Martin Hufbauer

Auger-electron-emitting radionuclides offer a distinctive route toward molecular-scale radiotherapy because their biological effects depend primarily on the nanoscale location of the decay event rather than on long-range tissue penetration. This review examines Auger-emitting radionuclides from a radiopharmaceutical perspective, integrating decay-associated physicochemical processes, cellular dosimetry, subcellular targeting, and translational relevance. We first discuss the physical determinants of Auger radiotoxicity, including Auger and Coster–Kronig electrons, internal-conversion electrons, local ionization density, and possible molecular consequences of highly localized Auger cascades. Cellular S values are used to illustrate how the same radionuclide can produce markedly different absorbed doses depending on whether activity is localized in the nucleus, cytoplasm, cell membrane, or neighboring cells. Iodine-125 incorporated into DNA as [¹²⁵I]iododeoxyuridine ([¹²⁵I]IUdR) remains the classical reference model for maximal Auger-mediated radiotoxicity. However, this direct DNA-incorporation model should not be generalized to receptor-targeted radiopharmaceuticals, which usually achieve indirect nuclear, chromatin-associated, perinuclear, membrane-associated, or vesicular localization rather than incorporation into DNA. These alternative source–target geometries may also produce biologically relevant effects, but they are mechanistically distinct from DNA-proximal [¹²⁵I]IUdR decay. Particular attention is given to iodine-123 versus iodine-125, the influence of physical half-life and specific activity, the interpretation of terbium-161 as a hybrid β⁻/internal-conversion/Auger emitter, and the overlooked radiobiological relevance of diagnostic Auger emitters such as technetium-99m, indium-111, and gallium-67. We conclude that Auger-emitter radiopharmaceuticals cannot be ranked by electron yield or decay scheme alone. Their therapeutic or toxicological relevance emerges from the integration of decay-associated physicochemical processes, cellular source–target dosimetry, intracellular trafficking, retention, and the temporal realization of dose delivery.

Despite epidermal turnover, the skin is host to a complex array of microbes, including viruses, such as HPV, which must infect and manipulate skin keratinocyte stem cells (KSCs) to survive. This crosstalk between the virome and KSC populations remains largely unknown. Here, we investigated the effect of HPV8 on KSCs using various mouse models. We observed that the HPV8 early region gene E6 specifically caused Lrig1 ⁺ hair follicle junctional zone KSC proliferation and expansion, which would facilitate viral transmission. Within Lrig1 ⁺ KSCs specifically, HPV8 E6 bound intracellular p300 to phosphorylate the STAT3 transcriptional regulatory node. This induced ΔNp63 expression, resulting in KSC expansion into the overlying epidermis. HPV8 was associated with 70% of human actinic keratoses. Together, these results define the “hit-and-run” mechanism for HPV8 in human actinic keratosis as an expansion of KSCs, which lack melanosome protection and are thus susceptible to sun light–induced malignant transformation.

The structured expression of several keratins in the skin is associated with differentiation status of the epidermal layers, whereas others are upregulated only during wound healing, in skin disorders and in cancers. One of these stress keratins, K17, is correlated with poor prognosis in various cancer types and its loss has been shown to decelerate tumour growth. K17 expression can also be detected in cutaneous squamous cell carcinomas (SCCs), where UV-irradiation and infection with cutaneous human papillomaviruses (HPVs) are important co-factors. It was previously reported that K17 is upregulated in papillomavirus (PV)-induced benign skin lesions in mice and induces an immunological status that is beneficial for tumour growth. In order to investigate whether K17 upregulation is induced by PVs, we analysed K17 levels in skin tumour specimens of different animal models and humans. Various immunofluorescence stainings were performed to identify K17 expression as well as levels of E-Cadherin, vimentin and CD271. Tissues were further analysed by PCRs, qPCRs and ELISA to control for PV activity. K17knockdown cells were generated and effects on viral life cycle were investigated by infection assays, qPCR and Western blotting. We could show that K17 is commonly expressed in skin tumours and that its presence is not directly linked to viral oncoprotein expression. Rather, K17 expression seems to be a marker of epithelial differentiation and its absence in tumour tissue is associated with an epithelial-to-mesenchymal transition. We further showed that the absence of K17 in skin tumours increases markers of cancer stem-like cells and negatively affects viral protein synthesis. Collectively, our data indicate that K17 expression is a common feature in skin tumourigenesis. While it is not primarily targeted by PV oncoproteins, our in vivo and in vitro data suggest that it is an important regulator of epithelial differentiation and thus may play a role in controlling viral protein synthesis.

