Therapeutic uses of soluble alpha-Klotho

This application is a U.S. national phase entry, pursuant to 35 U.S.C. §371, of PCT/US2010/060436, filed Dec. 15, 2010, which claims the priority of U.S. Provisional Application No. 61/286,880, filed Dec. 16, 2009.

The present invention relates to therapeutic uses of soluble alpha-Klotho.

Alpha-Klotho (aka Klotho) is a 114 kDa protein expressed primarily in the kidney, but also at low levels in other tissues including the parathyroid gland and choroid plexus of the brain. Various endogenous forms of Klotho exist, including a transmembrane form, a soluble form consisting of the extracellular domain which circulates in serum, and at least one soluble splice variant. Klotho is an obligatory partner of FGF23 in terms of both binding and signaling through its cognate FGF receptors, although FGF23-independent activities have been reported. FGF23 is a key regulator of phosphate homeostasis.

Klotho knockout mice develop a variety of kidney and age-related diseases, including tissue calcifications, vascular calcification, and osteopenia. Ectopic expression of the full-length Klotho protein in Klotho knockout mice can reverse many of these phenotypes. Adenoviral overexpression of transmembrane Klotho in various mouse models of renal disease produces beneficial effects. Renal Klotho expression decreases in patients with chronic kidney disease.

A Klotho translocation in man resulting in increased levels of serum Klotho is associated with hypophosphatemia, increased serum FGF23 and PTH levels, and rickets. An hypomorphic Klotho mutation in man was associated with hyperphosphatemia, increased serum FGF23 levels, and tumoral calcinosis. This has led to the hypothesis that chronic kidney disease and perhaps other age-related diseases may represent a state of Klotho insufficiency. Although anti-apoptotic/proliferative activities of the extracellular domain of Klotho in vitro have been reported, there are no published reports to date demonstrating an activity of a soluble form of Klotho in vivo, except for an effect recently reported on potassium excretion.

Human and mouse alpha-Klotho polypeptides are disclosed in U.S. Pat. No. 6,579,850. PCT application WO 2009/095372 discloses compositions for preventing or treating age-related conditions or metabolic disorders using Klotho fusion polypeptides comprising a Klotho protein and a fibroblast growth factor (FGF).

An objective for the present invention is to provide a simple therapeutic paradigm with flexibility and control in terms of dosing and reduced chance for exogenous drug-drug interactions. Many states of hyperphosphatemia, such as chronic kidney disease, are associated with increased FGF23 levels. Therefore, it is possible that administration of exogenous FGF23 (alone or in fusion forms) may be detrimental in certain situations. Delivery of soluble alpha-Klotho may be advantageous. The present invention derives from the surprising observations that soluble alpha-Klotho expressed in vivo is hypophosphatemic and moreover does not require exogenous FGF23 (intact or fused with Klotho) for its in vivo hypophosphatemic activities and results in an up-regulation of endogenous FGF23 levels (many-fold molar excess compared to soluble Klotho), which suggests that it might be important to keep in vivo FGF23-Klotho levels correctly balanced.

Thus, the present invention provides a method of treating or preventing hyperphosphatemia or calcinosis, hyperphosphatemia and calcinosis, chronic renal disease or chronic renal failure, chronic renal disease and chronic renal failure, tissue or vascular calcification, tissue and vascular calcification, albuminuria or proteinuria, or albuminuria and proteinuria in a patient, comprising administering to the patient an effective amount of soluble alpha-Klotho.

The present invention will be useful as a therapeutic approach where endogenous Klotho is insufficient and/or FGF23 levels are perturbed from normal. These conditions include kidney disease, tissue and vascular calcifications, hyperphosphatemia, osteopenia (particularly loss of BMD of cortical bone), and diseases or conditions exhibited by Klotho knockout mice, including arteriosclerosis, infertility, short life span, pulmonary emphysema, skin atrophy, anemia, thymic atrophy, ectopic calcifications including those of the kidney and vasculature, accumulation of renal interstitial matrix, glomerulosclerosis, and neuronal degeneration.

Additional examples of possible Klotho insufficiency include cancer, diabetes, heart disease, vascular disease, lung disease, bone disease, Parkinson's Disease, Alzheimer's Disease, Multiple Sclerosis, cachexia and Muscular Dystrophy.

