AS-924, a novel, orally active, bifunctional prodrug of ceftizoxime: physicochemical properties, oral absorption in animals, and antibacterial activity.

AS-924 is an oral prodrug of the antibiotic ceftizoxime (CTIZ), a parenteral use cephalosporin. This novel prodrug, produced by esterifying CTIZ with a lipophilic pivaloyloxymethyl (POM) group and introducing a water soluble L-alanyl group, is expected to increase the bioavailability and thereby, augment the antibacterial activity of CTIZ in vivo compared with existing prodrugs. To study the effect of the L-alanyl group in AS-924 on its bioavailability, the plasma concentration profiles of CTIZ in dogs were examined following the dosing of AS-924 and CTIZ-POM, in powder form, after pretreatment with the antacid ranitidine, and following the dosing of AS-924 after pretreatment with a gastrointestinal motility stimulant metoclopramide or suppressant scopolamine butylbromide. The absorption rate of AS-924 was constant under these different conditions due to its unique balance of lipophilicity and water solubility. CTIZ is as antibacterially active as pre-existing oral cephalosporins against Gram-positive clinical isolates, while being more active against all Gram-negative isolates-particularly Enterobacteriaceae and Haemophilus influenzae. A simulation model for the eradication profile of bacteria in computer programmed pharmacokinetic (PK) system was carried out to study the antibacterial action of CTIZ in human. CTIZ was proven to eradicate Streptococcus pneumoniae and H. influenzae effectively, while cefpodoxime (CPOD), the active moiety of CPOD proxetil, eradicated S. pneumoniae, but not H. influenzae. These results confirm that, AS-924 is a potent oral antibiotic and would be expected to be clinically effective and efficient.     

Effect of antacid pretreatment on the pharmacokinetics of AS-924, a novel ester-type cephem antibiotic--comparison with cefteram-pivoxil.

The effect of pretreatment with ranitidine, an antacid, on the absorption of AS-924, a novel prodrug-type cephem antibiotic derived from ceftizoxime (CTIZ), was examined in eight healthy adult male volunteers by the cross-over method, using cefteram-pivoxil (CTER-PI) as the control drug. The C(max) and area under the concentration (AUC) values and cumulative urinary excretion rate (0-24 h) of cefteram (CTER) after administration of CTER-PI decreased by 32, 38 and 37%, respectively, in the ranitidine pretreatment group whereas those of AS-924 were not affected by the antacid. The urinary levels of pivaloyl-carnitine determined to evaluate the solubility of these antibiotics in the gastrointestinal tract suggested that this was not affected by ranitidine. These results indicate that the absorption of CTER-PI was affected by pretreatment with ranitidine largely due to inactivation of this antibiotic in the gastrointestinal tract at high pH rather than to a decrease in solubility. In contrast, isomerization of AS-924 was hardly induced by the elevation of pH, thus demonstrating that AS-924 was less likely to be affected by pretreatment with antacids.     

Effects of gastrointestinal stimulant and suppressant pretreatment on the pharmacokinetics of AS-924, a novel ester-type cephem antibiotic.

The effects of pretreatment with the gastrointestinal stimulant domperidone and the suppressant scopolamine butylbromide on the absorption of AS-924, a novel prodrug-type cephem antibiotic, were investigated in six healthy adult male volunteers by a cross-over method. The T(max) of ceftizoxime (CTIZ), the active moiety of AS-924, was slightly prolonged by scopolamine butylbromide (T(max)=1.8 vs. 1.5 h for the group without pretreatment). However, there were no significant differences in pharmacokinetic parameters including T(max), cumulative urinary excretion rates of CTIZ and cumulative urinary excretion rates of pivaloylcarnitine for 12 h after the dosing between the pretreated and control groups. Domperidone did not affect the absorption of AS-924.     

Pharmacokinetics of cefcapene pivoxil and AS-924 in gastrectomized patients.

