Radiation therapy uses ionizing radiation to kill tumor cells by damaging DNA and other biomolecules either directly or via reactive oxygen species generated during water radiolysis. However, radiation effectiveness is often limited by normal tissue tolerance and tumor radioresistance, which motivates the use of radiosensitizers to enhance tumor response. Photosensitizers are being explored as radiosensitizers because they can promote the formation of additional reactive oxygen species and other reactive species under ionizing radiation. However, the mechanisms by which photosensitizers respond to ionizing radiation remain unclear, and reported radiosensitizing outcomes are not always consistent. This thesis therefore investigates the mechanism of how photosensitizers generate reactive oxygen species under different radiation conditions and assesses their potential as radiosensitizers across radiation therapy modalities with different dose rates....

The interaction between ionizing radiation and materials composed of high Z-number elements could be applied to enhance radiotherapy. In this work, we fabricated an ionizing radiation-sensitive nanoplatform by grafting chlorin e6 (Ce6) onto the surface of ultrasmall gold nanoparticles (Au NPs), aiming to enhance the radiation effects induced by different radiation sources. Poly(ethylene glycol) (PEG) was applied as the shape-controlling agent during the synthesis of Au nanoparticles. The as-prepared Au NPs show excellent monodispersity, with an average hydrodynamic diameter of around 5 nm. U87 and HeLa cell lines were utilized to evaluate the biological properties of the as-prepared Ce6–Au NPs. The Cell Counting Kit-8 (CCK-8) results reveal that the Ce6–Au NPs conjugate can significantly affect the growth of U87 cells under X-ray and 68Ga exposure, which is not seen for the pure Au NPs, Ce6, and physically mixed Ce6 and Au NPs. Moreover, the Ce6–Au NPs conjugate show evident cell prefoliation inhibition of U87 and HeLa cells under both X-ray and 18F-radiolabeled fluorodeoxyglucose (18F-FDG) exposure. These results indicate that interaction exists between Ce6 and Au NPs under radiation exposure. The mRNA sequencing results show that the tumor killing performance induced by Ce6–Au NPs may be due to regulation of the tumor microenvironment (TME) and immune-relevant signaling pathway. Our research proves that the rational combination of Au NPs and Ce6 can make better use of ionizing radiation energy and thus improve the therapeutic outcome of radiotherapy.

This study shows that coupling to designed plasmonic nanoparticles can modulate the electrophysiological function of proteins in living mammalian cells. Nanostar-shaped particles, that are robust to biological noise, are designed to enable near-field-coupling to plasma membrane-localized mutated Archaerhodopsin proteins in live cells. The coupled rhodopsins exhibit enhanced fluorescence and an increased response speed to membrane voltage. Incorporating this plasmonic enhancement into a Markov chain photocycle model of the Archaerhodopsin mutant QuasAr6a, shows an increased fluorescence emission rate and manipulation of the protein dynamics through a combination of photocycle transition rate enhancements. The results show an improvement in fluorescence and voltage-response dynamics of the functional QuasAr6a Archaerhodopsin mutant, beyond what has been achievable through genetic engineering. This opens up possibilities for engineering the biological functionality of proteins through plasmonics: manipulating protein photocycles could improve light sensitivity, change optogenetic applications, and lead to fluorescent biosensors with enhanced dynamics.

Boronic acid and ester-caged prodrugs have been widely investigated in cellular-generated hydrogen peroxide triggered release. Although it is well-known that ionizing radiation generates hydrogen peroxide in aqueous solution, using this approach to activate boronic acid or ester-based prodrugs suffers from low H₂ O₂ yields and thus low uncaging efficiency. However, the organochloride peroxyl radical formed from irradiating an aqueous solution of an organochloride may increase the uncaging efficiency. In this study, we used a boronic acid-caged coumarin derivative to quantify the yield of oxidation induced by clinical doses of radiation (less than 8 Gy), and boronic acid-caged gemcitabine to assess the activation of a prodrug upon irradiation. Irradiation of the coumarin derivative in phosphate buffered saline shows a low yield of 0.048 µM per Gy, and the prodrug after irradiation has only limited toxicity to the U87 cell line, indicating limited uncaging. The oxidation of boronic acid can be greatly enhanced by the peroxyl radical generated from irradiation of dilute PBS-organochloride solutions, with the yield increasing to 0.13 µM per Gy. Moreover, the oxidation by peroxyl radical can be catalyzed by N,N-dimethylaniline derivatives, increasing the yield to 0.19 µM per Gy. Clinical dose irradiation of the caged gemcitabine derivative in a solution of PBS with trichloroethanol and 2-(dimethylamino)benzoic acid shows efficient tumor cell killing and a comparable toxicity with that of the parent drug, indicating efficient uncaging.

