Evaluation of the use of phenothiazine compounds in the treatment of colon cancer and investigation of their mechanism of action

Epidemiological studies associate cancer and neurodegenerative diseases with each other. Amyloid precursor protein (APP), which is closely related to Alzheimer's disease, attracts attention in cancer research. Recent research indicates that inhibiting APP and its homologous family member APLP2 or inhibitors against proteolytic cleavage enzymes (such as α- and βsecretases) of these proteins reduces cancer cell proliferation. In this thesis, the effects of phenothiazine-structured compounds [toluidine blue (TBO) and 1,9- dimethyl-methylene blue (DMMB)] on cell viability, APP/APLP2 processing, and phosphatidyl inositol-3-kinase (PI3K)-AKT signaling pathway were evaluated using flow cytometry, MTT, and Western blot methods in HT 29 colon cancer cells. Cell viability was significantly reduced after 24 h of treatment of HT-29 cells with 0-10 μM TBO or 0-1.25 μM DMMB. Western blot results showed that both TBO and DMMB reduced the expressions of total APP, sAPPα and α-secretase ADAM10. While DMMB had a reducing effect on APLP2 and sAPLP2 levels, TBO did not cause any change. While both compounds had a reducing effect on expression levels of GSK-3β, which is one of the PI3K-AKT signaling substrates, they led to increase p-GSK-3β-Ser9 levels. Thus, the observed decrease in HT-29 cell viability has been attributed to direct effects of phenothiazine structured compounds on APP and/or APLP2 processing and their ability to decrease α-secretase, which is involved in the processing of these proteins and also their ability to increase of the inactive form of GSK-3β. As a result, it is thought that phenothiazines may contribute to new drug designs in the treatment of colon cancer due to their multiple effects on cancerrelated proteins. Keywords: