Page 144 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

142 CHAPTER 6 Laser-assisted cancer treatment

In addition to the tendency to be absorbed in NIR region and nontoxicity in the
absence of NIR irradiation, photosensitizer must successfully be accumulated in the
desired side and also it should be able to induce cell death via activating of dendritic
and T cells. In the following section, some photosensitizers making the above criteria
will be described.

6.3.1 Methylene blue
Methylene blue (MB) is one of the organic dyes being able to kill malignant cells.
Owing to its positive charged and low molecular weight, the interaction of MB with
mammalian cells increased lead to be chosen as a suitable candidate for PDT applica-
tion. Although MB commonly applied in antimicrobial PDT, there have been several
studies focusing on the application of MB in PDT due to its cost-effectivity and
availability. Samy et al. utilized MB for PDT to study the outcomes on basal cell
carcinoma in clinical stage. Complete treatment with good cosmetic outcomes was
observed in 11 out of 17 patients [41]. Currently, the application of MB is limited
due to the lack of stability after intravenous administration leading to the reduction of
leuco MB with no photosensitizing properties [42]. Encapsulation of MB in nanopar-
ticles to maintain their activity during blood circulation can be a solution.

6.3.2 Photogem
Photogem is originated from hematoporphyrin being one of the first generations
of the photosensitizers with photochemical properties similar to Photofrin. Photo-
gem got approved for clinical usage from “Brazilian Health Surveillance Agency
(ANVISA)” and “Pharmacology State Committee of the Russian Federation”. The
maximum absorption of Photogem is between 500 and 630 nm. Its main side effect is
related to the long-lasting photosensitivity in the body after several weeks of admin-
istration decreased by incorporating it into the drug delivery system. Low absorption
spectra of the Photogem in the therapeutic window and long-lasting photosensitiv-
ity led to introduce the second generation of photosensitizes including chlorins and
5-aminolevulinic acid [43].

6.3.3 Chlorins
Chlorins with strong light absorption in the therapeutic window mainly between 640
and 700 nm have absorbed great attention due to its natural origin. Being hydrophilic
reduced types of porphyrins, chlorins structure is similar to porphyrins. One of the
most studies chlorin used as a photosensitizer is mono-l-aspartyl chlorin e6 which
has two significant features including strong absorption between 650 and 680 nm and
a high yield of free radical production. Another promising photosensitizer belonged
to chlorin family is Photodithazine. It is one of the second generations of the pho-
tosensitizing agent with little skin photosensitivity [44]. Chlorins have been widely
used for oral cancer treatment [45]. In 2010, Parihar et al. investigated the effect