Concurrent inhibition of oncogenic and wild-type RAS-GTP for cancer therapy

RAS oncogenes (collectively NRAS, HRAS and especially KRAS) are among the most frequently mutated genes in cancer, with common driver mutations occurring at codons 12, 13 and 611. Small molecule inhibitors of the KRAS(G12C) oncoprotein have demonstrated clinical efficacy in patients with multiple cancer types and have led to regulatory approvals for the treatment of non-small cell lung cancer2,3. Nevertheless, KRASG12C mutations account for only around 15% of KRAS-mutated cancers4,5, and there are no approved KRAS inhibitors for the majority of patients with tumours containing other common KRAS mutations. Here we describe RMC-7977, a reversible, tri-complex RAS inhibitor with broad-spectrum activity for the active state of both mutant and wild-type KRAS, NRAS and HRAS variants (a RAS(ON) multi-selective inhibitor). Preclinically, RMC-7977 demonstrated potent activity against RAS-addicted tumours carrying various RAS genotypes, particularly against cancer models with KRAS codon 12 mutations (KRASG12X). Treatment with RMC-7977 led to tumour regression and was well tolerated in diverse RAS-addicted preclinical cancer models. Additionally, RMC-7977 inhibited the growth of KRASG12C cancer models that are resistant to KRAS(G12C) inhibitors owing to restoration of RAS pathway signalling. Thus, RAS(ON) multi-selective inhibitors can target multiple oncogenic and wild-type RAS isoforms and have the potential to treat a wide range of RAS-addicted cancers with high unmet clinical need. A related RAS(ON) multi-selective inhibitor, RMC-6236, is currently under clinical evaluation in patients with KRAS-mutant solid tumours (ClinicalTrials.gov identifier: NCT05379985).

cGMP-dependent kinase 2, Na+/H+ exchanger NHE3, and PDZ-adaptor NHERF2 co-assemble in apical membrane microdomains

AIM

Trafficking, membrane retention, and signal-specific regulation of the Na+/H+ exchanger 3 (NHE3) are modulated by the Na+/H+ Exchanger Regulatory Factor (NHERF) family of PDZ-adapter proteins. This study explored the assembly of NHE3 and NHERF2 with the cGMP-dependent kinase II (cGKII) within detergent-resistant membrane microdomains (DRMs, "lipid rafts") during in vivo guanylate cycle C receptor (Gucy2c) activation in murine small intestine.

METHODS

Small intestinal brush border membranes (siBBMs) were isolated from wild type, NHE3-deficient, cGMP-kinase II-deficient, and NHERF2-deficient mice, after oral application of the heat-stable Escherichia coli toxin (STa) analog linaclotide. Lipid raft and non-raft fractions were separated by Optiprep density gradient centrifugation of Triton X-solubilized siBBMs. Confocal microscopy was performed to study NHE3 redistribution after linaclotide application in vivo.

RESULTS

In the WT siBBM, NHE3, NHERF2, and cGKII were strongly raft associated. The raft association of NHE3, but not of cGKII, was NHERF2 dependent. After linaclotide application to WT mice, lipid raft association of NHE3 decreased, that of cGKII increased, while that of NHERF2 did not change. NHE3 expression in the BBM shifted from a microvillar to a terminal web region. The linaclotide-induced decrease in NHE3 raft association and in microvillar abundance was abolished in cGKII-deficient mice, and strongly reduced in NHERF2-deficient mice.

CONCLUSION

NHE3, cGKII, and NHERF2 form a lipid raft-associated signal complex in the siBBM, which mediates the inhibition of salt and water absorption by Gucy2c activation. NHERF2 enhances the raft association of NHE3, which is essential for its close interaction with the exclusively raft-associated activated cGKII.

ALK peptide vaccination restores the immunogenicity of ALK-rearranged non-small cell lung cancer

Anaplastic lymphoma kinase (ALK)-rearranged non-small cell lung cancer (NSCLC) is treated with ALK tyrosine kinase inhibitors (TKIs), but the lack of activity of immune checkpoint inhibitors (ICIs) is poorly understood. Here, we identified immunogenic ALK peptides to show that ICIs induced rejection of ALK+ tumors in the flank but not in the lung. A single-peptide vaccination restored priming of ALK-specific CD8+ T cells, eradicated lung tumors in combination with ALK TKIs and prevented metastatic dissemination of tumors to the brain. The poor response of ALK+ NSCLC to ICIs was due to ineffective CD8+ T cell priming against ALK antigens and is circumvented through specific vaccination. Finally, we identified human ALK peptides displayed by HLA-A*02:01 and HLA-B*07:02 molecules. These peptides were immunogenic in HLA-transgenic mice and were recognized by CD8+ T cells from individuals with NSCLC, paving the way for the development of a clinical vaccine to treat ALK+ NSCLC.

