Multivalent display of pendant pro-apoptotic peptides increases cytotoxic activity

Evolving strategies and application of proteins and peptide therapeutics in cancer treatment

Several proteins and peptides have therapeutic potential and can be used for cancer therapy. By binding to cell surface receptors and other indicators uniquely linked with or overexpressed on tumors compared to healthy tissue, protein biologics enhance the active targeting of cancer cells, as opposed to the passive targeting of cells by conventional small-molecule chemotherapeutics. This study focuses on peptide medications that exist to slow or stop tumor growth and the spread of cancer, demonstrating the therapeutic potential of peptides in cancer treatment. As an alternative to standard chemotherapy, peptides that selectively kill cancer cells while sparing healthy tissue are developing. A mountain of clinical evidence supports the efficacy of peptide-based cancer vaccines. Since a single treatment technique may not be sufficient to produce favourable results in the fight against cancer, combination therapy is emerging as an effective option to generate synergistic benefits. One example of this new area is the use of anticancer peptides in combination with nonpeptidic cytotoxic drugs or the combination of immunotherapy with conventional therapies like radiation and chemotherapy. This review focuses on the different natural and synthetic peptides obtained and researched. Discoveries, manufacture, and modifications of peptide drugs, as well as their contemporary applications, are summarized in this review. We also discuss the benefits and difficulties of potential advances in therapeutic peptides.

A Smart "Energy NanoLock" Selectively Blocks Oral Cancer Energy Metabolism through Synergistic Inhibition of Exogenous Nutrient Supply and Endogenous Energy Production

The major challenge in oral cancer is the lack of state-of-the-art treatment modality that effectively cures cancer while preserving oral functions. Recent insights into tumor metabolic dependency provide a therapeutic opportunity for exploring optimal treatment approaches. Herein, a smart responsive "Energy NanoLock" is developed to improve cancer metabolic intervention by simultaneously inhibiting nutrient supply and energy production. NanoLock is a pomegranate-like nanocomplex of cyclicRGD-modified carboxymethyl chitosan (CyclicRC, pI = 6.7) encapsulating indocyanine green and apoptotic peptides functionalized gold nanoparticles (IK-AuNPs), which together form a dual pH- and photoresponsive therapeutic platform. NanoLock exhibits good stability under physiological conditions, but releases small-size CyclicRC and IK-AuNPs in response to the tumor acidic microenvironment, leading to deep tumor penetration. CyclicRC targets integrins to inhibit tumor angiogenesis, and consequently blocks tumor nutrient supply. Meanwhile, IK-AuNPs specifically induce apoptotic peptides and photothermally mediated mitochondrial collapse, and consequently inhibits endogenous energy production, thereby facilitating cell death. Importantly, in both xenograft and orthotopic oral cancer models, NanoLock selectively eliminates tumors with little cross-reactivity with normal tissues, especially oral functions, resulting in prolonged survival of mice. Therefore, NanoLock provides a novel metabolic therapy to exploit synergistic inhibition of exogenous nutrient supply and endogenous energy production, which potentially advances oral cancer treatment.

Tailored protein-conjugated DNA nanoplatform for synergistic cancer therapy

Multidrug resistance (MDR) to chemotherapeutic drugs and targeted drug delivery are recurring issues in clinical cancer treatment. Here, a multifunctional fusion protein-DNA conjugate was designed as a co-delivery vehicle for anticancer peptides and chemotherapeutic drugs to combat both drug-resistant and drug-sensitive tumor cells. The fusion protein was constructed by fusing a PsTag polypeptide, a matrix metalloproteinase 2 (MMP2)-degradable domain, and the mitochondria-targeted pro-apoptotic peptide KLAKLAKKLAKLAK. Doxorubicin was efficiently loaded into the fusion protein pre-conjugated dendrimer-like DNA nanostructure. With the incorporation of enhanced stability, tumor targeting, and controlled-release elements, the tailored nanostructure can selectively enter tumor cells and synergistically exert antitumor activity with no significant adverse effects. Thus, these protein-conjugated DNA nanocarriers could be a potential co-delivery system for protein/peptide and chemotherapeutic drugs delivery in synergistic cancer therapy.