To investigate the effects of gastrectomy on the absorption of drugs, the blood concentrations of the active moieties, cefcapene (CCAP) and ceftizoxime (CTIZ), were determined in 36 gastrectomized patients after oral administration of cefcapene pivoxil (CCAP-PI) and AS-924, prodrug type cephem antibiotics with different solubility-profiles. In patients with gastrectomy, the C(max) and AUC for CCAP-PI whose solubility depended on the acidity of gastric juice, were lower than in the controls; whereas those for AS-924 were comparable with values in the control group. The T(max) was affected by the extent of gastrectomy; the T(max) value was the lowest in patients who had undergone total gastrectomy Roux-Y, followed by Billroth II and Billroth I procedure of subtotal gastrectomy. These results indicate the need to select drugs and to instruct gastrectomized patients regarding dosage and administration, taking the pharmacokinetics of drugs into consideration.     

Effects of the quantity of water and milk ingested concomitantly with AS-924, a novel ester-type cephem antibiotic, on its pharmacokinetics.

The effect of the quantity of water ingested concomitantly with drugs, on the absorption of AS-924, a novel prodrug-type cephem antibiotic, was studied in five healthy adult volunteers by a cross-over method, using cefteram-pivoxil (CTER-PI) as the control drug. In addition, the effect of milk on the absorption of AS-924 was also investigated. The absorption of CTER-PI was significantly reduced when administered together with 30 ml of water compared with its absorption when administered together with 150 ml of water, whereas no such reduction was found in the case of AS-924. Ingestion of milk did not significantly affect the absorption of AS-924. These results confirm that absorption of AS-924 after oral administration is not likely to be affected by the quantity of water taken concomitantly with the drug, nor by milk.     

Effects of food intake and age on the pharmacokinetics of AS-924, a novel ester-type cephem antibiotic. Comparison with cefpodoxime proxetil.

The effects of food intake and age on intestinal absorption of AS-924, a novel prodrug-type cephem antibiotic, were examined in 16 healthy adult volunteers (eight young volunteers and eight elderly volunteers) by the cross-over method, using cefpodoxime proxetil (CPOD-PR) as the control drug. The gastrointestinal absorption of AS-924 and CPOD-PR was increased slightly by food intake and the extent of increase was slightly greater after administration of CPOD-PR. The absorption of AS-924 was not affected by age, whereas intestinal absorption of CPOD-PR increased with age. In conclusion, these results confirmed that AS-924 has the unique characteristics as a novel prodrug and that its absorption is less likely to be affected by food intake and age.     

A novel orally active dopamine prodrug TA-870. II. Evidence that TA-870 is a dopamine prodrug

The mechanism of action of a new orally active dopamine (DA) prodrug, TA-870 (N-(N-acetyl-L-methionyl)-O,O-bis(ethoxycarbonyl)(DA) was studied. When TA-870 (1 mg/kg) was injected in anesthetized dogs, renal vascular resistance was decreased and renal blood flow was increased. The renal vasodilatory effect of TA-870 correlated with the plasma level of DA but not with the level of de-ethoxycarbonyl metabolite of TA-870 (i.e., N-(N-acetyl-L-methionyl)DA; DEC-TA-870). The renal vasodilatory effect of TA-870 was inhibited strongly by haloperidol and slightly by propranolol. Pretreatment with phenoxybenzamine enhanced the renal vasodilatory effect of TA-870. In the isolated rabbit splenic artery, TA-870 and DEC-TA-870 showed no effects, whereas dopamine showed a contracting effect, which was inhibited by phentolamine. In the propranolol- and phentolamine-treated splenic artery, TA-870 and DEC-TA-870 caused weak relaxant effects on PGF2 alpha-induced contraction. These effects were not antagonized by metoclopramide. On the other hand, DA showed a strong relaxant effect, which was competitively inhibited by metoclopramide. In addition, TA-870 and DEC-TA-870 further relaxed the artery that had been maximally relaxed by DA. We concluded that TA-870 and DEC-TA-870 exert weak vasodilatory effects that are different from that of DA in vitro, and that TA-870 exerts its vasodilatory effect after its conversion to free DA in vivo.     

Characterization of four distinct monoclonal antibodies specific to BmK AS-1, a novel scorpion bioactive polypeptide.