Targeting CCR7-PI3Kγ overcomes resistance to tyrosine kinase inhibitors in ALK-rearranged lymphoma

Anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitors (TKIs) show potent efficacy in several ALK-driven tumors, but the development of resistance limits their long-term clinical impact. Although resistance mechanisms have been studied extensively in ALK-driven non-small cell lung cancer, they are poorly understood in ALK-driven anaplastic large cell lymphoma (ALCL). Here, we identify a survival pathway supported by the tumor microenvironment that activates phosphatidylinositol 3-kinase γ (PI3K-γ) signaling through the C-C motif chemokine receptor 7 (CCR7). We found increased PI3K signaling in patients and ALCL cell lines resistant to ALK TKIs. PI3Kγ expression was predictive of a lack of response to ALK TKI in patients with ALCL. Expression of CCR7, PI3Kγ, and PI3Kδ were up-regulated during ALK or STAT3 inhibition or degradation and a constitutively active PI3Kγ isoform cooperated with oncogenic ALK to accelerate lymphomagenesis in mice. In a three-dimensional microfluidic chip, endothelial cells that produce the CCR7 ligands CCL19/CCL21 protected ALCL cells from apoptosis induced by crizotinib. The PI3Kγ/δ inhibitor duvelisib potentiated crizotinib activity against ALCL lines and patient-derived xenografts. Furthermore, genetic deletion of CCR7 blocked the central nervous system dissemination and perivascular growth of ALCL in mice treated with crizotinib. Thus, blockade of PI3Kγ or CCR7 signaling together with ALK TKI treatment reduces primary resistance and the survival of persister lymphoma cells in ALCL.

Comparative Analysis and Isoform-Specific Therapeutic Vulnerabilities of KRAS Mutations in Non-Small Cell Lung Cancer

PURPOSE

Activating missense mutations of KRAS are the most frequent oncogenic driver events in lung adenocarcinoma (LUAD). However, KRAS isoforms are highly heterogeneous, and data on the potential isoform-dependent therapeutic vulnerabilities are still lacking.

EXPERIMENTAL DESIGN

We developed an isogenic cell-based platform to compare the oncogenic properties and specific therapeutic actionability of KRAS-mutant isoforms. In parallel, we analyzed clinicopathologic and genomic data from 3,560 patients with non-small cell lung cancer (NSCLC) to survey allele-specific features associated with oncogenic KRAS mutations.

RESULTS

In isogenic cell lines expressing different mutant KRAS isoforms, we identified isoform-specific biochemical, biological, and oncogenic properties both in vitro and in vivo. These exclusive features correlated with different therapeutic responses to MEK inhibitors, with KRAS G12C and Q61H mutants being more sensitive compared with other isoforms. In vivo, combined KRAS G12C and MEK inhibition was more effective than either drug alone. Among patients with NSCLCs that underwent comprehensive tumor genomic profiling, STK11 and ATM mutations were significantly enriched among tumors harboring KRAS G12C, G12A, and G12V mutations. KEAP1 mutation was significantly enriched among KRAS G12C and KRAS G13X LUADs. KRAS G13X-mutated tumors had the highest frequency of concurrent STK11 and KEAP1 mutations. Transcriptomic profiling revealed unique patterns of gene expression in each KRAS isoform, compared with KRAS wild-type tumors.

CONCLUSIONS

This study demonstrates that KRAS isoforms are highly heterogeneous in terms of concurrent genomic alterations and gene-expression profiles, and that stratification based on KRAS alleles should be considered in the design of future clinical trials.

Tyrosine phosphatases regulate resistance to ALK inhibitors in ALK+ anaplastic large cell lymphoma

