PEGylation Confers Greatly Extended Half-Life and Attenuated Immunogenicity to Recombinant Methioninase in Primates

The potential of methioninase for cancer treatment

Cancer cells are addicted to L-methionine (L-Met) and have a much greater requirement for L-Met than normal cells due to excess transmethylation, termed the Hoffman effect. By targeting this vulnerability through dietary restriction of L-Met, researchers have been able to achieve promising results in inhibiting tumor growth and eradicating cancer cells. Methioninase (EC 4.4.1.11; METase) catalyzes the transformation of L-Met into α-ketobutyrate, ammonia, and methanethiol. The use of METase was initially limited due to its poor stability in vivo, high immunogenicity, and enzyme-induced inactivating antibodies. These issues could be partially resolved by PEGylation, encapsulation in erythrocytes, and various site-directed mutagenesis. The big breakthrough came when it was discovered that METase is effectively administered orally. The enzyme L-asparaginase is approved by the FDA for treatment of acute lymphoblastic leukemia. METase has more potential as a therapeutic since addiction to L-Met is a general and fundamental hallmark of cancer.

A review on L-methioninase in cancer therapy: Precision targeting, advancements and diverse applications for a promising future

Cancer remains a global health challenge, demanding novel therapeutic options due to the debilitating side effects of conventional treatments on healthy tissues. The review highlights the potential of L-methioninase, a pyridoxal-5-phosphate (PLP)-dependent enzyme, as a promising avenue in alternative cancer therapy. L-methioninase offers a unique advantage, its ability to selectively target and inhibit the growth of cancer cells without harming healthy cells. This selectivity arises because tumor cells lack an essential enzyme called methionine synthase, which healthy cells use to make the vital amino acid L-methionine. Several sources harbor L-methioninase, including bacteria, fungi, plants, and protozoa. Future research efforts can explore and exploit this diverse range of sources to improve the therapeutic potential of L-methioninase in the fight against cancer. Despite challenges, research actively explores microbial L-methioninase for its anticancer potential. This review examines the enzyme's side effects, advancements in combination therapies, recombinant technologies, polymer conjugation and novel delivery methods like nanoparticles, while highlighting the success of oral administration in preclinical trials. Beyond its promising role in cancer therapy, L-methioninase holds potential applications in food science, antioxidants, and various health concerns like diabetes, cardiovascular issues, and neurodegenerative diseases. This review provides a piece of current knowledge and future prospects of L-methioninase, exploring its diverse therapeutic potential.

Targeting Methionine Addiction of Cancer Cells with Methioninase

All types of cancer cells are addicted to methionine, which is known as the Hoffman effect. Restricting methionine inhibits the growth and proliferation of all tested types of cancer cells, leaving normal cells unaffected. Targeting methionine addiction with methioninase (METase), either alone or in combination with common cancer chemotherapy drugs, has been shown as an effective and safe therapy in various types of cancer cells and animal cancer models. About six years ago, recombinant METase (rMETase) was found to be able to be taken orally as a supplement, resulting in anecdotal positive results in patients with advanced cancer. Currently, there are 8 published clinical studies on METase, including two from the 1990s and six more recent ones. This review focuses on the results of clinical studies on METase-mediated methionine restriction, in particular, on the dosage of oral rMETase taken alone as a supplement or in combination with common chemotherapeutic agents in patients with advanced cancer.

Dietary Manipulation of Amino Acids for Cancer Therapy

Cancer cells cannot proliferate and survive unless they obtain sufficient levels of the 20 proteinogenic amino acids (AAs). Unlike normal cells, cancer cells have genetic and metabolic alterations that may limit their capacity to obtain adequate levels of the 20 AAs in challenging metabolic environments. However, since normal diets provide all AAs at relatively constant levels and ratios, these potentially lethal genetic and metabolic defects are eventually harmless to cancer cells. If we temporarily replace the normal diet of cancer patients with artificial diets in which the levels of specific AAs are manipulated, cancer cells may be unable to proliferate and survive. This article reviews in vivo studies that have evaluated the antitumor activity of diets restricted in or supplemented with the 20 proteinogenic AAs, individually and in combination. It also reviews our recent studies that show that manipulating the levels of several AAs simultaneously can lead to marked survival improvements in mice with metastatic cancers.

Targeted deprivation of methionine with engineered Salmonella leads to oncolysis and suppression of metastasis in broad types of animal tumor models

The strong dependency of almost all malignant tumors on methionine potentially offers a pathway for cancer treatment. We engineer an attenuated strain of Salmonella typhimurium to overexpress an L-methioninase with the aim of specifically depriving tumor tissues of methionine. The engineered microbes target solid tumors and induce a sharp regression in several very divergent animal models of human carcinomas, cause a significant decrease in tumor cell invasion, and essentially eliminate the growth and metastasis of these tumors. RNA sequencing analyses reveal that the engineered Salmonella reduce the expression of a series of genes promoting cell growth, cell migration, and invasion. These findings point to a potential treatment modality for many metastatic solid tumors, which warrants further tests in clinical trials.

IL-2K35C-moFA, a Long-Acting Engineered Cytokine with Decreased Interleukin 2 Receptor α Binding, Improved the Cellular Selectivity Profile and Antitumor Efficacy in a Mouse Tumor Model

Simple Summary

The application of IL-2 for treating cancer is limited owing to its toxicity and short half-life. Its high binding ability to IL-2 receptor α expands immunosuppressive Treg cells, which represents an undesirable toxicity in cancer immunotherapy. Moreover, its small molecular size is the reason for its short half-life. We solved these problems by using a covalent modification strategy of IL-2 variant IL-2K35C with fatty acid by maleimide chemistry, namely, IL-2K35C-moFA. The experiments performed in vitro and in vivo proved that IL-2K35C-moFA is a novel immunotherapeutic agent with the potential to selectively stimulate CD8⁺ T cells and NK cells. Compared to IL-2WT, IL-2K35C-moFA showed a specifically reduced potency for the stimulation of Treg cells. Our results also showed that fatty acid conjugation appears to be effective in half-life extension. The combination of selective lymphocyte expansion and its long half-life means IL-2K35C-moFA should be evaluated as a potential human immunotherapeutic in the future.

Abstract

Human interleukin 2 (IL-2) has shown impressive results as a therapeutic agent for cancer. However, IL-2-based cancer therapy is limited by strong Treg amplification owing to its high binding affinity to IL-2 receptor α (IL-2Rα) and its short half-life owing to its small molecular size. In this study, we solved these problems using a covalent modification strategy of the IL-2 variant, i.e., substituting cysteine (C) for lysine (K) at position 35, using octadecanedicarboxylic acid through maleimide chemistry, creating IL-2K35C-moFA. IL-2K35C-moFA was equipotent to human IL-2 wild type (IL-2WT) in activating tumor-killing CD8⁺ memory effector T cells (CD8⁺ T) and NK cells bearing the intermediate affinity IL-2 receptors, and less potent than IL-2WT on CTLL-2 cells bearing the high-affinity IL-2 receptors. Moreover, it was shown to support the preferential activation of IL-2 receptor β (IL-2Rβ) over IL-2Rα because of the mutation and fatty acid conjugation. In a B16F10 murine tumor model, IL-2K35C-moFA showed efficacy as a single dose and provided durable immunity for 1 week. Our results support the further evaluation of IL-2K35C-moFA as a novel cancer immunotherapy.

