Universal Linkage System Research Articles

High Quality Genomic Copy Number Data from Archival Formalin-Fixed Paraffin-Embedded Leiomyosarcoma: Optimisation of Universal Linkage System Labelling

Most soft tissue sarcomas are characterized by genetic instability and frequent genomic copy number aberrations that are not subtype-specific. Oligonucleotide microarray-based Comparative Genomic Hybridisation (array CGH) is an important technique used to map genome-wide copy number aberrations, but the traditional requirement for high-quality DNA typically obtained from fresh tissue has limited its use in sarcomas. Although large archives of Formalin-fixed Paraffin-embedded (FFPE) tumour samples are available for research, the degradative effects of formalin on DNA from these tissues has made labelling and analysis by array CGH technically challenging. The Universal Linkage System (ULS) may be used for a one-step chemical labelling of such degraded DNA. We have optimised the ULS labelling protocol to perform aCGH on archived FFPE leiomyosarcoma tissues using the 180k Agilent platform. Preservation age of samples ranged from a few months to seventeen years and the DNA showed a wide range of degradation (when visualised on agarose gels). Consistently high DNA labelling efficiency and low microarray probe-to-probe variation (as measured by the derivative log ratio spread) was seen. Comparison of paired fresh and FFPE samples from identical tumours showed good correlation of CNAs detected. Furthermore, the ability to macro-dissect FFPE samples permitted the detection of CNAs that were masked in fresh tissue. Aberrations were visually confirmed using Fluorescence in situ Hybridisation. These results suggest that archival FFPE tissue, with its relative abundance and attendant clinical data may be used for effective mapping for genomic copy number aberrations in such rare tumours as leiomyosarcoma and potentially unravel clues to tumour origins, progression and ultimately, targeted treatment.

DNA Fragmentation Simulation Method (FSM) and Fragment Size Matching Improve aCGH Performance of FFPE Tissues

Whole-genome copy number analysis platforms, such as array comparative genomic hybridization (aCGH) and single nucleotide polymorphism (SNP) arrays, are transformative research discovery tools. In cancer, the identification of genomic aberrations with these approaches has generated important diagnostic and prognostic markers, and critical therapeutic targets. While robust for basic research studies, reliable whole-genome copy number analysis has been unsuccessful in routine clinical practice due to a number of technical limitations. Most important, aCGH results have been suboptimal because of the poor integrity of DNA derived from formalin-fixed paraffin-embedded (FFPE) tissues. Using self-hybridizations of a single DNA sample we observed that aCGH performance is significantly improved by accurate DNA size determination and the matching of test and reference DNA samples so that both possess similar fragment sizes. Based on this observation, we developed a novel DNA fragmentation simulation method (FSM) that allows customized tailoring of the fragment sizes of test and reference samples, thereby lowering array failure rates. To validate our methods, we combined FSM with Universal Linkage System (ULS) labeling to study a cohort of 200 tumor samples using Agilent 1 M feature arrays. Results from FFPE samples were equivalent to results from fresh samples and those available through the glioblastoma Cancer Genome Atlas (TCGA). This study demonstrates that rigorous control of DNA fragment size improves aCGH performance. This methodological advance will permit the routine analysis of FFPE tumor samples for clinical trials and in daily clinical practice.

Dendrimer‐Based Macromolecular Conjugate for the Kidney‐Directed Delivery of a Multitargeted Sunitinib Analogue

The development of a macromolecular conjugate of a multitargeted tyrosine kinase inhibitor is described that can be used for renal-specific delivery into proximal tubular cells. A novel sunitinib analogue, that is, 17864, is conjugated to a NH(2) -PAMAM-G3 dendrimer via the platinum (II)-based Universal Linkage System (ULS™). The activity of 17864 is retained after coordination to the ULS linker alone or when coupled to NH(2) -PAMAM-G3. 17864-UlS-NH(2) -PAMAM-G3 is non-toxic to proximal tubular cells in vitro. After intravenous administration to mice, 17864-UlS-NH(2) -PAMAM-G3 rapidly and efficiently accumulates in the kidneys. These results are encouraging for future studies focusing on the development of novel therapeutics for the treatment of renal diseases.

