Oleic acid may be the key contributor in the BAMLET-induced erythrocyte hemolysis and tumoricidal action

Proteins and their functionalization for finding therapeutic avenues in cancer: Current status and future prospective

Despite the remarkable advancement in the health care sector, cancer remains the second most fatal disease globally. The existing conventional cancer treatments primarily include chemotherapy, which has been associated with little to severe side effects, and radiotherapy, which is usually expensive. To overcome these problems, target-specific nanocarriers have been explored for delivering chemo drugs. However, recent reports on using a few proteins having anticancer activity and further use of them as drug carriers have generated tremendous attention for furthering the research towards cancer therapy. Biomolecules, especially proteins, have emerged as suitable alternatives in cancer treatment due to multiple favourable properties including biocompatibility, biodegradability, and structural flexibility for easy surface functionalization. Several in vitro and in vivo studies have reported that various proteins derived from animal, plant, and bacterial species, demonstrated strong cytotoxic and antiproliferative properties against malignant cells in native and their different structural conformations. Moreover, surface tunable properties of these proteins help to bind a range of anticancer drugs and target ligands, thus making them efficient delivery agents in cancer therapy. Here, we discuss various proteins obtained from common exogenous sources and how they transform into effective anticancer agents. We also comprehensively discuss the tumor-killing mechanisms of different dietary proteins such as bovine α-lactalbumin, hen egg-white lysozyme, and their conjugates. We also articulate how protein nanostructures can be used as carriers for delivering cancer drugs and theranostics, and strategies to be adopted for improving their in vivo delivery and targeting. We further discuss the FDA-approved protein-based anticancer formulations along with those in different phases of clinical trials.

Drug-loaded oleic-acid grafted mesoporous silica nanoparticles conjugated with α-lactalbumin resembling BAMLET-like anticancer agent with improved biocompatibility and therapeutic efficacy

Despite its prominent therapeutic efficacy, chemotherapy has raised serious concerns due to the severe adverse effects and multidrug resistance evoked, which propels the search for safe and green therapeutic agents. BAMLET (bovine α-lactalbumin made lethal against tumor cell) is a well-known protein-based anticancer agent of selective tumoricidal activity. Here, we prepared oleic acid-modified mesoporous silica nanoparticles (OA-MSNs) conjugated with bovine α-lactalbumin, a lipoprotein complex resembling BAMLET formed on the surface of MSNs (MSN-BAMLET) to load the anticancer drug of docetaxel (DTX). Compared to that of OA-MSNs/DTX, the obtained MSN-BAMLET/DTX with a sustained and pH-responsive drug release behaviors exhibited good biocompatibility and enhanced cytotoxic effect against cancer cells. Moreover, the presence of lipoprotein complex in MSN-BAMLET contributed to the improved dispersion of the composite in solution and the inhibitory effect on the migration of cancer cells. Furthermore, the adsorption profiles of protein corona on the obtained nanoparticles were analyzed. It was found that the marked low amount and abundance of plasma proteins were adsorbed on the α-lactalbumin coated siliceous composite demonstrated its long circulation property. Finally, in vivo study showed that MSN-BAMLET/DTX contributed to the effective cancer ablation and the prolonged survival. Therefore, the constructed MSN-BAMLET of the mesoregular structure and peculiar tumoricidal effect provides a manipulable nanoplatform as drug nanocarrier for therapeutic applications.

Nanomedicine for increasing the oral bioavailability of cancer treatments

Abstract

Oral administration is an appealing route of delivering cancer treatments. However, the gastrointestinal tract is characterized by specific and efficient physical, chemical, and biological barriers that decrease the bioavailability of medications, including chemotherapeutics. In recent decades, the fields of material science and nanomedicine have generated several delivery platforms with high potential for overcoming multiple barriers associated to oral administration. This review describes the properties of several nanodelivery systems that improve the bioavailability of orally administered therapeutics, highlighting their advantages and disadvantages in generating successful anticancer oral nanomedicines.

Graphical Abstract

The mosquito protein AEG12 displays both cytolytic and antiviral properties via a common lipid transfer mechanism

The mosquito protein AEG12 is up-regulated in response to blood meals and flavivirus infection though its function remained elusive. Here, we determine the three-dimensional structure of AEG12 and describe the binding specificity of acyl-chain ligands within its large central hydrophobic cavity. We show that AEG12 displays hemolytic and cytolytic activity by selectively delivering unsaturated fatty acid cargoes into phosphatidylcholine-rich lipid bilayers. This property of AEG12 also enables it to inhibit replication of enveloped viruses such as Dengue and Zika viruses at low micromolar concentrations. Weaker inhibition was observed against more distantly related coronaviruses and lentivirus, while no inhibition was observed against the nonenveloped virus adeno-associated virus. Together, our results uncover the mechanistic understanding of AEG12 function and provide the necessary implications for its use as a broad-spectrum therapeutic against cellular and viral targets.

