The development of activatable lytic peptides for targeting triple negative breast cancer

Targeting androgen receptor (AR) with a synthetic peptide increases apoptosis in triple negative breast cancer and AR-expressing prostate cancer cell lines

BACKGROUND

The androgen receptor (AR) has been studied as an approach to cancer therapy.

AIMS

We used human breast cancer-derived cells with high, low, and very low expression levels of AR, in addition to prostate cancer-derived LNCaP and DU-145 cells as a positive and negative controls to examine apoptosis caused by a synthetic peptide that targets ARs.

METHODS AND RESULTS

The peptide was produced to inhibit AR transactivation in breast cancer cell lines. We then measured cell viability, caspase-3 activity, and the ratio of Bax/Bcl-2. The findings indicated that the peptide (100-500 nM) in the presence of dihydrotestosterone (DHT) reduced cell growth in cells with high and low expression level of AR (p < .001), but not in cells with very low levels of AR. Treatment with 100-500 nM of peptide activated caspase-3 and increased the ratio of Bax/Bcl-2 in cells with high and low expression levels of AR. Also, increasing concentrations of the peptide (100-500 nM) reduced BrdU incorporation in the presence of DHT and promoted apoptosis in cells with high and low expression levels of AR (p < .001).

CONCLUSION

The findings indicate the peptide significantly increased apoptosis in cancer cells.

Current therapeutic approaches and promising perspectives of using bioengineered peptides in fighting chemoresistance in triple-negative breast cancer

Breast cancer is a collation of malignancies that manifest in the mammary glands at the early stages. Among breast cancer subtypes, triple-negative breast cancer (TNBC) shows the most aggressive behavior, with apparent stemness features. Owing to the lack of response to hormone therapy and specific targeted therapies, chemotherapy remains the first line of the TNBC treatment. However, the acquisition of resistance to chemotherapeutic agents increase therapy failure, and promotes cancer recurrence and distant metastasis. Invasive primary tumors are the birthplace of cancer burden, though metastasis is a key attribute of TNBC-associated morbidity and mortality. Targeting the chemoresistant metastases-initiating cells via specific therapeutic agents with affinity to the upregulated molecular targets is a promising step in the TNBC clinical management. Exploring the capacity of peptides as biocompatible entities with the specificity of action, low immunogenicity, and robust efficacy provides a principle for designing peptide-based drugs capable of increasing the efficacy of current chemotherapy agents for selective targeting of the drug-tolerant TNBC cells. Here, we first focus on the resistance mechanisms that TNBC cells acquire to evade the effect of chemotherapeutic agents. Next, the novel therapeutic approaches employing tumor-targeting peptides to exploit the mechanisms of drug resistance in chemorefractory TNBC are described.

Development of sulfonium tethered peptides conjugated with HDAC inhibitor to improve selective toxicity for cancer cells

The anti-cancer peptides emerged as new weapons for cancer therapy due to their potent toxicity toward various cancer cells. However, their therapeutic promise is often limited by non-specific toxicity to normal cells. How to improve peptides' selectivity to cancer cells is always a matter to solve. In this manuscript, we designed a sulfonium tethered lytic peptide conjugated with a HDAC inhibitor to improve the selectivity of cancer cells. The sulfonium tethered lytic peptide with improved hydrophilicity and positive charge showed reduced toxicity to both cancer cells and normal cells. When conjugated with the HDAC inhibitor, this peptide showed increased toxicity to cancer cells. Besides, the stabilized peptide HDAC conjugate showed better serum stability than the linear peptide conjugate. For cellular function, the stabilized peptide conjugate could induce cancer cell apoptosis, cell cycle arrest, and influence multiple signal pathways through transcriptome analysis. This design may provide an alternative approach for the development of safe and effective anti-cancer drugs.

