Pharmacokinetics and pharmacodynamics of a human monoclonal anti-FGF23 antibody (KRN23) in the first multiple ascending-dose trial treating adults with X-linked hypophosphatemia.

In X-linked hypophosphatemia (XLH), serum fibroblast growth factor 23 (FGF23) is increased and results in reduced renal maximum threshold for phosphate reabsorption (TmP), reduced serum inorganic phosphorus (Pi), and inappropriately low normal serum 1,25 dihydroxyvitamin D (1,25[OH]2 D) concentration, with subsequent development of rickets or osteomalacia. KRN23 is a recombinant human IgG1 monoclonal antibody that binds to FGF23 and blocks its activity. Up to 4 doses of KRN23 were administered subcutaneously every 28 days to 28 adults with XLH. Mean ± standard deviation KRN23 doses administered were 0.05, 0.10 ± 0.01, 0.28 ± 0.06, and 0.48 ± 0.16 mg/kg. The mean time to reach maximum serum KRN23 levels was 7.0 to 8.5 days. The mean KRN23 half-life was 16.4 days. The mean area under the concentration-time curve (AUCn ) for each dosing interval increased proportionally with increases in KRN23 dose. The mean intersubject variability in AUCn ranged from 30% to 37%. The area under the effect concentration-time curve (AUECn ) for change from baseline in TmP per glomerular filtration rate, serum Pi, 1,25(OH)2 D, and bone markers for each dosing interval increased linearly with increases in KRN23 AUCn . Linear correlation between serum KRN23 concentrations and increase in serum Pi support KRN23 dose adjustments based on predose serum Pi concentration.

Prolonged Correction of Serum Phosphorus in Adults With X-Linked Hypophosphatemia Using Monthly Doses of KRN23.

CONTEXT: In X-linked hypophosphatemia (XLH), elevated fibroblast growth factor 23 (FGF23) decreases the renal tubular maximum reabsorption rate of phosphate/glomerular filtration rate (TmP/GFR) and serum inorganic phosphorus (Pi), resulting in rickets and/or osteomalacia. OBJECTIVE: The objective was to test the hypothesis that monthly KRN23 (anti-FGF23 antibody) would safely improve serum Pi in adults with XLH. DESIGN: Two sequential open-label phase 1/2 studies were done. SETTING: Six academic medical centers were used. PARTICIPANTS: Twenty-eight adults with XLH participated in a 4-month dose-escalation study (0.05-0.6 mg/kg); 22 entered a 12-month extension study (0.1-1 mg/kg). INTERVENTION: KRN23 was injected sc every 28 days. MAIN OUTCOME MEASURE: The main outcome measure was the proportion of subjects attaining normal serum Pi and safety. RESULTS: At baseline, mean TmP/GFR, serum Pi, and 1,25-dihydroxyvitamin D [1,25(OH)2D] were 1.6 ± 0.4 mg/dL, 1.9 ± 0.3 mg/dL, and 36.6 ± 14.3 pg/mL, respectively. During dose escalation, TmP/GFR, Pi, and 1,25(OH)2D increased, peaking at 7 days for TmP/GFR and Pi and at 3-7 days for 1,25(OH)2D, remaining above (TmP/GFR, Pi) or near [1,25(OH)2D] pre-dose levels at trough. After each of the four escalating doses, peak Pi was between 2.5 and 4.5 mg/dL in 14.8, 37.0, 74.1, and 88.5% of subjects, respectively. During the 12-month extension, peak Pi was in the normal range for 57.9-85.0% of subjects, and ≥25% maintained trough Pi levels within the normal range. Serum Pi did not exceed 4.5 mg/dL in any subject. Although 1,25(OH)2D levels increased transiently, mean serum and urinary calcium remained normal. KRN23 treatment increased biomarkers of skeletal turnover and had a favorable safety profile. CONCLUSIONS: Monthly KRN23 significantly increased serum Pi, TmP/GFR, and 1,25(OH)2D in all subjects. KRN23 has potential for effectively treating XLH.

Hepatic leukemia factor promotes resistance to cell death: implications for therapeutics and chronotherapy.

Physiological variation related to circadian rhythms and aberrant gene expression patterns are believed to modulate therapeutic efficacy, but the precise molecular determinants remain unclear. Here we examine the regulation of cell death by hepatic leukemia factor (HLF), which is an output regulator of circadian rhythms and is aberrantly expressed in human cancers, using an ectopic expression strategy in JB6 mouse epidermal cells and human keratinocytes. Ectopic HLF expression inhibited cell death in both JB6 cells and human keratinocytes, as induced by serum-starvation, tumor necrosis factor alpha and ionizing radiation. Microarray analysis indicates that HLF regulates a complex multi-gene transcriptional program encompassing upregulation of anti-apoptotic genes, downregulation of pro-apoptotic genes, and many additional changes that are consistent with an anti-death program. Collectively, our results demonstrate that ectopic expression of HLF, an established transcription factor that cycles with circadian rhythms, can recapitulate many features associated with circadian-dependent physiological variation.