Viruses have evolved complex and dynamic interactions with their host cells to enable viral replication. In recent years, insights have been gained into the increasingly important role of the host cell lipidome in the life cycle of several viruses. In particular, viruses target phospholipid signaling, synthesis, and metabolism to remodel their host cells into an optimal environment for their replication cycle. Conversely, phospholipids and their associated regulatory enzymes can interfere with viral infection or replication. This review highlights examples of different viruses that illustrate the importance of these diverse virus–phospholipid interactions in different cellular compartments, particularly the role of nuclear phospholipids and their association with human papillomavirus (HPV)‐mediated cancer development.

Persistent infections of the skin with the human papillomavirus of genus beta (β-HPV) in immunocompetent individuals are asymptomatic, but in immunosuppressed patients, β-HPV infections exhibit much higher viral loads on the skin and are associated with an increased risk of skin cancer. Unlike with HPV16, a high-risk α-HPV, the impact of β-HPV early genes on the innate immune sensing of viral nucleic acids has not been studied. Here, we used primary skin keratinocytes and U2OS cells expressing HPV8 or distinct HPV8 early genes and well-defined ligands of the nucleic-acid-sensing receptors RIG-I, MDA5, TLR3, and STING to analyze a potential functional interaction. We found that primary skin keratinocytes and U2OS cells expressed RIG-I, MDA5, TLR3, and STING, but not TLR7, TLR8, or TLR9. While HPV16-E6 downregulated the expression of RIG-I, MDA5, TLR3, and STING and, in conjunction with HPV16-E7, effectively suppressed type I IFN in response to MDA5 activation, the presence of HPV8 early genes showed little effect on the expression of these immune receptors, except for HPV8-E2, which was associated with an elevated expression of TLR3. Nevertheless, whole HPV8 genome expression, as well as the selective expression of HPV8-E1 or HPV8-E2, was found to suppress MDA5-induced type I IFN and the proinflammatory cytokine IL-6. Furthermore, RNA isolated from HPV8-E2 expressing primary human keratinocytes, but not control cells, stimulated a type I IFN response in peripheral blood mononuclear cells, indicating that the expression of HPV8-E2 in keratinocytes leads to the formation of stimulatory RNA ligands that require the active suppression of immune recognition. These results identify HPV8-E1 and HPV8-E2 as viral proteins that are responsible for the immune escape of β-HPV from the innate recognition of viral nucleic acids, a mechanism that may be necessary for establishing persistent β-HPV infections.

K14-HPV8-CER transgenic mice express the complete early genome region of human papillomavirus type 8 (HPV8) and develop skin tumours attributed to the expansion of the Lrig1+ stem cell population. The correlation between HPV8-induced changes in transcriptional output in the stem cell compartment remains poorly understood. To further understand the oncogenic pathways underlying skin tumour formation we examined the gene expression network in skin tumours of K14-HPV8-CER mice and compared the differentially expressed genes (DEG) with those of the Lrig1-EGFP-ires-CreERT2 mice. Here, we report 397 DEGs in skin tumours of K14-HPV8-CER mice, of which 181 genes were up- and 216 were down-regulated. Gene ontology and KEGG pathway enrichment analyses suggest that the 397 DEGs are acting in signalling pathways known to be involved in skin homeostasis. Interestingly, we found that HPV8 early gene expression subverts the expression pattern of 23 cellular genes known to be expressed in Lrig1+ keratinocytes. Furthermore, we identified putative upstream regulating transcription factors as well as miRNAs in the control of these genes. These data provide strong evidence that HPV8 mediated transcriptional changes may contribute to skin tumorigenesis, offering new insights into the mechanism of HPV8 driven oncogenesis.

