A phase I and pharmacodynamic evaluation of polyethylene glycol-conjugated L-asparaginase in patients with advanced solid tumors

Bacterial cellulose films for L-asparaginase delivery to melanoma cells

L-asparaginase (L-ASNase) is an enzyme that catalyzes the hydrolysis of L-asparagine to L-aspartic acid and ammonia and is used to treat acute lymphoblastic leukemia. It is also toxic to the cells of some solid tumors, including melanoma cells. Immobilization of this enzyme can improve its activity against melanoma tumor cells. In this work, the properties of bacterial cellulose (BC) and feasibility of BC films as a new carrier for immobilized L-ASNase were investigated. Different values of growth time were used to obtain BC films with different thicknesses and porosities, which determine the water content and the ability to adsorb and release L-ASNase. Fourier transform infrared spectroscopy confirmed the adsorption of the enzyme on the BC films. The total activity of adsorbed L-ASNase and its release were investigated for films grown for 48, 72 or 96 h. BC films grown for 96 h showed the most pronounced release as described by zero-order and Korsmayer-Peppas models. The release was characterized by controlled diffusion where the drug was released at a constant rate. BC films with immobilized L-ASNase could induce cytotoxicity in A875 human melanoma cells. With further development, immobilization of L-ASNase on BC may become a potent strategy for anticancer drug delivery to superficial tumors.

Development of a bioengineered Erwinia chrysanthemi asparaginase to enhance its anti-solid tumor potential for treating gastric cancer

Asparaginase has been traditionally applied for only treating acute lymphoblastic leukemia due to its ability to deplete asparagine. However, its ultimate anticancer potential for treating solid tumors has not yet been unleashed. In this study, we bioengineered Erwinia chrysanthemi asparaginase (ErWT), one of the US Food and Drug Administration-approved types of amino acid depleting enzymes, to achieve double amino acid depletions for treating a solid tumor. We constructed a fusion protein by joining an albumin binding domain (ABD) to ErWT via a linker (GGGGS)5 to achieve ABD-ErS5. The ABD could bind to serum albumin to form an albumin-ABD-ErS5 complex, which could avoid renal clearance and escape from anti-drug antibodies, resulting in a remarkably prolonged elimination half-life of ABD-ErS5. Meanwhile, ABD-ErS5 did not only deplete asparagine but also glutamine for ∼2 weeks. A biweekly administration of ABD-ErS5 (1.5 mg/kg) significantly suppressed tumor growth in an MKN-45 gastric cancer xenograft model, demonstrating a novel approach for treating solid tumor depleting asparagine and glutamine. Multiple administrations of ABD-ErS5 did not cause any noticeable histopathological abnormalities of key organs, suggesting the absence of acute toxicity to mice. Our results suggest ABD-ErS5 is a potential therapeutic candidate for treating gastric cancer.

Therapeutic Assessment of Targeting ASNS Combined with l-Asparaginase Treatment in Solid Tumors and Investigation of Resistance Mechanisms

Asparagine deprivation by l-asparaginase (L-ASNase) is an effective therapeutic strategy in acute lymphoblastic leukemia, with resistance occurring due to upregulation of ASNS, the only human enzyme synthetizing asparagine (Annu. Rev. Biochem. 2006, 75 (1), 629-654). l-Asparaginase efficacy in solid tumors is limited by dose-related toxicities (OncoTargets and Therapy 2017, pp 1413-1422). Large-scale loss of function genetic in vitro screens identified ASNS as a cancer dependency in several solid malignancies (Cell 2017, 170 (3), 564-576.e16. Cell 2017, 170 (3), 577-592.e10). Here we evaluate the therapeutic potential of targeting ASNS in melanoma cells. While we confirm in vitro dependency on ASNS silencing, this is largely dispensable for in vivo tumor growth, even in the face of asparagine deprivation, prompting us to characterize such a resistance mechanism to devise novel therapeutic strategies. Using ex vivo quantitative proteome and transcriptome profiling, we characterize the compensatory mechanism elicited by ASNS knockout melanoma cells allowing their survival. Mechanistically, a genome-wide CRISPR screen revealed that such a resistance mechanism is elicited by a dual axis: GCN2-ATF4 aimed at restoring amino acid levels and MAPK-BCLXL to promote survival. Importantly, pharmacological inhibition of such nodes synergizes with l-asparaginase-mediated asparagine deprivation in ASNS deficient cells suggesting novel potential therapeutic combinations in melanoma.

