Digital Ink and Surgical Dreams: Perceptions of Artificial Intelligence-Generated Essays in Residency Applications.

INTRODUCTION: Large language models like Chat Generative Pre-Trained Transformer (ChatGPT) are increasingly used in academic writing. Faculty may consider use of artificial intelligence (AI)-generated responses a form of cheating. We sought to determine whether general surgery residency faculty could detect AI versus human-written responses to a text prompt; hypothesizing that faculty would not be able to reliably differentiate AI versus human-written responses. METHODS: Ten essays were generated using a text prompt, "Tell us in 1-2 paragraphs why you are considering the University of Rochester for General Surgery residency" (Current trainees: n = 5, ChatGPT: n = 5). Ten blinded faculty reviewers rated essays (ten-point Likert scale) on the following criteria: desire to interview, relevance to the general surgery residency, overall impression, and AI- or human-generated; with scores and identification error rates compared between the groups. RESULTS: There were no differences between groups for %total points (ChatGPT 66.0 ± 13.5%, human 70.0 ± 23.0%, P = 0.508) or identification error rates (ChatGPT 40.0 ± 35.0%, human 20.0 ± 30.0%, P = 0.175). Except for one, all essays were identified incorrectly by at least two reviewers. Essays identified as human-generated received higher overall impression scores (area under the curve: 0.82 ± 0.04, P < 0.01). CONCLUSIONS: Whether use of AI tools for academic purposes should constitute academic dishonesty is controversial. We demonstrate that human and AI-generated essays are similar in quality, but there is bias against presumed AI-generated essays. Faculty are not able to reliably differentiate human from AI-generated essays, thus bias may be misdirected. AI-tools are becoming ubiquitous and their use is not easily detected. Faculty must expect these tools to play increasing roles in medical education.

Metabolism, Excretion, and Pharmacokinetics of Lorlatinib (PF-06463922) and Evaluation of the Impact of Radiolabel Position and Other Factors on Comparability of Data Across 2 ADME Studies.

While an initial clinical absorption, distribution, metabolism, and excretion (ADME) study (Study 1; N = 6) with 100 mg/100 µCi [14 C]lorlatinib, radiolabeled on the carbonyl carbon, confirmed that the primary metabolic pathways for lorlatinib are oxidation (N-demethylation, N-oxidation) and N-glucuronidation, it also revealed an unanticipated, intramolecular cleavage metabolic pathway of lorlatinib, yielding a major circulating benzoic acid metabolite (M8), and an unlabeled pyrido-pyrazole substructure. Concerns regarding the fate of unknown metabolites associated with this intramolecular cleavage pathway led to conduct of a second ADME study (Study 2; N = 6) of identical design but with the radiolabel positioned on the pyrazole ring. Results were similar with respect to the overall mass balance, lorlatinib plasma exposures, and metabolic profiles in excreta for the metabolites that retained the radiolabel in both studies. Differences were observed in plasma total radioactivity exposures (2-fold area under the plasma concentration-time curve from time 0 to infinity difference) and relative ratios of the percentage of dose recovered in urine vs feces (48% vs 41% in Study 1; 28% vs 64% in Study 2). In addition, an approximately 3-fold difference in the mean molar exposure ratio of M8 to lorlatinib was observed for values derived from metabolic profiling data relative to those derived from specific bioanalytical methods (0.5 vs 1.4 for Studies 1 and 2, respectively). These interstudy differences were attributed to a combination of factors, including alteration of radiolabel position, orthogonal analytical methodologies, and intersubject variability, and illustrate that results from clinical ADME studies are not unambiguous and should be interpreted within the context of the specific study design considerations.

A novel CXCR4 antagonist IgG1 antibody (PF-06747143) for the treatment of hematologic malignancies.

