Safety, tolerability, and pharmacokinetics of ribavirin in hepatitis C virus-infected patients with various degrees of renal impairment.

Ribavirin (RBV) is an integral part of standard-of-care hepatitis C virus (HCV) treatments and many future regimens under investigation. The pharmacokinetics (PK), safety, and tolerability of RBV in chronically HCV-infected patients with renal impairment are not well defined and were the focus of an open-label PK study in HCV-infected patients receiving RBV plus pegylated interferon. Serial RBV plasma samples were collected over 12 h on day 1 of weeks 1 and 12 from patients with moderate renal impairment (creatinine clearance [CLCR], 30 to 50 ml/min; RBV, 600 mg daily), severe renal impairment (CLCR, <30 ml/min; RBV, 400 mg daily), end-stage renal disease (ESRD) (RBV, 200 mg daily), or normal renal function (CLCR, >80 ml/min; RBV, 800 to 1,200 mg daily). Of the 44 patients, 9 had moderately impaired renal function, 10 had severely impaired renal function, 13 had ESRD, and 12 had normal renal function. The RBV dose was reduced because of adverse events (AEs) in 71% and 53% of severe and moderate renal impairment groups, respectively. Despite this modification, patients with moderate and severe impairment had 12-hour (area under the concentration-time curve from 0 to 12 h [AUC0-12]) values 36% (38,452 ng · h/ml) and 25% (35,101 ng · h/ml) higher, respectively, than those with normal renal function (28,192 ng · h/ml). Patients with ESRD tolerated a 200-mg daily dose, and AUC0-12 was 20% lower (22,629 ng · h/ml) than in patients with normal renal function. PK modeling and simulation (M&S) indicated that doses of 200 mg or 400 mg alternating daily for patients with moderate renal impairment and 200 mg daily for patients with severe renal impairment were the most appropriate dose regimens in these patients.

Expression of REX-1, a gene containing zinc finger motifs, is rapidly reduced by retinoic acid in F9 teratocarcinoma cells.

In the presence of retinoic acid (RA), cultured F9 murine teratocarcinoma stem cells differentiate into nontumorigenic cells resembling the extraembryonic endoderm of the early mouse embryo. By differential hybridization screening of an F9 cell cDNA library, we isolated a 1,745-nucleotide cDNA for a gene, REX-1 (for reduced expression), whose steady-state mRNA level began to decline in F9 cells in monolayer culture within 12 h after the addition of RA. By 48 to 96 h after RA treatment of F9 cells in monolayer culture, the REX-1 steady-state mRNA level was more than sevenfold lower than the level in undifferentiated F9 stem cells. The REX-1 mRNA decrease did not result from the reduction in cell growth rate associated with the differentiation process, since the REX-1 mRNA level did not decline in F9 cells that were partially growth arrested after 48 h of isoleucine deprivation. The RA-associated REX-1 mRNA decrease resulted primarily from a reduction in the transcription rate of the REX-1 gene in the presence of RA. In contrast to results in F9 cells, we have been unable thus far to detect REX-1 mRNA in day 7.5 to 12.5 mouse embryo RNA samples or in the P19 teratocarcinoma stem cell line. The putative REX-1 protein identified by DNA sequence analysis contains four repeats of the zinc finger nucleic acid-binding motif and a potential acidic activator domain, suggesting that REX-1 encodes a regulatory protein. The REX-1 gene is not identical to the previously reported murine genes that encode zinc finger-containing proteins.

Dominant negative retinoid X receptor beta inhibits retinoic acid-responsive gene regulation in embryonal carcinoma cells.