Abstract 1148: Array comparative genomic hybridization of diffuse intrinsic pontine glioma samples obtained from formalin fixed paraffin embedded autopsy specimens

Abstract We have recently optimized the method of formalin fixed paraffin embedded (FFPE) tissue processing for high resolution array comparative genomic hybridization (aCGH). This will facilitate the copy number assessment of number archival clinical surgical pathology specimens as well as biopsies with debated utility. Molecular characterization of archival specimens can potentially clarify the biology of diseases with unclear etiology and poor prognosis such as diffuse intrinsic pontine glioma (DIPG). In the case of DIPG, which is seldom biopsied, at present autopsy samples provide the only practical approach to studying this disorder. Here we performed aCGH on FFPE autopsy specimens obtained from children with DIPG. DNA was extracted from FFPE blocks obtained from autopsy on 14 pediatric DIPG patients using a modified Qiagen DNeasy kit. Non-enzymatic Universal Linkage System (ULS) chemical labeling was used to directly couple fluorescent dyes with the sample and reference DNAs (1ug each), which were then hybridized to 105k oligonucleotide CGH microarrays (Agilent). Arrays were scanned and data analyzed in Nexus Copy Number software. Twenty-one samples from 14 subjects were available for the study from which CGH was successfully performed on 18 samples representing 12 patients. All samples demonstrated DNA aberrations. Frequent DNA copy number changes included gain of 1q, 7p, and loss of 10q. High copy number amplification of known oncogenes was observed, including PDGFRA, EGFR, CCND1, and MYCN. Homozygous deletions of known tumor suppressor genes included PTEN and CDKN2A. Our tissue processing method demonstrates the feasibility of successfully using DNA derived from FFPE autopsy material for aCGH. The pediatric DIPG sample set was highly informative with the majority of specimens showing at least 1 abnormality related to a known cancer gene. Significant heterogeneity among DIPG patients as well as aberrations in candidate drug targets (KIT and EGFR) were observed. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1148.

Abstract B179: An improved method for array comparative genomic hybridization of formalin fixed paraffin embedded surgical pathology specimens

Abstract Array comparative genomic hybridization (aCGH) has been widely used on high quality DNA obtained from fresh tissue samples to investigate chromosomal abnormalities associated with different cancers. Formalin fixed paraffin embedded (FFPE) tissue samples are an ideal source for retrospective and prospective genomic profiling studies because they are abundant in the archives and are the most common derivative of clinical surgical pathology analyses. However, DNA degradation and cross linking due to tissue processing and storage conditions has limited their prior utility for molecular testing. Here, we report an improved and reliable method to isolate, purify, and label DNA from FFPE tissue samples for high resolution aCGH. Samples (n=67) were obtained from FFPE tissue blocks of >10yrs old and represented a variety of malignancies. Guided by hematoxylin and eosin stained sections, corresponding tissue block regions of maximal tumor cell density were targeted for extraction using a tissue microarray needle punch. Several changes to the Qiagen DNeasy kit, including buffers, temperatures, centrifugations, and elution conditions, were used to maximize DNA yield and produce a DNA derivative suitable for aCGH. Our method produced suitable DNA roughly 90% of the time, yet occasional impurities following Qiagen column purification persisted and manifested as a decreased 260/230 ratio, in which case we employed a simple additional column purification to render such samples usable. Non-enzymatic Universal Linkage System chemical labeling was used to directly couple fluorescent dyes with the sample and reference DNAs (1 ug each), which were then applied to an Agilent microarray. Data was analyzed in Nexus Copy Number software. Average DNA yield was 1 ug per 0.6mm needle core. Our optional clean up step typically raised the 260/230 ratio from 1.5 to above 2. The majorities of samples (87%) were successfully labeled and produced good quality aCGH profiles with a median DLR score of 0.25 and signal-to-noise ratio of 17. We were also able to set up a threshold of the amount of label incorporation that reliably predicted the success of the aCGH. This will guide us in the future to test only samples expected to pass QC measures and thus not waste costly microarray components. Our extraction and labeling method demonstrates the feasibility of successfully using DNA derived from FFPE tissue samples for aCGH, and brings this technique to the level of routine testing. Thus, our methodology removes many prior technical obstacles from aCGH based sample classification for diagnosis and clinical decision making using archival, current, and prospective FFPE specimens. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B179.