α-Lactalbumin, Amazing Calcium-Binding Protein

α-Lactalbumin (α-LA) is a small (Mr 14,200), acidic (pI 4–5), Ca²⁺-binding protein. α-LA is a regulatory component of lactose synthase enzyme system functioning in the lactating mammary gland. The protein possesses a single strong Ca²⁺-binding site, which can also bind Mg²⁺, Mn²⁺, Na⁺, K⁺, and some other metal cations. It contains several distinct Zn²⁺-binding sites. Physical properties of α-LA strongly depend on the occupation of its metal binding sites by metal ions. In the absence of bound metal ions, α-LA is in the molten globule-like state. The binding of metal ions, and especially of Ca²⁺, increases stability of α-LA against the action of heat, various denaturing agents and proteases, while the binding of Zn²⁺ to the Ca²⁺-loaded protein decreases its stability and causes its aggregation. At pH 2, the protein is in the classical molten globule state. α-LA can associate with membranes at neutral or slightly acidic pH at physiological temperatures. Depending on external conditions, α-LA can form amyloid fibrils, amorphous aggregates, nanoparticles, and nanotubes. Some of these aggregated states of α-LA can be used in practical applications such as drug delivery to tissues and organs. α-LA and some of its fragments possess bactericidal and antiviral activities. Complexes of partially unfolded α-LA with oleic acid are cytotoxic to various tumor and bacterial cells. α-LA in the cytotoxic complexes plays a role of a delivery carrier of cytotoxic fatty acid molecules into tumor and bacterial cells across the cell membrane. Perhaps in the future the complexes of α-LA with oleic acid will be used for development of new anti-cancer drugs.

Structures and mechanisms of formation of liprotides

Many proteins form complexes called liprotides with oleic acid and other cis-fatty acids under conditions where the protein is partially unfolded. The complexes vary in structure depending on the ratio of protein and lipid, but the most common structural organization is the core-shell structure, in which a layer of dynamic, partially unfolded and extended proteins surrounds a micelle-like fatty acid core. This structure, first reported for α-lactalbumin together with OA, resembles complexes formed between proteins and anionic surfactants like SDS. Liprotides first rose to fame through their anti-carcinogenic properties which still remains promising for topical applications though not yet implemented in the clinic. In addition, liprotides show potential in drug delivery thanks to the ability of the micelle core to solubilize and stabilize hydrophobic compounds, though applications are challenged by their sensitivity to acidic pH and dynamic exchange of lipids which makes them easy prey for serum "hoovers" such as albumin. However, liprotides are also of fundamental interest as a generic "protein complex structure", demonstrating the many and varied structural consequences of protein-lipid interactions. Here we provide an overview of the different types of liprotide complexes, ranging from quasi-native complexes via core-shell structures to multi-layer structures, and discuss the many conditions under which they form. Given the many variable types of complexes that can form, rigorous biophysical analysis (stoichiometry, shape and structure of the complexes) remains crucial for a complete understanding of the mechanisms of action of this fascinating group of protein-lipid complexes both in vitro and in vivo.

The novel therapeutic potential of bovine α-lactalbumin made lethal to tumour cells (BALMET) and oleic acid in oral squamous cell carcinoma (OSCC)

BACKGROUND

Since the serendipitous discovery of bovine α-lactalbumin made lethal to tumour cells (BAMLET)/human α-lactalbumin made lethal to tumour cells there has been an increased interest in the ability of the two components, oleic acid and α-lactalbumin, to form anti-cancer complexes. Here we have investigated the in-vitro efficacy of the BAMLET complex in killing oral cancer (OC) cells, determined the active component of the complex and investigated possible biological mechanisms.

MATERIALS AND METHODS

Two OC cell lines (±p53 mutation) and one dysplastic cell line were used as a model of progressive oral carcinogenesis. We performed cell viability assays with increasing BAMLET concentrations to determine the cytotoxic potential of the complex. We further analysed the individual components to determine their respective cytotoxicities. siRNA knockdown of p53 was used to determine its functional role in mediating sensitivity to BAMLET. Cell death mechanisms were investigated by flow cytometry, confocal microscopy and the lactate dehydrogenase assay.

RESULTS

Our results show that BAMLET is cytotoxic to the OC and dysplastic cell lines in a time and dose-dependent manner. The cytotoxic component was found to be oleic acid, which, can induce cytotoxicity even when not in complex. Our results indicate that the mechanism of cytotoxicity occurs through multiple simultaneous events including cell cycle arrest, autophagy like processes with a minor involvement of necrosis.

