Morphological Clues of Acute Monocytic Leukemia in COVID-19-Induced Transient Leukoerythroblastic Reaction with Monocytosis.

Viral infections, including those caused by COVID-19, can produce striking morphologic changes in peripheral blood. Distinguishing between reactive changes and abnormal morphology of monocytes remains particularly difficult, with low consensus rates reported amongst hematopathologists. Here, we report a patient who developed transient monocytosis of 11.06 × 109/L with 32% promonocytes and 1% blasts during hospitalization that was secondary to severe COVID-19 infection. Three days later, the clinical status of the patient improved and the WBC had decreased to 8.47 × 109/L with 2.2 × 109/L monocytes. Flow cytometry studies did not reveal immunophenotypic findings specific for an overt malignant population. At no time during admission did the patient develop cytopenia(s), and she was discharged upon clinical improvement. However, the peripheral blood sample containing promonocytes was sent for molecular testing with an extended next-generation sequencing myeloid panel and was positive for pathogenic NPM1 Type A and DNMT3A R882H mutations. Subsequently, despite an essentially normal complete blood count, the patient underwent a bone marrow assessment that showed acute myeloid leukemia with 77% promonocytes. This case emphasizes the critical importance of a full work up to exclude acute leukemia when classical promonocyte morphology is encountered in the peripheral blood. Promonocytes are not a part of the reactive changes associated with COVID-19 and remain specific to myeloid neoplasia.

Consensus Recommendations to Optimize the Detection and Reporting of NTRK Gene Fusions by RNA-Based Next-Generation Sequencing.

The detection of gene fusions by RNA-based next-generation sequencing (NGS) is an emerging method in clinical genetic laboratories for oncology biomarker testing to direct targeted therapy selections. A recent Canadian study (CANTRK study) comparing the detection of NTRK gene fusions on different NGS assays to determine subjects' eligibility for tyrosine kinase TRK inhibitor therapy identified the need for recommendations for best practices for laboratory testing to optimize RNA-based NGS gene fusion detection. To develop consensus recommendations, representatives from 17 Canadian genetic laboratories participated in working group discussions and the completion of survey questions about RNA-based NGS. Consensus recommendations are presented for pre-analytic, analytic and reporting aspects of gene fusion detection by RNA-based NGS.

CANTRK: A Canadian Ring Study to Optimize Detection of NTRK Gene Fusions by Next-Generation RNA Sequencing.

The Canadian NTRK (CANTRK) study is an interlaboratory comparison ring study to optimize testing for neurotrophic receptor tyrosine kinase (NTRK) fusions in Canadian laboratories. Sixteen diagnostic laboratories used next-generation sequencing (NGS) for NTRK1, NTRK2, or NTRK3 fusions. Each laboratory received 12 formalin-fixed, paraffin-embedded tumor samples with unique NTRK fusions and two control non-NTRK fusion samples (one ALK and one ROS1). Laboratories used validated protocols for NGS fusion detection. Panels included Oncomine Comprehensive Assay v3, Oncomine Focus Assay, Oncomine Precision Assay, AmpliSeq for Illumina Focus, TruSight RNA Pan-Cancer Panel, FusionPlex Lung, and QIAseq Multimodal Lung. One sample was withdrawn from analysis because of sample quality issues. Of the remaining 13 samples, 6 of 11 NTRK fusions and both control fusions were detected by all laboratories. Two fusions, WNK2::NTRK2 and STRN3::NTRK2, were not detected by 10 laboratories using the Oncomine Comprehensive or Focus panels, due to absence of WNK2 and STRN3 in panel designs. Two fusions, TPM3::NTRK1 and LMNA::NTRK1, were challenging to detect on the AmpliSeq for Illumina Focus panel because of bioinformatics issues. One ETV6::NTRK3 fusion at low levels was not detected by two laboratories using the TruSight Pan-Cancer Panel. Panels detecting all fusions included FusionPlex Lung, Oncomine Precision, and QIAseq Multimodal Lung. The CANTRK study showed competency in detection of NTRK fusions by NGS across different panels in 16 Canadian laboratories and identified key test issues as targets for improvements.

