Cancer cell membrane-derived nanoparticles block the expression of immune checkpoint proteins on cancer cells and coordinate modulatory activity on immunosuppressive macrophages.

Cancer is the most recurrent chronic disease in the world, with human hepatocellular carcinoma (HCC) being the second leading cause of death among neoplasias. The high frequency of HCC relapse and metastasis warrants the development of new diagnostic and therapeutic procedures. In advanced stages, neoplastic cells can evade immune surveillance and express immunosuppressive proteins and cytokines at tumor sites. Nanocomposites conjugated with immunomodulatory agents can increase the main mechanisms of cellular immunity. In this study, we used nanocarriers to transport oligonucleotide sequences (siRNAs) into cancer cells and leukocytes to modulate the activity of tumor microenvironment cells in vitro. Cell membrane-derived nanoparticles (MNPs) were synthesized with lipids and proteins from the plasma membrane of hepatic tumor cells to deliver a large amount of antigenic material to professional antigen-presenting cells (APCs), following their exposure to HCC and immunosuppressive macrophages. To establish a pro-inflammatory response, pure lipid MNPs were incorporated with monophosphoryl lipid A and siRNA to silence the c-MYC (myelocytomatosis) oncogene. Nanocarriers were tested for the following: (a) NP internalization into cancer and immunocompetent cells; (b) immunomodulatory activity by observing the expression of cell surface markers; and (c) in vitro cytotoxicity. The adsorption of plasma proteins on the MNPs surface and their effects on cellular uptake were also investigated. Our results indicate that the nanostructures are stable in biological suspensions, and can reduce CD47 and PD-L1 expression on cancer cells and simultaneously switch APC activity for an anti-tumor response.

Immunomodulatory properties of nanostructured systems for cancer therapy.

Based on statistical data reported in 2020, cancer was responsible for approximately 10 million deaths. Furthermore, 17 million new cases were diagnosed worldwide. Nanomedicine and immunotherapy have shown satisfactory clinical results among all scientific and technological alternatives for the treatment of cancer patients. Immunotherapy-based treatments comprise the consideration of new alternatives to hinder neoplastic proliferation and to reduce adverse events in the body, thereby promoting immune destruction of diseased cells. Additionally, nanostructured systems have been proven to elicit specific immune responses that may enhance anti-tumor activity. A new generation of nanomedicines, based on biomimetic and bioinspired systems, has been proposed to target tumors by providing immunomodulatory features and by enabling recovery of human immune destruction capacity against cancer cells. This review provides an overview of the aspects and the mechanisms by which nanomedicines can be used to enhance clinical procedures using the immune modulatory responses of nanoparticles (NPs) in the host defense system. We initially outline the cancer statistics for conventional and new treatment approaches providing a brief description of the human host defense system and basic principles of NP interactions with monocytes, leukocytes, and dendritic cells for the modulation of antitumor immune responses. A report on different biomimetic and bioinspired systems is also presented here and their particularities in cancer treatments are addressed, highlighting their immunomodulatory properties. Finally, we propose future perspectives regarding this new therapeutic strategy, highlighting the main challenges for future use in clinical practice.

Structural bases for a complete myotoxic mechanism: crystal structures of two non-catalytic phospholipases A2-like from Bothrops brazili venom.

Bothrops brazili is a snake found in the forests of the Amazonian region whose commercial therapeutic anti-bothropic serum has low efficacy for local myotoxic effects, resulting in an important public health problem in this area. Catalytically inactive phospholipases A2-like (Lys49-PLA2s) are among the main components from Bothrops genus venoms and are capable of causing drastic myonecrosis. Several studies have shown that the C-terminal region of these toxins, which includes a variable combination of positively charged and hydrophobic residues, is responsible for their activity. In this work we describe the crystal structures of two Lys49-PLA2s (BbTX-II and MTX-II) from B. brazili venom and a comprehensive structural comparison with several Lys49-PLA2s. Based on these results, two independent sites of interaction were identified between protein and membrane which leads to the proposition of a new myotoxic mechanism for bothropic Lys49-PLA2s composed of five different steps. This proposition is able to fully explain the action of these toxins and may be useful to develop efficient inhibitors to complement the conventional antivenom administration.

Crystallization and preliminary X-ray diffraction analysis of three myotoxic phospholipases A2 from Bothrops brazili venom.

Two myotoxic and noncatalytic Lys49-phospholipases A(2) (braziliantoxin-II and MT-II) and a myotoxic and catalytic phospholipase A(2) (braziliantoxin-III) from the venom of the Amazonian snake Bothrops brazili were crystallized. The crystals diffracted to resolutions in the range 2.56-2.05 Šand belonged to space groups P3(1)21 (braziliantoxin-II), P6(5)22 (braziliantoxin-III) and P2(1) (MT-II). The structures were solved by molecular-replacement techniques. Both of the Lys49-phospholipases A(2) (braziliantoxin-II and MT-II) contained a dimer in the asymmetric unit, while the Asp49-phospholipase A(2) braziliantoxin-III contained a monomer in its asymmetric unit. Analysis of the quaternary assemblies of the braziliantoxin-II and MT-II structures using the PISA program indicated that both models have a dimeric conformation in solution. The same analysis of the braziliantoxin-III structure indicated that this protein does not dimerize in solution and probably acts as a monomer in vivo, similar to other snake-venom Asp49-phospholipases A(2).