CONCLUSION

Deciphering the mechanism of cytotoxicity will aid treatment modalities for OC. This study highlights the potential of BAMLET as a novel therapeutic strategy in oral dysplastic and cancerous cells.

Meglumine-based supra-amphiphile self-assembled in water as a skin drug delivery system: Influence of unfrozen bound water in the system bioadhesiveness

Hexagonal liquid crystals and supramolecular polymers from meglumine-based supra-amphiphiles were developed as drug delivery systems to be applied on the skin. The influence of fatty acid unsaturation on the structure and mechanical properties was evaluated. Moreover, we have investigated the system biocompatibility and how the type of water could influence its bioadhesive properties. Meglumine-oleic acid (MEG-OA) was arranged as hexagonal liquid crystals at 30-70 wt% water content, probably due to its curvature and increased water solubility. Meglumine-stearic acid (MEG-SA) at 10-80 wt% water content self-assembled as a lamellar polymeric network, which can be explained by the low mobility of MEG-SA in water due to hydrophobic interactions between fatty acid chains and H-bonds between meglumine and water molecules. Both systems have shown suitable mechanical parameters and biocompatibility, making them potential candidates to encapsulate therapeutic molecules for skin delivery. Moreover, a strong positive correlation between the amount of unfrozen bound water in meglumine-based systems and the bioadhesion properties was observed. This work shows that a better understanding of the physicochemical properties of a drug delivery system is extremely important for the correlation with the desired biological response and, thus, improve the product performance for biomedical applications.

Protein-lipid complexes: molecular structure, current scenarios and mechanisms of cytotoxicity

Some natural proteins can be complexed with oleic acid (OA) to form an active protein-lipid formulation that can induce tumor-selective apoptosis. The first explored protein was human milk α-lactalbumin (α-LA), called HAMLET when composed with OA in antitumor form. Several groups have prepared active protein-lipid complexes using a variety of approaches, all of which depend on target protein destabilization or direct OA-protein incubation to alter pH to acid or alkaline condition. In addition to performing vital roles in inflammatory processes and immune responses, fatty acids can disturb different metabolic pathways and cellular signals. Therefore, the tumoricidal action of these complexes is related to OA rather than the protein that keeps OA in solution and acts as a vehicle for transferring OA molecules to tumor cells. However, other studies have suggested that the antitumor efficacy of these complexes was exerted by both protein and OA together. The potential is not limited to the anti-tumor activity of protein-lipid complexes but extends to other functions such as bactericidal activity. The protein shell enhances the solubility and stability of the bound fatty acid. These protein-lipid complexes are promising candidates for fighting various cancer types and managing bacterial and viral infections.

The Use of Human, Bovine, and Camel Milk Albumins in Anticancer Complexes with Oleic Acid

Oleic acid (OA) is a monounsaturated fatty acid that upon binding to milk proteins, such as α-lactalbumin and lactoferrin, forms potent complexes, which exert selective anti-tumor activity against malignant cells but are nontoxic for healthy normal cells. We showed that the interaction of OA with albumins isolated from human, bovine, and camel milk results in the formation of complexes with high antitumor activity against Caco-2, HepG-2, PC-3, and MCF-7 tumor cells. The antitumor effect of the complexes is mostly due to the action of oleic acid, similar to the case of OA complexes with other proteins. Viability of tumor cells is inhibited by the albumin-OA complexes in a dose dependent manner, as evaluated by the MTT assay. Strong induction of apoptosis in tumor cells after their treatment with the complexes was monitored by flow cytometry, cell cycle analysis, nuclear staining, and DNA fragmentation methods. The complex of camel albumin with OA displayed the most pronounced anti-tumor effects in comparison with the complexes of OA with human and bovine albumins. Therefore, these results suggest that albumins have the potential to be used as efficient and low cost means of tumor treatment.

Temperature, pH, and Molecular Packing Effects on the Penetration of Oleic Acid Monolayer by α-Lactalbumin

Recently, we reported on the interfacial behavior of mixed oleic acid (OA)-α-lactalbumin monolayer and its relevance in the formation of tumoricidal HAMLET (human α-lactalbumin made lethal to tumor cells)-like complex. This complex is probably formed in the gastrointestinal tract, but it has not been proved so far. The molecular base and the underlying physicochemical forces leading to such complexation remain to be known as well. There are also several other issues related with the complex stoichiometry that need to be fully explained. This study provides insight into the mechanism of temperature, pH, and physical state of monolayer-dependent binding of OA by the milk protein- apo-α-lactalbumin. Using the Langmuir and Langmuir-Blodgett approaches, we investigated the interactions between the OA monolayer and the apo-bovine α-lactalbumin (BLA III) at different pH, temperatures, and molecular packing. We found that the most favorable conditions for the formation of mixed OA-BLA III film are relevant to the gastric environment. The stabilization of OA-BLA III at the interface is associated with the conformational changes of protein in the presence of fatty acids induced by low pH and high temperature in the expanded monolayer. Our approach helps to understand the molecular mechanism of HAMLET/bovine α-lactalbumin made lethal to tumor cells formation in vivo.

