Quantum Dot anti-CD Conjugates:  Are They Potential Photosensitizers or Potentiators of Classical Photosensitizing Agents in Photodynamic Therapy of Cancer?

The present study examined the potential of quantum dot bioconjugates to sensitize cells to UV irradiation and to promote the photodynamic activity of the classical photosensitizers such as trifluoperazine (TFPZ) and sulfonated aluminum phthalocyanine (SALPC). Water-soluble CdSe nanocrystals were conjugated with anti-CD antibody with known specificity to leukemia cells. Quantum dot anti-CD conjugates were incubated with the leukemia cell line Jurkat to ensure specific interaction with the cell surface. This interaction was confirmed by fluorescent confocal microscopy. Furthermore, quantum dot anti-CD90-labeled leukemia cells were mixed with normal lymphocytes and subjected to UV irradiation in the presence or absence of a classical photosensitizer (TFPZ or SALPC). The cell fractions were separated by lectin-affinity column chromatography. The cell type was confirmed with fluorescent confocal microscopy and flow cytometry using appropriate antibodies; quantum dot anti-CD90 for leukemia cells, and PE-CD44 for normal lymphocytes. The viability of the separated cell fractions was determined using flow cytometry and the methyl tetrazolium test. The results demonstrated that quantum dot anti-CD conjugates sensitized leukemia cells to UV irradiation and promoted the effect of the classical photosensitizer SALPC. The results are discussed in the context of free radical generation during combined application of quantum dot bioconjugates and UV irradiation, as well as in the context of UV-mediated liberation of free Cd ions and their harmful effect on cell viability.