Gondi Kumar

Pharmacokinetics of Lenalidomide in Subjects With Various Degrees of Renal Impairment and in Subjects on Hemodialysis

The present study investigated the effect of renal impairment and hemodialysis on the pharmacokinetics of lenalidomide following a single 25‐mg oral dose in 30 subjects aged 39 to 76 years. A single 25‐mg dose was well tolerated by renally impaired subjects. Renal impairment did not alter the oral absorption, protein binding, or nonrenal elimination of lenalidomide. Mean urinary recovery of unchanged lenalidomide was 84% of the dose in subjects with normal renal function (creatinine clearance [CLCr] > 80 mL/min), and it declined to 69%, 38%, and 43% in subjects with mild (50 ≤ CLCr ≤ 80 mL/min), moderate (30 ≤ CLCr < 50 mL/min), and severe (CLCr < 30 mL/min) renal impairment, respectively. The differences in pharmacokinetic parameters between normal renal function and mild renal impairment were minor to modest (11%–32%). As renal impairment progressed to moderate, severe, or end‐stage renal disease, total and renal lenalidomide clearance decreased drastically, area under the concentration‐time curve increased by approximately 185% to 420%, and t1/2 was prolonged by approximately 6 to 12 hours. A 4‐hour hemodialysis removed 31% of lenalidomide in the body. Therefore, lenalidomide dose adjustments should be considered for patients with CLCr < 50 mL/min, and the recommendations are given for the starting doses.

Disposition, metabolism and mass balance of [14C]apremilast following oral administration

Apremilast is a novel, orally available small molecule that specifically inhibits PDE4 and thus modulates multiple pro- and anti-inflammatory mediators, and is currently under clinical development for the treatment of psoriasis and psoriatic arthritis. The pharmacokinetics and disposition of [14C]apremilast was investigated following a single oral dose (20 mg, 100 μCi) to healthy male subjects. Approximately 58% of the radioactive dose was excreted in urine, while faeces contained 39%. Mean Cmax, AUC0–∞ and tmax values for apremilast in plasma were 333 ng/mL, 1970 ng*h/mL and 1.5 h. Apremilast was extensively metabolized via multiple pathways, with unchanged drug representing 45% of the circulating radioactivity and <7% of the excreted radioactivity. The predominant metabolite was O-desmethyl apremilast glucuronide, representing 39% of plasma radioactivity and 34% of excreted radioactivity. The only other radioactive components that represented >4% of the excreted radioactivity were O-demethylated apremilast and its hydrolysis product. Additional minor circulating and excreted compounds were formed via O-demethylation, O-deethylation, N-deacetylation, hydroxylation, glucuronidation and/or hydrolysis. The major metabolites were at least 50-fold less pharmacologically active than apremilast. Metabolic clearance of apremilast was the major route of elimination, while non-enzymatic hydrolysis and excretion of unchanged drug were involved to a lesser extent.

Lenalidomide: in vitro evaluation of the metabolism and assessment of cytochrome P450 inhibition and induction.

PurposeTo assess the potential for drug–drug interactions between lenalidomide and substrates and inhibitors of cytochrome P450 (CYP) isozymes.MethodsIn vitro metabolism of lenalidomide by human liver microsomes, recombinant human CYPs and human hepatocytes was evaluated. The inhibitory and inductive effects of lenalidomide on the CYP activities were evaluated in human liver microsomes and cultured human hepatocytes, respectively.ResultsIn vitro incubation of lenalidomide with human liver microsomes, recombinant-CYP isozymes, and human hepatocytes did not result in Phase I or Phase II metabolism, confirming the low propensity of lenalidomide for metabolism in vivo in humans. In vitro, lenalidomide did not inhibit CYP isozymes in human liver microsomes and did not induce CYP activities in cultured human hepatocytes.ConclusionsLenalidomide is not a substrate, inhibitor, or inducer of CYP group of enzymes; clinically relevant pharmacokinetic drug–drug interactions are unlikely to occur between lenalidomide and co-administered CYP substrates or inhibitors.

Pomalidomide: evaluation of cytochrome P450 and transporter-mediated drug-drug interaction potential in vitro and in healthy subjects.

