Peptide-based inhibitors targeting the PD-1/PD-L1 axis: potential immunotherapeutics for cancer

The PD-1/PD-L1 complex belongs to the group of inhibitory immune checkpoints and plays a critical role in immune regulation. The PD-1/PD-L1 axis is also responsible for immune evasion of cancer cells, and this complex is one of the main targets of immunotherapies used in oncology. Treatment using immune checkpoint inhibitors is mainly based on antibodies. This approach has great therapeutic potential; however, it also has major drawbacks and can induce immune-related adverse events. Thus, there is a strong need for alternative, non-antibody-based therapies using small molecules, peptides, or peptidomimetics. In the present study, we designed, synthesized, and evaluated a set of PD-1-targeting peptides based on the sequence and structure of PD-L1. The binding of these peptides to PD-1 was investigated using SPR and ELISA. We also assessed their ability to compete with PD-L1 for binding to PD-1 and their inhibitory properties against the PD-1/PD-L1 complex at the cellular level. The best results were obtained for the peptide PD-L1(111-127)(Y112C-I126C), named (L11), which displaced PD-L1 from binding to PD-1 in the competitive assay and inhibited the formation of the PD-1/PD-L1 complex. The (L11) peptide also exhibited strong affinity for PD-1. NMR studies revealed that (L11) does not form a well-defined secondary structure; however, MD simulation indicated that (L11) binds to PD-1 at the same place as PD-L1. After further optimization of the structure, the peptide inhibitor obtained in this study could also be used as a potential therapeutic compound targeting the PD-1/PD-L1 axis.

BTLA-derived peptides as inhibitors of BTLA/HVEM complex formation - design, synthesis and biological evaluation

Immune checkpoints can be divided into co-stimulatory and co-inhibitory molecules that regulate the activation and effector functions of T cells. The co-inhibitory pathways mediated by ICPs are used by cancer cells to escape from immune surveillance, and therefore the blockade of these receptor/ligand interactions is one of the strategies used in the treatment of cancer. The two main pathways currently under investigation are CTLA-4/CD80/CD86 and PD-1/PD-L1, and the monoclonal Abs targeting them have shown potent immunomodulatory effects and activity in clinical environments. Another interesting target in cancer treatment is the BTLA/HVEM complex. Binding of BTLA protein on T cells to HVEM on cancer cells leads to inhibition of T cell proliferation and cytokine production. In the presented work, we focused on blocking the HVEM protein using BTLA-derived peptides. Based on the crystal structure of the BTLA/HVEM complex and MM/GBSA analysis performed here, we designed and synthesized peptides, specifically fragments of BTLA protein. We subsequently checked the inhibitory capacities of these compounds using ELISA and a cellular reporter platform. Two of these peptides, namely BTLA(35-43) and BTLA(33-64)C58Abu displayed the most promising properties, and we therefore performed further studies to evaluate their affinity to HVEM protein, their stability in plasma and their effect on viability of human PBMCs. In addition, the 3D structure for the peptide BTLA(33-64)C58Abu was determined using NMR. Obtained data confirmed that the BTLA-derived peptides could be the basis for future drugs and their immunomodulatory potential merits further examination.

Ultrasensitive electrochemical determination of the cancer biomarker protein sPD-L1 based on a BMS-8-modified gold electrode

This work describes the modification of a gold electrode with the BMS-8 compound that interacts with the Programmed Death-Ligand 1 (PD-L1), an immune checkpoint protein. The results show that we can confirm the presence of the sPD-L1 in the concentration range of 10^-18 to 10^-8 M using electrochemical impedance spectroscopy (EIS) with a limit of detection (LOD) of 1.87 × 10^-14 M for PD-L1 (S/N = 3.3) and at a concentration of 10^-14 M via cyclic voltammetry (CV). Additionally, high-resolution X-ray photoelectron spectroscopy (XPS), contact angle, and surface free energy measurements were applied to confirm the functionalization of the electrode. We investigated the selectivity of the electrode for other proteins: Programmed Death-1 (PD-1), cluster of differentiation 160 (CD160), and B- and T-lymphocyte attenuator (BTLA) at concentrations of 10^-8 M. Differentiation between PD-L1 and PD-1 was achieved based on the analysis of the capacitance effect frequency dispersion at the surface of the modified Au electrode with BMS-8 after incubation at various concentrations of PD-L1 and PD-1 proteins in the range of 10^-18 to 10^-8 M. Significant differences were observed in the heterogeneity of PD-L1 and PD-1. The results of the quasi-capacitance studies demonstrate that BMS-8 strongly and specifically interacts with the PD-L1 protein.

The effect of extender, method of thawing, and duration of storage on in vitro fertility measures of frozen-thawed boar sperm

