RPS: Novel phosphate binder oxylanthanum carbonate effectively reduced serum and urine phosphorus concentrations in animal models

Pramod Gupta, Atul Khare and Guru Reddy

Unicycive Therapeutics, Los Altos, CA, USA

Abstract

Objectives

Over 40% of dialysis patients have above-target phosphate. The efficacy and safety of oxylanthanum carbonate (OLC), a novel phosphate binder that forms the same insoluble phosphate complex as lanthanum carbonate, were assessed in two animal models.

Methods

Three groups of nephrectomized cats (n = 4 per group) received 0.0466 g OLC/kg body weight, 0.233 g OLC/kg body weight, or placebo. Six groups of rats (n = 6 per group) received placebo or 0.049, 0.099, 0.197, 0.394 or 0.788 g OLC/day. Endpoints included phosphate concentrations (urine, faecal and plasma) and serum lanthanum concentrations. All animals were observed for tolerance, injury and mortality.

Key Findings

In cats, urine phosphorus concentrations decreased across treatment groups and faecal phosphorus excretion increased in higher dose groups compared to control and lower dose groups. A clear but non-significant decline in plasma phosphate was observed. In rats, urine phosphorus concentrations also decreased in all groups. The majority of serum lanthanum concentrations for rats in treatment groups were not significantly different from those in control groups. The study drug was well tolerated in both models.

Conclusions

OLC was effective for phosphate management and efficacy may be dose dependent. OLC was safe and well tolerated, indicating that it should be evaluated in the target population of patients with hyperphosphatemia.

Keywords

oxylanthanum carbonate; phosphate binder; chronic kidney disease; end-stage renal disease; hyperphosphatemia

Materials and Methods

Nephrectomized cat model

The efficacy and safety of OLC were assessed in nephrectomized cats. Twelve cats (five male and seven female) that successfully underwent a two-stage partial renal ablation procedure were split into three groups (four cats per group), with one control group and two treatment groups. From Day –5 to 20, all groups were fed a standard commercially available wet cat diet with low phosphorus and protein. Beginning on Day 0, 0.0466 g OLC/kg body weight (1Å~ dose level) and 0.233 g OLC/kg body weight (5Å~ dose level) was administered once daily in the morning to Groups 2 and 3, respectively, mixed with the predetermined individual food ration.

Two whole blood samples were collected from the jugular vein of each animal on Days –2, –1, 8, 15 and 20: a 1.3 ml sample into a tube containing lithium heparin anticoagulant; a 5.0 ml sample into a tube containing EDTA anticoagulant. Within 90 min of collection, blood samples were centrifuged at 3000 g for 15 min in a refrigerated centrifuge (4ÅãC at Jouan centrifuge BR 4i, rotor 540). Plasma was removed into plain tubes and shipped to certified laboratories in styrofoam boxes with ice packs (samples for phosphorus, calcium, urea and creatinine) or on dry ice (samples for parathyroid hormone [PTH]) for analysis using standard assays. Plasma phosphorus, calcium, urea and creatinine were analysed at the Clinical Laboratory at Charles River Laboratories BioLabs in Glenamoy, Ireland. Plasma PTH analysis was performed at Cambridge Specialist Laboratory Services in Cambridge, UK.

Urine samples were collected on Day –3, –2, –1, 6, 7, 8, 13, 13, 15, 18, 19 and 20. The volume of each 24-h urine sample was recorded. Feces were collected on the same days and the quantity (weight) of each 24-h sample was recorded. Faeces were stored at or below –20ÅãC until dispatched on dry ice to LUFA Nord-West for analysis of phosphate levels.

Body weights were recorded pre-treatment (Days –5 and –1) and during treatment (Days 8, 15 and 20). Tolerance observations including lethargy, vomiting, salivation, diarrhoea, tachypnoea, dyspnoea, pruritis, and ataxia were recorded on Study Days 0, 8, 15 and 20.

Efficacy was assessed using urine, faeces and plasma phosphate levels pre-treatment (Days –3, –2 and –1) and during treatment (Days 6, 7, 8, 13, 14, 15, 18, 19 and 20). Renal function was monitored using plasma calcium, PTH, urea and creatinine concentrations pre-treatment (Day –2) and during treatment (Days 8, 15 and 20).

Rat model

The efficacy and safety of OLC were also evaluated in rats. Thirty-six male SD-HLA (SD) CVF rats with jugular vein cannulae were randomly assigned to control and treatment groups (six rats per group) and were treated for a total of seven consecutive days (Days 3–9). Group 1, the control group, received a vehicle diet. Groups 2, 3, 4, 5 and 6 received 0.049, 0.099, 0.197, 0.394 and 0.788 g OLC/day, respectively.

