Burosumab Improves Patient-Reported Outcomes in Adults With Tumor-Induced Osteomalacia: Mixed-Methods Analysis

Tumor-induced osteomalacia (TIO) is an ultra-rare disease caused by tumors that secrete fibroblast growth factor 23, leading to chronic hypophosphatemia, poor skeletal health, and impaired physical function. In a phase 2 trial (UX023T-CL201; NCT02304367; n = 14), 48 weeks of burosumab treatment restored phosphate homeostasis, with improvements in skeletal health, functional mobility, and patient-reported pain, fatigue, and health-related quality of life (HRQL) (SF-36 v2). Here, we report an exploratory mixed-methods analysis of change from baseline after 144 weeks of burosumab treatment alongside qualitative data from exit interviews with 8 of 14 trial participants to evaluate meaningful treatment effects from a patient perspective. The interview subset (n = 8) reported pain and fatigue and compromised HRQL at baseline. In the interviews, participants reported that compromised HRQL and pain were the most important aspects of the disease to treat; both were considered more bothersome than fatigue and compromised physical function and activities of daily living. Improvements in pain and fatigue after treatment were reported, some of which achieved statistically and/or clinically meaningful thresholds. Furthermore, improvements in SF-36 v2 scores were most pronounced in the Physical Component Score and its Physical Function and Bodily Pain domains. Overall, the interview subset provided descriptions of symptomatic improvement and its clinical meaningfulness, including physical function, participation in activities of daily living, and mental well-being. Thus, this exploratory mixed-methods analysis provides deeper understanding of patients' perception of clinical meaningfulness beyond that articulated in validated patient-reported outcome instruments. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Burosumab vs Phosphate/Active Vitamin D in Pediatric X-Linked Hypophosphatemia: A Subgroup Analysis by Dose Level

CONTEXT

In an open-label, randomized, controlled, phase 3 trial in 61 children aged 1 to 12 years with X-linked hypophosphatemia (XLH), burosumab improved rickets vs continuing conventional therapy with active vitamin D and phosphate.

OBJECTIVE

We conducted an analysis to determine whether skeletal responses differed when switching to burosumab vs continuing higher or lower doses of conventional therapy.

METHODS

Conventional therapy dose groups were defined as higher-dose phosphate [greater than 40 mg/kg] (HPi), lower-dose phosphate [40 mg/kg or less] (LPi), higher-dose alfacalcidol [greater than 60 ng/kg] or calcitriol [greater than 30 ng/kg] (HD), and lower-dose alfacalcidol [60 ng/kg or less] or calcitriol [30 ng/kg or less] (LD).

RESULTS

At week 64, the Radiographic Global Impression of Change (RGI-C) for rickets was higher (better) in children randomly assigned to burosumab vs conventional therapy for all prebaseline dose groups: HPi (+1.72 vs +0.67), LPi (+2.14 vs +1.08), HD (+1.90 vs +0.94), LD (+2.11 vs +1.06). At week 64, the RGI-C for rickets was also higher in children randomly assigned to burosumab (+2.06) vs conventional therapy for all on-study dose groups: HPi (+1.03), LPi (+1.05), HD (+1.45), LD (+0.72). Serum alkaline phosphatase (ALP) also decreased in the burosumab-treated patients more than in the conventional therapy group, regardless of on-study phosphate and active vitamin D doses.

CONCLUSION

Prior phosphate or active vitamin D doses did not influence treatment response after switching to burosumab among children with XLH and active radiographic rickets. Switching from conventional therapy to burosumab improved rickets and serum ALP more than continuing either higher or lower doses of phosphate or active vitamin D.

The efficacy and safety of burosumab in two patients with cutaneous skeletal hypophosphatemia syndrome

Cutaneous skeletal hypophosphatemia syndrome (CSHS) is an ultra-rare mosaic disorder manifesting as skeletal dysplasia and FGF23-mediated hypophosphatemia, with some experiencing extra-osseous/extra-cutaneous manifestations, including both benign and malignant neoplasms. Like other disorders of FGF23-mediated hypophosphatemia including X-linked hypophosphatemia (XLH) and tumor-induced osteomalacia (TIO), patients with CSHS have low serum phosphorus and active 1,25-dihydroxyvitamin D levels. Current treatment options for patients with CSHS include multiple daily doses of oral phosphorus and one or more daily doses of active vitamin D analog to correct the deficits. Recently, the fully human monoclonal antibody against FGF23 burosumab received US approval for the treatment of XLH and TIO, two rare diseases characterized by FGF23-mediated hypophosphatemia leading to rickets and osteomalacia. Given the similarities between the pathobiologies of these disorders and CSHS, we investigated the impact of burosumab on two patients, one pediatric and one adult, with CSHS who participated in separate, but similarly designed trials. In both the pediatric and adult patients, burosumab therapy was well-tolerated and contributed to clinically meaningful improvements in disease outcomes including normalization of phosphorus metabolism and markers of bone health, and improvements in skeletal abnormalities, fractures, and physical function. Reported adverse events were minimal, with only mild injection site reactions attributed to burosumab therapy. Together, these findings suggest that burosumab therapy is a promising therapeutic option for patients with CSHS.

OR21-2 Encaleret (CLTX-305) Restored Mineral Homeostasis in a Phase 2 Study in Autosomal Dominant Hypocalcemia Type 1 (ADH1)

Autosomal dominant hypocalcemia type 1 (ADH1), caused by gain-of-function variants in the gene encoding the calcium-sensing receptor (CaSR), is characterized by hypocalcemia, hyperphosphatemia, hypomagnesemia, low parathyroid hormone (PTH), and hypercalciuria. Conventional therapy (calcium and activated Vitamin D) worsens hypercalciuria and can lead to renal morbidity. Calcilytics (negative allosteric modulators of the CaSR) decrease the sensitivity of hyperactive receptors to extracellular calcium and normalize blood and urine abnormalities in ADH1 rodent models. Encaleret is an oral calcilytic under investigation as a potential treatment for ADH1.

