Synthesis and Evaluation of Imidazo[1,2-a]pyridine Analogues of the ZSTK474 Class of Phosphatidylinositol 3-Kinase Inhibitors.

Using a scaffold-hopping approach, imidazo[1,2-a]pyridine analogues of the ZSTK474 (benzimidazole) class of phosphatidylinositol 3-kinase (PI3K) inhibitors have been synthesized for biological evaluation. Compounds were prepared using a heteroaryl Heck reaction procedure, involving the palladium-catalysed coupling of 2-(difluoromethyl)imidazo[1,2-a]pyridines with chloro, iodo or trifluoromethanesulfonyloxy (trifloxy) substituted 1,3,5-triazines or pyrimidines, with the iodo intermediates being preferred in terms of higher yields and milder reaction conditions. The new compounds maintain the PI3K isoform selectivity of their benzimidazole analogues, but in general show less potency.

Synthesis and biological evaluation of sulfonamide analogues of the phosphatidylinositol 3-kinase inhibitor ZSTK474.

Replacement of one of the morpholine groups of the phosphatidylinositol 3-kinase (PI3K) inhibitor ZSTK474 (1) with sulfonamide containing substituents produced a new class of active and potent PI3Kα inhibitors. Solubility issues prevented all but the 6-amino derivative 17 from being evaluated in vivo, but the clear activity of this compound demonstrated that this class of PI3K inhibitor shows great promise.

Biological characterization of SN32976, a selective inhibitor of PI3K and mTOR with preferential activity to PI3Kα, in comparison to established pan PI3K inhibitors.

Multiple therapeutic agents have been developed to target the phosphatidylinositol 3-kinase (PI3K) signaling pathway, which is frequently dysregulated in cancer promoting tumor growth and survival. These include pan PI3K inhibitors, which target class Ia PI3K isoforms and have largely shown limited single agent activity with narrow therapeutic windows in clinical trials. Here, we characterize SN32976, a novel pan PI3K inhibitor, for its biochemical potency against PI3K isoforms and mTOR, kinase selectivity, cellular activity, pharmacokinetics, pharmacodynamics and antitumor efficacy relative to five clinically-evaluated pan PI3K inhibitors: buparlisib, dactolisib, pictilisib, omipalisib and ZSTK474.

Recent developments in anticancer drug delivery using cell penetrating and tumor targeting peptides.

Efficient intracellular trafficking and targeted delivery to the site of action are essential to overcome the current drawbacks of cancer therapeutics. Cell Penetrating Peptides (CPPs) offer the possibility of efficient intracellular trafficking, and, therefore the development of drug delivery systems using CPPs as cargo carriers is an attractive strategy to address the current drawbacks of cancer therapeutics. Additionally, the possibility of incorporating Tumor Targeting Peptides (TTPs) into the delivery system provides the necessary drug targeting effect.

Development of Rapidly Metabolized and Ultra-Short-Acting Ketamine Analogs.

Background: Ketamine is a well-established, rapidly acting dissociative anesthetic. Clinical use is limited by prolonged psychotomimetic phenomena on emergence, often requiring the coadministration of additional hypnotic drugs. We hypothesized that the development of ketamine ester analogs with ultrashort offset times might markedly reduce the dysphoric emergence phenomena and, hence, increase the utility of a ketamine-like hypnotic and analgesic.

Repurposing the chemical scaffold of the anti-arthritic drug Lobenzarit to target tryptophan biosynthesis in Mycobacterium tuberculosis.

The emergence of extensively drug-resistant strains of Mycobacterium tuberculosis (Mtb) highlights the need for new therapeutics to treat tuberculosis. We are attempting to fast-track a targeted approach to drug design by generating analogues of a validated hit from molecular library screening that shares its chemical scaffold with a current therapeutic, the anti-arthritic drug Lobenzarit (LBZ). Our target, anthranilate phosphoribosyltransferase (AnPRT), is an enzyme from the tryptophan biosynthetic pathway in Mtb.

Structure-activity relationships for ketamine esters as short-acting anaesthetics.

A series of aliphatic esters of the non-opioid anaesthetic/analgesic ketamine were prepared and their properties as shorter-acting analogues of ketamine itself were explored in an infused rat model, measuring the time after infusion to recover from both the anaesthetic (righting reflex) and analgesic (response to stimulus) effects. The potency of the esters as sedatives was not significantly related to chain length, but Me, Et and i-Pr esters were the more dose potent (up to twofold less than ketamine), whereas n-Pr esters were less potent (from 2- to 6-fold less than ketamine). For the Me, Et and i-Pr esters recovery from anaesthesia was 10-15-fold faster than from ketamine itself, and for the n-Pr esters it was 20-25-fold faster than from ketamine.

Synthesis and biological evaluation of novel phosphatidylinositol 3-kinase inhibitors: Solubilized 4-substituted benzimidazole analogs of 2-(difluoromethyl)-1-[4,6-di(4-morpholinyl)-1,3,5-triazin-2-yl]-1H-benzimidazole (ZSTK474).