Four monoclonal antibodies designed as 2#, 3#, 4# and 5# have been raised against a novel bioactive polypeptide BmK AS-1 purified from the Chinese scorpion Buthus martensi Karsch. All of these antibodies exhibited specific affinity with antigen by ELISA and Biosensor assay. Western blot analysis showed that 3# and 4# were able to recognize the denatured antigen, but not 2# and 5#. These antibodies could cross-react with BmK AS, but not with other types of BmK neurotoxins such as BmK I (an alpha-like toxin) and BmK IT (an excitatory insect-selective toxin), and in which only 5# can partially react with BmK IT2 (a depressant insect-selective toxin). Immunocytochemical staining demonstrated that 3#, 4# and 5# antibodies can visualize the antigen bound to the membrane of SK-N-SH neuroblast cells, with the exception of 2#. This suggests that either conformation alteration of receptor binding might be prone to nonvisualization or the epitope recognized by antibody 2# might be overlapped with receptor binding sites of antigen. The antibodies developed in the study should provide powerful new tools for investigating the structure/function relationship and pharmacological mechanism of scorpion neurotoxins.     

Clinical pharmacokinetics of XP13512, a novel transported prodrug of gabapentin

Gabapentin absorption occurs in only a limited region of the small intestine and saturates at doses used clinically, resulting in dose-dependent pharmacokinetics, high interpatient variability, and potentially ineffective drug exposure. XP13512/GSK1838262 is a novel transported prodrug of gabapentin that is absorbed throughout the entire length of the intestine by high-capacity nutrient transporters. In 4 studies of healthy volunteers (136 subjects total), the pharmacokinetics of XP13512 immediate- and extended-release formulations were compared with those of oral gabapentin. XP13512 immediate-release (up to 2800 mg single dose and 2100 mg twice daily) was well absorbed (>68%, based on urinary recovery of gabapentin), converted rapidly to gabapentin, and provided dose-proportional exposure, whereas absorption of oral gabapentin declined with increasing doses to <27% at 1200 mg. Compared with 600 mg gabapentin, an equimolar XP13512 extended-release dose provided extended gabapentin exposure (time to maximum concentration, 8.4 vs 2.7 hours) and superior bioavailability (74.5% vs 36.6%). XP13512 may therefore provide more predictable gabapentin exposure and decreased dosing frequency.     

TLK-286: a novel glutathione S-transferase-activated prodrug

Telik, Inc. (Palo Alto, CA, USA) is currently developing TLK-286, a novel prodrug that is preferentially activated by glutathione S-transferase P1-1 (GST-pi). TLK-286 is the lead clinical candidate from a group of rationally designed glutathione analogues designed to exploit high GST-pi levels in solid tumours and drug-resistant cell populations. This concept was based on extensive literature showing that the overexpression of GST-pi in human tumours is associated with malignancy, poor prognosis and the development of drug resistance. Thus, the selective targeting of susceptible tumour phenotypes is a strategy that should result in the release of more active drug in malignant cells compared with normal tissue, thereby achieving an improved therapeutic index. A number of published preclinical studies have confirmed the mechanism of action of this drug. In a series of Phase II clinical trials, TLK-286 was initially shown to have clinical activity and a favorable toxicity profile as a single agent in the salvage setting in ovarian, non-small cell lung, breast and colorectal cancers. Recently, Phase II trials have been reported that demonstrated TLK-286 is active and did not increase the toxicity in combination treatment regimens with standard chemotherapeutic agents, including platinums, taxanes and anthracyclines in previously treated patients with ovarian and non-small cell lung cancers, and in the first-line treatment setting in non-small cell lung cancer patients. TLK-286 is also presently under active testing in Phase III settings for non-small cell lung and ovarian cancers.     