Origin of Proteolytic Stability of Peptide-Brush Polymers as Globular Proteomimetics

Peptide-brush polymers (PBPs), wherein every side-chain of the polymers is peptidic, represent a new class of proteomimetic with unusually high proteolytic resistance while maintaining bioactivity. Here, we sought to determine the origin of this behavior and to assess its generality via a combined theory and experimental approach. A series of PBPs with various polymer backbone structures were prepared and examined for their proteolytic stability and bioactivity. We discovered that an increase in the hydrophobicity of the polymer backbones is predictive of an elevation in proteolytic stability of the side-chain peptides. Computer simulations, together with small-angle X-ray scattering (SAXS) analysis, revealed globular morphologies for these polymers, in which pendant peptides condense around hydrophobic synthetic polymer backbones driven by the hydrophobic effect. As the hydrophobicity of the polymer backbones increases, the extent of solvent exposure of peptide cleavage sites decreases, reducing their accessibility to proteolytic enzymes. This study provides insight into the important factors driving PBP aqueous-phase structures to behave as globular, synthetic polymer-based proteomimetics.

Design of Polymeric Carriers for Intracellular Peptide Delivery in Oncology Applications

In recent decades, peptides, which can possess high potency, excellent selectivity, and low toxicity, have emerged as promising therapeutics for cancer applications. Combined with an improved understanding of tumor biology and immuno-oncology, peptides have demonstrated robust antitumor efficacy in preclinical tumor models. However, the translation of peptides with intracellular targets into clinical therapies has been severely hindered by limitations in their intrinsic structure, such as low systemic stability, rapid clearance, and poor membrane permeability, that impede intracellular delivery. In this Review, we summarize recent advances in polymer-mediated intracellular delivery of peptides for cancer therapy, including both therapeutic peptides and peptide antigens. We highlight strategies to engineer polymeric materials to increase peptide delivery efficiency, especially cytosolic delivery, which plays a crucial role in potentiating peptide-based therapies. Finally, we discuss future opportunities for peptides in cancer treatment, with an emphasis on the design of polymer nanocarriers for optimized peptide delivery.

Emerging trends of receptor-mediated tumor targeting peptides: A review with perspective from molecular imaging modalities

Natural peptides extracted from natural components such are known to have a relatively short in-vivo half-life and can readily metabolize by endo- and exo-peptidases. Fortunately, synthetic peptides can be easily manipulated to increase in-vivo stability, membrane permeability and target specificity with some well-known natural families. Many natural as well as synthetic peptides target to their endogenous receptors for diagnosis and therapeutic applications. In order to detect these peptides externally, they must be modified with radionuclides compatible with single photon emission computed tomography (SPECT) or positron emission tomography (PET). Although, these techniques mainly rely on physiological changes and have profound diagnostic strength over anatomical modalities such as MRI and CT. However, both SPECT and PET observed to possess lack of anatomical reference frame which is a key weakness of these techniques, and unfortunately, cannot be available freely in most clinical centres especially in under-developing countries. Hence, it is need of the time to design and develop economic, patient friendly and versatile strategies to grapple with existing problems without any hazardous side effects. Optical molecular imaging (OMI) has emerged as a novel technique in field of medical science using fluorescent probes as imaging modality and has ability to couple with organic drugs, small molecules, chemotherapeutics, DNA, RNA, anticancer peptide and protein without adding chelators as necessary for radionuclides. Furthermore, this review focuses on difference in imaging modalities and provides ample knowledge about reliable, economic and patient friendly optical imaging technique rather radionuclide-based imaging techniques.

Advances in cancer treatment: a new therapeutic target, Annexin A2

Annexin A2 (ANXA2) is a calcium regulated phospholipid-binding protein. It is expressed in some tumor cells, endothelial cells, macrophages, and mononuclear cells, affecting cell survival and mediating interactions between intercellular and extracellular microenvironment. Aberrant expression of ANXA2 can be used as a potential predictive factor, diagnostic biomarker and therapeutic target in cancer therapy. Investigators used various technologies to target ANXA2 in a preclinical model of human cancers and demonstrated encouraging results. In this review article, we discuss the diagnosis and prognosis latent capacity of ANXA2 in progressive cancers, focus on the exploration of restorative interventions targeting ANXA2 in cancer treatment. Further, we comment on a promising candidate therapy that is conceivable for clinical translation.

