Aluminum sulphonated phthalocyanines as sensitizers for photodynamic therapy : cellular uptake, phototoxicity and sensitizer targeting in human leukemia cells

Author

Reshma Ahmed

Date of Award

12-1995

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Comparative and Experimental Medicine

Major Professor

Leon N. D. Potgieter

Committee Members

Jack Oliver, Joe Fuhr, Nazareth Gengozian, Stephen Wright

Abstract

There is a need to improve the selectivity of photodynamic therapy for better targeting of tumor cells. This was achieved by the in vitro targeting of liposome-encapsulated chloroaluminuim tetrasulfonated phthalocyanine with the monoclonal antibody PM-81 to CD15 expressed on CEM cells by using a biotin-streptavidin sandwich binding method. Three closely-related studies were done to achieve the above objective. A thorough review of the literature on photodynamic therapy, liposomes, chloroaluminum phthalocyanines, CD15 and autologous bone marrow transplantation is also presented. Initially, the non-targeted cytotoxicity of free and liposome-encapsulated chloroaluminum tetrasulfonated phthalocyanine (AIS₄PC) on human leukemia T cells (CEM) was examined. Liposomal encapsulation improved photosensitization of cells by the drug when compared to the free form. The phototoxicity of the liposome-encapsulated drug and free drug was proportional to the dose of both the sensitizer drug and light. Liposomes with the highest drug/lipid ratios were most potent than those with lower encapsulation. Cellular uptake kinetics of free and liposome drug were examined and the effect of several factors determined. GEM cells accumulated free and liposome-encapsulated sensitizer drug in a dose- and temperature-dependent manner but saturation levels within cells were not achieved even after 48 hours of exposure. Free drug uptake by cells was profoundly reduced by increasing concentrations of serum in the media; however, serum did not affect liposome drug incorporation into cells. Both free and liposome-encapsulated drugs apparently were endocytosed, because drug uptake that was highest at 37°C was significantly reduced at 4°C, a temperature at which endocytosis is inhibited. Even at the latter temperature uptake was considerable, and perhaps can be explained on the basis of pinocytosis. In most cases, increasing drug uptake corresponded with greater cytotoxicity of the drug species. The cellular antigen CD15 is the marker recognized by the monoclonal antibody (PM-81) used for drug targeting. Flow cytometric analysis indicated that CD15 expression was modulated by the phase of culture growth. The profile of markers on OEM cells was identified with a panel of monoclonal antibodies. Direct antigen-antibody interaction did not affect expression of CD15. In the last phase of this study the photosensitizer drug was targeted to CEM cells in vitro with PM-81 antibody, exploiting the biotin-streptavidin system. Targeted liposomes were 6 times more potent than the non-targeted species, and 4 times more potent than the free drug, even though liposome drug was present at an 8 fold lower drug concentration. The results of this study have implications for the ex-vivo purging of bone marrow to remove residual leukemic cells prior to autologous transplantation.

Recommended Citation

Ahmed, Reshma, "Aluminum sulphonated phthalocyanines as sensitizers for photodynamic therapy : cellular uptake, phototoxicity and sensitizer targeting in human leukemia cells. " PhD diss., University of Tennessee, 1995.
https://trace.tennessee.edu/utk_graddiss/9916