The chemokine receptor CXCR4 is highly expressed and associated with poor prognosis in multiple malignancies. Upon engagement by its ligand, CXCL12, CXCR4 triggers intracellular signaling pathways that control trafficking of cells to tissues where the ligand is expressed, such as the bone marrow (BM). In hematologic cancers, CXCR4-driven homing of malignant cells to the BM protective niche is a key mechanism driving disease and therapy resistance. We developed a humanized CXCR4 immunoglobulin G1 (IgG1) antibody (Ab), PF-06747143, which binds to CXCR4 and inhibits CXCL12-mediated signaling pathways, as well as cell migration. In in vivo preclinical studies, PF-06747143 monotherapy rapidly and transiently mobilized cells from the BM into the peripheral blood. In addition, PF-06747143 effectively induced tumor cell death via its Fc constant region-mediated effector function. This Fc-mediated cell killing mechanism not only enhanced antitumor efficacy, but also played a role in reducing the duration of cell mobilization, when compared with an IgG4 version of the Ab, which does not have Fc-effector function. PF-06747143 treatment showed strong antitumor effect in multiple hematologic tumor models including non-Hodgkin lymphoma (NHL), acute myeloid leukemia (AML), and multiple myeloma (MM). Importantly, PF-06747143 synergized with standard-of-care agents in a chemoresistant AML patient-derived xenograft model and in an MM model. These findings suggest that PF-06747143 is a potential best-in-class anti-CXCR4 antagonist for the treatment of hematologic malignancies, including in the resistant setting. PF-06747143 is currently in phase 1 clinical trial evaluation (registered at www.clinicaltrials.gov as #NCT02954653).

Metabolism, excretion and pharmacokinetics of [14C]glasdegib (PF-04449913) in healthy volunteers following oral administration.

1. The metabolism, excretion and pharmacokinetics of glasdegib (PF-04449913) were investigated following administration of a single oral dose of 100 mg/100 µCi [14C]glasdegib to six healthy male volunteers (NCT02110342). 2. The peak concentrations of glasdegib (890.3 ng/mL) and total radioactivity (1043 ngEq/mL) occurred in plasma at 0.75 hours post-dose. The AUCinf were 8469 ng.h/mL and 12,230 ngEq.h/mL respectively, for glasdegib and total radioactivity. 3. Mean recovery of [14C]glasdegib-related radioactivity in excreta was 91% of the administered dose (49% in urine and 42% in feces). Glasdegib was the major circulating component accounting for 69% of the total radioactivity in plasma. An N-desmethyl metabolite and an N-glucuronide metabolite of glasdegib represented 8% and 7% of the circulating radioactivity, respectively. Glasdegib was the major excreted component in urine and feces, accounting for 17% and 20% of administered dose in the 0-120 hour pooled samples, respectively. Other metabolites with abundance <3% of the total circulating radioactivity or dose in plasma or excreta were hydroxyl metabolites, a desaturation metabolite, N-oxidation and O-glucuronide metabolites. 4. Elimination of [14C]glasdegib-derived radioactivity was essentially complete, with similar contribution from urinary and fecal routes. Oxidative metabolism appears to play a significant role in the biotransformation of glasdegib.

PF-06463922, an ALK/ROS1 Inhibitor, Overcomes Resistance to First and Second Generation ALK Inhibitors in Preclinical Models.

We report the preclinical evaluation of PF-06463922, a potent and brain-penetrant ALK/ROS1 inhibitor. Compared with other clinically available ALK inhibitors, PF-06463922 displayed superior potency against all known clinically acquired ALK mutations, including the highly resistant G1202R mutant. Furthermore, PF-06463922 treatment led to regression of EML4-ALK-driven brain metastases, leading to prolonged mouse survival, in a superior manner. Finally, PF-06463922 demonstrated high selectivity and safety margins in a variety of preclinical studies. These results suggest that PF-06463922 will be highly effective for the treatment of patients with ALK-driven lung cancers, including those who relapsed on clinically available ALK inhibitors because of secondary ALK kinase domain mutations and/or brain metastases.

PF-06463922 is a potent and selective next-generation ROS1/ALK inhibitor capable of blocking crizotinib-resistant ROS1 mutations.