Thirteen adults (22-60y) with ADH1 due to 9 unique CASR variants participated in a 3-period, Phase 2b, open-label, dose-ranging study. Conventional therapy was discontinued prior to encaleret initiation. Period 1 (P1) was a 5-day inpatient dose-escalation course (n=6). Period 2 (P2) was a 5-day inpatient course (n=13) in which doses were individually titrated to normalize albumin-corrected blood calcium (cCa) and minimize hypercalciuria and hypophosphatemia. All 13 participants continued into Period 3 (P3), a 24-week outpatient maintenance period. Patients underwent serial 24hr blood and urine sampling in P1, P2, and in P3 at Weeks 8, 16, and 24, with additional outpatient laboratory timepoints.

The mean±SD encaleret dose at the end of P2, Day 5 (P2D5) was 94±64mg BID (range: 10-180 BID); by P3, Week 24 (P3W24), the mean was 78±67mg BID (5-190 BID). Encaleret was well-tolerated with no serious adverse events reported; there were no treatment discontinuations or study withdrawals.

Twenty-four hour mean±SD values from P2D5 (n=13) and P3W24 (n=12) compared to baseline are presented. Baseline PTH was low at 6.3±7.8 pg/mL (nl 10-65) and had normalized by P2D5 (40.5±37.5, p<0.01); this was sustained through P3W24 (31.3±20.8, p<0.01). Likewise, baseline hypocalcemia (cCa=7.1±0.4 mg/dL [nl 8.4-10.2]) corrected to 8.6±0.7 by P2D5 (p<0.01) and remained normal through P3W24 (9.0±0.6, p<0.01). Baseline urinary calcium was 395±216 mg/d (nl <250-300) and decreased to 179±108 by P2D5 (p<0.01) and 189±72 at P3W24 (p<0.05); urinary calcium excretion was normal in 10/12 patients at P3W24. Baseline phosphate decreased from 4.5±1.1 mg/dL (nl 2.3-4.7) to 3.2±0.7 on P2D5 (p<0.01) and was maintained through P3W24 (3.5±0.6, p<0.05). Magnesium increased from low- to mid-normal (baseline 1.7±0.2 mg/dL [nl 1.6-2.6]; P2D5 1.9±0.2 [p<0.01]; P3W24 2.0±0.2, [p<0.01]). 1,25-dihydroxy-Vitamin D increased from 19.5±4.4 pg/mL (nl 20-70) to 32.0±16.7 on P2D5 (p<0.05) and 30.2±14.0 on P3W24 (p<0.05). Bone turnover markers were not different between baseline (n=7, CTX=253±111 pg/mL; P1NP=34±10 mcg/L) and P2D5 (CTX=241±181, p=NS; P1NP=26±12, p=NS) but had increased by P3W24 (CTX=784±686, p<0.01; P1NP=102±87, p<0.01).

In conclusion, this study represents a molecularly targeted, precision medicine approach to the treatment of ADH1. The consistent and sustained results from all periods of this Phase 2 study establish a clinically meaningful efficacy, tolerability, and safety profile for encaleret as a potential treatment of adults with ADH1.

Presentation: Monday, June 13, 2022 11:15 a.m. - 11:30 a.m.

Autosomal Dominant Hypocalcemia Type 1: A Systematic Review

Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism due to activating variants of the calcium-sensing receptor gene (CASR). Inherited or de novo activating variants of the CASR alter the set point for extracellular calcium, resulting in inadequate parathyroid hormone (PTH) secretion and inappropriate renal calcium excretion leading to hypocalcemia and hypercalciuria. Conventional therapy includes calcium and activated vitamin D, which can worsen hypercalciuria, resulting in renal complications. A systematic literature review, using published reports from 1994 to 2021, was conducted to catalog CASR variants, to define the ADH1 clinical spectrum, and to determine the effect of treatment on patients with ADH1. There were 113 unique CASR variants reported, with a general lack of genotype/phenotype correlation. Clinical data were available in 191 patients; 27% lacked symptoms, 32% had mild/moderate symptoms, and 41% had severe symptoms. Seizures, the most frequent clinical presentation, occurred in 39% of patients. In patients with blood and urine chemistries available at the time of diagnosis (n = 91), hypocalcemia (99%), hyperphosphatemia (59%), low PTH levels (57%), and hypercalciuria (34%) were observed. Blood calcium levels were significantly lower in patients with severe symptoms compared with asymptomatic patients (6.8 ± 0.7 versus 7.6 ± 0.7 mg/dL [mean ± SD]; p < 0.0001), and the age of presentation was significantly lower in severely symptomatic patients (9.1 ± 15.0 versus 19.3 ± 19.4 years; p < 0.01). Assessments for complications including nephrocalcinosis, nephrolithiasis, renal impairment, and brain calcifications in 57 patients on conventional therapy showed that 75% had at least one complication. Hypercalciuria was associated with nephrocalcinosis, nephrolithiasis, renal impairment, or brain calcifications (odds ratio [OR] = 9.3; 95% confidence interval [CI] 2.4-37.2; p < 0.01). In 27 patients with urine calcium measures before and after starting conventional therapy, the incidence of hypercalciuria increased by 91% (p < 0.05) after therapy initiation. ADH1 is a condition often associated with severe symptomatology at presentation with an increase in the risk of renal complications after initiation of conventional therapy. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

The Resolution Rate of Pulmonary Embolism on CT Pulmonary Angiography: a Prospective Study

PURPOSE

To prospectively assess the rate of clot resolution from CT pulmonary angiography (CTPA) in patients with acute pulmonary embolism (PE).