Intervention in growth factor activated signaling pathways by renally targeted kinase inhibitors

Cell-specific targeting to renal tubular cells is an interesting approach to enhance the accumulation of drugs in the kidney. Low molecular weight proteins are rapidly filtered and extensively accumulate in proximal tubular cells. We therefore have used lysozyme (LZM, 14 kDa) as a tubular cell-specific carrier for the delivery of kinase inhibitors. Two different kinase inhibitors (LY364947 and erlotinib, directed to either the TGF-β receptor kinase or the EGF receptor) were individually conjugated to LZM via a novel platinum-based linker (Universal Linkage System; ULS). The cellular handling and pharmacological efficacy of the conjugates were evaluated in cultured proximal tubular cells (HK-2 cells). Both conjugates were efficiently internalized via endocytosis. TGF-β or EGF activated HK-2 cells showed a strong activation of the studied kinases and the conjugates inhibited these events, as was demonstrated by Western blotting of phosphorylated downstream mediators and quantitative gene expression analysis. In conclusion, we have developed tubular cell-specific kinase inhibitor–LZM conjugates via a novel linker strategy, which both showed to be effective in vitro. Future in vivo studies should show their potential for the treatment of renal diseases.

Organ- and Cell-Type Specific Delivery of Kinase Inhibitors: A Novel Approach in the Development of Targeted Drugs

During the past years, we have explored the cellular delivery of kinase inhibitors. Kinase inhibitors have selectivity for specific kinases but they lack cellular selectivity. This is exemplified by recent reports on cardiotoxicity of kinase inhibitors used in cancer treatment. We postulate that targeted cellular delivery of kinase inhibitors can improve their safety/toxicity profiles, as will be exemplified by recent published studies. Cell specific delivery of therapeutics is a quickly growing area of investigation. This innovative strategy employs carrier molecules that bind to receptors exposed on the surface of cell types involved in disease processes. Binding and receptor mediated internalization of the carrier facilitates local accumulation of the product in target cells. Upon systemic administration, this may create local drug depots in specific organs, while other tissues are avoided, thus favoring enhanced localized drug efficacy and reduced side-effects. Synthesis of targeted kinase inhibitor-carrier conjugates was achieved using a new approach, in which kinase inhibitors were bound to a platinum(II) atom, the so-called Universal Linkage System (ULS). We review this novel linkage chemistry and demonstrate the applicability of ULS for drug targeting approaches aiming at angiogenic endothelial cells, hepatic stellate cells, and kidney tubular cells. We will review important issues like drug release mechanism, safety of the linker, and pharmacokinetics of the products in animals. Finally, we review the pharmacological efficacy of the cellular targeted drug conjugates in experimental animal models, especially in renal and liver fibrosis models.

Organ- and Cell-Type Specific Delivery of Kinase Inhibitors: A Novel Approach in the Development of Targeted Drugs

During the past years, we have explored the cellular delivery of kinase inhibitors. Kinase inhibitors have selectivity for specific kinases but they lack cellular selectivity. This is exemplified by recent reports on cardiotoxicity of kinase inhibitors used in cancer treatment. We postulate that targeted cellular delivery of kinase inhibitors can improve their safety/toxicity profiles, as will be exemplified by recent published studies. Cell specific delivery of therapeutics is a quickly growing area of investigation. This innovative strategy employs carrier molecules that bind to receptors exposed on the surface of cell types involved in disease processes. Binding and receptor mediated internalization of the carrier facilitates local accumulation of the product in target cells. Upon systemic administration, this may create local drug depots in specific organs, while other tissues are avoided, thus favoring enhanced localized drug efficacy and reduced sideeffects. Synthesis of targeted kinase inhibitor-carrier conjugates was achieved using a new approach, in which kinase inhibitors were bound to a platinum(II) atom, the so-called Universal Linkage System (ULS). We review this novel linkage chemistry and demonstrate the applicability of ULS for drug targeting approaches aiming at angiogenic endothelial cells, hepatic stellate cells, and kidney tubular cells. We will review important issues like drug release mechanism, safety of the linker, and pharmacokinetics of the products in animals. Finally, we review the pharmacological efficacy of the cellular targeted drug conjugates in experimental animal models, especially in renal and liver fibrosis models. Keywords: Signal transduction, kinase inhibitors, drug targeting, intracellular delivery, fibrosis, inflammation, angiogenesis

Antibody microarray‐based profiling of complex specimens: systematic evaluation of labeling strategies

