Peptide drug development has made great progress in the last decade thanks to new production, modification, and analytic technologies. Peptides have been produced and modified using both chemical and biological methods, together with novel design and delivery strategies, which have helped to overcome the inherent drawbacks of peptides and have allowed the continued advancement of this field. A wide variety of natural and modified peptides have been obtained and studied, covering multiple therapeutic areas. This review summarizes the efforts and achievements in peptide drug discovery, production, and modification, and their current applications. We also discuss the value and challenges associated with future developments in therapeutic peptides.

The management of bacterial infections is becoming a major clinical challenge due to the rapid evolution of antibiotic resistant bacteria. As an excellent candidate to overcome antibiotic resistance, antimicrobial peptides (AMPs) that are produced from the synthetic and natural sources demonstrate a broad-spectrum antimicrobial activity with the high specificity and low toxicity. These peptides possess distinctive structures and functions by employing sophisticated mechanisms of action. This comprehensive review provides a broad overview of AMPs from the origin, structural characteristics, mechanisms of action, biological activities to clinical applications. We finally discuss the strategies to optimize and develop AMP-based treatment as the potential antimicrobial and anticancer therapeutics.

Though many studies were performed to assess the association between tumor necrosis factor-α (TNF-α) 238 G/A polymorphism and gastric cancer risk, there were no conclusive findings. A meta-analysis of previous published studies was performed to get a comprehensive assessment of the association between TNF-α 238 G/A polymorphisms and gastric cancer. The pooled odds ratios (ORs) and 95% confidence intervals (95 % CIs) were calculated to assess the association. Fifteen studies with a total of 7,795 participants were finally included into this meta-analysis. Overall, there was an obvious association between TNF-α 238 G/A polymorphism and increased risk of gastric cancer (A vs. G: OR = 1.32, 95% CI 1.02-1.72, P = 0.036; GA vs. GG: OR = 1.32, 95% CI 1.01-1.72, P = 0.042; and AA/GA vs. GG: OR = 1.34, 95% CI 1.02-1.76, P = 0.036). Subgroup analysis by ethnicity showed the statistically significant association between TNF-α 238 G/A polymorphism and gastric cancer was limited to Asian populations (A vs. G: OR = 1.59, 95% CI 1.29-1.97, P < 0.001; GA vs. GG: OR = 1.63, 95% CI 1.29-2.04, P < 0.001; and AA/GA vs. GG: OR = 1.64, 95%CI 1.31-2.05, P < 0.001), and there was no obvious association in Caucasians. In conclusion, TNF-α 238 G/A polymorphism is significantly associated with increased risk of gastric cancer, especially in Asians.

The neurokinin‐1 receptor (NK‐1R) antagonists are approved as treatment for chemotherapy‐associated nausea and vomiting in cancer patients. The emerging role of the substance P‐NK‐1R system in oncogenesis raises the possibility of repurposing well‐tolerated NK‐1R antagonists for cancer treatment. This study reports that human colorectal cancer (CRC) patients with high NK‐1R expression have poor survival, and NK‐1R antagonists SR140333 and aprepitant induce apoptotic cell death in CRC cells and inhibit CRC xenograft growth. This cytotoxicity induced by treatment with NK‐1R antagonists is mediated by induction of endoplasmic reticulum (ER) stress. ER stress triggers calcium release, resulting in the suppression of prosurvival extracellular signal‐regulated kinase (ERK)‐c‐Myc signaling. Along with ER calcium release, one ER stress pathway mediated by protein kinase RNA‐like ER kinase (PERK) is specifically activated, leading to increased expression of proapoptotic C/EBP‐homologous protein (CHOP). Moreover, NK‐1R antagonists enhance the efficacy of chemotherapy by increasing the sensitivity and overcoming resistance to 5‐fluorouracil in CRC cells through the induction of sustained ER stress and the consequent suppression of ERK‐c‐Myc signaling both in vitro and in vivo. Collectively, the findings provide novel mechanistic insights into the efficacy of NK‐1R antagonists either as a single agent or in combination with chemotherapy for cancer treatment.

Acute myeloid leukemia (AML) is a complex malignancy characterized by the clonal expansion of immature myeloid precursors. The standard treatment for newly diagnosed AML is chemotherapy consisting of cytosine arabinoside (Ara-C) and anthracyclines with disappointing clinical outcomes and severe adverse effects, such as symptomatic bradycardia, neurotoxicity. Thus, it is promising to treat AML through combination drug therapy to reduce the adverse effects of chemotherapeutics. In our recent published PNAS paper, we reported that NK-1R antagonists, both Aprepitant and SR140333, induce apoptosis of myeloid leukemia cells by inducing oxidative stress through mitochondrial calcium overload. We, therefore, tested the hypothesis of the combination Ara-C with NK-1R antagonist could enhance the efficacy of Ara-C. Methods: MTT assay was employed to detect the cell proliferation. Flow cytometry was applied to detect the cell cycle and necrosis. PI uptake and LDH release assay were used to detect the disintegration of the plasma membrane. Xenograft model was constructed to explore the effect of combination Ara-C with Aprepitant in vivo. Results: Our results showed that Aprepitant sensitizes HL60 cells to the cytotoxic effects of Ara-C more than 5-fold by enhancing G0/G1 cell cycle arrest and necrosis in vitro. Furthermore, Nec-1, a specific inhibitor of necroptosis, could recover the cell proliferative viability significantly. Attractively, once every 2-days regimen of Ara-C (5 mg/kg) and Aprepitant (10 mg/kg) via in situ injection dramatically reduced the tumor volume from 2175.0 ± 341.9 mm 3 in the vehicle group to 828.4 ± 232.4 mm 3 in the combination group without obvious toxicity in human myeloid leukemia xenograft mice. Conclusion: Taken together, reduced dose of Ara-C combination with moderate Aprepitant provides more effective therapeutical methods for AML treatment in vitro and in vivo with the elimination of the toxicity of Ara-C, which may pay new avenue for the usage of the routine chemotherapy drug Ara-C with low dose to enhance efficacy and reduce toxicity in clinical practice.

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