Retinoid X receptors (RXRs) heterodimerize with multiple nuclear hormone receptors and are thought to exert pleiotropic functions. To address the role of RXRs in retinoic acid- (RA) mediated gene regulation, we designed a dominant negative RXR beta. This mutated receptor, termed DBD-, lacked the DNA binding domain but retained the ability to dimerize with partner receptors, resulting in formation of nonfunctional dimers. DBD- was transfected into P19 murine embryonal carcinoma (EC) cells, in which reporters containing the RA-responsive elements (RAREs) were activated by RA through the activity of endogenous RXR-RA receptor (RAR) heterodimers. We found that DBD- had a dominant negative activity on the RARE reporter activity in these cells. P19 clones stably expressing DBD- were established; these clones also failed to activate RARE-driven reporters in response to RA. Further, these cells were defective in RA-induced mRNA expression of Hox-1.3 and RAR beta, as well as in RA-induced down-regulation of Oct3 mRNA. Gel mobility shift assays demonstrated that RA treatment of control P19 cells induces RARE-binding activity, of which RXR beta is a major component. However, the RA-induced binding activity was greatly reduced in cells expressing DBD-. By genomic footprinting, we show that RA treatment induces in vivo occupancy of the RARE in the endogenous RAR beta gene in control P19 cells but that this occupancy is not observed with the DBD- cells. These data provide evidence that the dominant negative activity of DBD- is caused by the lack of receptor binding to target DNA. Finally, we show that in F9 EC cells expression of DBD- leads to inhibition of the growth arrest that accompanies RA-induced differentiation. Taken together, these results demonstrate that RXR beta and partner receptors play a central role in RA-mediated gene regulation and in the control of growth and differentiation in EC cells.

Inhibition of estrogen-responsive gene activation by the retinoid X receptor beta: evidence for multiple inhibitory pathways.

The retinoid X receptor beta (RXR beta; H-2RIIBP) forms heterodimers with various nuclear hormone receptors and binds multiple hormone response elements, including the estrogen response element (ERE). In this report, we show that endogenous RXR beta contributes to ERE binding activity in nuclear extracts of the human breast cancer cell line MCF-7. To define a possible regulatory role of RXR beta regarding estrogen-responsive transcription in breast cancer cells, RXR beta and a reporter gene driven by the vitellogenin A2 ERE were transfected into estrogen-treated MCF-7 cells. RXR beta inhibited ERE-driven reporter activity in a dose-dependent and element-specific fashion. This inhibition occurred in the absence of the RXR ligand 9-cis retinoic acid. The RXR beta-induced inhibition was specific for estrogen receptor (ER)-mediated ERE activation because inhibition was observed in ER-negative MDA-MB-231 cells only following transfection of the estrogen-activated ER. No inhibition of the basal reporter activity was observed. The inhibition was not caused by simple competition of RXR beta with the ER for ERE binding, since deletion mutants retaining DNA binding activity but lacking the N-terminal or C-terminal domain failed to inhibit reporter activity. In addition, cross-linking studies indicated the presence of an auxiliary nuclear factor present in MCF-7 cells that contributed to RXR beta binding of the ERE. Studies using known heterodimerization partners of RXR beta confirmed that RXR beta/triiodothyronine receptor alpha heterodimers avidly bind the ERE but revealed the existence of another triiodothyronine-independent pathway of ERE inhibition. These results indicate that estrogen-responsive genes may be negatively regulated by RXR beta through two distinct pathways.

New retinoid X receptor subtypes in zebra fish (Danio rerio) differentially modulate transcription and do not bind 9-cis retinoic acid.

Retinoid X receptors (RXRs), along with retinoic acid (RA) receptors (RARs), mediate the effects of RA on gene expression. Three subtypes of RXRs (alpha, beta, and gamma) which bind to and are activated by the 9-cis stereoisomer of RA have been characterized. They activate gene transcription by binding to specific sites on DNA as homodimers or as heterodimers with RARs and other related nuclear receptors, including the vitamin D receptor, thyroid hormone receptors (TRs), and peroxisome proliferator-activated receptors. Two additional RXR subtypes (delta and epsilon) isolated from zebra fish cDNA libraries are described here; although both subtypes form DNA-binding heterodimers with RARs and TR, neither binds 9-cis RA, and both are transcriptionally inactive on RXR response elements. In cotransfection studies with TR, the delta subtype was found to function in a dominant negative manner, while the epsilon subtype had a slight stimulatory effect on thyroid hormone (T3)-dependent transcriptional activity. The discovery of these two novel receptors in zebra fish expands the functional repertoire of RXRs to include ligand-independent and dominant negative modulation of type II receptor function.

