Rasburicase: a potent uricolytic agent

Development of a continuous fermentation process for the production of recombinant uricase enzyme by Pichia pastoris

Recent studies in the biopharmaceutical industry have shown an increase in the productivity and production efficiency of recombinant proteins by continuous culture. In this research, a new upstream fermentation process was developed for the production of recombinant uricase in the methylotrophic yeast Pichia pastoris. Expression of recombinant protein in this system is under the control of the AOX1 promoter and therefore requires methanol as an inducing agent and carbon/energy source. Considering the biphasic growth characteristics of conventional fed-batch fermentation, physical separation of the growth and induction stages for better control of the continuous fermentation process resulted in higher dry-cell weight (DCW) and enhanced recombinant urate oxidase activity. The DCW and recombinant uricase activity enzyme for fed-batch fermentation were 79 g/L and 6.8 u/mL. During the continuous process, in the growth fermenter at a constant dilution rate of 0.025 h-1 , DCW increased to 88.39 g/L. In the induction fermenter, at methanol feeding rates of 30, 60, and 80 mL/h, a recombinant uricase activity was 4.13, 7.2, and 0 u/mL, respectively. The optimum methanol feeding regime in continuous fermentation resulted in a 4.5-fold improvement in productivity compared with fed-batch fermentation from 0.04 u/mL/h (0.0017 mg/mL/h) to 0.18 u/mL/h (0.0078 mg/mL/h).

Expanded Clinical Pharmacogenetics Implementation Consortium Guideline for Medication Use in the Context of G6PD Genotype

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is associated with development of acute hemolytic anemia in the setting of oxidative stress, which can be caused by medication exposure. Regulatory agencies worldwide warn against the use of certain medications in persons with G6PD deficiency, but in many cases, this information is conflicting, and the clinical evidence is sparse. This guideline provides information on using G6PD genotype as part of the diagnosis of G6PD deficiency and classifies medications that have been previously implicated as unsafe in individuals with G6PD deficiency by one or more sources. We classify these medications as high, medium, or low to no risk based on a systematic review of the published evidence of the gene-drug associations and regulatory warnings. In patients with G6PD deficiency, high-risk medications should be avoided, medium-risk medications should be used with caution, and low-to-no risk medications can be used with standard precautions, without regard to G6PD phenotype. This new document replaces the prior Clinical Pharmacogenetics Implementation Consortium guideline for rasburicase therapy in the context of G6PD genotype (updates at: www.cpicpgx.org).

The Role of the Intestine in the Development of Hyperuricemia

Gout is a common inflammatory arthritis caused by the deposition of sodium urate crystals in the joints. Hyperuricemia is the fundamental factor of gout. The onset of hyperuricemia is related to purine metabolism disorders or uric acid excretion disorders. Current studies have shown that the intestine is an important potential organ for the excretion of uric acid outside the kidneys. The excretion of uric acid of gut is mainly achieved through the action of uric acid transporters and the catabolism of intestinal flora, which plays an important role in the body’s uric acid balance. Here we reviewed the effects of intestinal uric acid transporters and intestinal flora on uric acid excretion, and provide new ideas for the treatment of hyperuricemia and gout.

Review of Hematological and Oncological Emergencies

Patients with hematological malignancies, both treated and untreated, or solid tumors undergoing treatment are at risk of life-threatening complications, which may present in the emergency department (ED). Such emergencies are diverse in etiology and often require prompt treatment. Traditional complications, such as febrile neutropenia, have had recent guideline updates, which incorporate new evidence and a new validated risk stratification tool. In addition, newer approaches to treatment, such as chimeric antigen receptor (CAR) T-cell therapy, are becoming more widely available and have unique associated toxicities. This review discusses the management of the following hematological and oncological emergencies likely to be encountered in the ED: febrile neutropenia, CAR T-cell toxicities, differentiation syndrome, tumor lysis syndrome, hypercalcemia of malignancy, and hyponatremia.

Acute Tumor Lysis Syndrome: A Metabolic Emergency in Cancer Patients

Tumor lysis syndrome (TLS) can be a life-threatening complication that occurs following the onset of chemotherapy treatment, most commonly in association with high-grade lymphoproliferative pathologies such as acute lymphoblastic leukemia and Burkitt lymphoma. The massive cell lysis caused by cytotoxic therapy leads to the rapid release in the blood of intracelullary products and the onset of severe metabolic and electrolytic complications (hyperkalemia, hyperphosphatemia, hypocalcemia and hyperuricemia) upto the acute renal failure. This article describes the incidence and pathophysiological basis of TLS, focusing on the new therapeutic strategies implemented over the last few years, especially with regard to the treatment of hyperuricemia. In particular, it highlights the characteristics of a recent drug, Rasburicase, as a safe and effective alternative, compared to traditional allopurinol therapy, for prophylaxis and treatment of children with hyperuricemia induced by chemotherapy.

Single-Dose Rasburicase Might Be Adequate To Overcome Tumor Lysis Syndrome In Hematological Malignancies

INTRODUCTION

Tumor lysis syndrome (TLS) is a commonly observed oncological emergency that requires prompt diagnosis and treatment. Rasburicase is a recombinant urate oxidase endorsed in TLS for the treatment of hyperuricemia. The effect of single-dose 7.5 mg rasburicase at longer follow-ups was not widely investigated.