Targeting of the Interleukin-13 Receptor (IL-13R)α2 Expressing Prostate Cancer by a Novel Hybrid Lytic Peptide

The IL-13Rα2 cell surface receptor is highly expressed in tumours such as prostate cancer. In this report, we evaluated the hypothesis that prostate cancer cells with enhanced IL-13Rα2 expression are a suitable target for the hybrid lytic peptide (Pep-1-Phor21) peptide, which is generated by fusing the IL-13Rα2 specific ligand (Pep-1) and a cell membrane disrupting lytic peptide (Phor21). The expression of IL-13Rα2 mRNA and protein in prostate cancer tissues and cell lines was assessed via real-time PCR (RT-PCR) and immunoblotting. The effect of Pep-1-Phor21 on the viability of prostate cancer cells grown in monolayers (2D) and microtissue spheroids (3D) was assessed via CellTox green cytotoxic assay. IL-13Rα2 expression and Pep-1-Phor21-mediated killing were also determined in the cells treated with epigenetic regulators (Trichostatin A (TSA) and 5-aza-2 deoxycytidine (5-Aza-dC)). The hybrid lytic peptide cytotoxic activity correlated with the expression of IL-13Rα2 in prostate cancer cell lines cultured as monolayers (2D) or 3D spheroids. In addition, TSA or 5-Aza-dC treatment of prostate cancer cells, particularly those with low expression of IL-13Rα2, enhanced the cells' sensitivity to the lytic peptide by increasing IL-13Rα2 expression. These results demonstrate that the Pep-1-Phor21 hybrid lytic peptide has potent and selective anticancer properties against IL-13Rα2-expressing prostate cancer cells.

Conditional Antimicrobial Peptide Therapeutics

Antimicrobial peptides (AMPs) constitute a promising class of alternatives to antibiotics to curb antimicrobial resistance. Nonetheless, their utility as a systemic agent is hampered by short circulation time and toxicity. Infection sites, analogous to tumors, harbor an aberrant microenvironment that has the potential to be exploited to develop conditionally activated therapeutics with an improved therapeutic index. In particular, we identified strategies to prolong systemic circulation of small, cationic AMPs in a mouse model of bacterial pneumonia. Specifically, we report an albumin-binding domain (ABD)-AMP conjugate as a long-circulating conditional AMP therapeutic with a masked activity that can be liberated by proteases in the infected tissue microenvironment. Our systemically administered conjugate enhanced the pulmonary delivery of active AMP while also reducing AMP exposure to other off-target organs. Importantly, this reduction in off-target exposure improved the safety profile of the AMP. The framework we present can be generalized to quantify and optimize the performance of this emerging class of conditional therapeutics.

A VEGFR targeting peptide-drug conjugate (PDC) suppresses tumor angiogenesis in a TACE model for hepatocellular carcinoma therapy

Transcatheter arterial chemoembolization (TACE) has become the preferred therapy for unresectable advanced hepatocellular carcinoma (HCC). However, the embolization of tumor-feeding arteries by TACE always leads to hypoxia-related tumor angiogenesis, which limited the therapeutic effect for HCC. In this paper, we used a VEGFR targeting peptide VEGF125 − 136 (QKRKRKKSRYKS) to conjugate with a lytic peptide (KLUKLUKKLUKLUK) to form a peptide-drug conjugate (PDC). We used cell affinity assay to detect the peptide binding ability to VEGFR highly expressed cell lines, and CCK8, cell apoptosis to confirm the cellular toxicity for different cell lines. Meanwhile, we created a VX2 tumor-bearing rabbit model to assess the in vivo anti-tumor effect of the peptide conjugate in combination with TAE. HE staining was used to verify the in vivo safety of the peptide conjugate. IHC was used to assess the anti-angiogenesis and cell toxicity of the peptide conjugate in tumor tissues. The peptide conjugate could not only target VEGFR in cell surface and inhibit VEGFR function, but also have potent anti-cancer effect. We luckily found the peptide conjugate showed potent cytotoxicity for liver cancer cell Huh7 (IC50 7.3 ± 0.74 μM) and endothelial cell HUVEC (IC50 10.7 ± 0.292 μM) and induced cell apoptosis of these two cell lines. We also found the peptide conjugate inhibited cell migration of HUVEC through wound healing assay. Besides, these peptides also showed better in vivo anti-tumor effect than traditional drug DOX through TACE in VX2 rabbit tumor model, and efficiently inhibit angiogenesis in tumor tissues with good safety. In conclusion, our work may provide an alternative option for clinical HCC therapy via TACE combination.

