Characterization of AST-001 non-clinical pharmacokinetics: A novel selective AKR1C3-activated prodrug in mice, rats, and cynomolgus monkeys.

AST-001 is a chemically synthesized inactive nitrogen mustard prodrug that is selectively cleaved to a cytotoxic aziridine (AST-2660) via aldo-keto reductase family 1 member C3 (AKR1C3). The purpose of this study was to investigate the pharmacokinetics and tissue distribution of the prodrug, AST-001, and its active metabolite, AST-2660, in mice, rats, and monkeys. After single and once daily intravenous bolus doses of 1.5, 4.5, and 13.5 mg/kg AST-001 to Sprague-Dawley rats and once daily 1 h intravenous infusions of 0.5, 1.5, and 4.5 mg/kg AST-001 to cynomolgus monkeys, AST-001 exhibited dose-dependent pharmacokinetics and reached peak plasma levels at the end of the infusion. No significant accumulation and gender differences were observed after 7 days of repeated dosing. In rats, the half-life of AST-001 was dose independent and ranged from 4.89 to 5.75 h. In cynomolgus monkeys, the half-life of AST-001 was from 1.66 to 5.56 h and increased with dose. In tissue distribution studies conducted in Sprague-Dawley rats and in liver cancer PDX models in female athymic nude mice implanted with LI6643 or LI6280 HepG2-GFP tumor fragments, AST-001 was extensively distributed to selected tissues. Following a single intravenous dose, AST-001 was not excreted primarily as the prodrug, AST-001 or the metabolite AST-2660 in the urine, feces, and bile. A comprehensive analysis of the preclinical data and inter-species allometric scaling were used to estimate the pharmacokinetic parameters of AST-001 in humans and led to the recommendation of a starting dose of 5 mg/m2 in the first-in-human dose escalation study.

TH-302, a hypoxia-activated prodrug with broad in vivo preclinical combination therapy efficacy: optimization of dosing regimens and schedules.

PURPOSE: Subregional hypoxia is a common feature of tumors and is recognized as a limiting factor for the success of radiotherapy and chemotherapy. TH-302, a hypoxia-activated prodrug selectively targeting hypoxic regions of solid tumors, delivers a cytotoxic warhead to the tumor, while maintaining relatively low systemic toxicity. The antitumor activity, different dosing sequences, and dosing regimens of TH-302 in combination with commonly used conventional chemotherapeutics were investigated in human tumor xenograft models. METHODS: Seven chemotherapeutic drugs (docetaxel, cisplatin, pemetrexed, irinotecan, doxorubicin, gemcitabine, and temozolomide) were tested in combination with TH-302 in eleven human xenograft models, including non-small cell lung cancer (NSCLC), colon cancer, prostate cancer, fibrosarcoma, melanoma, and pancreatic cancer. RESULTS: The antitumor activity of docetaxel, cisplatin, pemetrexed, irinotecan, doxorubicin, gemcitabine, and temozolomide was increased when combined with TH-302 in nine out of eleven models tested. Administration of TH-302 2-8 h prior to the other chemotherapeutics yielded superior efficacy versus other sequences tested. Simultaneous administration of TH-302 and chemotherapeutics increased toxicity versus schedules with dosing separations. In a dosing optimization study, TH-302 administered daily at 50 mg/kg intraperitoneally for 5 days per week in the H460 NSCLC model showed the optimal response with minimal toxicity. CONCLUSIONS: TH-302 enhances the activity of a wide range of conventional anti-neoplastic agents in a broad panel of in vivo xenograft models. These data highlight in vivo effects of schedule and order of drug administration in regimen efficacy and toxicity and have relevance to the design of human regimens incorporating TH-302.

Pharmacokinetics of TH-302: a hypoxically activated prodrug of bromo-isophosphoramide mustard in mice, rats, dogs and monkeys.

PURPOSE: To characterize the pharmacokinetics of the prodrug, TH-302, and its active metabolite, bromo-IPM (Br-IPM), in nonclinical species. METHODS: TH-302 was administered in single oral, intraperitoneal and intravenous bolus doses to mice, rats, dogs and monkeys as well as in acute and chronic safety studies in rats and dogs as a 30-min intravenous infusion given once a week for 3 weeks. Assessments were made using liquid chromatography-tandem mass spectrometry. RESULTS: TH-302 was extensively distributed with high systemic clearance exceeding hepatic plasma flow in all species studied, resulting in half-lives ranging between 8 min (mice) and over 4 h (rats). In rats, TH-302 exhibited linear kinetics following intravenous administration and good oral bioavailability. In acute and chronic safety studies, there was no accumulation of TH-302 following once weekly dosing for 3 weeks in the rat and dog. Br-IPM plasma concentrations were a small fraction of the TH-302 plasma concentrations with significantly smaller percentages present in dogs than in rats. Allometric scaling predicted that the systemic clearance and steady-state volume of distribution in humans would be 38.8 l/h/m(2) and 34.3 l/m(2), respectively, resulting in a terminal elimination half-life of about 36 min. These values were similar to those observed in patients with solid tumors (27.1 l/h/m(2), 23.5 l/m(2) and 47 min). CONCLUSIONS: TH-302 exhibited good safety, efficacy and pharmacokinetic properties in nonclinical species, translating into favorable properties in humans.