Cytotoxicity of apo bovine α-lactalbumin complexed with La3+ on cancer cells supported by its high resolution crystal structure

Cancer remains one of the biggest threats to human society. There are massive demands for compounds to selectively kill cancerous cells. Earlier studies have shown that bovine α -lactalbumin made lethal to tumor cells (BAMLET) becomes cytotoxic against cancer cells in complex with oleic acid {Hoque, M. et. al., PLoSOne8, e68390 (2013)}. In our study, we obtained bovine α-lactalbumin complexed with lanthanum ion (La³⁺-B-α-LA) and determined its high resolution crystal structure. The natural calcium binding site of bovine α-lactalbumin is replaced by lanthanum. The La³⁺ complex formation by B-α-apo-LA was also supported by various biophysical methods. Interestingly, our complex, La³⁺-B-α-LA exhibits much greater anticancer activity against breast cancer cells as compared to the reported BAMLET-oleic acid complex. This study shows that La³⁺-B-α-LA complex is preferentially more toxic to MCF-7 cells as compared to KB (oral cancer) and HeLa (cervical) cells, while almost non-toxic to the healthy cells that we studied. Our data indicates that the cytotoxicity of La³⁺-B-α-LA against cancer cells is through apoptotic path way. The higher anticancer activity of La³⁺-B-α-LA is attributable to the requisite structural changes induced in the protein by La³⁺ binding as supported by the crystal structure of the complex.

Liprotides kill cancer cells by disrupting the plasma membrane

HAMLET (human α-lactalbumin made lethal to tumour cells) is a complex of α-lactalbumin (aLA) and oleic acid (OA) which kills transformed cells, while leaving fully differentiated cells largely unaffected. Other protein-lipid complexes show similar anti-cancer potential. We call such complexes liprotides. The cellular impact of liprotides, while intensely investigated, remains unresolved. To address this, we report on the cell-killing mechanisms of liprotides prepared by incubating aLA with OA for 1 h at 20 or 80 °C (lip20 and lip80, respectively). The liprotides showed similar cytotoxicity against MCF7 cells, though lip80 acts more slowly, possibly due to intermolecular disulphide bonds formed during preparation. Liprotides are known to increase the fluidity of a membrane and transfer OA to vesicles, prompting us to focus on the effect of liprotides on the cell membrane. Extracellular Ca²⁺ influx is important for activation of the plasma membrane repair system, and we found that removal of Ca²⁺ from the medium enhanced the liprotides’ killing effect. Liprotide cytotoxicity was also increased by knockdown of Annexin A6 (ANXA6), a protein involved in plasma membrane repair. We conclude that MCF7 cells counteract liprotide-induced membrane permeabilization by activating their plasma membrane repair system, which is triggered by extracellular Ca²⁺ and involves ANXA6.

Exosomes for the Enhanced Tissue Bioavailability and Efficacy of Curcumin

Exosomes are extracellular microvesicles with a particle size of 30-100 nm and carry a cargo of proteins, lipids, RNA, and DNA. Their properties of shuttling in-and-out of the cells suggest that these particles can be exploited as a nano drug carrier. In this manuscript, we show that curcumin can be delivered effectively using milk-derived exosomes. Curcumin when mixed with exosomes in the presence of 10% ethanol:acetonitrile (1:1) provided a drug load of 18-24%, and the formulation stored at - 80°C was stable for 6 months as determined by particle size analysis, drug load, and antiproliferative activity. The uptake of exosomes by cancer cells involved caveolae/clathrin-mediated endocytosis. Oral administration of exosomal curcumin (ExoCUR) in Sprague-Dawley rats demonstrated 3-5 times higher levels in various organs versus free agent. ExoCUR showed enhanced antiproliferative activity against multiple cancer cell lines including, breast, lung, and cervical cancer compared with the free curcumin. ExoCUR showed significantly higher anti-inflammatory activity measured as NF-κB activation in human lung and breast cancer cells. To determine in vivo antitumor activity, nude mice bearing the cervical CaSki tumor xenograft were treated with ExoCUR by oral gavage, curcumin diet, exosomes alone, and PBS as controls. While curcumin via dietary route failed to elicit any effect, exosomes had a modest (25-30%) tumor growth inhibition. However, ExoCUR showed significant inhibition (61%; p < 0.01) of the cervical tumor xenograft. No gross or systemic toxicity was observed in the rats administered with the exosomes or ExoCUR. These results suggest that exosomes can be developed as potential nano carriers for delivering curcumin which otherwise has encountered significant tissue bioavailability issues in the past.