MAPK signaling regulates c-MYC for melanoma cell adaptation to asparagine restriction

Amino acid restriction is among promising potential cancer treatment strategies. However, cancer cells employ a multitude of mechanisms to mount resistance to amino acid restriction, which impede the latter's clinical development. Here we show that MAPK signaling activation in asparagine-restricted melanoma cells impairs GSK3-β-mediated c-MYC degradation. In turn, elevated c-MYC supports ATF4 translational induction by enhancing the expression of the amino acid transporter SLC7A5, increasing the uptake of essential amino acids, and the subsequent maintenance of mTORC1 activity in asparagine-restricted melanoma cells. Blocking the MAPK-c-MYC-SLC7A5 signaling axis cooperates with asparagine restriction to effectively suppress melanoma cell proliferation. This work reveals a previously unknown axis of cancer cell adaptation to asparagine restriction and informs mechanisms that may be targeted for enhanced therapeutic efficacy of asparagine limiting strategies.

Asparaginase induces selective dose- and time-dependent cytotoxicity, apoptosis, and reduction of NFκB expression in oral cancer cells

Asparaginase is fundamental to the treatment of haematological malignancies. However, little has been studied on the effects that asparaginase could exert on solid tumours. Thus, this study aimed to evaluate the effects of asparaginase on an oral carcinoma cell line. The cytotoxicity of asparaginase in SCC-9 (tongue squamous cell carcinoma) and HaCaT (human keratinocyte) cell lines was evaluated with MTT cell viability assay. The cells were treated with asparaginase at 0.04, 0.16, 0.63, 1.0, 1.5, 2.5, and 5.0 IU/mL. Dose-response curves and IC₅₀ values were obtained and the Tumour Selectivity Index (TSI) was calculated. The effect of asparaginase on procaspase-3 and nuclear factor κB (NFκB) expression was evaluated with western blot because it was reported that the overexpression of NFκB has been shown to contribute to tumour cell survival, proliferation, and migration. Caspase 3/7 staining was performed to identify cell death using flow cytometry. Effective asparaginase concentrations were lower for SCC-9 cells when compared to HaCaT cells. The cytotoxicity results at 48 and 72 hours were significantly different for SCC-9 cells. The TSI indicated that asparaginase was selective for the tumour cells. A decrease in procaspase-3 and NFκB protein levels was observed in SCC-9 cells. Furthermore, asparaginase resulted in significant apoptosis after 48 and 72 hours. Based on these results, asparaginase was cytotoxic in a dose- and time-dependent manner, induces apoptosis, and reduces NFκB expression in oral cancer cells. These results encourage further studies on the effectiveness of this enzyme as a treatment for solid tumours, especially head and neck cancer.

Translational reprogramming marks adaptation to asparagine restriction in cancer

While amino acid restriction remains an attractive strategy for cancer therapy, metabolic adaptations limit its effectiveness. Here we demonstrate a role of translational reprogramming in the survival of asparagine-restricted cancer cells. Asparagine limitation in melanoma and pancreatic cancer cells activates RTK-MAPK as part of a feedforward mechanism involving mTORC1-dependent increase in MNK1 and eIF4E, resulting in enhanced translation of ATF4 mRNA. MAPK inhibition attenuates translational induction of ATF4 and the expression of its target asparagine biosynthesis enzyme ASNS, sensitizing melanoma and pancreatic tumors to asparagine restriction, reflected in their growth inhibition. Correspondingly, low ASNS expression is among the top predictors of response to MAPK signaling inhibitors in melanoma patients and is associated with favorable prognosis, when combined with low MAPK signaling activity. While unveiling a previously unknown axis of adaptation to asparagine deprivation, these studies offer the rationale for clinical evaluation of MAPK inhibitors in combination with asparagine restriction approaches.