Using imaging methods to interrogate radiation-induced cell signaling.

There is increasing emphasis on the use of systems biology approaches to define radiation-induced responses in cells and tissues. Such approaches frequently rely on global screening using various high throughput 'omics' platforms. Although these methods are ideal for obtaining an unbiased overview of cellular responses, they often cannot reflect the inherent heterogeneity of the system or provide detailed spatial information. Additionally, performing such studies with multiple sampling time points can be prohibitively expensive. Imaging provides a complementary method with high spatial and temporal resolution capable of following the dynamics of signaling processes. In this review, we utilize specific examples to illustrate how imaging approaches have furthered our understanding of radiation-induced cellular signaling. Particular emphasis is placed on protein colocalization, and oscillatory and transient signaling dynamics.

Disorders of phosphorus homeostasis.

PURPOSE OF REVIEW: The study of phosphorus physiology and investigations into clinical disorders of phosphorus metabolism has blossomed over the past decade. Recent work has confirmed and further extended our knowledge of basic mechanisms of phosphorus metabolism. RECENT FINDINGS: This review will focus on FGF-23 and Klotho, and on the recent further dissection of their roles in phosphorus and skeletal metabolism. Additionally, this review will detail recent studies that implicate a role for these phosphaturic and vitamin D regulating factors in extraskeletal calcification, including that occurring in soft tissue and vascular beds. SUMMARY: These findings in total provide fertile ground for investigations into the cause and treatment of abnormal skeletal and extraskeletal calcification in patients with inherited hypophosphatemic disorders. More importantly, and certainly with wider potential clinical application, these studies likewise imply a role for these factors in the pathogenesis of accelerated cardiovascular disease that occurs in patients with the most common hyperphosphatemic disorder, chronic kidney disease. Future studies are needed to confirm a harmful or possibly even beneficial role for FGF-23 and other factors in these disease states, and to determine whether therapeutic manipulation of these factors does truly affect clinical outcomes in patients with hypophosphatemia and hyperphosphatemia.

Hypovitaminosis D in glycogen storage disease type I.

Glycogen storage disease type I (GSD I) is caused by inherited defects of the glucose 6-phosphatase complex, resulting in fasting hypoglycemia, lactic acidosis, hyperuricemia and hyperlipidemia. Sixteen out of 26 (61.5%) GSD I patients in our study had suboptimal levels (<30 ng/ml) of 25-hydroxyvitamin-D (25(OH)D) despite supplementation of vitamin D and/or vitamin D + calcium based on WHO standards in 24/26 (92.3%) patients. The restrictive nature of the GSD I diet, metabolic derangements and intestinal malabsorption seen in GSD I are possible reasons for the observed hypovitaminosis D. Our results suggest that measurement of 25(OH)D should be considered in the routine evaluation of GSD I patients.

Serum FGF23 levels in normal and disordered phosphorus homeostasis.

UNLABELLED: We investigated if the circulating levels of the phosphaturic factor FGF23 are elevated in subjects with XLH. Although we failed to find a statistically significant increase, FGF23 levels were significantly correlated with the degree of hypophosphatemia in XLH. In contrast, FGF23 levels were markedly increased in subjects with ESRD and correlated inversely with the degree of hyperphosphatemia. INTRODUCTION: Inactivating mutations of PHEX cause renal phosphate wasting in X-linked hypophosphatemic rickets (XLH) because of the accumulation of a phosphaturic hormone called phosphatonin. The recent discovery that FGF23 is the circulating phosphaturic factor in autosomal dominant hypophosphatemia raises the possibility that FGF23 is phosphatonin. METHODS: Fasting serum FGF23 levels and serum biochemical parameters were measured using a human FGF23 (C-terminal) ELISA assay in 11 subjects with XLH and 42 age-matched controls, 5 subjects with hypophosphatemia of unknown cause, and 14 hyperphosphatemic subjects with end stage renal disease (ESRD). Associations between variables were examined using the Spearman's correlation coefficient and linear regression analysis. RESULTS AND CONCLUSIONS: FGF23 (RU/ml) concentrations were not different (p = 0.11) between control and hypophosphatemic XLH subjects, but were significantly increased in hyperphosphatemic subjects with ESRD (p < 0.001). Western blot analysis found the presence of both full-length and C-terminal FGF23 fragments in serum from ESRD subjects. There was a strong inverse correlation between FGF23 and serum phosphorus (r = -0.60) and calcium and phosphorus (Ca x P) product (r = -0.65) in XLH, and a strong positive relationship between FGF23 and Pi (r = 0.50) and Ca x P product (r = 0.62) in ESRD. FGF23 levels were variably elevated in subjects with hypophosphatemia of unknown cause, one of which had tumor-induced osteomalacia (TIO). Removal of the tumor resulted in rapid reduction in serum FGF23 levels. These findings suggest that FGF23 has a possible role in mediating hypophosphatemia in XLH and TIO, but the overlapping levels of FGF23 in hypophosphatemic disorders and normal subjects indicate that serum phosphorus and FGF23 can also be independently regulated.