Antibody microarrays have often had limited success in detection of low abundant proteins in complex specimens. Signal amplification systems improve this situation, but still are quite laborious and expensive. However, the issue of sensitivity is more likely a matter of kinetically appropriate microarray design as demonstrated previously. Hence, we re-examined in this study the suitability of simple and inexpensive detection approaches for highly sensitive antibody microarray analysis. N-hydroxysuccinimidyl ester (NHS)- and Universal Linkage System (ULS)-based fluorescein and biotin labels used as tags for subsequent detection with anti-fluorescein and extravidin, respectively, as well as fluorescent dyes were applied for analysis of blood plasma. Parameters modifying strongly the performance of microarray detection such as labeling conditions, incubation time, concentrations of anti-fluorescein and extravidin and extent of protein labeling were analyzed and optimized in this study. Indirect detection strategies whether based on NHS- or ULS-chemistries strongly outperformed direct fluorescent labeling and enabled detection of low abundant cytokines with many dozen-fold signal-to-noise ratios. Finally, particularly sensitive detection chemistry was applied to monitoring cytokine production of stimulated peripheral T cells. Microarray data were in accord with quantitative cytokine levels measured by ELISA and Luminex, demonstrating comparable reliability and femtomolar range sensitivity of the established microarray approach.

Local Inhibition of Liver Fibrosis by Specific Delivery of a Platelet-Derived Growth Factor Kinase Inhibitor to Hepatic Stellate Cells

Liver fibrosis is characterized by excessive proliferation and activation of hepatic stellate cells (HSC), a process in which platelet-derived growth factor (PDGF) plays an important role. Inhibition of liver fibrosis via specific delivery of a PDGF kinase inhibitor to HSC might therefore be an attractive strategy. The HSC-selective carrier mannose-6-phosphate modified human serum albumin (M6PHSA) was equipped with a tyrosine kinase inhibitor, 4-chloro-N-[4-methyl-3-(4-pyridin-3-yl-pyrimidin-2-ylamino)-phenyl]-benzamide (PAP19) (an imatinib derivative), by means of the platinum-based universal linkage system (ULS). The antifibrotic activity of PAP19-M6PHSA was evaluated in culture-activated rat HSC and precision-cut liver slices from fibrotic rats. After 24-h incubation, both free inhibitor PAP19 and PAP19-M6PHSA showed potent activity, as determined by quantitative reverse transcription-polymerase chain reaction analysis of alpha-smooth muscle actin (alphaSMA) and procollagen 1a1. Next, we examined the organ distribution and antifibrotic activity of PAP19-M6PHSA in bile duct-ligated (BDL) rats. Male Wistar rats at day 10 after BDL were administered a single dose of PAP19-M6PHSA and sacrificed at 2 h, 1 day, or 2 days afterward. The accumulation of PAP19-M6PHSA in the liver was quantified by high-performance liquid chromatography analysis (30% of the injected dose at 2 h) and detected in the liver by staining of the carrier. Liver drug levels were sustained at 24 and 48 h after the single dose. Furthermore, PAP19-M6PHSA reduced collagen deposition (Sirius red staining) and alphaSMA staining of activated HSC at these time points in comparison with saline-treated rats. We therefore conclude that delivery of a PDGF-kinase inhibitor to HSC is a promising technology to attenuate liver fibrogenesis.

Rational Design of RGD–Albumin Conjugates for Targeted Delivery of the VEGF‐R Kinase Inhibitor PTK787 to Angiogenic Endothelium

Linking the unlinkable: Many new chemical entities lack reactive groups for use in the formation of reversible bonds, for example, to conjugate them for targeted drug delivery purposes. We succeeded with the noncovalent coupling of a potent signal transduction inhibitor to a protein backbone by applying the platinum-based universal linkage system. The resulting drug-targeting conjugates offer new potential for cancer treatment with minimal side effects.