Oncogenic c-ros oncogene1 (ROS1) fusion kinases have been identified in a variety of human cancers and are attractive targets for cancer therapy. The MET/ALK/ROS1 inhibitor crizotinib (Xalkori, PF-02341066) has demonstrated promising clinical activity in ROS1 fusion-positive non-small cell lung cancer. However, emerging clinical evidence has shown that patients can develop resistance by acquiring secondary point mutations in ROS1 kinase. In this study we characterized the ROS1 activity of PF-06463922, a novel, orally available, CNS-penetrant, ATP-competitive small-molecule inhibitor of ALK/ROS1. In vitro, PF-06463922 exhibited subnanomolar cellular potency against oncogenic ROS1 fusions and inhibited the crizotinib-refractory ROS1(G2032R) mutation and the ROS1(G2026M) gatekeeper mutation. Compared with crizotinib and the second-generation ALK/ROS1 inhibitors ceritinib and alectinib, PF-06463922 showed significantly improved inhibitory activity against ROS1 kinase. A crystal structure of the PF-06463922-ROS1 kinase complex revealed favorable interactions contributing to the high-affinity binding. In vivo, PF-06463922 showed marked antitumor activity in tumor models expressing FIG-ROS1, CD74-ROS1, and the CD74-ROS1(G2032R) mutation. Furthermore, PF-06463922 demonstrated antitumor activity in a genetically engineered mouse model of FIG-ROS1 glioblastoma. Taken together, our results indicate that PF-06463922 has potential for treating ROS1 fusion-positive cancers, including those requiring agents with CNS-penetrating properties, as well as for overcoming crizotinib resistance driven by ROS1 mutation.

Mechanistic understanding of translational pharmacokinetic-pharmacodynamic relationships in nonclinical tumor models: a case study of orally available novel inhibitors of anaplastic lymphoma kinase.

The orally available novel small molecules PF06463922 [(10R)-7-amino-12-fluoro-2,10,16-trimethyl-15-oxo-10,15,16,17-tetrahydro-2H-8,4-(metheno)pyrazolo[4,3-h][2,5,11]benzoxadiazacyclotetradecine-3-carbonitrile] and PF06471402 [(10R)-7-amino-12-fluoro-2,10,16-trimethyl-15-oxo-10,15,16,17-tetrahydro-2H-8,4-(azeno)pyrazolo[4,3-h][2,5,11]benzoxadiazacyclo-tetradecine-3-carbonitrile] are second-generation anaplastic lymphoma kinase (ALK) inhibitors targeted to both naïve and resistant patients with non-small cell lung cancer (NSCLC) to the first-generation ALK inhibitor crizotinib. The objectives of the present study were to characterize and compare the pharmacokinetic-pharmacodynamic (PKPD) relationships of PF06463922 and PF06471402 for target modulation in tumor and antitumor efficacy in athymic mice implanted with H3122 NSCLC cells expressing a crizotinib-resistant echinoderm microtubule-associated protein-like 4 (EML4)-ALK mutation, EML4-ALK(L1196M). Furthermore, the PKPD relationships for these ALK inhibitors were evaluated and compared between oral administration and subcutaneous constant infusion (i.e., between different pharmacokinetic [PK] profiles). Oral and subcutaneous PK profiles of these ALK inhibitors were adequately described by a one-compartment PK model. An indirect response model extended with a modulator fit the time courses of PF06463922- and PF06471402-mediated target modulation (i.e., ALK phosphorylation) with an estimated unbound EC50,in vivo of 36 and 20 nM, respectively, for oral administration, and 100 and 69 nM, respectively, for subcutaneous infusion. A drug-disease model based on the turnover concept fit tumor growth curves inhibited by PF06463922 and PF06471402 with estimated unbound tumor stasis concentrations of 51 and 27 nM, respectively, for oral administration, and 116 and 70 nM, respectively, for subcutaneous infusion. Thus, the EC50,in vivo to EC60,in vivo estimates for ALK inhibition corresponded to the concentrations required tumor stasis in all cases, suggesting that the pharmacodynamic relationships of target modulation to antitumor efficacy were consistent among the ALK inhibitors, even when the PK profiles with different administration routes were considerably different.

Translational pharmacokinetic-pharmacodynamic modeling for an orally available novel inhibitor of anaplastic lymphoma kinase and c-Ros oncogene 1.