Pomalidomide offers an alternative for patients with relapsed/refractory multiple myeloma who have exhausted treatment options with lenalidomide and bortezomib. Little is known about pomalidomides potential for drug–drug interactions (DDIs); as pomalidomide clearance includes hydrolysis and cytochrome P450 (CYP450)‐mediated hydroxylation, possible DDIs via CYP450 and drug‐transporter proteins were investigated in vitro and in a clinical study. In vitro pomalidomide was neither an inducer nor inhibitor of CYP450, nor an inhibitor of transporter proteins P glycoprotein (P‐gp), BCRP, OAT1, OAT3, OCT2, OATP1B1, and OATP1B3. Oxidative metabolism of pomalidomide was predominately mediated by CYP1A2 and CYP3A4, and pomalidomide was shown to be a P‐gp substrate. In healthy males, co‐administration of oral (4 mg) pomalidomide with ketoconazole (CYP3A/P‐gp inhibitor) or carbamazepine (CYP3A/P‐gp inducer) did not result in clinically relevant changes in pomalidomide exposure. Co‐administration of pomalidomide with fluvoxamine (CYP1A2 inhibitor) in the presence of ketoconazole approximately doubled pomalidomide exposure. Pomalidomide appears to have low potential for clinically relevant DDI and is unlikely to affect the clinical exposure of other drugs. Avoid co‐administration of strong CYP1A2 inhibitors unless medically necessary. Pomalidomide dose should be reduced by 50% if co‐administered with strong CYP1A2 inhibitors and strong CYP3A/P‐gp inhibitors.

Embryo-fetal exposure and developmental outcome of thalidomide following oral and intravaginal administration to pregnant rabbits.

Studies in pregnant rabbits were conducted to evaluate if there are any differences in the uptake of thalidomide into the intrauterine compartment and developmental toxicity risk following oral and intravaginal administration. Thalidomide concentrations in maternal plasma, yolk sac cavity (YSC) fluid and embryo following intravaginal administration were 2- to 7-fold lower than their respective levels after oral administration. Ratios of thalidomide concentration in YSC fluid to maternal plasma were similar between these two routes, indicating no difference in uptake into the intrauterine compartment. A rabbit embryo-fetal development study using oral and intravaginal thalidomide administration at 2mg/kg/day (a dose >10,000-fold higher than the expected amount of thalidomide in human semen) did not result in any developmental abnormalities. These data demonstrated no preferential transfer mechanism of thalidomide from vagina to conceptus, and no additional embryo-fetal developmental toxicity risks with thalidomide exposure via the vaginal route.

Modeling and Simulation to Probe the Pharmacokinetic Disposition of Pomalidomide R- and S-Enantiomers

Pomalidomide, a potent novel immunomodulatory agent, has been developed as a racemic mixture of its R- and S-isomers. Pharmacokinetic (PK) analyses were conducted to determine the PK disposition of the isomers from their PK profiles in humans and monkeys. Modeling and simulation were performed to describe the observed PK profiles and explore potential differences in isomer disposition and exposure. PK profiles of S- and R-isomers were measured in a human absorption, distribution, metabolism, and excretion study after oral administration of racemate. PK profiles of S- and R-isomers were measured in monkeys after intravenous and oral administration of S- or R-isomers and pomalidomide racemate. Modeling and simulation were performed using NONMEM 7.2 (Globomax, Ellicott City, MD) to describe the observed PK profiles of S- and R-isomers in humans and monkeys. The results showed that in humans, the in vivo elimination rate of pomalidomide isomers was lower than the R-/S-interconversion rate, resulting in no clinically relevant difference in overall exposure to the two isomers. However, in monkeys, the in vivo elimination rate was higher than the R-/S-interconversion rate, resulting in 1.72- and 1.55-fold differences in R- versus S-isomer exposures. Monte Carlo simulation indicated that exposure to R- and S-enantiomers in humans should be comparable even if single isomers are administered. Thus, in humans, rapid isomeric interconversion of pomalidomide isomers results in comparable exposure to R- and S-enantiomers regardless of whether pomalidomide is administered as a single enantiomer or as a racemate, therefore justifying the clinical development of pomalidomide as a racemate.