Molecular targeted treatment and drug delivery system for gastric cancer

Gastric cancer is still a major cancer worldwide. The early diagnosis rate of gastric cancer in most high incidence countries is low. At present, the overall treatment effect of gastric cancer is poor, and the median overall survival remains low. Most of the patients with gastric cancer are in an advanced stage when diagnosed, and drug treatment has become the main means. Thus, new targeted drugs and therapeutic strategies are the hope of improving the therapeutic effect of gastric cancer. In this review, we summarize the new methods and advances of targeted therapy for gastric cancer, including novel molecular targeted therapeutic agents and drug delivery systems, with a major focus on the development of drug delivery systems (drug carriers and targeting peptides). Elaborating these new methods and advances will contribute to the management of gastric cancer.

Fluorescent RGD-based pro-apoptotic peptide conjugates as mitochondria-targeting probes for enhanced anticancer activities

We have designed 2-domain anticancer peptides with RGD-based KLAK bi-functional short motifs (linear and cyclic analogues). RGD tripeptide acts as tumor blood vessel 'homing' motif while KLAK tetrapeptide internalized in mitochondria and causes cell apoptosis. All three peptides (RGDKLAK; HM, cyclic-RGDKLAK; HMC-1, and RGD-cyclic-KLAK; HMC-2) were conjugated with fluorescein isothiocyanate isomer-I (5-FITC; F) for in-vivo and in-vitro optical imaging studies. These fluorescent-peptide (FL-peptide) analogues were analyzed to possess α_vβ₃-integrin targeting affinity, high uptake in in-vitro cell binding assays followed by in-vivo tumor xenograft mice studies. Pharmacological profile reveals that F-HMC-1 analogue exhibited selectively and specifically higher affinity for α_vβ₃-integrin than other analogues in U87MG cells in comparison with HeLa cells. The subcutaneous U87MG tumor xenograft mice models clearly visualized the uptake of F-HMC-1 in tumor tissue in contrast with normal tissues with tumor-to-normal tissue ratio (T/NT = 15.9 ± 1.1) at 2 h post-injection. These results suggested that F-HMC-1 peptide has potential diagnostic applications for targeting α_vβ₃-integrin assessed by optical imaging study in U87MG tumor xenograft mice models.

Mechanistic Landscape of Membrane-Permeabilizing Peptides

Membrane permeabilizing peptides (MPPs) are as ubiquitous as the lipid bilayer membranes they act upon. Produced by all forms of life, most membrane permeabilizing peptides are used offensively or defensively against the membranes of other organisms. Just as nature has found many uses for them, translational scientists have worked for decades to design or optimize membrane permeabilizing peptides for applications in the laboratory and in the clinic ranging from antibacterial and antiviral therapy and prophylaxis to anticancer therapeutics and drug delivery. Here, we review the field of membrane permeabilizing peptides. We discuss the diversity of their sources and structures, the systems and methods used to measure their activities, and the behaviors that are observed. We discuss the fact that "mechanism" is not a discrete or a static entity for an MPP but rather the result of a heterogeneous and dynamic ensemble of structural states that vary in response to many different experimental conditions. This has led to an almost complete lack of discrete three-dimensional active structures among the thousands of known MPPs and a lack of useful or predictive sequence-structure-function relationship rules. Ultimately, we discuss how it may be more useful to think of membrane permeabilizing peptides mechanisms as broad regions of a mechanistic landscape rather than discrete molecular processes.

Pro-apoptotic peptides-based cancer therapies: challenges and strategies to enhance therapeutic efficacy

Cancer is a leading cause of death worldwide. Despite many advances in the field of cancer therapy, an effective cure is yet to be found. As a more potent alternative for the conventional small molecule anti-cancer drugs, pro-apoptotic peptides have emerged as a new class of anticancer agents. By interaction with certain members in the apoptotic pathways, they could effectively kill tumor cells. However, there remain bottleneck challenges for clinical application of these pro-apoptotic peptides in cancer therapy. In this review, we will overview the developed pro-apoptotic peptides and outline the widely adopted molecular-based and nanoparticle-based strategies to enhance their anti-tumor effects.

Polymeric therapeutic delivery systems for the treatment of infectious diseases

Infectious diseases caused by germs, parasites, fungi, virus and bacteria are one of the leading causes of death worldwide. Polymeric therapeutics are nanomedicines that offer several advantages making them useful for the treatment of infectious diseases such as targeted drug release mechanism, ability to maintain the drug concentration within a therapeutic window for a desired duration, biocompatibility with low immunogenicity and reduced drug toxicity resulting in enhanced therapeutic efficacy of the incorporated drug. Although polymeric therapeutics have been evaluated for the treatment of infectious diseases in vitro and in vivo with improved therapeutic efficacy, most treatments for infectious disease have not been evaluated using polymeric therapeutics. This review will focus on the applications of polymeric therapeutics for the treatment of infectious diseases (preclinical studies and clinical trials), with particular focus on parasitic and viral infections.

Adipose mesenchymal stem cells from osteoporotic donors preserve functionality and modulate systemic inflammatory microenvironment in osteoporotic cytotherapy

Maintenance of bone homeostasis against diseased microenvironments remains as a major challenge. Recently, mesenchymal stem cells (MSCs) have been unravelled as potent microenvironmental modulators, the systemic infusion of which in cytotherapy can prevent or rescue extensive bone loss via anti-inflammation. However, MSCs also accept microenvironmental regulations; particularly, MSCs from bone marrow (BMMSCs) are prone to pathological microenvironmental factors of bone. In this study, we discovered that BMMSCs from osteoporotic donors of ovariectomized (OVX) mice lost their anti-inflammatory capability and failed to prevent bone loss when infused back into OVX recipients. Nevertheless, MSCs from adipose tissues (ADMSCs) preserved their anti-inflammatory capacity, despite diseased microenvironments of OVX donors, and continued to show protective effects on bone in OVX recipients. In the cellular level, the anti-inflammatory superiority of osteoporotic donor-derived ADMSCs over BMMSCs existed in their distinctive capability to induce T-cell apoptosis, which was molecularly attributed to retained expression levels of critical immunomodulatory genes. Furthermore, these functional discrepancies of BMMSCs and ADMSCs were due to differential stemness, energy metabolism and anti-oxidative defence system, underlying general disparity in their cellular states. Collectively, our findings optimize osteoporotic cytotherapy by using ADMSCs in resistance to and in modulation of diseased microenvironments.

Administration of 5-methoxyindole-2-carboxylic acid that potentially targets mitochondrial dihydrolipoamide dehydrogenase confers cerebral preconditioning against ischemic stroke injury

The objective of this study was to investigate a possible role of mitochondrial dihydrolipoamide dehydrogenase (DLDH) as a chemical preconditioning target for neuroprotection against ischemic injury. We used 5-methoxyindole-2-carboxylic acid (MICA), a reportedly reversible DLDH inhibitor, as the preconditioning agent and administered MICA to rats mainly via dietary intake. Upon completion of 4 week's MICA treatment, rats underwent 1h transient ischemia and 24h reperfusion followed by tissue collection. Our results show that MICA protected the brain against ischemic stroke injury as the infarction volume of the brain from the MICA-treated group was significantly smaller than that from the control group. Data were then collected without or with stroke surgery following MICA feeding. It was found that in the absence of stroke following MICA feeding, DLDH activity was lower in the MICA treated group than in the control group, and this decreased activity could be partly due to DLDH protein sulfenation. Moreover, DLDH inhibition by MICA was also found to upregulate the expression of NAD(P)H-ubiquinone oxidoreductase 1(NQO1) via the Nrf2 signaling pathway. In the presence of stroke following MICA feeding, decreased DLDH activity and increased Nrf2 signaling were also observed along with increased NQO1 activity, decreased oxidative stress, decreased cell death, and increased mitochondrial ATP output. We also found that MICA had a delayed preconditioning effect four weeks post MICA treatment. Our study indicates that administration of MICA confers chemical preconditioning and neuroprotection against ischemic stroke injury.