Irradiation of aqueous solutions containing alkyl chlorides generates peroxyl radicals by reactions of alkyl chlorides, aqueous electrons, and dissolved oxygen. The peroxyl radical can oxidize thioethers to sulfoxides, a transformation that has relevance for targeted or triggered drug delivery. However, small-molecule alkyl chlorides can induce liver damage, which limits their potential for application in anticancer therapy. Here, we show that alkyl chlorides bound to a hydrophilic random copolymer chain behave similar to small-molecule alkyl chlorides. Our work shows that using polymeric alkyl chlorides can be an alternative to small-molecule alkyl chlorides provided that the alkyl chloride functionalities are easily accessible to aqueous electrons.

Photosensitizers have significant potential as radiosensitizers in cancer treatment, yet the mechanism of ionizing-radiation-induced singlet oxygen (¹O₂) generation remains unclear. Here, we systematically investigated ¹O₂ production by the photosensitizer Chlorin e6 (Ce6) using the Singlet Oxygen Sensor Green probe and imidazole/ p -nitroso- N , N -dimethylaniline detection methods, evaluating the effects of photon energy (X-rays up to 310 kV and ⁶⁰Co gamma rays at 1.17 and 1.33 MeV), dose, and dose rate. Ce6 produced more ¹O₂ with increasing photon energy. At 5 Gy, the lowest dose rate (0.005 Gy/min) yielded significantly more ¹O₂ than higher dose rates (7–0.05 Gy/min). Scavenging experiments identified superoxide anions (·O₂⁻) as a key intermediate. We propose that, unlike classical triplet-state photosensitization, ionizing radiation induces Ce6 radical cations (Ce6^⋅+), which react with radiation-induced ·O₂⁻ to generate ¹O₂. These findings suggest potential for photosensitizer-radiation combinations in low-dose-rate therapies, although further biological validation and consideration of tumor redox status are required.

The controlled release of drugs using local ionizing radiation presents a promising approach for targeted cancer treatment, particularly when applied in concurrent radio-chemotherapy. In these approaches, radiation-generated reactive species often play an important role. However, the reactive species that can be used to trigger release have low yield and lack selectivity. Here, we demonstrate the generation of highly oxidative species when aqueous solutions containing low concentrations of organochlorides (such as chloroform) are irradiated with ionizing radiation at therapeutically relevant doses. These reactive species were identified as peroxyl radicals, which formed in a reaction cascade between organochlorides and aqueous electrons. We employed stilbene-based probes to investigate the oxidation process, showing double bond oxidation and cleavage. To translate this reactivity into a radiation-sensitive material, we synthesized a micelle-forming amphiphilic block copolymer that has stilbene as the linker between two blocks. Upon exposure to ionizing radiation, the oxidation of stilbene led to the cleavage of the polymer, which induces the dissociation of the block-copolymer micelles and the release of loaded drugs.

The redox balance in tumor and diseased cells often leads to the production of reactive oxygen species (ROS). Many ROS-responsive materials based on sulfur oxidation have been reported with the goal of achieving controlled delivery at the tumor. However, these materials often lack responsiveness to low ROS concentrations present in the tumor environment. To address this, we use organocatalysis to achieve an enhanced response of thioether-based nanocarriers triggered by low concentrations of ROS. Using block copolymer micelles that can disassemble through thioether oxidation followed by ester hydrolysis, this work shows how an in-situ-formed imine oxidation catalyst can enhance disassembly kinetics at low millimolar hydrogen peroxide concentrations. The results show that with organocatalysis, Nile Red-loaded micelles release their cargo twice as fast compared to uncatalyzed conditions. This study highlights the potential of organocatalysis as a valuable strategy to enhance the responsiveness of biomarker-triggered delivery systems.