PATIENTS AND METHODS

Eighty-two patients included in the study with clinical TLS and laboratory TLS. The primary endpoint was the normalization of uric acid (<6mg/dL) within 24 hours of rasburicase administration, which was described as treatment success. The secondary endpoint was defined as having sustained response at the first week. The third endpoint was defined as the reaching the baseline renal function before TLS.

RESULTS

We found that the use of a 7.5 mg dose of rasburicase controlled uric acid in 74 of 82 (90,2%) patients at the 24th hour. In the first week, uric acid remained at normal levels in 69 of 82 (84,1%) patients. At 24 hours, the TLS risk group was the only predictor for failing uric acid normalization; at the end of the first week, no predictive factor was identified for failing uric acid normalization.

CONCLUSION

Rasburicase at 7.5 mg dose is an important agent for controlling laboratory and clinical TLS at 24 hours and extending its effect to the first week.

Enzyme Replacement Therapy for Genetic Disorders Associated with Enzyme Deficiency

Mutations in human genes might lead to loss of functional proteins, causing diseases. Among these genetic disorders, a large class is associated with the deficiency in metabolic enzymes, resulting in both an increase in the concentration of substrates and a loss in the metabolites produced by the catalyzed reactions. The identification of therapeutic actions based on small molecules represents a challenge to medicinal chemists because the target is missing. Alternative approaches are biology-based, ranging from gene and stem cell therapy, CRISPR/Cas9 technology, distinct types of RNAs, and enzyme replacement therapy (ERT). This review will focus on the latter approach that since the 1990s has been successfully applied to cure many rare diseases, most of them being lysosomal storage diseases or metabolic diseases. So far, a dozen enzymes have been approved by FDA/EMA for lysosome storage disorders and only a few for metabolic diseases. Enzymes for replacement therapy are mainly produced in mammalian cells and some in plant cells and yeasts and are further processed to obtain active, highly bioavailable, less degradable products. Issues still under investigation for the increase in ERT efficacy are the optimization of enzymes interaction with cell membrane and internalization, the reduction in immunogenicity, and the overcoming of blood-brain barrier limitations when neuronal cells need to be targeted. Overall, ERT has demonstrated its efficacy and safety in the treatment of many genetic rare diseases, both saving newborn lives and improving patients' life quality, and represents a very successful example of targeted biologics.

Revisiting the Effects of Xenon on Urate Oxidase and Tissue Plasminogen Activator: No Evidence for Inhibition by Noble Gases

Although chemically inert, Xe and other noble gases have been shown to have functional effects on biological systems. For example, Xe is a powerful anesthetic with neuroprotective properties. Recent reports have claimed that Xe inhibits the activity of tissue plasminogen activator (tPA) and urate oxidase (UOX), indicating that the use of Xe as an anesthetic may have undesirable side effects. Here, we revisited the methods used to demonstrate Xe inhibition of UOX and tPA, testing both indirect and direct gas delivery methods with variable bubble sizes and gas flowrates. Our results indicate that Xe or Kr do not affect the activity of UOX or tPA and that the previously reported inhibition is due to protein damage attendant to directly bubbling gases into protein solutions. The lack of evidence to support Xe inhibition of UOX or tPA alleviates concerns regarding possible side effects for the clinical application of Xe as an anesthetic. Furthermore, this study illustrates the importance of using indirect methods of gas dissolution for studying gas-protein interactions in aqueous solution.

Tumor lysis syndrome in childhood malignancies

BACKGROUND

Tumor lysis syndrome (TLS) is the most common life-threatening oncological emergency encountered by physicians treating children with lymphoproliferative malignancies. Healthcare providers should be aware of the condition in order to prevent occurrence and prompt timely management to avoid severe consequences.

OBJECTIVE

To provide an update on the current understanding, evaluation, and management of tumor lysis syndrome in childhood malignancies.

METHODS

A PubMed search was performed in Clinical Queries using the keywords 'tumor lysis syndrome' and 'malignancies' with Category limited to clinical trials and reviews for ages from birth to 18 years.

RESULTS

There were 22 clinical trials and 37 reviews under the search criteria. TLS is characterized by acute electrolyte and metabolic disturbances resulting from massive and abrupt release of cellular contents into the circulation due to breakdown of tumor cells. If left untreated, it can lead to multiorgan compromise and eventually death. Apart from close monitoring and medical therapies, early recognition of risk factors for development of TLS is also necessary for successful management.

CONCLUSIONS

Prophylactic measures to patients at risk of TLS include aggressive fluid management and judicious use of diuretics and hypouricemic agents. Both allopurinol and urate oxidase are effective in reducing serum uric acid. Allopurinol should be used as prophylaxis in low-risk cases while urate oxidase should be used as treatment in intermediate to high-risk cases. There is no evidence on better drug of choice among different urate oxidases. The routine use of diuretics and urine alkalinization are not recommended. Correction of electrolytes and use of renal replacement therapy may also be required during treatment of TLS.

Emergencies in haematology: tumour lysis syndrome

Tumour lysis syndrome (TLS) is a significant complication of haematologic malignancies and their management. The syndrome consists of laboratory abnormalities either alone (laboratory TLS) or with clinical sequelae including renal failure, seizures, and arrhythmias (clinical TLS). Clinical TLS is a predictor for worse overall morbidity and mortality in cancer patients, but can be prevented. Thus, accurate prognostication is critical to appropriate management of patients at risk for TLS, and incorporates both disease factors (tumour type and burden) and patient factors (baseline renal insufficiency or hyperuricaemia). Strategies to prevent TLS include hydration and allopurinol in low- and intermediate-risk patients and rasburicase in high-risk patients.