Acute myeloid leukaemia niche regulates response to L-asparaginase

Eradicating the malignant stem cell is the ultimate challenge in the treatment of leukaemia. Leukaemic stem cells (LSC) hijack the normal haemopoietic niche, where they are mainly protected from cytotoxic drugs. The anti-leukaemic effect of L-asparaginase (ASNase) has been extensively investigated in acute lymphoblastic leukaemia, but only partially in acute myeloid leukaemia (AML). We explored the susceptibility of AML-LSC to ASNase as well as the role of the two major cell types that constitute the bone marrow (BM) microenvironment, i.e., mesenchymal stromal cells (MSC) and monocytes/macrophages. Whilst ASNase was effective on both CD34⁺ CD38⁺ and CD34⁺ CD38^- LSC fractions, MSC and monocytes/macrophages partially counteracted the effect of the drug. Indeed, the production of cathepsin B, a lysosomal cysteine protease, by BM monocytic cells and by AML cells classified as French-American-British M5 is related to the inactivation of ASNase. Our work demonstrates that, while MSC and monocytes/macrophages may provide a protective niche for AML cells, ASNase has a cytotoxic effect on AML blasts and, importantly, LSC subpopulations. Thus, these features should be considered in the design of future clinical studies aimed at testing ASNase efficacy in AML patients.

Oncogene-Driven Metabolic Alterations in Cancer

Cancer is the leading cause of human deaths worldwide. Understanding the biology underlying the evolution of cancer is important for reducing the economic and social burden of cancer. In addition to genetic aberrations, recent studies demonstrate metabolic rewiring, such as aerobic glycolysis, glutamine dependency, accumulation of intermediates of glycolysis, and upregulation of lipid and amino acid synthesis, in several types of cancer to support their high demands on nutrients for building blocks and energy production. Moreover, oncogenic mutations are known to be associated with metabolic reprogramming in cancer, and these overall changes collectively influence tumor-microenvironment interactions and cancer progression. Accordingly, several agents targeting metabolic alterations in cancer have been extensively evaluated in preclinical and clinical settings. Additionally, metabolic reprogramming is considered a novel target to control cancers harboring un-targetable oncogenic alterations such as KRAS. Focusing on lung cancer, here, we highlight recent findings regarding metabolic rewiring in cancer, its association with oncogenic alterations, and therapeutic strategies to control deregulated metabolism in cancer.

A protease-resistant Escherichia coli asparaginase with outstanding stability and enhanced anti-leukaemic activity in vitro

L-Asparaginases (ASNases) have been used as first line drugs for paediatric Acute Lymphoblastic Leukaemia (ALL) treatment for more than 40 years. Both the Escherichia coli (EcAII) and Erwinia chrysanthemi (ErAII) type II ASNases currently used in the clinics are characterized by high in vivo instability, short half-life and the requirement of several administrations to obtain a pharmacologically active concentration. Moreover, they are sensitive to proteases (cathepsin B and asparagine endopeptidase) that are over-expressed by resistant leukaemia lymphoblasts, thereby impairing drug activity and pharmacokinetics. Herein, we present the biochemical, structural and in vitro antiproliferative characterization of a new EcAII variant, N24S. The mutant shows completely preserved asparaginase and glutaminase activities, long-term storage stability, improved thermal parameters, and outstanding resistance to proteases derived from leukaemia cells. Structural analysis demonstrates a modification in the hydrogen bond network related to residue 24, while Normal Mode-based geometric Simulation and Molecular Dynamics predict a general rigidification of the monomer as compared to wild-type. These improved features render N24S a potential alternative treatment to reduce the number of drug administrations in vivo and to successfully address one of the major current challenges of ALL treatment: spontaneous, protease-dependent and immunological inactivation of ASNase.