Intracellular Delivery of the p38 Mitogen-Activated Protein Kinase Inhibitor SB202190 [4-(4-Fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole] in Renal Tubular Cells: A Novel Strategy to Treat Renal Fibrosis

During renal injury, activation of p38 mitogen-activated protein kinase (MAPK) in proximal tubular cells plays an important role in the inflammatory events that eventually lead to renal fibrosis. We hypothesized that local inhibition of p38 within these cells may be an interesting approach for the treatment of renal fibrosis. To effectuate this, we developed a renal-specific conjugate of the p38 inhibitor SB202190 [4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole] and the carrier lysozyme. First, we demonstrated that SB202190 inhibited the expression of albumin-induced proinflammatory (monocyte chemoattractant protein-1) and transforming growth factor (TGF)-beta1-induced profibrotic (procollagen-Ialpha1) genes over 50% in renal tubular cells (normal rat kidney-52E). Next, we conjugated SB202190 via a carbamate linkage to lysozyme. However, this conjugate rapidly released the drug upon incubation in serum. Therefore, we applied a new platinum(II)-based linker approach, the so-called universal linkage system (ULS), which forms a coordinative bond with SB202190. The SB202190-ULS-lysozyme remained stable in serum but released the drug in kidney homogenates. SB202190-ULS-lysozyme accumulated efficiently in renal tubular cells and provided a local drug reservoir during a period of 3 days after a single intravenous injection. Treatment with SB202190-ULS-lysozyme inhibited TGF-beta1-induced gene expression for procollagen-Ialpha1 by 64% in HK-2 cells. Lastly, we evaluated the efficacy of a single dose of the conjugate in the unilateral renal ischemia-reperfusion rat model. A reduction of intrarenal p38 phosphorylation and alpha-smooth muscle actin protein expression was observed 4 days after the ischemia-reperfusion injury. In conclusion, we have developed a novel strategy for local delivery of the p38 MAPK inhibitor SB202190, which may be of use in the treatment of renal fibrosis.

Novel Role of Toll-Like Receptor 3 in Hepatitis C-Associated Glomerulonephritis

Hepatitis C virus (HCV) infection is frequently complicated by glomerulonephritis with immune complexes containing viral RNA. We examined the potential influence of Toll-like receptors (TLRs), specifically TLR3 recognition of viral dsRNA exemplified by polyriboinosinic:polyribocytidylic acid [poly(I:C) RNA]. Normal human kidney stained positive for TLR3 on mesangial cells (MCs), vascular smooth muscle cells, and collecting duct epithelium. Cultured MCs have low TLR3 mRNA levels with predominant intracellular protein localization, which was increased by tumor necrosis factor-alpha, interleukin (IL)-1beta, interferon (IFN)-gamma, and the TLR3 ligand poly(I:C) RNA. Poly(I:C) RNA stimulation of MCs increased mRNA and protein synthesis of IL-6, IL-1beta, M-CSF, IL-8/CXCL8, RANTES/CCL5, MCP-1/CCL2, and ICAM-I; it also increased anti-proliferative and proapoptotic effects, the latter of which was decreased by inhibiting caspase-8. In microdissected glomeruli of normal and non-HCV membranoproliferative glomerulonephritis biopsies, TLR3 mRNA expression was low. In contrast TLR3 mRNA expression was significantly increased in hepatitis C-positive glomerulonephritis and was associated with enhanced mRNA for RANTES/CCL5 and MCP-1/CCL2. We hypothesize that immune complexes containing viral RNA activate mesangial TLR3 during HCV infection, thereby contributing to chemokine/cytokine release and effecting proliferation and apoptosis. Thus, TLR3 expression on renal cells, and especially MCs, may establish a link between viral infections and glomerular diseases.

Genosensor Based on a Platinum(II) Complex as Electrocatalytic Label

Voltammetric genosensors on streptavidin-modified screen-printed carbon electrodes (SPCEs) for the detection of virulence nucleic acid determinants of pneumolysin (ply) and autolysin (lytA) genes, exclusively present on the genome of the human pathogen Streptococcus pneumoniae, were described. The oligonucleotide probes were immobilized on electrochemically pretreated SPCEs through the streptavidin/biotin reaction. After that, the hybridization reaction was carried out with labeled complementary targets on the electrode surface. The ply and lytA targets were labeled using the universal linkage system, which consists of the use of a platinum(II) complex that acts as coupling agent between targets and a, usually fluorescent, molecule label. In this case, the platinum(II) complex acts as a label itself because the analytical signal is achieved by measuring chronoamperometrically the current generated by the hydrogen evolution catalyzed by platinum. In nonstringent experimental conditions, these genosensors can detect 24.5 fmol of 20-mer oligonucleotide target and discriminate between a complementary oligo and an oligo with a three-base mismatch. In presence of 25% formamide in the hybridization buffer, a single-base mismatch on the oligonucleotide target can be detected.