Molecular and cellular pharmacology of the hypoxia-activated prodrug TH-302.

TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug (HAP) of bromo-isophosphoramide mustard currently undergoing clinical evaluation. Here, we describe broad-spectrum activity, hypoxia-selective activation, and mechanism of action of TH-302. The concentration and time dependence of TH-302 activation was examined as a function of oxygen concentration, with reference to the prototypic HAP tirapazamine, and showed superior oxygen inhibition of cytotoxicity and much improved dose potency relative to tirapazamine. Enhanced TH-302 cytotoxicity under hypoxia was observed across 32 human cancer cell lines. One-electron reductive enzyme dependence was confirmed using cells overexpressing human NADPH:cytochrome P450 oxidoreductase and radiolytic reduction established the single-electron stoichiometry of TH-302 fragmentation (activation). Examining downstream effects of TH-302 activity, we observed hypoxia-dependent induction of γH2AX phosphorylation, DNA cross-linking, and cell-cycle arrest. We used Chinese hamster ovary cell-based DNA repair mutant cell lines and established that lines deficient in homology-dependent repair, but not lines deficient in base excision, nucleotide excision, or nonhomologous end-joining repair, exhibited marked sensitivity to TH-302 under hypoxia. Consistent with this finding, enhanced sensitivity to TH-302 was also observed in lines deficient in BRCA1, BRCA2, and FANCA. Finally, we characterized TH-302 activity in the three-dimensional tumor spheroid and multicellular layer models. TH-302 showed much enhanced potency in H460 spheroids compared with H460 monolayer cells under normoxia. Multicellular layers composed of mixtures of parental HCT116 cells and HCT116 cells engineered to express an oxygen-insensitive bacterial nitroreductase showed that TH-302 exhibits a significant bystander effect.

Selective tumor hypoxia targeting by hypoxia-activated prodrug TH-302 inhibits tumor growth in preclinical models of cancer.

PURPOSE: Tumor hypoxia underlies treatment failure and yields a more aggressive, invasive, and metastatic cancer phenotype. TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug of the cytotoxin bromo-isophosphoramide mustard (Br-IPM). The purpose of this study is to characterize the antitumor activity of TH-302 and investigate its selective targeting of the hypoxic cells in human tumor xenograft models. EXPERIMENTAL DESIGN: Antitumor efficacy was assessed by tumor growth kinetics or by clonogenic survival of isolated cells after tumor excision. Hypoxic fractions (HF) were determined by immunohistochemistry and morphometrics of pimonidazole staining. Tumor hypoxia levels were manipulated by exposing animals to different oxygen concentration breathing conditions. The localization and kinetics of TH-302 induced DNA damage was determined by γH2AX immunohistochemistry. RESULTS: TH-302 antitumor activity was dose-dependent and correlated with total drug exposure. Correlation was found between antitumor activity and tumor HF across 11 xenograft models. Tumor-bearing animals breathing 95% O(2) exhibited attenuated TH-302 efficacy, with whereas those breathing 10% O(2) exhibited enhanced TH-302 efficacy, both compared with air (21% O(2)) breathing. TH-302 treatment resulted in a reduction in the volume of the HF 48 hours after dosing and a corresponding increase in the necrotic fraction. TH-302 induced DNA damage as measured by γH2AX was initially only present in the hypoxic regions and then radiated to the entire tumor in a time-dependent manner, consistent with TH-302 having a "bystander effect." CONCLUSIONS: The results show that TH-302 has broad antitumor activity and selectively targets hypoxic tumor tissues.

14-Aminocamptothecins: their synthesis, preclinical activity, and potential use for cancer treatment.

14-Aminocamptothecins were synthesized in good yields by treating camptothecin (1a) and 7-ethylcamptothecin (1b) with 90% fuming nitric acid either neat or in acetic anhydride and then followed by reduction of the resulting 14-nitrocamptothecins (2). 14-Aminocamptothecin (3a) and 7-ethyl-14-aminocamptothecin (3b) demonstrated excellent cytotoxic potency against human tumor cell lines in vitro, and they are not substrates for any of the major clinically relevant efflux pumps (MDR1, MRP1, and BCRP). 3a and 3b showed similar cytotoxicity against human and mouse bone marrow progenitor cells. This is in contrast to many camptothecin analogues, which are substrates for efflux pumps and are dramatically more toxic to human marrow cells relative to murine. 3a and 3b demonstrated significant brain penetration when dosed orally in mice. 3b showed significantly better efficacy relative to topotecan when dosed orally in the three ectopic xenograft models, H460, HT29, and PC-3. On the basis of its favorable in vitro and in vivo profile, 3b warrants future development.

