Peptides as innovative strategies to combat drug resistance in cancer therapy.

Drug resistance is the leading cause of treatment failure in patients with cancer. Thus, innovative therapeutic strategies are required to overcome this critical challenge and improve patient outcomes. In this review, we examine the potential of peptide-based therapies to combat drug resistance in cancer.

Cyclic tachyplesin I kills proliferative, non-proliferative and drug-resistant melanoma cells without inducing resistance.

Acquired drug resistance is the major cause for disease recurrence in cancer patients, and this is particularly true for patients with metastatic melanoma that carry a BRAF mutation. To address this problem, we investigated cyclic membrane-active peptides as an alternative therapeutic modality to kill drug-tolerant and resistant melanoma cells to avoid acquired drug resistance. We selected two stable cyclic peptides (cTI and cGm), previously shown to have anti-melanoma properties, and compared them with dabrafenib, a drug used to treat cancer patients with the BRAF mutation.

Molecular dynamics simulations support a preference of cyclotide kalata B1 for phosphatidylethanolamine phospholipids.

Kalata B1 (kB1), a naturally occurring cyclotide has been shown experimentally to bind lipid membranes that contain phosphatidylethanolamine (PE) phospholipids. Here, molecular dynamics simulations were used to explore its interaction with two phospholipids, palmitoyloleoylphosphatidylethanolamine (POPE), palmitoyloleoylphosphatidylcholine (POPC), and a heterogeneous membrane comprising POPC/POPE (90:10), to understand the basis for the selectivity of kB1 towards PE phospholipids. The simulations showed that in the presence of only 10 % POPE lipid, kB1 forms a stable binding complex with membrane bilayers.

Delivery to, and Reactivation of, the p53 Pathway in Cancer Cells Using a Grafted Cyclotide Conjugated with a Cell-Penetrating Peptide.

Peptides are promising drug modalities that can modulate protein-protein interactions, but their application is hampered by their limited ability to reach intracellular targets. Here, we improved the cytosolic delivery of a peptide blocking p53:MDM2/X interactions using a cyclotide as a stabilizing scaffold. We applied several design strategies to improve intracellular delivery and found that the conjugation of the lead cyclotide to the cyclic cell-penetrating peptide cR10 was the most effective.

Modified horseshoe crab peptides target and kill bacteria inside host cells.

Bacteria that occupy an intracellular niche can evade extracellular host immune responses and antimicrobial molecules. In addition to classic intracellular pathogens, other bacteria including uropathogenic Escherichia coli (UPEC) can adopt both extracellular and intracellular lifestyles. UPEC intracellular survival and replication complicates treatment, as many therapeutic molecules do not effectively reach all components of the infection cycle.

Cyclic peptide scaffold with ability to stabilize and deliver a helical cell-impermeable cargo across membranes of cultured cancer cells.

Cell penetrating peptides (CPPs) are valuable tools for developing anticancer therapies due to their ability to access intracellular targets, including protein-protein interactions. cPF4PD is a newly described CPP designed from a transduction domain of the human defense protein platelet factor 4 (PF4), that also has antimalarial activity. The cPF4PD peptide recapitulates the helical structure of the PF4 domain and maintains activity against intracellular malaria parasites a selective membrane-active mechanism.

Designed β-Hairpins Inhibit LDH5 Oligomerization and Enzymatic Activity.

Lactate dehydrogenase 5 (LDH5) is overexpressed in metastatic tumors and is an attractive target for anticancer therapy. Small-molecule drugs have been developed to target the substrate/cofactor sites of LDH5, but none has reached the clinic to date, and alternative strategies remain almost unexplored. Combining rational and computer-based approaches, we identified peptidic sequences with high affinity toward a β-sheet region that is involved in protein-protein interactions (PPIs) required for the activity of LDH5.

Mode-of-Action of Antimicrobial Peptides: Membrane Disruption vs. Intracellular Mechanisms.

Antimicrobial peptides are an attractive alternative to traditional antibiotics, due to their physicochemical properties, activity toward a broad spectrum of bacteria, and mode-of-actions distinct from those used by current antibiotics. In general, antimicrobial peptides kill bacteria by either disrupting their membrane, or by entering inside bacterial cells to interact with intracellular components. Characterization of their mode-of-action is essential to improve their activity, avoid resistance in bacterial pathogens, and accelerate their use as therapeutics.