Autophagy suppression potentiates the anti-glioblastoma effect of asparaginase in vitro and in vivo

Asparaginase has been reported to be effective in the treatment of various leukemia and several malignant solid cancers. However, the anti-tumor effect of asparaginase is always restricted due to complicated mechanisms. Herein, we investigated the mechanisms of how glioblastoma resisted asparaginase treatment and reported a novel approach to enhance the anti-glioblastoma effect of asparaginase. We found that asparaginase could induce growth inhibition and caspase-dependent apoptosis in U87MG/U251MG glioblastoma cells. Meanwhile, autophagy was activated as indicated by autophagosomes formation and upregulated expression of LC3-II. Importantly, abolishing autophagy using chloroquine (CQ) and LY294002 enhanced the cytotoxicity and apoptosis induced by asparaginase in U87MG/U251MG cells. Further study proved that Akt/mTOR and Erk signaling pathways participated in autophagy induction, while reactive oxygen species (ROS) served as an intracellular regulator for both cytotoxicity and autophagy in asparaginase-treated U87MG/U251MG cells. Moreover, combination treatment with autophagy inhibitor CQ significantly enhanced anti-glioblastoma efficacy of asparaginase in U87MG cell xenograft model. Taken together, our results demonstrated that inhibition of autophagy potentiated the anti-tumor effect of asparagine depletion on glioblastoma, indicating that targeting autophagy and asparagine could be a potential approach for glioblastoma treatment.

Erythrocyte encapsulated l-asparaginase (GRASPA) in acute leukemia

l-asparaginase, an enzyme originally derived from Escherichia coli, represents a major drug in the treatment of acute lymphoblastic leukemia. However, the occurrence of major adverse effects often leads to early withdrawal of the enzyme. Main side effects include immune-allergic reactions, coagulopathy, pancreatitis and hepatic disorders. Novel asparaginase formulations and alternative sources have been developed to address this issue, but the results were not totally satisfactory. l-asparaginase loaded red blood cells (RBCs; GRASPA) represent a new asparaginase presentation with reduced immunological adverse reactions. RBCs protect l-asparaginase, enhance its half-life and reduce the occurrence of adverse events. We reviewed the history, biology and clinical experiences with l-asparaginase, and the characteristics and first clinical experiences with GRASPA in the treatment of acute leukemia.

Enzyme therapeutics for systemic detoxification

Life relies on numerous biochemical processes working synergistically and correctly. Certain substances disrupt these processes, inducing living organism into an abnormal state termed intoxication. Managing intoxication usually requires interventions, which is referred as detoxification. Decades of development on detoxification reveals the potential of enzymes as ideal therapeutics and antidotes, because their high substrate specificity and catalytic efficiency are essential for clearing intoxicating substances without adverse effects. However, intrinsic shortcomings of enzymes including low stability and high immunogenicity are major hurdles, which could be overcome by delivering enzymes with specially designed nanocarriers. Extensive investigations on protein delivery indicate three types of enzyme-nanocarrier architectures that show more promise than others for systemic detoxification, including liposome-wrapped enzymes, polymer-enzyme conjugates, and polymer-encapsulated enzymes. This review highlights recent advances in these nano-architectures and discusses their applications in systemic detoxifications. Therapeutic potential of various enzymes as well as associated challenges in achieving effective delivery of therapeutic enzymes will also be discussed.

Knockdown of asparagine synthetase by RNAi suppresses cell growth in human melanoma cells and epidermoid carcinoma cells

Melanoma, the most aggressive form of skin cancer, causes more than 40,000 deaths each year worldwide. And epidermoid carcinoma is another major form of skin cancer, which could be studied together with melanoma in several aspects. Asparagine synthetase (ASNS) gene encodes an enzyme that catalyzes the glutamine- and ATP-dependent conversion of aspartic acid to asparagine, and its expression is associated with the chemotherapy resistance and prognosis in several human cancers. The present study aims to explore the potential role of ASNS in melanoma cells A375 and human epidermoid carcinoma cell line A431. We applied a lentivirus-mediated RNA interference (RNAi) system to study its function in cell growth of both cells. The results revealed that inhibition of ASNS expression by RNAi significantly suppressed the growth of melanoma cells and epidermoid carcinoma cells, and induced a G0/G1 cell cycle arrest in melanoma cells. Knockdown of ASNS in A375 cells remarkably downregulated the expression levels of CDK4, CDK6, and Cyclin D1, and upregulated the expression of p21. Therefore, our study provides evidence that ASNS may represent a potential therapeutic target for the treatment of melanoma.