Inhibition of both thioredoxin reductase and glutathione reductase may contribute to the anticancer mechanism of TH-302.

Selenium-containing thioredoxin reductase (TrxR) is an important target of cancer therapy. Many useful anticancer agents including bis-alkylating agents, cisplatin, and arsenic trioxide are known to interact with the selenocysteine dipeptide in the carboxy terminal region of thioredoxin reductase and inactivate its ability to reduce thioredoxin. Some investigators have postulated that the inactivation of TrxR may add to the cytotoxic potential of these anticancer agents. TH-302 is a newly developed antineoplastic drug which represents a potential new class of tumor selective hypoxia-activated prodrugs (HAPs). TH-302 is an inactive prodrug created by the covalent conjugation of 2-nitroimidazole as an oxygen sensor to bromo-isophosphoramide (Br-IPM). In the presence of severe hypoxia and near anoxia, the two imidazole sensor moiety undergoes reduction and the Br-IPM is released in situ. Bromo-IPM is a more potential analog of Chloro-IPM, the active alkylating moiety that is derived by activation of ifosfamide (IFO). We previously demonstrated that IFO could inhibit tumor TrxR activity and chloro-IPM is known to bind covalently to the seleno-cysteine dipeptide in thioredoxin reductase. The present study assessed the ability of TH-302 to activate in the tumors of mice-bearing hepatoma 22 (H22) and inactivate the tumor TrxR. In mice-bearing hepatoma 22 (H22) solid tumors, intraperitoneal (i.p.) injection with TH-302 at the dose of 200 mg/kg administered twice, a regimen which was well tolerated by the mice, significantly inhibited tumor growth. Also in this mice model, i.p. TH-302 at the dose of 300 mg/kg, which would be the maximum single i.p. administration dose tolerated by mice, and which induced only 2% body weight loss, significantly inhibited both TrxR and glutathione reductase (GR) activities by 46% (P < 0.001) and 60% (P < 0.001) as compared with the controls, respectively, at 3 h after the injection. Since TrxR is a key player in thioredoxin system and GR is the major reductase for the reduction of oxidized glutathione in glutathione system, the present results imply the anticancer effect of TH-302 is associated concurrently with modulation of TrxR and GR. These findings suggest that the anticancer activity of TH-302 in this model system may associate with both DNA alkylation and the modulation of TrxR and GR. In addition, they suggest that, by inhibition of these two critical reductases, with less glutathione available to intercept the reactive intermediates involved in DNA alkylation, the antitumor effects of the chemotherapy would be enhanced.

Potent and highly selective hypoxia-activated achiral phosphoramidate mustards as anticancer drugs.

A series of achiral hypoxia-activated prodrugs were synthesized on the basis of the DNA cross-linking toxin of the prodrug, ifosfamide. The hypoxia-selective cytotoxicity of several of the compounds was improved over previously reported racemic mixtures of chiral bioreductive phosphoramidate prodrugs. Prodrugs activated by 2-nitroimidazole reduction demonstrated up to 400-fold enhanced cytotoxicity toward H460 cells in culture under hypoxia versus their potency under aerobic conditions. Compounds were further assessed for their stability to cytochrome P450 metabolism using a liver microsome assay. The 2-nitroimidazole containing lead compound 3b (TH-302) was selectively potent under hypoxia and stable to liver microsomes. It was active in an in vivo MIA PaCa-2 pancreatic cancer orthotopic xenograft model as a monotherapy and demonstrated dramatic efficacy when used in combination with gemcitabine, extending survival with one of eight animals tumor free at day-44. Compound 3b has emerged as a promising antitumor agent that shows excellent in vivo efficacy and is currently being evaluated in the clinic.

Potent antitubulin tumor cell cytotoxins based on 3-aroyl indazoles.

A series of 3-aroyl indazoles was synthesized. Modification of the C-7 position resulted in a significant structure-activity relationship (SAR) with acetylene modifications conferring unusual potency in a tumor cell cytotoxicity assay. The most potent compounds exceeded the activity of combretastatin A4 (CA-4), showing single digit nM IC50 values against all cell lines tested including those with known efflux resistance pumps. The inhibition of in vitro tubulin polymerization was comparable to CA-4, consistent with tubulin being the target for these compounds. Competition binding experiments employing [3H]colchicine and purified tubulins demonstrated that the compound specifically binds to the colchicine site.