MATERIALS AND METHODS

This prospective cohort study included 290 patients (136 men, 154 women; mean age, 51.9 years) with acute PE. All patients had a CTPA at the presentation and had at least one follow-up within 6 months (mean 72.7 days). Sixty-four percent of patients had follow-up scans for research purposes within a pre-determined period (between 28 and 184 days; mean, 78.27 days) and 36 % had (between 2 and 184 days; mean, 62.78 days) for a clinical indication. The volume of each clot was measured using a semi-automated quantification program. The resolution rate was evaluated by interval-censored analysis.

RESULTS

The overall estimated probability of complete resolution was 42 % at 7 days, 56 % at 10 days, and 71 % at 45 days. Achieving complete resolution was significantly faster in patients with peripheral clots (HR: 1.78; CI: 1.05-3.03, p = 0.032) but slower in patients with consolidation and history of venous thromboembolism (VTE), (HR: 0.37; CI: 0.18-0.79, p = 0.01 and HR: 0.57; CI: 0.35-0.91, p = 0.019, respectively). Although the patients with cancer showed a faster resolution rate (HR: 1.67; CI: 1.05-2.68, p = 0.032), the mortality rate was significantly higher than non-cancer patients.

CONCLUSION

The resolution rate of clot burden in acute PE was associated with patients' clinical presentation variables and CTPA imaging biomarkers. This information may be incorporated into designing a prediction rule and determining the appropriate duration of anticoagulation therapy in patients with acute PE.

Effect of Burosumab Compared With Conventional Therapy on Younger vs Older Children With X-linked Hypophosphatemia

CONTEXT

Younger age at treatment onset with conventional therapy (phosphate salts and active vitamin D; Pi/D) is associated with improved growth and skeletal outcomes in children with X-linked hypophosphatemia (XLH). The effect of age on burosumab efficacy and safety in XLH is unknown.

OBJECTIVE

This work aimed to explore the efficacy and safety of burosumab vs Pi/D in younger (< 5 years) and older (5-12 years) children with XLH.

METHODS

This post hoc analysis of a 64-week, open-label, randomized controlled study took place at 16 academic centers. Sixty-one children aged 1 to 12 years with XLH (younger, n = 26; older, n = 35) participated. Children received burosumab starting at 0.8 mg/kg every 2 weeks (younger, n = 14; older, n = 15) or continued Pi/D individually titrated per recommended guidelines (younger, n = 12; older, n = 20). The main outcome measure included the least squares means difference (LSMD) in Radiographic Global Impression of Change (RGI-C) rickets total score from baseline to week 64.

RESULTS

The LSMD in outcomes through 64 weeks on burosumab vs conventional therapy by age group were as follows: RGI-C rickets total score (younger, +0.90; older, +1.07), total Rickets Severity Score (younger, -0.86; older, -1.44), RGI-C lower limb deformity score (younger, +1.02; older, +0.91), recumbent length or standing height Z-score (younger, +0.20; older, +0.09), and serum alkaline phosphatase (ALP) (younger, -31.15% of upper normal limit [ULN]; older, -52.11% of ULN). On burosumab, dental abscesses were not reported in younger children but were in 53% of older children.

CONCLUSION

Burosumab appears to improve outcomes both in younger and older children with XLH, including rickets, lower limb deformities, growth, and ALP, compared with Pi/D.

Sustained Efficacy and Safety of Burosumab, a Monoclonal Antibody to FGF23, in Children With X-Linked Hypophosphatemia

PURPOSE

In X-linked hypophosphatemia (XLH), excess fibroblast growth factor-23 causes hypophosphatemia and low calcitriol, leading to musculoskeletal disease with clinical consequences. XLH treatment options include conventional oral phosphate with active vitamin D, or monotherapy with burosumab, a monoclonal antibody approved to treat children and adults with XLH. We have previously reported outcomes up to 64 weeks, and here we report safety and efficacy follow-up results up to 160 weeks from an open-label, multicenter, randomized, dose-finding trial of burosumab for 5- to 12-year-old children with XLH.

METHODS

After 1 week of conventional therapy washout, patients were randomized 1:1 to burosumab every 2 weeks (Q2W) or every 4 weeks (Q4W) for 64 weeks, with dosing titrated based on fasting serum phosphorus levels between baseline and week 16. From week 66 to week 160, all patients received Q2W burosumab.

RESULTS

Twenty-six children were randomized initially into each Q2W and Q4W group and all completed treatment to week 160. In 41 children with open distal femoral and proximal tibial growth plates (from both treatment groups), total Rickets Severity Score significantly decreased by 0.9 ± 0.1 (least squares mean ± SE; P < 0.0001) from baseline to week 160. Fasting serum phosphorus increases were sustained by burosumab therapy throughout the study, with an overall population mean (SD) of 3.35 (0.39) mg/dL, within the pediatric normal range (3.2-6.1 mg/dL) at week 160 (mean change from baseline P < 0.0001). Most adverse events were mild to moderate in severity.

MAIN CONCLUSIONS

In children with XLH, burosumab administration for 160 weeks improved phosphate homeostasis and rickets and was well-tolerated. Long-term safety was consistent with the reported safety profile of burosumab.

CLINICALTRIALS.GOV

NCT02163577.

Diagnosis and Management of Tumor-induced Osteomalacia: Perspectives From Clinical Experience

Purpose

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of abnormal phosphate and vitamin D metabolism caused by typically small endocrine tumors that secrete fibroblast growth factor 23 (FGF23). TIO is characterized clinically by progressive musculoskeletal pain, fatigue, proximal muscle weakness, and multiple fractures, leading to long-term disability. Misdiagnosis and delayed diagnosis are common because of the nonspecific symptoms, and several years may elapse before patients receive an accurate diagnosis and appropriate treatment. Thus, it is vital that awareness of the appropriate recognition and management of TIO is increased among healthcare professionals who may encounter patients with suspected TIO.

Methods

A roundtable meeting was held on 10 January 2020 in Dallas, TX, USA, to gather perspectives on the diagnosis and treatment of TIO. The following topics were considered: clinical presentation, patient history, differential diagnosis, laboratory assessment, imaging, venous sampling, and treatment.