Targeting amino acid metabolism in cancer

Metabolic rewiring is a characteristic hallmark of cancer cells. This phenomenon sustains uncontrolled proliferation and resistance to apoptosis by increasing nutrients and energy supply. However, reprogramming comes together with vulnerabilities that can be used against tumor and can be applied in targeted therapy. In the last years, the genetic background of tumors has been identified thoroughly and new therapies targeting those mutations tested. Nevertheless, we propose that targeting the phenotype of cancer cells could be another way of treatment aiming to avoid drug resistance and non-responsiveness of cancer patients. Amino acid metabolism is part of the altered processes in cancer cells. Amino acids are building blocks and also sensors of signaling pathways regulating main biological processes. In this comprehensive review, we described four amino acids (asparagine, arginine, methionine, and cysteine) which have been actively investigated as potential targets for anti-tumor therapy. Asparagine depletion is successfully used for decades in the treatment of acute lymphoblastic leukemia and there is a strong implication to apply it to other types of tumors. Arginine auxotrophic tumors are great candidates for arginine-starvation therapy. Higher requirement for essential amino acids such as methionine and cysteine point out promising targetable weaknesses of cancer cells.

Photoimmunotherapy Retains Its Anti-Tumor Efficacy with Increasing Stromal Content in Heterotypic Pancreatic Cancer Spheroids

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease characterized by increased levels of desmoplasia that contribute to reduced drug delivery and poor treatment outcomes. In PDAC, the stromal content can account for up to 90% of the total tumor volume. The complex interplay between stromal components, including pancreatic cancer-associated fibroblasts (PCAFs), and PDAC cells in the tumor microenvironment has a significant impact on the prognoses and thus needs to be recapitulated in vitro when evaluating various treatment strategies. This study is a systematic evaluation of photodynamic therapy (PDT) in 3D heterotypic coculture models of PDAC with varying ratios of patient-derived PCAFs that simulate heterogeneous PDAC tumors with increasing stromal content. The efficacy of antibody-targeted PDT (photoimmunotherapy; PIT) using cetuximab (a clinically approved anti-EGFR antibody) photoimmunoconjugates (PICs) of a benzoporphyrin derivative (BPD) is contrasted with that of liposomal BPD (Visudyne), which is currently in clinical trials for PDT of PDAC. We demonstrate that both Visudyne-PDT and PIT were effective in heterotypic PDAC 3D spheroids with a low stromal content. However, as the stromal content increases above 50% in the 3D spheroids, the efficacy of Visudyne-PDT is reduced by up to 10-fold, while PIT retains its efficacy. PIT was found to be 10-, 19-, and 14-fold more phototoxic in spheroids with 50, 75, and 90% PCAFs, respectively, as compared to Visudyne-PDT. This marked difference in efficacy is attributed to the ability of PICs to penetrate and distribute homogeneously within spheroids with a higher stromal content and the mechanistically different modes of action of the two formulations. This study thus demonstrates how the stromal content in PDAC spheroids directly impacts their responsiveness to PDT and proposes PIT to be a highly suited treatment option for desmoplastic tumors with particularly high degrees of stromal content.

The past, present, and future of enzyme-based therapies

Enzyme-based therapeutics (EBTs) have the potential to tap into an almost unmeasurable amount of enzyme biodiversity and treat myriad conditions. Although EBTs were some of the first biologics used clinically, the rate of development of newer EBTs has lagged behind that of other biologics. Here, we review the history of EBTs, and discuss the state of each class of EBT, their potential clinical advantages, and the unique challenges to their development. Additionally, we discuss key remaining technical barriers that, if addressed, could increase the diversity and rate of the development of EBTs.

Use of Exogenous Enzymes in Human Therapy: Approved Drugs and Potential Applications

The development of safe and efficacious enzyme-based human therapies has increased greatly in the last decades, thanks to remarkable advances in the understanding of the molecular mechanisms responsible for different diseases, and the characterization of the catalytic activity of relevant exogenous enzymes that may play a remedial effect in the treatment of such pathologies. Several enzyme-based biotherapeutics have been approved by FDA (the U.S. Food and Drug Administration) and EMA (the European Medicines Agency) and many are undergoing clinical trials. Apart from enzyme replacement therapy in human genetic diseases, which is not discussed in this review, approved enzymes for human therapy find applications in several fields, from cancer therapy to thrombolysis and the treatment, e.g., of clotting disorders, cystic fibrosis, lactose intolerance and collagen-based disorders. The majority of therapeutic enzymes are of microbial origin, the most convenient source due to fast, simple and cost-effective production and manipulation. The use of microbial recombinant enzymes has broadened prospects for human therapy but some hurdles such as high immunogenicity, protein instability, short half-life and low substrate affinity, still need to be tackled. Alternative sources of enzymes, with reduced side effects and improved activity, as well as genetic modification of the enzymes and novel delivery systems are constantly searched. Chemical modification strategies, targeted- and/or nanocarrier-mediated delivery, directed evolution and site-specific mutagenesis, fusion proteins generated by genetic manipulation are the most explored tools to reduce toxicity and improve bioavailability and cellular targeting. This review provides a description of exogenous enzymes that are presently employed for the therapeutic management of human diseases with their current FDA/EMA-approved status, along with those already experimented at the clinical level and potential promising candidates.

Chronic Treatment of an Advanced Prostate-cancer Patient With Oral Methioninase Resulted in Long-term Stabilization of Rapidly Rising PSA Levels

BACKGROUND/AIM

Advanced prostate cancer is a recalcitrant disease with very limited treatment options. Our laboratory discovered methionine addiction, presumably a characteristic of all cancer types, including prostate cancer, which can be targeted by methionine restriction (MR), through treatment with oral recombinant methioninase (o-rMETase).

PATIENTS AND METHODS

o-rMETase was produced by fermentation of recombinant E. coli containing the Pseudomonas putida methioninase gene, and purified by column chromatography. An advanced prostate cancer patient received o-rMETase as a supplement, 500 units per day, divided into two oral doses of 250 units each.

RESULTS

Before treatment, the patient had a rapid rise in PSA levels, from 39 to 56 ng/ml, within 6 weeks. At the 15^th week of o-rMETase administration, the PSA levels stabilized at 62 ng/ml. No overt side effects were observed.

CONCLUSION

o-rMETase single treatment can be beneficial for advanced prostate cancer patients.