Introduction: The aim of this study was to identify early changes in the Wnt/beta-catenin signaling pathway in high-risk human papillomavirus (HPV) infected cervicovaginal cells and to correlate these changes with cell proliferation, apoptosis, and autophagic processes. Methods: We evaluated 91 cervicovaginal smears of women with (n = 41) and without (n = 50) HPV-DNA. Smears were stained against beta-catenin, c-myc, secreted frizzled-related protein 4 (sFRP4), cleaved caspase-3, and the autophagy markers Beclin-1 and light chain 3B. In addition, sFRP-1, -2, -3, -4, -5 mRNA levels were determined by quantitative reverse transcription-PCR in primary keratinocytes and FaDu cells expressing HPV16-E6, -E7, or -E6E7. Results: Our data indicated that the Wnt/beta-catenin signaling is activated in HPV (+) cervicovaginal cells that can already be detected in cells with no obvious changes in cellular morphology (HPV [+]/cyto [−]). These cells also had significantly higher sFRP4 levels when compared to HPV-negative samples. In primary keratinocytes, sFRP4 was found to be absent and sFRP1 and sFRP2 to be repressed in the presence of HPV16-E6 and E7. Interestingly, sFRP4 is expressed in FaDu cells and can be upregulated in the presence of E6E7. Curiously, SFRP4 expression correlated with an increase in the level of autophagic markers in HPV (+)/cyto (−) smears. Conclusion: In conclusion, the activation of the Wnt/beta-catenin signaling pathway and upregulation of sFRP4, paralleled by an activation of the autophagic pathway may represent predisposing cellular factors early after HPV infection which need to be further determined in larger study.

Human papillomaviruses (HPV) are non-enveloped DNA viruses infecting cutaneous and mucosal squamous epithelia. Sexually transmitted HPV-types that are carcinogenic to humans such as HPV16 can induce cervical and other anogenital cancers. Virus transmission through fomites such as inadequately disinfected gynecological equipment is a further potential transmission route. Since HPV cannot be easily grown in cell culture, polyomavirus SV40 has been used as a surrogate virus when testing the virucidal activity of chemical disinfectants. So far, studies that have compared the virucidal activity of different disinfectants against HPV and SV40 are lacking. Here, we evaluated the susceptibility of HPV16 pseudovirus and SV40 to seven active biocidal substances using quantitative suspension tests. Ethanol, glutaraldehyde (GTA), dodecyldipropylentriamin (DPTA), and ortho-phthalaldehydes (OPA) were able to reduce the infectivity of HPV16 pseudovirus >99.99% after 5 min. In contrast, isopropanol, peracetic acid (PAA), and quaternary ammonium compounds with alkylamines (QAC) only led to a slight or no reduction in infectivity. Concerning SV40, only GTA (60 min contact time), PAA, and OPA had virus-inactivating effects. In conclusion, the virucidal activity of three out of seven disinfectants tested was different for HPV16 pseudovirus and SV40. In this study, SV40 was shown to be a reliable surrogate virus for HPV when testing isopropanol-, GTA-, QAC-, and OPA-based disinfectants.

VEGF signaling regulated by the vascular endothelial growth factor receptor 2 (VEGFR2) plays a decisive role in tumor angiogenesis, initiation and progression in several tumors including HNSCC. However, the impact of HPV-status on the expression of VEGFR2 in OPSCC has not yet been investigated, although HPV oncoproteins E6 and E7 induce VEGF-expression. In a series of 56 OPSCC with known HPV-status, VEGFR2 expression patterns were analyzed both in blood vessels from tumor-free and tumor-containing regions and within tumor cells by immunohistochemistry using densitometry. Differences in subcellular colocalization of VEGFR2 with endothelial, tumor and stem cell markers were determined by double-immunofluorescence imaging. Immunohistochemical results were correlated with clinicopathological data. HPV-infection induces significant downregulation of VEGFR2 in cancer cells compared to HPV-negative tumor cells (p = 0.012). However, with respect to blood vessel supply, the intensity of VEGFR2 staining differed only in HPV-positive OPSCC and was upregulated in the blood vessels of tumor-containing regions (p < 0.0001). These results may suggest different routes of VEGFR2 signaling depending on the HPV-status of the OPSCC. While in HPV-positive OPSCC, VEGFR2 might be associated with increased angiogenesis, in HPV-negative tumors, an autocrine loop might regulate tumor cell survival and invasion.