Performance of MYC, BCL2, and BCL6 break-apart FISH in small biopsies with large B-cell lymphoma: a retrospective Cytopathology Hematopathology Interinstitutional Consortium study.

Introduction: Fluorescence in situ hybridization (FISH) is an essential ancillary study used to identify clinically aggressive subsets of large B-cell lymphomas that have MYC, BCL2, or BCL6 rearrangements. Small-volume biopsies such as fine needle aspiration biopsy (FNAB) and core needle biopsy (CNB) are increasingly used to diagnose lymphoma and obtain material for ancillary studies such as FISH. However, the performance of FISH in small biopsies has not been thoroughly evaluated or compared to surgical biopsies. Methods: We describe the results of MYC, BCL2, and BCL6 FISH in a series of 222 biopsy specimens, including FNAB with cell blocks, CNBs, and surgical excisional or incisional biopsies from 208 unique patients aggregated from 6 academic medical centers. A subset of patients had FNAB followed by a surgical biopsy (either CNB or excisional biopsy) obtained from the same or contiguous anatomic site as part of the same clinical workup; FISH results were compared for these paired specimens. Results: FISH had a low hybridization failure rate of around 1% across all specimen types. FISH identified concurrent MYC and BCL2 rearrangements in 20 of 197 (10%) specimens and concurrent MYC and BCL6 rearrangements in 3 of 182 (1.6%) specimens. The paired FNAB and surgical biopsy specimens did not show any discrepancies for MYC or BCL2 FISH; of the 17 patients with 34 paired cytology and surgical specimens, only 2 of the 49 FISH probes compared (4% of all comparisons) showed any discrepancy and both were at the BCL6 locus. One discrepancy was due to necrosis of the CNB specimen causing a false negative BCL6 FISH result when compared to the FNAB cell block that demonstrated a BCL6 rearrangement. Discussion: FISH showed a similar hybridization failure rate in all biopsy types. Ultimately, MYC, BCL2, or BCL6 FISH showed 96% concordance when compared across paired cytology and surgical specimens, suggesting FNAB with cell block is equivalent to other biopsy alternatives for evaluation of DLBCL or HGBCL FISH testing.

MAPK-negative feedback regulation confers dependence to JAK2V617F signaling.

Despite significant advances in developing selective JAK2 inhibitors, JAK2 kinase inhibitor (TKI) therapy is ineffective in suppressing the disease. Reactivation of compensatory MEK-ERK and PI3K survival pathways sustained by inflammatory cytokine signaling causes treatment failure. Concomitant inhibition of MAPK pathway and JAK2 signaling showed improved in vivo efficacy compared to JAK2 inhibition alone but lacked clonal selectivity. We hypothesized that cytokine signaling in JAK2V617F induced MPNs increases the apoptotic threshold that causes TKI persistence or refractoriness. Here, we show that JAK2V617F and cytokine signaling converge to induce MAPK negative regulator, DUSP1. Enhanced DUSP1 expression blocks p38 mediated p53 stabilization. Deletion of Dusp1 increases p53 levels in the context of JAK2V617F signaling that causes synthetic lethality to Jak2V617F expressing cells. However, inhibition of Dusp1 by a small molecule inhibitor (BCI) failed to impart Jak2V617F clonal selectivity due to pErk1/2 rebound caused by off-target inhibition of Dusp6. Ectopic expression of Dusp6 and BCI treatment restored clonal selectively and eradicated the Jak2V617F cells. Our study shows that inflammatory cytokines and JAK2V617F signaling converge to induce DUSP1, which downregulates p53 and establishes a higher apoptotic threshold. These data suggest that selectively targeting DUSP1 may provide a curative response in JAK2V617F-driven MPN.

Rational polypharmacological targeting of FLT3, JAK2, ABL, and ERK1 suppresses the adaptive resistance to FLT3 inhibitors in AML.

