PO-022 FISH probes for the detection of high-risk HPV nucleic acid in infected host cells

Introduction Infections by oncoviruses are an important risk factor for the development of neoplasms. Particularly, anogenital cancers are strongly associated with persistent infections by high-risk human papillomaviruses (HPV). In the case of cervical cancer the physical state of the virus seems to be an important prognostic marker. Especially the integration of viral DNA into the host cell genome bears the risk of following degenerations. Therefore, the early and sensitive detection is of high interest. Besides Pap-test and PCR, fluorescence in situ hybridization (FISH) is used for a quantitative and qualitative detection of HPV infections and risk assessment. Material and methods For analysis high-risk HPV FISH probes should be developed for standardised, type-specific and quantitative detection of HPV nucleic acid in host cells. Due to the short viral DNA sequence, present with just few copies, conventional FISH probes have little sensitivity. Therefore, we tested specific FISH probes targeting different regions of the HPV genome in combination with signal amplification. PCR-produced FISH probes were biotin labelled by direct incorporation of biotinylated nucleotides or nick translation. Our biotinylated HPV probes were tested on HPV-positive and –negative cells and detected using fluorescence labelled streptavidin or subsequent tyramide signal amplification. In addition to FISH, probes were used for chromogenic in situ hybridization. All analysis were performed with our fully automatized multicolor fluorescence imaging platform VideoScan. Results and discussions The presence of HPV DNA in cell lines was confirmed by (digital) PCR. The protocol for synthesis of biotinylated probes using HPV sequence specific primers and genomic DNA as template was successful. Biotin incorporation was checked with agarose gel electrophoresis and modified dot blot hybridization. In in situ hybridization experiments, our probes showed high signals in HPV high-copy number CaSki cells and a tissue model, compared to HPV negative samples. Conclusion Highly sensitive and specific FISH probes offer a great potential for the detection of HPV DNA in patient samples and thereby for the assessment of tumour risks. Using our probes, we got positive results in hybridization experiments using chromogenic and fluorescent detection methods with or without further amplification steps. Next, comparative FISH experiments will be performed to check probe sensitivity in cells containing few HPV copies and their practicability in biopsy derived tissue samples.