Complete Oral Bioavailability Research Articles

First-in-human pharmacokinetics of tamoxifen and its metabolites in the milk of a lactating mother: a case study

BackgroundBreast cancer represents the most frequent neoplasm diagnosed in women of childbearing age. When the tumour is oestrogen receptor-positive, tamoxifen is among the recommended endocrine treatments. Lactating women are advised not to breastfeed while receiving tamoxifen. However, information about tamoxifen transfer into breast milk is lacking.MethodsWe measured the concentration of tamoxifen and its metabolites by liquid chromatography-tandem mass spectrometry in the milk of a nursing mother that was treated for pregnancy-associated breast cancer diagnosed a few months after delivery. She was advised not to breastfeed her child and she collected milk samples for 23 days while the baby was fed with formula.ResultsTamoxifen concentrations in milk increased reaching a maximum of 214 nM. The two active metabolitesZ-4-hydroxy-tamoxifen and Z-endoxifen, could not be quantified in milk the first days after tamoxifen intake, but increased over time and reached clinically significant levels after day 18.ConclusionThis study demonstrates for the first time in human that tamoxifen and its metabolites transfer into milk. Since tamoxifen has a complete oral bioavailability, a long half-life (>7 days) and may interfere with the normal development of the infant, mothers should not breastfeed during tamoxifen treatment.

Buparlisib is a brain penetrable pan-PI3K inhibitor

Characterization of the genomic landscapes of intracranial tumours has revealed a clear role for the PI3K-AKT-mTOR pathway in tumorigenesis and tumour maintenance of these malignancies, making phosphatidylinositol 3-kinase (PI3K) inhibition a promising therapeutic strategy for these tumours. Buparlisib is a novel pan-PI3K inhibitor that is currently in clinical development for various cancers, including primary and secondary brain tumours. Importantly however, earlier studies have revealed that sufficient brain penetration is a prerequisite for antitumor efficacy against intracranial tumours. We therefore investigated the brain penetration of buparlisib using a comprehensive set of in vitro and in vivo mouse models. We demonstrate that buparlisib has an excellent brain penetration that is unaffected by efflux transporters at the blood-brain barrier, complete oral bioavailability and efficient intracranial target inhibition at clinically achievable plasma concentrations. Together, these characteristics make buparlisib the ideal candidate for intracranially-targeted therapeutic strategies that involve PI3K inhibition.

Abstract 4843: NMS-P293, a PARP-1 selective inhibitor with no trapping activity and high CNS penetration, possesses potent in vivo efficacy and represents a novel therapeutic option for brain localized metastases and glioblastoma

Abstract NMS-P293 is a novel, potent and selective small molecule inhibitor of poly (ADP-ribose) polymerase (PARP-1 Kd = 2 nM). NMS-P293 inhibits the poly-ADP ribosylation (PAR) induced by DNA damage, leading to the inability of homologous repair deficient (HRD) tumor cells to repair damage and to apoptotic death, while sparing normal cells. NMS-P293 significantly differs from other PARP inhibitors in several respects. Firstly, while possessing potent in vitro and in vivo efficacy in HRD tumors (e.g. BRCA, PTEN loss), it does not induce “DNA trapping”, i.e. the formation of PARP-chromatin complexes. Secondly, NMS-293 is not a substrate of PgP mediated drug efflux, believed to be a mechanism of resistance to current PARP inhibitors. Finally, NMS-P293 extensively crosses the blood brain barrier in rats and mice, with a brain/plasma ratio of 4-10, significantly higher than that of major comparators and opening the potential for treating primary brain tumors and brain metastasis with PARP inhibitor therapy. Extensive preclinical profiling revealed that NMS-P293 possesses favourable drug-like characteristics, which include high in vitro cross-species metabolic stability, lack of cytochrome interaction, and excellent pharmacokinetic profile, with low clearance and nearly complete oral bioavailability in both rodents and non rodents. Preclinical efficacy and PK/PD studies were conducted to assess the mechanism of action of NMS-P293 in an HRD setting, the MDA-MD-436 (BRCA1 mutant) human breast cancer xenograft model. Inhibition of PAR was observed in tumors following single oral administration of 50 mg/kg NMS-P293, with a > 95% decrease of this biomarker persisting for > 24 h. Inverse correlation was observed between intratumoral PAR levels and NMS-P293 concentrations in plasma and in tumor. Significantly, levels of NMS-P293 in tumor were consistently higher (> 3.5-fold) than in plasma, with an intratumoral concentration of > 2 μM at 24 h, in line with the prolonged PAR inhibition. In agreement with these PD effects, NMS-P293, orally administered as single agent, induced potent dose-related growth inhibition of BRCA mutated tumor model, with cured animals. Furthermore, NMS-P293 also possesses potent synergistic efficacy and tolerability in combination with temozolomide (TMZ) in glioblastoma (GBM) tumor models, including TMZ resistant MGMT hypomethylated GBMs. The unique preclinical features of NMS-P293, which includes a highly permissive profile in GLP drug safety studies, render this compound an appealing candidate for clinical development, both as a single agent and in drug combination therapy regimes. Citation Format: Alessia Montagnoli, Gianluca Papeo, Sonia Rainoldi, Francesco Caprera, Marina Ciomei, Eduard Felder, Daniele Donati, Antonella Isacchi, Arturo Galvani. NMS-P293, a PARP-1 selective inhibitor with no trapping activity and high CNS penetration, possesses potent in vivo efficacy and represents a novel therapeutic option for brain localized metastases and glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4843.