Despite significant advancements in developing selective FMS-like tyrosine kinase 3 (FLT3) inhibitors, resistance to treatment is common even on continued therapy. Acquisition of on-target mutations or adaptation to MAPK, JAK2, and ABL signaling pathways drive treatment failure and disease relapse. Although combinatorial targeting of all escape routes in preclinical models demonstrated its efficacy, the clinical application is challenging owing to drug-drug interaction and differing pharmacokinetics of the inhibitors. We reasoned that selective polypharmacological targeting could lead to a durable response with reduced toxicity. A cell-based screening was carried out to identify inhibitors targeting FLT3, RAS-MAPK, BCR-ABL, and JAK2 to target the adaptive resistance observed with FLT3 inhibitors. Here, we show that pluripotin is an equipotent inhibitor of FLT3, BCR-ABL, and JAK2 in addition to inhibiting Ras-GAP and extracellular signal-regulated kinase 1 (ERK1). Structural modeling studies revealed that pluripotin is a type II kinase inhibitor that selectively binds with inactive conformations of FLT3, ABL, and JAK2. Pluripotin showed potent inhibitory activity on both mouse and human cells expressing FLT3ITD, including clinically challenging resistant mutations of the gatekeeper residue, F691L. Likewise, pluripotin suppressed the adaptive resistance conferred by the activation of RAS-MAPK pathways, BCR-ABL, and JAK2 signaling. Treatment with pluripotin curbed the progression of acute myeloid leukemia (AML) in multiple in vivo models including patient-derived primary AML cells in mouse xenotransplants. As a proof of concept, we demonstrate that targeted polypharmacological inhibition of key signaling nodes driving adaptive resistance can provide a durable response.

Ttc39c is upregulated during skeletal muscle atrophy and modulates ERK1/2 MAP kinase and hedgehog signaling.

Tetratricopeptide repeat domain containing 39c (Ttc39c) is expressed in skeletal muscle and is transcriptionally activated in response to neurogenic atrophy in mice. Expression analysis using quantitative polymerase chain reaction and Western blots revealed that Ttc39c is expressed in both proliferating and differentiated muscle cells, peaking during early differentiation and then decreasing as cells progress further through the differentiation process. To further analyze the transcriptional regulation of Ttc39c, promoter fragments of the gene were cloned and fused with the secreted alkaline phosphatase reporter gene. The Ttc39c reporter plasmids were then transfected into cultured mouse muscle cells and found to have transcriptional activity. Furthermore, overexpression of MyoD and myogenin resulted in significant transcriptional repression of the Ttc39c reporter genes. To determine subcellular localization, an expression plasmid with the Ttc39c complementary DNA fused with green fluorescent protein was transfected into muscle cells and analyzed by confocal fluorescent microscopy showing that Tct39c localizes exclusively to the cytoplasm of cultured cells. To assess potential function in muscle, Ttc39c was overexpressed leading to vitiated muscle cell differentiation, impaired ERK1/2 MAP Kinase and Hedgehog signaling, and increased expression of IFT144 and IFT43, which are part of the IFT-A complex involved in retrograde transport in primary cilia. Interestingly, Ttc39c knockdown also resulted in inhibition of muscle cell differentiation and impaired Hedgehog and MAP Kinase signaling but did not affect IFT144 or IFT433 expression. The results of this study demonstrate that muscle cell differentiation is sensitive to abnormal Ttc39c expression and that normal Ttc39c expression appears to be necessary for proper MAP Kinase and Hedgehog signal transduction in developing muscle cells.

Sonic Hedgehog Activates Phospholipase A2 to Enhance Smoothened Ciliary Translocation.

The G protein-coupled receptor Smoothened (Smo) is the signal transducer of the Sonic Hedgehog (Shh) pathway. Smo signals through G protein-dependent and -independent routes, with G protein-independent canonical signaling to Gli effectors requiring Smo accumulation in the primary cilium. The mechanisms controlling Smo activation and trafficking are not yet clear but likely entail small-molecule binding to pockets in its extracellular cysteine-rich domain (CRD) and/or transmembrane bundle. Here, we demonstrate that the cytosolic phospholipase cPLA2α is activated through Gßγ downstream of Smo to release arachidonic acid. Arachidonic acid binds Smo and synergizes with CRD-binding agonists, promoting Smo ciliary trafficking and high-level signaling. Chemical or genetic cPLA2α inhibition dampens Smo signaling to Gli, revealing an unexpected contribution of G protein-dependent signaling to canonical pathway activity. Arachidonic acid displaces the Smo transmembrane domain inhibitor cyclopamine to rescue CRD agonist-induced signaling, suggesting that arachidonic acid may target the transmembrane bundle to allosterically enhance signaling by CRD agonist-bound Smo.