Design, synthesis and biological evaluation of folate-targeted photodynamic therapy agents

Photodynamic therapy (PDT) is a cancer treatment approach that uses a tumor-localizing drug called photosensitizer; this, when activated by light of an appropriate wavelength, interacts with molecular oxygen to form toxic species known as singlet oxygen, which causes cellular destruction. Lack of selectivity has been a major drawback to the use of this treatment modality. Therefore, directly targeting cancer cells offers a unique advantage in terms of an increase accumulation of the drug, sparing healthy tissues and minimizing the amount of precision that is needed in light delivery.;Folic acid is used as the target molecule because the mammalian folate receptor binds folic acid and its conjugates with relatively high affinity and preferentially promotes endocytosis. These folate receptors are highly overexpressed on a number of cancer cells. Hence, cancer cells can be tricked into attracting and ingesting a photosensitizer that is attached to folate molecules and because of these folate receptors, the photosensitizer will be delivered into the cell for an onward photodamage.;Folic acid-malachite green conjugate, folic acid-crosslink hemoglobin and folic acid-Squaraine dye (SBA) conjugates have been synthesized and characterized by HPLC, 1H NMR, UV-VIS and high resolution mass spectrometry. All spectroscopic data support the desired structure of the conjugates. Crosslinked hemoglobin was incorporated into the folate-malachite green conjugate to provide oxygen in hypoxic tumors.;Biological evaluation including accumulation, competitive and phototoxicity studies of the conjugate have been explored using HeLa and SH-SY5Y cells. The images from the accumulation and competitive assays show that the uptake of the conjugates was via folate receptor-mediated endocytosis. In addition, results from the phototoxicity studies show that 65% of HeLa cells and 49% of SH-SY5Y cells were killed by the folate-malachite green conjugate. Further, 50% and 37% of HeLa and SH-SY5Y cells were respectively killed when treated with folate-SBA conjugate. In addition, 56% and 33% respectively of HeLa and SHSY5Y cells were killed when exposed to folate-crosslink hemoglobin conjugate. However, for all the three conjugates, the phototoxicity assay results from the non-folate conjugates (control) did not show any appreciable cell death.;These results demonstrate that the attachment of folic acid to the photoactive compounds increased its cellular uptake and subsequently its phototoxicity. However, incorporating hemoglobin into the folate-malachite green conjugate did not increase its phototoxicity.