Safety and tolerability of available urate-lowering drugs: a critical review

INTRODUCTION

Urate-lowering therapy (ULT) is the cornerstone of gout management, which is a widespread chronic illness characterized by hyperuricemia, arthropathy, tophus development, and urolithiasis. Since asymptomatic increased serum urate levels are associated with a higher risk of cardiovascular, renal and metabolic disorders, a larger use of ULTs in the general population is expected in the near future.

AREAS COVERED

This review will focus on the safety and tolerability profile of the available urate-lowering drugs: xanthine oxidase inhibitors (XOIs), uricosuric agents and injectable uricases.

EXPERT OPINION

Older drugs for ULT like allopurinol are well studied and extensively described from typical adverse effects (mild skin rash) to unusual fatal reactions, while febuxostat seems to be overall well tolerated. More evidence is required to define the safety profile of topiroxostat, arhalofenate, tranilast, and sulfinpyrazone. Furthermore, there are some unanswered questions about the pharmacological interactions of probenecid and the hepatotoxicity of benzbromarone. Despite a limited use in clinical practice, combination therapy with lesinurad or verinurad and XOI is not frequently accompanied by side effects. Rasburicase and pegloticase are usually well tolerated with some specific exceptions. Before prescribing UL drugs, physicians should take into account their safety profile tailoring the treatment on the patient characteristics.

Concordance between glucose-6-phosphate dehydrogenase (G6PD) genotype and phenotype and rasburicase use in patients with hematologic malignancies

Phenotypic rather than genotypic tests remain the gold standard for diagnosing glucose-6-phosphate dehydrogenase (G6PD) deficiency. However, with increasing use of genomic arrays and whole exome or genome sequencing, G6PD genetic data are increasingly available. We examined the utility of G6PD genetic data in patients with hematologic malignancies and the association of G6PD genotype and phenotype with rasburicase-induced methemoglobinemia. We analyzed G6PD activity for 990 patients. Genotype data were available from the Affymetrix DMET array (n=379), whole exome sequencing (n=374), and/or the Illumina exome array (n=634) for 645 patients. Medical records of 341 patients with methemoglobin measures were assessed for the administration of rasburicase. We observed 5 non-synonymous SNPs, 4 of which were known to be associated with deficient G6PD activity (WHO Class I-III). Genotyping 367 males resulted in a positive predictive value of 81.8% (47.8–96.8%), and two males with a Class I-III allele having normal activity both received a red blood cell transfusion prior to the activity assay. However, genotyping males had only 39.1% (20.5–61.2%) sensitivity. Two of the 12 heterozygous females had deficient G6PD activity. Rasburicase-induced methemoglobinemia occurred in 6 patients, 5 of whom had at least one Class I-III allele, despite 2 of these having normal G6PD activity. We conclude that although an apparent nondeficient genotype does not necessarily imply a normal phenotype, a deficient genotype result indicates a deficient phenotype in those without transfusions, and may be a useful adjuct to phenotype to prevent adverse drug reactions.

Single 6-mg dose of rasburicase: The experience in a large academic medical center

Background

Tumor lysis syndrome is an oncologic emergency due to the release of tumor cell contents, leading to metabolic derangements. Rasburicase, a recombinant urate oxidase, catabolizes uric acid. At our institution, we administer a single 6-mg dose of rasburicase to patients who are at risk for tumor lysis syndrome. We aimed to assess the efficacy of single 6-mg dose of rasburicase and explore risk factors associated with rasburicase failure.

Methods

We report results in 92 adult patients who had a baseline uric acid greater than 7.5 mg/dL and received a single 6-mg dose of rasburicase for the management of tumor lysis syndrome. Responders were defined as those whose uric acid was less than or equal to 7.5 mg/dL within 24–36 h of rasburicase administration. The primary end point was response based on uric acid level. Secondary end points included response to rasburicase in association with lactate dehydrogenase, serum creatinine, calcium, phosphorus, blood pH, and oncologic diagnosis.

Results

Median age was 65 years and 70% were men. Most patients had leukemia (32%) or lymphoma (40%). Eighty-seven of 92 patients (95%), who received single 6-mg dose of rasburicase, achieved a uric acid less than 7.5 mg/dL within 24–36h of dosing. Body mass index was similar between responders and non-responders: 28.6 kg/m2 vs. 26.6 kg/m2, respectively, p = 0.6. Baseline lactate dehydrogenase levels were similar between the groups: 756 U/L vs. 892 U/L, respectively, p = 0.33. Blood pH values documented within 24 h of first dose of rasburicase were also similar between the two groups (n = 30; 7.33 vs. 7.34 respectively, p = 0.6). However, median baseline uric acid was lower in responders than non-responders: 12.3 mg/dL vs. 17.3 mg/dL, respectively, p = 0.012. Baseline serum creatinine and creatinine clearance were similar between responders and non-responders (2.2 mg/dL vs. 3.95 mg/dL; p = 0.12 and 29 mL/min vs. 16 mL/min; p = 0.11, respectively).