An orally available macrocyclic small molecule, PF06463922 [(10R)-7-amino-12-fluoro-2,10,16-trimethyl-15-oxo-10,15,16,17-tetrahydro-2H-8,4-(metheno)pyrazolo[4,3-h][2,5,11]benzoxadiazacyclotetradecine-3-carbonitrile], is a selective inhibitor of anaplastic lymphoma kinase (ALK) and c-Ros oncogene 1 (ROS1). The objectives of the present study were to characterize the pharmacokinetic-pharmacodynamic relationships of PF06463922 between its systemic exposures, pharmacodynamic biomarker (target modulation), and pharmacologic response (antitumor efficacy) in athymic mice implanted with H3122 non-small cell lung carcinomas expressing echinoderm microtubule-associated protein-like 4 (EML4)-ALK mutation (EML4-ALK(L1196M)) and with NIH3T3 cells expressing CD74-ROS1. In these nonclinical tumor models, PF06463922 was orally administered to animals with EML4-ALK(L1196M) and CD74-ROS1 at twice daily doses of 0.3-20 and 0.01-3 mg/kg per dose, respectively. Plasma concentration-time profiles of PF06463922 were adequately described by a one-compartment pharmacokinetic model. Using the model-simulated plasma concentrations, a pharmacodynamic indirect response model with a modulator sufficiently fit the time courses of target modulation (i.e., ALK phosphorylation) in tumors of EML4-ALK(L1196M)-driven models with EC50,in vivo of 36 nM free. A drug-disease model based on an indirect response model reasonably fit individual tumor growth curves in both EML4-ALK(L1196M)- and CD74-ROS1-driven models with the estimated tumor stasis concentrations of 51 and 6.2 nM free, respectively. Thus, the EC60,in vivo (52 nM free) for ALK inhibition roughly corresponded to the tumor stasis concentration in an EML4-ALK(L1196M)-driven model, suggesting that 60% ALK inhibition would be required for tumor stasis. Accordingly, we proposed that the EC60,in vivo for ALK inhibition corresponding to the tumor stasis could be considered a minimum target efficacious concentration of PF06463922 for cancer patients in a phase I trial.

Discovery of (10R)-7-amino-12-fluoro-2,10,16-trimethyl-15-oxo-10,15,16,17-tetrahydro-2H-8,4-(metheno)pyrazolo[4,3-h][2,5,11]-benzoxadiazacyclotetradecine-3-carbonitrile (PF-06463922), a macrocyclic inhibitor of anaplastic lymphoma kinase (ALK) and c-ros oncogene 1 (ROS1) with preclinical brain exposure and broad-spectrum potency against ALK-resistant mutations.

Although crizotinib demonstrates robust efficacy in anaplastic lymphoma kinase (ALK)-positive non-small-cell lung carcinoma patients, progression during treatment eventually develops. Resistant patient samples revealed a variety of point mutations in the kinase domain of ALK, including the L1196M gatekeeper mutation. In addition, some patients progress due to cancer metastasis in the brain. Using structure-based drug design, lipophilic efficiency, and physical-property-based optimization, highly potent macrocyclic ALK inhibitors were prepared with good absorption, distribution, metabolism, and excretion (ADME), low propensity for p-glycoprotein 1-mediated efflux, and good passive permeability. These structurally unusual macrocyclic inhibitors were potent against wild-type ALK and clinically reported ALK kinase domain mutations. Significant synthetic challenges were overcome, utilizing novel transformations to enable the use of these macrocycles in drug discovery paradigms. This work led to the discovery of 8k (PF-06463922), combining broad-spectrum potency, central nervous system ADME, and a high degree of kinase selectivity.

Design of potent and selective inhibitors to overcome clinical anaplastic lymphoma kinase mutations resistant to crizotinib.

Crizotinib (1), an anaplastic lymphoma kinase (ALK) receptor tyrosine kinase inhibitor approved by the U.S. Food and Drug Administration in 2011, is efficacious in ALK and ROS positive patients. Under pressure of crizotinib treatment, point mutations arise in the kinase domain of ALK, resulting in resistance and progressive disease. The successful application of both structure-based and lipophilic-efficiency-focused drug design resulted in aminopyridine 8e, which was potent across a broad panel of engineered ALK mutant cell lines and showed suitable preclinical pharmacokinetics and robust tumor growth inhibition in a crizotinib-resistant cell line (H3122-L1196M).