Anaplastic large cell lymphomas (ALCLs) frequently carry oncogenic fusions involving the anaplastic lymphoma kinase (ALK) gene. Targeting ALK using tyrosine kinase inhibitors (TKIs) is a therapeutic option in cases relapsed after chemotherapy, but TKI resistance may develop. By applying genomic loss-of-function screens, we identified PTPN1 and PTPN2 phosphatases as consistent top hits driving resistance to ALK TKIs in ALK+ ALCL. Loss of either PTPN1 or PTPN2 induced resistance to ALK TKIs in vitro and in vivo. Mechanistically, we demonstrated that PTPN1 and PTPN2 are phosphatases that bind to and regulate ALK phosphorylation and activity. In turn, oncogenic ALK and STAT3 repress PTPN1 transcription. We found that PTPN1 is also a phosphatase for SHP2, a key mediator of oncogenic ALK signaling. Downstream signaling analysis showed that deletion of PTPN1 or PTPN2 induces resistance to crizotinib by hyperactivating SHP2, the MAPK, and JAK/STAT pathways. RNA sequencing of patient samples that developed resistance to ALK TKIs showed downregulation of PTPN1 and PTPN2 associated with upregulation of SHP2 expression. Combination of crizotinib with a SHP2 inhibitor synergistically inhibited the growth of wild-type or PTPN1/PTPN2 knock-out ALCL, where it reverted TKI resistance. Thus, we identified PTPN1 and PTPN2 as ALK phosphatases that control sensitivity to ALK TKIs in ALCL and demonstrated that a combined blockade of SHP2 potentiates the efficacy of ALK inhibition in TKI-sensitive and -resistant ALK+ ALCL.

Abstract LT018: The perivascular niche protects ALK+ lymphoma cells from ALK inhibition through the CCL19/21-CCR7 axis

The ALK inhibitor crizotinib showed promising therapeutic efficacy for relapsed/refractory Anaplastic Large Cell Lymphoma (R/R ALCL). However, a fraction of ALK+ R/R ALCL patients do not achieve complete remission due to crizotinib resistance that develops within the first 3 months of therapy. In patients that achieve complete remission, crizotinib discontinuation causes rapid disease relapses due to the expansion of persister lymphoma cells never completely eradicated by the ALK inhibitor. There is, in fact, growing evidence that ALK+ ALCL can persist for years in patients being undetectable. ALCL grows around blood and lymphatic vessels in the lymph node. We hypothesize that this perivascular niche provides pro-survival signals contributing to ALK+ ALCL persistence and TKI resistance. By RNA-seq analysis on ALK+ ALCL cells and scRNA-seq analysis in one ALK+ ALCL primary sample, we found that ALK+ cells expressed the C-C chemokine receptor type 7 (CCR7), while endothelial cells and fibroblasts expressed the unique CCR7 ligands, the chemokine (C-C motif) ligand 19 (CCL19) and 21 (CCL21). Therefore, we explored whether the CCL19/21-CCR7 chemokine-receptor signaling axis could be involved in the persistence of ALK+ ALCL cells during ALK inhibitor treatment. We show that treatment with crizotinib caused upregulation of CCR7 in ALK+ ALCL cells via STAT3, as demonstrated by ChIP-seq data. Besides, stimulation of ALK+ ALCL cells with both CCL19/21 potently activated the MAPK signaling and sustained MAPK activation during ALK inhibition by crizotinib. Mechanistically, we demonstrate that this MAPK activation was mediated by PI3Kγ-dependent CCR7 signaling. This effect was more marked in human ALK+ ALCL cells that express high levels of PI3Kγ, while it was strongly reduced in murine lymphoma PI3KγKO cells, generated from NPM-ALK transgenic mice crossed with PI3KγKO mice. Treatment with the PI3Kγ/δ dual inhibitor duvelisib abrogated the MAPK phosphorylation induced by CCL19/21. When we knocked-out the CCR7 gene via CRISPR/Cas9, human ALK+ ALCL showed markedly reduced activation of the MAPK pathway upon stimulation with CCL19/21. Next, we developed a microphysiological model of ALCL cells in the perivascular niche with a 3D vasculature using a microfluidic chip. In this model, ALCL cells circulate inside the chip in continuous contact with a perfusable vasculature. We, then, demonstrated that the presence of endothelial cells conferred resistance to crizotinib and sustained cell viability of CCR7WT cells, whereas the protective effect was lost in CCR7KO cells. In in vivo experiments, CCR7 was required for lymphoma cell survival and diffusion to the brain during crizotinib treatment. Overall, our results suggest that the perivascular niche could promote the survival of ALK+ ALCL persister cells and protect them from the effect of ALK TKIs via the CCL19/21-CCR7 axis. The disruption of this survival axis could contribute to eradicating minimal residual disease in combination with ALK TKI.