Proglucagon-Derived Peptides as Therapeutics

Initially discovered as an impurity in insulin preparations, our understanding of the hyperglycaemic hormone glucagon has evolved markedly over subsequent decades. With description of the precursor proglucagon, we now appreciate that glucagon was just the first proglucagon-derived peptide (PGDP) to be characterised. Other bioactive members of the PGDP family include glucagon-like peptides -1 and -2 (GLP-1 and GLP-2), oxyntomodulin (OXM), glicentin and glicentin-related pancreatic peptide (GRPP), with these being produced via tissue-specific processing of proglucagon by the prohormone convertase (PC) enzymes, PC1/3 and PC2. PGDP peptides exert unique physiological effects that influence metabolism and energy regulation, which has witnessed several of them exploited in the form of long-acting, enzymatically resistant analogues for treatment of various pathologies. As such, intramuscular glucagon is well established in rescue of hypoglycaemia, while GLP-2 analogues are indicated in the management of short bowel syndrome. Furthermore, since approval of the first GLP-1 mimetic for the management of Type 2 diabetes mellitus (T2DM) in 2005, GLP-1 therapeutics have become a mainstay of T2DM management due to multifaceted and sustainable improvements in glycaemia, appetite control and weight loss. More recently, longer-acting PGDP therapeutics have been developed, while newfound benefits on cardioprotection, bone health, renal and liver function and cognition have been uncovered. In the present article, we discuss the physiology of PGDP peptides and their therapeutic applications, with a focus on successful design of analogues including dual and triple PGDP receptor agonists currently in clinical development.

Combination Methionine-methylation-axis Blockade: A Novel Approach to Target the Methionine Addiction of Cancer

BACKGROUND/AIM

Cancers are selectively sensitive to methionine (MET) restriction (MR) due to their addiction to MET which is overused for elevated methylation reactions. MET addiction of cancer was discovered by us 45 years ago. MR of cancer results in depletion of S-adenosylmethionine (SAM) for transmethylation reactions, resulting in selective cancer-growth arrest in the late S/G₂-phase of the cell cycle. The aim of the present study was to determine if blockade of the MET-methylation axis is a highly-effective strategy for cancer chemotherapy.

MATERIALS AND METHODS

In the present study, we demonstrated the efficacy of MET-methylation-axis blockade using MR by oral-recombinant methioninase (o-rMETase) combined with decitabine (DAC), an inhibitor of DNA methylation, and an inhibitor of SAM synthesis, cycloleucine (CL). We determined a proof-of-concept of the efficacy of the MET-methylation-axis blockade on a recalcitrant undifferentiated/unclassified soft-tissue sarcoma (USTS) patient-derived orthotopic xenograft (PDOX) mouse model.

RESULTS

The o-rMETase-CL-DAC combination regressed the USTS PDOX with extensive cancer necrosis.

CONCLUSION

The new concept of combination MET-methylation-axis blockade is effective and can now be tested on many types of recalcitrant cancer.

Response of Triple-negative Breast Cancer Liver Metastasis to Oral Recombinant Methioninase in a Patient-derived Orthotopic Xenograft (PDOX) Model

BACKGROUND/AIM

The aim of this study was to establish a patient-derived orthotopic xenograft (PDOX) mouse model of liver metastasis of triple-negative breast cancer (TNBC) and examine the efficacy of oral recombinant methioninase (o-rMETase) on the liver metastasis.

MATERIALS AND METHODS

TNBC from a patient was implanted in the left hepatic lobe of nude mice to simulate liver metastasis in a PDOX model. Ten days later, all mice underwent laparotomy to measure tumor size and were randomized to three groups: control; o-rMETase 100 U once daily (qd); and o-rMETase 200 U qd. After 9 days of treatment, all mice were sacrificed.

RESULTS

At the end of the treatment period for the liver metastasis, the size of liver metastases was 372.6 mm³ in the control group; 160.0 mm³ in the o-rMETase 100 U group; and 245.3 mm³ in the o-rMETase 200 U group. All mice had ascites and 12 out of 14 mice in all groups had mesenteric lymph-node metastasis, as re-metastasis. The mean body-condition score was 1.5 in the control group; 2.4 in the o-rMETase 100 U group; and 2.6 in the o-rMETase 200 U group (control group vs. o-rMETase 200 U group, p<0.05).

CONCLUSION

The TNBC liver metastasis was highly aggressive resulting in re-metastasis and ascites. o-rMETase tended to inhibit the liver metastasis and significantly improved the mouse body-condition score. This new PDOX model of TNBC liver metastasis will be useful for identifying effective agents for this recalcitrant disease.

Oral Methioninase Inhibits Recurrence in a PDOX Mouse Model of Aggressive Triple-negative Breast Cancer

BACKGROUND/AIM

The aim of the study was to use a triple-negative breast cancer (TNBC) patient-derived orthotopic xenograft (PDOX) model to examine the efficacy of oral recombinant methioninase (o-rMETase) against this recalcitrant disease.

MATERIALS AND METHODS

The TNBC tumor from a patient was implanted in the right 4^th inguinal mammary fat pad of nude mice. Two weeks later, the mice underwent tumorectomy with grossly-negative surgical margins. Two days after tumorectomy the mice were divided in two groups: one control and one treated with o-rMETase.

RESULTS

Tumors recurred in all mice. On day 11, the mean recurrent tumor volumes were 936.7 mm³ in the control group and 450.9 mm³ in the o-rMETase group (p<0.05). On day 15, the mean recurrent tumor volumes were 3392.5 mm³ in the control group and 1603.5 mm³ in the o-rMETase group. The mean recurrent tumor weights were 2.1 g in the control group and 1.1 g in the o-rMETase group on day 15.

CONCLUSION

o-rMETase is an effective adjuvant treatment for aggressive TNBC.

Oral recombinant methioninase increases TRAIL receptor-2 expression to regress pancreatic cancer in combination with agonist tigatuzumab in an orthotopic mouse model

Methionine addiction is a fundamental and general hallmark of cancer. Gene expression analysis showed that methionine restriction (MR) of methionine-addicted cancer cells increases TNF-related apoptosis-induced ligand receptor-2 (TRAIL-R2) expression. Here, we determined the effects of MR on TRAIL-R2 targeted therapy in pancreatic cancer by the TRAIL-R2 agonist tigatuzumab. Human pancreatic cancer cell lines were cultured in control or methionine-free medium. The effects of MR on TRAIL-R2 expression and sensitivity to tigatuzumab were evaluated in vitro. An orthotopic pancreatic cancer mouse model was established to evaluate the efficacy of MR using oral recombinant methioninase (o-rMETase), and the efficacy of tigatuzumab and their combination. MR enabled tigatuzumab-induced apoptosis, by increasing TRAIL-R2 expression in pancreatic cancer cells in vitro. The protein expression level of the melanoma-associated antigen MAGED2, which reduces TRAIL-R2 expression, was decreased by MR. In the orthotopic pancreatic cancer mouse model, o-rMETase increased TRAIL-R2 expression level in the tumors and enabled the antitumor efficacy of tigatuzumab. MR, effected by o-rMETase, enabled the efficacy of the TRAIL-R2 agonist tigatuzumab by increasing TRAIL-R2 expression in pancreatic cancer. Our results suggest that o-rMETase has clinical potential for treating pancreatic cancer.