DDX41 is required for cGAS-STING activation against DNA virus infection.

Upon binding double-stranded DNA (dsDNA), cyclic GMP-AMP synthase (cGAS) is activated and initiates the cGAS-stimulator of IFN genes (STING)-type I interferon pathway. DEAD-box helicase 41 (DDX41) is a DEAD-box helicase, and mutations in DDX41 cause myelodysplastic syndromes (MDSs) and acute myeloid leukemia (AML). Here, we show that DDX41-knockout (KO) cells have reduced type I interferon production after DNA virus infection. Unexpectedly, activations of cGAS and STING are affected in DDX41 KO cells, suggesting that DDX41 functions upstream of cGAS. The recombinant DDX41 protein exhibits ATP-dependent DNA-unwinding activity and ATP-independent strand-annealing activity. The MDS/AML-derived mutant R525H has reduced unwinding activity but retains normal strand-annealing activity and stimulates greater cGAS dinucleotide-synthesis activity than wild-type DDX41. Overexpression of R525H in either DDX41-deficient or -proficient cells results in higher type I interferon production. Our results have led to the hypothesis that DDX41 utilizes its unwinding and annealing activities to regulate the homeostasis of dsDNA and single-stranded DNA (ssDNA), which, in turn, regulates cGAS-STING activation.

CAP-ACP Workload Model for Advanced Diagnostics in Precision Medicine.

OBJECTIVES: In precision medicine, where oncologic management is tailored to the individual's clinical and genetic profiles, advanced diagnostic testing provides prognostic information and guides management in a growing number of malignancies. There is a need to capture the work pathologists perform to meet this demand by providing medically relevant, timely, and accurate testing results. This work includes not only direct patient consults (interpretation of results and issuing reports) but the administrative and medical oversight as well as the research needed to provide the necessary quality assurance, quality control, direction, and framework for the laboratory. METHODS: An expert panel of Canadian pathologists involved in advanced diagnostics was convened to establish and beta test a model for workload assessment in advanced diagnostics. RESULTS: All aspects of the advanced diagnostics workload were detailed and applied to models based on members' experience, including medical oversight, administration, and the introduction of new testing and platforms. Models for biomarker testing were developed for simple and complex or multiplexed assays, and a detailed model was developed to assess the workload for next-generation sequencing-based assays. CONCLUSIONS: This paper provides the first detailed proposal for capturing an advanced diagnostic workload to enable appropriate pathologist allotment for performing all the steps required to run an advanced diagnostic service.

Imaging Immune Cells Using Fc Domain Probes in Mouse Cancer Xenograft Models.

Tracking immune responses is complex due to the mixture of cell types, variability in cell populations, and the dynamic environment. Tissue biopsies and blood analysis can identify infiltrating and circulating immune cells; however, due to the dynamic nature of the immune response, these are prone to sampling errors. Non-invasive targeted molecular imaging provides a method to monitor immune response, which has advantages of providing whole-body images, being non-invasive, and allowing longitudinal monitoring. Three non-specific Fc-containing proteins were labeled with near-infrared dye IRDye800CW and used as imaging probes to assess tumor-infiltrating immune cells in FaDu and A-431 xenograft models. We showed that Fc domains localize to tumors and are visible by fluorescent imaging. This tumor localization appears to be based on binding tumor-associated immune cells and some xenografts showed higher fluorescent signals than others. The Fc domain alone bound to different human immune cell types. The Fc domain can be a valuable research tool to study innate immune response.

Pre-clinical study of IRDye800CW-nimotuzumab formulation, stability, pharmacokinetics, and safety.

