| Camptothecin (CPT) and its derivatives are a new class of anticancer agents. They inhibit cellular enzyme DNA topoisomerase I and trigger a cascade of events leading to apoptosis. CPT exists in two forms depending on pH: At basic or physiological neutral pH, the equilibrium favors the formation of the carboxylate form which is highly toxic with low activity, whereas at pH below 5 essentially all drug is in lactone form which has high biological activity. In this project, PLGA microspheres were studied as potential delivery vehicles for CPT.; PLGA microspheres with three CPT loadings were first developed and characterized. Analysis of drug stability revealed that the unreleased CPT in the microspheres remained in its active lactone form over the entire release duration. There was no interaction between CPT and PLGA matrix. This indicated that the acidic microenvironment in the microspheres was the primary reason for the stability of drug in microspheres.; In vitro antitumor activities of CPT on B16 melanoma and RAW264.7 macrophage cells were then evaluated. Antitumor activity on the tumor cells was enhanced, and the toxicity on splenocytes was reduced after CPT was encapsulated in PLGA microspheres. These results could be partially due to quick uptake of microspheres by the cells.; In vivo antitumor efficiency of CPT in solution and in microspheres was evaluated using melanoma mice as live animal models of tumor. CPT in both forms significantly reduced the tumor size and prolonged the lifetime of mice when compared to the controls. In addition, CPT in microspheres was found to have stronger tumor size inhibition than that in solution form.; The modulation of LPS to antitumor activity of CPT on B16 and RAW264.7 cells were investigated. LPS acted synergistically along with CPT in both forms. Western blotting study found that the amount of the molecular target of CPT, DNA topoisomerase I, in both cells was increased when the cells were treated with LPS. This increase probably made the cells more sensitive to CPT, and could be a reason behind the synergistic effects.; In summary, this study concluded that PLGA microspheres were suitable delivery vehicles for CPT. |