Formation mechanism of α-lactalabumin/oleic acid complex characterized by 2D correlation analysis

Partially unfolded α-lactalbumin (ALA) forms a complex with oleic acid (OA) that exhibits cytotoxic activity. In this study, for the first time, the pH-induced formation mechanism for ALA/OA complexes with two different molar ratios was investigated at the molecular level. For a deeper understanding of the formation mechanism of the two different ALA/OA complexes with decreasing pH, principal component analysis (PCA) and two-dimensional (2D) correlation spectroscopy were used to examine the pH-dependent IR spectra of ALA/OA complexes. By tracking the secondary structural variations in the ALA/OA complexes with decreasing pH, we successfully elucidated the formation mechanism of the ALA/OA complexes at the molecular level. The results showed that the secondary structures of theses complexes exhibited the greatest change between pH4 and pH3.5 and that the components that mainly contributed to the pH-induced transition from the N-state to the A-state were dissimilar in the two different ALA/OA complexes.

Divergent Anticancer Activity of Free and Formulated Camel Milk α-Lactalbumin

Alpha-lactalbumin (α-LA), a small milk calcium-binding globular protein, is known to possess noticeable anticancer activity, which is determined by the ability of this protein to form complexes with oleic acid (OA). To date, in addition to human and bovine α-LA, the ability to form such anti-tumor complexes with OA was described for goat and camel α-LA. Although the mechanisms of the anticancer activity of human and bovine α-LA are already well-studied, little is currently known about the anticancer action of this camel protein. The goal of this study was to fill this gap and to analyze the anticancer and pro-apoptotic activities of camel α-LA in its free form (α-cLA) and as an OA-containing complex (OA-α-cLA) using four human cancer cell lines, including Caco-2 colon cancer cells, PC-3 prostate cancer cells, HepG-2 hepatoma cells, and MCF-7 breast cancer cells as targets. The anti-tumor activities of OA-α-cLA and α-cLA were analyzed using MTT test, annexin/PI staining, cell cycle analysis, nuclear staining, and tyrosine kinase (TK) inhibition methods. We show here that the OA-α-cLA complex does not affect normal cells but has noticeable anti-cancer activity, especially against MCF-7 cells, thus boosting the anticancer activity of α-cLA and improving the selectivity of OA. The OA-α-cLA complex mediated cancer cell death via selective induction of apoptosis and cell-cycle arrest at lower IC₅₀ than that of free α-cLA by more than two folds. However, OA induced apoptosis at higher extent than OA-α-cLA and α-cLA. OA also caused unselective apoptosis-dependent cell death in both normal and cancer cells to a similar degree. The apoptosis and cell-cycle arresting effect of OA-α-cLA may be attributed to the TK inhibition activity of OA. Therefore, OA-α-cLA serves as efficient anticancer complex with two functional components, α-cLA and OA, possessing different activities. This study declared the effectiveness of OA-α-cLA complex as a promising entity with anticancer activity, and these formulated OA-camel protein complexes constitute an auspicious approach for cancer remedy, particularly for breast cancer.

Exosomal formulation of anthocyanidins against multiple cancer types

Over the last two decades, berries and berry bioactives, particularly anthocyanins and their aglycones anthocyanidins (Anthos) have demonstrated excellent anti-oxidant, anti-proliferative, apoptotic and anti-inflammatory properties. However, their physicochemical and pharmacokinetic limitations such as, low permeability, and poor oral bioavailability are considered as unfavorable properties for development as drugs. Therefore there is a need to develop systems for efficient systemic delivery and robust bioavailability. In this study we prepared nano-formulation of bilberry-derived Anthos using exosomes harvested from raw bovine milk. Exosomal formulation of Anthos enhanced antiproliferative and anti-inflammatory effects compared with the free Anthos against various cancer cells in vitro. Our data also showed significantly enhanced therapeutic response of exosomal-Anthos formulation compared with the free Anthos against lung cancer tumor xenograft in nude mice. The Anthos showed no signs of gross or systemic toxicity in wild-type mice. Thus, exosomes provide an effective alternative for oral delivery of Anthos that is efficacious, cost-effective, and safe, and this regimen can be developed as a non-toxic, widely applicable therapeutic agent.