BACKGROUND: Epidermal growth factor receptor (EGFR) is a target for cancer therapy as it is overexpressed in a wide variety of cancers. Therapeutic antibodies that bind EGFR are being evaluated in clinical trials as imaging agents for positron emission tomography and image-guided surgery. However, some of these antibodies have safety concerns such as infusion reactions, limiting their use in imaging applications. Nimotuzumab is a therapeutic monoclonal antibody that is specific for EGFR and has been used as a therapy in a number of countries. METHODS: Formulation of IRDye800CW-nimotuzumab for a clinical trial application was prepared. The physical, chemical, and pharmaceutical properties were tested to develop the specifications to determine stability of the product. The acute and delayed toxicities were tested and IRDye800CW-nimotuzumab was determined to be non-toxic. Non-compartmental pharmacokinetics analysis was used to determine the half-life of IRDye800CW-nimotuzumab. RESULTS: IRDye800CW-nimotuzumab was determined to be non-toxic from the acute and delayed toxicity study. The half-life of IRDye800CW-nimotuzumab was determined to be 38 ± 1.5 h. A bi-exponential analysis was also used which gave a t1/2 alpha of 1.5 h and t1/2 beta of 40.8 h. CONCLUSIONS: Here, we show preclinical studies demonstrating that nimotuzumab conjugated to IRDye800CW is safe and does not exhibit toxicities commonly associated with EGFR targeting antibodies.

Diagnostic Variation in p53 Usage for Endometrial Carcinoma Diagnosis: Implications for Molecular Subtyping.

Immunostaining for p53 is widely but variably used when diagnosing endometrial carcinoma (EC). Mutant-pattern p53 staining can support a diagnosis of serous carcinoma, and also serve as a surrogate test for identifying the "serous-like" subset of aggressive EC identified by The Cancer Genome Atlas characterized by high numbers of somatic copy number abnormalities. We, retrospectively, assessed WHO histotype, usage of p53 immunostaining, and p53 status in a consecutive series of biopsies showing EC from a single hospital. Of 79 ECs, 59 (75%) were low-grade EC (LGEC), 13 (16%) high-grade EC (HGEC), and 7 (9%) were serous. p53 immunostaining was performed at the time of diagnosis in 27/79 (34%) biopsies; 6/7 of serous histotype, 11/13 HGEC, and 10/59 LGEC. Mutant-pattern p53 staining was present in 6/6 serous, 2/11 HGEC, and 2/10 LGEC. The remaining 53 tumors subsequently had p53 immunostaining done; all 49 LGEC showed wild-type staining and the serous carcinoma and 1/2 HGEC showed mutant pattern staining. While there are no guidelines on using p53 in endometrial biopsies, this study shows consistent usage in high-grade histotypes and variable usage in LGEC. As 100% (7/7) of serous EC and 3% (2/59) of the LGECs showed mutant-pattern p53 staining, histotype may serve as a surrogate for p53 assessment, such that only HGEC or ambiguous carcinomas should be routinely subjected to p53 immunostaining.

A Novel Cell-Penetrating Antibody Fragment Inhibits the DNA Repair Protein RAD51.

DNA damaging chemotherapies are successful in cancer therapy, however, the damage can be reversed by DNA repair mechanisms that may be up-regulated in cancer cells. We hypothesized that inhibiting RAD51, a protein involved in homologous recombination DNA repair, would block DNA repair and restore the effectiveness of DNA damaging chemotherapy. We used phage-display to generate a novel synthetic antibody fragment that bound human RAD51 with high affinity (KD = 8.1 nM) and inhibited RAD51 ssDNA binding in vitro. As RAD51 is an intracellular target, we created a corresponding intrabody fragment that caused a strong growth inhibitory phenotype on human cells in culture. We then used a novel cell-penetrating peptide "iPTD" fusion to generate a therapeutically relevant antibody fragment that effectively entered living cells and enhanced the cell-killing effect of a DNA alkylating agent. The iPTD may be similarly useful as a cell-penetrating peptide for other antibody fragments and open the door to numerous intracellular targets previously off-limits in living cells.

Targeted Molecular and Immunohistochemical Analyses of Endometrial Clear Cell Carcinoma Show that POLE Mutations and DNA Mismatch Repair Protein Deficiencies Are Uncommon.