The interactions of lenalidomide with human uptake and efflux transporters and UDP-glucuronosyltransferase 1A1: lack of potential for drug-drug interactions.

AbstractPurpose Lenalidomide is an immunomodulatory agent used for the treatment of myelodysplastic syndromes and multiple myeloma. Renal clearance of lenalidomide is the predominant elimination route and is approximately twofold greater than the glomerular filtration rate (GFR), suggesting the potential contribution of an active secretory mechanism. In vitro studies were conducted to examine whether lenalidomide is a substrate of drug transporters, namely P-glycoprotein (P-gp), human breast cancer resistance protein (BCRP), multidrug resistance proteins (MRP1, MRP2, MRP3), organic anion transporters (OAT1, OAT3), organic cation transporters (OCT1 and OCT2), human organic cation transporter novel 1 and 2 (OCTN1 and OCTN2), multidrug and toxin extrusion (MATE1) and organic anion transporting polypeptide (OATP1B1). Lenalidomide was also evaluated as an inhibitor of P-gp, BCRP, MRP2, OCT2, OAT1, OAT3, OATP1B1, OATP1B3 and bile salt export pump (BSEP). In addition, inhibition of UDP-glucuronosyltransferase 1A1 (UGT1A1) variants by lenalidomide was also assessed.MethodCells or vesicles expressing each of the human transporters were used for uptake and inhibition studies, with appropriate probe substrates and known inhibitors.ResultsResults of these studies indicate that the lenalidomide is not a substrate for the transporters examined, except that it is weak substrate of P-gp. None of the transporters studied were inhibited by lenalidomide. Lenalidomide is not an inhibitor of UGT1A1*1/*1 or its polymorphic variants UGT1A1*1/*28 and UGT1A1*28/*28.ConclusionsDrug interactions are unlikely to occur when lenalidomide is co-administered with substrates or inhibitors of these transporters. In addition, lenalidomide is unlikely to cause interactions when co-administered with substrates of UGT1A1.

SALL4 mediates teratogenicity as a thalidomide-dependent cereblon substrate

AbstractTargeted protein degradation via small-molecule modulation of cereblon offers vast potential for the development of new therapeutics. Cereblon-binding therapeutics carry the safety risks of thalidomide, which caused an epidemic of severe birth defects characterized by forelimb shortening or phocomelia. Here we show that thalidomide is not teratogenic in transgenic mice expressing human cereblon, indicating that binding to cereblon is not sufficient to cause birth defects. Instead, we identify SALL4 as a thalidomide-dependent cereblon neosubstrate. Human mutations in SALL4 cause Duane-radial ray, IVIC, and acro-renal-ocular syndromes with overlapping clinical presentations to thalidomide embryopathy, including phocomelia. SALL4 is degraded in rabbits but not in resistant organisms such as mice because of SALL4 sequence variations. This work expands the scope of cereblon neosubstrate activity within the formerly ‘undruggable’ C2H2 zinc finger family and offers a path toward safer therapeutics through an improved understanding of the molecular basis of thalidomide-induced teratogenicity.Thalidomide-induced degradation of the transcription factor SALL4 in a cereblon-dependent manner provides an explanation for the teratogenic effects.

In vitro metabolism of a novel JNK inhibitor tanzisertib: interspecies differences in oxido-reduction and characterization of enzymes involved in metabolism