TLK-286: a novel glutathione S-transferase-activated prodrug

Background: Based partially on encouraging findings from preclinical models, interest has grown in therapeutic inhibition of NF-κB to limit inflammatory injury during sepsis. However, NF-κB also regulates protective responses, and predicting the net survival effects of such inhibition may be difficult. Objectives: To highlight the caution necessary with this therapeutic approach, we review our investigations in a mouse sepsis model with parthenolide and ethyl pyruvate, two NF-κB inhibitors proposed for clinical study. Results: Consistent with published studies, parthenolide decreased NF-κB binding activity and inflammatory cytokine release from lipopolysaccharide (LPS) stimulated RAW 264.7 cells in vitro. In LPS-challenged mice (C57BL/6J), however, while both agents decreased lung and kidney NF-κB binding activity and plasma cytokines early (1 – 3 h), these measures were increased later (6 – 12 h) in patterns differing significantly over time. Furthermore, despite studying several doses of parthenolide (0.25 – 4.0 mg/kg) and ethyl pyruvate (0.1 – 100 mg/kg), each produced small but consistent decreases in survival which overall were significant (p ≤ 0.04 for each agent). Conclusion: While NF-κB inhibitors hold promise for inflammatory conditions such as sepsis, caution is necessary. Clear understanding of the net effects of NF-κB inhibitors on outcome will be necessary before such agents are used clinically.     

Pharmacological profile of AS-9705, a novel benzotriazolecarboxamide derivative,as a gastroprokinetic agent with potent anti-emetic activity

The pharmacological profile of AS-9705 ((R)-N-(1-ethyl-1H-hexahydroazepin-3- yl)-6- methoxy-1H-benzotriazole-5-carboxamide fumarate monohydrate, CAS 219622-61-4), a novel gastroprokinetic agent with potent anti-emetic activity, was investigated in the present study. AS-9705 inhibited [3H]spiperone binding to human dopamine D2.long receptors, and [3H]R(+)-7-OH-DPAT binding to human dopamine D3 receptors (IC50 values of 58.5 +/- 14.0 and 60.8 +/- 7.8 (nmol/l), respectively) and had negligible affinity (IC50 > 10 mumol/l) for other neurotransmitter recognition sites examined. Moreover, in ferrets or dogs, AS-9705 dose-dependently inhibited emesis induced by R(+)-7-OH-DPAT and apomorphine with ID50 values of 0.05 mg/kg p.o. and 0.04 mg/kg p.o., respectively. AS-9705 dose-dependently enhanced normal gastric emptying and potently inhibited the delay in gastric empting induced by apomorphine, morphine, cisplatin, clonidine and cholecystokinin in rats. Furthermore, in conscious fasting dogs, AS-9705 dose-dependently stimulated gastric motility. In conclusion, AS-9705 is a novel gastroprokinetic agent with potent antiemetic activity and minimal CNS adverse effects and is, therefore, worthy of clinical investigation.     

Phase I study of ceftizoxime, a new cephalosporin. Single-dose study

A phase I study of ceftizoxime, a new cephalosporin, was performed in 29 subjects. No abnormalities were observed in subjective symptoms, laboratory test results, or physical test results at estimated therapeutic doses of 500 mg intramuscularly, 500 and 1000 mg intravenously, and 2000 mg drip infusion. It is concluded, therefore, that the drug is safe for clinical use. The mean peak serum concentration was dose dependent. The mean serum concentrations of ceftizoxime in man at 5 minutes after 500 and 1000 mg by intravenous bolus were 58.4 and 112.8 micrograms/ml, respectively, which exceed the MIC80 against most pathogens tested. Thus, 500 or 1000 mg was estimated to be the therapeutic dose. The distribution volume of ceftizoxime was 16.0 to 18.6 liters, the total clearance was 135.6 to 154.9 ml/min, and the half-life in the beta-phase was 1.36 to 1.39 hours. Ceftizoxime is mainly excreted in the urine as unchanged drug, at an excretion rate in the 24-hour urine of approximately 80 per cent.     

Effect of AS-2646, a novel antiulcer agent on gastric mucosal defensive factors in rats

The effects of AS-2646 on the acute gastric mucosal lesions induced by various noxious agents and the gastric mucosal defensive factors were studied in rats, and the following results were obtained: 1) AS-2646 (5-100 mg/kg, p.o.) dose-dependently inhibited the formation of the mucosal lesions induced by ethanol, ethanol-HCl, taurocholate-HCl and serotonin, and its anti-lesion spectrum was the widest among the compounds (cimetidine, pirenzepine, sulpiride and prostaglandin E1) examined here. 2) AS-2646 (5-10 mg/kg, p.o.) not only improved the changes of gastric mucosal hemodynamics induced by the blood removal and/or the reserpine treatment, but also inhibited the mucosal lesions induced by them. 3) AS-2646 (2-20 mg/kg, p.o.) antagonized the decrease in the surface gastric mucus and mucosal hexosamine contents induced by stress and/or aspirin. 4) AS-2646 (2-20 mg/kg, p.o.) caused no significant effect on the gastric mucosal prostaglandin E2 levels. 5) AS-2646 inhibited Campylobacter pylori in vitro. These results indicate that AS-2646 may be useful as a novel antiulcer drug with the defensive factor-potentiating and anti-Campylobacter pylori effects.     

