Boosting the anti-tumor activity of natural killer cells by caripe 8 - A Carapichea ipecacuanha isolated cyclotide.

Cyclotides are head-to-tail cyclized peptides with a unique cystine-knot motif. Their structure provides exceptional resistance against enzymatic, chemical, or thermal degradation compared to other peptides. Peptide-based therapeutics promise high specificity, selectivity and lower immunogenicity, making them safer alternatives to small molecules or large biologicals. Cyclotides were researched due to their anti-cancer properties by inducing apoptosis in tumor cells in the past, but the impact of cyclotides on cytotoxic immune cells was poorly studied. Natural Killer (NK) cells are cytotoxic innate lymphoid cells and play an important role in the defense against infected, stressed and transformed cells. NK cells do not need prior sensitization and act in an antigen independent manner, holding promising potential in the field of immunotherapy. To investigate the effect of immunomodulatory cyclotides on NK cells, we evaluated several peptide-enriched plant extracts on NK cell mediated cytotoxicity. We observed that the extract samples derived from Carapichea ipecacuanha (Brot.) L. Andersson augments the killing potential of mouse NK cells against different tumor targets in vitro. Subsequent isolation of cyclotides from C. ipecacuanha extracts led to the identification of a primary candidate that enhances cytotoxicity of both mouse and human NK cells. The augmented killing is facilitated by the increased degranulation capacity of NK cells. In addition, we noted a direct toxic effect of caripe 8 on tumor cells, suggesting a dual therapeutic potential in cancer treatment. This study offers novel insights how natural peptides can influence NK cell cytotoxicity. These pre-clinical findings hold significant promise for advancing current immunotherapeutic approaches.

The nature inspired peptide [T20K]-kalata B1 induces anti-tumor effects in anaplastic large cell lymphoma.

Ribosomally synthesized and post-translationally modified peptides, such as plant cyclotides, are a diverse group of natural products well known as templates in drug discovery and therapeutic lead development. The cyclotide kalata B1 (kB1) has previously been discovered as immunosuppressive agent on T-lymphocytes, and a synthetic version of this peptide, [T20K]kB1 (T20K), has been effective in reducing clinical symptoms, such as inflammation and demyelination, in a mouse model of multiple sclerosis. Based on its T-cell modulatory impact we studied the effects of T20K and several analogs on the proliferation of anaplastic large cell lymphoma (ALCL), a heterogeneous group of clinically aggressive diseases associated with poor prognosis. T20K, as a prototype drug candidate, induces apoptosis and a proliferation arrest in human lymphoma T-cell lines (SR786, Mac-2a and the Jurkat E6.1) in a concentration dependent fashion, at least partially via increased STAT5 and p53 signaling. In contrary to its effect on IL-2 signaling in lymphocytes, the cytokine levels are not altered in lymphoma cells. In vivo mouse experiments revealed a promising activity of T20K on these cancer cells including decreased tumor weight and increased apoptosis. This study opens novel avenues for developing cyclotide-based drug candidates for therapy of patients with ALCL.

STAT5 Is a Key Regulator in NK Cells and Acts as a Molecular Switch from Tumor Surveillance to Tumor Promotion.

UNLABELLED: Natural killer (NK) cells are tightly regulated by the JAK-STAT signaling pathway and cannot survive in the absence of STAT5. We now report that STAT5-deficient NK cells can be rescued by overexpression of BCL2. Our experiments define STAT5 as a master regulator of NK-cell proliferation and lytic functions. Although NK cells are generally responsible for killing tumor cells, the rescued STAT5-deficient NK cells promote tumor formation by producing enhanced levels of the angiogenic factor VEGFA. The importance of VEGFA produced by NK cells was verified by experiments with a conditional knockout of VEGFA in NK cells. We show that STAT5 normally represses the transcription of VEGFA in NK cells, in both mice and humans. These findings reveal that STAT5-directed therapies may have negative effects: In addition to impairing NK-cell-mediated tumor surveillance, they may even promote tumor growth by enhancing angiogenesis. SIGNIFICANCE: The importance of the immune system in effective cancer treatment is widely recognized. We show that the new signal interceptors targeting the JAK-STAT5 pathway may have dangerous side effects that must be taken into account in clinical trials: inhibiting JAK-STAT5 has the potential to promote tumor growth by enhancing NK-cell-mediated angiogenesis.

Loss of STAT3 in murine NK cells enhances NK cell-dependent tumor surveillance.

The members of the signal transducer and activator of transcription (STAT) family of transcription factors modulate the development and function of natural killer (NK) cells. NK cell-mediated tumor surveillance is particularly important in the body's defense against hematological malignancies such as leukemia. STAT3 inhibitors are currently being developed, although their potential effects on NK cells are not clear. We have investigated the function of STAT3 in NK cells with Stat3(Δ/Δ)Ncr1-iCreTg mice, whose NK cells lack STAT3. In the absence of STAT3, NK cells develop normally and in normal numbers, but display alterations in the kinetics of interferon-γ (IFN-γ) production. We report that STAT3 directly binds the IFN-γ promoter. In various in vivo models of hematological diseases, loss of STAT3 in NK cells enhances tumor surveillance. The reduced tumor burden is paralleled by increased expression of the activating receptor DNAM-1 and the lytic enzymes perforin and granzyme B. Our findings imply that STAT3 inhibitors will stimulate the cytolytic activity of NK cells against leukemia, thereby providing an additional therapeutic benefit.