Neutron scattering shows a droplet of oleic acid at the center of the BAMLET complex

The anti-cancer complex, Bovine Alpha-lactalbumin Made LEthal to Tumors (BAMLET), has intriguing broad-spectrum anti-cancer activity. Although aspects of BAMLET's anti-cancer mechanism are still not known, it is understood that it involves the oleic acid or oleate component of BAMLET being preferentially released into cancer cell membranes leading to increased membrane permeability and lysis. The structure of the protein component of BAMLET has previously been elucidated by small angle X-ray scattering (SAXS) to be partially unfolded and dramatically enlarged. However, the structure of the oleic acid component of BAMLET and its disposition with respect to the protein component was not revealed as oleic acid has the same X-ray scattering length density (SLD) as water. Employing the difference in the neutron SLDs of hydrogen and deuterium, we carried out solvent contrast variation small angle neutron scattering (SANS) experiments of hydrogenated BAMLET in deuterated water buffers, to reveal the size, shape, and disposition of the oleic acid component of BAMLET. Our resulting analysis and models generated from SANS and SAXS data indicate that oleic acid forms a spherical droplet of oil incompletely encapsulated by the partially unfolded protein component. This model provides insight into the anti-cancer mechanism of this cache of lipid. The model also reveals a protein component "tail" not associated with the oleic acid component that is able to interact with the tail of other BAMLET molecules, providing a plausible explanation of how BAMLET readily forms aggregates. Proteins 2017; 85:1371-1378. © 2017 Wiley Periodicals, Inc.

Augmenting the cytotoxicity of oleic acid-protein complexes: Potential of target-specific antibodies

HAMLET (Human Alpha-Lactalbumin Made LEthal to Tumor cells), a complex of oleic acid (OA) with partially unfolded human α-lactalbumin, shows remarkable toxicity towards a spectrum of tumor cells as well as few differentiated cells including mammalian erythrocytes. Human erythrocytes, for this reason, have been used as convenient model cells to study toxic properties of the OA complexes. The toxicity of HAMLET-like complexes, prepared using immunoglobulin gamma (IgG) isolated from the sera of rabbits immunized with human erythrocytes as well as those unimmunized, towards the red cells was investigated. The OA complex of the IgG prepared by the heat-treatment procedure comprised of protein monomers and oligomers with bound OA. The IgG in the complexes retained most secondary but only partial tertiary structure and complex formation with OA did not abolish the ability of anti-erythrocyte IgG to bind to the erythrocytes. Anti-erythrocyte IgG-OA complexes were remarkably more hemolytic than those prepared using non-specific IgG, while complexes prepared using affinity purified anti-erythrocyte IgG were most effective in hemolyzing the cells. The work suggests that antibodies that exhibit affinity towards target cells may be useful in the preparation of selective and highly toxic OA complexes for the cells.

Milk-derived exosomes for oral delivery of paclitaxel

In this report milk-derived exosomes have been investigated for oral delivery of the chemotherapeutic drug paclitaxel (PAC) as an alternative to conventional i.v. therapy for improved efficacy and reduced toxicity. PAC-loaded exosomes (ExoPAC) were found to have a particle size of ~108 nm, a narrow particle size distribution (PDI ~0.190), zeta potential (~ -7 mV) and a practical loading efficiency of ~8%. Exosomes and ExoPAC exhibited excellent stability in the presence of simulated-gastrointestinal fluids, and during the storage at -80 °C. A sustained release of PAC was also observed up to 48 h in vitro using PBS (pH 6.8). Importantly, ExoPAC delivered orally showed significant tumor growth inhibition (60%; P<0.001) against human lung tumor xenografts in nude mice. Treatment with i.p. PAC at the same dose as ExoPAC, however, showed modest but statistically insignificant inhibition (31%). Moreover, ExoPAC demonstrated remarkably lower systemic and immunologic toxicities as compared to i.v. PAC.

Protein-dependent Membrane Interaction of A Partially Disordered Protein Complex with Oleic Acid: Implications for Cancer Lipidomics

Bovine α-lactalbumin (BLA) forms cytotoxic complexes with oleic acid (OA) that perturbs tumor cell membranes, but molecular determinants of these membrane-interactions remain poorly understood. Here, we aim to obtain molecular insights into the interaction of BLA/BLA-OA complex with model membranes. We characterized the folding state of BLA-OA complex using tryptophan fluorescence and resolved residue-specific interactions of BLA with OA using molecular dynamics simulation. We integrated membrane-binding data using a voltage-sensitive probe and molecular dynamics (MD) to demonstrate the preferential interaction of the BLA-OA complex with negatively charged membranes. We identified amino acid residues of BLA and BLA-OA complex as determinants of these membrane interactions using MD, functionally corroborated by uptake of the corresponding α-LA peptides across tumor cell membranes. The results suggest that the α-LA component of these cytotoxic complexes confers specificity for tumor cell membranes through protein interactions that are maintained even in the lipid complex, in the presence of OA.