Emerging Fusarium and Alternaria Mycotoxins: Occurrence, Toxicity and Toxicokinetics

Emerging Fusarium and Alternaria mycotoxins gain more and more interest due to their frequent contamination of food and feed, although in vivo toxicity and toxicokinetic data are limited. Whereas the Fusarium mycotoxins beauvericin, moniliformin and enniatins particularly contaminate grain and grain-based products, Alternaria mycotoxins are also detected in fruits, vegetables and wines. Although contamination levels are usually low (µg/kg range), higher contamination levels of enniatins and tenuazonic acid may occasionally occur. In vitro studies suggest genotoxic effects of enniatins A, A1 and B1, beauvericin, moniliformin, alternariol, alternariol monomethyl ether, altertoxins and stemphyltoxin-III. Furthermore, in vitro studies suggest immunomodulating effects of most emerging toxins and a reproductive health hazard of alternariol, beauvericin and enniatin B. More in vivo toxicity data on the individual and combined effects of these contaminants on reproductive and immune system in both humans and animals is needed to update the risk evaluation by the European Food Safety Authority. Taking into account new occurrence data for tenuazonic acid, the complete oral bioavailability, the low total body clearance in pigs and broiler chickens and the limited toxicity data, a health risk cannot be completely excluded. Besides, some less known Alternaria toxins, especially the genotoxic altertoxins and stemphyltoxin III, should be incorporated in risk evaluation as well.

Estradiol prodrugs (EP) for efficient oral estrogen treatment and abolished effects on estrogen modulated liver functions

Oral compared to parenteral estrogen administration is characterized by reduced systemic but prominent hepatic estrogenic effects on lipids, hemostatic factors, GH-/IGF I axis, angiotensinogen. In order to avoid such adverse metabolic effects of oral treatment, estradiol (E2) prodrugs (EP) were designed which bypass the liver tissue as inactive molecules. Carbone17-OH sulfonamide [-O2–NH2] substituted esters of E2 (EC508, others) were synthesized and tested for carbonic anhydrase II (CA-II) binding. CA II in erythrocytes is thought to oppose extraction of EP from portal vein blood during liver passage. Ovariectomized (OVX, day minus 14) rats were orally treated once daily from day 1–3. Sacrifice day 4. Uteri were dissected and weighed. Cholesterol fractions and angiotensinogen were determined in plasma. Oral E2 and ethinyl estradiol (EE) generated dose related uterine growth and important hepatic estrogenic effects. EP induced uterine growth at about hundred-fold lower doses. This was possible with almost absent effects on plasma cholesterol or angiotensinogen. Preliminary pharmacokinetic studies with EC508 used intravenous and oral administration in male rats. Resulting blood levels revealed complete oral bioavailability. Further high blood- but low plasma concentrations indicated erythrocyte binding of EC508 in vivo as potential mechanism of low extraction at liver passage. Very high systemic estrogenicity combined with markedly lower or absent adverse hepatic estrogenic effects is evidence for a systemic release of E2 from sulfonamide EP. In conclusion, tested oral EP bypass the liver in erythrocytes furnishing systemic estradiol at hydrolysis. This mechanism avoids the hepatic estrogenic impact of conventional oral estrogen therapy.