Schematic presentation of the design of VEGFR targeting peptide conjugate (QR-KLU) and the antineoplastic efficacy of peptide QR-KLU in vitro and in vivo.

Integrated Design of a Membrane-Lytic Peptide-Based Intravenous Nanotherapeutic Suppresses Triple-Negative Breast Cancer

Membrane-lytic peptides offer broad synthetic flexibilities and design potential to the arsenal of anticancer therapeutics, which can be limited by cytotoxicity to noncancerous cells and induction of drug resistance via stress-induced mutagenesis. Despite continued research efforts on membrane-perforating peptides for antimicrobial applications, success in anticancer peptide therapeutics remains elusive given the muted distinction between cancerous and normal cell membranes and the challenge of peptide degradation and neutralization upon intravenous delivery. Using triple-negative breast cancer as a model, the authors report the development of a new class of anticancer peptides. Through function-conserving mutations, the authors achieved cancer cell selective membrane perforation, with leads exhibiting a 200-fold selectivity over non-cancerogenic cells and superior cytotoxicity over doxorubicin against breast cancer tumorspheres. Upon continuous exposure to the anticancer peptides at growth-arresting concentrations, cancer cells do not exhibit resistance phenotype, frequently observed under chemotherapeutic treatment. The authors further demonstrate efficient encapsulation of the anticancer peptides in 20 nm polymeric nanocarriers, which possess high tolerability and lead to effective tumor growth inhibition in a mouse model of MDA-MB-231 triple-negative breast cancer. This work demonstrates a multidisciplinary approach for enabling translationally relevant membrane-lytic peptides in oncology, opening up a vast chemical repertoire to the arms race against cancer.

Anti-cancer peptide-based therapeutic strategies in solid tumors

Background

Nowadays, conventional medical treatments such as surgery, radiotherapy, and chemotherapy cannot cure all types of cancer. A promising approach to treat solid tumors is the use of tumor-targeting peptides to deliver drugs or active agents selectively.

Result

Introducing beneficial therapeutic approaches, such as therapeutic peptides and their varied methods of action against tumor cells, can aid researchers in the discovery of novel peptides for cancer treatment. The biomedical applications of therapeutic peptides are highly interesting. These peptides, owing to their high selectivity, specificity, small dimensions, high biocompatibility, and easy modification, provide good opportunities for targeted drug delivery. In recent years, peptides have shown considerable promise as therapeutics or targeting ligands in cancer research and nanotechnology.

Conclusion

 This study reviews a variety of therapeutic peptides and targeting ligands in cancer therapy. Initially, three types of tumor-homing and cell-penetrating peptides (CPPs) are described, and then their applications in breast, glioma, colorectal, and melanoma cancer research are discussed.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

CpACpP: In Silico Cell-Penetrating Anticancer Peptide Prediction Using a Novel Bioinformatics Framework

Cell-penetrating anticancer peptides (Cp-ACPs) are considered promising candidates in solid tumor and hematologic cancer therapies. Current approaches for the design and discovery of Cp-ACPs trust the expensive high-throughput screenings that often give rise to multiple obstacles, including instrumentation adaptation and experimental handling. The application of machine learning (ML) tools developed for peptide activity prediction is importantly of growing interest. In this study, we applied the random forest (RF)-, support vector machine (SVM)-, and eXtreme gradient boosting (XGBoost)-based algorithms to predict the active Cp-ACPs using an experimentally validated data set. The model, CpACpP, was developed on the basis of two independent cell-penetrating peptide (CPP) and anticancer peptide (ACP) subpredictors. Various compositional and physiochemical-based features were combined or selected using the multilayered recursive feature elimination (RFE) method for both data sets. Our results showed that the ACP subclassifiers obtain a mean performance accuracy (ACC) of 0.98 with an area under curve (AUC) ≈ 0.98 vis-à-vis the CPP predictors displaying relevant values of ∼0.94 and ∼0.95 via the hybrid-based features and independent data sets, respectively. Also, the predicting evaluation of Cp-ACPs gave accuracies of ∼0.79 and 0.89 on a series of independent sequences by applying our CPP and ACP classifiers, respectively, which leaves the performance of our predictors better than the earlier reported ACPred, mACPpred, MLCPP, and CPPred-RF. The described consensus-based fusion method additionally reached an AUC of 0.94 for the prediction of Cp-ACP (http://cbb1.ut.ac.ir/CpACpP/Index).