A range of 4-substituted derivatives of the pan class I PI 3-kinase inhibitor 2-(difluoromethyl)-1-[4,6-di-(4-morpholinyl)-1,3,5-triazin-2-yl]-1H-benzimidazole (ZSTK474) were prepared in a search for more soluble analogs. 4-Aminoalkoxy substituents provided the most potent derivatives, with the 4-O(CH2)3NMe2 analog (compound 14) being identified as displaying the best overall activity in combination with good aqueous solubility (25 mg/mL for the hydrochloride salt). This compound was tested in a U87MG xenograft model, but displayed less potency than ZSTK474 as a result of an unfavorable pharmacokinetic profile.

Structure-activity relationships for 4-anilinoquinoline derivatives as inhibitors of the DNA methyltransferase enzyme DNMT1.

A series of 4-anilinoquinoline derivatives related to the known inhibitor SGI-1027, containing side chains of varying pK(a), were prepared by acid-catalysed coupling of the pre-formed side chains with 4-chloroquinolines. The compounds were evaluated for their ability to reduce the level of DNMT1 protein in HCT116 human colon carcinoma cells by Western blotting. With a very strongly basic N-methylpyridinium side chain, only NHCO-linked compounds were effective, whereas less strongly basic ((diaminomethylene)hydrazono)ethyl or 3-methylpyrimidine-2,4-diamine side chains allowed both NHCO- and CONH-linked compounds to show activity.

Synthesis and biological evaluation of novel analogues of the pan class I phosphatidylinositol 3-kinase (PI3K) inhibitor 2-(difluoromethyl)-1-[4,6-di(4-morpholinyl)-1,3,5-triazin-2-yl]-1H-benzimidazole (ZSTK474).

A structure-activity relationship (SAR) study of the pan class I PI 3-kinase inhibitor 2-(difluoromethyl)-1-[4,6-di(4-morpholinyl)-1,3,5-triazin-2-yl]-1H-benzimidazole (ZSTK474) identified substitution at the 4 and 6 positions of the benzimidazole ring as having significant effects on the potency of substituted derivatives. The 6-amino-4-methoxy analogue displayed a greater than 1000-fold potency enhancement over the corresponding 6-aza-4-methoxy analogue against all three class Ia PI 3-kinase enzymes (p110α, p110β, and p110δ) and also displayed significant potency against two mutant forms of the p110α isoform (H1047R and E545K). This compound was also evaluated in vivo against a U87MG human glioblastoma tumor xenograft model in Rag1(-/-) mice, and at a dose of 50 mg/kg given by ip injection at a qd × 10 dosing schedule it dramatically reduced cancer growth by 81% compared to untreated controls.

Structure of the D-alanylgriseoluteic acid biosynthetic protein EhpF, an atypical member of the ANL superfamily of adenylating enzymes.

The structure of EhpF, a 41 kDa protein that functions in the biosynthetic pathway leading to the broad-spectrum antimicrobial compound D-alanylgriseoluteic acid (AGA), is reported. A cluster of approximately 16 genes, including ehpF, located on a 200 kbp plasmid native to certain strains of Pantoea agglomerans encodes the proteins that are required for the conversion of chorismic acid to AGA. Phenazine-1,6-dicarboxylate has been identified as an intermediate in AGA biosynthesis and deletion of ehpF results in accumulation of this compound in vivo.

A new class of quinoline-based DNA hypomethylating agents reactivates tumor suppressor genes by blocking DNA methyltransferase 1 activity and inducing its degradation.

Reactivation of silenced tumor suppressor genes by 5-azacytidine (Vidaza) and its congener 5-aza-2'-deoxycytidine (decitabine) has provided an alternate approach to cancer therapy. We have shown previously that these drugs selectively and rapidly induce degradation of the maintenance DNA methyltransferase (DNMT) 1 by a proteasomal pathway. Because the toxicity of these compounds is largely due to their incorporation into DNA, it is critical to explore novel, nonnucleoside compounds that can effectively reactivate the silenced genes.

Crystal structure of the pyocyanin biosynthetic protein PhzS.

The human pathogen Pseudomonas aeruginosa produces pyocyanin, a blue-pigmented phenazine derivative, which is known to play a role in virulence. Pyocyanin is produced from chorismic acid via the phenazine pathway, nine proteins encoded by a gene cluster. Phenazine-1-carboxylic acid, the initial phenazine formed, is converted to pyocyanin in two steps that are catalyzed by the enzymes PhzM and PhzS.

Phenazine-1-carboxamides: structure-cytotoxicity relationships for 9-substituents and changes in the H-bonding pattern of the cationic side chain.

A series of phenazine-1-carboxamides were prepared, including variations in both chromophore substituents and the nature of the cationic side chain. The novel side-chain analogues were prepared from the corresponding phenazine-1-carboxylic acids via Schmidt conversion to the 1-amines and from the corresponding 1-halides. Structure-cytotoxicity relationships for these compounds in a panel of tumor cell lines showed that there is very limited scope for variation of the structure of the 1-carboxamide side chain, consistent with the recent structural model of how tricyclic carboxamides bind to DNA.