The present invention also provides a method of reducing blood pressure or calcific atherosclerotic plaque burden, or reducing blood pressure and calcific atherosclerotic plaque burden in a patient, comprising administering an effective amount of soluble alpha-Klotho to the patient; a method of lowering serum phosphate levels in a patient, comprising administering an effective amount of soluble alpha-Klotho to the patient; a method of increasing FGF23 in a patient, comprising administering an effective amount of soluble alpha-Klotho to the patient; use of soluble alpha-Klotho in the manufacture of a medicament for treating or preventing hyperphosphatemia or calcinosis, hyperphosphatemia and calcinosis, chronic renal disease or chronic renal failure, chronic renal disease and chronic renal failure, tissue or vascular calcification, tissue and vascular calcification, albuminuria or proteinuria, or albuminuria and proteinuria; use of soluble alpha-Klotho in the manufacture of a medicament for reducing blood pressure or calcific atherosclerotic plaque burden, or reducing blood pressure and calcific atherosclerotic plaque burden; use of soluble alpha-Klotho in the manufacture of a medicament for lowering serum phosphate levels; use of soluble alpha-Klotho in the manufacture of a medicament for increasing FGF23; use of soluble alpha-Klotho in treating or preventing hyperphosphatemia or calcinosis, hyperphosphatemia and calcinosis, chronic renal disease or chronic renal failure, chronic renal disease and chronic renal failure, tissue or vascular calcification, tissue and vascular calcification, albuminuria or proteinuria, or albuminuria and proteinuria; use of soluble alpha-Klotho in reducing blood pressure or calcific atherosclerotic plaque burden, or reducing blood pressure and calcific atherosclerotic plaque burden; use of soluble alpha-Klotho in lowering serum phosphate levels; and use of soluble alpha-Klotho in increasing FGF23.

Soluble alpha-Klotho is selected from the group consisting of SEQ ID NO: 11, SEQ ID NO: 5, SEQ ID NO: 7, and SEQ ID NO: 9; most preferably, SEQ ID NO: 5.

The term “soluble alpha-Klotho” as used herein, refers to soluble active fragments of Klotho or the extracellular domain (ECD) of Klotho, including soluble human Klotho (SEQ ID NO: 4), soluble rat Klotho (SEQ ID NO: 6), soluble mouse Klotho (SEQ ID NO: 1), soluble monkey Klotho (SEQ ID NO: 8), human Klotho extracellular domain (ECD) (SEQ ID NO: 5), rat Klotho ECD (SEQ ID NO: 7), mouse Klotho ECD (SEQ ID NO: 11), and monkey Klotho ECD (SEQ ID NO: 9).

The term “treating” (or “treat” or “treatment”) means slowing, stopping, reducing, or reversing the progression or severity of a symptom, disorder, condition, or disease.

The term “preventing” (or “prevent” or “prevention”) refers to a decrease in the occurrence of a symptom, disorder, condition, or disease or decrease in the risk of acquiring a symptom, disorder, condition, or disease or its associate symptoms in a subject.

A “patient” is a mammal, preferably a human.

The term “effective amount” refers to the amount or dose of soluble alpha-Klotho, which provides the desired treatment upon single or multiple dose administration to a patient.

Effects of AAV8-mediated Soluble Klotho Overexpression in Normal Mice

The in vivo effects of elevated soluble Klotho levels in serum are assessed in the following studies. Overexpression of Klotho is confirmed by directly measuring mouse serum Klotho levels by enzyme-linked immunosorbent assay (ELISA). Effects of Klotho overexpression on serum phosphate, calcium, FGF23 and PTH are examined.

To induce an increase in serum Klotho levels, an adenoviral system is employed. The extracellular domain (ECD) of mouse Klotho protein with a CD33 N-terminal signal sequence (SEQ ID NO: 2) is packaged into a recombinant hybrid adeno-associated viral vector 2/8 (AAV8). Expression of Klotho is driven by a liver-specific thyroxine binding globulin (TBG) promoter.

Normal male C57B16 mice are used in this study at 8-9 weeks of age. Mice are given a single retro-orbital injection of vehicle, or virus (mouse Klotho ECD with a CD33 N-terminal signal sequence (SEQ ID NO: 2) or LacZ control (SEQ ID NO: 3)). Viral dose range for Klotho ECD is 1×10 10 to 1×10 11 genomic copies per mouse. Serum is obtained from the mice at 2, 4 and 8 weeks. A subset of mice is sacrificed at week 2. The remaining mice are bled at week 4 and at the time of sacrifice (week 8).

Mouse Klotho ELISA

Mouse Klotho protein in mouse serum is measured in a sandwich ELISA assay, in which mouse Klotho is captured with an antibody coated on a plate, then captured Klotho is measured using a labeled second antibody.

Each well of a 96-well plate is coated with 70 μL of goat anti-mouse Klotho polyclonal capture antibody (R&D Systems AF1819, 2 μg/mL in carbonate buffer, pH 9.6). Standard curve is run in triplicate, while samples are run in duplicate. The plate is sealed and incubated at 4° C. overnight. The wells are aspirated and washed twice with washing buffer (20 mM Tris (hydroxymethyl) aminomethane, pH 7.4, 0.15 M NaCl, 0.1% Tween-20), using an automatic plate washer. The plates are blocked with 200 μL blocking buffer per well (5% Carnation Instant milk in the above washing buffer) for 1-4 hours at room temperature.

Mouse serum samples are diluted in SeraSub® (CST Technologies) at a 1:2 dilution. Standards are prepared with mouse Klotho ECD (SEQ ID NO: 10), diluted in 50% SeraSub®, 50% pooled mouse serum (Bioreclamation, catalog #MSESRM), such that the standard curve diluent contains the same proportion of mouse serum to SeraSub® as the samples. Next, 50 μL of each sample is added to the antibody-coated wells in duplicate (or triplicate, in the case of the standards). The plates are incubated for 1.5 hours at room temperature. The wells are then washed 3 times with washing buffer.