Abstract 1. In vitro metabolism of Tanzisertib [(1S,4R)-4-(9-((S)tetrahydrofuran-3-yl)-8-(2,4,6-trifluorophenylamino)-9H-purin-2-ylamino) cyclohexanol], a potent, selective c-Jun amino-terminal kinase (JNK) inhibitor, was investigated in mouse, rat, rabbit, dog, monkey and human hepatocytes over 4 h. The extent of metabolism of [14C]tanzisertib was variable, with <10% metabolized in dog and human, <20% metabolized in rabbit and monkey and >75% metabolized in rat and mouse. Primary metabolic pathways in human and dog hepatocytes, were direct glucuronidation and oxidation of cyclohexanol to a keto metabolite, which was subsequently reduced to parent or cis-isomer, followed by glucuronidation. Rat and mouse produced oxidative metabolites and cis-isomer, including direct glucuronides and sulfates of tanzisertib and cis-isomer. 2. Enzymology of oxido-reductive pathways revealed that human aldo-keto reductases AKR1C1, 1C2, 1C3 and 1C4 were responsible for oxido-reduction of tanzisertib, CC-418424 and keto tanzisertib. Characterizations of enzyme kinetics revealed that AKR1C4 had a high affinity for reduction of keto tanzisertib to tanzisertib compared to other isoforms. These results demonstrate unique stereoselectivity of the reductive properties documented by human AKR1C enzymes for the same substrate. 3. Characterization of UGT isoenzymes in glucuronidation of tanzisertib and CC-418424 revealed that, tanzisertib glucuronide was catalyzed by: UGT1A1, 1A4, 1A10 and 2B4, while CC-418424 glucuronidation was catalyzed by UGT2B4 and 2B7.

Abstract 5666: Albumin and paclitaxel co-localize in endocytic vesicles in HUVEC cells, and uptake is blocked by Cremophor EL.

Nab ® -paclitaxel is an albumin-bound nanoparticle formulation of paclitaxel (ptx) that does not contain Cremophor EL (CrEL), and results in higher drug levels in xenografts and increased clinical activity in breast and lung cancers compared to ptx formulated with CrEL (Taxol ® ). Above the critical micellar concentration of 0.009%, CrEL forms long-lived micelles in circulation that can sequester ptx (peak plasma concentration in clinical use is 0.3%). Previous studies have shown CrEL reduces ptx binding to albumin, and Taxol ® has reduced association with, and transport across endothelial cells compared to nab ® -ptx (Desai, CCR 2006). Endothelial cells take up albumin, which is trafficked into recycling or transcytosis pathways or into lysosomes for degradation. Here, we explore mechanisms of uptake and trafficking of albumin and ptx in endothelial cells and the effect of CrEL on these events. Using fluorescence microscopy, we visualized the uptake of rhodamine-albumin and fluorescent ptx (Flutax). Albumin was present in EEA1-positive early endosomes and LAMP1-positive lysosomes. Notably, ptx was also present in vesicular structures and was often co-localized with albumin. The uptake of albumin was blocked by increasing concentrations (0.003%-0.3%) of CrEL, and also by inhibitors of caveolin-mediated endocytosis including indomethacin (blocks internalization of caveolae) and methyl-β-cyclodextrin (prevents formation of lipid rafts). The effect of CrEL on paclitaxel and albumin cellular uptake was confirmed by flow cytometry studies. 0.3% CrEL reduced the uptake of Flutax in DMSO, Flutax-modified nab ® -ptx, and FITC-labeled albumin to close to background levels in both HUVEC and PC3 cells. Thus, in addition to its drug sequestration activity, CrEL directly affects endocytosis. We further evaluated CrEL effects on Flutax and ptx transport across endothelial monolayers in transwell chambers using a fluorescence detection assay. Two-fold more ptx crossed monolayers exposed to Flutax-containing nab ® -ptx as compared to Taxol ® . The effects of 0.001% to 0.3% CrEL on ptx transport at varying timepoints were investigated by mass spectrometry. Dose-dependent inhibition was observed, with a 3-fold reduction in transported ptx at 24 hrs. In summary, we have demonstrated that ptx co-localizes with albumin in endothelial cells, suggesting that the nab-ptx complex can remain intact within cells. Furthermore, CrEL interferes with albumin uptake at clinically relevant concentrations, thereby affecting paclitaxel cellular uptake and transport. These mechanistic studies further elucidate the basis of increased delivery of drug into the target cells by the nab ® -ptx formulation as compared to Taxol ® . Citation Format: Xiping Liu, Carrie Brachmann, Sean Hong, Shijuan Wu, Zeen Tong, Tapas De, Willard Foss, Gondi Kumar, Sekhar Surapaneni, Rajesh Chopra, Daniel Pierce, Carla Heise. Albumin and paclitaxel co-localize in endocytic vesicles in HUVEC cells, and uptake is blocked by Cremophor EL. [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 5666. doi:10.1158/1538-7445.AM2013-5666