Pan-FGFR inhibition leads to blockade of FGF23 signaling, soft tissue mineralization, and cardiovascular dysfunction.

The fibroblast growth factor receptors (FGFR) play a major role in angiogenesis and are desirable targets for the development of therapeutics. Groups of Wistar Han rats were dosed orally once daily for 4 days with a small molecule pan-FGFR inhibitor (5mg/kg) or once daily for 6 days with a small molecule MEK inhibitor (3mg/kg). Serum phosphorous and FGF23 levels increased in all rats during the course of the study. Histologically, rats dosed with either drug exhibited multifocal, multiorgan soft tissue mineralization. Expression levels of the sodium phosphate transporter Npt2a and the vitamin D-metabolizing enzymes Cyp24a1 and Cyp27b1 were modulated in kidneys of animals dosed with the pan-FGFR inhibitor. Both inhibitors decreased ERK phosphorylation in the kidneys and inhibited FGF23-induced ERK phosphorylation in vitro in a dose-dependent manner. A separate cardiovascular outcome study was performed to monitor hemodynamics and cardiac structure and function of telemetered rats dosed with either the pan-FGFR inhibitor or MEK inhibitor for 3 days. Both compounds increased blood pressure (~+ 17 mmHg), decreased heart rate (~-75 bpm), and modulated echocardiography parameters. Our data suggest that inhibition of FGFR signaling following administration of either pan-FGFR inhibitor or MEK inhibitor interferes with the FGF23 pathway, predisposing animals to hyperphosphatemia and a tumoral calcinosis-like syndrome in rodents.

Quantitative prediction of repaglinide-rifampicin complex drug interactions using dynamic and static mechanistic models: delineating differential CYP3A4 induction and OATP1B1 inhibition potential of rifampicin.

Repaglinide is mainly metabolized by cytochrome P450 enzymes CYP2C8 and CYP3A4, and it is also a substrate to a hepatic uptake transporter, organic anion transporting polypeptide (OATP)1B1. The purpose of this study is to predict the dosing time-dependent pharmacokinetic interactions of repaglinide with rifampicin, using mechanistic models. In vitro hepatic transport of repaglinide, characterized using sandwich-cultured human hepatocytes, and intrinsic metabolic parameters were used to build a dynamic whole-body physiologically-based pharmacokinetic (PBPK) model. The PBPK model adequately described repaglinide plasma concentration-time profiles and successfully predicted area under the plasma concentration-time curve ratios of repaglinide (within ± 25% error), dosed (staggered 0-24 hours) after rifampicin treatment when primarily considering induction of CYP3A4 and reversible inhibition of OATP1B1 by rifampicin. Further, a static mechanistic "extended net-effect" model incorporating transport and metabolic disposition parameters of repaglinide and interaction potency of rifampicin was devised. Predictions based on the static model are similar to those observed in the clinic (average error ∼19%) and to those based on the PBPK model. Both the models suggested that the combined effect of increased gut extraction and decreased hepatic uptake caused minimal repaglinide systemic exposure change when repaglinide is dosed simultaneously or 1 hour after the rifampicin dose. On the other hand, isolated induction effect as a result of temporal separation of the two drugs translated to an approximate 5-fold reduction in repaglinide systemic exposure. In conclusion, both dynamic and static mechanistic models are instrumental in delineating the quantitative contribution of transport and metabolism in the dosing time-dependent repaglinide-rifampicin interactions.

Effective targeting of Hedgehog signaling in a medulloblastoma model with PF-5274857, a potent and selective Smoothened antagonist that penetrates the blood-brain barrier.