Endometrial clear cell carcinoma (ECCC) is an uncommon histotype without unique identified molecular alterations. Recently, The Cancer Genome Atlas molecular subtypes have been reported in ECCC. ECCC cases were collected from 11 institutions with diagnoses confirmed by morphologic review and immunohistochemistry. DNA mismatch repair (MMR) proteins, p53 expression, and ARID1A expression was assessed by immunohistochemistry on tissue microarrays. Targeted next-generation sequencing was completed for POLE, TP53, KRAS, and PIK3CA. Pathogenicity of mutations was determined using MutationTaster and PolyPhen databases. For p53, immunohistochemistry and sequencing were complimentarily used to assess the p53 status. Of 57 cases, 46 were considered prototypical ECCC by morphology and immunohistochemical profile (Napsin A-positive and ER-negative). Three cases were excluded because of insufficient sample for complete immunohistochemical analysis, and 6 had failed sequencing, resulting in 37 cases. Of the 37 remaining cases, 6/37 (16%) had predicted pathogenic mutations in the exonuclease domain of POLE with an allelic frequency >10%; however, no hot-spot mutations were identified. No cases were MMR-deficient. The gene most commonly affected was TP53 (59%, 22/37), followed by KRAS (13%, 2/15) and PIK3CA (13%, 2/15). The current study is the largest molecular analysis of pure ECCC reported to date. When strict classification criteria are applied, MMR-deficient and POLE mutated subtypes are not represented. Further consensus on what represents a deleterious POLE mutations is needed. The findings support separately studying histologically/immunohistochemically defined ECCC to identify characteristic molecular alterations in future studies.

89Zr-nimotuzumab for immunoPET imaging of epidermal growth factor receptor I.

RATIONALE: Epidermal growth factor receptor (EGFR) upregulation is associated with enhanced proliferation and drug resistance in a number of cancers. Nimotuzumab is a humanized monoclonal antibody with high affinity for EGFR. The objective of this study was to determine if 89Zr-DFO-nimotuzumab could be suitable for human use as a PET probe for quantifying EGFR in vivo. METHODS: To evaluate the pharmacokinetics, biodistribution, microPET imaging, radiation dosimetry, and normal tissue toxicity in tumor and non-tumor bearing mice of 89Zr-desferoxamine-nimotuzumab (89Zr-DFO-nimotuzumab) of a product prepared under GMP conditions. Nimotuzumab was conjugated to DFO and radiolabeled with 89Zr. 89Zr-DFO-nimotuzumab was characterized by in vitro gel-electrophoresis, biolayer interferometry (BLI) and flow cytometry. 89Zr-DFO-nimotuzumab was evaluated in vivo by microPET and ex vivo by biodistribution in healthy and EGFR-positive tumor bearing mice. RESULTS: Flow cytometry with A431 cells showed no significant difference in the dissociation constant of nimotuzumab (13 ± 2 nM) compared with DFO-nimotuzumab (17 ± 4 nM). PET imaging in mice xenografts showed persistently high tumor uptake with the highest uptake obtained in DLD-1 xenograft (18.3 %IA/cc) at 168 hp.i. The projected human effective dose was low and was 0.184 mSv/MBq (0.679 rem/mCi) in females and 0.205 mSv/MBq (0.757 rem/mCi) in males. There was no apparent normal tissue toxicity as shown by cell blood counts and blood biochemistry analyses at 168-fold and 25-fold excess of the projected human radioactive and mass dose of the agent. CONCLUSION: 89Zr-DFO-nimotuzumab had low organ absorbed dose and effective dose that makes it suitable for potential human use.

EPHB6 augments both development and drug sensitivity of triple-negative breast cancer tumours.

