Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Physics

Department

Physics

First Advisor

Michael Antosh

Abstract

The use of radiation is broad in biological systems, in different areas of research mostly in health.

Radiation is used to kill cancer. In radiation therapy proper calculation is done so that a maximum dose is delivered to the cancer. Inspite of this precaution, radiation effects healthy tissue. This effect is especially dangerous when the tumor is located near important organs. Thus in radiation therapy, it is important to reduce the dose and the damage to the healthy tissues and organs. The damage on the healthy tissues due to radiation therapy in cancer could be reduced by reducing the radiation dose to get the same treatment effect or by enhancing the radiation. The enhancement of radiation effect in vitro and in vivo can be obtained by targeted drug delivery on the cancer. Also photo dynamic therapy can be supplemented by the use of radiation therapy on the cancer by targeted drug delivery.

Another use is the development of a bio dosimeter. In a large scale nuclear event it is important to measure the radiation dose exposed to humans. Also it is likely that the people who are exposed to radiation are not wearing the dosimeter. So a method of estimating radiation dose to a person exposed to radiation without a physical dosimeter would be a very useful procedure. One possible method is the use of gene expression analysis, which is based on the fact that the expression of the genes will change due to the absorbed radiation. So developing a biological dosimeter based on the gene expression analysis could quantify the radiation dose given to the patients during radiation therapy or to assess the risk of cancer developing in the general population. This biological dosimeter could even be used when the physical dosimeters are insufficient to estimate the risk caused by the radiation exposure or even years after being exposed to nuclear accidents.

The main goal of the work presented here is to investigate the following topics

  • Use of gold pHLIP to enhance the radiation effect in cancer cells
  • Review on the in vivo research done to enhance radiation using gold nanoparticles
  • Analyze the gene expression results from irradiated drosophila melanogaster to develop a biological dosimeter.
  • Use of X-ray to activate targeted Copper Cysteamine nanoparticles photosensitizer to reduce tumor size in mice.

A review work I have done on the researches related to enhancement of radiation using gold nanoparticles in tumor bearing mice showed that the targeted nanoparticles are a promising method for achieving radiation enhancement due to their shape, size, surface chemistry and the properties of the nanoparticles.

Gold nanoparticles are susceptible to X-rays compared to tissues and release extra electrons by Auger effect when the tumor treated with gold is irradiated. These auger electrons have low energy and are localized within the tumor site killing the cancer cells. However tumor targeting peptide pHLIP (pH Low Insertion Peptide) conjugated to gold nanoparticle specifically targets low pH medium (tumor) which when irradiated reduces the risk of killing healthy tissues near by and increases the uptake of the particles in the cancer mostly in the cellular membranes compared to only gold. The experimental results on cellular uptake of gold showed that there was an enhancement of gold uptake by 52% at low pH compared to normal pH (P value = .008)and also in targeted gold by 34% compared to non targeted gold at low pH (P value = .023). The images obtained by distribution of gold experiment showed that the cellular uptake of gold-pHLIP is higher compared to gold alone. The targeting of plasma membrane by gold-pHLIP is seen clearly on all the images and some staining of internal organelles and nuclei membranes as well. The clonogenic assay experiment at 1.5Gray radiation showed a statistically significant 24% decrease in survival for cells treated with gold-pHLIP at low pH compared with cells treated with no gold. Also a statistically significant 21% decrease in survival for cells treated with gold-pHLIP at low pH compared with cells treated with gold alone. Thus Gold nanoparticles conjugated with pHLIP significantly increases the amount of gold particles in cancer cells thus enhancing the radiation effect and increasing the amount of cancer cell death from radiation.

Copper cysteamine nanoparticles placed in the tumor site release cytotoxic singlet oxygen molecules on irradiation. The Cu-Cy nanoparticles being photosensitizers kill tumor when activated by radiation. Photosensitizers are limited to shallow tumors. Here we use X-radiation to photosensitize the pHLIP targeted Cu-Cy nanoparticles to kill even the deeply seated tumors in vivo. The results from the in vivo experiment we have done shows significant tumor destruction under X-ray activation. ANOVA analysis showed that the mice treated with targeted particles had a significantly different tumor sizes than mice treated with no particles, as well as mice treated with non-targeted particles. Also the use of targeted copper cysteamine nanoparticles affected the survival time after irradiation, compared to irradiation using no particles on mice. This work confirms the effectiveness of Copper Cysteamine nanoparticles, targeted to tumors, as a photosensitizer when activated by radiation therapy. Thus the aid of radiation therapy to photodynamic therapy by the use of tumor targeted CuCy nanoparticles efficiently does tumor destruction shrinkage with the increase in mice survival.

Gene expression analysis on a published data showed that the expression of genes are radiation dose dependent and some genes behaving predictably as a function of radiation dose at different time points after radiation can be used as a bio dosimeter. The data analysis showed that 6 genes from drosophila melanogaster show linear response (R2 > 0.9) with radiation dose at all time points after irradiation. Four of these genes have human homologues. Dropping off the lowest radiation dose (10 roentgen being very low for the fruit flies), 13 genes show a linear response with dose at all time points including 5 of 6 genes in whole data set. Of these 13 genes, 4 have human homologues and 8 have known functions. The Irbp (inverted repeat – binding protein) gene among the above is very important as it is a DNA repair gene. It is reasonable to predict that DNA damage is linear with radiation dose; thus, it is logical that some DNA repair genes may respond linearly in expression. Irbp has homologues in organisms that are as complex as humans and chimpanzees and in organisms as Japanese rice. The expression of this panel of gene, particularly those with human homologues, could potentially be used as the biological indicator of radiation exposure in dosimeter applications.

Thus we could use radiation to kill tumors more effectively or the development of a biological dosimeter could help people to estimate the risk of cancer caused due to their exposure to radiation.

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