Investigation of the Structure-Activity Relationships of Aza-A-Ring Indenoisoquinoline Topoisomerase I Poisons.

Several indenoisoquinolines have shown promise as anticancer agents in clinical trials. Incorporation of a nitrogen atom into the indenoisoquinoline scaffold offers the possibility of favorably modulating ligand-binding site interactions, physicochemical properties, and biological activities. Four series of aza-A-ring indenoisoquinolines were synthesized in which the nitrogen atom was systematically rotated through positions 1, 2, 3, and 4. The resulting compounds were tested to establish the optimal nitrogen position for topoisomerase IB (Top1) enzyme poisoning activity and cytotoxicity to human cancer cells. The 4-aza compounds were the most likely to yield derivatives with high Top1 inhibitory activity. However, the relationship between structure and cytotoxicity was more complicated since the potency was influenced strongly by the side chains on the lactam nitrogen. The most cytotoxic azaindenoisoquinolines 45 and 46 had nitrogen in the 2- or 3-positions and a 3'-dimethylaminopropyl side chain, and they had MGM GI50 values that were slightly better than the corresponding indenoisoquinoline 64.

Antibacterial Characterization of Novel Synthetic Thiazole Compounds against Methicillin-Resistant Staphylococcus pseudintermedius.

Staphylococcus pseudintermedius is a commensal organism of companion animals that is a significant source of opportunistic infections in dogs. With the emergence of clinical isolates of S. pseudintermedius (chiefly methicillin-resistant S. pseudintermedius (MRSP)) exhibiting increased resistance to nearly all antibiotic classes, new antimicrobials and therapeutic strategies are urgently needed. Thiazole compounds have been previously shown to possess potent antibacterial activity against multidrug-resistant strains of Staphylococcus aureus of human and animal concern. Given the genetic similarity between S. aureus and S. pseudintermedius, this study explores the potential use of thiazole compounds as novel antibacterial agents against methicillin-sensitive S. pseudintermedius (MSSP) and MRSP. A broth microdilution assay confirmed these compounds exhibit potent bactericidal activity (at sub-microgram/mL concentrations) against both MSSA and MRSP clinical isolates while the MTS assay confirmed three compounds (at 10 µg/mL) were not toxic to mammalian cells. A time-kill assay revealed two derivatives rapidly kill MRSP within two hours. However, this rapid bactericidal activity was not due to disruption of the bacterial cell membrane indicating an alternative mechanism of action for these compounds against MRSP. A multi-step resistance selection analysis revealed compounds 4 and 5 exhibited a modest (two-fold) shift in activity over ten passages. Furthermore, all six compounds (at a subinihibitory concentration) demonstrated the ability to re-sensitize MRSP to oxacillin, indicating these compounds have potential use for extending the therapeutic utility of ß-lactam antibiotics against MRSP. Metabolic stability analysis with dog liver microsomes revealed compound 3 exhibited an improved physicochemical profile compared to the lead compound. In addition to this, all six thiazole compounds possessed a long post-antibiotic effect (at least 8 hours) against MRSP. Collectively the present study demonstrates these synthetic thiazole compounds possess potent antibacterial activity against both MSSP and MRSP and warrant further investigation into their use as novel antimicrobial agents.

Discovery of potent indenoisoquinoline topoisomerase I poisons lacking the 3-nitro toxicophore.

3-Nitroindenoisoquinoline human topoisomerase IB (Top1) poisons have potent antiproliferative effects on cancer cells. The undesirable nitro toxicophore could hypothetically be replaced by other functional groups that would retain the desired biological activities and minimize potential safety risks. Eleven series of indenoisoquinolines bearing 3-nitro bioisosteres were synthesized. The molecules were evaluated in the Top1-mediated DNA cleavage assay and in the National Cancer Institute's 60 cell line cytotoxicity assay. The data reveal that fluorine and chlorine may substitute for the 3-nitro group with minimal loss of Top1 poisoning activity. The new information gained from these efforts can be used to design novel indenoisoquinolines with improved safety.

DUPA conjugation of a cytotoxic indenoisoquinoline topoisomerase I inhibitor for selective prostate cancer cell targeting.

Prostate-specific membrane antigen (PSMA) is overexpressed in most prostate cancer cells while being present at low or undetectable levels in normal cells. This difference provides an opportunity to selectively deliver cytotoxic drugs to prostate cancer cells while sparing normal cells that lack PSMA, thus improving potencies and reducing toxicities. PSMA has high affinity for 2-[3-(1,3-dicarboxypropyl)ureido]pentanedioic acid (DUPA) (Ki = 8 nM). After binding to a DUPA-drug conjugate, PSMA internalizes, unloads the conjugate, and returns to the surface. In the present studies, an indenoisoquinoline topoisomerase I inhibitor was conjugated to DUPA via a peptide linker and a drug-release segment that facilitates intracellular cleavage to liberate the drug cargo. The DUPA-indenoisoquinoline conjugate exhibited an IC50 in the low nanomolar range in 22RV1 cell cultures and induced a complete cessation of tumor growth with no toxicity, as determined by loss of body weight and death of treated mice.