Pharmacokinetics of Polyethylene Glycol-Modified Canine Uricase Following Single and Multiple Intravenous Injections in Cynomolgus Monkeys

BACKGROUND AND OBJECTIVE

Polyethylene glycol-modified canine uricase (PEG-UHC) prepared with a lower-molecular-weight (5 kDa) PEG is used to treat gout. This study investigated the comparative pharmacokinetics of single and multiple doses of PEG-UHC administered intravenously and a single dose of uricase (UHC) administered intravenously in cynomolgus monkeys.

METHODS

A noncompartmental model was used to fit the plasma drug concentration-time curve and calculate the pharmacokinetic parameters of PEG-UHC, which were compared with those obtained for UHC at the equivalent dose (2 mg/kg). To study the pharmacokinetics after multiple dose administration, cynomolgus monkeys were administered five intravenous injections of PEG-UHC (0.5 mg/kg), with one injection performed every 15 days.

RESULTS

The area under the curve (AUC) and the maximum plasma concentration (C_max) of PEG-UHC were positively correlated with dose, whereas plasma half-life (t_1/2) and clearance (CL) did not change significantly with increasing dose, suggesting that these pharmacokinetic characteristics are linear. Intravenous PEG-UHC exhibited an average t_1/2 that was 125.79 times longer and an AUC_0-t that was 64.45 times larger than the corresponding values for UHC at the same dose (2 mg/kg), while the CL of PEG-UHC was 1/72.73 times the CL of intravenous UHC. The plasma drug concentration reached a steady state after five injections, and the t_1/2 values following the first and last drug administration did not differ significantly.

CONCLUSION

Our data show that PEG-UHC is markedly superior to UHC in terms of duration of action, and that the pharmacokinetics of PEG-UHC in cynomolgus monkeys are linear. Sequential administration of PEG-UHC did not accelerate drug clearance. Our findings provide the basis for future clinical studies of PEG-UHC.

Catalytic Roles of Coenzyme Pyridoxal-5'-phosphate (PLP) in PLP-dependent Enzymes: Reaction Pathway for Methionine-γ-lyase-catalyzed L-methionine Depletion

Pyridoxal-5'-phosphate (PLP), the active form of vitamin B₆, is an important and versatile coenzyme involved in a variety of enzymatic reactions, accounting for about 4% of all classified activities. However, the detailed catalytic reaction pathways for PLP-dependent enzymes remain to be explored. Methionine-γ-lyase (MGL), a promising alternative anti-tumor agent to conventional chemotherapies whose catalytic mechanism is highly desired for guiding further development of re-engineered enzymes, was used as a representative PLP-dependent enzyme, and the catalytic mechanism for L-Met elimination by MGL was explored at the first-principles quantum mechanical/molecular mechanical (QM/MM) level with umbrella sampling. The QM/MM calculations revealed that the enzymatic reaction pathway consists of 4 stages for a total of 19 reaction steps with five intermediates captured in available crystal structures. Furthermore, the more comprehensive role of PLP was revealed. Besides the commonly known role of "electron sink", coenzyme PLP can also assist proton transfer and temporarily store the excess proton generated in some intermediate states by using its hydroxyl group and phosphate group. Thus, PLP is participated in most of the 19 steps. This study not only provided a theoretical basis for further development and re-engineering MGL as a potential anti-tumor agent, but also revealed the comprehensive role of PLP which could be used to explore the mechanisms of other PLP-dependent enzymes.

Nonclinical immunogenicity risk assessment of therapeutic proteins

Therapeutic protein drugs have significantly improved the management of many severe and chronic diseases. However, their development and optimal clinical application are complicated by the induction of unwanted immune responses. Therapeutic protein-induced antidrug antibodies can alter drug pharmacokinetics and pharmacodynamics leading to impaired efficacy and occasionally serious safety issues. There has been a growing interest over the past decade in developing methods to assess the risk of unwanted immunogenicity during preclinical drug development, with the aim to mitigate the risk during the molecular design phase, clinical development and when products reach the market. Here, we discuss approaches to therapeutic protein immunogenicity risk assessment, with attention to assays and in vivo models used to mitigate this risk.

Doxebo (doxorubicin-free Doxil-like liposomes) is safe to use as a pre-treatment to prevent infusion reactions to PEGylated nanodrugs

The increasing use in the last decade of PEGylated nanodrugs such as Doxil® has seen a rise in the number of associated occurrences of hypersensitivity reactions (HSRs). These reactions (also called infusion reactions or IR), can range from harmless symptoms to life-threatening reactions. Current means to prevent IR include the prophylactic use of antihistamines and steroids, but they cannot ensure total prevention. We previously showed that an intravenous injection of doxorubicin-free Doxil-like PEGylated nano-liposomes (Doxebo) prior to Doxil treatment suppresses Doxil-induced complement activation-related pseudoallergy (CARPA) in pigs, a model of human hypersensitivity reactions to Doxil. However, in order to use Doxebo to prevent Doxil-induced IR, we have to prove its safety and that it does not affect Doxil's performance. Here we show that Doxebo itself does not have toxic effects on the host or tumor, and it does not interfere with Doxil's antitumor activity in mice. Blood, microscopic and macroscopic organ evaluation of rats after repeated administration confirm the lack of intrinsic adverse effect of Doxebo. Likewise, the repeated injection of Doxebo before Doxil did not impact Doxil's pharmacokinetics in plasma and therefore does not cause accelerated blood clearance (ABC). Taken together with our previous publications, these data suggest that the injection of Doxebo prior to Doxil administration can help protect against Doxil-induced IR without adversely affecting treatment efficacy and safety.

Biomedical applications of nanoflares: Targeted intracellular fluorescence probes

Nanoflares are intracellular probes consisting of oligonucleotides immobilized on various nanoparticles that can recognize intracellular nucleic acids or other analytes, thus releasing a fluorescent reporter dye. Single-stranded DNA (ssDNA) complementary to mRNA for a target gene is constructed containing a 3'-thiol for binding to gold nanoparticles. The ssDNA "recognition sequence" is prehybridized to a shorter DNA complement containing a fluorescent dye that is quenched. The functionalized gold nanoparticles are easily taken up into cells. When the ssDNA recognizes its complementary target, the fluorescent dye is released inside the cells. Different intracellular targets can be detected by nanoflares, such as mRNAs coding for genes over-expressed in cancer (epithelial-mesenchymal transition, oncogenes, thymidine kinase, telomerase, etc.), intracellular levels of ATP, pH values and inorganic ions can also be measured. Advantages include high transfection efficiency, enzymatic stability, good optical properties, biocompatibility, high selectivity and specificity. Multiplexed assays and FRET-based systems have been designed.

Lipo-PEG-PEI complex as an intracellular transporter for protein therapeutics

Background

Protein or peptide drugs are emerging therapeutics for treating human diseases. However, current protein drugs are typically limited to acting on extracellular/cell membrane components associated with the diseases, while intracellular delivery of recombinant proteins replaces or replenishes faulty/missing proteins and remains inadequate. In this study, we developed a convenient and efficient intracellular protein delivery vehicle.

Materials and methods

A cationic liposomal polyethylenimine and polyethylene glycol complex (LPPC) was developed to noncovalently capture proteins for protein transfer into cells via endocytosis. β-glucuronidase (βG) was used in vitro and in vivo as a model enzyme to demonstrate the enzymatic activity of the intracellular transport of a protein.