Cyclic gomesin, a stable redesigned spider peptide able to enter cancer cells.

Anticancer chemo- and targeted therapies are limited in some cases due to strong side effects and/or drug resistance. Peptides have received renascent interest as anticancer therapeutics and are currently being considered as alternatives and/or as complementary to biologics and small-molecule drugs. Gomesin, a disulfide-rich host defense peptide expressed in the Brazilian spider Acanthoscurria gomesiana selectively targets and disrupts cancer cell membranes.

Safer In Vitro Drug Screening Models for Melioidosis Therapy Development.

Melioidosis is a neglected tropical disease caused by the Gram-negative soil bacterium Current antibiotic regimens used to treat melioidosis are prolonged and expensive, and often ineffective because of intrinsic and acquired antimicrobial resistance. Efforts to develop new treatments for melioidosis are limited by the risks associated with handling pathogenic , which restricts research to facilities with biosafety level three containment. Closely related nonpathogenic can be investigated under less stringent biosafety level two containment, and we hypothesized that they could be used as model organisms for developing therapies that would also be effective against .

Antimicrobial Peptide Mimetics Based on a Diphenylacetylene Scaffold: Synthesis, Conformational Analysis, and Activity.

Mimics of natural antimicrobial peptides are promising compounds to fight the rising threat of multi-drug resistant bacteria. Here we report the design, synthesis and conformational analysis of a new class of antimicrobial peptide mimetics incorporating a diphenylacetylene scaffold. Within a small set of compounds, we observe a correlation between amphiphilicity, the efficiency of partitioning into negatively charged membranes and antibacterial activity.

Discovery and mechanistic studies of cytotoxic cyclotides from the medicinal herb .

Cyclotides are plant-derived peptides characterized by an ∼30-amino acid-long cyclic backbone and a cystine knot motif. Cyclotides have diverse bioactivities, and their cytotoxicity has attracted significant attention for its potential anticancer applications. (Linn) F.

Is the Mirror Image a True Reflection? Intrinsic Membrane Chirality Modulates Peptide Binding.

Peptides with pharmaceutical activities are attractive drug leads, and knowledge of their mode-of-action is essential for translation into the clinic. Comparison of native and enantiomeric peptides has long been used as a powerful approach to discriminate membrane- or receptor-mediated modes-of-action on the basis of the assumption that interactions with cell membranes are independent of peptide chirality. Here, we revisit this paradigm with the cyclotide kalata B1, a drug scaffold with intrinsic membrane-binding activity whose enantiomer is less potent than native peptide.

Cyclic Analogues of Horseshoe Crab Peptide Tachyplesin I with Anticancer and Cell Penetrating Properties.

Tachyplesin-I (TI) is a host defense peptide from the horseshoe crab that has outstanding potential as an anticancer therapeutic lead. Backbone cyclized TI (cTI) has similar anticancer properties to TI but has higher stability and lower hemolytic activity. We designed and synthesized cTI analogues to further improve anticancer potential and investigated structure-activity relationships based on peptide-membrane interactions, cellular uptake, and anticancer activity.

Characterization of Tachyplesin Peptides and Their Cyclized Analogues to Improve Antimicrobial and Anticancer Properties.

Tachyplesin I, II and III are host defense peptides from horseshoe crab species with antimicrobial and anticancer activities. They have an amphipathic β-hairpin structure, are highly positively-charged and differ by only one or two amino acid residues. In this study, we compared the structure and activity of the three tachyplesin peptides alongside their backbone cyclized analogues.

Cell Membrane Composition Drives Selectivity and Toxicity of Designed Cyclic Helix-Loop-Helix Peptides with Cell Penetrating and Tumor Suppressor Properties.

The tumor suppressor protein p53 is inactive in a large number of cancers, including some forms of sarcoma, breast cancer, and leukemia, due to overexpression of its intrinsic inhibitors MDM2 and MDMX. Reactivation of p53 tumor suppressor activity, via disruption of interactions between MDM2/X and p53 in the cytosol, is a promising strategy to treat cancer. Peptides able to bind MDM2 and/or MDMX were shown to prevent MDM2/X:p53 interactions, but most possess low cell penetrability, low stability, and/or high toxicity to healthy cells.