Inhibition of the Smoothened (Smo) represents a promising therapeutic strategy for treating malignant tumors that are dependent on the Hedgehog (Hh) signaling pathway. PF-5274857 is a novel Smo antagonist that specifically binds to Smo with a K(i) of 4.6 ± 1.1 nmol/L and completely blocks the transcriptional activity of the downstream gene Gli1 with an IC(50) of 2.7 ± 1.4 nmol/L in cells. This Smo antagonist showed robust antitumor activity in a mouse model of medulloblastoma with an in vivo IC(50) of 8.9 ± 2.6 nmol/L. The downregulation of Gli1 is closely linked to the tumor growth inhibition in patched(+/-) medulloblastoma mice. Mathematical analysis of the relationship between the drug's pharmacokinetics and Gli1 pharmacodynamics in patched(+/-) medulloblastoma tumor models yielded similar tumor and skin Gli1 IC(50) values, suggesting that skin can be used as a surrogate tissue for the measurement of tumor Gli1 levels. In addition, PF-5274857 was found to effectively penetrate the blood-brain barrier and inhibit Smo activity in the brain of primary medulloblastoma mice, resulting in improved animal survival rates. The brain permeability of PF-5274857 was also confirmed and quantified in nontumor-bearing preclinical species with an intact blood-brain barrier. PF-5274857 was orally available and metabolically stable in vivo. These findings suggest that PF-5274857 is a potentially attractive clinical candidate for the treatment of tumor types including brain tumors and brain metastasis driven by an activated Hh pathway.

Expression and functional analysis of hepatic cytochromes P450, nuclear receptors, and membrane transporters in 10- and 25-week-old db/db mice.

Proper characterization of animal models used for efficacy and safety assessment is crucial. The present study focuses on characterizing proteins that are important components of the absorption, distribution, metabolism, and elimination of xenobiotics. Hepatic gene expression of Cyp2b10, Cyp2c29, Cyp3a11, Cyp2e1, Cyp4a10, Nr1i2, Nr1i3, slco1a1, slco1a4, slco1b2, abcb1b, abcc2, and abcg2 was examined using the real-time polymerase chain reaction method in male db/db mice, a commonly used type II diabetes model. We evaluated age and disease effects on gene expression and enzymatic activity in 10- and 25-week-old db/db and 25-week-old C57BLKS/J (strain-matched lean control) mice. Functional analysis was conducted in hepatic microsomes for Cyp2b, Cyp2c, and Cyp3a using cytochrome P450-specific substrates. There were no significant age- or disease-dependent changes in the expression of Cyp3a11 and Cyp3a activity in the db/db mice. The mRNA levels and the activities of Cyp2b10 and Cyp2c29 in the 25-week-old db/db mice decreased significantly compared with those of the 10-week-old db/db mice. There was a significant age-dependent increase in Cyp4a10 expression noted. The most marked expression change in db/db mice versus a control was the ∼400-fold reduction of mRNA expression of slco1a1. Slco1a4 and sloc1b2 showed increased expression compared with that in an age-matched control, whereas abcb1b showed decreased expression. No expression changes were observed for Cyp2e1, Nr1i2, Nr1i3, abcc2, and abcg2. Our data demonstrate that significant expression and activity differences exist between the db/db and the lean control mice, which are probably age- and disease-dependent.

Elucidating the effect of final-day dosing of rifampin in induction studies on hepatic drug disposition and metabolism.

Because rifampin (RIF) induces hepatic enzymes and inhibits uptake transporters, dosing a drug that is a dual substrate of enzymes and uptake transporters on the final day of an inducing regimen should exhibit less inductive effect than dosing on the following day in the absence of RIF, since RIF decreases drug uptake into liver. In vitro and in vivo rat studies were conducted using digoxin as a model substrate. Digoxin was administered to an uninduced control group to obtain baseline values. The second group (induced with dexamethasone) received digoxin alone, mimicking administration of a test drug 1 day following completion of an induction regimen, whereas the third group (induced) received digoxin with RIF mimicking the concomitant dosing on the final day of an induction regimen. Results from hepatocyte concentration-time course studies showed that compared with uninduced control (26.9 +/- 1.3 microM . min/mg), digoxin area under the time-concentration curve (AUC) in induced cells when no RIF is present decreased significantly (13.7 +/- 0.9 microM . min/mg; p < 0.01), suggesting induction of Cyp3a. However, digoxin AUC for induced cells in the presence of RIF (27.3 +/- 0.9 microM . min/mg) matched the control. Rat pharmacokinetic studies showed that compared with digoxin clearance in uninduced controls (7.08 +/- 1.57 ml/min/kg), digoxin clearance in induced rats increased 2-fold (15.6 +/- 3.7 ml/min/kg; p < 0.001), but when RIF was coadministered in the induced rats, digoxin clearance (7.14 +/- 1.24 ml/min/kg) overlapped with control. That is, concomitant dosing of RIF and digoxin masked the inductive effect. To observe full inductive effects, test drugs should be administered 1 day after final dosing of RIF to minimize potential organic anion transporting polypeptide inhibition effects.