Abstract 1223: NMS-P293, a novel potent and selective PARP-1 inhibitor with high antitumor efficacy and tolerability

Abstract Poly(ADP-ribose) polymerase-1 (PARP-1) has a well-established role in the signaling and repair of DNA and is a prominent target in oncology. Inhibition of PARP-1 is synthetically lethal with loss of function of the BRCA1 and BRCA2 tumor suppressor genes, as well with additional DNA repair defects. Tumor cells harboring defects in DNA repair pathways can thus be selectively targeted with PARP-1 inhibitors, and several such compounds are at different stages of clinical investigation in diverse tumor types, either as single agents or in combination regimens. However none of these agents selectively inhibits PARP-1 within the PARP family of enzymes: all drugs currently in clinical development, as well as the vast majority of preclinical compounds described to date potently cross-inhibit PARP-2, due to the high sequence homology between the two enzymes. Although PARP-2 is reported to be involved in DNA single-strand break repair, its contribution to total cellular levels of DNA damage-induced PARP activity is minimal (5-10%). Gene ablation studies show that loss of both PARP-1 and -2 function is incompatible with normal embryonic development, while PARP-2 single knockout mice show a variety of defects, including impaired erythropoiesis, thymopoiesis adipogenesis and spermatogenesis, increased neuronal loss after ischemic damage and higher risk of pancreatitis following chemical insult. We therefore reasoned that a potent and highly selective PARP-1 inhibitor might represent a significant advancement over currently available agents targeting both PARP-1 and -2, since sparing of PARP-2 inhibition potentially limits on target side-effects and offers greater opportunity for combination with other chemotherapeutic agents. Here we describe the preclinical characterization of NMS-P293, a novel highly potent PARP-1 inhibitor possessing >200-fold selectivity versus PARP-2. In cells, NMS-P293 inhibits hydrogen peroxide induced poly ADP-ribose (PAR) synthesis with an IC50 in the single digit nanomolar range, confirming expected mechanism of action in cells. NMS-P293 is selectively active on tumor cell lines defective in the HR repair pathway, such as pTEN and BRCA mutated lines, while sparing DNA repair proficient cells and normal myelocytes. NMS-P293 possesses favorable ADME properties including a low efflux ratio, high cross-species metabolic stability, low clearance and nearly complete oral bioavailability in rodents and non rodents. Oral administration to mice bearing BRCA mutated breast cancer xenografts resulted in complete tumor regressions and cures. The highly favorable preclinical characteristics of NMS-P293 make this compound a promising candidate for further development. Citation Format: Alessia Montagnoli, Sonia Rainoldi, Antonella Ciavolella, Dario Ballinari, Francesco Caprera, Lucio Ceriani, Rosita Lupi, Marina Ciomei, Eduard Felder, Antonella Isacchi, Daniele Donati, Arturo Galvani, Gianluca Papeo. NMS-P293, a novel potent and selective PARP-1 inhibitor with high antitumor efficacy and tolerability. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1223.

Abstract 2851: Preclinical characterization of NMS-P648, a novel and potent PARP-1/-3 inhibitor