Distinct binding determinants for 9-cis retinoic acid are located within AF-2 of retinoic acid receptor alpha.

Retinoids exert their physiological action by interacting with two families of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs), which regulate gene expression by forming transcriptionally active heterodimeric RAR/RXR or homodimeric RXR/RXR complexes on DNA. Retinoid receptor activity resides in several regions, including the DNA and ligand binding domains, a dimerization interface, and both a ligand-independent (AF-1) and a ligand-dependent (AF-2) transactivation function. While 9-cis retinoic acid (RA) alone is the cognate ligand for the RXRs, both 9-cis RA and all-trans RA (t-RA) compete for binding with high affinity to the RARs. This latter observation suggested to us that the two isomers may interact with a common binding site. Here we report that RAR alpha has two distinct but overlapping binding sites for 9-cis RA and t-RA. Truncation of a human RAR alpha to 419 amino acids yields a receptor that binds both t-RA and 9-cis RA with high affinity, but truncation to amino acid 404 yields a mutant receptor that binds only t-RA with high affinity. Remarkably, this region also defines a C-terminal boundary for AF-2, as addition of amino acids 405 to 419 restores receptor-mediated gene activity to a truncated human RAR alpha lacking this region. It is interesting to speculate that binding of retinoid stereoisomers to unique sites within an RAR may function with AF-2 to cause differential activation of retinoid-responsive gene pathways.

Retinoic acid induces down-regulation of several growth factors and proto-oncogenes in a human embryonal cancer cell line.

The human teratocarcinoma cell NTERA-2 cl. D1 (NT2/D1) is a cloned embryonal cancer cell line that differentiates into a neuronal phenotype and other cellular lineages after treatment with retinoic acid (RA). We examined the regulated expression of growth factors and proto-oncogenes in NT2/D1 cells. We studied RNA levels after six days of RA treatment to assess gene expression coincident with observed morphologic differentiation. Three growth factors were markedly down-regulated following RA treatment: Hst-1/kFGF and TGF-alpha expression became undetectable by Northern analysis and bFGF expression was substantially reduced. Minimal decline was seen for c-myc, N-myc, c-fos, and c-myb. Increased expression with differentiation was seen for the human homeotic genes Hox 2.1 and Hox 2.2. Assay of RNA levels daily after one to six days of RA treatment showed that the growth factor down-regulation inversely correlated with the homeotic gene up-regulation. Nuclear run-on studies showed low transcriptional rates for these homeotic genes, Hst-1/kFGF, and TGF-alpha that did not measurably change with RA treatment. To explore whether these regulated genes in NT2/D1 play a role in human testicular cancer, we examined RNA levels in a panel of human germ cell cancer lines. Hst-1/kFGF and bFGF are commonly expressed in five of seven male germ cell cancer lines. These data show that specific proto-oncogenes and growth factors are down-regulated with RA treatment of the NT2/D1 cell and that some of these regulated genes are often expressed in human germ cell cancer lines.

Glucokinase gene locus transgenic mice are resistant to the development of obesity-induced type 2 diabetes.

