Expression, bioactivity, and clinical assessment of recombinant feline erythropoietin

Adeno-associated virus-vectored erythropoietin gene therapy for anemia in cats with chronic kidney disease

BACKGROUND

A treatment of chronic kidney disease (CKD)-associated anemia in cats is needed. SB-001 is an adeno-associated virus-vectored (AAV)-based gene therapeutic agent that is administered intramuscularly, causing the expression of feline erythropoietin.

HYPOTHESIS/OBJECTIVE

We hypothesized that SB-001 injection would lead to a sustained increase in PCV in cats with CKD-associated anemia.

ANIMALS

Twenty-three cats with International Renal Interest Society (IRIS) Stage 2 to 4 CKD-associated anemia were enrolled at 4 veterinary clinics.

METHODS

In a prospective clinical trial, cats were treated with 1 of 3 regimens of SB-001 (Lo 1.2 × 109 genome copies [GCs] on Day 0; Lo ± Hi [supplemental 2nd dose of 3.65 × 109 GC on Day 42]; Hi 3.65 × 109 GC IM on Day 0) and followed for 70 days.

RESULTS

A response to SB-001 at any time between Day 28 and Day 70 was seen in 86% (95% confidence interval 65, 97%) of all cats. There was a significant (P < .003) increase in PCV from Day 0 to Day 28 (mean increase 6 ± 6 percentage points [pp]; n = 21), Day 42 (8 ± 9 pp; n = 21), Day 56 (10 ± 11 pp; n = 17), and Day 70 (13 ± 14 pp, n = 14). Twelve cats were hypertensive at baseline, 4 of which developed encephalopathy during the study. An additional 6 cats became hypertensive during the study.

CONCLUSIONS AND CLINICAL IMPORTANCE

Results of this study suggest that SB-001 therapy represents a suitable single injection treatment that can address nonregenerative anemia in cats with CKD. It was generally well tolerated; however, hypertension and encephalopathy developed in some cats as previously described in association with erythropoiesis-stimulating agent therapy.

Feline non-regenerative anemia: Diagnostic and treatment recommendations

PRACTICAL RELEVANCE

Non-regenerative anemia, or anemia with reticulocytopenia, is a daily diagnosis in feline practice.

CLINICAL CHALLENGES

The disease processes underlying non-regenerative anemia are many and diverse. A major diagnostic evaluation may be required to correctly diagnose and treat the underlying cause.

AUDIENCE

All veterinarians caring for cats will face the diagnostic and therapeutic challenge of non-regenerative anemia. Readers will benefit from the review of diagnostic testing and therapeutic options for non-regenerative anemia.

EVIDENCE BASE

This review summarizes the currently available literature informing diagnostic and treatment recommendations related to non-regenerative anemia. The evidence available to support the recommendations in this review is graded as low and includes predominantly expert opinion, case reports and cases series, on which the authors' interpretation/consensus is based.

ACVIM consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats

An update to the 2007 American College of Veterinary Internal Medicine (ACVIM) consensus statement on the identification, evaluation, and management of systemic hypertension in dogs and cats was presented at the 2017 ACVIM Forum in National Harbor, MD. The updated consensus statement is presented here. The consensus statement aims to provide guidance on appropriate diagnosis and treatment of hypertension in dogs and cats.

The Use of Darbepoetin to Stimulate Erythropoiesis in the Treatment of Anemia of Chronic Kidney Disease in Dogs

Background

Darbepoetin alfa (darbepoetin) is an erythropoiesis‐stimulating agent used for the treatment of anemia secondary to chronic kidney disease (CKD) in dogs, but reports describing response are lacking.

Hypothesis/Objectives

To evaluate the effectiveness of darbepoetin in dogs with anemia secondary to CKD, dosing protocols, and adverse events.

Animals

Thirty‐three client‐owned dogs with naturally occurring CKD, including 26 with comorbidities.

Methods

Multi‐institutional retrospective study.

