Doxorubicin coupled to lactosaminated human albumin remains confined within mouse liver cells after the intracellular release from the carrier

Unraveling the versatility of human serum albumin - A comprehensive review of its biological significance and therapeutic potential

Human serum albumin (HSA) is a multi-domain macromolecule with diverse ligand binding capability because of its ability to allow allosteric modulation despite being a monomeric protein. Physiologically, HSA act as the primary carrier for various exogenous and endogenous compounds and fatty acids, and alter the pharmacokinetic properties of several drugs. It has antioxidant properties and is utilized therapeutically to improve the drug delivery of pharmacological agents for the treatment of several disorders. The flexibility of albumin in holding various types of drugs coupled with a variety of modifications makes this protein a versatile drug carrier with incalculable potential in therapeutics. This review provides a brief outline of the different structural properties of HSA, and its various binding sites, moreover, an overview of the genetic, biomedical, and allosteric modulation of drugs and drug delivery aspects of HSA is also included, which may be helpful in guiding advanced clinical applications and further research on the therapeutic potential of this extraordinary protein.

Artificial Glycoproteins as a Scaffold for Targeted Drug Therapy

Akin to a cellular "fingerprint," the glycocalyx is a glycan-enriched cellular coating that plays a crucial role in mediating cell-to-cell interactions. To gain a better understanding of the factors that govern in vivo recognition, artificial glycoproteins were initially created to probe changes made to the accumulation and biodistribution of specific glycan assemblies through biomimicry. As a result, the organ-specific accumulation for a variety of glycoproteins decorated with simple and/or complex glycans was identified. Additionally, binding trends with regard to cancer cell selectivity were also investigated. To exploit the knowledge gained from these studies, numerous groups thus became engaged in developing targeted drug methodologies based on the use of artificial glycoproteins. This has either been done through adopting the glycoprotein scaffold as a drug carrier, or to directly glycosylate therapeutic proteins/enzymes to localize their biological activity. The principle aim of this Review is to present the foundational research that has driven artificial glycoprotein-based targeting and subsequent adaptations with potential therapeutic applications.

Extending Half Life of H-Ferritin Nanoparticle by Fusing Albumin Binding Domain for Doxorubicin Encapsulation

Nanoparticles based on the heavy chain of the human ferritin (HFn) are arousing growing interest in the field of drug delivery due to their exceptional characteristics. However, the unsatisfied plasma half life of HFn substantially limits its application as a delivery platform for antitumor agents. Herein we fused an albumin binding domain (ABD) variant that basically derives from the streptococcal protein G and possesses a long-acting characteristic in serum albumin to the N-terminus of the HFn for the aim of half-life extension. This ABD-HFn construct was highly expressed and fully self-assembled into symmetrical and spherical structure in E. coli bacteria. The purified ABD-HFn showed a similar particle size with wild-type HFn and also exhibited an extremely high binding affinity with human serum albumin. To evaluate the therapeutic potential of this ABD-HFn construct in terms of half-life extension, we encapsulated a model antitumor agent doxorubicin (DOX) into the ABD-HFn. Significantly outstanding loading efficacy of above 60 molecules doxorubicin for each ABD-HFn cage was achieved. The doxorubicin-loaded ABD-HFn nanoparticle was characterized and further compared with the recombinant HFn counterpart. The ABD-HFn/DOX nanoparticle showed dramatically improved stability and comparable cell uptake rate when compared with HFn/DOX counterpart. Pharmacokinetics study in Sprague-Dawley rats showed that ABD-HFn/DOX nanoparticle possessed significantly prolonged plasma half life of ∼17.2 h, exhibiting nearly 19 times longer than that of free doxorubicin and 12 times for HFn/DOX. These optimal results indicated that fusion with ABD will be a promising strategy to extend the half life for protein-based nanoparticles.