Conclusions

Higher baseline uric acid levels were observed in patients who did not respond to the first rasburicase dose. In our study, uric acid levels normalized in 95% of patients after a single 6-mg dose of rasburicase indicating that a single 6-mg dose of rasburicase may be sufficient to manage tumor lysis syndrome, for most patients.

Oncologic Metabolic Emergencies

Cancer and its therapies may lead to several metabolic emergencies that emergency providers (EPs) should be well-versed in identifying and managing. With prompt recognition and treatment initiation in the emergency department, lives can be saved and quality of life maintained. Most oncologic metabolic emergencies occur in advanced cancer states, but some follow initiation of treatment or may be the presenting syndrome that leads to the cancer diagnosis. This article reviews the 2 most emergent oncologic metabolic diagnoses: tumor lysis syndrome and hypercalcemia of malignancy. A discussion on associated cancers and conditions, pathogenesis and pathophysiology, and management recommendations is included.

Catalytic Mechanisms for Cofactor-Free Oxidase-Catalyzed Reactions: Reaction Pathways of Uricase-Catalyzed Oxidation and Hydration of Uric Acid

First-principles quantum mechanical/molecular mechanical (QM/MM)-free energy calculations have been performed to uncover how uricase catalyzes metabolic reactions of uric acid (UA), demonstrating that the entire reaction process of UA in uricase consists of two stages-oxidation followed by hydration. The oxidation consists of four steps: (1) chemical transformation from 8-hydroxyxythine to an anionic radical via a proton transfer along with an electron transfer, which is different from the previously proposed electron-transfer mechanism that involves a dianion intermediate (UA^2-) during the catalytic reaction process; (2) proton transfer to the O₂^- anion (radical); (3) diradical recombination to form a peroxo intermediate; (4) dissociation of H₂O₂ to generate the dehydrourate. Hydration, for the most favorable pathway, is initiated by the nucleophilic attack of a water molecule on dehydrourate, along with a concerted proton transfer through residue Thr69 in the catalytic site. According to the calculated free energy profile, the hydration is the rate-determining step, and the corresponding free energy barrier of 16.2 kcal/mol is consistent with that derived from experimental kinetic data, suggesting that the computational insights into the catalytic mechanisms are reasonable. The mechanistic insights not only provide a mechanistic base for future rational design of uricase mutants with improved catalytic activity against uric acid as an improved enzyme therapy, but also are valuable for understanding a variety of other cofactor-free oxidase-catalyzed reactions involving an oxygen molecule.

Oral uricase eliminates blood uric acid in the hyperuricemic pig model

An elevated level of serum uric acid-hyperuricemia, is strongly associated with the development of gout and chronic kidney disease (CKD) which is often accompanied by a significantly reduced glomerular filtration rate (GFR). In the present study, we investigated the extra-renal elimination of uric acid via the intestine in a healthy pig model and the effect of oral uricase therapy on plasma uric acid concentrations in pigs with induced hyperuricemia and CKD. The experiment was conducted on eleven, ten-week-old pigs (n = 11). The porcine model of CKD was developed by performing 9/10 nephrectomy surgery on eight pigs. A stable model of hyperuricemia was established in only five of the eight nephrectomized pigs by frequent injections of uric acid (UA) into the jugular vein. All pigs (three healthy pigs and five CKD pigs) were operated for implantation of jugular vein catheters and the three healthy pigs also had portal vein catheters inserted. Blood uric acid concentrations were measured spectrophotometrically, using the Uric Acid Assay Kit (BioAssay Systems, Hayward, USA). The piglets with CKD received orally administered uricase (treatment) and served as their own controls (without uricase supplementation). Oral uricase therapy significantly decreased plasma uric acid concentrations in pigs with CKD, whereas hyperuricemia was observed in the pigs whilst not being treated with uricase. Urinary uric acid excretion was similar during both the treatment and control periods during the first 8 h and 24 h after UA infusions in the CKD pigs. To demonstrate the elimination of UA via the intestine, the healthy pigs were infused with UA into the jugular vein. The blood collected from the jugular vein represents circulating UA concentrations and the blood collected from the portal vein represents the concentration of UA leaving the intestine. The final (after 2 h) concentration of UA was significantly lower in blood collected from the portal vein compared to that collected from the jugular vein (3.34 vs. 2.43 mg/dL, respectively, p = 0.024). The latter allows us to suggest that UA is eliminated from the blood via the gut tissue.

Prevention and treatment of tumor lysis syndrome, and the efficacy and role of rasburicase

Tumor lysis syndrome (TLS) is a potentially life-threatening condition that occurs in oncologic and hematologic patients with large tumor burden, either due to cytotoxic therapy or, less commonly, spontaneously because of massive tumor cell lysis. TLS is clinically characterized by acute renal failure, hyperuricemia, hyperkalemia, hyperphosphatemia, and hypocalcemia. While limited options are available for treating TLS, identifying patients at high risk for developing TLS and prevention in high-risk patients remain an important aspect in the treatment of cancer patients. In general, treatment of TLS consists of intensive hydration, stimulation of diuresis, and, more specifically, in the use of allopurinol and rasburicase. Rasburicase, a recombinant urate oxidase, rapidly and effectively reduces hyperuricemia, which subsequently significantly decreases the risk of acute renal failure and other clinical manifestations of TLS. For this review, a comprehensive literature search using the term “tumor lysis syndrome” and/or “rasburicase” was performed considering articles listed in MEDLINE. Incidence, prevention, and therapy of TLS with a special focus on the role of rasburicase are discussed. We evaluated 120 relevant articles including 35 case reports, 32 clinical trials, and 14 meta-analyses.

