Biomedical Engineering – From Theory to Applications

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374 Biomedical Engineering – From Theory to Applications liver cancer. Neutron sources for BNCT are limited to nuclear reactors and these are available in the US, Japan, several European countries, and Argentina (Bregadze et al., 2001; Evstigneeva et al., 2003; Fronczek et al., 2005; Ol’shevskaya et al., 2006; Vicente et al., 2003). Boron-containing porphyrins have excellent tumor-localizing properties (Vicente, 2001) and have been proposed for dual application as boron delivery agents and photosensitizers for PDT in brain tumors (Rosenthal, 2003). 4.1.2 Anticancer drugs A series of interesting gold(III) meso-tetraarylporphyrin complexes with relevant antiproliferative effects on CNE1 human cancer cell lines were described by Che et al. (2003). Among them, the complex Au(III)(p-H-TPP)]Cl was found to be more cytotoxic for CNE1 than cisplatin. The lack of cross-resistance suggested that gold(III) porphyrins and cisplatin induced cytotoxicity through different mechanisms. Replacement of Au(III) with Zn(II) drastically reduced the drug potency. Cationic Mn porphyrins may be advantageous compared to other anti-cancer drugs, owing to their ability to afford pain management in cancer patients (Rabbani et al., 2009). 4.1.3 Carriers for anti-cancer drugs The tumor-affinity of porphyrins has been exploited for designing porphyrin–anticancer drug conjugates. Brunner et al. created a series of porphyrin–platinum conjugates by combining porphyrin with cytotoxic platinum complexes (Brunner, 2004; Lottner, 2002). Zhou reported some porphyrin – DNA-alkylation-agent conjugates (Zhou, 2006) and Guo et al. (2003, 2004) prepared conjugates by linking porphyrin with other nitrogen heterocyclic species. However none of the conjugates mentioned above may be considered as a prodrug, since they do not release the actual drug. The first example of a porphyrin anticancer prodrug was reported in 2008 and consists of three parts: a porphyrin, a photocleavable onitrobenzyl moiety as a light-triggered group, and a parent anticancer drug Tegafur (Lin et al., 2008). The prodrug is significantly less toxic than its parent anticancer drug Tegafur, which is released upon photoactivation. Combined with the up-to-date medical fiber optic technique, the light-triggered porphyrin anticancer prodrugs may find useful applications in chemotherapy to minimize side effects of anticancer drugs and in the light-controllable anticancer drug dosing (McCoy et al., 2007). 4.2 Chronic pain management Severe pain syndromes reduce the quality of life of patients with inflammatory and neoplastic diseases, partly because reduced analgesic effectiveness of chronic opiate therapy leads to escalating doses and distressing side effects. Peroxynitrite (ONOO −) and its reactive oxygen precursor superoxide (O2 •−), are critically important in the development of pain. Metalloporphyrins have the highest rate constants for scavenging O2 − and ONOO− and were shown to alleviate conditions originating from oxidative stress, such as diabetes, cancer, radiation injury, and central nervous system injuries, including morphine antinociceptive tolerance (Salvemini & Neuman, 2010, Salvemini et al., 2011). The most potent ONOO− scavengers and superoxide dismutase mimics reported so far are cationic Mn(III) N-alkylpyridylporphyrins (Fig. 10) (Batinić-Haberle et al, 1999; Rebouças et al., 2008a; Rebouças et al., 2008b).
Trends in Interdisciplinary Studies Revealing Porphyrinic Compounds Multivalency Towards Biomedical Application Fig. 10. Metalloporphyrins reported as radical scavengers 4.3 Photodiagnosis The intriguing “tumor-localization” nature of porphyrins prompted the development of porphyrin-based diagnostic pharmaceuticals for different imaging modalities (Lipson, 1961; Nelson, 1991) or radioactive tracers (Nakajima et al., 1993) for tumor detection with encouraging results (Lee et al., 2010). 4.3.1 Contrast media for MRI Magnetic resonance imaging (MRI) with molecular probes offers the potential to monitor physiological parameters with high spatial and temporal resolution, but the construction of cell-permeable imaging agents remains a challenge. Membrane permeability, optical activity, and high relaxivity of porphyrin-based contrast agents offer exceptional functionality for in-vivo imaging. It was recently shown that a porphyrin-based MRI molecular imaging agent, Mn-(DPA-C2)2-TPPS3, effectively penetrates cells and persistently stains living brain tissue in intracranially injected rats. Due to cromogenicity, its distribution can also be observed by histology (Chen, 1984; Lee, 2010; Shahbazi-Gahrouei, 2001). Porphyrin-based complexes were also identified as necrosis-avid contrast agents (NACAs) for noninvasive MRI identification of acute myocardial infarction, assessment of tissue or organ viability, and therapeutic evaluation after interventional therapies (Ni, 2008). 4.3.2 NIR fluorescent probes The NIR region of the spectrum offers considerable opportunities for diagnosis because of the lack of interference with endogenous absorbers such as haeme pigments and melanin. In this region, light is able to penetrate deeper into tissue, thus offering routes to the therapy of blood vessel disorders and larger or deeper seated malignancies. Although the greatest activity in the synthesis of NIR-absorbing compounds for therapeutic intent has come from the porphyrin area, with bacteriochlorins and texaphyrins being promising derivatives, none of them is yet in everyday use (Wainwright M., 2010). 5. Current limitations and future trends Only a small part of the impressive number of synthesized porphyrinic compounds is highly efficient in PDT, so the quest for the ideal photosensitizer still continues. 375
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BIOMEDICAL ENGINEERING - FROM THEOR
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VI Contents Chapter 9 Targeted Magn
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X Preface stand-alone and readers c
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110 Method (Detection) Analyte Matr
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120 6. Conclusion Biomedical Engine
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150 5. Conclusions Biomedical Engin
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162 1 st phase : half year 4 2 nd p
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166 7. Innovative active training B
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172 12. Maturing projects’ story
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180 16. Acknowledgments Biomedical
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190 R* M M M M MR*M O O O O M O R*
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196 Fig. 9. Chemical structure of 5
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198 Relative Intensity (AU) Biomedi
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204 2. Preparation of IO nanopartic
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256 3. Deposition techniques Biomed
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454 In this case, the eigenvalues a
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456 where Biomedical Engineering -
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