Results

This report provides a summary of our collective experiences in the management of TIO.

Main conclusions

Laboratory tests are mandatory to expedite TIO diagnosis and should include measurement of fasting serum phosphorus, renal phosphate reabsorption, serum 1,25-dihydroxyvitamin D, and serum FGF23 levels. Functional and anatomical imaging are essential to locate the FGF23-secreting tumor(s) causing TIO. Surgical resection is often a curative treatment when the tumor can be localized; however, better management of patients who cannot be operated on with targeted therapies is needed. Further efforts to increase awareness of TIO within the medical community, and education on recommended diagnostic and treatment pathways are required to improve the management of this debilitating disease.

Population Pharmacokinetics and Pharmacodynamics of Burosumab in Adult and Pediatric Patients With X-linked Hypophosphatemia

Burosumab is a fully human monoclonal antibody against fibroblast growth factor 23, which has been approved to treat X‐linked hypophosphatemia (XLH) in adult and pediatric patients. The present work describes the pharmacokinetics (PK) of burosumab and the pharmacokinetic‐pharmacodynamic (PK‐PD) relationship between burosumab and serum phosphorus in adult and pediatric patients with XLH. A total of 2844 measurable serum concentrations of burosumab and 6047 measurable serum concentrations of phosphorus in 277 subjects from 9 clinical studies were included in the population PK and PK‐PD modeling. The serum concentration of burosumab following a subcutaneous administration was well described by a population PK model comprising a first‐order absorption, 1‐compartmental distribution, and a linear elimination. The relationship between serum burosumab and serum phosphorus was adequately described by a sigmoid maximal efficacy model. Body weight was the only covariate associated with PK and PK‐PD parameters. No other intrinsic factors affected PK or PK‐PD relationship in adult and pediatric patients with XLH. Further simulations helped to guide the dosing regimen of burosumab in adult and pediatric patients with XLH including age groups with no clinical data.

Burosumab Provides Sustained Improvement in Phosphorus Homeostasis and Heals Rickets in Children Aged 1 to 4 Years With X-Linked Hypophosphatemia (XLH)

XLH is the most common heritable rickets. Affected children have high levels of circulating FGF23 that cause hypophosphatemia with consequent rickets and lower limb deformity. Burosumab, a fully human monoclonal antibody that binds FGF23, is FDA-approved for the treatment of XLH in children ≥6 months old and adults. Herein, we report final, 3-year safety and efficacy data from an open-label, phase 2 study of burosumab in children 1 to &lt;5 years old at baseline (NCT02750618).

Eligibility required hypophosphatemia and radiographic evidence of rickets. The primary efficacy endpoint was change from baseline in fasting serum phosphorus (Pi). Secondary endpoints included Rickets Severity Score (RSS) and Radiographic Global Impression of Change (RGI-C). Patients received burosumab subcutaneous Q2W starting at 0.8 mg/kg for 160 weeks (64-week treatment + 96-week treatment extension periods).

All 13 enrolled patients completed the 64-week treatment period; 1 left the study to transition to commercially available burosumab, and 12 completed all 160 weeks. Baseline mean (SD) age was 2.9 (1.1) years; 69% were boys; all had previously received oral phosphate salts and active vitamin D.

Burosumab rapidly corrected fasting serum Pi with mean (SD) levels of 2.5 (0.3) mg/dL at Baseline, 3.7 (0.5) mg/dL at Week 1 (W1), 3.4 (0.5) mg/dL at W64, and 3.4 (0.5) mg/dL at W160 (normal range: 3.2–6.1 mg/dL). Lower RSS indicated improved rickets. Total RSS decreased from 2.9 (1.4) at Baseline to 1.2 (0.5) at W40 and to 0.9 (0.5) at W64 and was maintained through W160 [1.0 (0.6)]. Positive RGI-C scores indicate healing rickets relative to Baseline. Global RGI-C scores indicating substantial healing (≥+2) at W40 [+2.2 (0.3)] and W64 [+2.2 (0.4)] were maintained through W160 [+2.2 (0.4)]. Similarly, lower limb deformity RGI-C scores were +1.2 (0.6) at W40 and +1.5 (0.5) at W64, and sustained healing was evident at W160 [+2.0 (0.3)]. Wrist and knee RSSs and RGI-C scores similarly improved. The upper limit of normal for serum ALP ranged from 297 to 345 U/L depending on the child’s age and sex. Mean ALP was 549 (194) U/L at Baseline, normalized by W40 [335 (88) U/L], and was sustained through W160 [302 (71) U/L].

The burosumab safety profile over 160 weeks resembled previous pediatric studies; no new safety concerns emerged. All patients had ≥1 treatment-emergent adverse event (TEAE). All TEAEs were mild (Grade 1) or moderate (Grade 2) except for one patient with a grade 3 TEAE (food allergy) and one with a grade 3 TEAE (increased serum amylase, 92% salivary/8% pancreatic). One patient had a serious TEAE (dental abscess leading to hospitalization). These grade 3 and serious TEAEs were considered unrelated to study drug.

Burosumab rapidly restored Pi homeostasis, improved rickets, and normalized serum ALP in children with XLH aged 1 to &lt;5 years with no new safety concerns. Improvements were maintained during the 3 years of treatment.

