Preventing cervical cancer: the Pap test and the HPV vaccine

Electrochemical Immunosensor for Ultra-Low Detection of Human Papillomavirus Biomarker for Cervical Cancer

Human papillomavirus (HPV) is the causative agent for cervical cancer. Of the various types of HPV, the high-risk HPV-16 type is the most important antigenic high-risk HPV. In this work, the antigenic HPV-16 L1 peptide was immobilized on a glassy carbon electrode and used to detect several concentrations of the anti-HPV-16 L1 antibody, and vice versa. Two electrode platforms were used: onion-like carbon (OLC) and its polyacrylonitrile (OLC-PAN) composites. Both platforms gave a wide linear concentration range (1.95 fg/mL to 6.25 ng/mL), excellent sensitivity (>5.2 μA/log ([HPV-16 L1, fg/mL]), and extra-ordinarily low limit of detection (LoD) of 1.83 fg/mL (32.7 aM) and 0.61 fg/mL (10.9 aM) for OLC-PAN and OLC-based immunosensors, respectively. OLC-PAN modified with the HPV-16 L1 protein showed low LoD for the HPV-16 L1 antibody (2.54 fg/mL, i.e., 45.36 aM), proving its potential use for screening purposes. The specificity of detection was proven with the anti-ovalbumin antibody (anti-OVA) and native ovalbumin protein (OVA). An immobilized antigenic HPV-16 L1 peptide showed insignificant interaction with anti-OVA in contrast with the excellent interaction with anti-HPV-16 L1 antibody, thus proving high specificity. The application of the immunosensor as a potential point-of-care (PoC) diagnostic device was investigated with screen-printed carbon electrodes, which detected ultra-low (ca. 0.7 fg/mL ≈ 12.5 aM) and high (ca. 12 μg/mL ≈ 0.21 μM) concentrations. This study represents the lowest LoD reported for HPV-16 L1. It opens the door for further investigation with other electrode platforms and realization of PoC diagnostic devices for screening and testing of HPV biomarkers for cervical cancer.

Obtaining an immunoaffinity monolithic material: poly(GMA-co-EDMA) functionalized with an HPV-derived peptide using a thiol-maleimide reaction

Metabolites have great potential for the design of biomarkers, since their presence or absence provides valuable information about a biological system. In this context, polyclonal antibodies are important metabolites for diagnostic procedures, but in some pathologies, it has been found that these metabolites are present at low concentrations, so it could be difficult to detect them. In this investigation, an organic monolithic material of poly(GMA-co-EDMA) was functionalized with a peptide via Michael addition (thiol-maleimide) click chemistry. The peptide, covalently bound to the monolith, contains the SPINNTKPHEAR sequence derived from the human papilloma virus L1 protein. It was determined that the obtained monolithic support allows selectively isolating polyclonal antibodies against the SPINNTKPHEAR sequence, since they are retained on the chemical surface of the material by an immunoaffinity interaction. The monolithic material functionalization protocol reported here could be applied to incorporate any peptide with a terminal cysteine in order to recover a specific analyte. A new method was developed for isolating and pre-concentrating antibodies using monolithic materials, which could contribute to the improvement of disease detection strategies based on immunoaffinity interactions.

Utility of P16 expression and Ki-67 proliferation index in ASCUS and ASC-H pap tests

Current cervical screening uses a combination of cytology and high-risk human papillomavirus (HR-HPV) analysis in cases of atypical squamous cells of undetermined significance (ASCUS) and atypical squamous cells cannot exclude high-grade intraepithelial lesion (ASC-H). These diagnoses are subject to interobserver variability and HR-HPV analysis can be limited by sampling inadequacy. This study correlates immunoexpression of P16 and Ki-67 in residual cervicovaginal material against cytology category and HR-HPV status. Eighteen pap tests were selected: 8 ASCUS, 4 ASC-H, and 6 controls (2 LSIL and 4 HSIL). Digene Hybrid Capture II test was used to detect HR-HPV. The cytospins were stained for P16/Ki-67. Pap tests, P16, Ki-67, HR-HPV result and available biopsies were correlated. P16 expression correlated with HR-HPV status in 15/17 cases. Discordant cases (1 ASCUS and 1 ASC-H) were +P16/-HR-HPV. Ki-67 correlated with HR-HPV in 8/15 cases. Discordant cases were +HR-HPV/- Ki-67 (HSIL, LSIL, and ASC-H one each), and -HR-HPV/+Ki-67 (3 ASCUS, 1 LSIL, 1 ASC-H). Two cases were + P16/+ Ki-67/- HR-HPV. None were - P16/- Ki-67/+ HR-HPV. Histologic follow-up in 13 cases varied from benign to CIN III. Two cases of +P16/ - Ki-67/- HR-HPV had benign cervical biopcies. Although a small sample size, our findings show a utility for adjunct P16/ Ki-67 in addition to HR-HPV testing in cases of squamous atypia when HR-HPVs are non-detected due to low DNA copies, or missed lesions in cervical biopsies.