Triple-negative breast cancer (TNBC) tumours that lack expression of oestrogen, and progesterone receptors, and do not overexpress the HER2 receptor represent the most aggressive breast cancer subtype, which is characterised by the resistance to therapy in frequently relapsing tumours and a high rate of patient mortality. This is likely due to the resistance of slowly proliferating tumour-initiating cells (TICs), and understanding molecular mechanisms that control TICs behaviour is crucial for the development of effective therapeutic approaches. Here, we present our novel findings, indicating that an intrinsically catalytically inactive member of the Eph group of receptor tyrosine kinases, EPHB6, partially suppresses the epithelial-mesenchymal transition in TNBC cells, while also promoting expansion of TICs. Our work reveals that EPHB6 interacts with the GRB2 adapter protein and that its effect on enhancing cell proliferation is mediated by the activation of the RAS-ERK pathway, which allows it to elevate the expression of the TIC-related transcription factor, OCT4. Consistent with this, suppression of either ERK or OCT4 activities blocks EPHB6-induced pro-proliferative responses. In line with its ability to trigger propagation of TICs, EPHB6 accelerates tumour growth, potentiates tumour initiation and increases TIC populations in xenograft models of TNBC. Remarkably, EPHB6 also suppresses tumour drug resistance to DNA-damaging therapy, probably by forcing TICs into a more proliferative, drug-sensitive state. In agreement, patients with higher EPHB6 expression in their tumours have a better chance for recurrence-free survival. These observations describe an entirely new mechanism that governs TNBC and suggest that it may be beneficial to enhance EPHB6 action concurrent with applying a conventional DNA-damaging treatment, as it would decrease drug resistance and improve tumour elimination.

Quantitative and multiplexed DNA methylation analysis using long-read single-molecule real-time bisulfite sequencing (SMRT-BS).

BACKGROUND: DNA methylation has essential roles in transcriptional regulation, imprinting, X chromosome inactivation and other cellular processes, and aberrant CpG methylation is directly involved in the pathogenesis of human imprinting disorders and many cancers. To address the need for a quantitative and highly multiplexed bisulfite sequencing method with long read lengths for targeted CpG methylation analysis, we developed single-molecule real-time bisulfite sequencing (SMRT-BS). RESULTS: Optimized bisulfite conversion and PCR conditions enabled the amplification of DNA fragments up to ~1.5 kb, and subjecting overlapping 625-1491 bp amplicons to SMRT-BS indicated high reproducibility across all amplicon lengths (r=0.972) and low standard deviations (≤0.10) between individual CpG sites sequenced in triplicate. Higher variability in CpG methylation quantitation was correlated with reduced sequencing depth, particularly for intermediately methylated regions. SMRT-BS was validated by orthogonal bisulfite-based microarray (r=0.906; 42 CpG sites) and second generation sequencing (r=0.933; 174 CpG sites); however, longer SMRT-BS amplicons (>1.0 kb) had reduced, but very acceptable, correlation with both orthogonal methods (r=0.836-0.897 and r=0.892-0.927, respectively) compared to amplicons less than ~1.0 kb (r=0.940-0.951 and r=0.948-0.963, respectively). Multiplexing utility was assessed by simultaneously subjecting four distinct CpG island amplicons (702-866 bp; 325 CpGs) and 30 hematological malignancy cell lines to SMRT-BS (average depth of 110X), which identified a spectrum of highly quantitative methylation levels across all interrogated CpG sites and cell lines. CONCLUSIONS: SMRT-BS is a novel, accurate and cost-effective targeted CpG methylation method that is amenable to a high degree of multiplexing with minimal clonal PCR artifacts. Increased sequencing depth is necessary when interrogating longer amplicons (>1.0 kb) and the previously reported bisulfite sequencing PCR bias towards unmethylated DNA should be considered when measuring intermediately methylated regions. Coupled with an optimized bisulfite PCR protocol, SMRT-BS is capable of interrogating ~1.5 kb amplicons, which theoretically can cover ~91% of CpG islands in the human genome.

Allosteric lariat peptide inhibitors of Abl kinase.

Going against tradition: although most kinase inhibitors are ATP competitive, lariat peptides inhibit Abl kinase activity in an ATP-uncompetitive manner. Further, lariat peptides discriminated Src family kinases, and recognize the allosteric region that lies adjacent to the ATP binding pocket in the Abl kinase catalytic cleft.

The EphB6 receptor cooperates with c-Cbl to regulate the behavior of breast cancer cells.