Abstract PARP-1 and PARP-2 are nuclear enzymes activated by DNA strand breaks and are involved in recruitment of DNA repair proteins to sites of damage. PARP-1 and PARP-2 share partially overlapping functions, as shown by the embryonic lethality of double knockout mice compared to animals with single ablation either gene, which are viable. Despite this partial functional redundancy, PARP-1, but not PARP-2, inhibition has been shown to be synthetically lethal with defects in homologous recombination such as BRCA gene mutations. All PARP inhibitors that are currently under clinical investigation inhibit both PARP-1 and PARP-2, due to the high sequence similarity between the catalytic domains of the two enzymes. A third member of the family, PARP-3, has lower homology with PARP-1 and -2 and is much less well characterized, although it is known that its activity is stimulated by double strand breaks and that it promotes DNA repair through an error prone repair pathway, non-homologous end joining (NHEJ). PARP-3 inhibition is thus presumed to be synthetically lethal with other, alternative DNA repair pathway deficiencies. We report preclinical characterization of NMS-P648, a selective PARP-1/-3 inhibitor, with a dissociation constants (KD), of 0.9 nM on PARP-1 and with greater than four hundred-fold less affinity for PARP-2, as assessed by direct binding assay. In cells, NMS-P648 inhibits hydrogen peroxide induced poly ADP-ribose (PAR) synthesis with an IC50 of 1 nM, confirming expected mechanism of action and indicating that inhibition of PARP-2 is not required for this process. NMS-P648 has favourable ADME properties, including stability in liver microsome incubation assays, low efflux ratio in the CACO2 assay and an excellent pharmacokinetic profile, with complete oral bioavailability and exposure levels that increase proportionally with dose. Testing NMS-P648 on a panel of more than 100 human tumor cell lines using a 2D colony forming assay format revealed that 7 cell lines were highly sensitive to the compound (IC50 <0.5 μM). As expected for an inhibitor of DNA repair, NMS-P648 induced S-phase cell cycle arrest and the formation of nuclear γH2AX foci in sensitive cell lines, suggesting the induction of stalled or damaged replication forks, followed by cell death. Responsive lines were of diverse tissue origin and included BRCA mutated lines, as well as lines resistant to standard chemotherapeutic agents and to known PARP 1/2 inhibitors, indicating a unique activity profile. Translational and bioinformatic studies are ongoing, aimed at identifying determinants of NMS-P648 sensitivity that might drive patient population selection.The discovery that potent PARP-1/-3 dual inhibitors such as NMS-P648 possess a unique sensitivity profile provides an innovative opportunity in the field of therapeutic intervention in DNA repair processes. Citation Format: Alessia Montagnoli, Gianluca Papeo, Sonia Rainoldi, Alessandra Cirla, Antonella Ciavolella, Clara Albanese, Michele Modugno, Roberta Bosotti, Alessio Somaschini, Giovanni Carapezza, Rosita Lupi, Dario Ballinari, Marina Ciomei, Enrico Pesenti, Daniele Donati, Antonella Isacchi, Arturo Galvani. Preclinical characterization of NMS-P648, a novel and potent PARP-1/-3 inhibitor. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2851. doi:10.1158/1538-7445.AM2015-2851

STIMULATION OF THE IV TO ORAL SWITCH OF BIOAVAILABLE DRUGS BY PHONE CALLS IN A BELGIAN TERTIARY CARE HOSPITAL

Introduction: Early switch from intravenous to oral administration of drugs with an almost complete oral bioavailability, can have important benefits. Drugs with almost complete bioavailability, like clindamycin (Dalacin®), levofloxacin (Tavanic®) and paracetamol (Perfusalgan®/Dafalgan ®), are very suitable for an early intravenous to oral switch in patients whose gastrointestinal absorption is intact. The aim of this study was to investigate the impact of direct phone contact between pharmacist and clinician on the intravenous to oral switch and to evaluate the reasons, mentioned by clinicians, that prevented an early switch.Materials & Methods: The project was initiated in a Belgian 1900-bed tertiary care hospital with a poster, communicated through the hospital’s intranet and spread to every hospital ward. During one month, all prescriptions for intravenous clindamycin, levofloxacin and paracetamol were evaluated. The treating clinician was contacted by phone to evaluate if an intravenous to oral switch was possible.Results: Clinicians were contacted concerning 377 patients. For 58.7% of patients, the switch from intravenous to oral administration was made. In case of refusal, several reasons were mentioned by the clinician, some more appropriate than others.Conclusion: Despite several appropriate reasons preventing an early intravenous to oral switch, there are still some aberrant opinions circulating in the hospital environment. Active interventions of pharmacists to stimulate intravenous to oral switch, using phone contact with the treating clinicians, can possibly be an adequate technique to stimulate intravenous to oral switch, but this needs to be further optimized.

Abstract 3259: Novel isoquinolinone derivatives with dual PARP-1/PARP-3 inhibitory activity are highly active against pTEN mutated colorectal cancer and glioblastoma models..