Burosumab for the Treatment of Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is caused by phosphaturic mesenchymal tumors producing fibroblast growth factor 23 (FGF23) and is characterized by impaired phosphate metabolism, skeletal health, and quality of life. UX023T-CL201 is an ongoing, open-label, phase 2 study investigating the safety and efficacy of burosumab, a fully human monoclonal antibody that inhibits FGF23, in adults with TIO or cutaneous skeletal hypophosphatemia syndrome (CSHS). Key endpoints were changes in serum phosphorus and osteomalacia assessed by transiliac bone biopsies at week 48. This report focuses on 14 patients with TIO, excluding two diagnosed with X-linked hypophosphatemia post-enrollment and one with CSHS. Serum phosphorus increased from baseline (0.52 mmol/L) and was maintained after dose titration from week 22 (0.91 mmol/L) to week 144 (0.82 mmol/L, p < 0.0001). Most measures of osteomalacia were improved at week 48: osteoid volume/bone, osteoid thickness, and mineralization lag time decreased; osteoid surface/bone surface showed no change. Of 249 fractures/pseudofractures detected across 14 patients at baseline, 33% were fully healed and 13% were partially healed at week 144. Patients reported a reduction in pain and fatigue and an increase in physical health. Two patients discontinued: one to treat an adverse event (AE) of neoplasm progression and one failed to meet dosing criteria (receiving minimal burosumab). Sixteen serious AEs occurred in seven patients, and there was one death; all serious AEs were considered unrelated to treatment. Nine patients had 16 treatment-related AEs; all were mild to moderate in severity. In adults with TIO, burosumab exhibited an acceptable safety profile and was associated with improvements in phosphate metabolism and osteomalacia. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research..

X-Linked Hypophosphatemia: A New Era in Management

X-linked hypophosphatemia (XLH) is a rare, hereditary, progressive musculoskeletal disease that often causes pain and short stature, as well as decreased physical function, mobility, and quality of life. Hypophosphatemia in XLH is caused by loss of function mutations in the phosphate-regulating endopeptidase homolog X-linked (PHEX) gene, resulting in excess levels of the phosphate-regulating hormone fibroblast growth factor 23 (FGF23), which leads to renal phosphate wasting and decreased serum 1,25-dihydroxyvitamin D production. Historically, treatment options were limited to oral phosphate and active vitamin D analogues (conventional management) dosed several times daily in an attempt to improve skeletal mineralization by increasing serum phosphorus. The recent approval of burosumab, a fully human monoclonal antibody to FGF23, has provided a new, targeted treatment option for patients with XLH. This review summarizes our current understanding of XLH, the safety and efficacy of conventional management and burosumab, existing recommendations for managing patients, and unanswered questions in the field.

Deformable liposomes as enhancer of caffeine penetration through human skin in a Franz diffusion cell test

OBJECTIVE

The permeation of hydrophilic molecules through the skin is still a challenge due to the barrier posed by stratum corneum, the outermost layer of the skin. Liposomes have frequently been used as carriers for different types of drugs and may also function as permeation enhancers. Propylene glycol has also been used as an edge activator in liposomes to increase the permeation. The aim of this work was to prepare liposomes containing an edge activator and loaded with caffeine to evaluate the potential of caffeine reaching the deeper layers in the skin.

METHODS

The formulations were prepared by a top-down process using high-pressure homogenization at 200 00 psi for 10 min. They were characterized by size, polydispersity index (PI), zeta potential (ZP), pH, caffeine content and encapsulation efficiency (EE%) on preparation (time zero) and after 30 days. Cytotoxicity of blank and loaded liposomes was assessed by MTT proliferation assay with a normal keratinocyte cell line (HaCaT). In vitro permeation tests were performed with human skin in Franz cells over 24 h, and caffeine concentration was determined in the skin surface, stratum corneum, dermo-epidermal fraction and receptor medium by HPLC.

RESULTS

The caffeine liposomes with (DL-Caf) or without propylene glycol (CL-Caf) showed, respectively, mean size 94.5 and 95.4 nm, PI 0.48 and 0.42, ZP + 1.3 and + 18.1 mV and caffeine content of 78.57 and 80.13%. IC₅₀ values of caffeine in DL-Caf (3.59 v/v %) and CL-Caf (3.65 v/v %) were not significantly different from conventional blank liposome (3.27 v/v %). The DL-Caf formulation presented the best capability to enhance the caffeine permeation through the skin, resulting 1.94-folds higher than caffeine solution. Furthermore, the caffeine flux from DL-Caf was 1.56- and 3.05-folds higher than caffeine solution and CL-Caf, respectively. On the other hand, CL-Caf showed the lowest caffeine penetration revealing the importance of edge activator to aid hydrophilic drug penetration to all skin layers.

CONCLUSION

The DL-Caf formulation tested was able to improve the permeation of caffeine through the stratum corneum and dermo-epidermal layers, suggesting that this delivery system may be effective for deep skin delivery of hydrophilic drugs.

Nephropathic Cystinosis: A Distinct Form of CKD-Mineral and Bone Disorder that Provides Novel Insights into the Regulation of FGF23

BACKGROUND

The rare lysosomal storage disease nephropathic cystinosis presents with renal Fanconi syndrome that evolves in time to CKD. Although biochemical abnormalities in common causes of CKD-mineral and bone disorder have been defined, it is unknown if persistent phosphate wasting in nephropathic cystinosis is associated with a biochemical mineral pattern distinct from that typically observed in CKD-mineral and bone disorder.

METHODS

We assessed and compared determinants of mineral homeostasis in patients with nephropathic cystinosis across the predialysis CKD spectrum to these determinants in age- and CKD stage-matched patients, with causes of CKD other than nephropathic cystinosis.

RESULTS

The study included 50 patients with nephropathic cystinosis-related CDK and 97 with CKD from other causes. All major aspects of mineral homeostasis were differentially effected in patients with CKD stemming from nephropathic cystinosis versus other causes. Patients with nephropathic cystinosis had significantly lower percent tubular reabsorption of phosphate and fibroblast growth factor-23 (FGF23) at all CKD stages, and lower blood phosphate in CKD stages 3-5. Linear regression analyses demonstrated lower FGF23 levels in nephropathic cystinosis participants at all CKD stages when corrected for eGFR and age, but not when adjusted for serum phosphate.