Recent Advances in Therapeutic Peptides for Breast Cancer Treatment

Breast cancer is a heterogeneous malignancy and is the second leading cause of mortality among women around the world. Increasing the resistance to anti-cancer drugs in breast cancer cells persuades researchers to search the novel therapeutic approaches for the treatment of this malignancy. Among the novel methods, therapeutic peptides that target and disrupt tumor cells have been of great interest. Therapeutic peptides are short amino acid monomer chains with high specificity to bind and modulate a protein interaction of interest. Several advantages of peptides, such as specific binding on tumor cells surface, low molecular weight, and low toxicity on normal cells, make the peptides appealing therapeutic agents against solid tumors, particularly breast cancer. Also, the National Institutes of Health (NIH) describes therapeutic peptides as a suitable candidate for the treatment of drug-resistant breast cancer. In this review, we attempt to review the different therapeutic peptides against breast cancer cells that can be used in the treatment and diagnosis of the malignancy. Meanwhile, we presented an overview of peptide vaccines that have been developed for the treatment of breast cancer.

Targeting Cancer Heterogeneity with Immune Responses Driven by Oncolytic Peptides

Accumulating preclinical and clinical evidence indicates that high degrees of heterogeneity among malignant cells constitute a considerable obstacle to the success of cancer therapy. This calls for the development of approaches that operate - or enable established treatments to operate - despite such intratumoral heterogeneity (ITH). In this context, oncolytic peptides stand out as promising therapeutic tools based on their ability to drive immunogenic cell death associated with robust anticancer immune responses independently of ITH. We review the main molecular and immunological pathways engaged by oncolytic peptides, and discuss potential approaches to combine these agents with modern immunotherapeutics in support of superior tumor-targeting immunity and efficacy in patients with cancer.

Cytotoxic and antitumor peptides as novel chemotherapeutics

Covering: up to 2020Treatment resistance and drug-induced refractory malignancies pose significant challenges for current chemotherapy drugs. There have been increasing research efforts aimed at developing novel chemotherapeutics, especially from natural products and related derivatives. Natural cytotoxic peptides, an emerging source of chemotherapeutics, have exhibited the advantage of overcoming drug resistance and displayed broad-spectrum antitumor activities in the clinic. This highlight examines the increasingly popular cytotoxic peptides from isolated natural products. In-depth review of several peptides provides examples for how this novel strategy can lead to the improved anti-tumor effects. The mechanisms and current application of representative natural cytotoxic peptides (NCPs) have also been discussed, with a particular focus on future directions for interdisciplinary research.

miR-155 increases stemness and decitabine resistance in triple-negative breast cancer cells by inhibiting TSPAN5

Effective therapeutic targets for triple-negative breast cancer (TNBC), a special type of breast cancer (BC) with rapid metastasis and poor prognosis, are lacking, especially for patients with chemotherapy resistance. Decitabine (DCA) is a Food and Drug Administration-approved DNA methyltransferase inhibitor that has been proven effective for the treatment of tumors. However, its antitumor effect in cancer cells is limited by multidrug resistance. Cancer stem cells (CSCs), which are thought to act as seeds during tumor formation, regulate tumorigenesis, metastasis, and drug resistance through complex signaling. Our previous study found that miR-155 is upregulated in BC, but whether and how miR-155 regulates DCA resistance is unclear. In this study, we demonstrated that miR-155 was upregulated in CD24^- CD44⁺ BC stem cells (BCSCs). In addition, the overexpression of miR-155 increased the number of CD24^- CD44⁺ CSCs, DCA resistance and tumor clone formation in MDA-231 and BT-549 BC cells, and knockdown of miR-155 inhibited DCA resistance and stemness in BCSCs in vitro. Moreover, miR-155 induced stemness and DCA resistance by inhibiting the direct target gene tetraspanin-5 (TSPAN5). We further confirmed that overexpression of TSPAN5 abrogated the effect of miR-155 in promoting stemness and DCA resistance in BC cells. Our data show that miR-155 increases stemness and DCA resistance in BC cells by targeting TSPAN5. These data provide a therapeutic strategy and mechanistic basis for future possible clinical applications targeting the miR-155/TSPAN5 signaling axis in the treatment of TNBC.

