M.Sc. / Established therapies currently in use for the treatment of breast cancer are high risk, since their employment harbors multiple undesirable and detrimental side effects. In many cases these are associated with poor therapeutic outcome managing only to briefly extend patient lifespan. As a result, many newly designed treatments have surfaced that aim to effectively remove cancerous tissue and improve survival rates while minimizing the aggressive onsets to the patient. Photodynamic Therapy (PDT) has, for a long time, been targeted as a combatant for cancer. Its therapeutic mechanism is based on the tumor-specific intracellular localization of a photosynthetic compound, i.e: photosensitizer, prior to its irradiation-mediated excitation thereby generating high levels of reactive oxygen species (ROS). At the molecular level, this causes irreversible photodamage to vital intracellular targets resulting in cell death. The plasma membrane-, mitochondrial-, lysosomal-, and endoplasmic reticulum systems are all prime targets of PDT and vary in susceptibility depending on both the type of cancer being treated and the photosensitizer administered. Newly designed photosensitizers are governed by their enhanced structural properties to localize and therefore target certain areas of a cell. Since each cancer type has a unique set of susceptible and resistant characteristics, knowledge of each new photosensitizers’ range, efficiency, and mechanism of cell death is required. This enables pairing of these drugs to appropriate cancer types for maximal PDT effect. Here, two newly designed metallo-phthalocyanine photosensitizers, AlPcSmix and GePcSmix, were analyzed for their photodynamic effect on the estrogen-positive, breast cancer cell line, MCF-7. Being one of the most reliable cell lines, it is a prominent research model because it mimics the problems encountered with tumor resistance to therapy induced cell death via pathway restrictions. Photosensitizer administration and excitation by light irradiation to this cell culture system was therefore referred to as in vitro Photodynamic Treatment (in vitro PDT) and not Therapy. ii Initial dosage and time responsive studies confirmed that 35 μM AlPcSmix and 115 μM GePcSmix both excited using 15 J/cm2 at 680 nm proved most effective in reducing viability, whilst individually contributing little adverse influence to cellular homeostasis. Using these dosages, in vitro PDT analysis on several cellular parameters indicated a complex mode of cell death was induced. Morphology revealed typical markers consistent with apoptotic, autophagic and necrotic cell death while variations in proliferation and cytotoxicity levels were inconsistent with stress responses observed. This correlated with the detection for four common apoptotic markers which also revealed discrepancies within the death pathway as possible mutational deficiencies may have rendered MCF-7 cellular systems incomplete. Taken together, the wide range of cellular parameters studied suggests cells undergo a mixture of death modes interchanging via a complex system of molecular switches over time that concludes in secondary necrosis. This was attributed to the assortment of sulphonated phthalocyanine species enabling a broad intracellular distribution range coupled with the non-specific targeting action typical of the ROS generated, in addition to the absence of a phagocytic conclusion to the death process. In vitro PDT with AlPcSmix was shown to harbor a greater toxicity to GePcSmix as cells completed the death response within a shorter time period however, both promoted MCF-7 population cell death sufficient enough to warrant further study for their use as potential agents in the PDT of breast cancer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:6619 |
| Date | 23 November 2009 |
| Creators | Horne, Tamarisk Kerry |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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