## 4 Applications of CDs in Cancer Theranosis
### Cancer Therapy via Drug Delivery, PTT, PDT, PTT+PDT, siRNA Delivery, SDT, and Gas Therapy  
#### 4.2.1 Drug Delivery  
CDs have emerged as promising nanocarriers for targeted drug delivery. By surface functionalization or surface modification of CDs, they can be engineered to transport therapeutic drugs to specific target sites. The fluorescence properties of CDs allow for the visualization of the drug delivery to the cancer site. The DOX is commonly used in chemotherapy because of its effective anticancer activity. However, its use is limited owing to its nonspecific nature, poor water solubility, and toxicity to normal cells [155]. Thus, the delivery of DOX using CDs can be an effective approach to improve the therapeutic effects and minimize the side effects of DOX through enhanced water solubility and specificity. [PERSON] et al. synthesized hyaluronic acid-modified CDs (HA-CDs) for targeted drug delivery using breast cancer (4T1)-bearing BALB/c mice [156]. HA was used as a targeting ligand of cluster determinant 44 receptors overexpressed on cancer cells. The DOX was  
Figure 9: **(a)** In vivo imaging of C6 glioma-bearing mice after tail vein administration of CD-Asp and (**b**) ex vivo imaging of the brain 90 min after IV administration of CD-Asp [134]. **(c)** In vivo imaging of cancer-bearing mice after administration with LAAM GUA-CDs/Cy5-siRNA-2 via tail vein and (**d**) ex vivo fluorescence images of cancers and organs after dissection at 5 h after IV administration [153]. The color scale indicates intensities in units of radiance. loaded onto HA-CDs through 4-carboxybenzaladehyde (p-CBA) as a pH-sensitive linker, enabling controlled drug release under acidic conditions at the cancer site. The enhanced cancer accumulation of HA-CD@p-CBA-DOX could be attributed to the active targeting by HA and the passive targeting by the EPR effect. The study demonstrated that the HA-CD@p-CBA-DOX significantly inhibited cancer growth, showing a cancer growth inhibitory rate of 78.53%, compared with 57.07% of the free DOX (Figure 10a,b). [PERSON] et al. investigated the anticancer efficacy of CD-PEI-DOX in BALB/c nude mice bearing liver cancers (MHCC-97L) [157]. In their study, the cancer-bearing mice were injected with PBS, free DOX, and CD-PEI-DOX through the tail veins. The results demonstrated that all DOX treatment groups exhibited significant inhibition of cancer growth compared to the PBS control group (Figure 10c,d), but the CD-PEI-DOX group exhibited the lowest cancer growth rate compared to the other groups. These findings suggested that the CD-PEI-DOX could potentially improve the therapeutic efficacy of DOX by maximizing its accumulation at the cancer site. [PERSON] et al. developed a targeted drug delivery system using green fluorescent CDs (GCDs) conjugated with PEG and transferrin (Tf) to load DOX for the effective treatment of cancer [158]. In their work, cancer-bearing mice were divided into four groups with IV administration: control (PBS), GCD-PEG-Tf, free DOX, and GCD-PEG-Tf@DOX. The results showed that both the GCD-PEG-Tf and free DOX groups exhibited rapid cancer growth, as shown in Figure 10e,f, whereas the GCD-PEG-Tf@DOX-treated mice exhibited significant cancer growth inhibition. This enhanced cancer suppression was attributed to the ability of GCD-PEG-Tf@DOX to selectively target cancer cells and longer circulation time in vivo, highlighting its potential as a targeted drug delivery and cancer therapy. Figure 10: **(a)** Photographs of dissected cancers on the 15 th day after IV administration and (b) cancer volume changes after IV administration into 4T1 cancer-bearing mice (***\(p<0.001\)) [156]. **(c)** Photographs of dissected cancers on the 33 rd day after IV administration into MHCC-97L cancer-bearing mice and (d) cancer volume changes after administration (***\(p<0.0001\)) [157]. **(e)** Photographs of the dissected cancers on the 18 th day after IV administration and (f) cancer size changes after IV administration (*\(p<0.01\); **\(p<0.001\)) [158].