A multicenter, open-label, Phase 1 study evaluating the safety and tolerability of pegaspargase in combination with gemcitabine in advanced metastatic solid tumors and lymphoma

PURPOSE

To evaluate the maximum tolerated dose, safety profile, pharmacokinetics, and pharmacodynamics of pegaspargase (PEG-ASP) in combination with gemcitabine in patients with advanced metastatic solid tumors and lymphoma.

METHODS

We conducted a multicenter, open label, nonrandomized, Phase 1 dose escalation study designed to evaluate up to 10 cohorts of patients with advanced or metastatic solid tumors and lymphoma. Seventeen patients were treated with of PEG-ASP in combination with gemcitabine.

RESULTS

The study was terminated early because the doses for PEG-ASP suggested for de-escalation were predicted not to provide desired sustained asparaginase concentrations based on the analysis of treated patients.

Engineering of Helicobacter pylori L-asparaginase: characterization of two functionally distinct groups of mutants

Bacterial L-asparaginases have been used as anti-cancer drugs for over 4 decades though presenting, along with their therapeutic efficacy, several side effects due to their bacterial origin and, seemingly, to their secondary glutaminase activity. Helicobacter pylori type II L-asparaginase possesses interesting features, among which a reduced catalytic efficiency for L-GLN, compared to the drugs presently used in therapy. In the present study, we describe some enzyme variants with catalytic and in vitro cytotoxic activities different from the wild type enzyme. Particularly, replacements on catalytic threonines (T16D and T95E) deplete the enzyme of both its catalytic activities, once more underlining the essential role of such residues. One serendipitous mutant, M121C/T169M, had a preserved efficiency vs L-asparagine but was completely unable to carry out L-glutamine hydrolysis. Interestingly, this variant did not exert any cytotoxic effect on HL-60 cells. The M121C and T169M single mutants had reduced catalytic activities (nearly 2.5- to 4-fold vs wild type enzyme, respectively). Mutant Q63E, endowed with a similar catalytic efficiency versus asparagine and halved glutaminase efficiency with respect to the wild type enzyme, was able to exert a cytotoxic effect comparable to, or higher than, the one of the wild type enzyme when similar asparaginase units were used. These findings may be relevant to determine the role of glutaminase activity of L-asparaginase in the anti-proliferative effect of the drug and to shed light on how to engineer the best asparaginase/glutaminase combination for an ever improved, patients-tailored therapy.

Poly(2-vinyl-4,4-dimethylazlactone)-functionalized magnetic nanoparticles as carriers for enzyme immobilization and its application

Fabrication of various efficient enzyme reactors has triggered increasing interests for its extensive applications in biological and clinical research. In this study, magnetic nanoparticles were functionalized by a biocompatible reactive polymer, poly(2-vinyl-4,4-dimethylazlactone), which was synthesized by reversible addition-fragmentation chain transfer polymerization. Then, the prepared polymer-modified magnetic nanoparticles were employed as favorable carriers for enzyme immobilization. l-Asparaginase was selected as the model enzyme to fabricate the enzyme reactor, and the prepared enzyme reactor exhibited high loading capacity of 318.0 μg mg(-1) magnetic nanoparticle. Interestingly, it has been observed that the enzymolysis efficiency increased slightly with the lengthened polymer chain, resulting from the increased immobilization amount of enzyme. Meanwhile, the immobilized enzyme could retain more than 95.7% activity after 10 repeated uses and maintain more than 72.6% activity after 10 weeks storage. Moreover, an extracorporeal shunt system was simulated to estimate the potential application capability of the prepared l-asparaginase reactor in acute lymphoblastic leukemia treatment.