Results

The endocytosed protein/LPPC complexes escaped from lysosomes, and the bound protein dissociated from LPPC in the cytosol. The enzymatic activity of βG was well preserved after intracellular delivery in vitro and in vivo.

Conclusion

Using LPPC as an intracellular protein transporter for protein therapeutics, we illustrated that LPPC may be an effective and convenient tool for studying diseases and developing therapeutics.

Enzymes in Metabolic Anticancer Therapy

Cancer treatment has greatly improved over the last 50 years, but it remains challenging in several cases. Useful therapeutic targets are normally unique peculiarities of cancer cells that distinguish them from normal cells and that can be tackled with appropriate drugs. It is now known that cell metabolism is rewired during tumorigenesis and metastasis as a consequence of oncogene activation and oncosuppressors inactivation, leading to a new cellular homeostasis typically directed towards anabolism. Because of these modifications, cells can become strongly or absolutely dependent on specific substrates, like sugars, lipids or amino acids. Cancer addictions are a relevant target for therapy, as removal of an essential substrate can lead to their selective cell-cycle arrest or even to cell death, leaving normal cells untouched. Enzymes can act as powerful agents in this respect, as demonstrated by asparaginase, which has been included in the treatment of Acute Lymphoblastic Leukemia for half a century. In this review, a short outline of cancer addictions will be provided, focusing on the main cancer amino acid dependencies described so far. Therapeutic enzymes which have been already experimented at the clinical level will be discussed, along with novel potential candidates that we propose as new promising molecules. The intrinsic limitations of their present molecular forms, along with molecular engineering solutions to explore, will also be presented.

Safety and Toxicity of Recombinant Methioninase and Polyethylene Glycol (PEG) Recombinant Methioninase in Primates

Methionine (MET) is a general metabolic therapeutic target in cancer, whereby cancer cells have an elevated requirement for MET, termed MET dependence. We have developed recombinant L-methionine α-deamino-γ-mercaptomethane lyase (recombinant methioninase [rMETase, EC 4.4.1.11]) as targeted therapy of all cancer types. Pharmacokinetics, MET depletion, antigenicity, and toxicity of rMETase were examined in macaque monkeys. Pharmacokinetic analysis showed that rMETase was eliminated with a T_1/2 of 2.49 h. A 2-week i.v. administration of 4000 units/kg every 8 h/day for 2 weeks resulted in a steady-state depletion of plasma MET to less than 2 μM. The only manifest toxicity was decreased food intake and slight weight loss. Serum albumin and red-cell values declined transiently during treatment. Rechallenge on day 28 resulted in anaphylactic shock and death in one animal. Pretreatment with hydrocortisone prevented the anaphylactic reaction. Anti-rMETase antibodies (at 10^-3) were found after the first challenge, increased to 10^-6 after the fourth challenge, and decreased to 10^-2 by 2 months post-therapy. Therefore, the therapeutic potential of rMETase is limited by its short plasma half-life and immunologic effects, including high antibody production in mice and anaphylactic reactions in monkeys. To overcome these limits, rMETase has been coupled to methoxypolyethylene glycol succinimidyl glutarate polyethylene glycol (MEGC-PEG-5000). The pharmacokinetics, antigenicity, and toxicity of MEGC-PEG-rMETase in macaque monkeys were evaluated using an escalating-dose strategy. In pharmacokinetic studies, a single 4000 units/kg dose showed that MEGC-PEG-rMETase holoenzyme activity was eliminated with a biological half-life of 1.3 h, and the MEGC-PEG-rMETase apoenzyme was eliminated with a biological half-life of 90 h, a 36-fold increase compared with non-PEGylated rMETase. The disparity in the T_½ of the apoenzyme and the holoenzyme reflects the loss of co-factor pyridoxal-L-phosphate of the circulating MEGC-PEG-rMETase. A 7-day i.v. administration of 4000 units/kg every 12 h resulted in a steady-state depletion of plasma MET to <5 μmol/L. The only manifest toxicity was decreased food intake and slight weight loss. Red cell values and hemoglobin declined transiently. Subsequent challenges did not result in any immunologic reactions. Anti-MEGC-PEG-rMETase antibodies were 100- to 1000-fold less than antibodies elicited by naked rMETase, thereby suggesting clinical potential of MEGC-PEG-rMETase as a broad anticancer agent.

Redox Responsive Polymersomes for Enhanced Doxorubicin Delivery

In the present investigation, the potential of a novel, self-assembled, biocompatible, and redox-sensitive copolymer system with disulfide bond was explored for doxorubicin (DOX) delivery through polymersome nanostructures of ∼120 nm. The polymer system was synthesized with less steps, providing a high yield of 86%. The developed polymersomes showed admirable biocompatibility with high dose tolerability in vitro and in vivo. The colloidal stability of DOX-loaded polymersomes depicted a stable and uniform particle size over a period of 72 h. The cellular internalization of polymersomes was assessed in HeLa and MDA-MB-231 cell lines, where enhanced cellular internalization was observed. The dose-dependent cytotoxicity was observed for DOX-loaded polymersomes by MTT cytotoxicity assay in the above cell lines. The tumor suppression studies were assessed in Ehrlich ascites tumor (EAT) carrying Swiss albino mice, where polymersomes exhibited a 7.16-fold reduction in tumor volume correlated with control and 5.39-fold higher tumor inhibition capacity compared to conventional chemotherapy (free DOX treatment). The developed polymersomes gave safer insights concerning DOX associated toxicities by histopathology and serum biochemistry analysis. Thus, results focus on the potential of redox responsive polymersomes for efficacious and improved DOX therapy with enhanced antitumor activity and insignificant cardiotoxicity which can be translated to clinical settings.

Hyaluronic acid-modified polyamidoamine dendrimer G5-entrapped gold nanoparticles delivering METase gene inhibits gastric tumor growth via targeting CD44+ gastric cancer cells

BACKGROUND

Gastric cancer (GC) is the second most common leading cause of cancer-related death. Cancer stem cell (CSC) with the mark of CD44 played an important role in GC. rMETase was wildly exploited as chemotherapeutic option for GC. Polymers synthetic nanoparticle drug delivery systems have been commonly used for cancer therapy. With the decorating of Hyaluronic acid (HA), a receptor of CD44, nanoparticles exhibit with good biocompatibility and aqueous solubility.

METHODS

The characteristic of nanoparticles (NPs) was analyzed by TEM and DLS. The viability and proliferation of GC cells were examined by MTT assays. The levels of CD44, Cyt C, and c-caspase 3 were examined by Western blot. The level of ROS was measured by DCFH-DA assays. The morphology of tissues was detected using hematoxylin-eosin (H&E) stain. Nude mice xenograft models were used to evaluate the effect of HA-PAMAM-Au-METase on GC.

RESULTS

The transfection of rMETase carried by HA-G5 PAMAM-Au visibly inhibited the proliferation and tumorsphere formation of GC cells through obviously enhancing METase activity. Elevation of METase activity suppressed the proliferation of CD44(+) GC cells through down-regulating MET in cellular supernatant that resulted in the increase of Cyc C and ROS levels. The number of CD44(+) GC cells in nude mice injected with G5 PAMAM-Au-METase decorated by HA was markly declined resulting in the inhibition of tumor growth.