Biotinylated anti-Klotho antibody (50 μL biotinylated goat anti-mouse Klotho polyclonal, diluted to 2 μg/mL in blocking buffer) is added to each well and incubated for 45 minutes at room temperature. The wells are then washed 3 times with washing buffer. Then, 50 μL of peroxidase-conjugated streptavidin is added to the wells, and the plate is incubated for 30 minutes at room temperature. Next, 50 μL of chromogenic substrate (i.e., OPD substrate, Sigma, catalog #P-6912) is added to each well and allowed to develop at room temperature for 2-4 minutes. The reaction is stopped by adding 100 μL 1N HCl to each well. The absorbance of the wells is read at 490 nm on a Molecular Devices SpectraMax250 plate reader. The average absorbance from duplicate wells is determined, back-calculations for dilutions are made, and the resulting values are listed in Table 1, below.

Intact FGF23 ELISA

Intact FGF23 levels are measured using a commercially-available human intact FGF23 ELISA kit (Kainos Laboratories, catalog #CY-4000). Manufacturer's instructions are followed. Sera are diluted at various concentrations such that the values are within the range of the standard curve for quantification. Standard curve ranges from 3-800 pg/mL. The assumption is made that the ELISA has 100% cross-reactivity to mouse Klotho. The average absorbance from duplicate wells is determined, back-calculations for dilutions are made, and the resulting values are listed in Table 1, below.

Intact PTH ELISA

Intact PTH levels are measured using a commercially-available mouse intact PTH ELISA kit (Immutopics, catalog #60-2300). Manufacturer's instructions are followed, with the exception that only 1 replicate is measured. Standard curve ranges from 36-3500 pg/mL. Results are listed in Table 1, below.

Serum Phosphate and Calcium Measurements

Serum is collected and analyzed for calcium and inorganic phosphorous. Calcium levels are determined by a colorimetric method in which o-cresolphthalein complexone reacts with calcium in the sample at alkaline pH to form calcium-o-cresolphthalein complex. The calcium concentration is directly proportional to the color intensity of this complex and is photometrically measured with an automated chemistry analyzer. Inorganic phosphorous combines with ammonium molybdate under acidic conditions to form an ammonium molybdate complex. The concentration of this complex is also measured photometrically. Roche Calcium and Inorganic Phosphorous reagent kits are utilized for this analysis, as well as either a Hitachi 912 or Hitachi Modular Analytics Chemistry analyzer (Roche Diagnostics). Results are listed in Table 1, below.

Serum levels of Klotho (determined by ELISA) in vehicle-treated mice in this study are in the range of those reported in the literature [Kurosu et al., Science, 2005]. Overexpression of soluble Klotho is achieved, through use of an AAV2/8 system, compared to serum Klotho levels in vehicle-treated mice. While the amplitude of the increase in serum levels of Klotho appears to decline over time, levels remain elevated compared to vehicle throughout the study. The maximum increase of Klotho serum levels measured in this study was approximately 24-fold over vehicle. Serum levels of FGF23 are statistically significantly increased in mice with elevated serum Klotho levels (maximal increase approximately 807-fold). The increase in serum FGF23 persists throughout the study. PTH levels are elevated at both the week 2 and 8 time points (week 4 not tested) in mice over-expressing soluble Klotho. Serum phosphate levels are statistically significantly and dose-responsively reduced at all time points, with maximal reduction of approximately 56% from vehicle. These data demonstrate that increased soluble Klotho serum levels lead to a decrease in levels of serum phosphate. Serum calcium is slightly but statistically significantly elevated early at the lowest dose (week 2) compared to vehicle, then is reduced at weeks 4 and 8 in mice over-expressing serum soluble Klotho (maximal reduction approximately 8%).

A repeat study of similar design confirmed that administration of soluble Klotho via AAV2/8 (viral dose ranging from 1×10 9 to 3×10 11 genomic copies per mouse) resulted in increased serum Klotho levels (levels as high as 800 ng/mL), increased serum FGF23 levels, and decreased serum phosphate and calcium. PTH was only measured at weeks 10 and 12, at which times no significant changes were observed.

Mouse Klotho

(SEQ ID NO: 1)

Mouse Klotho Extracellular Domain (ECD) -

CD33 N-terminal Signal Sequence

(SEQ ID NO: 2)

LacZ Control

(SEQ ID NO: 3)

Human Klotho

(SEQ ID NO: 4)

Human Klotho ECD

(SEQ ID NO: 5)

Rat Klotho

(SEQ ID NO: 6)

Rat Klotho ECD

(SEQ ID NO: 7)

Monkey Klotho

(SEQ ID NO: 8)

Monkey Klotho ECD

(SEQ ID NO: 9)

Mouse Klotho ECD - His tagged: 36-983

(SEQ ID NO: 10)

Mouse Klotho ECD

(SEQ ID NO: 11)