Risk of anaphylaxis with repeated courses of rasburicase: a Research on Adverse Drug Events and Reports (RADAR) project

BACKGROUND

Rasburicase, a recombinant urate oxidase, is used to rapidly metabolize uric acid in patients with hyperuricaemia. Rasburicase is an immunogenic therapeutic protein, which has been shown to elicit antibody response in 64 % of healthy volunteers within 1-6 weeks after the initial course, with persistent antibodies for over 1 year. Drug labelling indicates that anaphylaxis rarely occurs (in <1 % of patients) after a single course of therapy with rasburicase, but there are no data available on the incidence of anaphylaxis in patients receiving a subsequent rasburicase course.

OBJECTIVE

The objective of this study was to determine the incidence of anaphylaxis after multiple treatment courses of rasburicase.

METHODS

A retrospective chart review was performed on 97 consecutively treated patients who received repeated courses of rasburicase for hyperuricaemia.

RESULTS

None of the 97 patients who were reviewed experienced anaphylaxis during the first rasburicase course; however, six patients (6.2 %) experienced anaphylaxis during a subsequent rasburicase treatment course (p = 0.03).

CONCLUSION

Anaphylaxis after a second course of rasburicase appears to occur more frequently than described in the US Food and Drug Administration-approved package insert for initial treatment courses. Given the serious nature of anaphylactic events, caution is advised when administering repeated courses of rasburicase.

Tumor lysis syndrome in the emergency department: challenges and solutions

Tumor lysis syndrome (TLS) is the most common oncologic emergency. It is caused by rapid tumor cell destruction and the resulting nucleic acid degradation during or days after initiation of cytotoxic therapy. Also, a spontaneous form exists. The metabolic abnormalities associated with this syndrome include hyperkalemia, hyperphosphatemia, hypocalcemia, hyperuricemia, and acute kidney injury. These abnormalities can lead to life-threatening complications, such as heart rhythm abnormalities and neurologic manifestations. The emergency management of overt TLS involves proper fluid resuscitation with crystalloids in order to improve the intravascular volume and the urinary output and to increase the renal excretion of potassium, phosphorus, and uric acid. With this therapeutic strategy, prevention of calcium phosphate and uric acid crystal deposition within renal tubules is achieved. Other measures in the management of overt TLS are prescription of hypouricemic agents, renal replacement therapy, and correction of electrolyte imbalances. Hyperkalemia should be treated quickly and aggressively as its presence is the most hazardous acute complication that can cause sudden death from cardiac arrhythmias. Treatment of hypocalcemia is reserved for patients with electrocardiographic changes or symptoms of neuromuscular irritability. In patients who are refractory to medical management of electrolyte abnormalities or with severe cardiac and neurologic manifestations, early dialysis is recommended.

Germline oncopharmacogenetics, a promising field in cancer therapy

Pharmacogenetics (PGx) is the study of the relationship between inter-individual genetic variation and drug responses. Germline variants of genes involved in drug metabolism, drug transport, and drug targets can affect individual response to medications. Cancer therapies are characterized by an intrinsically high toxicity; therefore, the application of pharmacogenetics to cancer patients is a particularly promising method for avoiding the use of inefficacious drugs and preventing the associated adverse effects. However, despite continuing efforts in this field, very few labels include information about germline genetic variants associated with drug responses. DPYD, TPMT, UGT1A1, G6PD, CYP2D6, and HLA are the sole loci for which the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) report specific information. This review highlights the germline PGx variants that have been approved to date for anticancer treatments, and also provides some insights about other germline variants with potential clinical applications. The continuous and rapid evolution of next-generation sequencing applications, together with the development of computational methods, should help to refine the implementation of personalized medicine. One day, clinicians may be able to prescribe the best treatment and the correct drug dosage based on each patient's genotype. This approach would improve treatment efficacy, reduce toxicity, and predict non-responders, thereby decreasing chemotherapy-associated morbidity and improving health benefits.

Pharmacodynamic analysis of intravenous recombinant urate oxidase using an indirect pharmacological response model in healthy subjects

AIM

Pharmacodynamic analysis of intravenous recombinant urate oxidase produced by Escherichia coli was performed in healthy subjects using a pharmacokinetic/pharmacodynamic (PK/PD) model.

METHODS

A randomized, single-blind, placebo-controlled study was performed in 40 healthy Chinese subjects (4 groups of 10 subjects each, placebo 4:1 ratio) who received infusions of uricase (single doses of 0.1, 0.2, and 0.3 mg/kg; multiple doses of 0.2 mg·kg(-1)·d(-1) for 7 d). PK profiles were determined through plasma uricase activity, and PD profiles were established using uric acid levels in plasma and urine. The plasma PD parameter was estimated as changes in plasma uric acid levels as the effect in the indirect response model. Adverse events were also monitored.

RESULTS

A two-compartment PK model with constant iv input and first-order output was used to describe the kinetic process of plasma uricase. The low value (2.8 U/L) of drug concentration that achieved 50% of maximum effect (EC50) indicated that low plasma uricase concentrations were sufficient to produce pharmacological effects. A strong relationship (r(2)=0.9991) between the mean uric acid concentration in blood and the mean uric acid excretion rate in urine in the range of 11 to 30 h after single dosing was found. Infusions of uricase were well tolerated in all subjects.