CONCLUSION

HA-G5 PAMAM-Au-METase significantly suppressed tumor growth of GC by targeted damaging the mitochondrial function of CD44(+) gastric CSCs.

Exploiting methionine restriction for cancer treatment

Normal cells can synthesize sufficient methionine for growth requirements from homocysteine and 5-methyltetrahydrofolate and vitamin B12. However, many cancer-cell types require exogenous methionine for survival and therefore methionine restriction is a promising avenue for treatment. While the lack of the methionine salvage enzyme methylthioadenosine phosphorylase (MTAP) deficiency is associated with methionine dependence in cancer cells, there are other causes for tumors to require exogenous methionine. In this review we describe studies that show restricting methionine to certain cancers by diet or by enzyme depletion, alone or in combination with certain chemotherapeutics is a promising antitumor strategy. The basis for methionine dependence in tumor cells is also briefly reviewed.

Antimicrobial peptides with selective antitumor mechanisms: prospect for anticancer applications

In the last several decades, there have been significant advances in anticancer therapy. However, the development of resistance to cancer drugs and the lack of specificity related to actively dividing cells leading to toxic side effects have undermined these achievements. As a result, there is considerable interest in alternative drugs with novel antitumor mechanisms. In addition to the recent approach using immunotherapy, an effective but much cheaper therapeutic option of pharmaceutical drugs would still provide the best choice for cancer patients as the first line treatment. Ribosomally synthesized cationic antimicrobial peptides (AMPs) or host defense peptides (HDP) display broad-spectrum activity against bacteria based on electrostatic interactions with negatively charged lipids on the bacterial surface. Because of increased proportions of phosphatidylserine (negatively charged) on the surface of cancer cells compared to normal cells, cationic amphipathic peptides could be an effective source of anticancer agents that are both selective and refractory to current resistance mechanisms. We reviewed herein the prospect for AMP application to cancer treatment, with a focus on modes of action of cationic AMPs.

Recombinant methioninase combined with doxorubicin (DOX) regresses a DOX-resistant synovial sarcoma in a patient-derived orthotopic xenograft (PDOX) mouse model

Synovial sarcoma (SS) is a recalcitrant subgroup of soft tissue sarcoma (STS). A tumor from a patient with high grade SS from a lower extremity was grown orthotopically in the right biceps femoris muscle of nude mice to establish a patient-derived orthotopic xenograft (PDOX) mouse model. The PDOX mice were randomized into the following groups when tumor volume reached approximately 100 mm³: G1, control without treatment; G2, doxorubicin (DOX) (3 mg/kg, intraperitoneal [i.p.] injection, weekly, for 2 weeks; G3, rMETase (100 unit/mouse, i.p., daily, for 2 weeks); G4 DOX (3mg/kg), i.p. weekly, for 2 weeks) combined with rMETase (100 unit/mouse, i.p., daily, for 2 weeks). On day 14 after treatment initiation, all therapies significantly inhibited tumor growth compared to untreated control, except DOX: (DOX: p = 0.48; rMETase: p < 0.005; DOX combined with rMETase < 0.0001). DOX combined with rMETase was significantly more effective than both DOX alone (p < 0.001) and rMETase alone (p < 0.05). The relative body weight on day 14 compared with day 0 did not significantly differ between any treatment group or untreated control. The results indicate that r-METase can overcome DOX-resistance in this recalcitrant disease.

Anti-CD73 and anti-OX40 immunotherapy coupled with a novel biocompatible enzyme prodrug system for the treatment of recurrent, metastatic ovarian cancer

Approximately 75% of ovarian cancer is diagnosed once metastasis to the peritoneal cavity has occurred. A large proportion of patients eventually develop platinum-resistive tumors, which are considered terminal. In order to provide an alternative a novel fusion protein, mCTH-ANXA5, has been developed for the treatment of recurrent, metastatic ovarian cancer. The fusion protein combines annexin V (ANXA5), an ovarian tumor and tumor vasculature targeting protein, with mutated cystathionine gamma-lyase (mCTH), an enzyme that converts selenomethionine (SeMet) into toxic methylselenol, which generates reactive oxygen species and eventual tumor cell death. In order to further enhance the therapeutic efficacy, anti-CD73 and anti-OX40 immunostimulants were combined with mCTH-ANXA5, resulting in an increase of survival by 100% from 12 to 24 days post-therapy and decrease tumor burden in mice with orthotopic metastatic ovarian cancer. Further evaluation of the combination therapy revealed a strong antibody-mediated immune response, and an increased infiltration of cytotoxic T-cells along with a decrease in tumor promoting immune cells. This study demonstrates the efficacy of a synergistic, multi-drug system by attacking the tumor as well as enlisting the body's own defense system to treat the patient.

Antitumor Synergism and Enhanced Survival with a Tumor Vasculature-Targeted Enzyme Prodrug System, Rapamycin, and Cyclophosphamide

Mutant cystathionine gamma-lyase was targeted to phosphatidylserine exposed on tumor vasculature through fusion with Annexin A1 or Annexin A5. Cystathionine gamma-lyase E58N, R118L, and E338N mutations impart nonnative methionine gamma-lyase activity, resulting in tumor-localized generation of highly toxic methylselenol upon systemic administration of nontoxic selenomethionine. The described therapeutic system circumvents systemic toxicity issues using a novel drug delivery/generation approach and avoids the administration of nonnative proteins and/or DNA required with other enzyme prodrug systems. The enzyme fusion exhibits strong and stable in vitro binding with dissociation constants in the nanomolar range for both human and mouse breast cancer cells and in a cell model of tumor vascular endothelium. Daily administration of the therapy suppressed growth of highly aggressive triple-negative murine 4T1 mammary tumors in immunocompetent BALB/cJ mice and MDA-MB-231 tumors in SCID mice. Treatment did not result in the occurrence of negative side effects or the elicitation of neutralizing antibodies. On the basis of the vasculature-targeted nature of the therapy, combinations with rapamycin and cyclophosphamide were evaluated. Rapamycin, an mTOR inhibitor, reduces the prosurvival signaling of cells in a hypoxic environment potentially exacerbated by a vasculature-targeted therapy. IHC revealed, unsurprisingly, a significant hypoxic response (increase in hypoxia-inducible factor 1 α subunit, HIF1A) in the enzyme prodrug-treated tumors and a dramatic reduction of HIF1A upon rapamycin treatment. Cyclophosphamide, an immunomodulator at low doses, was combined with the enzyme prodrug therapy and rapamycin; this combination synergistically reduced tumor volumes, inhibited metastatic progression, and enhanced survival. Mol Cancer Ther; 16(9); 1855-65. ©2017 AACR.

Tuning the Drug Loading and Release of DNA-Assembled Gold-Nanorod Superstructures

The use of DNA to assemble inorganic nanoparticles into superstructures is an emerging strategy to build non-toxic delivery vehicles for targeting diseases in the body. The impact of the core-satellite nanosystem design in mediating drug storage, drug release (via heat), and killing of HeLa cells in culture is investigated.