Results

The median starting dosage and highest dosage of darbepoetin administered were 0.5 and 0.8 μg/kg SC once weekly, respectively. Response to treatment was defined as achieving a packed cell volume (PCV) ≥30% or an increase in PCV ≥10%. Twenty‐eight of 33 dogs (85%) achieved a PCV ≥30% and 22 of 33 (67%) dogs achieved an increase in PCV ≥10%. Median time to achieve a PCV ≥30% was 29 days. A higher starting dosage was associated with achieving an increase in PCV ≥10% (P = .01). No dog sustained a response at a dosing interval >q21d. Potential adverse events included increased blood pressure requiring treatment (n = 12), seizures (n = 5), vomiting (n = 3), diarrhea (n = 3), and possible pure red cell aplasia (PRCA) (n = 2).

Conclusions and Clinical Importance

Darbepoetin, when combined with treatment of comorbidities, is an effective treatment for anemia secondary to CKD in dogs. A dosing interval >q21d was ineffective at maintaining a response to treatment. PRCA was a possible adverse event in 2 of 33 dogs (6%).

The influence of artificially introduced N-glycosylation sites on the in vitro activity of Xenopus laevis erythropoietin

Erythropoietin (EPO), the primary regulator of erythropoiesis, is a heavily glycosylated protein found in humans and several other mammals. Intriguingly, we have previously found that EPO in Xenopus laevis (xlEPO) has no N-glycosylation sites, and cross-reacts with the human EPO (huEPO) receptor despite low homology with huEPO. In this study, we introduced N-glycosylation sites into wild-type xlEPO at the positions homologous to those in huEPO, and tested whether the glycosylated mutein retained its biological activity. Seven xlEPO muteins, containing 1–3 additional N-linked carbohydrates at positions 24, 38, and/or 83, were expressed in COS-1 cells. The muteins exhibited lower secretion efficiency, higher hydrophilicity, and stronger acidic properties than the wild type. All muteins stimulated the proliferation of both cell lines, xlEPO receptor-expressing xlEPOR-FDC/P2 cells and huEPO receptor-expressing UT-7/EPO cells, in a dose-dependent manner. Thus, the muteins retained their in vitro biological activities. The maximum effect on xlEPOR-FDC/P2 proliferation was decreased by the addition of N-linked carbohydrates, but that on UT-7/EPO proliferation was not changed, indicating that the muteins act as partial agonists to the xlEPO receptor, and near-full agonists to the huEPO receptor. Hence, the EPO-EPOR binding site in X. laevis locates the distal region of artificially introduced three N-glycosylation sites, demonstrating that the vital conformation to exert biological activity is conserved between humans and X. laevis, despite the low similarity in primary structures of EPO and EPOR.

Generation of a felinized swine endothelial cell line by expression of feline decay-accelerating factor

Embryonic stem cell research has facilitated the generation of many cell types for the production of tissues and organs for both humans and companion animals. Because ≥30% of pet cats suffer from chronic kidney disease (CKD), xenotransplantation between pigs and cats has been studied. For a successful pig to cat xenotransplant, the immune reaction must be overcome, especially hyperacute rejection. In this study, we isolated the gene for feline decay-accelerating factor (fDAF), an inhibitor of complement proteins, and transfected a swine endothelial cell line with fDAF to "felinize" the pig cells. These fDAF-expressing cells were resistant to feline serum containing anti-pig antibodies, suggesting that felinized pig cells were resistant to hyperacute rejection. Our results suggest that a "felinized" pig kidney can be generated for the treatment of CKD in cats in the future.

Nonregenerative anemia: mechanisms of decreased or ineffective erythropoiesis

In veterinary medicine, anemia without an appropriate compensatory hematopoietic response is termed nonregenerative. Nonregenerative anemia is a common clinical entity, occurring as a result of diminished or ineffective erythropoiesis in association with many types of pathology. This article reviews nonregenerative anemia in domestic animals, emphasizing mechanisms of disease, and also covers other conditions associated with nonregenerative anemia in people. Many aspects of nonregenerative anemia in animals are worthy of further investigation, from molecular mechanisms of disease to epidemiologic impacts.

