Enhancement of Aminolevulinic Acid-Mediated Protoporphyrin IX for Cancer Fluorescence Detection and Photodynamic Therapy

• Main Author: Mansi, Matthew
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2022
• Subjects: Medicine; Pharmacology; Physics
• ISBN: 9798209887430

Photodynamic therapy (PDT) and photodynamic diagnosis (PDD) are FDA-approved treatment modalities for both cancerous and non-cancerous disease states. Photosensitizers are chemicals that absorb photons and convert light energy to generate reactive oxygen species (ROS) through photochemical reactions. Additionally, photosensitizers are often fluorescent which can allow them to be used as imaging agents. While PDT relies on the combination of a photosensitizer, light, and molecular oxygen to induce cytotoxicity via the generation of ROS, PDD utilizes the fluorescent nature of the photosensitizer to help visualize target tissue. Aminolevulinic acid (ALA) is a prodrug that is metabolized in the heme biosynthetic pathway to the photosensitizer protoporphyrin IX (PpIX), a fluorescent porphyrin that can be used for both PDT and PDD. Although nearly all types of human cells produce PpIX, tumor cells have been found to have more PpIX production and accumulation than normal cells. Selective accumulation of PpIX in cancer cells facilitates PDT, fluorescence tumor detection, and image-guided tumor resection. Clinically, ALA treated tumors often show heterogeneous PpIX fluorescence, which causes an increase in surgical margins. The major reason for this phenomenon has yet to be elucidated. Leading theories all stem from heterogeneity in tumor genetics. Accumulation of PpIX in tumor cells is determined by one major concept, PpIX synthesis must be greater than its conversion and efflux. PpIX synthesis is determined by the availability of ALA uptake as well as the activity of the first seven enzymes in the heme biosynthesis pathway. Any defects in ALA uptake or synthesis of PpIX can be catastrophic for accumulation. Even if PpIX is synthesized in abundance, cells have the ability to rid themselves of PpIX by conversion it to heme or effluxing into the extracellular space. The enzyme solely responsible for the conversion of PpIX is called ferrochelatase (FECH). It inserts one ferrous iron atom into PpIX to form heme. Additionally, cells rid themselves of PpIX by utilizing ABCG2 transporters. These transporters are located on both the mitochondria (where PpIX is synthesized) and on the lipid membrane. High ABCG2 activity effectively keeps PpIX from accumulating. Our study strives to capitalize on phenotypic genotypic abnormalities in cancer cells with clinically approved drugs in efforts to enhance PpIX fluorescence for the benefit of PDT and PDD. We found that cancer cells lines from various origins including breast, pancreatic, head/neck, and skin responded to clinically approved drugs that we repurposed for the enhancement of PpIX fluorescence. These drugs targeted cancers cell’s ability to rid themselves of PpIX by either inhibiting FECH or ABCG2. Our study continues to move the field forward not only by gaining a better understanding of abnormalities seen in cancer cell heme biosynthesis but with attempts capitalize abnormalities through chemical intervention. This work has led to the submission of a manuscript (Chapter 2) and has contributed to several other manuscripts. Results seen in chapters 3 and 4 will be submitted for publication in the near future. Below are the manuscripts this work has either contributed to or has been the subject of.