A natural product, Piperlongumine (PL), increases tumor cells sensitivity to NK cell killing.

Natural Killer (NK) cells are components of innate immune surveillance against transformed cells. NK cell immunotherapy has attracted attention as a promising strategy for cancer treatment, whose antitumor effects, however, require further improvement. The use of small molecules with immunomodulatory potentials and selective tumor-killing possesses the potential to complement immunotherapy. This study demonstrated that Piperlongumine (PL), a natural alkaloid obtained from long pepper fruit, alone has antitumor and anti-proliferative potential on all the tested tumors in vitro. PL pretreatment of tumor cells also potentiates their susceptibility to NK cell cytolysis at the doses where NK cell functions were preserved. Importantly, PL suppresses both NK -sensitive MHC-I -deficient and MHC-I -sufficient tumor growth in vivo. Mechanistically, PL induces misfolded proteins, impedes autophagy, increases ROS and tumor conjugation with NK cells. Furthermore, PL enhances the expression of NK cell-activating receptors on NK cells and its ligands on tumor cells, possibly leading to increased susceptibility to NK cell killing. Our findings showed the antitumor and immunomodulatory potential of PL, which could be explored to complement NK cell immunotherapy for cancer treatment.

Piperlongumine and some of its analogs inhibit selectively the human immunoproteasome over the constitutive proteasome.

The natural small molecule piperlongumine A is toxic selectively to cancer cells in vitro and in vivo. This toxicity has been correlated with cancer cell ROS, DNA damage and apoptotic cell death increases. We demonstrate here a new mechanistic property of piperlongumine: it inhibits selectively human immunoproteasome with no noticeable inhibition of human constitutive proteasome. This result suggests that immunoproteasome inhibition, a mechanism independent of ROS elevation, may also partly play a role in the anticancer effects observed with piperlongumine. Structure-activity relationships of piperlongumine analogs suggest that the lactam (piperidonic) ring of piperlongumine A may be replaced by the linear olefin -NHCO-CH2=CH2 to improve both in vitro inhibitory efficiency against immunoproteasome and cellular toxicity.

Human Platelets Utilize Cycloxygenase-1 to Generate Dioxolane A3, a Neutrophil-activating Eicosanoid.

Eicosanoids are important mediators of fever, pain, and inflammation that modulate cell signaling during acute and chronic disease. We show by using lipidomics that thrombin-activated human platelets generate a new type of eicosanoid that both stimulates and primes human neutrophil integrin (Mac-1) expression, in response to formylmethionylleucylphenylalanine. Detailed characterization proposes a dioxolane structure, 8-hydroxy-9,11-dioxolane eicosatetraenoic acid (dioxolane A3, DXA3). The lipid is generated in nanogram amounts by platelets from endogenous arachidonate during physiological activation, with inhibition by aspirin in vitro or in vivo, implicating cyclooxygenase-1 (COX). Pharmacological and genetic studies on human/murine platelets revealed that DXA3 formation requires protease-activated receptors 1 and 4, cytosolic phospholipase A2 (cPLA2), Src tyrosine kinases, p38 MAPK, phospholipase C, and intracellular calcium. From data generated by purified COX isoforms and chemical oxidation, we propose that DXA3 is generated by release of an intermediate from the active site followed by oxygenation at C8. In summary, a new neutrophil-activating platelet-derived lipid generated by COX-1 is presented that can activate or prime human neutrophils, suggesting a role in innate immunity and acute inflammation.

[Antigenicity studies of prulifloxacin (NM441)].

Antigenicity of prulifloxacin, a new antibacterial agent, and that of its active metabolite (NM394) were investigated using guinea pigs and mice in this study. In the study with guinea pigs, the animals were immunized with prulifloxacin by oral administration, the predetermined clinical route, and with prulifloxacin alone or emulsified with Freund's complete adjuvant (FCA) by s.c. When active systemic anaphylaxis (ASA) test and passive cutaneous anaphylaxis (PCA) test of these animals were conducted by eliciting with NM394 alone or protein conjugate (NM394-GPSA) of NM394 and guinea pig serum albumin (GPSA), no ASA and PCA reactions were observed. When guinea pigs were immunized subcutaneously with protein conjugate (NM394-BSA) of NM394 and bovine serum albumin (BSA) together with FCA, ASA and PCA reactions were positive by eliciting with NM394-GPSA or NM394-BSA, but were negative by eliciting with NM394 alone. In the study with mice, the animals were immunized orally with prulifloxacin and intraperitoneally with prulifloxacin alone or suspended with aluminum hydroxide gel (alum). When rat PCA test of sera from these mice was conducted by eliciting with NM394 or NM394-GPSA, no positive PCA reaction was observed. When mice were immunized intraperiotneally with NM394-BSA together with alum, PCA reactions were positive by eliciting with NM394-GPSA or NM394-BSA, but were negative by eliciting with NM394 alone. These results show that prulifloxacin has no immunogenicity to guinea pigs and mice, and NM394 as its active form has no eliciting potential to anti-NM394-BSA antibody.