Albumin Binding Domain Fusing R/K-X-X-R/K Sequence for Enhancing Tumor Delivery of Doxorubicin

For the purpose of improving the tumor delivery of doxorubicin (DOX), a kind of peptide-DOXO conjugate was designed and prepared, in which the peptide composed of an albumin-binding domain (ABD) and a tumor-specific internalizing sequence (RGDK or RPARPAR) was conjugated to a (6-maleimidocaproyl) hydrazone derivative of doxorubicin (DOXO-EMCH). The doxorubicin uptake by lung cancer cell line of A549 evidenced that the conjugates are capable of being internalized through a tumor-specific sequence mediated manner, and the intracellular imaging of distribution in A549 cell demonstrated that the conjugated doxorubicin can be delivered to the cell nucleus. The A549 cell cytotoxicity of peptide-DOXO conjugates was presented with IC₅₀ values and shown in the range of about 9-11 μM. Pharmacokinetics study revealed that both conjugates exhibited nearly 5.5 times longer half-time than DOX, and about 4 times than DOXO-EMCH. The in vivo growth inhibitions of the two peptide-DOXO conjugates on BALB/c nude mice bearing A549 tumor (47.78% for ABD-RGDK-DOXO and 47.09% for ABD-RPARPAR-DOXO) were much stronger than that of doxorubicin and DOXO-EMCH (24.28% and 25.67% respectively) at a doxorubicin equivalent dose. Besides, the in vivo fluorescence imaging study confirmed that the peptide markedly increased the payload accumulation in tumor tissues and indicated that albumin binding domain fusing tumor-specific sequence effectively enhanced the tumor delivery of doxorubicin and thus improved its therapeutic potency.

The antitumor activity of a lactosaminated albumin conjugate of doxorubicin in a chemically induced hepatocellular carcinoma rat model compared to sorafenib

BACKGROUND

Worldwide, consistent survival benefit for chemotherapy in hepatocellular carcinoma (HCC) is a golden goal for concerned researchers. Nexavar^® (sorafenib) is the only approved agent that achieved touchable successes in this regard. Thus, there is a pressing medical need for new promising drugs to improve HCC therapy.

AIMS

our designed lactosaminated albumin conjugate of doxorubicin (L-HSA-DOXO) that rapidly and preferentially accumulates in the liver is compared, for the first time at its MTD, with doxorubicin and sorafenib, not only for antitumor efficacy but also for overall survival.

METHODS

HCC was induced in male Wistar rats with N-nitrosodiethylamine added to drinking water (100mg/L) for 8 weeks. Endpoints were antitumor efficacy, tolerability and overall survival.

RESULTS

L-HSA-DOXO proved to be superior at least over doxorubicin in the majority of assessed endpoints. Circulating AFP-L3% was diminished in L-HSA-DOXO (14.5%) and sorafenib (18.4%) groups compared to DENA (31.1%) and doxorubicin (29.5%) groups. This superiority was further confirmed by Western blot analyses of some novel HCC biomarkers. Survival study reinforced consistent benefits of both L-HSA-DOXO and sorafenib.

CONCLUSIONS

L-HSA-DOXO shows at least comparable activity to sorafenib which clinically achieves only ∼3 months overall survival benefit. Combination of these two agents could act beneficially or synergistically via two different modes of action to fight HCC.

Albumin-drug conjugates in the treatment of hepatic disorders

INTRODUCTION

This review deals with the use of serum albumin (SA) as a carrier for the selective delivery of drugs to liver cells.

AREAS COVERED

The synthesis and properties of the SA conjugates prepared to enhance the performance of the drugs used in the treatment of viral hepatitis, hepatocellular carcinoma (HCC), liver micrometastases and hepatic fibrosis are reported.

EXPERT OPINION

Studies in humans and laboratory animals demonstrated the capacity of SA conjugates to accomplish a liver targeting of the drugs, but at the same time underscored their limits and drawbacks, which can explain why to date these complexes did not reach a practical application. The major drawback is the need of administration by intravenous route, which prevents long-term daily treatments as required by some liver pathologies, such as chronic virus hepatitis and fibrosis. At present, only a conjugate carrying doxorubicin and addressed to the treatment of HCC showed in laboratory animals a solid potentiality to improve the value of the coupled drug. In the future, conjugation to SA could remain a successful strategy to permit the administration of drugs with rapid resolutive effects inside liver cells without causing severe extrahepatic adverse reactions.