A phase II clinical trial of polyethylene glycol-conjugated L-asparaginase in patients with advanced ovarian cancer: Early closure for safety

The anti-angiogenic activity of L-asparaginase (L-ASP) and the sensitivity of ovarian cancer cell lines to L-ASP has been previously demonstrated by preclinical findings. The aim of this clinical trial was to translate those findings and evaluate the activity of polyethylene glycol-conjugated L-asparaginase (PEG-ASP or pegaspargase) in advanced ovarian cancer. Women with recurrent ovarian cancer and good end-organ function were enrolled in an open-label phase II trial of PEG-ASP at a dose of 2,000 IU/m² by intravenous infusion every 2 weeks. Patients were evaluated for response every 8 weeks and for toxicity on an ongoing basis. Early stopping rules for toxicity and activity were included. Four patients were enrolled and received a total of 7 treatment cycles. The study ended accrual by invoking an early stopping rule, after excessive toxicity was identified in patients. Drug-related toxicities included grade 2 pancreatitis, fatigue, neutropenia, hypoalbuminemia, weight loss, dehydration, decreased fibrinogen and 1 case of grade 3 hypersensitivity reaction during cycle 2. One patient died during the study. No patients were evaluable for response. PEG-ASP was poorly tolerated in this group of advanced-stage ovarian cancer patients and no conclusions regarding activity may be drawn. Further studies of PEG-ASP in ovarian cancer patients are not recommended.

Poly(ethylene glycol)-Prodrug Conjugates: Concept, Design, and Applications

Poly(ethylene glycol) (PEG) is the most widely used polymer in delivering anticancer drugs clinically. PEGylation (i.e., the covalent attachment of PEG) of peptides proteins, drugs, and bioactives is known to enhance the aqueous solubility of hydrophobic drugs, prolong circulation time, minimize nonspecific uptake, and achieve specific tumor targetability through the enhanced permeability and retention effect. Numerous PEG-based therapeutics have been developed, and several have received market approval. A vast amount of clinical experience has been gained which has helped to design PEG prodrug conjugates with improved therapeutic efficacy and reduced systemic toxicity. However, more efforts in designing PEG-based prodrug conjugates are anticipated. In light of this, the current paper highlights the synthetic advances in PEG prodrug conjugation methodologies with varied bioactive components of clinical relevance. In addition, this paper discusses FDA-approved PEGylated delivery systems, their intended clinical applications, and formulations under clinical trials.

Prevention and management of asparaginase/pegasparaginase-associated toxicities in adults and older adolescents: recommendations of an expert panel

The rapidly increasing use of pegasparaginase (pegASNase) in adults, after a half century of use of asparaginase (ASNase) in children, has prompted a need for guidelines in the management and prevention of toxicities of asparagine depletion in adults. Accordingly, an initial set of recommendations are provided herein. Major advantages of pegASNase are its 2-3-week duration of action, in contrast to less than 3 days with native ASNase, and the flexibility of intravenous or intramuscular administration of pegASNase and associated patient and physician convenience. The most frequent toxicities of both types of ASNase are hepatic and pancreatic, with pancreatitis being the most serious. Other toxicities are hypersensitivity reactions, thrombosis, nausea/vomiting, and fatigue. Whether or not the replacement of one dose of pegASNase for 6-9 doses of native ASNase can be achieved in adults with similar efficacy and acceptable toxicities to those achieved in children remains to be established.

Targeting methionine auxotrophy in cancer: discovery & exploration

INTRODUCTION

Amino acid auxotrophy or the metabolic defect which renders cancer incapable of surviving under amino acid depleted conditions is being exploited and explored as a therapeutic against cancer. Early clinical data on asparagine- and arginine-depleting drugs have demonstrated low toxicity and efficacy in melanoma, hepatocellular carcinoma and acute lymphoblastic leukemia. Methionine auxotrophy is a novel niche currently under exploration for targeting certain cancers.