Recombinant Engineering of L-Methioninase Using Two Different Promoter and Expression Systems and in vitro Analysis of Its Anticancer Efficacy on Different Human Cancer Cell Lines

Recombinant methioninase (rMETase) is an enzyme that has antitumor activity. In this work, METase gene from Pseudomonas putida ATTCC 8209 was cloned to pT7-7 plasmid (yielded, PT7-METase-R7 clone) and expressed in E. coli strain BL21 (DE3). A protein band with a molecular massof 42 kDa was visualized by SDS-PAGE. The applied protocol yielded a total protein of 3.13 g with a recovery of 66.89% and a specific activity of 18.59 U mg-1 which considered as a low yield. However, when the METase gene was cloned to the vector (pTrc99A, clone: pTrc99A-MET-3) cells of E. coli JM109 yielded a total protein of 32.63 g with a recovery of 41.62% and a specific activity of 54.86 U mg-1 which revealed that the enhancement of METase gene expression by trc promoter was more than the T7 RNA polymerase promoter. The t1/2 of the rMETase was 2 h asanalyzed in mice by IV injection. Antitumor efficacy of rMETase was studied in five human cancer cell lines. At 1 U mL-1 the growth rate of treated colon cancer cell lines, Colo205 and SW620, with rMETase was 46 and 32% relative to control, respectively. With the ovarian cancer cell line (A2780) rMETase produced an inhibition effect of 54% at 1.5 U mL-1. In addition, the growth rate was reduced to 45 and 53% with the skin cancer cell line (A375) and the breast cancer cell line (MCF-7), respectively. These results indicate the feasibility of rMETase for use as a potent antitumor agent.

Biochemical and Pharmacokinetic Properties of PEGylated Cystathionine γ-Lyase from KF723837

Cystathionine &#947;-lyase (CGL) was purified to its electrophoretic homogeneity from<i> Aspergillus carneus</i> by various chromatographic approaches. The purified enzyme has four identical subunits of 52 kDa based on SDS and native PAGE analyses. To improve its structural stability, purified CGL was modified by covalent binding to polyethylene glycol moieties. The specific activity of free-CGL and PEG-CGL was 59.71 and 48.71 U/mg, respectively, with a PEGylation yield of 81.5 and 70.7% modification of surface ε-amino groups. Free- and modified CGL have the same pattern of pH stability (8.0-9.0). At 50°C, the thermal stability [half-life time (T_1/2)] of PEG-CGL was increased by 40% in comparison to free-CGL. The activity of CGL was completely inhibited by hydroxylamine and Hg⁺², with no effect by EDTA. Free-CGL (0.04 m<smlcap>M</smlcap>^-1s^-1) and PEG-CGL (0.03 m<smlcap>M</smlcap>^-1s^-1) have a similar catalytic efficiency to <smlcap>L</smlcap>-cystathionine as a substrate. The inhibition constant values of propargylglycine were 0.31 and 0.52 µ<smlcap>M</smlcap> for the free- and PEG-CGL, respectively. By in vitro proteolysis, PEG-CGL retains >50% of its initial activity compared to <10% of the free-CGL for acid protease for 30 min. From in vivo pharmacokinetics in New Zealand white rabbits, the T_1/2 was 19.1 and 28.9 h for the Holo free-CGL and PEG-CGL, respectively, ensuring the role of PEGylation on shielding the CGL surface from proteolytic attack, reducing its antigenicity, and stabilizing its internal Schiff base. By external infusion of pyridoxal 5′-phosphate (10 µ<smlcap>M</smlcap>), the T_1/2 of free- and PEG-CGL was prolonged to 24 and 33 h, respectively, so dissociation of pyridoxal 5′-phosphate was one of the main causes of loss of enzyme activity. The biochemical and hematological responses of rabbits to free- and PEG-CGL were assessed, with relative similarity to the negative control, confirming the nil toxicity of enzymes. The titer of IgG was duplicated in response to free- versus PEG-CGL after 45 days. To the best of our knowledge, this is the first report concerned with purification and PEGylation of CGL from fungi, with higher affinity for <smlcap>L</smlcap>-cystathionine. With further molecular studies, CGL will be a promising enzyme against various cardiovascular diseases and antioxidant deficiency, as well as for generation of a neurotransmitter (H₂S).

Glioblastoma multiforme: emerging treatments and stratification markers beyond new drugs

Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults. The standard therapy for GBM is maximal surgical resection followed by radiotherapy with concurrent and adjuvant temozolomide (TMZ). In spite of the extensive treatment, the disease is associated with poor clinical outcome. Further intensification of the standard treatment is limited by the infiltrating growth of the GBM in normal brain areas, the expected neurological toxicities with radiation doses >60 Gy and the dose-limiting toxicities induced by systemic therapy. To improve the outcome of patients with GBM, alternative treatment modalities which add low or no additional toxicities to the standard treatment are needed. Many Phase II trials on new chemotherapeutics or targeted drugs have indicated potential efficacy but failed to improve the overall or progression-free survival in Phase III clinical trials. In this review, we will discuss contemporary issues related to recent technical developments and new metabolic strategies for patients with GBM including MR (spectroscopy) imaging, (amino acid) positron emission tomography (PET), amino acid PET, surgery, radiogenomics, particle therapy, radioimmunotherapy and diets.

Shaping bio-inspired nanotechnologies to target thrombosis for dual optical-magnetic resonance imaging

Arterial and venous thrombosis are among the most common causes of death and hospitalization worldwide. Nanotechnology approaches hold great promise for molecular imaging and diagnosis as well as tissue-targeted delivery of therapeutics. In this study, we developed and investigated bioengineered nanoprobes for identifying thrombus formation; the design parameters of nanoparticle shape and surface chemistry, i.e. incorporation of fibrin-binding peptides CREKA and GPRPP, were investigated. Two nanoparticle platforms based on plant viruses were studied - icosahedral cowpea mosaic virus (CPMV) and elongated rod-shaped tobacco mosaic virus (TMV). These particles were loaded to carry contrast agents for dual-modality magnetic resonance (MR) and optical imaging, and both modalities demonstrated specificity of fibrin binding in vitro with the presence of targeting peptides. Preclinical studies in a carotid artery photochemical injury model of thrombosis confirmed thrombus homing of the nanoprobes, with the elongated TMV rods exhibiting significantly greater attachment to thrombi than icosahedral (sphere-like) CPMV. While in vitro studies confirmed fibrin-specificity conferred by the peptide ligands, in vivo studies indicated the nanoparticle shape had the greatest contribution toward thrombus targeting, with no significant contribution from either targeting ligand. These results demonstrate that nanoparticle shape plays a critical role in particle deposition at the site of vascular injury. Shaping nanotechnologies opens the door for the development of novel targeted diagnostic and therapeutic strategies (i.e., theranostics) for arterial and venous thrombosis.