Lactosaminated human albumin, a hepatotropic carrier of drugs

A selective delivery of drugs to liver can be obtained by conjugation with galactosyl terminating macromolecules. The conjugates selectively enter hepatocytes after interaction of the carrier galactose residues with the asialoglycoprotein receptor (ASGP-R) present only on these cells. Within hepatocytes the conjugates are transported to lysosomes where the drug is set free from the carrier, becoming concentrated in liver cells. The present article reviews the liver targeting of drugs obtained with lactosaminated albumin (L-SA), a neoglycoprotein exposing galactosyl residues. We report: (1) experiments which demonstrate the antiviral efficacy of the L-H(human)SA-ara-AMP conjugate in laboratory animals and in humans with viral hepatitis; (2) the property of a L-HSA conjugate with fluorodeoxyuridine to produce concentrations of the drug higher in hepatic sinusoids than in systemic circulation, with the potential of accomplishing a loco-regional, noninvasive treatment of liver micrometastases; (3) the increased anticancer activity of doxorubicin (DOXO) when coupled to L-HSA on all the forms of chemically induced rat hepatocellular carcinomas including those which do not express the ASGP-R.

Albumin as a drug carrier: design of prodrugs, drug conjugates and nanoparticles

Albumin is playing an increasing role as a drug carrier in the clinical setting. Principally, three drug delivery technologies can be distinguished: coupling of low-molecular weight drugs to exogenous or endogenous albumin, conjugation with bioactive proteins and encapsulation of drugs into albumin nanoparticles. The accumulation of albumin in solid tumors forms the rationale for developing albumin-based drug delivery systems for tumor targeting. Clinically, a methotrexate-albumin conjugate, an albumin-binding prodrug of doxorubicin, i.e. the (6-maleimido)caproylhydrazone derivative of doxorubicin (DOXO-EMCH), and an albumin paclitaxel nanoparticle (Abraxane) have been evaluated clinically. Abraxane has been approved for treating metastatic breast cancer. An alternative strategy is to bind a therapeutic peptide or protein covalently or physically to albumin to enhance its stability and half-life. This approach has been applied to peptides with antinociceptive, antidiabetes, antitumor or antiviral activity: Levemir, a myristic acid derivative of insulin that binds to the fatty acid binding sites of circulating albumin, has been approved for the treatment of diabetes. Furthermore, Albuferon, a fusion protein of albumin and interferon, is currently being assessed in phase III clinical trials for the treatment of hepatitis C and could become an alternative to pegylated interferon. This review gives an account of the different drug delivery systems which make use of albumin as a drug carrier with a focus on those systems that have reached an advanced stage of preclinical evaluation or that have entered clinical trials.

Efficacy of doxorubicin coupled to lactosaminated albumin on rat hepatocellular carcinomas evaluated by ultrasound imaging

BACKGROUND/AIMS

Doxorubicin was conjugated with lactosaminated human albumin, a hepatotropic drug carrier, in order to increase its efficacy in the treatment of hepatocellular carcinoma. In rats bearing hepatocellular carcinomas induced by diethylnitrosamine, lactosaminated human albumin coupled doxorubicin enhanced the drug concentrations in the tumours and lowered those in extrahepatic tissues. The aim of the present study was to investigate the effects of lactosaminated human albumin coupled doxorubicin on the growth of established rat hepatocellular carcinomas induced by diethylnitrosamine.

METHODS

Lactosaminated human albumin coupled doxorubicin and the free drug were i.v. administered to rats twice a week for 4 weeks at the single dose of 1 microg/g. Growth of individual tumours was followed through time by ultrasonography.

RESULTS

In the control animals injected with saline the mean area of the tracked tumours significantly increased during the whole period of treatment. In the group of rats treated with lactosaminated human albumin coupled doxorubicin the mean area of the followed hepatocellular carcinomas remained practically unchanged. The free drug inhibited tumour growth only in the first period of drug administration. Lactosaminated human albumin coupled doxorubicin also hindered the development of new neoplastic nodules, which was unaffected by the free drug.

CONCLUSIONS

The results support lactosaminated human albumin coupled doxorubicin as a promising agent for a systemic chemotherapy of hepatocellular carcinomas to treat noncurable patients.