Thymoquinone, an active constituent of Nigella sativa seeds, binds with bilirubin and protects mice from hyperbilirubinemia and cyclophosphamide-induced hepatotoxicity

Some reports indicate that thymoquinone (TQ), the main constituent of Nigella sativa seeds, is hepatoprotective. The aim of this study was to determine whether TQ is able to bind directly to bilirubin, and whether TQ or liposomal formulation of TQ (Lip-TQ) can reduce cyclophosphamide (CYP)-induced liver toxicity, serum bilirubin level in mice. The binding of TQ with bilirubin was studied by UV-VIS, fluorescence and Near-UV CD spectroscopy. Inhibition of binding of bilirubin to erythrocytes by TQ was also examined. To increase the in vivo efficacy, Lip-TQ was prepared and used against CYP-induced toxicity. The protective role of TQ or Lip-TQ against CYP-induced toxicity was assessed by determining the liver function parameters, the levels of superoxide dismutase (SOD) and catalase (CAT), and histological studies. It was found that TQ binds to bilirubin and significantly inhibits the binding of bilirubin to erythrocytes. Lip-TQ (10 mg/kg) significantly reduced the levels of aspartate transaminase (AST) from 254 ± 48 to 66 ± 18 IU/L (P < 0.001), alanine transaminase (ALT) from 142 ± 28 to 47.8 ± 16 IU/L (P < 0.05) and serum bilirubin from 2.8 ± 0.50 to 1.24 ± 0.30 mg/dl (P < 0.05). Treatment with Lip-TQ reduced the CYP-induced inflammation and hemorrhage in liver tissues. Moreover, treatment with free or Lip-TQ protected the activity of SOD and CAT in CYP-injected mice. Therefore, TQ can reduce the level of bilirubin in systemic circulation in disease conditions that lead to hyperbilirubinemia and liver toxicity and hence may be used as a supplement in the treatment of liver ailments.

Behaviour of oleic acid-depleted bovine alpha-lactalbumin made LEthal to tumor cells (BAMLET)

Oleic acid (OA) complexes of human alpha-lactalbumin (α-LA) and several other proteins are effective in the killing of a variety of tumor cells.

Stable Self-Assembly of Bovine α-Lactalbumin Exhibits Target-Specific Antiproliferative Activity in Multiple Cancer Cells

Self-assembly of a protein is a natural phenomenon; however, the process can be performed under a suitable condition in vitro. Since proteins are nontoxic, biodegradable, and biocompatible in nature, they are used in various industrial applications such as biocatalyst, therapeutic agent, and drug carriers. Moreover, their flexible structural state and specific activity are being used as sensors and immensely attract many new applications. However, the inherent potential of protein self-assembly for various applications is yet to be explored in detail. In this study, spherical self-assembly of bovine α-lactalbumin (nsBLA) was synthesized using an optimized ethanol-mediated desolvation process with an average diameter of approximately 300 nm. The self-assembly was found to be highly stable against thermal, pH, and proteases stress. When nsBLA was administered in various cancer cells, it demonstrated high cytotoxicity in three different cancer cells via reactive oxygen species (ROS) generation, whereas it exhibited negligible toxicity in normal human and murine cells. When nsBLA was conjugated with folic acid, it improved the cytotoxicity and perhaps mediated through enhanced cellular uptake in cancer cells through binding with folate receptors. Further, experimental results confirmed that the cancer cell death induced by nsBLA was not caused by apoptosis but a necrotic-like death mechanism. When compared with a well-known protein-based anticancer agent BAMLET (bovine α-lactalbumin made lethal against tumor cell), the self-assembled BLA clearly exhibited higher cytotoxicity to cancer cells than BAMLET. While BAMLET exhibits poor biocompatibility, our nsBLA demonstrated excellent biocompatibility to normal cells. Therefore, in this study, we prepared self-assembled α-lactalbumin that exhibits strong inherent antiproliferative potential in multiple cancer cells which can be used for efficient therapeutic approach in cancer.

The cytotoxicity of BAMLET complexes is due to oleic acid and independent of the α-lactalbumin component

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We synthesized three different BAMLET complexes consisting of oleic acid coupled to bovine α-lactalbumin.

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Oleic acid micelles alone are tumoricidal at equimolar concentrations of oleic acid bound in the BAMLET complexes.

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α-Lactalbumin is non-toxic to cells even when delivered to their cytoplasm.

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Both, BAMLET and oleic acid micelles showed no selective cytotoxicity to cancer cells.