CONCLUSION

The PK/PD model predicted the effective dose to be 0.1 mg/kg in healthy subjects. The excretion rate of uric acid in urine may be used as a new index for pharmacological effects in further clinical trials.

Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for rasburicase therapy in the context of G6PD deficiency genotype

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is associated with development of acute hemolytic anemia (AHA) induced by a number of drugs. We provide guidance as to which G6PD genotypes are associated with G6PD deficiency in males and females. Rasburicase is contraindicated in G6PD-deficient patients due to the risk of AHA and possibly methemoglobinemia. Unless preemptive genotyping has established a positive diagnosis of G6PD deficiency, quantitative enzyme assay remains the mainstay of screening prior to rasburicase use. The purpose of this article is to help interpret the results of clinical G6PD genotype tests so that they can guide the use of rasburicase. Detailed guidelines on other aspects of the use of rasburicase, including analyses of cost-effectiveness, are beyond the scope of this document. Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines are published and updated periodically on https://www.pharmgkb.org/page/cpic to reflect new developments in the field.

Treatment of Burkitt lymphoma in adults

Since its initial description in 1958, Burkitt lymphoma has become a prototype for our understanding of the pathogenesis and optimal treatment of aggressive lymphomas. The evolution of the treatment of this disease is explored and current therapeutic approaches evaluated. Special issues in the treatment of Burkitt lymphoma will also be discussed, including considerations in patients infected with HIV and current views on prophylactic measures and treatment of tumor lysis syndrome.

Development of a new LC-MS/MS based enzyme activity assay for recombinant urate oxidase in plasma and its application to pharmacokinetics in human

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the determination of recombinant urate oxidase in human plasma. This assay was based on the determination of enzyme reaction product, (15)N-allantoin, and phenacetin was used as an internal standard (IS). Separation was achieved on a C18 column by the mobile phase of 30% water (containing 0.5% formic acid) and 70% methanol. Quantification was done using multiple reaction monitoring (MRM) mode to monitor the precursor-to-product ion transitions of m/z 161 → m/z 118 for (15)N-allantoin and m/z 180 → m/z 110.1 for IS at positive ionization mode. The calibration curve was established over the range of 2.077-42.06 U/l and the correlation coefficient was larger than 0.99. The intra-day and inter-day relative standard deviations were less than 10.6%. Accuracy determined at three concentrations ranged between 98.6% and 109.2%. This method was successfully applied to a pharmacokinetic study of intravenous recombinant urate oxidase produced from Escherichia coli in Chinese healthy volunteers.

Oncologic emergencies

OBJECTIVES

To provide an up-to-date review of current literature on the pathophysiology, diagnosis, and management of five key malignancy-related complications: superior vena cava syndrome, malignant pericardial effusion, malignant spinal cord compression, hypercalcemia, and acute tumor lysis syndrome.

DATA SOURCES

Database searches and review of relevant medical literature.

DATA SYNTHESIS

Malignancy-related complications demand increased attention from intensivists due to their frequency and increasing cancer prevalence. Although such complications portend a poor prognosis, proper acute management can improve short-term outcomes by facilitating either definitive care of the underlying malignancy or the institution of appropriate palliative measures.

CONCLUSIONS

Knowledge of malignancy-induced complications in critically ill patients expedites the ability of the intensivist to properly manage them. Five complications commonly requiring emergency management are addressed in this review. Specifically, superior vena cava syndrome may warrant radiation, chemotherapy, vascular stenting, or surgical resection. Malignant pericardial effusion may require emergency pericardiocentesis if cardiac tamponade develops. Malignant spinal cord compression demands immediate spinal imaging, glucocorticoids, and either surgery or radiation. Hypercalcemia requires aggressive intravenous hydration and a bisphosphonate. Acute tumor lysis syndrome necessitates intravenous hydration, rasburicase, and management of associated electrolyte abnormalities.

Risk evaluation, prophylaxis, and treatment of tumor lysis syndrome: consensus of an Italian expert panel

INTRODUCTION

Tumor lysis syndrome (TLS) is a life-threatening complication in patients with hematological disease and/or solid tumors that results from rapid, large-scale tumor necrosis occurring spontaneously, or more commonly, as a result of chemotherapy. TLS is characterized by metabolic and electrolyte imbalances that include hyperuricemia, hyperkalemia, hyperphosphatemia, and hypocalcemia. Identification of risk groups as well as early detection of TLS is crucial for the establishment of appropriate strategies of prophylaxis and treatment.

METHODS

A review of the peer-reviewed literature on TLS between 1990 and 2011 was conducted via a systematic search of the PubMed database using the keywords "TLS" [AND] "management," "risk evaluation," "prophylaxis," and "treatment." An expert opinion-based approach was used to review the national and international recommendations and guidelines on the topic.

RESULTS

The PubMed search produced 90 results, all of which were evaluated. These studies, together with a recent international consensus panel provided recommendations for evaluating the risk of TLS and providing prophylaxis. Five algorithms are presented that consider all of the factors when assessing the risk for neoplastic disease in general, and specifically for leukemia and lymphoma.

CONCLUSION

The present report provides clinicians with an easily consultable tool to guide the evidence-based management of this oncohematological emergency.