Transgenic mice that overexpress the entire glucokinase (GK) gene locus have been previously shown to be mildly hypoglycemic and to have improved tolerance to glucose. To determine whether increased GK might also prevent or diminish diabetes in diet-induced obese animals, we examined the effect of feeding these mice a high-fat high-simple carbohydrate low-fiber diet (HF diet) for 30 weeks. In response to this diet, both normal and transgenic mice became obese and had similar BMIs (5.3 +/- 0.1 and 5.0 +/- 0.1 kg/m2 in transgenic and non-transgenic mice, respectively). The blood glucose concentration of the control mice increased linearly with time and reached 17.0 +/- 1.3 mmol/l at the 30th week. In contrast, the blood glucose of GK transgenic mice rose to only 9.7 +/- 1.2 mmol/l at the 15th week, after which it returned to 7.6 +/- 1.0 mmol/l by the 30th week. The plasma insulin concentration was also lower in the GK transgenic animals (232 +/- 79 pmol/l) than in the controls (595 +/- 77 pmol/l), but there was no difference in plasma glucagon concentrations. Together, these data indicate that increased GK levels dramatically lessen the development of both hyperglycemia and hyperinsulinemia associated with the feeding of an HF diet.

The mouse Dlx-2 (Tes-1) gene is expressed in spatially restricted domains of the forebrain, face and limbs in midgestation mouse embryos.

The pattern of RNA expression of the murine Dlx-2 (Tes-1) homeobox gene is described in embryos ranging in age from E8.5 through E11.5. Dlx-2 is a vertebrate homologue of the Drosophila Distal-less (Dll) gene. Dll expression in the Drosophila embryo is principally limited to the primordia of the brain, head and limbs. Dlx-2 is also expressed principally in the primordia of the forebrain, head and limbs. Within these regions it is expressed in spatially restricted domains. These include two discontinuous regions of the forebrain (basal telencephalon and ventral diencephalon), the branchial arches, facial ectoderm, cranial ganglia and limb ectoderm. Several mouse and human disorders have phenotypes which potentially are the result of mutations in the Dlx genes.

The discovery of 9-cis retinoic acid: a hormone that binds the retinoid-X receptor.

Two classes of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid-X receptors (RXRs), mediate the physiologic activity of retinoids. The RXRs can form biologically active heterodimers with the RARs and with other nuclear receptors, including the vitamin-D, thyroid hormone, and peroxisome proliferator-activated receptors. Thus, the RXRs may play a pivotal role in modulating the action of other hormones or ligands. The RXRs were originally classified as orphan receptors whose cognate ligand was unknown until recently, when 9-cis retinoic acid (9-cis RA) was discovered to bind directly and activate this family of receptors. Since 9-cis RA also binds and activates the RARs, it is interesting to speculate that this natural ligand may regulate a broad range of physiologic processes by mediating transcriptional activity through both RAR- and RXR-linked pathways.

The retinoid receptors.

The retinoid receptors belong to a large superfamily of ligand-inducible transcription factors that include the steroid, vitamin D and thyroid hormone receptors, the peroxisome proliferator-activated receptor, the insect edysteroid receptor, and a number of orphan receptors whose ligands are unknown. All nuclear receptors have several well-characterized structural domains, including a conserved DNA-binding domain, and a ligand binding domain at the carboxyl terminus of the receptor. The RAR and RXR classes of nuclear retinoic acid receptors are each composed of alpha, beta and gamma subtypes with more than one isoform for each receptor subtype. Data from many investigators suggest there are RAR- and RXR-dependent gene pathways, and that the individual receptor subtypes may control distinct gene expression patterns. In addition, RXR has been found to heterodimerize with other nuclear receptors to form active transcriptional complexes, which influence the activity of a variety of gene pathways important in growth and differentiation. As a result, retinoids have been useful clinical agents in Dermatology and Oncology. However, upon prolonged exposure to retinoic acid, resistance to retinoids has often been encountered both in the clinical setting and in long-term cell culture (HL60R and RAC65 cells). In the latter case, retinoid resistance has been associated with a mutation in the RAR gene which transcribes a RAR receptor truncated at the C-terminal end. These mutated RAR receptors exhibit a reduced affinity for retinoic acid while retaining the ability to bind to a retinoic acid response element on DNA. As a result, these mutant receptors exhibit dominant-negative activity by binding to the DNA without activating transcription and by competing with other receptors for sites on the response element. In fact, dominant-negative activity may be very important in the development of many neoplastic diseases, including acute promyelocytic leukemia (APL), where a t(15;17) chromosomal translocation fuses the PML gene to the RAR gene, to produce a PML-RAR fusion protein in large excess in the cell. However, retinoid resistance in the patient is most probably the result of pharmacokinetic problems, whereby, with continuous retinoid treatment, the plasma levels of retinoic acid gradually decrease to below that required to maintain differentiation of leukemic cells in vivo. A major challenge for drug discovery is to design a drug which circumvents these pharmacokinetic problems either by designing novel drug delivery systems or by employing retinoids which do not bind to CRABP, such as 9-c-RA.(ABSTRACT TRUNCATED AT 400 WORDS)

