Activating JAK-mutations confer resistance to FLT3 kinase inhibitors in FLT3-ITD positive AML in vitro and in vivo

An important limitation of FLT3 tyrosine kinase inhibitors (TKIs) in FLT3-ITD positive AML is the development of resistance. To better understand resistance to FLT3 inhibition, we examined FLT3-ITD positive cell lines which had acquired resistance to midostaurin or sorafenib. In 6 out of 23 TKI resistant cell lines we were able to detect a JAK1 V658F mutation, a mutation that led to reactivation of the CSF2RB-STAT5 pathway. Knockdown of JAK1, or treatment with a JAK inhibitor, resensitized cells to FLT3 inhibition. Out of 136 patients with FLT3-ITD mutated AML and exposed to FLT3 inhibitor, we found seven different JAK family mutations in six of the cases (4.4%), including five bona fide, activating mutations. Except for one patient, the JAK mutations occurred de novo (n = 4) or displayed increasing variant allele frequency after exposure to FLT3 TKI (n = 1). In vitro each of the five activating variants were found to induce resistance to FLT3-ITD inhibition, which was then overcome by dual FLT3/JAK inhibition. In conclusion, our data characterize a novel mechanism of resistance to FLT3-ITD inhibition and may offer a potential therapy, using dual JAK and FLT3 inhibition.

CCL5 mediates target-kinase independent resistance to FLT3 inhibitors in FLT3-ITD-positive AML

FLT3‐ITD tyrosine kinase inhibitors (TKI) show limited clinical activity in acute myeloid leukemia (AML) due to emerging resistance. TKI resistance is mediated by secondary FLT3‐ITD mutations only in a minority of cases. We hypothesize that the cytokine CCL5 protects AML cells from TKI‐mediated cell death and contributes to treatment resistance. We generated PKC412‐ and sorafenib‐resistant MOLM‐13 cell lines as an in vitro model to study TKI resistance in AML. Increased CCL5 levels were detected in supernatants from PKC412‐resistant cell lines compared to TKI‐sensitive cells. Moreover, CCL5 treatment of TKI‐sensitive cells induced resistance to PKC412. In resistant cell lines with high CCL5 release, we observed a significant downregulation of the CCL5‐receptor CCR5 and CXCR4. In these cell lines, TKI resistance could be partly overcome by addition of the CXCR4‐receptor antagonist plerixafor. Microarray and intracellular flow cytometry analyses revealed increased p‐Akt or p‐Stat5 levels in PKC412‐resistant cell lines releasing high amounts of CCL5. Treatment with the CXCR4 antagonist plerixafor, αCCL5, or CCR5‐targeting siRNA led to a decrease of p‐Akt‐positive cells. Transient transfection of sensitive MOLM‐13 cells with a CCL5‐encoding vector mediated resistance against PKC412 and led to an increase in p‐Akt‐positive and p‐Stat5‐positive cells. Isolated AML blasts from patients treated with PKC412 revealed that CCL5 transcript levels increase significantly at relapse. Taken together, our findings indicate that CCL5 mediates resistance to FLT3‐TKIs in FLT3‐ITD‐mutated AML and could possibly serve as a biomarker to predict drug resistance.

--LUBAC deficiency perturbs TLR3 signaling to cause immunodeficiency and autoinflammation

LUBAC components interact with the TLR3 signaling cascade at different levels, thereby tightly controlling TLR3-mediated innate immunity.

The linear ubiquitin chain assembly complex (LUBAC), consisting of SHANK-associated RH-domain–interacting protein (SHARPIN), heme-oxidized IRP2 ubiquitin ligase-1 (HOIL-1), and HOIL-1–interacting protein (HOIP), is a critical regulator of inflammation and immunity. This is highlighted by the fact that patients with perturbed linear ubiquitination caused by mutations in the Hoip or Hoil-1 genes, resulting in knockouts of these proteins, may simultaneously suffer from immunodeficiency and autoinflammation. TLR3 plays a crucial, albeit controversial, role in viral infection and tissue damage. We identify a pivotal role of LUBAC in TLR3 signaling and discover a functional interaction between LUBAC components and TLR3 as crucial for immunity to influenza A virus infection. On the biochemical level, we identify LUBAC components as interacting with the TLR3-signaling complex (SC), thereby enabling TLR3-mediated gene activation. Absence of LUBAC components increases formation of a previously unrecognized TLR3-induced death-inducing SC, leading to enhanced cell death. Intriguingly, excessive TLR3-mediated cell death, induced by double-stranded RNA present in the skin of SHARPIN-deficient chronic proliferative dermatitis mice (cpdm), is a major contributor to their autoinflammatory skin phenotype, as genetic coablation of Tlr3 substantially ameliorated cpdm dermatitis. Thus, LUBAC components control TLR3-mediated innate immunity, thereby preventing development of immunodeficiency and autoinflammation.