Inhibitory effect of indomethacin farnesil, a novel antiinflammatory prodrug, on carrageenin-induced inflammation in rats

Antiinflammatory effects of indomethacin farnesil (IMF), a novel prodrug of indomethacin, was examined after both oral and local administration. In the air pouch carrageenin-induced inflammation, an oral dose of IMF exerted dose dependent inhibitory effects on the accumulation of inflammatory exudate fluid and the migration of leukocytes into the exudate. Both the increased vascular permeability and the prostaglandin E2 levels in the exudate fluid were reduced by IMF. Significant levels of free indomethacin were detected in the pouch fluid. In spite of the inability of IMF to inhibit prostaglandin synthesis in a cell free cyclooxygenase system, IMF injected locally inhibited carrageenin paw edema, and the inhibitory effect was comparable to that of indomethacin itself. When injected locally into the paw together with carrageenin, 14C-IMF was effectively converted to its active metabolite, indomethacin. The indomethacin concentration in the paw tissue was comparable to that of indomethacin injected paws with the same molar dose of free indomethacin.     

Peptide leukotriene antagonistic activity of AS-35, a new antiallergic drug.

The effects of 9-[(4-acetyl-3-hydroxy-2-n-propylphenoxy) methyl]-3-(1H-tetrazol-5-yl)-4H-pyrido[1,2-a]pyrimidin-4-one (AS-35), a newly synthesized compound, on leukotrienes (LTs) antagonistic activities were investigated in vitro and in vivo. In isolated guinea pig preparations, AS-35 antagonized LTC4-, LTD4- and LTE4-induced contractions of the ileum with IC50 values of 8 nM, 4 nM and 3 nM, respectively. In the trachea, the agent also antagonized LTD4- and LTE4-induced contractions with IC50 values of 10 nM and 20 nM, respectively. However, LTC4-induced tracheal contraction in the presence of L-serine borate was not antagonized by AS-35. Histamine-, acetylcholine-, serotonin- and bradykinin-induced contractions of the ileum, carbachol-, prostaglandin D2-, prostaglandin F2 alpha-induced contractions of the trachea and LTB4-induced chemotaxis of rat polymorphonuclear leukocytes were not inhibited by AS-35. As to the in vivo models, AS-35 (i.v.) dose-dependently antagonized bronchoconstriction induced by i.v.-injection of LTC4 and LTD4 in anesthetized guinea pigs, but did not inhibit histamine-induced bronchoconstriction. Oral administration of AS-35 also antagonized LTD4- as well as antigen-induced LT-mediated bronchoconstriction. In addition, LTD4-induced increase in the cutaneous vascular permeability of guinea pig was inhibited by the drug (p.o.). These results indicate that AS-35 is an orally effective, potent and selective peptide LT antagonist.     

Preparation and physicochemical characterization of a novel water-soluble prodrug of carbamazepine