GnRH-R-Targeted Lytic Peptide Sensitizes BRCA Wild-type Ovarian Cancer to PARP Inhibition

EP-100 is a synthetic lytic peptide that specifically targets the gonadotropin-releasing hormone receptor on cancer cells. To extend the utility of EP-100, we aimed to identify effective combination therapies with EP-100 for ovarian cancer and explore potential mechanisms of this combination. A series of in vitro (MTT assay, immunoblot analysis, reverse-phase protein array, comet assay, and immunofluorescence staining) and in vivo experiments were carried out to determine the biological effects of EP-100 alone and in combination with standard-of-care drugs. EP-100 decreased the viability of ovarian cancer cells and reduced tumor growth in orthotopic mouse models. Of five standard drugs tested (cisplatin, paclitaxel, doxorubicin, topotecan, and olaparib), we found that the combination of EP-100 and olaparib was synergistic in ovarian cancer cell lines. Further experiments revealed that combined treatment of EP-100 and olaparib significantly increased the number of nuclear foci of phosphorylated histone H2AX. In addition, the extent of DNA damage was significantly increased after treatment with EP-100 and olaparib in comet assay. We performed reverse-phase protein array analyses and identified that the PI3K/AKT pathway was inhibited by EP-100, which we validated with in vitro experiments. In vivo experiment using the HeyA8 mouse model demonstrated that mice treated with EP-100 and olaparib had lower tumor weights (0.06 ± 0.13 g) than those treated with a vehicle (1.19 ± 1.09 g), EP-100 alone (0.62 ± 0.78 g), or olaparib alone (0.50 ± 0.63 g). Our findings indicate that combining EP-100 with olaparib is a promising therapeutic strategy for ovarian cancer.

Lipopeptisomes: Anticancer peptide-assembled particles for fusolytic oncotherapy

Anticancer peptides (ACPs) are cationic amphiphiles that preferentially kill cancer cells through folding-dependent membrane disruption. Although ACPs represent attractive therapeutic candidates, particularly against drug-resistant cancers, their successful translation into clinical practice has gone unrealized due to their poor bioavailability, serum instability and, most importantly, severe hemolytic toxicity. Here, we exploit the membrane-specific interactions of ACPs to prepare a new class of peptide-lipid particle, we term a lipopeptisome (LP). This design sequesters loaded ACPs within a lipid lamellar corona to avoid contact with red blood cells and healthy tissues, while affording potent lytic destruction of cancer cells following LP-membrane fusion. Biophysical studies show ACPs rapidly fold at, and integrate into, liposomal membranes to form stable LPs with high loading efficiencies (>80%). Rational design of the particles to possess lipid combinations mimicking that of the aberrant cancer cell outer leaflet allows LPs to rapidly fuse with tumor cell membranes and afford localized assembly of loaded ACPs within the bilayer. This leads to preferential fusolytic killing of cancer cells with minimal collateral toxicity towards non-cancerous cells and erythrocytes, thereby imparting clinically relevant therapeutic indices to otherwise toxic ACPs. Thus, integration of ACPs into self-assembled LPs represents a new delivery strategy to improve the therapeutic utility of oncolytic agents, and suggests this technology may be added to targeted combinatorial approaches in precision medicine. STATEMENT OF SIGNIFICANCE: Despite their significant clinical potential, the therapeutic utility of many ACPs has been limited by their collateral hemolysis during administration. Leveraging the membrane-specific interactions of ACPs, here we prepare self-assembled peptide-lipid nanoparticles, or 'lipopeptisomes' (LPs), capable of preferentially fusing with and lysing cancer cell membranes. Key to this fusolytic action is the construction of LPs from lipids simulating the cancer cell outer leaflet. This design recruits the oncolytic peptide payload into the carrier lamella and allows for selective destruction of cancer cells without disrupting healthy cells. Consequently, LPs impart clinically relevant therapeutic indexes to previously toxic ACPs, and thus open new opportunities to improve the clinical translation of oncolytics challenged by narrow therapeutic windows.