[¹⁸F]PARPi Imaging Is Not Affected by HPV Status In Vitro

Abstract

Background. Human papillomavirus- (HPV-) associated oropharyngeal squamous cell carcinomas (OPSCCs) are clinically and pathologically distinct from HPV-negative tumors. Here, we explore whether HPV affects functional biomarkers, including γH2AX, RAD51, and PARP1. Moreover, the role of [18F]PARPi as a broadly applicable imaging tool for head and neck carcinomas is investigated. Methods. HPV-positive and HPV-negative cell lines were used to evaluate the γH2AX, RAD51, and PARP1 expression with immunoblotting and immunofluorescence. Effects of external beam ionizing radiation were investigated in vitro, and survival was investigated via colony-formation assay. [18F]PARPi uptake experiments were performed on HPV-negative and HPV-positive cell lines to quantify PARP1 expression. PARP1 IHC and γH2AX foci were quantified using patient-derived oropharyngeal tumor specimens. Results. Differences in DNA repair were detected, showing higher RAD51 and γH2AX expression in HPV-positive cell lines. Clonogenic assays confirm HPV-positive cell lines to be significantly more radiosensitive. PARP1 expression levels were similar, irrespective of HPV status. Consequently, [18F]PARPi uptake assays demonstrated that this tracer is internalized in cell lines independently from their HPV status. Conclusion. The HPV status, often used clinically to stratify patients, did not affect PARP1 levels, suggesting that PARP imaging can be performed in both HPV-positive and HPV-negative patients. This study confirms that the PET imaging agent [18F]PARPi could serve as a general clinical tool for oropharyngeal cancer patients.

DNA Repair Enzyme Poly(ADP-Ribose) Polymerase 1/2 (PARP1/2)-Targeted Nuclear Imaging and Radiotherapy

“…Replacing the cyclopropyl moiety of olaparib with a fluorobenzene ring led to the radiochemically stable [ 18 F]PARPi , which was developed in the Reiner lab in 2015. A large body of preclinical work subsequently explored the utility of [ 18 F]PARPi for a variety of potential applications, such as diagnosis of brain, head, and neck cancers [ 26 , 36 , 37 ], quantification of PARPi target engagement [ 38 ], efficacy assessment of PARPi treatment, and for differentiation between malignant and non-malignant lesions in lymphomas and gliomas [ 39 , 40 ]. This tracer has also been clinically translated, which is detailed in Section 4 .…”

“…The study showed that [ 18 F]PARPi uptake was limited to tumor tissue and showed higher uptake in orthotopic tongue tumor xenografts compared to the surrounding tongue, which was not the case for [ 18 F]FDG, indicating its feasibility for clinical applications in head and neck cancer imaging. Another study found that human papilloma virus (HPV)-positive and negative oropharyngeal cancer cells showed similar PARP1 expression and [ 18 F]PARPi uptake, suggesting the tracer as an HPV-independent imaging tool for imaging in oropharyngeal cancer patients [ 36 ].…”