The use of nanoparticles with high atomic (Z) number have been known to attenuate X-rays and the unique properties associated with gold nanoparticles makes them as potent radiosensitizers for enhancing Radiotherapy (RT) treatments. The interaction of high Z materials with the X-rays results in photoelectric absorption which leads to generation of photoelectrons. These low energy photoelectrons can deliver lethal energy in the close proximity. The success of cancer radiation therapy relies heavily on the effective delivery of radiation dose to the tumor site sparing the surrounding normal tissues. To overcome the limitations associated with increasing the radiation dose, due to normal tissue toxicities, the feasibility of radiosensitizing the tumor using gold nanoparticles provide a promising alternative. Targeting gold nanoparticles based formulations to the tumor prior to radiation therapy will result in radiation dose enhancement, by generating secondary photoelectrons, locally inside the tumor and thereby minimizing the dose dependent toxicity to non-specific neighboring tissues. Here, we have developed different Gold nanoparticles based formulations to locally radiosensitize the tumor cells in three different cancer models. For targeting pancreatic cancers, we have fabricated a new generation of GNPs formulation which are 3-4 nm in diameter and surface passivated with hetero-bifunctional PEG, fluorophore AlexaFlour 647 and peptide RGD. This formulation showed a 2.8-fold in vitro cell kill enhancement with X-rays, as demonstrated by clonogenic survival assays. In vivo studies confirmed the highly specific tumor uptake in tumor endothelial cells in orthotopic pancreatic tumor mice model. The combined treatment in animals treated with GNPs and radiation (10Gy) showed the maximum endothelial cells damage, as confirmed with confocal imaging of the tumor sections and CD31 immunostaining. For targeting the lung cancer, we have used the same GNPs formulation but adopted a inhalation/instillation (INH) route for administering the nanoparticles in vivo in transgenic lung cancer mice model as opposed to customary intravenous (i.v) route. Fluorescence imaging and ex-vivo electron microcopy results showed a 4.7 times higher concentration of GNPs in the lung tumors of mice when using INH delivery compared to i.v. approach. The survival studies with these animals are currently underway. For using these radiosensitizing nanoparticles in brachytherapy applications, we have incorporated GNPs in modified brachytherapy spacers to enhance radiation dose locally in tumor without any additional surgical intervention. These spacers are normally placed inside the tumor to spatially distribute the radioactive seeds. The incorporation of GNPs in these spacers allowed for enhancing the radiation dose by the GNPs released from the spacers. These spacers have same morphology (5 mm in length and 0.8 mm in diameter) as commercial spacers with additional radiosensitizing properties because of doped GNPs. We have shown the time dependent release of the GNPs as a function of size of GNPs from the spacers into the tumor by optical imaging. We have further incorporated the GNPs based brachytherapy spacer with the immunoadjuvants, anti-CD40 to combine the radiation and immunotherapy in a single platform. The preliminary results indicate that gold nanoparticles based nanoplatform shows promise as a potential theranostic radiosensitizer which allows for combining multiple therapies in a single platform. This work is supported by ARMY/ W81XWH-12-1-0154, NSF DGE 0965843, HHS/5U54CA151881-02, NCI R03CA164645, NCI1 K01CA17247801, the Electronics Materials Research Institute at Northeastern University, and Brigham and Women's Hospital. Citation Format: Rajiv Kumar, Wilfred Ngwa, Vinit Joshi, Sijumon Kunjachan, Ross Berbeco, Mike Makrigiorgos, Srinivas Sridhar. Gold nanoparticles based platforms for localized radiosensitization in cancer radiation therapy. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr B41.
Adamantyl groups are key structural subunit commonly used in many marketed drugs targeting diseases ranging from viral infections to neurological disorders. The metabolic disposition of adamantyl compounds has been mostly studied using LC-MS based approaches. However, metabolite quantities isolated from biological preparations are often insufficient for unambiguous structural characterization by NMR. In this work, we utilized microcoil NMR in conjunction with LC-MS to characterize liver microsomal metabolites of an adamantyl based CB2 agonist AM9338, 1-(3-(1H-1,2,3-triazol-1-yl) propyl)-N-(adamantan-1-yl)-1H-indazole-3-carboxamide, a candidate compound for potential multiple sclerosis treatment. We have identified a total of 9 oxidative metabolites of AM9338 whereas mono- or di-hydroxylation of the adamantyl moiety is the primary metabolic pathway. While it is generally believed that the tertiary adamantyl carbons are the preferred sites of CYP450 oxidation, both the mono- and di-hydroxyl metabolites of AM9338 show that the primary oxidative sites are located on the secondary adamantyl carbons. To our knowledge this di-hydroxylated metabolite is a novel adamantyl metabolite that has not been reported before. Further, the stereochemistry of both mono- and di-hydroxyl adamantyl metabolites has been determined using NOE correlations. Furthermore, docking of AM9338 into the CYP3A4 metabolic enzyme corroborates with our experimental findings, and the modelling results also provide a possible mechanism for the unusual susceptibility of adamantyl secondary carbons to metabolic oxidations. The novel dihydroxylated AM9338 metabolite identified in this study, along with the previously known adamantyl metabolites, gives a more complete picture of the metabolic disposition for adamantyl compounds.
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