Cancer invasiveness plays a major role in the mortality of patients with solid tumors, and deregulated cell adhesion and migration are suspected to drive invasive behavior. Since Eph receptor tyrosine kinases control both cell attachment and migration, they may act to define the level of cancer invasiveness. EphB6 is an unusual Eph receptor, lacking catalytic capacity due to alterations in its kinase domain. Interestingly, increased metastatic activity is associated with reduced EphB6 receptor expression in several tumor types, including breast cancer. This emphasizes the potential of EphB6 to act as a suppressor of cancer aggressiveness; however, the mechanism of its action is not well understood. We show that restoration of EphB6 expression in invasive breast cancer cells supports actin-dependent spreading and attachment and blocks invasiveness. EphB6 stimulation induces its tyrosine phosphorylation, which is crucial for its function and is mediated by the EphB4 receptor. This is accompanied by EphB6-c-Cbl interaction and phosphorylation of c-Cbl partner, the Abl kinase. Cbl silencing suppresses Abl phosphorylation, cell adhesion, and morphologic changes and blocks the ability of EphB6 to inhibit invasiveness, confirming its importance for EphB6 activity. Despite its crucial role in EphB6 responses, EphB4 also acts in an EphB6-independent manner to enhance invasive activity, suggesting that cancer invasiveness may be defined by the balance in the EphB6-EphB4 system. Overall, our observations suggest a new role for EphB6 in suppressing cancer invasiveness through c-Cbl-dependent signaling, morphologic changes, and cell attachment and indicate that EphB6 may represent a useful prognostic marker and a promising target for therapeutic approaches.

Loss of imprinting of the insulin-like growth factor II (IGF2) gene in esophageal normal and adenocarcinoma tissues.

To evaluate loss of imprinting (LOI) and expression of the IGF2 gene in matched esophageal normal and adenocarcinoma tissues, we studied a prospective cohort of 77 patients who underwent esophageal resection between 1998 and 2003. IGF2 imprinting status was determined by reverse transcription-polymerase chain reaction (PCR) following ApaI digestion, and quantitative PCR was used to evaluate IGF2 expression, which was correlated with clinicopathologic findings, disease-free and overall survival. In total, 32% (14/44) of informative tissues showed loss of IGF2 imprinting, with a strong correlation between the tumor and normal esophageal epithelia (Kappa = 0.89, P < 0.01). Normal epithelia with LOI had increased expression of IGF2 [median: 2.91, 95% confidence interval (CI): 0.93-5.06] compared with imprinted normal epithelia (median: 1.13, 95% CI: 0.85-1.39) (P = 0.03). In contrast, tumors with LOI had significantly reduced IGF2 expression (median: 1.87, 95% CI: 0.53-5.21) compared with normally imprinted tumors (median: 6.79, 95% CI: 3.39-15.89) (P = 0.016). Patients below the age of 65 years with normally imprinted tumors had significantly reduced 5 year disease-free survival (DFS) (24%) compared with patients whose tumors had LOI for IGF2 (55%) (P = 0.03). Cox regression analysis showed that IGF2 overexpression was associated with significantly reduced disease-free survival (P = 0.04). We conclude that in a subgroup of younger patients, loss of IGF2 imprinting was associated with improved outcome following esophageal resection. Expression of IGF2 in esophageal adenocarcinoma and normal esophageal epithelia depended on imprinting status and tissue type, suggesting novel molecular regulatory mechanisms in esophageal tumorigenesis.

RIZ1 is potential CML tumor suppressor that is down-regulated during disease progression.