The clinical management of tumour lysis syndrome in haematological malignancies

Tumour lysis syndrome (TLS) is caused by the disintegration of malignant cells, usually following the instigation of chemotherapy, although it may already be established at the time of initial presentation in a minority of cases. As a direct consequence of malignant cell breakdown, intracellular ions, proteins, nucleic acids and their metabolites are released into the plasma causing the characteristic metabolic abnormalities of TLS; hyperuricaemia, hyperkalaemia, hyperphosphataemia and hypocalcaemia. In many cases the release of large amounts intracellular contents is so abrupt that the normal homeostatic mechanisms are rapidly overwhelmed and without prompt, effective management, the clinical effects of TLS soon become apparent.

A review of tumour lysis syndrome with targeted therapies and the role of rasburicase

WHAT IS KNOWN AND OBJECTIVE

Tumour lysis syndrome (TLS) is an oncologic emergency with potentially devastating consequences classically associated with cytotoxic chemotherapy. In recent years, molecularly targeted drugs have assumed an increasingly important role in cancer therapeutics. The possibility of TLS is often overlooked in this setting. Rasburicase, a recombinant urate oxidase, is remarkably effective in treating hyperuricemia, thought to be central to the pathogenesis of renal injury in TLS. Our objective is to review the literature on TLS especially as it pertains to targeted therapies and summarize current knowledge and provide future directions regarding the role of rasburicase in the management of TLS.

METHODS

A MEDLINE search was conducted using PubMed and the keyphrase 'tumor lysis syndrome' to identify articles describing TLS with a broad range of novel anti-cancer agents. Meeting abstracts were also reviewed. Additionally, the biomedical literature was searched using the keyword 'rasburicase'.

RESULTS AND DISCUSSION

Tumour lysis syndrome has been described with nearly every class of 'targeted therapy'. This is not surprising as any drug causing death of cancer cells by any mechanism may lead to TLS in the appropriate setting. Although there is a wealth of evidence suggesting that rasburicase is extremely effective in correcting hyperuricemia, prospective trials showing that it improves hard outcomes such as acute renal failure, need for dialysis and mortality are lacking. Furthermore, much lower doses and durations of therapy than approved appear to be effective in controlling hyperuricemia, potentially leading to enormous cost savings.

WHAT IS NEW AND CONCLUSION

Any effective cancer therapy can lead to TLS. Physicians should consider the risk of TLS on a case-by-case basis and determine appropriate prophylaxis. The role of rasburicase continues to evolve. Randomized controlled trials evaluating clinically relevant outcomes are needed.

Oncologic emergencies

Oncologic emergencies represent a wide variety of conditions that can occur at any time during the course of a malignancy, from an initial presenting manifestation in someone with an undiagnosed cancer, to end-stage incurable metastatic disease. Emergent conditions can also arise after a malignancy has been in remission for many years, even decades, so clinicians must be aware of any prior history of cancer in patients. Oncologic emergencies include conditions caused by the cancer itself or side effects of therapy. Emergent conditions include metabolic, cardiac, neurologic, or infectious disorders. Many of these emergencies are imminently life-threatening, and can occur in patients with curable disease (such as lymphomas or leukemias); however, many also present in patients with incurable advanced disease. Prompt recognition and treatment of these conditions can lead to markedly improved quality and quantity of life.

Effect of allopurinol versus urate oxidase on methotrexate pharmacokinetics in children with newly diagnosed acute lymphoblastic leukemia

BACKGROUND

Allopurinol and urate oxidase are both effective in preventing or treating hyperuricemia during remission induction therapy for lymphoid malignancies, but to the authors' knowledge, their effects on concomitant anticancer drug therapy have not been compared.

METHODS

The authors compared plasma methotrexate pharmacokinetics in pediatric patients with newly diagnosed acute lymphoblastic leukemia who received concomitant allopurinol (n = 20) versus those treated with nonrecombinant or recombinant urate oxidase (n = 96) during high-dose methotrexate administration before conventional remission induction therapy.

RESULTS

The minimum plasma concentration of uric acid was significantly (P < .0001) lower after urate oxidase treatment than the concentration after allopurinol treatment. Methotrexate clearance was significantly higher (median, 117.1 mL/minute/m(2) vs 91.1 mL/minute/m(2); P = .019) in patients who received urate oxidase. A higher proportion of patients in the allopurinol group had elevated methotrexate plasma concentrations (36% vs 7%; P = .003) and experienced mucositis (45% vs 16%; P = .003) after methotrexate treatment compared with the urate oxidase group.

CONCLUSIONS

The lower rate of methotrexate clearance in patients who received allopurinol likely reflected a less potent hypouricemic effect of allopurinol, leading to precipitation of uric acid in renal tubules. Hence, during remission induction therapy for lymphoid malignancies, the authors concluded that renally excreted drugs should be monitored closely, especially in patients who are receiving allopurinol.