The effects of ligand valency and density on the targeting ability of multivalent nanoparticles based on negatively charged chitosan nanoparticles

It has been shown that multivalent ligands could significantly enhance the binding avidity compared with the monovalent ones; therefore, once incorporated into nanoparticles, they promote superior targeting ability without increasing the ligand density. Although ligand valency and density play a key role on the targeting ability of corresponding nanoparticles, these facotrs remain largely unexplored and detailed studies are lacking. Herein, a series of multivalent ligands with certain valencies (FA_n, n indicates the valency of ligand: n=3, 5, 7) has been conveniently synthesized by conjugating different copies of folate ligands with poly(acrylic acid) (PAA). Negatively charged chitosan nanoparticles (CTS-SA NPs) have been utilized as proper multivalent platforms because they can strongly suppress non-specific protein adsorption and cellular uptake without interfering with the targeting ability of multivalent ligands. Subsequently, the structure of CTS-SA NPs has been modified using different amounts of FA_n to form multivalent nanoparticles (FA_n-CTS-SA NPs) with various valencies and densities. A series of specific investigations of them suggested that the cellular uptake of multivalent nanoparticles has largely varied with the ligand valency variation even at similar ligand densities; and also largely varied with ligand density variation even at the same ligand valencies. The intermediate valency and density values determined in the current study (ie., 5 and 2.4wt%, respectively) have provided the best cellular uptake, facilitating superior targeting ability at relatively low ligand valency and density. Unexpectedly, no conspicuous difference has been observed during endocytotic inhibition assays with single inhibitors, which may be attributed to the synergetic endocytotic mechanism with multiple pathways of multivalent nanoparticles. The optimal multivalent nanoparticles have also exhibited excellent biocompatibility, long-term stability in vitro and enhanced circulation time in vivo, thus demonstrating their potential for targeted drug delivery.

Two birds, one stone: dual targeting of the cancer cell surface and subcellular mitochondria by the galectin-3-binding peptide G3-C12

Active tumor-targeting approaches using specific ligands have drawn considerable attention over the years. However, a single ligand often fails to simultaneously target the cancer cell surface and subcellular organelles, which limits the maximum therapeutic efficacy of delivered drugs. We describe a polymeric delivery system modified with the G3-C12 peptide for sequential dual targeting. In this study, galectin-3-targeted G3-C12 peptide was conjugated onto the N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer for the delivery of _D(KLAKLAK)₂ (KLA) peptide. G3-C12-HPMA-KLA exhibited increased receptor-mediated internalization into galectin-3-overexpressing PC-3 cells. Furthermore, G3-C12 peptide also directed HPMA-KLA conjugates to mitochondria. This occurred because the apoptosis signal triggered the accumulation of galectin-3 in mitochondria, and the G3-C12 peptide that specifically bound to galectin-3 was trafficked along with its receptor intracellularly. As a result, G3-C12-HPMA-KLA disrupted the mitochondrial membrane, increased the generation of reactive oxygen species (ROS) and induced cytochrome c release, which ultimately resulted in enhanced cytotoxicity. An in vivo study revealed that the G3-C12 peptide significantly enhanced the tumor accumulation of the KLA conjugate. In addition, G3-C12-HPMA-KLA exhibited the best therapeutic efficacy and greatly improved the animal survival rate. Our work demonstrates that G3-C12 is a promising ligand with dual-targeting functionality.

Tumor-penetrating peptide fused to a pro-apoptotic peptide facilitates effective gastric cancer therapy

KLA (sequence, KLAKLAKKLAKLAK) is a peptide which leads to programmed cell death by disrupting the mitochondrial membrane. However, low penetration in tumors greatly limits its application and efficacy. To develop a KLA-based cancer therapy, KLA-iRGD, a recombinant protein was constructed. It consists of the KLA peptide and iRGD (CRGDKGPDC), a tumor-homing peptide with high penetration into tumor tissue and cells. The conjugated KLA exhibits pro-apoptotic activity to prevent the growth of a tumor once it is inside the cell. Once KLA-iRGD is internalized in cultured tumor cells, via the activation of the receptor neuropilin-1, it spreads extensively throughout the mass of the tumor. The recombinant KLA-iRGD protein showed antitumor activity in vivo in mice and in vitro in tumor cell lines. Repeated treatment with KLA-iRGD greatly prevented tumor growth, resulting in a considerable reduction in tumor volume. According to our data, KLA-iRGD may serve as a potential anticancer agent with limited systemic toxicity and high selectivity for the treatment of MKN45 gastric cancer, which may lead to the enhancement of new targeted anticancer agents.

