Photodynamic therapy (PDT) is a powerful strategy to eliminate a variety of tumor and alloreactive T cells. While the cytotoxic effect of the novel rhodamine-derived TH9402 photosensitizer has been attributed to the generation of radical oxygen species, the cell death pathways involved have not been extensively investigated. In this study, we evaluated the ability of PDT to induce apoptosis and necrosis in EL4 cells, and assessed its underlying molecular mechanisms. We found that the dominant mode of cell death after PDT was influenced by the conditions of treatment. PDT using TH9402 triggers a caspase-dependent intrinsic apoptotic pathway. However, the incapacity of caspase inhibition to block the induction of apoptosis and to limit cell death indicates that apoptosis induced by PDT also involves a caspase-independent pathway. The observation that the TH9402 photosensitizer mediates cytotoxicity through activation of a number of death pathways suggests that it could effectively limit the capacity of tumor cells to become resistant to TH9402. / Secondly, PDT using TH9402 induces a time- and dose-dependent decrease in target cell viability resulting in high levels of elimination of multiple myeloma cells. In an attempt to evaluate the clinical relevance of these findings and simulate minimal residual disease in an apheresis product, the combination of RPMI-8226 myeloma cells admixed with human apheresis cells from healthy donors was PDT treated. Again high levels of elimination of myeloma cells were observed while sparing normal cells. This important cytotoxic activity was observed in conditions which preserve more that 50% of hematopoietic progenitor cells. These results strongly suggest that TH9402 PDT represents an appealing strategy in ex vivo purging of autologous stem cell transplants in patients with multiple myeloma. / Finally, we have found that immunization with PDT-treated whole tumor cells was able to delay tumor cell growth. This finding encouraged us to investigate whether a DC-based PDT vaccine could protect from tumor cell progression. In this study, purified DCs were generated from murine bone marrow. We also identified a cytokine combination capable of promoting DC activation. Under these conditions, PDT-treated tumor cells did not increase IL-12 production by DCs, but they provoked partial maturation of DCs. Once these activated DCs were loaded with whole tumor cells treated by PDT, a tumor protection effect was observed in two different murine models in vivo. Such a vaccine may be particularly useful when tumor cells do not represent a pure cell population and are rather dispersed among normal cells. The present studies therefore uncovered unique apoptotic pathways of TH9402 PDT, and identified two appealing approaches to take advantage clinically of those peculiar photochemical properties in an attempt to improve the survival of patients with cancer.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.102491 |
| Date | January 2006 |
| Creators | Dai, Qin Yong, 1967- |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | © Qin Yong Dai, 2006 |
| Relation | alephsysno: 002563464, proquestno: AAINR27767, Theses scanned by UMI/ProQuest. |
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