*Integrins in Ovarian Cancer: Survival Pathways, Malignant Ascites and Targeted Photochemistry DOI: http://dx.doi.org/10.5772/intechopen.106725*

Fluorescence imaging of cancer relies on the selective accumulation of fluorescent agents in cancer cells. αvβ3 integrins are the most common targets in integrin-targeted fluorescent imaging studies. For instance, the fluorescent probe squaraine was covalently attached to one (monovalent) and two (divalent) cyclic RGD peptides by Shaw and colleagues to target ovarian cancer cells that overexpress αvβ3 integrins [167]. Uptake of the divalent probe in OVCAR4 cells was 2.2-fold higher than the monovalent probe, based on fluorescence imaging. Consistently, tumors grown in nude mice and imaged with the divalent probe were almost three times more fluorescent compared to tumors given the monovalent probe, and six times more fluorescent than tumors that received non-conjugated squaraine. To explore the potential of integrin-targeted, fluorescence-guided resection in ovarian cancer, Alvero *et al.* created a PLGA-PEG nanoparticle to target αvβ3 integrins in OCSC1-F2 ovarian cancer cells using an RGD peptide and three different fluorescent dyes: DIR, C6, and ICG [168]. The resulting conjugates enabled the investigators to visualize both the tumorassociated vasculature and intraperitoneal ovarian cancer micrometastases as small as 100 μm in a xenograft model. These studies demonstrate the potential of using αvβ3-targeted agents for fluorescence guided resection in ovarian cancer. An additional important consideration for this approach is the accuracy of tumor detection. This concern was addressed in a study by Harlaar *et al.*, who found that the diagnostic accuracy of an αvβ3-targeted agent in combination with an NIR fluorescence intraoperative imaging system was 96.5%, with a sensitivity of 95% and a specificity of 88% [169].

In comparison to RGD peptides that have been relatively widely used to target integrins, less commonly used peptides, such as "OA02", have been synthesized to bind an α3 integrin subunit [170]. An *in vivo* study by Aina *et al.* used nude mice bearing ES-2 tumors to evaluate three different forms of this peptide: OA02-biotin-Cy5.5, OA02-Cy5.5, and OA02-AlexaFluo 680. Results showed that OA02-Cy5.5 and OA02- AlexaFluo 680 exhibited fast and specific tumor uptake that sustained a fluorescence signal for approximately 70 minutes. Although the cellular uptake of OA02 biotin-Cy5.5 was slower than other peptide variants, the duration of the fluorescence signal was 24 hours. To confirm that α3 integrins were mediating the binding of OA02 peptides to ES-2 tumors, mice were injected with an anti-α3 monoclonal antibody, which blocked binding of the peptides to the tumors.

The value of targeting integrins has also been explored in the context of PTT, which involves the interaction of electromagnetic radiation (typically NIR light) with a photothermal agent to generate heat, leading to tissue hyperthermia. In a study by Zhou *et al.*, the selectivity of silica-coated gold nanorods for ovarian cancer cells increased using hyaluronic acid and an RGD peptide that bind to CD44 and αvβ3 integrin, respectively [171]. The targeted nanoparticle showed high selectivity for SKOV3 cells but not for non-cancerous HOSEpiC cells. The nanorods were also loaded with doxorubicin (DOX) to increase cytotoxicity. PTT using the dual-targeted, DOX-loaded gold nanorods, and irradiation with an 808 nm laser at a high-power density (2 W/cm<sup>2</sup> ), exhibited the highest cytotoxicity to SKOV3 cells among all experimental groups. Subsequent experiments have revealed that the release of DOX is pH-sensitive and triggered by NIR irradiation. DOX release may be influenced by hyaluronidase-mediated degradation of hyaluronic acid in low pH environments, and the disruption of the interaction between DOX and silica, respectively. An overview of photochemistry-based studies that focus on modulating or targeting integrins in the context of ovarian cancer is presented in **Figure 5**.

### **Figure 5.**

*Integrins as targets for fluorescence imaging and photochemical or photothermal treatment in ovarian cancer. Current research focuses on using RGD tripeptide-conjugated PS or PTT agents to target ovarian cancer cells that overexpress integrins (left), or to modulate integrin activity and inhibit cancer cell adhesion to secondary sites by low level cellular photodamage (right).*

In summary, targeting integrins is a promising strategy for both anti-cancer PDT and fluorescence imaging. Since most PSs also have fluorescent properties, novel nanocarriers with integrin-targeting molecules can be used in theranostic applications and in real-time image-guided PDT of ovarian cancer. The potential of integrintargeted PDT warrants further evaluation.
