Development of Novel Tumor-Targeted Compounds for Boron Neutron Capture Therapy

Glioblastoma multiforme (GBM) represents the most common primary brain tumor among adults. Despite surgical resection and aggressive chemoradiotherapy regimens, the current 2- and 5-year survival rates are only 27% and 9.8%, respectively. The low survival stems from the poor response to conventional therapy and underscores the critical need to develop new therapeutic approaches for GBM treatment. The high recurrence rate observed in GBM is in part attributed to the hypoxic (poorly oxygenated) tumor microenvironment. Hypoxic tumor conditions have been shown to increase metastasis, promote angiogenesis, and confer resistance to chemotherapy and radiation. Hypoxic tissues are inherently radiation resistant due to a diminished oxygen enhancement effect. Additionally, limited diffusion of oxygen and small molecules to hypoxic tissues mitigates the efficacy of chemotherapeutics. Therefore, due to its unique mechanism of cell death, boron neutron capture therapy (BNCT) has the potential to become an alternative treatment modality for cancer patients where radiation and chemotherapy have fallen short. However, before the full clinical potential of BNCT is realized, there is a dire need to either develop novel tumor-targeted compounds or improve the localized delivery of existing BNCT agents. The work outlined in this dissertation aims to address both these needs. First, a series of novel boronated compounds have been synthesized capable of targeting the hypoxic (and often therapy resistant) tumor microenvironment. Second, the local tumor delivery of several boronated agents has been improved utilizing a thermal sensitive liposome delivery system. BNCT utilizes the nuclear fission reaction that occurs when a boron-10 isotope (10B) captures a neutron. Upon 10B neutron capture, the resulting unstable 11B isotope undergoes a nuclear fission reaction (10B(n,α,γ)7Li ) to release an alpha particle (4He), lithium-7 (7Li) ion and gamma radiation. The generated particles have a limited path length of approximately 5-10 microns, thereby localizing the cytotoxic effect. Therefore, the biggest treatment hurdle for BNCT is the requirement to preferentially deliver boron to the tumor with minimal accumulation in the surrounding normal tissue. Therefore, we hypothesized that the hypoxic tumor microenvironment could be exploited to improve preferential delivery of boronated compounds to the tumor. To begin the dissertation, a novel boronated 2-nitroimidazole derivative (B-381) has been synthesized in a single step reaction. It has long been recognized that 2-nitroimidazole derivatives have preferential retention in hypoxic cells compared to normoxic cells. Therefore, we hypothesized that B-381 would have preferential retention in hypoxic glioma cells by exploiting the unique metabolism and retention of 2-nitroimidazoles in hypoxia. Towards this end, the cellular uptake of B-381 in D54 glioma cells was evaluated in vitro and in vivo compared to 4-borono-L-phenylalanine (BPA), the most commonly investigated agent in BNCT clinical trials. Unlike BPA, B-381 illustrated preferential retention in hypoxic glioma cells compared to normoxic glioma cells in vitro. In vivo, B-381 illustrated significantly higher long-term tumor retention compared to BPA, with 9.5-fold and 6.5-fold higher boron levels at 24 and 48 h, respectively. While these initial studies supported the unique retention of B-381 in hypoxic cells, it was desirable to improve the total boron content delivered to the tumor. To further improve total boron content delivered to the tumor, thermal sensitive liposomes (TSLs) were investigated. A DPPC/DSPC/DSPE-PEG2000 /Cholesterol TSL was designed capable of having a stable drug payload at 37°C while releasing \u3e90% of the drug payload at 42°C. Therefore, by locally inducing mild hyperthermia in vivo (42-43oC), it is possible to trigger a localized release of boronated drug within the tumor vasculature. Using both B-381 and BPA, TSLs can significantly improve tumor boron delivery at 42°C compared to normal tissue temperature (37°C). In summary, B-381 is effectively administered as both a free agent or incorporated into a thermal sensitive liposome formulation. B-381 represents a new class of BNCT agents in which their selectivity to tumors is based on a hypoxic tumor metabolism. Further studies are warranted to evaluate boronated 2-nitroimidazoles as well as boron-containing thermal sensitive liposomes for future BNCT clinical trials

Molecularly targeted therapies in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy that remains incurable because most patients will eventually relapse or become refractory to the treatments. Although the treatments have improved, the major problem in MM is the resistance to therapy. Novel agents are currently in development for the treatment of relapsed/refractory MM, including immunomodulatory drugs, proteasome inhibitors, monoclonal antibodies, cell signaling targeted therapies, and strategies targeting the tumor microenvironment. We have previously reviewed in detail the contemporary immunomodulatory drugs, proteasome inhibitors, and monoclonal antibodies therapies for MM. Therefore, in this review, we focused on the role of molecular targeted therapies in the treatment of relapsed/refractory multiple myeloma, including cell signaling targeted therapies (HDAC, PI3K/AKT/mTOR, p38 MAPK, Hsp90, Wnt, Notch, Hedgehog, and cell cycle) and strategies targeting the tumor microenvironment (hypoxia, angiogenesis, integrins, CD44, CXCR4, and selectins). Although these novel agents have improved the therapeutic outcomes for MM patients, further development of new therapeutic agents is warranted