CONCLUSIONS

Nephropathic cystinosis CKD patients have mineral abnormalities that are distinct from those in CKD stemming from other causes. Persistently increased urinary phosphate excretion maintains serum phosphate levels within the normal range, thus protecting patients with nephropathic cystinosis from elevations of FGF23 during early CKD stages. These findings support the notion that phosphate is a significant driver of increased FGF23 levels in CKD and that mineral abnormalities associated with CKD are likely to vary depending on the underlying renal disease.

OR29-06 Burosumab Improves Biochemical, Skeletal, and Clinical Features of Tumor-Induced Osteomalacia Syndrome

Tumor-induced Osteomalacia (TIO) is a rare condition in which excess FGF23 produced by a tumor leads to renal phosphate wasting, impaired 1,25(OH)₂D synthesis, osteomalacia, fractures, weakness, fatigue, and decreased mobility. In an ongoing open-label Phase 2 study (NCT02304367), 17 adults with TIO or cutaneous skeletal hypophosphatemia syndrome (CSHS) were enrolled and received burosumab, a fully human monoclonal antibody against FGF23. Key endpoints were changes in serum phosphorus and osteomalacia as assessed from trans-iliac crest bone biopsies. This report excludes 3/17 subjects who did not have TIO: 2 subjects diagnosed with X-linked hypophosphatemia post-enrollment and 1 subject with CSHS. Serum phosphorus increased from baseline (BL; 1.60 mg/dL) and was maintained after titration, from Week (W) 22 (2.85 mg/dL, dosing cycle midpoint) to W144 (2.56 mg/dL, dosing cycle endpoint, p<0.0001). Serum TmP/GFR and 1,25(OH)₂D also increased with burosumab. Eleven subjects underwent paired bone biopsies at BL and W48. Osteoid volume/bone volume decreased from a mean ± SE of 17.6% ± 5.9% at BL to 12.1% ± 4.7% at W48 (p=0.086). Mean ± SE osteoid thickness decreased from 16.5 ± 3.6 µm to 11.3 ± 2.8 µm (p<0.05). Using imputation (Dempster et al. 2012), mineralization lag time decreased from a mean ± SE of 1598 ± 420 days to 1032 ± 712 days (p=0.41). Osteoid surface/bone surface showed no change from BL (mean ± SE BL: 57% ± 9%, W48: 57% ± 7%). Of 249 areas identified with increased uptake on bone scan at BL, 68 (27%) and 81 (33%) were fully healed at W96 and W144, respectively; 56 (23%) and 32 (13%) were partially healed at W96 and W144, respectively. Mean (SD) Global Fatigue Score decreased from 5.6 (2.5) at BL to 3.5 (3.0) at W48, and to 3.8 (2.2) at W144 (both p<0.01). All 3 domains of the Brief Pain Inventory decreased with burosumab (W144 Pain Severity and Pain Interference p<0.05), indicating reduced pain. The SF-36 mean (SD) physical component summary score increased from 33 (10) at BL to 39 (10) at W48 (p<0.05) and to 41 (12) at W144 (p<0.01), indicating improved physical functioning. The mean (SD) number of sit-to-stand repetitions, an assessment of proximal muscle function, increased from 6.7 (4.2) at BL to 8.5 (4.2) at W48 (n=10; p<0.01). All subjects had ≥1 adverse event (AE). Two subjects discontinued: 1 to undergo chemotherapy to treat an AE of neoplasm progression and 1 failed to meet serum phosphorus dosing criteria and therefore received minimal burosumab dosing. There were 16 serious AEs in 7 subjects, all unrelated to drug. Of the 6 subjects with a serious AE of tumor progression/compression, 5 had a history of tumor progression prior to enrollment. There was 1 death, considered unrelated to treatment. In adults with TIO Syndrome, burosumab was associated with improvements in phosphate metabolism, osteomalacia, skeletal metabolism/fracture healing, physical functioning, fatigue, pain, and quality of life.

SUN-356 Burosumab Resulted in Greater Clinical Improvements Compared with Higher-dose Conventional Therapy in Children with X-linked Hypophosphatemia (XLH)

In XLH, excess circulating FGF23 causes hypophosphatemia, rickets, lower limb deformity, and impaired growth and mobility. An active-controlled, phase 3 trial (CL301; NCT02915705) showed treatment with burosumab, a fully human monoclonal antibody against FGF23, resulted in significantly greater improvements in all of these outcomes in children with XLH, compared with continuing oral phosphate and active vitamin D as conventional therapy (Pi/D) per established guidelines. In a post-hoc analysis, we compared children who received burosumab vs those who received an average 64-week oral phosphate daily dose &gt;40 mg/kg (higher-dose Pi) vs ≤40 mg/kg (lower-dose Pi). Sixty-one children with XLH (1–12 years-old) were randomized 1:1 after a 7-day Pi/D washout to receive burosumab (n=29) starting at 0.8 mg/kg subcutaneously Q2W or to resume Pi/D (n=32) titrated by their investigator, for 64 weeks. Eligibility criteria included Rickets Severity Score (RSS) ≥2.0 despite prior Pi/D treatment. Of the 32 subjects randomized to Pi/D, 12 received average higher-dose Pi and 20 received average lower-dose Pi (as specified above). The primary endpoint was rickets healing, using the Radiographic Global Impression of Change (RGI-C) Scale. At week 64, the improvement in the least square (LS) mean (LS mean [±SE; 95%CI]) RGI-C Global Score for rickets was greater on burosumab (+2.06 [0.072; 1.92, 2.20]) compared with either higher-dose (+1.02 [0.241; 0.55, 1.50]) or lower-dose (+1.04 [0.162; 0.73, 1.36]) Pi. The mean decrease in the total RSS from baseline was also greater on burosumab (-2.23 [0.117; -2.46, -2.00]) compared with higher-dose (-0.87 [0.264; -1.39, -0.35] or lower-dose (-1.09 [0.180; -1.45, -0.74]) Pi. Similarly, the mean RGI-C Lower Limb Deformity Score was greater on burosumab (+1.25 [0.170; 0.92, 1.59]) compared with either higher-dose (+0.32 [0.188; -0.05, 0.69]) or lower-dose (+0.26 [0.146; -0.02, 0.55]) Pi. Adverse events including hypersensitivity and injection site reactions, were more frequent with burosumab, and were mild to moderate in severity overall. No discontinuations occurred. In conclusion, children with XLH treated with burosumab had greater improvements in rickets and lower limb deformity compared with subjects receiving higher or lower doses of Pi.