Pegylated feline granulocyte colony-stimulating factor increases neutrophil levels in cats

Neutropenia can often be corrected by treatment with granulocyte-colony stimulating factor (G-CSF) and off-label use of commercial human G-CSF (HuG-CSF) is a commonly used treatment for neutropenic animals. However, long-term HuG-CSF treatment can be associated with adverse effects, including neutropenia. Here, feline (Fe) G-CSF was produced in Pichia pastoris, pegylated (Peg) FeG-CSF and tested in cats. A randomized controlled clinical trial was conducted to evaluate the efficacy of PegFeG-CSF compared to FeG-CSF or HuG-CSF in FIV-infected (n=14), FIV-uninfected healthy cats (n=19), and in HuG-CSF-induced neutropenic cats (n=4). Daily FeG-CSF doses induced higher neutrophil production than HuG-CSF after the second week of treatment (P ⩽ 0.002). Weekly doses of PegFeG-CSF induced higher neutrophil counts and showed greater sustained activity than weekly doses of FeG-CSF. PegFeG-CSF provided the most therapeutic and sustainable neutrophil production (P<0.001) in both FIV-uninfected and FIV-infected cats, without the development of neutralizing antibodies. Conversely, all HuG-CSF-treated cats developed neutralizing antibodies, suggesting cross-reactive antibodies to endogenous G-CSF in a majority of the cases with severe neutropenia. Strikingly, when PegFeG-CSF was used to rescue cats with HuG-CSF-induced neutropenia, clinically normal neutrophil numbers returned. Thus, PegFeG-CSF appears to be a superior treatment for neutropenia in feline patients.

Xenotransplanted embryonic kidney provides a niche for endogenous mesenchymal stem cell differentiation into erythropoietin-producing tissue

Recent findings have demonstrated that stem cells can differentiate into mature tissue when supplied with a niche containing factors identical to those in the normal developmental program. A niche for the development of an organ can be provided by xenotransplantation of a similar developing organ. However, this process has many technical, safety, and ethical concerns. Here, we established xenotransplantation models that control endogenous mesenchymal stem cell (MSC) differentiation into mature erythropoietin (EPO)-producing tissue in a niche provided by a developing xenometanephros. Transplantation of rat metanephroi into mouse omentum, and similarly pig metanephroi into cat omentum, led to the recruitment of host cells and EPO production. EPO-expressing cells were not differentiated from integrating vessels because they did not coexpress endothelial markers (Tie-2 and VE-cadherin). Instead, EPO-expressing cells were shown to be derived from circulating host cells, as shown by enhanced green fluorescent protein (EGFP) expression in the grown transplants of chimeric mice bearing bone marrow from a transgenic mouse expressing EGFP under the control of the EPO promoter. These results suggest that donor cell recruitment and differentiation in a xenotransplanted developing organ may be consistent between species. The cells responsible for EPO expression were identified as MSCs by injecting human bone marrow-derived MSCs and endothelial progenitor cells into NOD/SCID mice. Furthermore, using metanephroi from transgenic ER-E2F1 suicide-inducible mice, the xenotissue component could be eliminated, leaving autologous EPO-producing tissue. Our findings may alleviate adverse effects due to long-lasting immunosuppression and help mitigate ethical concerns.

A lentiviral gene therapy strategy for the in vitro production of feline erythropoietin

Nonregenerative anemia due to chronic renal failure is a common problem in domestic cats. Unfortunately, administration of recombinant human erythropoietin often only improves anemia temporarily due to antibody development. In this in vitro study, feline erythropoietin cDNA was cloned from feline renal tissue and utilized in the construction of a replication-defective lentiviral vector. The native recombinant feline erythropoietin (rfEPO) sequence was confirmed by sequencing. Upon viral vector infection of human 293H cells, Crandall Renal Feline Kidney cell line and primary feline peripheral blood mononuclear cells, bioactive rfEPO protein was produced. The presence of cellular rfEPO cDNA was confirmed by standard PCR, production of abundant rfEPO mRNA was confirmed by real-time PCR, and secretion of rfEPO protein was demonstrated by Western blot analyses, while rfEPO protein bioactivity was confirmed via an MTT proliferation bioassay. This in vitro study demonstrates the feasibility of a replication-defective lentiviral vector delivery system for the in vitro production of biologically active feline erythropoietin. Anemic cats with chronic renal failure represent a potential in vivo application of a lentiviral gene therapy system.

The use of darbepoetin to stimulate erythropoiesis in anemia of chronic kidney disease in cats: 25 cases

BACKGROUND

Anemia is present in 30-65% in cats with chronic kidney disease (CKD) and few long-term treatment options exist. Darbepoetin is effective in treating anemia of kidney disease in humans and may be used in cats.