AREAS COVERED

In this review we explore the discovery of methionine auxotrophy followed by in vitro, in vivo and patient data on targeting cancer with methionine depletion. We end with a small discussion on bioengineering, pegylation and red blood cell encapsulation as mechanisms for decreasing immunogenicity of methionine-depleting drugs. We hope to provide a platform for future pharmacology, toxicology and cytotoxicity studies with methionine depletion therapy and drugs.

EXPERT OPINION

Although methionine auxotrophy seems as a viable target, extensive research addressing normal versus cancer cell toxicity needs to be conducted. Further research also needs to be conducted into the molecular mechanism associated with methionine depletion therapy. Finally, novel methods need to be developed to decrease the immunogenicity of methionine-depleting drugs, a current issue with protein therapeutics.

Peg-asparaginase for acute lymphoblastic leukemia

IMPORTANCE OF THE FIELD

Asparaginase is a prominent component of pediatric and adolescent treatment for acute lymphoblastic leukemia. These treatment regimens are now being employed in adults. Knowledge of the efficacy and toxicity of asparaginase preparations is essential when using these treatments. AREAS COVERED BY THIS REVIEW: The search terms used were asparaginase, leukemia, pegylated, oncaspar, adolescent and young adult. Literature was searched in Pubmed/Medline with no limitations on year of publication. Abstracts from the American Society of Hematology meetings and the American Society of Clinical Oncology were searched from 2004 - 2008 using the same terms.

WHAT THE READER WILL GAIN

The reader will gain knowledge of the tolerability and efficacy of pegylated asparaginase when treating acute lymphoblastic leukemia.

TAKE HOME MESSAGE

Pegylated asparaginase is generally well tolerated in adult patients with efficacy that appears to be at least equivalent to native asparaginase preparations.

Stable-labeled analogues and reliable quantification of nonprotein biomarkers by LC–MS/MS

Background: The aim was to develop, and establish as suitable to begin assessment by full validation, a quantitative LC–MS/MS method for asparagine in human plasma. Therein, to utilize a stable-labeled analogue of asparagine to act as surrogate analyte, producing complete calibration curves and corresponding QC samples and another m/z distinct stable-labeled analogue to act as internal standard. Results: From two candidates, the surrogate analyte was selected through statistical comparisons of concentration–response data and the resultant method employed protein precipitation and LC on an unmodified silica column with multiple reaction monitoring detection mode. The calibration range was 50–10,000 ng/ml. Conclusion: This method was successfully proven to meet the accuracy and precision acceptance criteria of current bioanalytical method validation guidelines.

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.

PEG-asparaginase

L-asparaginases have been established components in the treatment of acute leukemias for nearly 40 years. Their antitumor effect results from the depletion of asparagine, an amino acid essential to leukemic cells, and subsequent inhibition of protein synthesis leading to considerable cytotoxicity. The efficacy of L-asparaginases has been limited by a high rate of hypersensitivity reactions and development of anti-asparaginase antibodies, which neutralize their activity. PEG-asparaginase, a form of Escherichia coli L-asparaginase covalently linked to polyethylene glycol, was rationally synthesized to decrease immunogenicity of the enzyme and prolong its half-life. In recent years, clinical trials have established the importance of intramuscular PEG-asparaginase in frontline pediatric and adult acute lymphoblastic leukemia therapy. Present studies are evaluating the feasibility of intravenous PEG-asparaginase administration.

Pharmacological and clinical evaluation of L-asparaginase in the treatment of leukemia

L-Asparaginase is an effective antineoplastic agent, used in the acute lymphoblastic leukemia chemotherapy. It has been an integral part of combination chemotherapy protocols of pediatric acute lymphoblastic leukemia for almost 3 decades. The potential of L-asparaginase as a drug of leukemia has been a matter of discussion due to the high rate of allergic reactions exhibited by the patients receiving the medication of this enzyme drug. Frequent need of intramuscular injection has been another disadvantage associated with the native preparation. However, of late these clinical complications seem to have been addressed by modified versions of L-asparaginase. PEG-L-asparaginase proves to be most effective in this regard. It becomes important to discuss the efficacy of L-asparaginase as an antileukemic drug vis-a-vis these disadvantages. In this review, an attempt has been made to critically evaluate the pharmacological and clinical potential of various preparations of L-asparaginase as a drug. Advantages of PEG-L-asparaginase over native preparations and historical developments of therapy with l-asparaginase have also been outlined in the review below.