Abstract Inhibitors of the poly(ADP-ribose) polymerases (PARPs) family of proteins are currently in clinical trials as potential anticancer agents. PARP-1 is a key nuclear enzyme activated by DNA strand breaks and its activation contributes to the recruitment of DNA repair and checkpoint proteins to the sites of damage. PARP-2 shows overlapping functions with PARP-1, as demonstrated by the embryonic lethality phenotype observed in double knockout mice, compared with the viability observed for single knockout of either gene. Genetic disruption in mice of PARP-2, but not of PARP-1, has been reported to affect different processes including spermatogenesis, adipogenesis, and thymocyte survival. It has been demonstrated that BRCA1 and BRCA2-deficient cell lines are sensitive towards PARP inhibition through prevention of DNA damage repair. However, recent studies have highlighted new potential genetic backgrounds in which PARP inhibition may have a therapeutic rationale. Accordingly, it has been reported that tumor cell lines bearing PTEN mutations, or with defects in mismatch repair genes are sensitive to PARP inhibitors. Here we describe the in vitro and in vivo characterization of small molecule inhibitors belonging to the isoquinolinone chemical class, with dual PARP-1 and PARP-3 inhibitory activity and which are selective versus PARP-2. Representative compounds of the class, such as NMS-P914, whose co-crystal structure with the human PARP-1 catalytic domain will be shown, and NMS-P648, are endowed with nanomolar potency against PARP-1 and PARP-3, are >100 selective versus PARP-2, possess almost complete oral bioavailability in the mouse and excellent in vitro ADMET properties across species. In cells, NMS-P914 and NMS-P648 inhibit DNA damage-induced PARP-1 activity with an IC50 of 1 nM and display single agent cytotoxicity in BRCA deficient breast tumor cell lines (IC50 < 100 nM). Interestingly, NMS-P914 and other members of the class also display similar potency against colorectal cancer and glioblastoma cell lines bearing defects in pTEN and in mismatch repair genes, and are active against glioblastoma cell lines resistant to temozolomide, irinotecan and to known PARP inhibitors such as olaparib and veliparib. In combination studies, NMS-P914 was found to be synergistic with temozolomide, both in temozolomide sensitive and resistant glioblastoma contexts. Furthermore, combination of NMS-P914 with temozolomide gives prolonged tumor regression without increasing temozolomide toxicity in vivo, showing better tolerability compared to temozolomide combination with olaparib. Citation Format: Alessia Montagnoli, Sonia Rainoldi, Stefania Mazzoleni, Antonella Ciavolella, Rosita Lupi, Elena Casale, Marina Ciomei, Enrico Pesenti, Daniele Donati, Arturo Galvani, Gianluca Papeo. Novel isoquinolinone derivatives with dual PARP-1/PARP-3 inhibitory activity are highly active against pTEN mutated colorectal cancer and glioblastoma models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3259. doi:10.1158/1538-7445.AM2013-3259

Discovery of a Potent and Selective Free Fatty Acid Receptor 1 Agonist with Low Lipophilicity and High Oral Bioavailability

The free fatty acid receptor 1 (FFA1, also known as GPR40) mediates enhancement of glucose-stimulated insulin secretion and is emerging as a new target for the treatment of type 2 diabetes. Several FFA1 agonists are known, but the majority of these suffer from high lipophilicity. We have previously reported the FFA1 agonist 3 (TUG-424). We here describe the continued structure-activity exploration and optimization of this compound series, leading to the discovery of the more potent agonist 40, a compound with low lipophilicity, excellent in vitro metabolic stability and permeability, complete oral bioavailability, and appreciable efficacy on glucose tolerance in mice.

Abstract 691: In vitro and in vivo characterization of selective orally available Parp-1 inhibitors with demonstrated antitumor efficacy in BRCA negative cancer models