Development of recombinant methioninase to target the general cancer-specific metabolic defect of methionine dependence: a 40-year odyssey

INTRODUCTION

All tested cancer cell types are methionine dependent in that the cells arrest and eventually die when deprived of methionine, a condition that is generally nontoxic to normal cells. Methionine dependence is the only known general metabolic defect in cancer. Methionine-deprived cancer cells arrest at the S/G2 phase, an unusual position for cell cycle arrest. In order to exploit the cancer-specific metabolic defect of methionine dependence, methioninases were developed.

AREAS COVERED

The present Expert Opinion describes the phenomena of methionine dependence and a methioninase cloned from Pseudomonas putida (chemical name: l-methionine α-deamino-γ-mercaptomethane lyase [EC 4.4.1.11]). The cloned methioninase, termed recombinant methioninase, or rMETase, has been tested in mouse models of human cancer as well as in macaque monkeys and a pilot Phase I trial of human cancer patients. Efficacy of rMETase has been demonstrated against various cancer types in mouse models.

EXPERT OPINION

The most promising application of rMETase therapy is in sequential combination therapy, whereby the cancer cells within a tumor are trapped in S/G2 by methioninase treatment and then treated with chemotherapeutic agents active against cells in S/G2.

Purification and immobilization of L-arginase from thermotolerant Penicillium chrysogenum KJ185377.1; with unique kinetic properties as thermostable anticancer enzyme

L-Arginase, hydrolyzing L-arginine to L-ornithine and urea, is a powerful anticancer, L-arginine-depleting agent, against argininosuccinate synthase expressing tumors. Otherwise, the higher antigenicity and lower thermal stability of this enzyme was the main biochemical hurdles. Since, the intrinsic thermal stability of enzymes follow the physiological temperature of their producer, thus, characterization of L-arginase from thermotolerant Penicillium chrysogenum was the objective of this study. L-Arginase (Arg) was purified to its homogeneity from P. chrysogenum by 10.1-fold, with 37.0 kDa under denaturing PAGE, optimum reaction at 50 °C, pH stability (6.8-7.9), with highest molar ratio of constitutional arginine, glutamic acid, lysine and aspartic acid. The purified enzyme was PEGylated and immobilized on chitosan, with 41.9 and 22.1 % yield of immobilization. At 40 °C, the T1/2 value of free-Arg, PEG-Arg and Chit-Arg was 10.4, 15.6, 20.5 h, respectively. The free-Arg and Chit-Arg have a higher affinity to L-arginine (K m 4.8 mM), while, PEG-Arg affinity was decreased by about 3 fold (K m 15.2 mM). The inhibitory constants to the free and PEG-Arg were relatively similar towards HA and PPG. The IC50 for the free enzyme against HEPG-2 and A549 tumor cells was 0.136 and 0.165 U/ml, comparing to 0.232 and 0.496 U/ml for PEG-Arg, respectively. The in vivo T1/2 to the free Arg and PEG-Arg was 16.4 and 20.4 h, respectively as holo-enzyme. The residual L-arginine level upon using free Arg was 156.9 and 144.5 µM, after 6 and 8 h, respectively, regarding to initials at 253.6 µM, while for Peg-Arg the level of L-arginine was nil till 7 h of initial dosing. The titer of IgG was induced by 10-15 % in response to free-Arg after 28 days comparing to IgG titer for PEG-Arg.

Targeted enzyme prodrug therapy for metastatic prostate cancer - a comparative study of L-methioninase, purine nucleoside phosphorylase, and cytosine deaminase

BACKGROUND

Enzyme prodrug therapy shows promise for the treatment of solid tumors, but current approaches lack effective/safe delivery strategies. To address this, we previously developed three enzyme-containing fusion proteins targeted via annexin V to phosphatidylserine exposed on the tumor vasculature and tumor cells, using the enzymes L-methioninase, purine nucleoside phosphorylase, or cytosine deaminase. In enzyme prodrug therapy, the fusion protein is allowed to bind to the tumor before a nontoxic drug precursor, a prodrug, is introduced. Upon interaction of the prodrug with the bound enzyme, an anticancer compound is formed, but only in the direct vicinity of the tumor, thereby mitigating the risk of side effects while creating high intratumoral drug concentrations. The applicability of these enzyme prodrug systems to treating prostate cancer has remained unexplored. Additionally, target availability may increase with the addition of low dose docetaxel treatment to the enzyme prodrug treatment, but this effect has not been previously investigated. To this end, we examined the binding strength and the cytotoxic efficacy (with and without docetaxel treatment) of these enzyme prodrug systems on the human prostate cancer cell line PC-3.

RESULTS

All three fusion proteins exhibited strong binding; dissociation constants were 0.572 nM for L-methioninase-annexin V (MT-AV), 0.406 nM for purine nucleoside phosphorylase-annexin V (PNP-AV), and 0.061 nM for cytosine deaminase-annexin V (CD-AV). MT-AV produced up to 99% cell death (p < 0.001) with limited cytotoxicity of the prodrug alone. PNP-AV with docetaxel created up to 78% cell death (p < 0.001) with no cytotoxicity of the prodrug alone. CD-AV with docetaxel displayed up to 60% cell death (p < 0.001) with no cytotoxicity of the prodrug alone. Docetaxel treatment created significant increases in cytotoxicity for PNP-AV and CD-AV.

CONCLUSIONS

Strong binding of fusion proteins to the prostate cancer cells and effective cell killing suggest that the enzyme prodrug systems with MT-AV and PNP-AV may be effective treatment options. Additionally, low-dose docetaxel treatment was found to increase the cytotoxic effect of the annexin V-targeted therapeutics for the PNP-AV and CD-AV systems.

Multivalent antiviral XTEN-peptide conjugates with long in vivo half-life and enhanced solubility

XTENs are unstructured, nonrepetitive protein polymers designed to prolong the in vivo half-life of pharmaceuticals by introducing a bulking effect similar to that of poly(ethylene glycol). While XTEN can be expressed as a recombinant fusion protein with bioactive proteins and peptides, therapeutic molecules of interest can also be chemically conjugated to XTEN. Such an approach permits precise control over the positioning, spacing, and valency of bioactive moieties along the length of XTEN. We have demonstrated the attachment of T-20, an anti-retroviral peptide indicated for the treatment of HIV-1 patients with multidrug resistance, to XTEN. By reacting maleimide-functionalized T-20 with cysteine-containing XTENs and varying the number and positioning of cysteines in the XTENs, a library of different peptide–polymer combinations were produced. The T-20-XTEN conjugates were tested using an in vitro antiviral assay and were found to be effective in inhibiting HIV-1 entry and preventing cell death, with the copy number and spacing of the T-20 peptides influencing antiviral activity. The peptide–XTEN conjugates were also discovered to have enhanced solubilities in comparison with the native T-20 peptide. The pharmacokinetic profile of the most active T-20-XTEN conjugate was measured in rats, and it was found to exhibit an elimination half-life of 55.7 ± 17.7 h, almost 20 times longer than the reported half-life for T-20 dosed in rats. As the conjugation of T-20 to XTEN greatly improved the in vivo half-life and solubility of the peptide, the XTEN platform has been demonstrated to be a versatile tool for improving the properties of drugs and enabling the development of a class of next-generation therapeutics.