DOI
https://doi.org/10.25772/H6ES-Q313
Defense Date
2012
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Matthew Hartman
Abstract
Cancer remains one of the most dreaded diseases due to inevitable suffering and possible fatality. Only cardiac disease has caused more deaths than cancer. Present day cancer treatment involves radiation, surgery or chemotherapy. In chemotherapy, an anti-tumoral drug is used to treat the tumor either by killing or stalling the growth of the tumor cells. In certain types of cancer, for e.g. metastatic breast cancer, the first line of therapy is often chemotherapy. But the inability of current clinically approved drugs to selectively target tumor cells, ultimately results in side effects. To reduce these side effects, prodrug therapies have been developed. A prodrug is defined as a drug molecule inactivated by a temporary cap or carrier, subsequently removed by an external intra or extracellular stimulus. Several prodrug strategies such as ADEPT (Antibody–Directed Enzyme Prodrug Therapy) have been tested in clinical trials but have thus far met with limited success. In the wake of these limitations, development of photo-activatable prodrugs may be particularly desirable for minimizing the adverse side effects associated with current cancer chemotherapeutics. Photodynamic therapy (PDT) is a light dependent tumor treatment modality that has existed for many years. PDT involves a photosensitizer which is administered to the patient and later activated using the light of wavelengths between 650-800 nm. The activated photosensitizer creates singlet oxygen, which acts as cytotoxic agent to the tumor cells. But this approach has several drawbacks including slow uptake of the photosensitizer by the tumor cells and the dependence on molecular oxygen that is not always present at even moderate levels in the tumor tissues. To address these limitations of PDT, we developed a new prodrug concept called ‘Photocaged Permeability’ in our first project, and demonstrated drug delivery using this approach. The basis of this concept is that, by attaching a hydrophilic molecule to the drug via a photosensitive linker, the permeability of the drug could be restrained. But the drug could be released at the site of the tumor after irradiating with UV light. To achieve this goal, we designed and synthesized a photosensitive drug conjugate that was comprised of doxorubicin attached to a negatively charged, cell impermeable molecule, EDANS (5-((2-Aminoethyl) amino) naphthalein-1-sulfonic acid) via a photosensitive nitroveratryl linker. Later, we performed MTT (cell viability) assays using esophageal adenocarcinoma (JH-EsoAd1) cells to determine the efficiency of our drug conjugate to induce cell death. As expected our drug conjugate was able to induce cell death, but only in presence of light. But in the dark, the cells remained unaffected. Also, we did several control studies to substantiate the fact that the cell death was actually due to drug release but not due to light or other entities. Further, we performed FACS (Fluorescence Assisted Cell Sorting) and confocal assays to show that in dark, the drug conjugate did not permeate cells. But upon irradiation with UV light, the drug was released from the conjugate, permeated the cells and induced cell death. A weakness of the above mentioned approach is that the drug is “decaged” or photo-released from the conjugates only under UV light; which cannot be translated to physiological conditions. This is because the UV light cannot penetrate deeper than 5 mm into the human skin. As a result, tumor cells that are deeply embedded in the human body cannot be treated using these approaches. To address this problem, Near Infrared (NIR) light could be used as it penetrates deeper than UV. Recently, several groups have reported using Upconverting Nanoparticles (UCNP) for the purpose of drug activation. The basis of this phenomenon is that the incidence of NIR light on these particles initiates multi-photon processes, eventually emitting UV/VIS wavelengths. The advantage of the NIR is that it deeply penetrates into the human skin. In our latest project, we have designed a drug conjugate that would be attached to UCNPs. We envision that after grafting the drug conjugate onto the nanoparticles and irradiating it with NIR drug release will occur as a result of upconversion. The above two systems describes novel methodologies for controlled release of the drug. To further improve the efficacy of the drug action, we designed new photosensitive systems based on the concept of targeted drug delivery. Targeted drug delivery is a treatment methodology in which the modified chemotherapeutic drug with higher tumor affinity could be concentrated in the tumor tissues. In certain cases, the receptors of tumor cells are targeted for the purpose of therapy. Receptors are cell surface proteins that are expressed on their plasma membrane. A select few of them such as Folic Acid Receptor (FAR) and PSMA (Prostate Specific Membrane Antigen) are overexpressed in malignant cells. In our new designs, we attached folic acid and urea based (DUPA) ligand, which were previously reported to bind to FAR and PSMA receptors respectively. Cell studies are currently underway to determine the specificity of these drug conjugates in targeting tumor cells. Once we demonstrate the above drug delivery strategies in vitro and later in vivo, we will have established novel drug delivery systems that could potentially be applied towards chemotherapeutic treatment.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
December 2012