The Importance of 6-Aminohexanoic Acid as a Hydrophobic, Flexible Structural Element

Mono-amino acid linkers enable highly potent small molecule-drug conjugates by conditional release

The endosome cleavable linkers have been widely employed by antibody-drug conjugates and small molecule-drug conjugates (SMDCs) to control the accurate release of payloads. An effective linker should provide stability in systemic circulation but efficient payload release at its targeted tumor sites. This conflicting requirement always leads to linker design with increasing structural complexity. Balance of the effectiveness and structural complexity presents a linker design challenge. Here, we explored the possibility of mono-amino acid as so far the simplest cleavable linker (X-linker) for SMDC-based auristatin delivery. Within a diverse set of X-linkers, the SMDCs differed widely in bioactivity, with one (Asn-linker) having significantly improved potency (IC50 = 0.1 nM) and fast response to endosomal cathepsin B cleavage. Notably, this SMDC, once grafted with effector protein fragment crystallizable (Fc), demonstrated a profound in vivo therapeutic effect in aspects of targetability, circulation half-life (t1/2 = 73 h), stability, and anti-tumor efficacy. On the basis of these results, we believe that this mono-amino acid linker, together with the new SMDC-Fc scaffold, has significant potential in targeted delivery application.

A Modified Tridecapeptide Probe for Imaging Cell Junction

Cell junctions, which are typically associated with dynamic cytoskeletons, are essential for a wide range of cellular activities, including cell migration, cell communication, barrier function and signal transduction. Observing cell junctions in real-time can help us understand the mechanisms by which they regulate these cellular activities. This study examined the binding capacity of a modified tridecapeptide from Connexin 43 (Cx43) to the cell junction protein zonula occludens-1 (ZO-1). The goal was to create a fluorescent peptide that can label cell junctions. A cell-penetrating peptide was linked to the modified tridecapeptide. The heterotrimeric peptide molecule was then synthesized. The binding of the modified tridecapeptide was tested using pulldown and immunoprecipitation assays. The ability of the peptide to label cell junctions was assessed by adding it to fixed or live Caco-2 cells. The testing assays revealed that the Cx43-derived peptide can bind to ZO-1. Additionally, the peptide was able to label cell junctions of fixed cells, although no obvious cell junction labeling was observed clearly in live cells, probably due to the inadequate affinity. These findings suggest that labeling cell junctions using a peptide-based strategy is feasible. Further efforts to improve its affinity are warranted in the future.

Evaluating the In Vitro Activity and Safety of Modified LfcinB Peptides as Potential Colon Anticancer Agents: Cell Line Studies and Insect-Based Toxicity Assessments

Anticancer peptides are increasingly being considered as alternative treatments for cancer due to their potency, selectivity, and low toxicity. Previously, the peptide LfcinB (21-25)Pal showed in vitro anticancer effects against the Caco-2 colon cancer cell line (half-maximal inhibitory concentration (IC50): 86 μM). In this study, we developed modifications to the peptide sequence to increase its anticancer activity. Sequence modifications were made such as the inclusion of amino hexanoic acid (Ahx), N-terminal biotinylation, acetylation, and substitutions of Orn for Arg and/or d-Arg by l-Arg. The molecules were synthesized using manual solid-phase peptide synthesis (SPPS), and their synthetic feasibility (SAScore) ranged from 6.2 to 7.6. The chromatographic purities of the synthesized peptides were greater than 89%. We found that Ahx-RWQWRWQWR and RWQWRWQW-Orn showed activity against both Caco-2 and HT-29 cell lines and decreased IC50 values by approx. 50% in Caco-2 cells (IC50: 40 μM) when compared to the parent peptide RWQWRWQWR. Moreover, the modified peptides demonstrated lower hemolytic effects, with values <10% at 200 μg/mL. Toxicity was assessed using the Galleria mellonella model and the half-maximal lethal dose (LD50) for the best peptides was >100 mg/kg, indicating that their toxicity is classified as moderately toxic or lower. In contrast, cisplatin showed an LD50 of 13 mg/Kg. The designed anticancer peptides presented good in vitro activity and low toxicity, making them promising molecules for future drug development studies.

Evaluation of Linkers' Influence on Peptide-Based Piezoelectric Biosensors' Sensitivity to Aldehydes in the Gas Phase