Radical properties governing the hypoxia-selective cytotoxicity of antitumor 3-amino-1,2,4-benzotriazine 1,4-dioxides.

Revealing the free radical mechanism by which the anticancer drug tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide) induces hypoxia-selective cytotoxicity, is seen as a way forward to develop clinically useful bioreductive drugs against chemo- and radiation-resistant hypoxic tumor cells. Our previous studies point to the formation of an active benzotriazinyl radical following the one-electron reduction of tirapazamine and its elimination of water from the initial reduction intermediate, and have suggested that this species is a cytotoxin. In this paper we have used pulse radiolysis to measure the one-electron reduction potentials of the benzotriazinyl radicals E(B*,H(+)/B) of 30 analogues of tirapazamine as well as the one-electron reduction potentials of their two-electron reduced metabolites, benzotriazine 1-oxides E(B/B*-).

Oxidation of 2-deoxyribose by benzotriazinyl radicals of antitumor 3-amino-1,2,4-benzotriazine 1,4-dioxides.

Tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide) is the lead bioreductive drug in clinical trials as an anticancer agent to kill refractory hypoxic cells of solid tumors. It has long been known that, upon metabolic one-electron reduction, tirapazamine induces lethal DNA double strand breaks in hypoxic cells. These strand breaks arise from radical damage to the ribose moiety of DNA, and in this pulse radiolysis and product analysis study we examine mechanistic aspects of the dual function of tirapazamine and analogues in producing radicals of sufficient power to oxidize 2-deoxyribose to form radicals, as well as the ability of the compounds to oxidize the resulting deoxyribose radicals to generate the strand breaks.

DNA-targeted 1,2,4-benzotriazine 1,4-dioxides: potent analogues of the hypoxia-selective cytotoxin tirapazamine.

Tirapazamine (TPZ, 1,2,4-benzotriazin-3-amine 1,4-dioxide) is a bioreductive hypoxia-selective cytotoxin, currently in phase II/III clinical trials in combination with radiotherapy and with cisplatin-based chemotherapy. We have prepared a series of 1,2,4-benzotriazine 1,4-dioxide (BTO) analogues of TPZ where a DNA-targeting chromophore is attached at the 3-position via a flexible linker. DNA binding affinity was modified through variation of the chromophore or the pK(a) of the linker chain.

Activation of 3-amino-1,2,4-benzotriazine 1,4-dioxide antitumor agents to oxidizing species following their one-electron reduction.

The mechanism by which a benzotriazine 1,4-dioxide class of anticancer drugs produce oxidizing radicals following their one-electron reduction has been investigated using tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide, 1) and its 6-methoxy (6), 7-dimethylamino (7), and 8-methyl (8) analogues. By measuring the changes in absorption with pH, we found that the radical anions undergo protonation with radical pK(r) values of 6.19 +/- 0.

Structure-activity relationships of 1,2,4-benzotriazine 1,4-dioxides as hypoxia-selective analogues of tirapazamine.

Tirapazamine (TPZ, 1,2,4-benzotriazin-3-amine 1,4-dioxide) is a bioreductive hypoxic cytotoxin currently in Phase II/III clinical trials in combination with radiotherapy and with cisplatin-based chemotherapy. As part of a program to develop TPZ analogues with improved solubility/potency and therapeutic indices, we synthesized 34 1,2,4-benzotriazin-3-amine 1,4-dioxides (BTO) to examine structure-activity relationships (SAR) for ring substitution. The electronic, hydrophobic, and steric parameters of substituents at the 5-, 6-, 7-, and 8-positions were systematically varied, and the aqueous solubility and one-electron reduction potentials [E(1)] of the analogues were determined.

Structure-activity relationships for pyrido-, imidazo-, pyrazolo-, pyrazino-, and pyrrolophenazinecarboxamides as topoisomerase-targeted anticancer agents.

Heterocyclic phenazinecarboxamides were prepared by condensation of aminoheterocycles and 2-halo-3-nitrobenzoic acids, followed by reductive ring closure and amidation. They showed similar inhibition of paired cell lines that underexpressed topo II or overexpressed P-glycoprotein, indicating a non topo II mechanism of cytotoxicity and indifference to P-glycoprotein mediated multidrug resistance. Compounds with a fused five-membered heterocyclic ring were generally less potent than the pyrido[4,3-a]phenazines.

Synthesis and evaluation of unsymmetrical bis(arylcarboxamides) designed as topoisomerase-targeted anticancer drugs.

Symmetrical dimers of lipophilic intercalating chromophores linked by cation-containing chains have recently been shown to have broad-spectrum in vivo anticancer activity. We report the preparation and evaluation of a series of both symmetric and unsymmetric dimers of a variety of intercalating chromophores of varied DNA binding strength, including naphthalimides, acridines, phenazines, oxanthrenes and 2-phenylquinolines. The unsymmetrical dimers were prepared by sequential coupling of the chromophores to linkers with selectively protected primary terminal amines to ensure high yields and unequivocal product.