Use of Horseradish Peroxidase- and Fluorescein-modified Cisplatin Derivatives for Simultaneous Labeling of Nucleic Acids and Proteins

Microarray platforms will change immunochemical and nucleic acid-based analysis of cell homogenates and body fluids compared with classic analyses. Microarrays use labeled target and immobilized probes, rather than fixed targets and labeled probes. We describe a method for simultaneous labeling of nucleic acids and proteins. Horseradish peroxidase- and fluorescein-modified cisplatin derivatives were used for labeling of nucleic acids and proteins. These reagents, called the Universal Linkage System (ULS), bind to sulfur- and nitrogen-donor ligands present in amino acids and nucleotides. For automated screening of proteins and nucleic acids on microarrays, it is advantageous to label these biomolecules without pre- or postpurification procedures. The labeling of antibodies and nucleic acids in whole serum was therefore pursued. Immunoglobulins in nonpurified serum were labeled efficiently enough to be used for immunochemistry. To investigate whether protein-adapted labeling allowed nucleic acid labeling as well, 1 microg of plasmid DNA was added to 1 microL of serum. DNA and serum proteins were simultaneously labeled, and this labeled DNA could be used as a probe for direct fluorescence in situ hybridization. ULS provides a direct labeling tool for the (simultaneous) modification of proteins and nucleic acids even in unpurified samples.

New strategy for multi-colour fluorescence in situ hybridisation: COBRA: COmbined Binary RAtio labelling.

Multicolour in situ hybridisation (MFISH) is increasingly applied to karyotyping and detection of chromosomal abnormalities. So far 27 colour analyses have been described using fluorescently labelled chromosome painting probes in a so-called combinatorial approach. In this paper a new strategy is presented to use efficiently the currently available number of spectrally separated fluorophores in order to increase the multiplicity of MFISH. We introduce the principle of COBRA (COmbined Binary RAtio labelling), which is based on the simultaneous use of combinatorial labelling and ratio labelling. Human chromosome painting in 24 colours is accomplished using four fluorophores only. Three fluorophores are used pair wise for ratio labelling of a set of 12 chromosome painting probes. The second set of 12 probes is labelled identically but is also given a binary label (fourth fluorophore). The COBRA method is demonstrated on normal human chromosomes and on a lymphoma (JVM) cell line, using probes enzymatically labelled with fluorescein, lissamine and cy5 as primary fluorophores, and diethylaminocoumarin (DEAC), a blue dye, as combinatorial fourth label to demonstrate incorporated digoxigenin. In addition, the principle was tested using chemical labelling. The first set of 12 painting probes was therefore labelled by ULS (Universal Linkage System), using DEAC, cy3 and cy5 as primary labels, and the second set was labelled similarly, but also contained a digoxigenin-ULS label, which was indirectly stained with fluorescein. Subsequently, a mathematical analysis is presented and methods are indicated for achieving an MFISH multiplicity of 48, 96 or even higher using existing technology.

Application of a new, universal DNA labeling system in the PCR mediated diagnoses of Chlamydia trachomatis and human papillomavirus type 16 infection in cervical smears

Non-isotopic DNA labeling procedures are essential for integration of DNA diagnostics into the clinical laboratory. A newly developed reagent was tested for use in reversed hybridisation identification of DNA fragments generated by polymerase chain reaction (PCR) amplification of Chlamydia trachomatis or human papilloma virus type 16 (HPV16) DNA isolated from cervical smears. The platinum-containing chemical compound, equipped with a biotin hapten, enables versatile ‘one tube’ labeling of amplified DNA. A HPV16-specific probe was immobilised on a nylon strip and reverse hybridisation with the biotin labeled DNA took place. To determine the value of this new, nonisotopic label in combination with clinical material, 98 cervical smears 54 of which contained HPV16, and 51 cervical smears 26 of which contained C. trachomatis, were analysed. The novel type of non-radioactive analysis appeared to be as sensitive as its isotopic counterpart. The DNA isolation and purification method require modification only in samples of poor quality. The labeling procedure is simple, versatile and can be included as a universal linkage system in any PCR test for the detection and identification of DNA molecules.