Doxorubicin coupled to lactosaminated albumin: effect of heterogeneity in drug load on conjugate disposition and hepatocellular carcinoma uptake in rats

Coupling to lactosaminated human albumin (L-HSA) makes doxorubicin (DOXO) an effective drug against chemically induced rat hepatocellular carcinomas (HCCs). In the conjugate there is a large heterogeneity in the number of DOXO molecules bound to one L-HSA molecule. After lyophilization, the molecules with the higher DOXO load form large complexes (C-DOXOL), whereas those with low drug load (C-DOXOS) have the size of the carrier L-HSA. In the present experiments, we demonstrated that in C-DOXOL the molecules are not linked by covalent bonds, but are strongly aggregated probably because of mutual drug-drug interaction between the DOXO residues. In healthy rats and in animals with HCCs which received the same dose (1 microg/g) of DOXO injected in C-DOXOL or in C-DOXOS forms, penetration of the drug in tumors and in tissues was more rapid after administration of the former complex. Three hours after injection of both conjugate forms the intracellular release of DOXO from the carrier was completed. The AUCs from 0.5 to 4h of the levels of the released DOXO in HCCs, surrounding liver and bone marrow of animals injected with C-DOXOL were similar to those calculated in animals given C-DOXOS. This suggests that after administration of the dose of DOXO used in the present experiments the conjugate molecules with lower or higher drug load can exert comparable pharmacological and toxic effects.

Coupling of lactose molecules to the carrier protein hinders the spleen and bone marrow uptake of doxorubicin conjugated with human albumin

Several attempts have been made to enhance doxorubicin (DOXO) concentrations in tumour cells by drug conjugation with human albumin (HSA). HSA-DOXO has the drawback of causing DOXO accumulation in spleen and bone marrow, with a consequent leucopoenia not produced when lactose molecules are coupled to the carrier protein. In the present experiments we demonstrated that the effect of HSA lactosamination is not a consequence of a more rapid disappearance from the bloodstream of the lactosaminated conjugate (L-HSA-DOXO), which is rapidly internalized by the liver through the asialoglycoprotein receptor, but is due to a hindered uptake by spleen and bone marrow cells caused by the coupled lactose molecules. Experiments in vitro showed that HSA-DOXO produced an inhibition of murine macrophage proliferation not caused by L-HSA-DOXO. This result can be explained by higher amounts of the former conjugate entering in these cells and suggests macrophages as the cell type responsible for the spleen and bone marrow internalization of HSA-DOXO hindered by lactose coupling. Importantly, lactosamination of HSA did not reduce the marked uptake of HSA-DOXO by chemically induced rat hepatocellular carcinoma. L-HSA-DOXO, by avoiding DOXO accumulation in bone marrow is an attractive candidate for clinical trials against tumors which were found to actively internalize this conjugate in laboratory animals, such as hepatocellular carcinoma.

A conjugate of doxorubicin with lactosaminated albumin enhances the drug concentrations in all the forms of rat hepatocellular carcinomas independently of their differentiation grade

BACKGROUND/AIMS

Doxorubicin (DOXO) was coupled to lactosaminated human serum albumin (L-HSA) in order to enhance the drug concentration in the well differentiated hepatocellular carcinomas (HCCs), which can accumulate L-HSA through the asialoglycoprotein receptor. In the present experiments we compared the DOXO concentrations produced by this conjugate (L-HSA-DOXO) and by the uncoupled drug in the well, moderately, and poorly differentiated rat HCCs.

METHODS

The same dose (1 microg/g) of free or L-HSA coupled-DOXO was injected in rats with HCCs induced by diethylnitrosamine. At different times, the animals were killed and the neoplastic nodules of liver were isolated. Their differentiation grade was determined histologically and their DOXO content was measured.

RESULTS

Unexpectedly, we found that also in the poorly differentiated forms of HCCs, which display no or only a poor capacity of accumulating L-HSA, the conjugate raised DOXO levels that were approximately twofold higher than those produced by the free drug.

CONCLUSIONS

The conjugate L-HSA-DOXO could improve the potential of DOXO in the treatment of all HCCs, including the poorly differentiated tumors that are the common forms in the advanced disease for which an effective chemotherapy is particularly needed.

