Date of Award
Doctor of Philosophy in Physics
Oleg A. Andreev
Cancer is the second leading cause of death in the United States after heart disease. Because the frequency of cancer diagnoses is correlated with life expectancy, we can expect the rate of cancer diagnosis to increase with the increase of life expectancy. Additionally, cancer treatments are notoriously costly and challenging due to the heterogeneity of the cancer cell population. For these reasons, devising methods to study the characteristics, efficiently diagnose and treat cancer is extremely important.
Warburg effect has been considered as the most unique mechanism that differ cancer cells from normal cells. Normally, most of the healthy cells predominantly produce energy by a low rate of glycolysis and oxidation of pyruvate in mitochondria, called oxidative phosphorylation. In the 1920s, Otto Warburg observed that tumors uptake a massive amount of glucose compared to its surrounding healthy tissues. Additionally, glycolysis was continued even in the presence of oxygen, called aerobic glycolysis. Cancer cells trend to metabolize excessive uptake of glucose and ferment to lactate unlike normal cells, even in the presence of oxygen and fully functioning mitochondria. This high rate of aerobic glycolysis in cancer cells is known as Warburg effect, which has been studied extensively especially after 2000s. Cancer cells have an unusually high rate of glycolysis and subsequently lactic acid fermentation to produce energy for cell activities, even under aerobic conditions, a seemingly inefficient way of producing energy.
It is recognized that cancer tumors undergo acidification due to the Warburg effect and the overexpression of carbonic anhydrase enzymes at the surfaces of cancer cells, making acidity a universal tumor characteristic, and following the micro calories exchange during glycolytic fermentation. The more invasive the cancer is, the greater the extra-cellular acidosis and heat production.
The pH (Low) Insertion Peptides comprise a novel class of pH-sensitive targeting agents that spontaneously insert into cell membranes under acidic conditions. Therefore, the applicability of pHLIP® peptides to tumor-targeting applications is an obvious choice for investigation, it could be reconstructed with many different types of imaging and therapeutic agents. The membrane associated folding mechanism of action of pHLIP is triggered by low pH. The high concentration of proton in the low pH environment increase the protonation of the protonatable residues in pHLIP, which increase the overall hydrophobicity and drives the peptide into the hydrophobic core of the membrane, where it forms transmembrane helix. The two terminus of the peptide, one stays in the extracellular space while the other one pass through the membrane and locates into the cytoplasm.
With the creation of SNARF-pHLIP® construct in this work, it will allow me to measure the extra-cellular pH at the surface on the membrane of individual cancer cells. This will provide an advantage over measuring the bulk extra-cellular pH since it will result in higher contrast between normal, metastatic and non-metastatic cells, furthermore this novel construct could help with cancer diagnosing. I will apply it to metastatic and non-metastatic cancer cell lines. This will showcase that non-metastatic and metastatic cells can be distinguished from each other quickly and easily by their individual surface pHs.
Enhanced permeability and retention (EPR) effect is how most of the approved nanomedicinal products work though for cancer imaging and therapy. However, the heterogenous of cancers made them impossible to universally target. Extracellular acidity has been identified as a common property of cancerous cells, hence we can apply pHLIP® as a novel agent to coat noisome, making it has a high uptake near cancer cells.
Wei, Da, "PHYSICAL CHARACTERIZATION OF WARBURG EFFECT IN CANCER CELLS" (2018). Open Access Dissertations. Paper 759.