Nebulized anionic guanidinylated O-carboxymethyl chitosan/N-2-hydroxypropyltimehyl ammonium chloride chitosan nanoparticles for siRNA pulmonary delivery: preparation, characterization and in vitro evaluation

This study developed a pH-sensitive anionic system composed of guanidinylated O-carboxymethyl chitosan (GOCMCS) and N-2-hydroxypropyltimehyl ammonium chloride chitosan (N-2-HACC) for efficient siRNA delivery to the lungs following nebulization. About 16.8% of guanidine groups were incorporated into O-carboxymethyl chitosan (OCMCS) with the aid of O-methylisourea. Gel electrophoresis images demonstrated that siRNA was successfully encapsulated in nanoparticles ranging from 150 to 180 nm with zeta potential of about -17 mV. The nanoparticles containing GOCMCS existed superior transfection performance compared with their amino-based analogs. The evaluation in vitro revealed that nanoparticles were internalized into A549 cells by energy-dependent endocytosis, then achieved endosomal escape by direct transmembrane penetration of guanidine moieties as well as swelling behavior of nanoparticles due to the pH sensitivity of GOCMCS. The mRNA level of survivin gene was down-regulated to 6.9% using GOCMCS/N-2-HACC/siSurvivin NPs. The survivin siRNA mediated by nanoparticles caused 30% of cell growth inhibition and induced 19.45% of cell apoptosis, which was comparable to Lipofectamin2000. After nebulization of siRNA-loaded nanoparticles, the stability of siRNA was maintained and fine particle fractions were detected by two-stage impinger that accounted for more than 60%. These results suggested that GOCMCS/N-2-HACC nanoparticles possessed potential as safe and efficient carrier for siRNA pulmonary delivery.

Synthesis and evaluation of multivalent M2pep peptides for targeting alternatively activated M2 macrophages

The tumor microenvironment in the majority of cancers is known to favor polarization of tumor-associated macrophages (TAMs) to alternatively activated M2 phenotype, promoting disease progression and reducing patient survival. Effective therapy targeting this M2 macrophage population is thus a promising adjuvant to approved cancer therapies. One of the challenges in targeting M2-like TAMs is a lack of high affinity targeting ligand with good selectivity over anti-tumor M1-like TAMs. We have previously identified an M2 macrophage-targeting peptide (M2pep) that binds preferentially to murine M2 macrophages and M2-like TAMs. A fusion peptide of M2pep with pro-apoptotic peptide KLA (M2pepKLA) was further used to reduce TAM population in vivo but high concentrations and frequent dosing were required due to low binding affinity of M2pep for M2 macrophage. The goal of this study was to develop more potent TAM depletion constructs by increasing the valency of both the M2pep targeting and KLA drug domains. Divalent and tetravalent displays of M2pep ([M2pep]2-Biotin and [M2pep]4-Biotin) were synthesized and evaluated for improvement in binding avidity to the murine macrophages. High avidity and selective binding of [M2pep]2-Biotin to M2 macrophages were achieved with at least 10-fold lower concentration than required for monovalent M2pep activity. Increasing M2pep valency to four, however, resulted in a reduction in both binding activity and selectivity. Surprisingly, both divalent and tetravalent M2pep, without conjugation of any cytotoxic drug cargo, exhibited M2 macrophage-selective toxicity not observed in monovalent M2pep treatment. We next synthesized divalent M2pep with monovalent and divalent KLA ([M2pep]2-[KLA] and [M2pep]2-[KLA]2) to evaluate its enhanced potency compared to M2pepKLA. While both constructs were significantly more toxic than M2pepKLA to primary, bone marrow-derived M2 macrophage, desired selectivity was retained only with [M2pep]2-[KLA]. Finally, we evaluated all multivalent M2pep and M2pepKLA analogs using a syngeneic CT-26 tumor cell suspension. In this setting, [M2pep]4-Biotin and [M2pep]2-[KLA]2 exhibited selective toxicity to both M2-like TAMs and malignant cells but not to M1-like TAMs. Therefore, these constructs are promising anti-cancer constructs with dual-modality mechanisms: malignant cell killing and TAM-based immunomodulation.