Polissacarídeos sulfatados de algas pardas inibem o crescimento tumoral através da modulação de macrófagos

Abstract

Cancer is highly complex and composed of various non-tumor cells that contribute, along with tumor cells, to the formation of the tumor microenvironment (TME) that promotes tumor progression and increased aggressiveness. Among the non-tumor cells embedded in the TME, tumor-associated macrophages (TAMs) play a crucial role. Macrophages exhibit high phenotypic plasticity, capable of displaying both an anti-tumor profile when activated through the classical pathway (M1-like phenotype) and a pro-tumor profile characteristic of TAMs when subjected to alternative activation (predominantly M2 marker phenotype). Indeed, TAMs are often associated with a poorer prognosis for the patient. Sulfated polysaccharides (SPs), especially fucoidans from brown algae, have emerged in recent years as potent modifiers of biological response, enhancing anti-tumor responses through immunomodulation. Previous studies by the group demonstrated that sulfated polysaccharides from the alga Dictyota caribaea were able to inhibit the tumor growth of the S-180 cell line in vivo, despite not showing direct cytotoxicity against this cell line in vitro. Furthermore, the conditioned medium (CM) of these activated macrophages exhibited an antiproliferative effect against murine B16-F10 melanoma cells in vitro. This study is divided into two chapters and aimed to evaluate the antitumor effect of fucoidans from Dictyota caribaea (Dc-SP) and Macrocystis pyrifera (Mp-SP), regarding their ability to inhibit tumor growth and modulate macrophages towards an M1 phenotype. In Chapter I, a RAW 264.7 macrophage cell line was stimulated with Dc-SP (10, 100, 250 μg/mL) or LPS (100 ng/mL), and phenotypic markers of M1 macrophage polarization were evaluated. In Chapter II, in addition to the evaluation of macrophage polarization of RAW 264.7 cells activated with Mp-SP in vitro, tumor-associated macrophages in the TME of mice transplanted with B16-F10 were characterized. Tumors and organs were collected, and TAMs were isolated for phenotypic characterization using specific M1 and M2 markers via flow cytometry. Furthermore, the antitumor effect of the combination of Mp-SP (50 mg/kg) with the chemotherapeutic agent Dacarbazine (50 mg/kg) was investigated in vivo. Under in vitro conditions, stimulation with Dc-SP and Mp-SP was able to polarize RAW 264.7 macrophages towards the M1 profile, with increased production of nitric oxide (NO), increased expression of surface markers CD86 and MHC II, and intracellular marker iNOS. For Mp-SP, it was observed that part of the antitumor effect presented in this study was associated with modulation of the TAM phenotypic profile. Immunophenotyping of TAMs isolated from tumors in mice treated with Mp-SP showed a reduction in the expression of the M2 marker (CD206) and an increase in the expression of one of the main markers for M1 (iNOS), which was related to the inhibition of tumor growth in the animals. Furthermore, the combination of Mp-SP with Dacarbazine resulted in a reduction in tumor growth when compared to the saline-treated groups or groups treated with PS and Dacarbazine alone. These data indicate that both fucoidans promote polarization of TAMs towards an M1-like profile, and that Mp-SP was able to reduce the number of TAMs with an M2-like phenotype, and this effect contributes to its antitumor efficacy. Additionally, the immunostimulation of Mp-SP in the TME may have contributed to the therapeutic sensitization of dacarbazine in the antitumor effect when combined with fucoidan.