ESCUELA DE DOCTORADO

 
Tesis Doctorales de la Universidad de Alcalá
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ISOLATION, SYNTHESIS AND NANOENCAPSULATION OF CYTOTOXIC COMPOUNDS FROM PLECTRANTHUS SPP
Autor/aGonçalves Garcia, Catarina Alexandra
DepartamentoBiología de Sistemas
Director/aDias de Mendonça Rijo, Patricia
Codirectores/asDíaz Lanza, Ana María; Beco Pinto Reis, Ana Catarina
Fecha de defensa04/03/2019
CalificaciónSobresaliente Cum Laude
ProgramaCiencias de la Salud (RD 99/2011)
Mención internacionalSi
ResumenCancer is a disease that affects millions of people worldwide. Overall, despite improvement on the existent therapies, their toxic side effects have triggered the search for compounds with cytotoxic potential and/or effective targeted delivery systems that might decrease the occurrence of toxic side effects. In this work, the cytotoxic potential of abietane diterpenes, namely 6,7-dehydroroyleanone, was explored. A commonly known genus used in traditional medicine was selected to explore the antitumoral potential of such compounds: the Plectranthus genus. As such, an overall study of the Plectranthus derived-abietane cytotoxic diterpenes was described. According to this study, a group of abietane diterpenes stands out from the rest of the compounds, with a consistent cytotoxic potential: the royleanones. As such, several Plectranthus spp. were selected for extraction with different solvents and 31 extracts were performed, and their antiproliferative properties tested. Antimicrobial and preliminar toxicity assays demonstrated that five extracts presented an antiproliferative profile: P. aliciae, P. japonicus, P. madagascariensis var. ¿Lynne¿, P. stylesii and P. strigosus. When tested for in vitro cytotoxicity tests on tumoral cell lines, the most active extract was found to be P. strigosus, which possesses a potent secondary metabolite, parvifloron D. Additionally, P. madagascariensis was also regarded as one of the most active extracts, so this plant was selected for the isolation of the abietane 6,7-dehydroroyleanone (DHR), and its extraction has been optimized. Also, DHR was found to induce cellular death through the activation of the intrinsic apoptotic cascade, without being a substrate of the multidrug-resistance (MDR) efflux pump P-glycoprotein (P-gp). DHR was further encapsulated into hybrid nanoparticles, and an increase on cytotoxicity was seen, thus implying that this might be a good delivery system for this royleanone. DHR was also thermally and structurally characterized as a stable and lipophilic compound, with no polymorphism profile. In order to address its poor solubility in water, a lipid-drug conjugate was prepared in order allow the formation of DHR self-assembled nanoparticles. The prepared nanoassemblies proved to be an effective way to disperse this compound in water. Finally, DHR and a previously isolated royleanone (7¿-acetoxy-6ß-hydroxyroyleanone, AHR) were studied regarding their reactivity. Microwave-assisted Mitsunobu reactions have been conducted on both molecules, and stability issues were recorded. In addition, when tested on preliminar toxicity models, no increase on the toxic profile was registered. DHR was also subjected to carbamoylation and benzoylation, but similar results were obtained. AHR was subjected to hydrogenation and benzoylation and its benzoylated derivative has shown stability and a slight activity increase when tested on Artemia salina. For AHR, benzoylation seems to be a decisive step for improving the lead¿s biological activity, given that, the product obtained through the use of 4-chlorobenzoyl chloride increases cytotoxicity in different cell lines. Overall, this work provides valuable information regarding the cytotoxic profile of royleanones, namely, DHR. It also highlights the cellular targets that are responsible for its cellular cytotoxicity and delivers first-hand information regarding its thermal stability. Always aiming the development of new effective compounds with antitumoral activity, this work also focuses on the reactivity of abietane diterpenes belonging to the royleanones sub-class.