Frozen-thawed boar sperm (FTS) has reduced in vitro and in vivo life span compared to liquid semen. Experiments tested whether extenders, thawing procedures, and storage temperatures could extend the fertile life span of FTS. Experiment 1 tested the effect of six extenders on postthaw motility (MOT) and viability (VIA). Straws from boars (n = 6) were thawed, diluted into each extender, and evaluated at 20, 60, and 120 minutes. There was a trend (P = 0.08) for an extender-by-time interaction for MOT and effect of extender and time for MOT (P < 0.0001) and extender (P = 0.10) and time (P < 0.0001) for VIA. Experiment 2 evaluated the effect of temperature and time of thawing on in vitro fertility at intervals after thawing. Straws (0.5 mL) from different boar ejaculates (n = 15) were thawed at 50 °C for 10, 20, or 30 seconds or at 70 °C for 5, 10, or 20 seconds and evaluated at 5, 30, and 60 minutes. There was an effect of thawing treatment on MOT, VIA, and ACR (viable sperm with intact acrosomes, P < 0.0001) and an effect of time of evaluation (P < 0.0001) on MOT and ACR. Thawing at 70 °C for 20 seconds reduced (P < 0.05) MOT, VIA, and ACR compared to other treatments. Experiment 3 tested the effects of storage temperature and time after thawing using 20 ejaculates. Samples were thawed, diluted, and allotted to storage at 17 °C, 26 °C, or 37 °C with evaluation at 2, 6, 12, and 24 hours. There was a storage temperature and time effect and an interaction for MOT and VIA (P < 0.0001). Storage at 17 °C and 26 °C increased (P < 0.05) MOT over all times (38.5%) compared to 37 °C (26%), whereas MOT was reduced at intervals. Viability was also greatest with 17 °C and 26 °C compared to 37 °C and was also affected by time and decreased with time. These results indicate that FTS can be held at 17 °C or 26 °C for up to 2 hours before use and would allow for preparation of multiple doses. These data suggest in vitro fertility of FTS is affected by extenders, thawing, and storage.

The basis of decreased recombination in certain outcrosses of Neurospora crassa

Crossing over in a multiply marked segment of linkage group I was conspicuously reduced in outcrosses between a marked laboratory strain and each of six unrelated wild-collected strains, compared with crosses between inbred laboratory strains. The marked chromosome segment was transferred intact from the inbred strain to one of the wild-collected strains by seven recurrent backcrosses, and conversely, the corresponding segment of the wild strain was transferred to the inbred background by backcrossing to the multiply marked laboratory strain. Recombination was then monitored in crosses from parents having the marked and unmarked chromosome segments from the same or from unrelated sources. Meiotic crossing-over in the marked segment remained low in crosses between parents that were dissimilar with respect to genetic background, but crossing over was restored to a high level when the genetic background of both parents was that of the inbred laboratory strain, regardless of the source of the marked segments. Reduced recombination in outcrosses was therefore not due to heterologies in the marked segment but must be attributed to modifiers that are unlinked or distant from the monitored region.

Synaptic adjustment of inversion loops in Neurospora crassa

Heterozygotes for three long inversions on chromosome 1 were analyzed by serial reconstruction from electron micrographs. Measurements of loop lengths at different meiotic prophase substages revealed that the homologous synapsis of the inverted region was gradually replaced by nonhomologous synapsis as loops were eliminated during pachytene. This synaptic adjustment was apparently not affected by crossovers which occurred within the 150- and 160-cM long loops.

Two kinds of "recombination nodules" in Neurospora crassa

Two morphological types of recombination nodules, termed early and late, are recognized in Neurospora crassa. Eighty nuclei at different substages were used to determine numbers of nodules per nucleus, distribution of nodules along the nucleolus-organizing chromosome, and distribution of nodules among the two largest chromosomes. Early nodules appear at the synaptonemal complex at early zygotene and increase in number during zygotene until a dramatic reduction occurs at zygotene-pachytene transition. Thereafter early nodules are steadily eliminated until they disappear by diplotene. Late nodules are also present during zygotene. Their number doubles at the zygotene-pachytene transition and stays at this level until diplotene. The total number of nodules is rather constant through zygotene and pachytene. Distribution of bivalents with 0, 1, 2, etc. nodules follows a Poisson distribution at zygotene, but not at pachytene, where variance is less than the mean, indicating positive interference. Nodules are distributed nonrandomly along the nucleolus-organizer bivalent. The pattern differs slightly in nuclei of different origin. Nuclei with unusual synaptonemal complexes sustain normal levels of recombination by having the same amount of nodules as normal nuclei. In abnormal nuclei nodules are preferentially associated with normal segments. It is proposed that early nodules do not participate in any form of recombination but have a role in finding an appropriate site for a crossing-over event. Morphological change to the late type indicates that the site has been reached and the exchange event can be mediated by the late nodule.

Presence of abnormal synaptonemal complexes in heterothallic species of Neurospora

Synaptonemal complex abnormalities are frequent in reconstructed meiotic prophase nuclei of Neurospora crassa and Neurospora intermedia. Three kinds of synaptonemal complex anomalies were seen: lateral component splits, lateral component junctions, and multiple complexes. The anomalies apparently are formed during or after the pairing process, as they were not seen in the largely unpaired early zygotene chromosomes. Their presence at all the other substages from mid-zygotene to late pachytene indicates that they are not eliminated before the synaptonemal complex decomposes at diplotene. Abnormal synaptonemal complexes were seen in all 19 crosses of N. crassa and N. intermedia that were examined, including matings between standard laboratory strains, inversions, Spore killers, and strains collected from nature. The frequency of affected nuclei and degree of abnormality within a nucleus varied in different matings. No abnormalities were present in the homothallic species Neurospora africana and Neurospora terricola. Structural chromosome aberrations, introgression, and heterozygosity have been eliminated as causes for pairing disorder. The abnormal synaptonemal complexes seemingly do not interfere with normal ascus development and ascospore formation. The affected nuclei are not aborted during meiotic prophase, nor are they eliminated by abortion of mature asci. The abnormal meiocytes do not lead to aneuploidy, as judged by the low frequency of white ascospores in crosses between wild type strains that have many abnormalities. Thus, the abnormal synatonemal complexes do not appear to prevent chiasma formation between homologues.