Doxorubicin coupled to lactosaminated albumin: Effects on rats with liver fibrosis and cirrhosis

BACKGROUND

The conjugate of doxorubicin with lactosaminated human albumin has the potential of increasing the doxorubicin efficacy in the treatment of hepatocellular carcinomas expressing the asialoglycoprotein receptor. However, coupled doxorubicin also accumulates in the liver, which might damage hepatocytes.

AIMS

To verify whether coupled doxorubicin impairs liver function in rats with liver fibrosis and cirrhosis.

METHODS

Coupled doxorubicin was administered using the same schedule which exerted an antineoplastic effect on rat hepatocellular carcinomas (4-weekly injections of doxorubicin at 1 microg/g). Liver fibrosis/cirrhosis was produced by carbon tetrachloride (CCl4) poisoning. Liver samples were studied histologically. Serum parameters of liver function and viability were determined.

RESULTS

In normal rats, administration of coupled doxorubicin neither caused microscopic changes of hepatocytes nor modified serum liver parameters. In rats with fibrosis/cirrhosis, although a selective doxorubicin accumulation within the liver followed coupled doxorubicin administration, the drug did not have a detrimental effect on the histology of the liver and, among serum liver tests, only alanine aminotransferase and aspartate aminotransferase levels were moderately modified.

CONCLUSIONS

Coupled doxorubicin can be administered to rats with liver fibrosis/cirrhosis without inducing a severe liver damage. If further studies will confirm the efficacy and safety of this compound, coupled doxorubicin therapy may open a new perspective in the treatment of hepatocellular carcinoma.

Doxorubicin coupled to lactosaminated albumin inhibits the growth of hepatocellular carcinomas induced in rats by diethylnitrosamine

BACKGROUND/AIMS

The hepatocyte receptor for asialoglycoproteins internalizes galactosyl terminating macromolecules which can be used as hepatotropic drug carriers. Since this receptor is also expressed on the cells of well differentiated human hepatocellular carcinomas (HCCs), we studied whether conjugation of doxorubicin (DOXO) with lactosaminated human albumin (L-HSA) increases the drug efficacy on HCCs induced in rats by diethylnitrosamine (DENA).

METHODS

DENA was given in the drinking water for 8 weeks. One week after the last day of DENA administration, animals were randomly assigned to three groups. Each group was administered with either saline, free or coupled DOXO (1 microg/g). Rats received 4 weekly intravenous injections. One week after the last administration, rats were killed and HCC development was evaluated by counting the tumor nodules on the surface of hepatic lobes.

RESULTS

In rats treated with L-HSA coupled DOXO the number of neoplastic nodules was significantly lower (P < 0.05) than that counted in animals injected with saline or with free DOXO. Coupled DOXO did not decrease body rat weight, which was markedly reduced by the free drug.

CONCLUSIONS

Conjugation with L-HSA increased the antineoplastic efficacy and decreased the systemic toxicity of DOXO administered to rats with HCCs produced by DENA.

Methotrexate-modified superparamagnetic nanoparticles and their intracellular uptake into human cancer cells

A magnetic nanoparticle conjugate was developed that can potentially serve both as a contrast enhancement agent in magnetic resonance imaging and as a drug carrier in controlled drug delivery, targeted at cancer diagnostics and therapeutics. The conjugate is made of iron oxide nanoparticles covalently bound with methotrexate (MTX), a chemotherapeutic drug that can target many cancer cells whose surfaces are overexpressed by folate receptors. The nanoparticles were first surface-modified with (3-aminopropyl)trimethoxysilane to form a self-assembled monolayer and subsequently conjugated with MTX through amidation between the carboxylic acid end groups on MTX and the amine groups on the particle surface. Drug release experiments demonstrated that MTX was cleaved from the nanoparticles under low pH conditions mimicking the intracellular conditions in the lysosome. Cellular viability studies in human breast cancer cells (MCF-7) and human cervical cancer cells (HeLa) further demonstrated the effectiveness of such chemical cleavage of MTX inside the target cells through the action of intracellular enzymes. The intracellular trafficking model proposed was supported through nanoparticle uptake studies which demonstrated that cells expressing the human folate receptor internalized a higher level of nanoparticles than negative control cells.

