Folate-Targeted Surface-Enhanced Resonance Raman Scattering Nanoprobe Ratiometry for Detection of Microscopic Ovarian Cancer

Abstract

Ovarian cancer has a unique pattern of metastatic spread, in that it initially spreads locally within the peritoneal cavity. This is in contrast to most other cancer types, which metastasize early on via the blood stream to distant sites. This unique behavior opens up an opportunity for local application of both therapeutic and imaging agents. Upon initial diagnosis, 75% of patients already present with diffuse peritoneal spread involving abdominal organs. Complete resection of all tumor implants has been shown to be a major factor for improved survival. Unfortunately, it is currently not possible for surgeons to visualize microscopic implants, impeding their removal and leading to tumor recurrences and poor outcomes in most patients. Thus, there is a great need for new intraoperative imaging techniques that can overcome this hurdle. We devised a method that employs folate receptor (FR)-targeted surface-enhanced resonance Raman scattering (SERRS) nanoparticles (NP), as folate receptors are typically overexpressed in ovarian cancer. We report a robust ratiometric imaging approach using anti-FR-SERRS-NPs (αFR-NPs) and non-targeted SERRS-NPs (nt-NPs) multiplexing. We term this method of ‘Topically Applied Surface Enhanced Resonance Raman Ratiometric Spectroscopy’ (“TAS3RS” (\tasers\) for short). TAS3RS successfully enabled the detection of tumor lesions in a murine model of human ovarian adenocarcinoma regardless of their size or localization. Tumors as small as 370 μm were detected as confirmed by bioluminescence imaging and histological staining. TAS3RS holds promise for intraoperative detection of microscopic residual tumors and could reduce recurrence rates in ovarian cancer and other diseases with peritoneal spread.

Cancer characterization and diagnosis with SERS-encoded particles

“…Nanostars and nanorods accumulate the electromagnetic field at their tips, giving rise to very strong single particle SERS intensities (Alvarez-Puebla et al 2010). Similar approaches as for spherical colloids were applied for the preparation of SEPs using Au nanostars functionalized with thiolated PEG (Morla-Folch et al 2014;Yuan et al 2012), or coated with silica shells (Andreou et al 2016;Henry et al 2016;Huang et al 2016;Mir-Simon et al 2015;Oseledchyk et al 2017). Figure 2d, h shows Au nanostars coated with Ag and silica, respectively.…”

“…In fact, it has been demonstrated that SEPs can adhere to tumor tissues in less than minutes, although the nonspecifically adsorbed SEPs must be removed by washing the tissue with serum (Wang et al 2014a). The obstacle set by the high background distribution of non-specifically bound nanoparticles can be overcome by implementing ratiometric approaches where one of the SEP type in the particle cocktail is used as a nonspecific internal reference to visually enhance the preferential adhesion of other targeting nanoparticles on tumor tissues (Mallia et al 2015;Oseledchyk et al 2017;Pallaoro et al 2011). Implementation of these methods is rather straightforward for SERS imaging due to the high degree of multiplexing provided by the narrow Raman linewidths.…”

“…This mechanism exploits the preferred accumulation of nanoparticles, within a certain size range and surface charge, on cancer tissue as compared to normal tissues, a unique biological mechanism ascribed to an enhanced permeability and retention (EPR) effect (Maeda et al 2013). The EPR effect was also exploited in the application of SEPs to intraoperative targeted SERS imaging (here, SEPs are injected into the patient's body before the operation) (Andreou et al 2016;Oseledchyk et al 2017). This (Fig.…”

“…While active targeting methods have proven to significantly reduce the dissipation of SEPs to healthy tissues and organs with respect to passive approaches, still toxicity and clearance issues remain major concerns associated with the systemic route of administration (such as via intravenous injections). Thus, when allowed, alternative strategies to circumvent these problems have been exploited, including topical spray-like applications (Mallia et al 2015;Zavaleta et al 2013) and direct intratumoral injections (Dinish et al 2014;Oseledchyk et al 2017).…”

“…As previously discussed, ratiometric approaches can address these limitations. A paradigmatic example is provided by the recent work of Oseledchyk et al (2017), which devised a topically applied SERS ratiometric method to delineate ovarian cancer lesions as small as 370 μm in a murine model of human ovarian adenocarcinoma on the peritoneum and visceral surfaces after intraperitoneal injection. The unique behavior of metastatic diffusion of ovarian cancer, which initially spreads locally within the peritoneal cavity, paves the way for the local application of SEPs in the fast intraoperative detection of microscopic residual tumors during surgery.…”