Surface passivation of carbon nanoparticles with branched macromolecules influences near infrared bioimaging

A superior and commercially exploitable 'green synthesis' of optically active carbon nanoparticle (OCN) is revealed in this work. The naked carbon particles (<20 nm) were derived from commercial food grade honey. The fluorescence properties of these particles were significantly enhanced by utilizing hyberbranched polymer for surface passivation. A dramatic increase in near infrared emission was achieved compared to a linear polymer (PEG) coated carbon nanoparticles. Interestingly, as passivating agent becomes more extensively branched (pseudo generation 2 to 4), the average radiant efficiency amplifies considerably as a direct result of the increasing surface area available for light passivation. The particles showed negligible loss of cell viability in presence of endothelial cells in vitro. Preliminary in vivo experiment showed high contrast enhancement in auxiliary lymphnode in a mouse model. The exceptionally rapid lymphatic transport of these particles suggests that such an approach may offer greater convenience and reduced procedural expense, as well as improved surgical advantage as the patient is positioned on the table for easier resection

A green synthesis of carbon nanoparticles from honey and their use in real-time photoacoustic imaging

Imaging sentinel lymph nodes (SLN) could provide us with critical information about the progression of a cancerous disease. Real-time high-resolution intraoperative photoacoustic imaging (PAI) in conjunction with a near-infrared (NIR) probe may offer opportunities for the immediate imaging for direct identification and resection of SLN or collecting tissue samples. In this work a commercially amenable synthetic methodology is revealed for fabricating luminescent carbon nanoparticles with rapid clearance properties. A one-pot “green” technique is pursued, which involved rapid surface passivation of carbon nanoparticles with organic macromolecules (e.g., polysorbate, polyethyleneglycol) in solvent-free conditions. Interestingly, the naked carbon nanoparticles are derived for the first time, from commercial food grade honey. Surface coated particles are markedly smaller (∼7 nm) than previously explored particles (gold, single-walled carbon nanotubes, copper) for SLN imaging. The results indicate an exceptionally rapid signal enhancement (∼2 min) of the SLN. Owing to their strong optical absorption in the NIR region, tiny size and rapid lymphatic transport, this platform offers great potential for faster resection of SLN and may lower complications caused in axillary investigation by mismarking with dyes or low-resolution imaging techniques

A green synthesis of carbon nanoparticles from honey and their use in real-time photoacoustic imaging

Imaging sentinel lymph nodes (SLN) could provide us with critical information about the progression of a cancerous disease. Real-time high-resolution intraoperative photoacoustic imaging (PAI) in conjunction with a near-infrared (NIR) probe may offer opportunities for the immediate imaging for direct identification and resection of SLN or collecting tissue samples. In this work a commercially amenable synthetic methodology is revealed for fabricating luminescent carbon nanoparticles with rapid clearance properties. A one-pot “green” technique is pursued, which involved rapid surface passivation of carbon nanoparticles with organic macromolecules (e.g., polysorbate, polyethyleneglycol) in solvent-free conditions. Interestingly, the naked carbon nanoparticles are derived for the first time, from commercial food grade honey. Surface coated particles are markedly smaller (∼7 nm) than previously explored particles (gold, single-walled carbon nanotubes, copper) for SLN imaging. The results indicate an exceptionally rapid signal enhancement (∼2 min) of the SLN. Owing to their strong optical absorption in the NIR region, tiny size and rapid lymphatic transport, this platform offers great potential for faster resection of SLN and may lower complications caused in axillary investigation by mismarking with dyes or low-resolution imaging techniques

Radioprotection by Hymenialdisine-Derived Checkpoint Kinase 2 Inhibitors

DNA damage induced by ionizing radiation activates the ataxia telangiectasia mutated pathway, resulting in apoptosis or DNA repair. The serine/threonine checkpoint kinase (Chk2) is an important transducer of this DNA damage signaling pathway and mediates the ultimate fate of the cell. Chk2 is an advantageous target for the development of adjuvant drugs for cancer therapy, because inhibition of Chk2 allows normal cells to enter cell cycle arrest and DNA repair, whereas many tumors bypass cell cycle checkpoints. Chk2 inhibitors may thus have a radioprotective effect on normal cells. We report herein a class of natural product derived Chk2 inhibitors, exemplified by indoloazepine <b>1</b>, that elicit a strong ATM-dependent Chk2-mediated radioprotection effect in normal cells and p53 wt cells, but not p53 mutant cells (>50% of all cancers). This study represents the first example of a radioprotective effect in human cells other than T-cells and implicates a functional ATM pathway as a requirement for IR-induced radioprotection by this class of Chk2 inhibitors. Several of the hymenialdisine-derived analogues inhibit Chk2 at nanomolar concentrations, inhibit autophosphorylation of Chk2 at Ser516 in cells, and increase the survival of normal cells following ionizing radiation