Enhanced uptake of lactosaminated human albumin by rat hepatocarcinomas: implications for an improved chemotherapy of primary liver tumors

BACKGROUND/AIMS

The hepatocyte receptor for asialoglycoproteins (ASGP-R) internalizes macromolecules exposing galactosyl residues (MEGRs) which can be used as liver-addressed drug carriers. This receptor was also found on the cells of the large majority of well differentiated hepatocarcinomas (HCCs). The aim of the present experiments was to ascertain whether ASGP-R of HCCs is functionally active and these tumors can internalize higher quantities of MEGRs than extra-hepatic tissues.

METHODS

We injected radioactive lactosaminated human albumin (L-HSA) in rats with HCCs produced by nitroso-diethylamine and measured the radioactivity of tumors, surrounding liver, heart, intestine and kidney. L-HSA is a MEGR successfully used in humans as a hepatotropic drug carrier.

RESULTS

The levels of radioactivity of HCCs were two to three times lower than those of surrounding liver, but several times higher than those of extra-hepatic tissues. L-HSA accumulation in the tumors mainly occurred via the ASGP-R, as indicated by the 20 times lower penetration of non-lactosaminated HSA. L-HSA uptake by the well-differentiated tumors were four times higher compared with that by the poorly differentiated forms.

CONCLUSIONS

The present results suggest that in the chemotherapy of HCCs expressing the ASGP-R the extra-hepatic toxicity of anticancer agents can be reduced by conjugation to L-HSA.

A novel method for coupling doxorubicin to lactosaminated human albumin by an acid sensitive hydrazone bond: synthesis, characterization and preliminary biological properties of the conjugate

The expression of the asialoglycoprotein receptor on the cells of the large majority of the well differentiated hepatocellular carcinomas can be exploited to improve the chemotherapy of these tumours by coupling anticancer agents to macromolecules taken up by the receptor. In line with this approach, in previous experiments we coupled doxorubicin (DOXO) to lactosaminated human albumin (L-HSA) using the (6-maleimidocaproyl)hydrazone derivative of the drug as an acid sensitive linker. Encouraging results were obtained in laboratory animals using L-HSA-DOXO. This conjugate, however, has the disadvantage of a difficult synthesis, which requires protein thiolation with iminothiolane and can hinder its preparation on a large scale. Here we describe a very simple method of coupling. The HS-groups required for the reaction with the maleimide moiety of DOXO-EMCH are made available in L-HSA by a cleavage of the protein disulphides achieved with tris(2-carboxyethyl) phosphine (TCEP). Contrary to thiolic reducing agents, the use of TCEP eliminates the need of an inert atmosphere and allows a one-step coupling reaction, without purification of the reduced protein before the addition of DOXO-EMCH. As the previous L-HSA-DOXO conjugate, the new conjugate accomplishes a very efficient liver targeting of the drug. This novel method of synthesis should facilitate the preparation of L-HSA-DOXO in the amounts required for clinical studies.

Liver-targeted doxorubicin: effects on rat regenerating hepatocytes

BACKGROUND/AIMS

The conjugate of doxorubicin (DOXO) with lactosaminated human albumin (L-HSA) has the potential of improving DOXO efficacy in the treatment of hepatocellular carcinomas (HCCs) expressing the asialoglycoprotein receptor (ASGP-R). In view of an adjuvant chemotherapy with L-HSA-DOXO after the surgical removal of the tumour, in the present experiments we verified whether DOXO accumulation produced by the conjugate can impair the liver regeneration following hepatic resection in non-cirrhotic liver.

METHODS

Using saline-injected hepatectomised rats as controls, we studied the effects of the conjugate on the ultrastructure of regenerating hepatocytes and evaluated [3H]thymidine incorporation, mitotic index and rate of DNA recovery in the liver remnant.

RESULTS

L-HSA-DOXO caused a selective drug accumulation in liver remnant, with low DOXO levels in extra-hepatic tissues. It did not change the ultrastructure of hepatocytes and did not increase serum alanine aminotransferase. It decreased [3H]thymidine incorporation and mitotic index, causing a moderate delay in hepatic DNA recovery.

CONCLUSIONS

The experiments indicate a substantial resistance of rat regenerating hepatocytes to high intracellular concentrations of DOXO. They support the possibility of using L-HSA-DOXO in an adjuvant chemotherapy after the surgical removal of HCCs which maintain the ASGP-R.