The retinoid receptors.

The retinoid receptors belong to a large superfamily of ligand-inducible transcription factors that include the steroid, vitamin D and thyroid hormone receptors, the peroxisome proliferator-activated receptor, the insect edysteroid receptor, and a number of orphan receptors whose ligands are unknown. All nuclear receptors have several well-characterized structural domains, including a conserved DNA-binding domain, and a ligand binding domain at the carboxyl terminus of the receptor. The RAR and RXR classes of nuclear retinoic acid receptors are each composed of alpha, beta and gamma subtypes with more than one isoform for each receptor subtype. Data from many investigators suggest there are RAR- and RXR-dependent gene pathways, and that the individual receptor subtypes may control distinct gene expression patterns. In addition, RXR has been found to heterodimerize with other nuclear receptors to form active transcriptional complexes, which influence the activity of a variety of gene pathways important in growth and differentiation. As a result, retinoids have been useful clinical agents in Dermatology and Oncology. However, upon prolonged exposure to retinoic acid, resistance to retinoids has often been encountered both in the clinical setting and in long-term cell culture (HL60R and RAC65 cells). In the latter case, retinoid resistance has been associated with a mutation in the RAR gene which transcribes a RAR receptor truncated at the C-terminal end. These mutated RAR receptors exhibit a reduced affinity for retinoic acid while retaining the ability to bind to a retinoic acid response element on DNA. As a result, these mutant receptors exhibit dominant-negative activity by binding to the DNA without activating transcription and by competing with other receptors for sites on the response element. In fact, dominant-negative activity may be very important in the development of many neoplastic diseases, including acute promyelocytic leukemia (APL), where a t(15;17) chromosomal translocation fuses the PML gene to the RAR gene, to produce a PML-RAR fusion protein in large excess in the cell. However, retinoid resistance in the patient is most probably the result of pharmacokinetic problems, whereby, with continuous retinoid treatment, the plasma levels of retinoic acid gradually decrease to below that required to maintain differentiation of leukemic cells in vivo. A major challenge for drug discovery is to design a drug which circumvents these pharmacokinetic problems either by designing novel drug delivery systems or by employing retinoids which do not bind to CRABP, such as 9-c-RA.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of the chimeric retinoic acid receptor RARalpha/VDR.