Lipid–protein complexes comprised of oleic acid (OA) non-covalently coupled to human/bovine α-lactalbumin, named HAMLET/BAMLET, display cytotoxic properties against cancer cells. However, there is still a substantial debate about the role of the protein in these complexes. To shed light into this, we obtained three different BAMLET complexes using varying synthesis conditions. Our data suggest that to form active BAMLET particles, OA has to reach critical micelle concentration with an approximate diameter of 250 nm. Proteolysis experiments on BAMLET show that OA protects the protein and is probably located on the surface, consistent with a micelle-like structure. Native or unfolded α-lactalbumin without OA lacked any tumoricidal activity. In contrast, OA alone killed cancer cells with the same efficiency at equimolar concentrations as its formulation as BAMLET. Our data show unequivocally that the cytotoxicity of the BAMLET complex is exclusively due to OA and that OA alone, when formulated as a micelle, is as toxic as the BAMLET complex. The contradictory literature results on the cytotoxicity of BAMLET might be explained by our finding that it was imperative to sonicate the samples to obtain toxic OA.

Oleic acid complex of bovine α-lactalbumin induces eryptosis in human and other erythrocytes by a Ca(2+)-independent mechanism

BACKGROUND

Complexes of oleic acid (OA) with milk α-lactalbumin, received remarkable attention in view of their selective toxicity towards a spectrum of tumors during the last two decades. OA complexes of some structurally related/unrelated proteins are also tumoricidal. Erythrocytes are among the few differentiated cells that are sensitive and undergo hemolysis when exposed to the complexes.

METHODS

The effects of OA complex of bovine α-lactalbumin (Bovine Alpha-lactalbumin Made LEthal to Tumor cells, BAMLET) on human, goat and chicken erythrocytes on calcein leakage, phosphatidylserine exposure, morphological changes and hemolysis were studied by confocal microscopy, FACS analysis, scanning electron microscopy and measuring hemoglobin release.

RESULTS

Erythrocytes exposed to BAMLET undergo eryptosis-like alterations as revealed by calcein leakage, surface phosphatidylserine exposure and transformation to echinocytes at low concentrations and hemolysis when the concentration of the complex was raised. Ca(2+) was not essential and restricted the alterations when included in the medium. The BAMLET-induced alterations in human erythrocytes were prevented by the cation channel inhibitors, amiloride and BaCl2 but not by inhibitors of thiol proteases, sphingomyelinase and by the antioxidant N-acetyl cysteine.

CONCLUSIONS

The work shows for the first time that low concentrations of BAMLET induces eryptosis in erythrocytes by a novel mechanism not requiring Ca(2+) and hemolysis by detergent-like action by the released OA at higher concentrations.

GENERAL SIGNIFICANCE

The study points out to the need for a comprehensive evaluation of the toxicity of OA complexes of α-lactalbumin and other proteins towards erythrocytes and other differentiated cells before being considered for therapy.

Self-assembled β-lactoglobulin-oleic acid and β-lactoglobulin-linoleic acid complexes with antitumor activities

β-Lactoglobulin (β-LG) can bind to fatty acids such as oleic acid (OA) and linoleic acid (LA). Another whey protein, α-lactalbumin (α-LA), can also bind to OA to give the complex α-LA-OA, which has antitumor properties. Based on reports that the activity of α-LA-OA is highly dependent on OA, as well as the acquisition of similar complexes using other proteins, such as lysozyme and lactoferrin, we speculated whether β-LG could also kill tumor cells after binding to other fatty acids. Therefore, we prepared complexes of β-LG with OA (β-LG-OA) and LA (β-LG-LA) in the current study and evaluated them in terms of antitumor activity and thermostability using the methylene blue method and differential scanning calorimetry, respectively. The structural features of these complexes were also evaluated using fluorescence spectroscopy and circular dichroism. The binding dynamics of OA and LA to β-LG were studied using isothermal titration calorimetry. Cell viability results revealed that β-LG-LA and β-LG-OA exhibited similar antitumor activities. Interestingly, the binding of β-LG to LA led to an increase in its thermostability, whereas its binding to OA had very little effect. The environments of the tryptophan residues in the β-LG-OA and β-LG-LA complexes were very different, with the residues being blue- and red-shifted, respectively. Furthermore, the hydrophobic regions in β-LG were buried after binding of OA, which was slightly changed in β-LG-LA. Circular dichroism results showed that β-LG-OA enhanced the tertiary structure, which was partially lost in β-LG-LA. There were more binding sites for OA than for LA on β-LG, although the binding constants of the 2 fatty acids were similar, with both acids interacting with the protein though van der Waals and hydrogen bonding interactions. This study could help provide a deeper understanding of the structural basis for formation of antitumor protein-fatty acid complexes.