anthracenyl or acridine orange DNA‐binding groups have been synthesized so as to obtain compounds that would display synergistic effects between platination and intercalation of DNA. Study of their interaction with supercoiled DNA indicated that the anthracenyl‐containing complex L²Pt displays a covalent type of binding, whereas the acridine orange counterpart L³Pt shows a combination of intercalative and covalent binding modes with a strong contribution from the former. L²Pt showed a very strong cytotoxic effect on ovarian carcinoma cell lines A2780 and A2780cisR, which are, respectively, sensitive to and resistant to cisplatin. In these cell lines, L²Pt is nine to 27 times more cytotoxic than cisplatin. In the sensitive cell line, L³Pt showed a cytotoxic activity similar to that of cisplatin, but like L²Pt was able significantly to overcome cisplatin cross‐resistance. Cell‐uptake studies showed that L²Pt accumulates preferentially in the cytoplasm, whereas L³Pt reaches the cell nucleus more easily, as clearly visualized by time‐lapse confocal imaging of live A2870 cells. Altogether, these findings seem to indicate that interaction with biological targets other than DNA might be involved in the mechanism of action of L²Pt because this compound, despite having a weaker ability to target the cell nucleus than L³Pt , as well as an inferior DNA affinity, is nevertheless more cytotoxic. Furthermore, ultrastructural studies of A2870 cells exposed to L²Pt and L³Pt revealed that these complexes induce different alterations in cell morphology, thus indicating the involvement of different modes of action in cell death.     

Design,Synthesis, and in vitro Biological Evaluation of 3,5‐Dimethylisoxazole Derivatives as BRD4 Inhibitors

BRD4 has been identified as a potential target for blocking proliferation in a variety of cancer cell lines. In this study, 3,5‐dimethylisoxazole derivatives were designed and synthesized with excellent stability in liver microsomes as potent BRD4 inhibitors, and were evaluated for their BRD4 inhibitory activities in vitro. Gratifyingly, compound 11 h [3‐((1‐(2,4‐difluorophenyl)‐1H‐1,2,3‐triazol‐4‐yl)methyl)‐6‐(3,5‐dimethylisoxazol‐4‐yl)‐4‐phenyl‐3,4‐dihydroquinazolin‐2(1H)‐one] exhibited robust potency for BRD4(1) and BRD4(2) inhibition with IC₅₀ values of 27.0 and 180 nm , respectively. Docking studies were performed to illustrate the strategy of modification and analyze the conformation in detail. Furthermore, compound 11 h was found to potently inhibit cell proliferation in the BRD4‐sensitive cell lines HL‐60 and MV4‐11, with IC₅₀ values of 0.120 and 0.09 μm , respectively. Compound 11 h was further demonstrated to downregulate c‐Myc levels in HL‐60 cells. In summary, these results suggest that compound 11 h is most likely a potential BRD4 inhibitor and is a lead compound for further investigations.     

Synthesis,Biological Evaluation of 1,1‐Diarylethylenes as a Novel Class of Antimitotic Agents

The cytotoxic activities of 23 new isocombretastatin A derivatives with modifications on the B‐ring were investigated. Several compounds exhibited excellent antiproliferative activity at nanomolar concentrations against a panel of human cancer cell lines. Compounds isoFCA‐4 ( 2 e ), isoCA‐4 ( 2 k ) and isoNH₂CA‐4 ( 2 s ) were the most cytotoxic, and strongly inhibited tubulin polymerization with IC₅₀ values of 4, 2 and 1.5 μM , respectively. These derivatives were found to be 10‐fold more active than phenstatin and colchicine with respect to growth inhibition but displayed similar activities as tubulin polymerization inhibitors. In addition, cell cycle arrest in the G₂/M phase and subsequent apoptosis was observed in three cancer cell lines when treated with these compounds. The disruptive effect of 2 e , 2 k and 2 s on the vessel‐like structures formed by human umbilical vein endothelial cells (HUVEC) suggest that these compounds may act as vascular disrupting agents. Both compounds 2 k and 2 s have the potential for further prodrug modification and development as vascular disrupting agents for treatment of solid tumors.     

Enantiospecific Synthesis and Cytotoxicity Evaluation of Oximidine II Analogues

Analogues of the anticancer natural product oximidine II were prepared and evaluated for cytotoxicity. One analogue of oximidine II that carries a C15 allylic amide side chain as well as two analogues with C15 vinyl sulfone side chains were found to lack cytotoxicity against the cancer cell line SK‐Mel‐5, thereby confirming the necessity of the C15 enamide side chain of oximidine II for cytotoxicity. Four analogues, designed by comparative molecular similarity index analysis (CoMSIA), that feature a less complex macrolactone scaffold were prepared and tested. The two analogues carrying a C15 vinyl sulfone group and the two analogues with a C15 oximidine II enamide side chain showed weak cytotoxicity against the SK‐Mel‐5 cell line and other cell lines, indicating that the designed simplified macrocycles cannot replace the oximidine II macrocycle.     

Semisynthetic Latrunculin Derivatives as Inhibitors of Metastatic Breast Cancer: Biological Evaluations,Preliminary Structure–Activity Relationship and Molecular Modeling Studies

The microfilament cytoskeleton protein actin plays an important role in cell biology and affects cytokinesis, morphogenesis, and cell migration. These functions usually fail and become abnormal in cancer cells. The marine‐derived macrolides latrunculins A and B, from the Red Sea sponge Negombata magnifica, are known to reversibly bind actin monomers, forming 1:1 stoichiometric complexes with G‐actin, disrupting its polymerization. To identify novel therapeutic agents for effective treatment of metastatic breast cancer, several semisynthetic derivatives of latrunculin A with diverse steric, electrostatic, and hydrogen bond donor and acceptor properties were rationally prepared. Analogues were designed to modulate the binding affinity toward G‐actin. Examples of these reactions are esterification, acetylation, and N‐alkylation. Semisynthetic latrunculins were then tested for their ability to inhibit pyrene‐conjugated actin polymerization, and subsequently assayed for their antiproliferative and anti‐invasive properties against MCF7 and MDA‐MB‐231 cells using MTT and invasion assays, respectively.