A Phase I-II trial of polyethylene glycol-conjugated L-asparaginase in patients with multiple myeloma

BACKGROUND

Multiple myeloma remains an incurable disease. New agents are needed to improve therapy for patients with this disease. Previous investigators evaluated in vitro sensitivity of myeloma cells to polyethylene glycol-conjugated L-asparaginase (PEG-L-asparaginase) using the human tumor clonogenic assay. Of the 19 myeloma samples evaluated, 63% were inhibited at 0.075 IU/mL, and 74% were inhibited at 0.75 IU/mL. PEG-L-asparaginase is a form of Escherichia coli-derived L-asparaginase that is bound covalently to polyethylene glycol. Compared with the native form, it has a longer half-life and is less likely to cause allergic reactions.

METHODS

The authors conducted a Phase I-II trial using PEG-L-asparaginase as a single agent in patients with recurrent and/or refractory multiple myeloma.

RESULTS

Twenty-two patients received a median of two doses of PEG-L-asparaginase. In the 17 patients who are evaluable for response, a complete response was observed in one patient after four doses, and stable disease was observed in eight patients. Progression of disease was the reason for termination from study in the remaining eight patients. The median survival was 31.7 months, with four patients who were alive at 72 months after the start of therapy. Grade 3-4 toxicity was noted by the PEG-L-asparaginase 2000 mg/m(2) level. Severe allergic reactions were noted only at the highest dose level.

CONCLUSIONS

Current data suggest that the maximal tolerated dose for single agent PEG-L-asparaginase in relapse/refractory multiple myeloma patients is 1000 mg/m(2) every 4 weeks. We could not identify any correlation between dose, plasma level and response. In this advanced group of patients we noted stable disease and/or response in 52% of evaluable patients. PEG-L-asparaginase has lower tolerance when used in the standard dosage as a single agent in this group of patients. We therefore recommend further studying of PEG-L-asparaginase dose of 1000 mg/m(2) on alternate weeks with steroids and/or other immune modulators.

Photo-control of the interaction between endothelial cells and photo-cation generatable water-soluble polymers

In this study photo-control of the non-biospecific interaction between endothelial cell membranes and photo-cation generatable water-soluble polymers were examined. The water-soluble polymers contained triphenylmethane leucohydroxide (malachite green) groups (contents: 0.4 and 1.6 mol%), which dissociate into triphenylmethyl cations and counter hydroxide ions upon ultraviolet light (UV) irradiation, and were prepared by free radical copolymerization of diphenyl(4-vinylphenyl)methane leucohydroxide and acrylamide. The nature and magnitude of the interaction was quantitatively assessed by direct luminescence measurement of the intracellular calcium ion concentration using a calcium-sensitive photoprotein, aequorin. When a PBS buffer of the photoreactive copolymers were added, prior to UV irradiation, to a PBS suspension of cultured bovine endothelial cells loaded with aequorin, no detectable elevation of Ca(2+) was measured. In contrast, cationic copolymers, derived from the photoreactive copolymers after UV irradiation at a wavelength of 290<lambda<410 nm, induced an immediate transient increase in the cytosolic free Ca(2+) concentration due to a Ca(2+) inflow from the extracellular space into the cells, which may be due to non-biospecific transmembrane stimulation. Longer UV irradiation exposures of the copolymers and higher concentrations of the polymers, with higher contents of the photodissociable group, resulted in more Ca(2+) inflow with little cellular damage. The photo-cation generatable copolymers developed here made possible to control the non-biospecific interaction with endothelial cell membranes by UV irradiation condition, and composition and amount of the copolymer.