Safety and efficacy of rasburicase (SR29142) in a Japanese phase II study

The purpose of this study was to investigate the safety profile of SR29142 when administered as a single agent both prior to chemotherapy and during treatment, and to compare the efficacy of SR29142 administered at two dose levels in adult Japanese patients with leukemia or lymphoma. During this open-label, multicenter, phase II study, patients received SR29142 for 5 days, administered at either 0.15 or 0.20 mg/kg per day. Chemotherapy was started 4–24 h after the first infusion of SR29142. The primary end-point was overall response rate, defined as the normalization of plasma uric acid to 7.5 mg/dL or less, from 48 h after the first infusion to 24 h after the last infusion of SR29142. SR29142-related adverse events including hypersensitivity (allergic) reactions were assessed. Overall, 50 patients received SR29142 at either 0.15 mg/kg per day (n = 25) or 0.20 mg/kg per day (n = 25) followed by chemotherapy. The overall response rate was 100.0% (95% confidence interval, 86.3–100.0%) with 0.15 mg/kg and 96.0% (95% confidence interval, 79.6–99.9%) with 0.20 mg/kg. Both dose levels of SR29142 were equally effective at reducing plasma uric acid levels. In six patients, seven drug-related adverse events of grade 1/2 occurred before chemotherapy. SR29142-related, hypersensitivity-associated reactions occurred in three patients, and rash, anorexia, application site pain and pyrexia occurred in one patient each; only five patients (10%) showed anti-SR29142 antibodies by day 29. In conclusion, SR29142 is effective at reducing plasma uric acid levels with a tolerable safety profile as a single agent both prior to chemotherapy and during treatment.

Anti-cancer PEG-enzymes: 30 years old, but still a current approach

PEGylation (i.e. the covalent link of PEG strands) is a well known technique used to improve pharmaceutical properties of bioactive proteins and peptides. Even in cancer therapy some proteins, in particular enzymes, can find many applications, because of their antiproliferative action or ability to reduce side effects of chemotherapies, but to do so they need to be properly formulated. Unfortunately, formulation alone can not fulfil all the requirements to yield a safe and successful protein preparation for therapeutic applications. In particular, for many proteins fast clearance from the body and potential immunogenicity are severe limitations, which can not be easily overcome without taking into consideration a purposely designed drug delivery system. Among the approaches in the field of drug delivery, PEGylation has so far been the best choice for protein delivery. Here, we describe some examples of PEGylated enzymes useful in antitumoral therapies and the most recent advances in this field.

Rasburicase represents a new tool for hyperuricemia in tumor lysis syndrome and in gout

Hyperuricemia is a feature of several pathologies and requires an appropriate and often early treatment, owing to the severe consequences that it may cause. A rapid and massive raise of uric acid, during tumor lysis syndrome (TLS), and also a lower and chronic hyperuricemia, as in gout, mainly damage the kidney. To prevent or treat these consequences, a new therapeutic option is represented by rasburicase, a recombinant form of an enzyme, urate oxidase. This enzyme converts hypoxanthine and xanthine into allantoin, a more soluble molecule, easily cleared by kidney. The several types of urate oxidase have followed each other, with progressive reduction of adverse reactions. The most important among them are allergenicity and the development of antibodies which compromise their effectiveness. Nevertheless, a limit of rasburicase's use remains its cost, which obliges to a judicious choice to prevent TLS in high risk patients with cancer and in case of allergy or impossibility to take allopurinol orally both in TLS and in gout. A large body of evidence confirms the efficacy and safety of rasburicase, even in comparison to the standard drugs used in the aforementioned pathologies.

Clinical trials in crystal arthropathy

A few clinical trials have evaluated therapeutic agents for crystal-associated arthropathy. Most of the studies are uncontrolled and observational. Management of patients who have acute crystal arthropathies usually is symptomatic with long-term management depending on crystal composition. In trials of gout, studies focus on acute symptomatic treatment, foregoing chronic management, which is aimed at reducing the concentration of serum urate. In those who have calcium crystals, however, there is no definitive or effective long-term treatment in chronic gout. The xanthine oxidase inhibitor and uricosurics are the agents used most commonly. Newer compounds in clinical trials show promise as effective and safe therapeutic options.

Recombinant urate oxidase (rasburicase) for the prevention and treatment of tumor lysis syndrome in patients with hematologic malignancies

In this multicenter, nonrandomized, open-label clinical trial conducted from July 2003 to July 2004, recombinant urate oxidase (rasburicase) was administered to patients at risk for tumor lysis syndrome before or during the initiation of chemotherapy. Forty-five patients were enrolled, including 18 children (10 with acute lymphoblastic leukemia, 6 with high-grade lymphoma, and 2 with acute myeloid leukemia) and 27 adults (8 with acute lymphoblastic leukemia, 4 with high-grade lymphoma, 9 with multiple myeloma, and 6 with acute myeloid leukemia). The age ranged from 3 to 98 years, with a median age of 7 years in children and 59.3 years in adults. There were 14 males and 4 females in the pediatric group and 18 males and 9 females in the adult group. Rasburicase 0.2 mg/kg was administered intravenously once a day for 2-6 days, for a median of 3 days in children and of 4 days in adults. After 3 days of treatment, the median uric acid levels in the 18 children decreased from 10.5 mg/dl (range 8-18.6) to 0.5 mg/dl (range 0.0-1.7). Similarly, in the 27 adults, the median levels decreased from 10.8 mg/dl (range 8-24.4) to 0.5 mg/dl (range 0.0-1.6). No significant changes were observed in serum potassium, calcium, and phosphorus concentrations. None of the patients required dialysis for acute renal failure. Rasburicase was very well tolerated, with only 1 adult having grade 1 vomiting. We conclude that rasburicase is safe and highly effective for preventing the complications of tumor lysis syndrome in patients with hematologic malignancies.