In vitro and in vivo correlation of hepatic transporter effects on erythromycin metabolism: characterizing the importance of transporter-enzyme interplay.

The effects of hepatic uptake and efflux transporters on erythromycin (ERY) disposition and metabolism were examined by comparing results from rat hepatic microsomes, freshly isolated hepatocytes, and in vivo studies. Uptake studies carried out in freshly isolated rat hepatocytes showed that ERY and its metabolite (N-demethyl-ERY) are substrates of Oatp1a4 and Oatp1b2. Whereas rifampin and GG918 [GF120918: N-{4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl}-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamine] exerted minimal effects on metabolism in microsomes, rifampin (2.5 microM) and GG918 (0.5 microM) significantly decreased and increased ERY metabolism in hepatocytes, respectively. Concentration-time course studies further demonstrated that, compared with the intracellular N-demethyl-ERY control area under the curve (AUC) (0.795 +/- 0.057 microM . min), a decreased AUC (0.513 +/- 0.028 microM . min, p < 0.005) was observed when ERY was coincubated with rifampin, and an increased AUC (2.14 +/- 0.21 microM . min, p < 0.05) was found when GG918 was present. The results of the i.v. bolus studies showed that, compared with the ERY clearance of the controls (47.2 +/- 12.5 ml/min/kg for the rifampin group and 42.1 +/- 5.7 for the GG918 group), a decreased blood clearance, 29.8 +/- 6.1 ml/min/kg (p < 0.05) and 21.7 +/- 9.0 ml/min/kg (p < 0.01), was observed when rifampin or GG918, respectively, was coadministered. When either inhibitor was codosed with ERY, volume of distribution at steady state was unchanged, but t1/2 and mean residence time significantly increased compared with the controls. Hepatic uptake and efflux transporters modulate intracellular concentrations of ERY, thereby affecting metabolism. The interplay of transporters and enzymes must be considered in evaluating potential drug-drug interactions.

Hepatic microsome studies are insufficient to characterize in vivo hepatic metabolic clearance and metabolic drug-drug interactions: studies of digoxin metabolism in primary rat hepatocytes versus microsomes.

The effects of hepatic uptake and efflux transporters on metabolism of digoxin were examined in isolated rat hepatocytes versus microsomes. The metabolic clearance estimated from microsomes was 4.59 +/- 0.69 ml/min/kg. However, the metabolic clearance estimated from hepatocytes was 15.9 +/- 3.0 ml/min/kg. The former did not correlate with in vivo clearance (12.9 ml/min/kg) for digoxin. Rifampin (an organic anion-transporting peptide 2 inhibitor) or GG918 [GF120918 (N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide)] (a potent P-glycoprotein inhibitor) were used to estimate effects of uptake or efflux transporters on digoxin metabolism. Whereas both inhibitors exerted minimal effects on metabolism in microsomes, rifampin and GG918 significantly decreased and increased digoxin metabolism in hepatocytes, respectively. Concentration-time course studies further demonstrated that, compared with the area under the curve (AUC) of control (15.6 +/- 0.1 microM . min), an increase of AUC (20.1 +/- 0.5 microM . min, p < 0.005) was observed when digoxin was coincubated with rifampin and a decrease of AUC (14.1 +/- 0.1 microM . min, p < 0.01) when GG918 was also present. Digoxin primary metabolite concentrations changed directionally in an inverse manner with parent drug concentrations, as would be expected. These results strongly suggest that the hepatic uptake and efflux transporters that are found in hepatocytes, but not in microsomes, modulate intracellular concentration of digoxin and thus affect metabolism. We conclude that the interplay of transporters and enzymes must be considered in defining the intrinsic metabolic clearance of the liver and in evaluating potential drug-drug interactions.