Blood samples for determination of serum phosphorus and creatinine concentrations (sampling volume approximately 300 μl) were collected approximately 3–4.4 h post-dose on Days 1–11. Blood samples for determination of serum lanthanum concentrations (sampling volume approximately 900 μl) were collected on Days 3 and 9 only. The animals had access to drinking water and food prior to sample collection. Blood samples were taken via the jugular vein or jugular vein cannula. Samples were collected on ice, protected from light, into gel microtainers containing no anticoagulant and centrifuged for serum preparation. Urine was collected on wet ice prior to daily diet administration at 24-h intervals from Day –2 to 11 for the determination of phosphorus and creatinine concentrations. Urine and serum samples for phosphorus and creatinine analysis were sent to the Clinical Chemistry Department at MPI Research in Mattawan, MI and analysed using an Olympus AU600 Clinical Chemistry Analyzer (USA). Samples for serum lanthanum analysis were sent on dry ice to Exygen Research, Inc. (State College, PA, USA) for analysis using inductively coupled argon plasma mass spectrometry (ICP-MS, Elan 6000, Perkin Elmer Sciex, USA).

For safety, all animals were observed for mortality, morbidity, injury and the availability of food and water twice daily. Body weights were measured before randomization on Day –2 and then once daily prior to diet administration beginning on Day –1. Food consumption was measured daily beginning on Day –2, and food efficiency and test article consumption were calculated. Animals that died during the study received complete necropsy examinations.

Efficacy endpoints included urine concentrations of phosphate, creatinine, and phosphate/creatinine ratio, and serum concentrations of phosphate, creatinine, phosphate/creatinine ratio and serum lanthanum.

Descriptive statistics consisted of means with a 95% confidence interval, standard deviations, standard errors of the mean and n values. For each endpoint and time period, an analysis of variance (ANOVA) was performed using treatment as an effect. If statistical significance (P < 0.05) was found, then follow-up analyses were conducted using Group Pair-Wise analysis procedures. Statistical analyses were conducted using SAS.

Results

Nephrectomized cats

In the nephrectomized cat study, urine phosphorus concentrations decreased for all animals in the treatment groups during OLC treatment compared to pre-treatment. Mean urine phosphorus concentrations decreased by 285 mg/l (1161 mg/l pre-treatment to 876 mg/l) and 1026 mg/l (1500 mg/l pre-treatment to 474 mg/l) in the 0.0466 g OLC/kg/day and 0.233 g OLC/kg/day groups, respectively (Figure 1).

Figure 1.

Faecal phosphorus excretion increased during treatment for cats in the higher dose group compared to the control and lower dose group (Figure 2). Mean phosphorus increased by 2800 mg/kg dry matter (10 900 mg/kg dry matter to 13 700 mg/kg dry matter), 275 mg/kg dry matter (11 025 mg/kg dry matter to 11 300 mg/kg dry matter) and 1475 mg/kg dry matter (10 875 mg/kg dry matter to 12 350 mg/kg dry matter) in the 0.233 g OLC/kg/day, 0.0466 g OLC/kg/day and control groups, respectively.

Figure 2.

When phosphate concentrations were plotted as a percentage of pre-treatment concentrations, a clear but nonsignificant decline in plasma phosphate was observed (P = 0.335 and 0.066 for the 0.0466 g OLC/kg body weight 0.233 g OLC/kg body weight groups, respectively).

One adverse event consisting of one animal in the 0.233 g OLC/kg/day group with clear and watery vomit on Day 0 was observed, but no diet was visible in the vomit. There was no overall difference for mean plasma urea and creatinine values between dose groups. All cats in all groups had normal levels
for plasma phosphate and calcium throughout the study. All cats gained or maintained weight during the study.

Sprague Dawley rats

In the rat study, urine phosphorus concentrations decreased in all groups during treatment. Mean urine phosphorus concentrations dropped by 0.1, 2.3, 3.0 and 3.5 mg/day in the control, 0.197, 0.394 and 0.788 g OLC/day groups, respectively. On Day 7, mean serum phosphorus concentrations were generally lower in the treatment groups than in the control group, with –10%, –25%, +3% and –21% change from baseline in the control, 0.197, 0.394 and 0.788 g OLC/day groups, respectively. The majority of serum lanthanum concentrations for animals in the treatment groups were not significantly different from those in control animals.

With the exception of the 0.099 g OLC/day dose group, mean body weights decreased by the end of the study. The decrease in body weight was highest in the control group (~5% relative to pre-study mean weight). The number of unscheduled deaths was 2, 1, 2 and 0 in the control, 0.099, 0.394, and 0.788 g OLC/day groups, respectively. The deaths occurred randomly, unrelated to treatment.