Life-threatening triclopyr poisoning due to diethylene glycol monoethyl ether solvent

INTRODUCTION

Triclopyr is a synthetic auxin-like herbicide. It is considered to have low toxicity and there are few reports of poisoning. We report two cases of life-threatening toxicity following ingestions of 250 mL of 50 g/L triclopyr co-formulated with diethylene glycol monoethyl ether (DEGEE).

CASE REPORTS

A 79-year-old male with a background of hypertension and atrial fibrillation presented two hours after ingestion with sedation, a severe high anion gap metabolic acidosis, raised osmolar gap and an aspiration pneumonitis. He was ventilated and dialysed for 10 h with resolution of the acidaemia. He was discharged home on day 33. A 66-year-old male with a past history of alcoholism and hypertension presented following a collapse. He had sedation, a severe high anion gap metabolic acidosis with a raised osmolar gap, acute kidney injury and vasodilatory shock. He was ventilated and received dialysis for 43 h. He had poor neurological recovery and died on day 10.

DISCUSSION

Ingestion of triclopyr formulations can produce life-threatening toxicity. In large poisonings of triclopyr co-formulated with DEGEE, a high anion gap metabolic acidosis appears to be due to the glycol ether solvent rather than triclopyr itself. Management should focus on good supportive care including dialysis for significant metabolic acidosis.

Treatment of Autosomal Dominant Hypocalcemia Type 1 With the Calcilytic NPSP795 (SHP635)

Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism caused by heterozygous, gain-of-function mutations of the calcium-sensing receptor gene (CAR). Individuals are hypocalcemic with inappropriately low parathyroid hormone (PTH) secretion and relative hypercalciuria. Calcilytics are negative allosteric modulators of the extracellular calcium receptor (CaR) and therefore may have therapeutic benefits in ADH1. Five adults with ADH1 due to four distinct CAR mutations received escalating doses of the calcilytic compound NPSP795 (SHP635) on 3 consecutive days. Pharmacokinetics, pharmacodynamics, efficacy, and safety were assessed. Parallel in vitro testing with subject CaR mutations assessed the effects of NPSP795 on cytoplasmic calcium concentrations (Ca²⁺_i ), and ERK and p38^MAPK phosphorylation. These effects were correlated with clinical responses to administration of NPSP795. NPSP795 increased plasma PTH levels in a concentration-dependent manner up to 129% above baseline (p = 0.013) at the highest exposure levels. Fractional excretion of calcium (FECa) trended down but not significantly so. Blood ionized calcium levels remained stable during NPSP795 infusion despite fasting, no calcitriol supplementation, and little calcium supplementation. NPSP795 was generally safe and well-tolerated. There was significant variability in response clinically across genotypes. In vitro, all mutant CaRs were half-maximally activated (EC₅₀ ) at lower concentrations of extracellular calcium (Ca²⁺_o ) compared to wild-type (WT) CaR; NPSP795 exposure increased the EC₅₀ for all CaR activity readouts. However, the in vitro responses to NPSP795 did not correlate with any clinical parameters. NPSP795 increased plasma PTH levels in subjects with ADH1 in a dose-dependent manner, and thus, serves as proof-of-concept that calcilytics could be an effective treatment for ADH1. Albeit all mutations appear to be activating at the CaR, in vitro observations were not predictive of the in vivo phenotype or the response to calcilytics, suggesting that other parameters impact the response to the drug. © 2019 American Society for Bone and Mineral Research.

Autoimmune hyperphosphatemic tumoral calcinosis in a patient with FGF23 autoantibodies

Hyperphosphatemic familial tumoral calcinosis (HFTC)/hyperostosis-hyperphosphatemia syndrome (HHS) is an autosomal recessive disorder of ectopic calcification due to deficiency of or resistance to intact fibroblast growth factor 23 (iFGF23). Inactivating mutations in FGF23, N-acetylgalactosaminyltransferase 3 (GALNT3), or KLOTHO (KL) have been reported as causing HFTC/HHS. We present what we believe is the first identified case of autoimmune hyperphosphatemic tumoral calcinosis in an 8-year-old boy. In addition to the classical clinical and biochemical features of hyperphosphatemic tumoral calcinosis, the patient exhibited markedly elevated intact and C-terminal FGF23 levels, suggestive of FGF23 resistance. However, no mutations in FGF23, KL, or FGF receptor 1 (FGFR1) were identified. He subsequently developed type 1 diabetes mellitus, which raised the possibility of an autoimmune cause for hyperphosphatemic tumoral calcinosis. Luciferase immunoprecipitation systems revealed markedly elevated FGF23 autoantibodies without detectable FGFR1 or Klotho autoantibodies. Using an in vitro FGF23 functional assay, we found that the FGF23 autoantibodies in the patient's plasma blocked downstream signaling via the MAPK/ERK signaling pathway in a dose-dependent manner. Thus, this report describes the first case, to our knowledge, of autoimmune hyperphosphatemic tumoral calcinosis with pathogenic autoantibodies targeting FGF23. Identification of this pathophysiology extends the etiologic spectrum of hyperphosphatemic tumoral calcinosis and suggests that immunomodulatory therapy may be an effective treatment.