HYPOTHESIS/OBJECTIVE

To evaluate the use of darbepoetin, a recombinant analog of human erythropoietin, to stimulate erythropoiesis, and to effectively treat anemia of kidney disease in cats.

ANIMALS

Twenty-five of 66 cats that received ≥ 2 doses of darbepoetin at the Animal Medical Center between January 2005 and December 2009 were included in this study.

METHODS

Cats were included in the study if they received darbepoetin and follow-up data were available for at least 56 days and had CKD as a primary clinical diagnosis. Cats were excluded if they were treated with darbepoetin but did not have kidney disease. Response to treatment was defined as reaching or exceeding a target packed red blood cell volume or hematocrit of 25%.

RESULTS

Fourteen of 25 cats responded. Thirteen of those 14 cats received a dosage of 1 μg/kg/wk or higher. Presumptive adverse effects included vomiting, hypertension, seizures, and fever.

CONCLUSIONS AND CLINICAL RELEVANCE

Darbepoetin is effective for treatment of anemia of kidney disease in cats. Pure red cell aplasia appears to be less common with darbepoetin than with epoetin usage.

Clinicopathological variables predicting progression of azotemia in cats with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is common in geriatric cats, but often appears to be stable for long periods of time.

OBJECTIVES

To describe CKD progression and identify risk factors for progression in newly diagnosed azotemic cats.

ANIMALS

A total of 213 cats with CKD (plasma creatinine concentration > 2 mg/dL, urine specific gravity < 1.035) were followed up until progression occurred or for at least 1 year; 132, 73, and 8 cats were in International Renal Interest Society (IRIS) stages 2, 3, and 4, respectively.

METHODS

Progression was defined as a 25% increase in plasma creatinine concentration. Logistic regression was used to assess variables at diagnosis that were associated with progression within 1 year. Changes in IRIS stage during follow-up also were described. Cases that remained in stages 2 or 3, but did not have renal function assessed in the last 60 days of life, were excluded from analysis of the proportion reaching stage 4.

RESULTS

Of the cats, 47% (101) progressed within 1 year of diagnosis. High plasma phosphate concentration and high urine protein-to-creatinine ratio (UPC) predicted progression in all cats. Low PCV and high UPC independently predicted progression in stage 2 cats, whereas higher plasma phosphate concentration predicted progression in stage 3 cats; 19% (18/94) of cats diagnosed in stage 2; and 63% (34/54) of cats diagnosed in stage 3 reached stage 4 before they died.

CONCLUSIONS

Proteinuria, anemia, and hyperphosphatemia may reflect more progressive kidney disease. Alternatively, they may be markers for mechanisms of progression such as tubular protein overload, hypoxia, and nephrocalcinosis.

Anemia of renal disease: what it is, what to do and what's new

PATIENT GROUP

It is estimated that 15-30% of geriatric cats will develop chronic kidney disease (CKD), and that 30-65% of these cats will develop anemia as their renal disease worsens. Anemia of renal disease is multifactorial in its pathogenesis, but the main cause is reduced production of erythropoietin, a renal hormone that controls the bone marrow's production of red blood cells, as kidney disease progresses.

PRACTICAL RELEVANCE

It is important to recognize the presence of anemia of renal disease so that adequate treatment may be instituted to improve quality of life and metabolic function. Erythrocyte-stimulating agents (ESAs), such as epoetin alfa, epoetin beta and darbepoetin alfa, have been developed to counteract the effects of decreased erythropoietin production by the kidneys. These treatments, which are the focus of this review, have 83% similarity in amino acid sequence to the feline hormone. On average, the target packed cell volume (>25%) is reached within 3-4 weeks of ESA therapy.

CLINICAL CHALLENGES

The use of ESAs has been associated with a number of complications, such as iron deficiency, hypertension, arthralgia, fever, seizures, polycythemia and pure red cell aplasia (PRCA). Darbepoetin has a prolonged half-life compared with epoetin and thus can be given only once a week, instead of three times a week. The incidence of PRCA appears to be decreased with darbepoetin use when compared with epoetin use in cats.