Abstract Poly (ADP-ribose) polymerase 1 and 2 (Parp-1 and Parp-2) are nuclear enzymes responsible for signaling the presence of DNA damages by catalyzing the addition of ADP-ribose units to DNA, histones and various DNA repair enzymes, thus facilitating DNA repair. Parp-1 has been gaining increasing interest as a therapeutic target for cancer in combination with DNA damaging agents but also as single agent in particular tumor settings, such as BRCA mutated tumors. While Parp-1 knock out mice are viable and display only defects in DNA repair, double Parp-1 and Parp-2 knock-out are embryonic lethal indicating that the absence of Parp-1 and Parp-2 is less tolerated in normal cells. We confirmed this concept in vitro by RNAi of Parp-1 and Parp-2, showing that the inhibition of Parp-1 alone is enough to kill tumor cells but spares normal cells. Hence a selective Parp-1 inhibitor might have a better safety profile, particularly in view of a long treatment. Here we report the discovery and the in vitro and in vivo characterization of a novel class of potent, orally available Parp-1 selective small molecule inhibitors with no activity on other Parp isoforms such as Parp-2, −3 and −5a (tankyrase), which differentiates it from current clinical Parp inhibitors. The most potent compounds were further evaluated in vitro and in vivo. These compounds are highly potent in inhibiting DNA damage-induced Parp-1 activity in cells and exhibit selective anti-proliferative and pro-apoptotic activity in tumor cell lines harbouring defects in DNA repair. In vivo, the compounds show an excellent pharmacokinetic profile with almost complete oral bioavailability and demonstrate efficacy as a single agent in xenograft tumor models with DNA repair deficiencies superior to reference Parp inhibitors. These compounds are very well tolerated with no overt toxicity even after prolonged exposure and their mechanism of action is confirmed both in tumors and peripheral blood cells of treated mice. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 691.

In vitro activity and in vivo efficacy of icofungipen (PLD-118), a novel oral antifungal agent, against the pathogenic yeast Candida albicans.

Icofungipen (PLD-118) is the representative of a novel class of antifungals, beta amino acids, active against Candida species. It has been taken through phase II clinical trials. The compound actively accumulates in yeast, competitively inhibiting isoleucyl-tRNA synthetase and consequently disrupting protein biosynthesis. As a result, in vitro activity can be studied only in chemically defined growth media without free amino acids that would compete with the uptake of the compound. The MIC of icofungipen was reproducibly measured in a microdilution assay using yeast nitrogen base medium at pH 6 to 7 after 24 h of incubation at 30 to 37 degrees C using an inoculum of 50 to 100 CFU/well. The MICs for 69 Candida albicans strains ranged from 4 to 32 microg/ml. This modest in vitro activity contrasts with the strong in vivo efficacy in C. albicans infection. This was demonstrated in a lethal model of C. albicans infection in mice and rats in which icofungipen showed dose-dependent protection at oral doses of 10 to 20 mg/kg of body weight per day in mice and 2 to 10 mg/kg/day in rats. The in vivo efficacy was also demonstrated against C. albicans isolates with low susceptibility to fluconazole, indicating activity against azole-resistant strains. The efficacy of icofungipen in mice and rats was not influenced by concomitant administration of equimolar amounts of L-isoleucine, which was shown to antagonize its antifungal activity in vitro. Icofungipen shows nearly complete oral bioavailability in a variety of species, and its in vivo efficacy indicates its potential for the oral treatment of yeast infections.

Pharmacodynamic properties of methotrexate and AminotrexateTM during weekly therapy

4-Amino-pteroyl-glutamic acid (Aminotrexate; AMT) has several advantages over the related antifolate methotrexate (MTX), including greater potency, complete oral bioavailability, and greater accumulation by leukemic blasts in vitro. We compared the pharmacodynamic properties of AMT (given orally at 4 mg/m2 in two divided doses per week) and MTX (100 mg/m2 in four divided doses per week) among children with acute lymphoblastic leukemia. We find AMT and MTX to have equivalent penetration into the bone marrow compartment of these patients, as indicated by the steady-state concentrations within mature red blood cells (RBCs). However, MTX concentrations in the cerebrospinal fluid after oral dosage are significantly greater than AMT. To confirm these clinical observations, mice were treated four weekly injections of AMT or MTX, at a 1:20 dosage ratio, and tissue antifolate content was then determined over the subsequent 22 days. We confirm the selective exclusion of AMT from the CNS compartment, while showing equivalent accumulation of AMT and MTX in the RBCs, liver, spleen, kidneys and testes. Finally, we demonstrate that AMT, MTX, and their predominant polyglutamate species are equipotent inhibitors of their target intracellular enzyme dihydrofolate reductase, emphasizing the critical nature of steady-state tissue accumulation in determining the relative cytotoxic potency of these two antifolates.