The chimeric receptor, RARalpha/VDR, contains the DNA-binding domain of the retinoic acid receptor (RARalpha) and the ligand-binding domain of the vitamin D receptor (VDR). The ligand-binding properties of RARalpha/VDR are equivalent to that of VDR, with an observed Kd for 1alpha,25 dihydroxy-vitamin D3 (D3) of 0.5 nM. In CV-1 cells, both RARalpha and RARalpha/VDR induce comparable levels of ligand-mediated transcriptional activity from the retinoic acid responsive reporter gene, beta(RARE)3-TK-luciferase, in the presence of the ligand predicted from the receptor ligand-binding domain. Two chimeric RAR receptors were constructed which contained the ligand-binding domain of the estrogen receptor (ER): RARalpha/ER and ER/RARalpha/ER. Both RARalpha/ER and ER/RARalpha/ER bind beta-estradiol with high affinity, and are transcriptionally active only from palindromic RAREs (TREpal and/or (TRE3)3). Only RARalpha/VDR matched in kind and degree the functional characteristics of RARalpha: (1) maximally active from the beta(RARE); (2) moderately active from the TREs; (3) inactive from the retinoic X receptor response elements (RXREs) ApoA1 and CRBP II; (4) forms heterodimers with RXRalpha; and (5) binds to the betaRARE. F9 embryonal carcinoma cell lines were generated which express RARalpha/VDR mRNA (F9RARalpha/VDR cells) and compared with F9 wild-type (F9-Wt) cells, which do not express VDR mRNA. Treatment with all-trans retinoic acid (tRA) inhibits cell growth and induces the differentiation morphology in both F9-Wt and F9-RARalpha/VDR cells; whereas, treatment with D3 is similarly effective only for F9-RARalpha/VDR cells. It is concluded RARalpha/VDR is an useful 'tool' to pinpoint, or to augment transcription from RAREs in gene pathways controlled by RAR without inhibiting the retinoid responsiveness of endogenous RARs.

Obesity genes: molecular genetic approaches to drug target identification.

The environment for developing novel therapeutic agents has undergone dramatic change over the past decade. Innovative strategies for identifying and utilizing molecular targets linked to particular human diseases are replacing the classic approach of screening chemical compounds for potential therapeutic action on unknown targets. Since genetic components are involved in many known diseases, mouse and human genetics, positional cloning and other molecular biology-based approaches are now used to identify genes that are associated with these diseases. It is thought that identification of these disease-linked genes may lead to the discovery and understanding of the physiologically relevant biochemical pathways underlying the disease processes. Clearly, a knowledge of these biochemical pathways will provide future molecular targets, enzymes or receptors, that will offer opportunities to apply modern methods of high throughput screening, medicinal chemistry, parallel synthesis and combinatorial chemistry for drug discovery. In this manuscript, we illustrate how mouse genetics and molecular biology-based approaches have led to the identification of all five known single gene mutations that cause obesity in mice. Additionally, we describe how identification of these genes has helped unravel underlying biochemical pathways that regulate behavioral, metabolic and neuroendocrine responses in rodents.

A phase I, randomized, open-label study of the multiple-dose pharmacokinetics of vemurafenib in patients with BRAF V600E mutation-positive metastatic melanoma.

PURPOSE: This study characterized the multiple-dose pharmacokinetics of vemurafenib 240-960 mg twice daily (bid) in BRAF(V600E) mutation-positive metastatic melanoma patients, using the commercial formulation (240-mg microprecipitated bulk powder film-coated tablets). METHODS: Melanoma patients (N = 52) were randomly allocated to four vemurafenib dose cohorts (240, 480, 720, or 960 mg bid for 14 days). After the day 15 morning dose, doses were interrupted until day 22, at which point patients were restarted on vemurafenib. Serial pharmacokinetic samples were collected after the morning dose on days 1, 9, and 15; trough pharmacokinetic samples were collected on day 2. RESULTS: Vemurafenib concentration increased with multiple doses to steady state at day 15; C(max), AUC(0-8h), and AUC(0-168h) increased between 3.3- and 3.8-fold across the fourfold dose range tested. Statistical analysis indicated dose proportionality across the dose range of 240-960 mg bid. Day 15 mean accumulation ratios (ratio of AUC(0-8h) on day 15/AUC(0-8h) on day 1) ranged from ~19 to 25 across cohorts. At steady state, the peak-to-trough ratio for vemurafenib exhibited a relatively flat concentration-time profile throughout the bid dosing interval. During dose interruption (days 15-22), mean vemurafenib trough concentrations decreased to minimal levels; vemurafenib exhibited a mean terminal phase half-life of 31.5-38.4 h. CONCLUSIONS: Vemurafenib plasma concentration accumulates with multiple bid doses of 240 mg. Vemurafenib exposure (AUC and C(max)) is dose proportional over the 240- to 960-mg bid dose range and exhibits constant drug levels over the bid dosing interval.