Synthesis and antibacterial evaluation of a novel series of synthetic phenylthiazole compounds against methicillin-resistant Staphylococcus aureus (MRSA).

Methicillin-resistant Staphylococcus aureus infections are a significant global health challenge in part due to the emergence of strains exhibiting resistance to nearly all classes of antibiotics. This underscores the urgent need for the rapid development of novel antimicrobials to circumvent this burgeoning problem. Previously, whole-cell screening of a library of 2,5-disubstituted thiazole compounds revealed a lead compound exhibiting potent antimicrobial activity against MRSA. The present study, conducting a more rigorous analysis of the structure-activity relationship of this compound, reveals a nonpolar, hydrophobic functional group is favored at thiazole-C2 and an ethylidenehydrazine-1-carboximidamide moiety is necessary at C5 for the compound to possess activity against MRSA. Furthermore, the MTS assay confirmed analogs 5, 22d, and 25 exhibited an improved toxicity profile (not toxic up to 40 µg/mL to mammalian cells) over the lead 1. Analysis with human liver microsomes revealed compound 5 was more metabolically stable compared to the lead compound (greater than eight-fold improvement in the half-life in human liver microsomes). Collectively the results presented demonstrate the novel thiazole derivatives synthesized warrant further exploration for potential use as future antimicrobial agents for the treatment of multidrug-resistant S. aureus infections.

Design, synthesis, and biological evaluation of indenoisoquinoline rexinoids with chemopreventive potential.

Nuclear receptors, such as the retinoid X receptor (RXR), are proteins that regulate a myriad of cellular processes. Molecules that function as RXR agonists are of special interest for the prevention and control of carcinogenesis. The majority of these ligands possess an acidic moiety that is believed to be key for RXR activation. This communication presents the design, synthesis, and biological evaluation of both acidic and nonacidic indenoisoquinolines as new RXR ligands. In addition, a comprehensive structure-activity relationship study is presented that identifies the important features of the indenoisoquinoline rexinoids. The ease of modification of the indenoisoquinoline core and the lack of the necessity of a carboxyl group for activity make them an attractive and unusual family of RXR agonists. This work establishes a structural foundation for the design of new and novel rexinoid cancer chemopreventive agents.

Synthesis and biological evaluation of indenoisoquinolines that inhibit both tyrosyl-DNA phosphodiesterase I (Tdp1) and topoisomerase I (Top1).

Tyrosyl-DNA phosphodiesterase I (Tdp1) plays a key role in the repair of damaged DNA resulting from the topoisomerase I (Top1) inhibitor camptothecin and a variety of other DNA-damaging anticancer agents. This report documents the design, synthesis, and evaluation of new indenoisoquinolines that are dual inhibitors of both Tdp1 and Top1. Enzyme inhibitory data and cytotoxicity data from human cancer cell cultures were used to establish structure-activity relationships. The potencies of the indenoisoquinolines against Tdp1 ranged from 5 µM to 111 µM, which places the more active compounds among the most potent known inhibitors of this target. The cytotoxicity mean graph midpoints ranged from 0.02 to 2.34 µM. Dual Tdp1-Top1 inhibitors are of interest because the Top1 and Tdp1 inhibitory activities could theoretically work synergistically to create more effective anticancer agents.

Identification, synthesis, and biological evaluation of metabolites of the experimental cancer treatment drugs indotecan (LMP400) and indimitecan (LMP776) and investigation of isomerically hydroxylated indenoisoquinoline analogues as topoisomerase I poisons.

Hydroxylated analogues of the anticancer topoisomerase I (Top1) inhibitors indotecan (LMP400) and indimitecan (LMP776) have been prepared because (1) a variety of potent Top1 poisons are known that contain strategically placed hydroxyl groups, which provides a clear rationale for incorporating them in the present case, and (2) the hydroxylated compounds could conceivably serve as synthetic standards for the identification of metabolites. Indeed, incubating LMP400 and LMP776 with human liver microsomes resulted in two major metabolites of each drug, which had HPLC retention times and mass fragmentation patterns identical to those of the synthetic standards. The hydroxylated indotecan and indimitecan metabolites and analogues were tested as Top1 poisons and for antiproliferative activity in a variety of human cancer cell cultures and in general were found to be very potent. Differences in activity resulting from the placement of the hydroxyl group are explained by molecular modeling analyses.