Pharmacokinetics of S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro- 3-trifluoromethyl-phenyl)-propionamide in rats, a non-steroidal selective androgen receptor modulator

1. S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide (also known as S-4) is a non-steroidal selective androgen receptor modulator demonstrating tissue-selective androgenic and anabolic effects. The purpose of the present study was to examine the systemic pharmacokinetics, elimination and oral bioavailability of S-4 in rats.2. Thirty-five male Sprague–Dawley rats weighing approximately 250 g were randomly assigned to one of seven treatment groups. Intravenous doses of 0.5, 1, 10, and 30 mg kg−1 were given via a jugular catheter. Oral doses of 1, 10 and 30 mg kg−1 were administered via gavage. Plasma concentrations were determined using a validated high-performance liquid chromatography or by a high-performance liquid chromatography/mass spectrometry method.3. Clearances ranged between 1.0 and 2.1 ml min−1 kg−1 and varied with dose. The volume of distribution was approximately 0.448 l kg−1 in all treatment groups. Oral bioavailability was also dose dependent, with the lower doses showing complete oral bioavailability. The half-life of S-4 over the dose range tested was between 2.6 and 5.3 h.4. It was demonstrated that S-4 is rapidly absorbed, slowly cleared, and has a moderate volume of distribution in rats. The pharmacokinetics and oral bioavailability of S-4 indicate that it is an excellent candidate for clinical development.

Pharmacokinetics and metabolism of endothelin receptor antagonist: Contribution of kidneys in the overallin vivo N-demethylation

In vivo clearance of BMS-182874 was primarily due to metabolism via stepwise N-demethylation. Despite in vivo clearance approached ca 50% of the total liver plasma flow, BMS-182874 was completely bioavailable after oral administration in rats. Saturable first-pass metabolism and the role of extrahepatic tissue were evaluated as possible reasons for complete oral bioavailability despite extensive metabolic clearance. Pharmacokinetic parameters were obtained after an intravenous and a range of oral doses of BMS-182874 in rats. Bile and urine were collected from bile-duct cannulated (BDC) rats and the in vivo metabolic pathways of BMS-182874 were evaluated. Pharmacokinetics of BMS-182874 were also compared in nephrectomized (renally impaired) vs. sham-operated control rats. Oral bioavailability of BMS-182874 averaged 100%, indicating that BMS-182874 was completely absorbed and the first-pass metabolism (liver or intestine) was negligible. The AUC and Cmax values increased dose-proportionally, indicating kinetics were linear within the oral dose range of 13 to 290 mmole/kg. After intravenous administration of BMS-182874 to BDC rats, about 2% of intact BMS-182874 was recovered in excreta, indicating that BMS-182874 was cleared primarily via metabolism in vivo. The major metabolite circulating in plasma was the mono-N-desmethyl metabolite and the major metabolite recovered in excreta was the di-N-desmethyl metabolite. In vivo clearance of BMS-182874 was significantly reduced in nephrectomized rats. These observations suggest saturable first-pass metabolism is unlikely to be a mechanism for complete oral bioavailability of BMS-182874. Reduced clearance observed in the nephrectomized rats suggests that extrahepatic tissues (e.g., kidneys) may play an important role in the in vivo clearance of xenobiotics that are metabolized via N-demethylation.

Linezolid: an oxazolidinone antimicrobial agent.

The pharmacology, antimicrobial activity, pharmacokinetics, clinical efficacy, and adverse effects of linezolid are reviewed. Linezolid, the only oxazolidinone antimicrobial approved for use in the United States, has significant activity against gram-positive bacteria, including penicillin-, cephalosporin-, and vancomycin-resistant species. Linezolid inhibits bacterial protein synthesis via binding to the 50S ribosomal subunit to prevent translation. The drug lacks cross-resistance with other antimicrobials. Linezolid is primarily excreted renally as unchanged drug. The measured plasma half-life of four to five hours permits twice-daily administration for all indicated infections. Virtually complete oral bioavailability allows for 1:1 conversion between the intravenous and oral dosage forms. Controlled comparative clinical trials demonstrate that linezolid is effective in the treatment of vancomycin-resistant Enterococcus faecium and methicillin-resistant Staphylococcus aureus (MRSA) infections, nosocomial and community-acquired pneumonia, and skin and skin-structure infections due to susceptible organisms. The recommended dosage is 600 mg i.v. or p.o. twice daily for all indications except uncomplicated skin and skin-structure infections (400 mg twice daily); adjustments for mild to moderate renal or hepatic impairment are not necessary. Clinically important interactions with monoamine oxidase inhibitors have not been observed. Reversible myelosuppression has been observed in a few patients. Linezolid has gram-positive activity comparable to that of vancomycin, is effective in a variety of infections, and is well tolerated, with diarrhea, headache, and nausea being the most frequently reported adverse effects. Linezolid provides a reasonable therapeutic alternative for patients with vancomycin-resistant E. faecium infections and patients infected with MRSA who cannot tolerate vancomycin.