The pharmacokinetics of peginterferon alfa-2a and ribavirin in African American, Hispanic and Caucasian patients with chronic hepatitis C.

BACKGROUND: Amongst Caucasian, Hispanic and African Americans with genotype 1 hepatitis C virus (HCV), there is a wide variation in response to treatment with peginterferon alfa-2a (PEG-IFN alfa-2a) and ribavirin. AIM: To evaluate the pharmacokinetics (PK) of PEG-IFN alfa-2a and ribavirin among these three groups. METHODS: Forty-seven patients with genotype 1 CHC (17 African Americans, 14 Hispanics and 16 Caucasians) received 8 weeks of PEG-IFN alfa-2a (180 µg/week) and ribavirin (1000 or 1200 mg/day). PEG-IFN alfa-2a serum concentrations and ribavirin plasma concentrations were measured following the first dose and at week 8. Pharmacokinetic parameters (C(max), T(max), AUC, CL/F) were estimated using noncompartmental methods. RESULTS: There was no difference in the pharmacokinetic parameters for PEG-IFN alfa-2a following single-dose or steady-state administration between African American or Hispanic patients compared with Caucasian patients. Ribavirin pharmacokinetic parameters were similar between Hispanic and Caucasian patients for single-dose and steady-state administration. The single-dose C(max) was 33% lower (P < 0.05) in African American compared with Caucasian patients. Other ribavirin single-dose and steady-state pharmacokinetic parameters were slightly decreased (approximately 20% lower) in African American patients, but were not considered clinically meaningful. CONCLUSIONS: No differences were observed in PEG-IFN alfa-2a pharmacokinetic parameters between African American or Hispanic patients compared with Caucasian patients. For ribavirin, no differences were observed in pharmacokinetic parameters between Hispanic and Caucasian patients. While a trend towards increased ribavirin clearance and decreased exposure was observed in African American patients vs. Caucasian patients, the differences were small and not considered clinically meaningful (Clinical Trial Number: NP17354).

Pharmacokinetically guided phase 1 trial of the IGF-1 receptor antagonist RG1507 in children with recurrent or refractory solid tumors.

PURPOSE: This pediatric phase I study was designed to identify the doses of RG1507, a monoclonal antibody against the Type 1 Insulin-like Growth Factor Receptor (IGF1R), that achieves exposures equivalent to those achieved in adults at recommended doses. EXPERIMENTAL DESIGN: Children with relapsed or refractory solid tumors were treated using the same doses and administration schedules of RG1507 (3 and 9 mg/kg/wk, and 16 mg/kg every 3 weeks [q3W]) as those studied in adults. Detailed pharmacokinetic (PK) sampling was performed after the first dose; selected peak and trough levels were subsequently obtained. Target exposures were ≥85% of mean areas under concentration x time curves (AUCs) in adults at doses of 9 mg/kg/wk and 16 mg/kg q3W. A maximum tolerated dose could be identified if dose-limiting toxicities (DLT) occurred. RESULTS: Thirty-one evaluable patients aged 3-17 years were enrolled at 3 mg/kg/wk (n = 3), 9 mg/kg/wk (n = 18), or 16 mg/kg q3W (n = 10). There were no DLTs. At 9 mg/kg/wk the mean AUC(0-7d) (21,000 µg h/mL) exceeded the target (16,000 µg h/mL). At 16 mg/kg q3W, the mean AUC(021d) (70,000 µg h/mL) exceeded the target (59,400 µg h/mL). Clearance normalized to body weight was age dependent. There were no objective responses. Seven patients had stable disease for >12 weeks, including two patients with osteosarcoma with stable disease for 52+ and 78+ weeks. CONCLUSIONS: The recommended doses of RG1507 in children with solid tumors are 9 mg/kg/wk and 16 mg/kg q3W. This flexible design is well suited for trials of agents associated with limited toxicity.