Identification, synthesis, and biological evaluation of the metabolites of 3-amino-6-(3'-aminopropyl)-5H-indeno[1,2-c]isoquinoline-5,11-(6H)dione (AM6-36), a promising rexinoid lead compound for the development of cancer chemotherapeutic and chemopreventive agents.

Activation of the retinoid X receptor (RXR), which is involved in cell proliferation, differentiation, and apoptosis, is a strategy for cancer chemotherapy and chemoprevention, and 3-amino-6-(3'-aminopropyl)-5H-indeno[1,2-c]isoquinoline-5,11-(6H)dione (AM6-36) (3) is among the few RXR ligands known. The presently reported studies of 3 include its binding to human plasma proteins, metabolic stability using human liver microsomes, metabolism by human liver microsomes and hepatocytes, and in vivo disposition in rat serum, liver, and mammary tissue. Compound 3 was 75% bound to human plasma proteins, and its metabolic stability was much greater than propranolol. One phase I metabolite was formed by human liver microsomes, seven phase I and II metabolites were formed by human hepatocytes, and five metabolites were detected in rat serum and liver after oral administration. The putative metabolites predicted using LC-MS-MS were synthesized to confirm their structures and to provide sufficient material for investigation of induction of RXRE transcriptional activity and inhibition of NFκB.

Design, synthesis, and biological evaluation of potent quinoline and pyrroloquinoline ammosamide analogues as inhibitors of quinone reductase 2.

A variety of ammosamide B analogues have been synthesized and evaluated as inhibitors of quinone reductase 2 (QR2). The potencies of the resulting series of QR2 inhibitors range from 4.1 to 25,200 nM. The data provide insight into the structural parameters necessary for QR2 inhibitory activity. The natural product ammosamide B proved to be a potent QR2 inhibitor, and the potencies of the analogues generally decreased as their structures became more distinct from that of ammosamide B. Methylation of the 8-amino group of ammosamide B was an exception, resulting in an increase in quinone reductase 2 inhibitory activity from an IC(50) of 61 nM to IC(50) 4.1 nM.

Efficient total synthesis of ammosamide B.

A total synthesis of ammosamide B, a metabolite of the marine-derived Streptomyces strain CNR-698, has been executed in nine steps and 6.9% overall yield. The key step involves the condensation of a 4,6-diBoc-protected 1,3,4,6-tetraaminobenzene derivative with dimethyl 2-ketoglutaconate, which effectively constructs the pyrrolidinone ring and the quinoline ring in a single step. This contributes a unique approach to the synthesis of pyrroloquinoline alkaloids that offers the advantages of brevity and relatively high overall yield.

Synthesis and characterization of monosaccharide-derived carbamates as low-molecular-weight gelators.

Sugar-based low-molecular-weight gelators are an interesting new class of compounds that are important in supramolecular chemistry and for the preparation of advanced materials. Previously, we synthesized a series of ester and carbamate derivatives of 4,6-O-benzylidene methyl-alpha-D-glucopyranoside and found that monosubstituted alkynyl esters with five to seven carbons and monosubstituted carbamates with saturated five- and seven-carbon chains are good gelators. To understand the structural requirement for the gelation of the carbamate derivatives (O-linked carbamates), a diverse series of analogs, including alkynyl, aryl, and alkyl halide derivatives, were prepared and analyzed. We found that for gelation the O-linked carbamate derivatives have different structural preferences than the ester derivatives. To exhibit gellation, the ester analogs favor alkyl-containing terminal acetylene groups and the carbamoyl derivatives prefer saturated hydrocarbons. Both the esters and the carbamates showed good gelation properties when they were functionalized with aryl side chains. We also synthesized and screened a new series of carbamates (N-linked carbamates) in which the nitrogen atom of the carbamate group is directly attached to the sugar ring. The N-linked carbamates are good gelators for aqueous DMSO and ethanol solutions, and two of the compounds are also able to form gels in pure water. Optical microscopy and scanning electron microscopy were used to characterize several representative gels. In general, long, narrow, uniform fibrous networks were observed for effective gelators. The structure-gelation correlation obtained here can be used in the design of new sugar-based low-molecular-weight gelators.

Synthesis of casimiroin and optimization of its quinone reductase 2 and aromatase inhibitory activities.

An efficient method has been developed to synthesize casimiroin (1), a component of the edible fruit of Casimiroa edulis, on a multigram scale in good overall yield. The route was versatile enough to provide an array of compound 1 analogues that were evaluated as QR2 and aromatase inhibitors. In addition, X-ray crystallography studies of QR2 in complex with compound 1 and one of its more potent analogues has provided insight into the mechanism of action of this new series of QR2 inhibitors. The initial biological investigations suggest that compound 1 and its analogues merit further investigation as potential chemopreventive or chemotherapeutic agents.