Recent findings qualified aldehydes as potential biomarkers for disease diagnosis. One of the possibilities is to use electrochemical biosensors in point-of-care (PoC), but these need further development to overcome some limitations. Currently, the primary goal is to enhance their metrological parameters in terms of sensitivity and selectivity. Previous findings indicate that peptide OBPP4 (KLLFDSLTDLKKKMSEC-NH₂) is a promising candidate for further development of aldehyde-sensitive biosensors. To increase the affinity of a receptor layer to long-chain aldehydes, a structure stabilization of the peptide active site via the incorporation of different linkers was studied. Indeed, the incorporation of linkers improved sensitivity to and binding of aldehydes in comparison to that of the original peptide-based biosensor. The tendency to adopt disordered structures was diminished owing to the implementation of suitable linkers. Therefore, to improve the metrological characteristics of peptide-based piezoelectric biosensors, linkers were added at the C-terminus of OBPP4 peptide (KLLFDSLTDLKKKMSE-linker-C-NH₂). Those linkers consist of proteinogenic amino acids from group one: glycine, L-proline, L-serine, and non proteinogenic amino acids from group two: β-alanine, 4-aminobutyric acid, and 6-aminohexanoic acid. Linkers were evaluated with in silico studies, followed by experimental verification. All studied linkers enhanced the detection of aldehydes in the gas phase. The highest difference in frequency (60 Hz, nonanal) was observed between original peptide-based biosensors and ones based on peptides modified with the GSGSGS linker. It allowed evaluation of the limit of detection for nonanal at the level of 2 ppm, which is nine times lower than that of the original peptide. The highest sensitivity values were also obtained for the GSGSGS linker: 0.3312, 0.4281, and 0.4676 Hz/ppm for pentanal, octanal, and nonanal, respectively. An order of magnitude increase in sensitivity was observed for the six linkers used. Generally, the linker's rigidity and the number of amino acid residues are much more essential for biosensors' metrological characteristics than the amino acid sequence itself. It was found that the longer the linkers, the better the effect on docking efficiency.

In Silico and In Vivo Studies of a Tumor-Penetrating and Interfering Peptide with Antitumoral Effect on Xenograft Models of Breast Cancer

The combination of a tumor-penetrating peptide (TPP) with a peptide able to interfere with a given protein-protein interaction (IP) is a promising strategy with potential clinical application. Little is known about the impact of fusing a TPP with an IP, both in terms of internalization and functional effect. Here, we analyze these aspects in the context of breast cancer, targeting PP2A/SET interaction, using both in silico and in vivo approaches. Our results support the fact that state-of-the-art deep learning approaches developed for protein-peptide interaction modeling can reliably identify good candidate poses for the IP-TPP in interaction with the Neuropilin-1 receptor. The association of the IP with the TPP does not seem to affect the ability of the TPP to bind to Neuropilin-1. Molecular simulation results suggest that peptide IP-GG-LinTT1 in a cleaved form interacts with Neuropilin-1 in a more stable manner and has a more helical secondary structure than the cleaved IP-GG-iRGD. Surprisingly, in silico investigations also suggest that the non-cleaved TPPs can bind the Neuropilin-1 in a stable manner. The in vivo results using xenografts models show that both bifunctional peptides resulting from the combination of the IP and either LinTT1 or iRGD are effective against tumoral growth. The peptide iRGD-IP shows the highest stability to serum proteases degradation while having the same antitumoral effect as Lin TT1-IP, which is more sensitive to proteases degradation. Our results support the development of the TPP-IP strategy as therapeutic peptides against cancer.

In Vitro Antifungal Activity of Chimeric Peptides Derived from Bovine Lactoferricin and Buforin II against Cryptococcus neoformans var. grubii

Cryptococcosis is associated with high rates of morbidity and mortality. The limited number of antifungal agents, their toxicity, and the difficulty of these molecules in crossing the blood-brain barrier have made the exploration of new therapeutic candidates against Cryptococcus neoformans a priority task. To optimize the antimicrobial functionality and improve the physicochemical properties of AMPs, chemical strategies include combinations of peptide fragments into one. This study aimed to evaluate the binding of the minimum activity motif of bovine lactoferricin (LfcinB) and buforin II (BFII) against C. neoformans var. grubii. The antifungal activity against these chimeras was evaluated against (i) the reference strain H99, (ii) three Colombian clinical strains, and (iii) eleven mutant strains, with the aim of evaluating the possible antifungal target. We found high activity against these strains, with a MIC between 6.25 and 12.5 µg/mL. Studies were carried out to evaluate the effect of the combination of fluconazole treatments, finding a synergistic effect. Finally, when fibroblast cells were treated with 12.5 µg/mL of the chimeras, a viability of more than 65% was found. The results obtained in this study identify these chimeras as potential antifungal molecules for future therapeutic applications against cryptococcosis.

Host-genotype-dependent cecal microbes are linked to breast muscle metabolites in Chinese chickens

In chickens, the effect of host genetics on the gut microbiota is not fully understood, and the extent to which the heritable gut microbes affect chicken metabolism and physiology is still an open question. Here, we explored the interactions among chicken genetics, the cecal microbiota and metabolites in breast muscle from ten chicken breeds in China. We found that different chicken breeds displayed distinct cecal microbial community structures and functions, and 15 amplicon sequence variants (ASVs) were significantly associated with host genetics through different genetic loci, such as those related to the intestinal barrier function. We identified five heritable ASVs significantly associated with 53 chicken muscle metabolites, among which the Megamonas probably affected lipid metabolism through the production of propionate. Our study revealed that the chicken genetically associated cecal microbes may have the potential to affect the bird’s physiology and metabolism.

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The cecal microbiota are different among ten chicken breeds

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The chicken genetics influences the cecal microbiota structures and functions

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The chicken heritable cecal microbes are associated with muscle metabolites

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Megamonas may affect lipid metabolism by the production of propionate