Skeletal Consequences of Nephropathic Cystinosis

Nephropathic cystinosis is a rare lysosomal storage disorder. Patients present in the first year of life with renal Fanconi syndrome that evolves to progressive chronic kidney disease (CKD). Despite the multiple risk factors for bone disease, the frequency and severity of skeletal disorders in nephropathic cystinosis have not been described. We performed systematic bone and mineral evaluations of subjects with cystinosis seen at the NIH (n = 30), including history and physical examination, serum and urine biochemistries, DXA, vertebral fracture assessment, skeletal radiographs, and renal ultrasound. Additionally, histomorphometric analyses are reported on six subjects seen at the UCLA Bone and Mineral Metabolism Clinic. In NIH subjects, mean age was 20 years (range, 5 to 44 years), 60% were CKD stages G1 to G4, and 40% had a renal transplant. Mean bone mineral density (BMD) Z-scores were decreased in the femoral neck, total hip, and 1/3 radius (p < 0.05). Low bone mass at one or more sites was present in 46% of subjects. Twenty-seven percent of subjects reported one or more long bone fractures. Thirty-two percent of subjects had incidental vertebral fractures, which were unrelated to transplant status. Long-bone deformity/bowing was present in 64%; 50% had scoliosis. Diffuse osteosclerosis was present in 21% of evaluated subjects. Risk factors included CKD, phosphate wasting, hypercalciuria, secondary hyperparathyroidism, hypovitaminosis D, male hypogonadism, metabolic acidosis, and glucocorticoid/immunosuppressive therapy. Sixty-one percent of the non-transplanted subjects had ultrasonographic evidence of nephrocalcinosis or nephrolithiasis. Histomorphometric analyses showed impaired mineralization in four of six studied subjects. We conclude that skeletal deformities, decreased bone mass, and vertebral fractures are common and relevant complications of nephropathic cystinosis, even before renal transplantation. Efforts to minimize risk factors for skeletal disease include optimizing mineral metabolism and hormonal status, combined with monitoring for nephrocalcinosis/nephrolithiasis. © 2018 This article is a U.S. Government work and is in the public domain in the USA.

Topical and cutaneous delivery using nanosystems

The goal of topical and cutaneous delivery is to deliver therapeutic and other substances to a desired target site in the skin at appropriate doses to achieve a safe and efficacious outcome. Normally, however, when the stratum corneum is intact and the skin barrier is uncompromised, this is limited to molecules that are relatively lipophilic, small and uncharged, thereby excluding many potentially useful therapeutic peptides, proteins, vaccines, gene fragments or drug-carrying particles. In this review we will describe how nanosystems are being increasingly exploited for topical and cutaneous delivery, particularly for these previously difficult substances. This is also being driven by the development of novel technologies, which include minimally invasive delivery systems and more precise fabrication techniques. While there is a vast array of nanosystems under development and many undergoing advanced clinical trials, relatively few have achieved full translation to clinical practice. This slow uptake may be due, in part, to the need for a rigorous demonstration of safety in these new nanotechnologies. Some of the safety aspects associated with nanosystems will be considered in this review.

Cost-effectiveness analysis of treatment strategies for initial Clostridium difficile infection

Clostridium difficile infection (CDI) is costly. Current guidelines recommend metronidazole as first-line therapy and vancomycin as an alternative. Recurrence is common. Faecal microbiota transplantation (FMT) is an effective therapy for recurrent CDI (RCDI). This study explores the cost-effectiveness of FMT, vancomycin and metronidazole for initial CDI. We constructed a decision-analytic computer simulation using inputs from published literature to compare FMT with a 10-14-day course of oral metronidazole or vancomycin for initial CDI. Parameters included cure rates (baseline value (range)) for metronidazole (80% (65-85%)), vancomycin (90% (88-92%)) and FMT(91% (83-100%)). Direct costs of metronidazole, vancomycin and FMT, adjusted to 2011 dollars, were $57 ($43-72), $1347 ($1195-1499) and $1086 ($815-1358), respectively. Our effectiveness measure was quality-adjusted life years (QALYs). One-way and probabilistic sensitivity analyses were conducted from the third-party payer perspective. Analysis using baseline values showed that FMT($1669, 0.242 QALYs) dominated (i.e. was less costly and more effective) vancomycin ($1890, 0.241 QALYs). FMT was more costly and more effective than metronidazole ($1167, 0.238 QALYs), yielding an incremental cost-effectiveness ratio (ICER) of $124 964/QALY. One-way sensitivity analyses showed that metronidazole dominated both strategies if its probability of cure were >90%; FMT dominated if it cost <$584. In a probabilistic sensitivity analysis at a willingness-to-pay threshold of $100 000/QALY, metronidazole was favoured in 55% of model iterations; FMT was favoured in 38%. Metronidazole, as the first-line treatment for CDIs, is less costly. FMT and vancomycin are more effective. However, FMT is less likely to be economically favourable, and vancomycin is unlikely to be favourable as first-line therapy when compared with FMT.

Solute-vehicle-skin interactions in percutaneous absorption: the principles and the people

An appreciation of solute-vehicle-skin interactions underpins our current understanding of the processes of percutaneous absorption as well as in the prediction of the extent of absorption. This understanding has been reached through principles developed and validated over the last century through the work of a number of authors, including Dale Wurster, Takeru Higuchi, Irvin Blank, Robert Scheuplein, Gordon Flynn, Boyd Poulsen and Tom Franz, as well as by many scientists from my and younger generations. Their work has led to an appreciation of the rate-limiting steps in percutaneous penetration, the role played by the physicochemical properties of the solute, vehicle and skin and the variability that may arise from using various experimental/mathematical/pharmacokinetic models to quantify absorption as well as enabling the prediction of local and systemic efficacy and toxicity. In addition, unexpected behaviour may result from non-ideality in solute-vehicle-skin effects, including dehydration, chemical enhancement, supersaturation, metabolism, sequestration and vascular effects, including those of nanosystems on the local vasculature. In general, in vitro skin penetration profiles are predictive of in vivo profiles but a number of exceptions also exist.