Deciphering the mechanism of cytotoxicity and cancer-selective activity of the delocalized lipophilic cation D112

• Author / Creator

  Yang, Ning

• Chemotherapeutic drugs that are used in anti-cancer treatments often cause death of both cancerous and noncancerous cells. This non-selective toxicity is the root cause of untoward side effects that limits the effectiveness of therapy. To improve the therapeutic options for cancer patients, there is a pressing need to identify novel compounds with a greater discrimination for cancer cells. Delocalized lipophilic compounds (DLCs) are a class of molecules that have long been investigated for therapeutic potential in oncology. These compounds enter mitochondria in response to the electrochemical potential gradient across the inner membrane. In particular, the high negative inside properties of cancer mitochondria are proposed to facilitate selective accumulation into cancer mitochondria. Following uptake, DLCs induce cell death through various mechanisms. While the inhibitory effects to cancer mitochondria are well-demonstrated in vitro, toxicities identified from in vivo studies have precluded clinical development. Identifying novel DLCs with enhanced efficiency and selectivity are thus critical next steps for this class of molecules. D112 is a cyanine-based dye that was identified by the Eastman Kodak Company as a photosensitizer for use in photographic emulsions. Initial observations that cyanine dyes with certain reduction potentials inhibited mitosis of sea urchin eggs triggered the company to initiate a drug-screening program to test these compounds for cytotoxicity against cancer cells. Approximately 2000 dyes were evaluated in this program, and D112 emerged as a lead compound based on its selectivity against a human colon cancer cell line relative to a normal monkey kidney epithelial cell line. Despite these intriguing results, investigations into D112 were not pursued due to changes in industry priorities. We decided to revive investigations on D112 to evaluate its potential as a novel anticancer agent. In this thesis, I first characterized D112-induced cell death in cancer cells and identified that D112 induced apoptosis through a mitochondrial-centered pathway. Its selective cytotoxicity against cancer cells was demonstrated in a panel of cell lines derived from solid tumors. In addition, insights into the molecular mechanisms of D112-induced toxicity indicated that D112 preferentially accumulated in cancer mitochondria, where it interacted with mitochondrial DNA, induced ROS production and caused mitochondrial DNA damage. D112-induced ROS was a critical upstream mediator, as ROS inhibition prevented Bax activation and subsequent apoptosis. Anti-cancer cell cytotoxicity of D112 was thus likely a function of both selective cancer cell uptake and cancer cell sensitivity to oxidative stress. Finally, encouraged by the observation that D112 induced ROS-mediated apoptosis, we investigated methodologies with which to increase the apoptotic index between cancer and non-transformed cells. In consideration of the inherent fluorescent properties of D112, we therefore tested the effect of photo-activation on D112 toxicity, and found D112's cancer-selective toxicity was greatly potentiated by photo-activation. Thus, results from this thesis identify D112 as a potential new prototype for drug development, and in conjunction with photodynamic therapy might lead to an appropriate therapeutic window for D112-based cancer treatment in the future.

• Subjects / Keywords

  • Photodynamic therapy
  • Anti-cancer
  • Reactive oxygen species
  • Mitochondrial-targeting
  • Delocalized lipophilic cation
  • D112

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3T14V09V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.