BACKGROUND: RIZ1 expression and activity are reduced in many cancers. In AML cell lines and patient material, RIZ1 expression is reduced relative to normal bone marrow. In chronic myelogenous leukemia (CML), blastic transformation is associated with loss of heterozygosity in the region where RIZ1 is located. RIZ1 is a PR domain methyltransferase that methylates histone H3 lysine 9, a modification important for transcriptional repression. In CML blast crisis cell lines RIZ1 represses insulin-like growth factor-1 expression and autocrine signaling. Together these observations suggest that RIZ1 may have a role in the chronic phase to blast crisis transition in CML. RESULTS: In CML patient material, we observed that RIZ1 expression was decreased during progression from chronic phase to blast crisis. RIZ1 was expressed in mature myeloid and CD34+ cells demonstrating that decreased RIZ1 expression in blast crisis is not due to an increased immature cell population. Expression of RIZ1 CML blast crisis cell lines decreased proliferation, increased apoptosis, and enhanced differentiation. CONCLUSION: RIZ1 is a candidate tumor suppressor gene whose expression is decreased in blast crisis. Loss of RIZ1 activity results in decreased apoptosis and differentiation and enhanced proliferation. Together these results suggest that loss of RIZ1 expression will lead to an increase in myeloid blast cell population resulting in CML progression.

Cytogenetic abnormality 46,XX,add(21)(q11.2) in a patient with follicular dendritic cell sarcoma.

The case of a patient with follicular dendritic cell (FDC) sarcoma with chromosomal aberration add(21)(q11.2) is described. Cytogenetic studies showed the karyotype 46,XX,add(21)(q11.2)[3]/46,XX[17], although the encoded protein involved was not clarified. The abnormal pattern was quite simple, and different from a previous report. The clinical course of the FDC sarcoma in this case has been indolent, as for most FDC sarcoma patients. Although this patient suffered from breast carcinoma 6 years after the onset of FDC sarcoma, the carcinoma showed different histological and phenotypic profiles.

Fli-1 expression in malignant melanoma.

Friend leukemia integration site 1 (Fli-1) has been reported as the first nuclear marker of endothelial differentiation; it is expressed in leukocytes and recently demonstrated in melanomas. Formalin-fixed, paraffin-embedded tissue sections from 97 melanomas including 69 cases of primary and 28 metastatic melanomas were evaluated by immunohistochemistry. Five melanoma cell lines were evaluated by Western blot and immunocytochemistry. Fli-1 expression was observed in all cell lines. Fli-1 expression was higher in metastatic than in primary tumors (r=0.208, p=0.041, Spearman correlation), it positively correlated with Ki-67 expression (r=0.233, p=0.022, Spearman correlation), and the presence of an ulcer in the primary tumor (r=0.267, p=0.030, Spearman correlation). Therefore, the expression of Fli-1 in malignant melanoma appears to be associated with biologically more aggressive tumors.

In human leukemia cells ephrin-B-induced invasive activity is supported by Lck and is associated with reassembling of lipid raft signaling complexes.

Proteins of the ephrin-B group operate in nonlymphoid cells through the control of their migration and attachment, and are crucial for the development of the vascular, lymphatic, and nervous systems. Ephrin-B activity is deregulated in various nonlymphoid malignancies; however, their precise role in cancer has only started to be addressed. We show here that ephrin-B1, a member of the ephrin-B group, is expressed in pediatric T-cell leukemias, including leukemia cell line Jurkat. Treatment of Jurkat cells with ephrin-B-stimulating EphB3 enhances ephrin-B1 phosphorylation and induces its relocalization into lipid rafts. These events are mediated by the T lineage-specific kinase, Lck, as ephrin-B1 phosphorylation and lipid raft association are blocked in the Lck-deficient clone of Jurkat, JCAM1.6. Ephrin-B1 also induces colocalization of the CrkL and Rac1 cytoskeleton regulators and initiates in leukemic cells a strong repulsive response. The absence of Lck blocks ephrin-B1-induced signaling and repulsion, confirming the essential role for Lck in ephrin-B1-mediated responses. This shows a new role for ephrin-B1 in the regulation of leukemic cells through the Lck-dependent Rac1 colocalization with its signaling partner, CrkL, in lipid rafts. In agreement with its repulsive action, ephrin-B1 seems to support metastatic properties of leukemic cells, as suppression of ephrin-B1 signaling inhibits their invasiveness. Because ephrin-B1-activating EphB proteins are ubiquitously expressed, our findings suggest that ephrin-B1 is likely to play an important role in the regulation of malignant T lymphocytes through the control of lipid-raft-associated signaling, adhesion, and invasive activity, and therefore may represent a novel target for cancer treatment.