Department of Pharmacy, Pharmaceutical Technology and Physical Chemistry, Faculty of Pharmacy and Food Sciences, University of Barcelona, Avda., Joan XXIII, 27⁻31, 08028 Barcelona, Catalonia, Spain.
Nstitut de Nanociència i Nanotecnologia, IN2UB, Facultat de Química, Diagonal 645, 08028 Barcelona, Catalonia, Spain.
Molecules. 2018 Jun 28;23(7):1567. doi: 10.3390/molecules23071567.
Photothermal therapy is a kind of therapy based on increasing the temperature of tumoral cells above 42 °C. To this aim, cells must be illuminated with a laser, and the energy of the radiation is transformed in heat. Usually, the employed radiation belongs to the near-infrared radiation range. At this range, the absorption and scattering of the radiation by the body is minimal. Thus, tissues are almost transparent. To improve the efficacy and selectivity of the energy-to-heat transduction, a light-absorbing material, the photothermal agent, must be introduced into the tumor. At present, a vast array of compounds are available as photothermal agents. Among the substances used as photothermal agents, gold-based compounds are one of the most employed. However, the undefined toxicity of this metal hinders their clinical investigations in the long run. Magnetic nanoparticles are a good alternative for use as a photothermal agent in the treatment of tumors. Such nanoparticles, especially those formed by iron oxides, can be used in combination with other substances or used themselves as photothermal agents. The combination of magnetic nanoparticles with other photothermal agents adds more capabilities to the therapeutic system: the nanoparticles can be directed magnetically to the site of interest (the tumor) and their distribution in tumors and other organs can be imaged. When used alone, magnetic nanoparticles present, in theory, an important limitation: their molar absorption coefficient in the near infrared region is low. The controlled clustering of the nanoparticles can solve this drawback. In such conditions, the absorption of the indicated radiation is higher and the conversion of energy in heat is more efficient than in individual nanoparticles. On the other hand, it can be designed as a therapeutic system, in which the heat generated by magnetic nanoparticles after irradiation with infrared light can release a drug attached to the nanoparticles in a controlled manner. This form of targeted drug delivery seems to be a promising tool of chemo-phototherapy. Finally, the heating efficiency of iron oxide nanoparticles can be increased if the infrared radiation is combined with an alternating magnetic field.
光热疗法是一种基于将肿瘤细胞的温度升高到 42°C 以上的治疗方法。为此，细胞必须用激光照射，而辐射的能量则转化为热量。通常，所使用的辐射属于近红外辐射范围。在这个范围内，身体对辐射的吸收和散射最小。因此，组织几乎是透明的。为了提高能量到热转换的效率和选择性，必须将光吸收材料，即光热剂，引入肿瘤中。目前，有大量的化合物可用作光热剂。在用作光热剂的物质中，基于金的化合物是最常用的之一。然而，这种金属的毒性不明确，从长远来看阻碍了它们的临床研究。磁性纳米粒子是作为肿瘤治疗用光热剂的一种很好的替代品。这些纳米粒子，特别是氧化铁形成的纳米粒子，可以与其他物质结合使用，或者本身就可以用作光热剂。磁性纳米粒子与其他光热剂的结合为治疗系统增加了更多的功能：纳米粒子可以通过磁场被引导到感兴趣的部位（肿瘤），并且可以对它们在肿瘤和其他器官中的分布进行成像。单独使用时，磁性纳米粒子在理论上存在一个重要的局限性：它们在近红外区域的摩尔吸收系数较低。纳米粒子的受控聚集可以解决这个缺点。在这种情况下，所指示的辐射的吸收更高，能量转化为热量的效率比单个纳米粒子更高。另一方面，可以将其设计为治疗系统，其中在红外光照射后，磁性纳米粒子产生的热量可以以受控的方式释放附着在纳米粒子上的药物。这种形式的靶向药物输送似乎是化学光疗的一种有前途的工具。最后，如果将红外辐射与交变磁场结合使用，可以提高氧化铁纳米粒子的加热效率。