N-Acyl-urea derivatives of carbamazepine (CBZ) were synthesized through the reactions of iminostilbene with acyl-isocyanates to form N-glycyl-carbamazepine (N-Gly-CBZ, after a deprotection step) or N-acetyl-carbamazepine (N-acetyl-CBZ). N-Gly-CBZ was isolated as its water-soluble HCl salt and was designed to act as a prodrug and convert to CBZ and glycine in vivo by enzymatic cleavage of the acyl-urea bond. The stability pH-rate profiles for N-Gly-CBZ and N-acetyl-CBZ were determined. The stability of N-Gly-CBZ was found to range over four orders of magnitude with its greatest stability at pH 3–4 and a t₉₀ value of 5.9 day at pH 4 at 25°C. From the fit of the pH rate profile two pK_a values were estimated to be 7.2 (terminal amine) and 10.0 (imide), which were independently verified using UV–visible spectroscopic analysis. The solubility of N-Gly-CBZ in aqueous solution was determined in the range of pH 5.5–7.5. The intrinsic solubility of the neutral form of the prodrug was found to be 4.4 mg/mL, and the solubility of the prodrug increased exponentially (log linear) as pH was decreased below its pK_a1 value. N-Gly-CBZ was found to have an aqueous solubility in excess of 50 mg/mL at pH 4. The presence of N-Gly-CBZ was found to increase the aqueous solubility of CBZ, a degradation product. CBZ showed an 8.6-fold greater solubility in an aqueous solution containing 23 mg/mL of N-Gly-CBZ than in water alone. The solubilization of CBZ by N-Gly-CBZ was investigated by examining the diffusion coefficients of the predominant species in D₂O and was found to be more consistent with stacking complex formation than micelle formation. The stability of N-Gly-CBZ makes a ready-to-use parenteral formulation impractical, but a freeze-dried preparation for reconstitution appears to be feasible. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1810–1825, 2010     

Metabolism, pharmacokinetics and excretion of a novel hypoxia activated cytotoxic prodrug, TH-302, in rats

The metabolism, pharmacokinetics and excretion of a hypoxically activating prodrug developed for the treatment of cancer, TH-302, were studied in rats following intravenous administration of 50 mg/kg [(14)C]-TH-302. The pharmacokinetics of TH-302 was characterized by a short half-life of 12.3 min, a high clearance of 2.29 L/h/kg and a volume of distribution of 0.627 L/kg. In intact and bile duct-cannulated rats, TH-302 was extensively metabolized with total recovery in excreta of 68.1% and 85.8%, respectively, with equal amounts excreted through urine and bile. Quantitative whole body autoradiography showed rapid distribution of [(14)C]-TH-302 associated radioactivity with the highest concentrations in the kidney and small intestinal content, suggesting significant biliary excretion and/or gut secretion. TH-302 was metabolized via (i) hydrolysis to form 2-bromoethyl amine RM3 (7.5%); (ii) monoglutathione conjugation and subsequently to the mercapturic acid RM13 (7.5%); and (iii) diglutathione conjugation followed by hydrolysis to form the dicysteine conjugate RM5 (6.5%). A large percentage (19.7%) of the dose in the excreta was associated with unidentified polar metabolites RM1 and RM2. TH-302 was the predominant circulating component in plasma and the two major metabolites in plasma were the cysteine conjugate RM8 and mercapturic acid RM13.     

Metabolism,pharmacokinetics and excretion of a novel hypoxia activated cytotoxic prodrug,TH-302, in rats

1. The metabolism, pharmacokinetics and excretion of a hypoxically activating prodrug developed for the treatment of cancer, TH-302, were studied in rats following intravenous administration of 50?mg/kg [¹⁴C]-TH-302.

2. The pharmacokinetics of TH-302 was characterized by a short half-life of 12.3?min, a high clearance of 2.29?L/h/kg and a volume of distribution of 0.627?L/kg.

3. In intact and bile duct-cannulated rats, TH-302 was extensively metabolized with total recovery in excreta of 68.1% and 85.8%, respectively, with equal amounts excreted through urine and bile.

4. Quantitative whole body autoradiography showed rapid distribution of [¹⁴C]-TH-302 associated radioactivity with the highest concentrations in the kidney and small intestinal content, suggesting significant biliary excretion and/or gut secretion.

5. TH-302 was metabolized via (i) hydrolysis to form 2-bromoethyl amine RM3 (7.5%); (ii) monoglutathione conjugation and subsequently to the mercapturic acid RM13 (7.5%); and (iii) diglutathione conjugation followed by hydrolysis to form the dicysteine conjugate RM5 (6.5%).

6. A large percentage (19.7%) of the dose in the excreta was associated with unidentified polar metabolites RM1 and RM2.

7. TH-302 was the predominant circulating component in plasma and the two major metabolites in plasma were the cysteine conjugate RM8 and mercapturic acid RM13.