Evaluation of 3-[18F]fluoro-alpha-fluoromethyl-p-tyrosine as a tracer for striatal tyrosine hydroxylase activity

3-[18F]Fluoro-alpha-fluoromethyl-p-tyrosine (3-F-FMPT) was evaluated as a tracer for CNS tyrosine hydroxylase (TH) activity in rodents and in a rhesus monkey. Results of in vitro experiments using rat striatal homogenates showed that the introduction of fluorine into the 3-phenyl position did not significantly alter the ability of FMPT to act as a TH-activated L-aromatic amino acid decarboxylase (L-AAAD) inhibitor. These studies further showed that 3-F-FMPT-induced L-AAAD inhibition was dose-dependent. Furthermore, striatal homogenates prepared from rats pretreated with the potent TH inhibitor alpha-methyl-p-tyrosine was found to have diminished 3-F-FMPT-induced L-AAAD inhibition. However, despite these promising in vitro results, the biodistribution of this compound in mice showed low brain uptake and fast clearance through the kidneys. A PET study using a Rhesus monkey injected with 3-[18F]F-FMPT confirmed the results obtained in mice, i.e. negligible brain uptake but high localization in the bladder. We conclude that 3-[18F]F-FMPT would not be useful as a tracer for cerebral TH activity.

Effect of galanin on food intake in rats: involvement of lateral and ventromedial hypothalamic sites

Galanin has previously been reported to elicit feeding in satiated animals when injected into the hypothalamic paraventricular nucleus. It is not known, however, 1) whether this action is due to activation of feeding signals or suppression of satiety signals or both or 2) whether other hypothalamic regions such as the lateral hypothalamus (LH) or the ventromedial hypothalamus (VMH) are involved in this action. The effects of galanin on food intake were therefore examined in satiated and in fasted rats both after intracerebroventricular injection (0.1, 1, and 10 micrograms/10 microliters) and after microinjection (1 and 5 micrograms/0.5 microliters) into the LH and VMH. Twenty minutes after intracerebroventricular injection, galanin significantly and dose dependently augmented food intake by up to sevenfold in freely feeding rats and by up to 79% in fasted animals. The galanin-induced augmentation of cumulative food intake up to 2 h after injection was due to the initial increase in food consumption during the 0 to 20-min interval. This suggests that galanin acts by activation of feeding behavior and not by suppression of satiety signals in these fasted animals, in which satiety signals are presumably not initially operative. Twenty minutes after intrahypothalamic injections into both the LH and VMH, galanin (5 micrograms) significantly increased food consumption, fivefold in freely feeding rats and 30-35% in fasted rats. Thus stimulation of feeding by centrally injected galanin also involves loci within the LH and VMH.

Visualization of dopamine nerve terminals by positron tomography using [18F]fluoro-beta-fluoromethylene-m-tyrosine

[18F]-6-Fluoro-beta-fluoromethylene-m-tyrosine ([18F]FFMMT) was evaluated as a potential imaging agent for dopamine nerve terminals using positron emission tomography (PET). Biodistribution and time course of this tracer in mice after i.p. injection was consistent with the distribution of dopamine. PET imaging studies involving rhesus macaques showed specific uptake in the dopamine-rich caudate-putamen region. This specific localization was blocked by inhibiting the enzyme L-aromatic amino acid decarboxylase and the transport of the tracer into brain was shown to be stereospecific. These results show the promise of L-[18F]FFMMT as a PET tracer in monitoring degeneration of the CNS dopamine system.