Eficiência do cotratamento com RNA de interferência e tamoxifeno no câncer de mama

Abstract

Breast cancer was the second most common type of neoplasia in 2020 and caused the highest mortality rate among women. Tamoxifen (TMX) is the most used drug in hormone therapy against breast cancer. Over time, a drop in the effectiveness of the drug has been observed due to the emergence of resistance on the part of cancer cells. On the other hand, some studies claim that silencing of HOXB7 gene resensitizes breast cancer cells resistant to TMX. HOXB7 silencing can be achieved through targeted therapies, such as RNA interference therapy (RNAi), which consists of mRNA degradation through specific pairing of small interfering RNA molecules (siRNA). However, effective delivery of these small molecules depends on transfection agents such as nanoparticles. Thus, the objective of this thesis was to evaluate the in vitro and in vivo delivery efficiency of siRNA molecules from hybrid nanoparticles and to evaluate the antitumor activity of HOXB7 gene silencing with and without co-treatment with TMX. PEG-coated calcium phosphate (NP) nanoparticles were produced by self-association of constituents. The NP had approximately 74 nm with a PdI of 0,1, a rounded and homogeneous morphology and an encapsulation efficiency of 50%. Furthermore, the NP remained stable for at least 180 days if stored at 4 °C and after freeze-drying (p>0.05). Also, they were immediately resistant to temperatures of up to 40 °C and faced disassociation in acidic conditions. Furthermore, NP encapsulating siRNA complementary to the HOXB7 gene (NP-siHOXB7) promoted a slight reduction in cell viability in 24 h (p<0.05), while empty NP (NP-mock) was not cytotoxic (p>0.05). The migratory potential of cells after NP-siHOXB7 treatment was significantly reduced (p<0.05) after 24 h. These last two results were corroborated by significant silencing of the GFP gene in transformed lung cancer cells (p<0.05). The nanoformulation did not present hemolytic activity (p>0.05). No difference in size and PdI were observed after NP purification (p>0.05). In an orthotopic and xenographic breast tumor model in mice, HOXB7 gene silencing of 50% was observed in tumor tissue. Although no significant difference in tumor volume was observed between the groups treated in 14 days at the concentration tested, there was no loss of individuals in the co-treatment group, unlike the control group. Additionally, the evaluation of hematological and biochemical parameters shows that TMX treatment was slightly toxic. Given these results, it can be inferred that the nanocarrier was considered efficient in delivering siRNA both in cells and in animal models and is a promising candidate for intravenous delivery of genetic material. A larger sample size and variation in test concentration must be considered to expand the antitumor effect analysis promoted by HOXB7 gene silencing and its cotreatment with TMX.