Peptide-Membrane Interactions Affect the Inhibitory Potency and Selectivity of Spider Toxins ProTx-II and GpTx-1.

Gating modifier toxins (GMTs) from spider venom can inhibit voltage gated sodium channels (Nas) involved in pain signal transmission, including the Na1.7 subtype. GMTs have a conserved amphipathic structure that allow them to interact with membranes and also with charged residues in regions of Na that are exposed at the cell surface.

PHAB toxins: a unique family of predatory sea anemone toxins evolving via intra-gene concerted evolution defines a new peptide fold.

Sea anemone venoms have long been recognized as a rich source of peptides with interesting pharmacological and structural properties, but they still contain many uncharacterized bioactive compounds. Here we report the discovery, three-dimensional structure, activity, tissue localization, and putative function of a novel sea anemone peptide toxin that constitutes a new, sixth type of voltage-gated potassium channel (K) toxin from sea anemones. Comprised of just 17 residues, κ-actitoxin-Ate1a (Ate1a) is the shortest sea anemone toxin reported to date, and it adopts a novel three-dimensional structure that we have named the Proline-Hinged Asymmetric β-hairpin (PHAB) fold.

Defense Peptides Engineered from Human Platelet Factor 4 Kill Plasmodium by Selective Membrane Disruption.

Malaria is a serious threat to human health and additional classes of antimalarial drugs are greatly needed. The human defense protein, platelet factor 4 (PF4), has intrinsic antiplasmodial activity but also undesirable chemokine properties. We engineered a peptide containing the isolated PF4 antiplasmodial domain, which through cyclization, retained the critical structure of the parent protein.

Gating modifier toxins isolated from spider venom: Modulation of voltage-gated sodium channels and the role of lipid membranes.

Gating modifier toxins (GMTs) are venom-derived peptides isolated from spiders and other venomous creatures and modulate activity of disease-relevant voltage-gated ion channels and are therefore being pursued as therapeutic leads. The amphipathic surface profile of GMTs has prompted the proposal that some GMTs simultaneously bind to the cell membrane and voltage-gated ion channels in a trimolecular complex. Here, we examined whether there is a relationship among spider GMT amphipathicity, membrane binding, and potency or selectivity for voltage-gated sodium (Na) channels.

Structure, Function, and Biosynthetic Origin of Octapeptin Antibiotics Active against Extensively Drug-Resistant Gram-Negative Bacteria.

Resistance to the last-resort antibiotic colistin is now widespread and new therapeutics are urgently required. We report the first in toto chemical synthesis and pre-clinical evaluation of octapeptins, a class of lipopeptides structurally related to colistin. The octapeptin biosynthetic cluster consisted of three non-ribosomal peptide synthetases (OctA, OctB, and OctC) that produced an amphiphilic antibiotic, octapeptin C4, which was shown to bind to and depolarize membranes.

Mechanisms of bacterial membrane permeabilization by crotalicidin (Ctn) and its fragment Ctn(15-34), antimicrobial peptides from rattlesnake venom.

Crotalicidin (Ctn), a cathelicidin-related peptide from the venom of a South American rattlesnake, possesses potent antimicrobial, antitumor, and antifungal properties. Previously, we have shown that its C-terminal fragment, Ctn(15-34), retains the antimicrobial and antitumor activities but is less toxic to healthy cells and has improved serum stability. Here, we investigated the mechanisms of action of Ctn and Ctn(15-34) against Gram-negative bacteria.

Redesigned Spider Peptide with Improved Antimicrobial and Anticancer Properties.

Gomesin, a disulfide-rich antimicrobial peptide produced by the Brazilian spider Acanthoscurria gomesiana, has been shown to be potent against Gram-negative bacteria and to possess selective anticancer properties against melanoma cells. In a recent study, a backbone cyclized analogue of gomesin was shown to be as active but more stable than its native form. In the current study, we were interested in improving the antimicrobial properties of the cyclic gomesin, understanding its selectivity toward melanoma cells and elucidating its antimicrobial and anticancer mode of action.