Molecular structures and compositions of trans-1,2-dichlorocyclohexane and trans-1,2-difluorocyclohexane in the gas phase: an electron-diffraction investigation.

The structures and compositions of gaseous trans-1,2-dichloro- (DCCH) and trans-1,2-difluorocyclohexane (DFCH), each of which may exist with the halogen atoms in a diaxial (aa) or diequatorial (ee) conformation, have been investigated by electron diffraction. The analysis was aided by rotational constants from microwave spectroscopy for the ee form of DFCH and by ab initio and density functional theory molecular orbital calculations for all species. The skeletons of the molecules have similar parameter values, but for the Cl-C-C-Cl and F-C-C-F fragments there are significant differences between the corresponding C-C-X bond angles and the X-C-C-X torsion angles in the two systems. There are also significant differences between the values of these parameters in the aa and ee forms of the same system. The composition of DCCH at 100 degrees C was measured to be 60(4)% aa, and that of DFCH at 70 degrees C was 42(7)% aa; the uncertainties are estimated 2sigma. From the preferred B3LYP/aug-cc-pVTZ calculations, the predicted theoretical composition is 51.2% aa for DCCH and 40.8% aa for DFCH. (Calculations at the levels B3LYP/6-31G(d) and MP2/6-31G(d) give similar results for DCCH, but both predict more aa than ee for DFCH.) Values (r(g)/A and angle(alpha)/degree) for some of the more important parameters of the aa/ee forms of DCCH are = 1.525(4)/1.525(6), C-Cl = 1.806(2)/1.787(2), angleC2-C1-Cl = 107.3(3)/111.5(3), angleC1-C2-C3 = 113.9(5)/111.6(5), angleC2-C3-C4 = 111.3(12)/109.9(12), and Cl-C2-C3-Cl = 165.3(9)/-59.4(9); and for DFCH C-C = 1.525(6)/1.520(9), C-F = 1.398(2)/1.390(2), angleC2-C1-F = 106.5(6)/109.2(6), angleC1-C2-C3 = 111.4(9)/110.9(9), angleC2-C3-C4 = 113.1(10)/113.1(10), and F-C2-C3-F = 171.1(37)/-67.2(37). The structures and compositions are discussed.

DNA binding ligands with in vivo efficacy in murine models of bacterial infection: optimization of internal aromatic amino acids.

DNA binding ligands with potent antimicrobial activity against Gram-positive bacteria were further optimized by variation of the internal aromatic amino acids. This modification led to compounds with improved in vivo efficacy in lethal murine models of peritonitis (methicillin-resistant S. aureus, MRSA) and lung infection (S. pneumoniae).

DNA binding ligands targeting drug-resistant Gram-positive bacteria. Part 2: C-terminal benzimidazoles and derivatives.

The synthesis and in vitro potency of DNA minor-groove binding antibacterials lacking the C-terminal amide bond are described. The crescent shaped molecules bear the positively charged amino group at an internal pyrrole unit instead of the C-terminus. Three structural parameters were investigated: the N-terminal unit, the internal amino group, and the C-terminal ring system. Several compounds demonstrated good in vitro potency against various Gram-positive bacteria and some molecules were moderately active against Escherichia coli, a representative Gram-negative strain.

DNA binding ligands targeting drug-resistant bacteria: structure, activity, and pharmacology.

We describe the lead optimization and structure-activity relationship of DNA minor-groove binding ligands, a novel class of antibacterial molecules. These compounds have been shown to target A/T-rich sites within the bacterial genome and, as a result, inhibit DNA replication and RNA transcription. The optimization was focused on N-terminal aromatic heterocycles and C-terminal amines and resulted in compounds with improved in vivo tolerability and excellent in vitro antibacterial potency (MIC >/= 0.031 microg/mL) against a broad range of Gram-positive pathogens, including drug-resistant strains such as methicillin-resistant Stapylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae (PRSP), and vancomycin-resistant Enterococcus faecalis (VRE). In a first proof-of-concept study, a selected compound (35) showed in vivo efficacy in a mouse peritonitis model against methicillin-sensitive S. aureus infection with an ED(50) value of 30 mg/kg.

4,5-dehydro- and 4,5,15,16-bis(dehydro)octafluoro[2.2]paracyclophanes: facile generation and extraordinary Diels-Alder reactivity.

Dehydroiodination of 4-iodo- and 4,15-diiodo-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane by treatment with KO(t)Bu in the presence of benzene, naphthalene, anthracene, and [2.2]paracyclophane affords each of the corresponding Diels-Alder mono- and bis-cycloadducts derived from the presumed aryne intermediates in high yield. Monoadducts of t-butylbenzene and furan are also obtained in excellent yield. All of the products were characterized by their NMR spectra, with four of them also being confirmed by X-ray crystallography. The extraordinary selectivity/reactivity of the aryne intermediate is discussed.