Oxazolidinones

The oxazolidinones represent a novel chemical class of synthetic antimicrobial agents. They exhibit an unique mechanism of protein synthesis inhibition and generally display bacteriostatic activity against many important human pathogens, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and penicillin- and cephalosporin-resistant Streptococcus pneumoniae. Linezolid, the oxazolidinone which has been selected for clinical development, has near complete oral bioavailability plus favourable pharmacokinetic and toxicity profiles. Results from experimental models of infection and phase II trials reveal linezolid to be highly active in vivo against infections due to many common gram-positive pathogens. The role of linezolid remains to be determined in phase III clinical trials, but it shows great promise as an alternative to glycopeptides and streptogramins to treat serious infections due to resistant gram-positive organisms. Further modification of the oxazolidinone nucleus may yield agents with even greater potency and with novel spectra of activity.

Comparison of the kinetics of glyburide and its active metabolites in humans

The pharmacokinetics of glyburide (Gb) and its active metabolites, 4-trans-hydroxyglibenclamide (M1) and 3-cis-hydroxyglibenclamide (M2), were compared in eight healthy subjects. After an overnight fast, each subject received a 3.5-mg single dose of Gb, M1 or M2 intravenously in random cross-over order. For comparison, a 3.5-mg oral dose of micronized formulation of Gb was also given in a test. The subjects continued to fast until standard meals were given at 0.5 and 5.5 h after each dose. Serum samples and urine fractions were collected for 10 h. Serum concentrations of Gb, M1 and M2, and urine concentrations of M1 and M2 were determined by a selective and sensitive liquid chromatographic method. The two metabolites had very similar pharmacokinetic profiles, except for volume of distribution and renal clearance. Estimated mean volume of distribution, total and renal clearance of M1 and M2 were 20.8 +/- 8.4 litres, 11.9 +/- 1.7 litres/h, 13.5 +/- 3.7 litres/h and 15.5 +/- 5.5 litres, 10.4 +/- 1.3 litres/h, 8.6 +/- 1.6 litres/h, respectively. Estimates of the volume of distribution and total clearance were significantly higher than those of Gb, which were 7.44 +/- 1.53 litres, 4.42 +/- 0.56 litres/h intravenously and 9.32 +/- 2.79 litres, 4.09 +/- 0.45 litres/h orally. There was no significant difference in total metabolite urine recovery between intravenous or oral administration of Gb, suggesting almost complete oral bioavailability of the micronized glibenclamide formulation.

Pharmacokinetics of galanthamine in humans and corresponding cholinesterase inhibition

Measurements were done to determine the plasma concentrations of galanthamine and two of its metabolites, as well as the corresponding inhibition of acetylcholinesterase activity in erythrocytes after applying 5 and 10 mg galanthamine hydrobromide as a constant-rate intravenous infusion for 30 minutes and single oral doses of 10 mg in eight healthy male volunteers. The data obtained revealed first-order pharmacokinetics, complete oral bioavailability, and a mean terminal half-life of 5.68 hours (95% confidence interval, 5.17 to 6.25 hours). Renal clearance accounted for only 25% of the total plasma clearance (CL = 0.34 L.kg-1.hr-1). Only negligible quantities of the putative metabolites, epigalanthamine and galanthaminone, were detected in blood and urine. The inhibition of acetylcholinesterase activity was closely correlated with the pharmacokinetics of galanthamine, a median maximal value of 53% being achieved by applying 10 mg galanthamine intravenously. Analysis of in vitro and ex vivo concentration responses revealed no differences, indicating that no metabolites of galanthamine exert additional inhibition of acetylcholinesterase activity.