EVIDENCE BASE

There is limited published evidence to date to underpin the use of ESAs in cats. This review draws on the relevant publications that currently exist, and the authors' personal experience of using these therapies for over 5 years.

Therapies for feline chronic kidney disease. What is the evidence?

Practical relevance Successful treatment and prevention of kidney disease in pet animals requires a multidimensional approach to identify and eliminate causes or exacerbating factors, provide professional examination and care on a regular basis, and plan and implement a comprehensive treatment program when necessary.

Evidence base Over the years, many therapeutic and preventive interventions have been developed or advocated for chronic kidney disease (CKD), but evidence of efficacy or effectiveness is often lacking or highly variable. Accordingly, the main objective of this systematic review was to identify and critically appraise the evidence supporting various approaches to managing feline CKD; namely, fluid therapy, calcitrioi therapy, antihypertensive therapy, ACE inhibitor therapy, erythropoietic hormone replacement therapy, potassium supplementation, antioxidant supplementation, alkalinization therapy, dietary phosphorus restriction and intestinal phosphate binders, therapeutic renal foods, assisted feeding, dialysis and renal transplantation.

Gene therapy by electroporation for the treatment of chronic renal failure in companion animals

Background

Growth hormone-releasing hormone (GHRH) plasmid-based therapy for the treatment of chronic renal failure and its complications was examined. Companion dogs (13.1 ± 0.8 years, 29.4 ± 5.01 kg) and cats (13.2 ± 0.9 years, 8.5 ± 0.37 kg) received a single 0.4 mg or 0.1 mg species-specific plasmid injection, respectively, intramuscularly followed by electroporation, and analyzed up to 75 days post-treatment; controls underwent electroporation without plasmid administration.

Results

Plasmid-treated animals showed an increase in body weight (dogs 22.5% and cats 3.2%) compared to control animals, and displayed improved quality of life parameters including significant increases in appetite, activity, mentation and exercise tolerance levels. Insulin-like growth factor I (IGF-I, the downstream effector of GHRH) levels were increased in the plasmid treated animals. Hematological parameters were also significantly improved. Protein metabolism changes were observed suggesting a shift from a catabolic to an anabolic state in the treated animals. Blood urea nitrogen and creatinine did not show any significant changes suggesting maintenance of kidney function whereas the control animal's renal function deteriorated. Treated animals survived longer than control animals with 70% of dogs and 80% of cats surviving until study day 75. Only 17% and 40% of the control dogs and cats, respectively, survived to day 75.

Conclusion

Improved quality of life, survival and general well-being indicate that further investigation is warranted, and show the potential of a plasmid-based therapy by electroporation in preventing and managing complications of renal insufficiency.

Expression of erythropoietin in cats treated with a recombinant adeno-associated viral vector

OBJECTIVE

To characterize the biological effects of IM administration of a recombinant adeno-associated virus serotype 2 (rAAV2) vector containing feline erythropoietin (fEPO) cDNA and determine whether readministration of the vector or removal of muscle tissue at the injection sites alters those effects.

ANIMALS

10 healthy 7-week-old specific pathogen-free cats.

PROCEDURE

Cats received 1 X 10(7) infective units (iU; n = 3), 1 X 10(8) iU (3), or 1 X 10(9) iU (2) of rAAV2-fEPO vector IM (day 0). Two control cats received an rAAV2 vector containing the LacZ gene (1 X 10(9) iU, IM). In all cats, hematologic variables and serum fEPO concentration were measured at intervals; anti-rAAV2 antibody titer was measured on day 227. In cats that did not respond to treatment, the rAAV2-fEPO vector was readministered. Injection sites were subsequently surgically removed.

RESULTS

Compared with control cats, cats treated with 1 X 10(9) iU of rAAV2-fEPO vector had increased Hct and serum fEPO concentrations. One of these cats developed pure RBC aplasia; its Hct normalized following injection site excision. Cats receiving lower doses of vector had no response; on retreatment, 1 of those cats developed sustained erythrocytosis that persisted despite injection site removal and the others did not respond or responded transiently. Antibodies against rAAV2 were detected in all vector-treated cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Gene therapy may be an effective treatment for cats with hypoproliferative anemia. However, rAAV2-fEPO vector administration may result in pure RBC aplasia or pathologic erythrocytosis, and injection site removal does not consistently abolish the biological response.