Citation Format: Cristina Mastini, Marco Campisi, Carlotta Costa, Chiara Ambrogio, Giulia Germena, Silvia Peola, Cinzia Martinengo, Enrico Patrucco, Ines Mota, Maddalena Arrigoni, Martina Olivero, Raffaele Calogero, Valeria Chiono, Roger D. Kamm, Emilio Hirsch, Jon C. Aster, Claudia Voena, Roberto Chiarle. The perivascular niche protects ALK+ lymphoma cells from ALK inhibition through the CCL19/21-CCR7 axis [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr LT018.

Abstract PO-50: Phophatases modulate resistance to ALK inhibitors in anaplastic large-cell lymphoma

Introduction: Anaplastic large-cell lymphomas (ALCL) frequently carry oncogenic fusions involving the anaplastic lymphoma kinase (ALK) gene. The ALK fusions activate several signaling pathways, promoting cell growth, migration, and survival. Chemotherapy is the standard treatment for ALCL patients, but about 30% of patients relapse. Targeting ALK using tyrosine kinase inhibitors (TKIs) has shown promising results, and the FDA recently granted breakthrough therapy designation to crizotinib for use in patients with relapsed/refractory ALK+ ALCL. However, resistance to crizotinib develops in ALK+ ALCL patients secondary to ALK mutations or unknown mechanisms. In this study, we aimed at elucidating unknown bypass mechanisms of crizotinib resistance in ALK+ ALCL.

Methods: We used Genome-wide CRISPR-Cas9 Knockout Screening (GeCKO.v2) to identify candidate genes that contribute to resistance to crizotinib. Four different ALCL cell lines were infected with Lenti-GeCKO libraries. After treatment with crizotinib for 14 days to select for resistant cells, next-generation sequencing was performed on crizotinib-resistant cells to identify candidate resistance genes. Top candidates were selected for validation assays and further analyses.

Results: Genomic loss-of-function screens identified two phosphatases, PTPN1 and PTPN2, in all ALCL cell lines as consistent top hits driving resistance to crizotinib. Functional validation of these candidate genes showed that single loss of either PTPN1 or PTPN2 generates immediate resistance to crizotinib and other ALK TKIs such as alectinib and lorlatinib. Consistently, RNA-seq in patients who developed resistance to crizotinib showed downregulation of PTPN1 or PTPN2 expression. By multiple assays, we demonstrate that PTPN1 and PTPN2 are phosphatases that de-phosphorylate ALK, thereby regulating its overall phosphorylation levels and activity. In addition, we found that PTPN1, but not PTPN2, is also a phosphatase of SHP2, a key mediator of oncogenic ALK signaling. Downstream signaling analysis showed that deletion of PTPN1 or PTPN2 induces resistance to crizotinib by hyperactivating the MAPK and JAK/STAT pathways. A treatment that combined crizotinib and a recently developed SHP2 inhibitor (SHP099) completely blocked the sustained MAPK activation and reverted crizotinib resistance in vitro and in vivo.

Conclusions: We discovered that PTPN1 and PTPN2 are ALK phosphatases that control sensitivity to ALK TKIs in ALCL. Combined inhibition of SHP2 is a potential therapeutic approach to overcome resistance to ALK TKIs in ALCL.

Citation Format: Elif Atabay, Qi Wang, Taek-Chin Cheong, Nina Prokoph, Chiara Ambrogio, Ines Mota, Achille Pich, Enrico Patrucco, Claudia Voena, Roberto Chiarle. Phophatases modulate resistance to ALK inhibitors in anaplastic large-cell lymphoma [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-50.

Abstract PO-17: Microphysiologic model of ALK+ anaplastic large cell lymphoma and vascular interactions predicts drug efficacy in a 3D microfluidic chip

Anaplastic large-cell lymphoma (ALCL) initially responds well to anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitor (TKI) therapies (e.g., crizotinib); however, resistance appears once the treatment is concluded and persistent cells are not eradicated. ALCL preferentially grows around blood and lymphatic vessel in the lymph node, and our preliminary data have shown that CCL19/21-CCR7 chemokine-receptor signaling axis might be involved in TKI resistance of ALCL cells. To investigate this mechanism, we developed a microphysiologic model of ALCL interacting with a 3D vasculature using a microfluidic chip. Microfluidic technology has the potential to impact cancer diagnosis and therapy by overcoming the limitations of 2D culture. These ex vivo models are able to uncover the continuous interactions and chemokine signaling that exist between cells of the tumor microenvironment (TME) and evaluate the preclinical efficacy of novel and personalized cancer therapeutics. Two ALK+ ALCL cell lines (COST and Karpas299) were knocked out by CRISPR/Cas9 of the CCR7 receptor, transduced with GFP for microscopic visualization. A commercial microfluidic chip with a central gel channel, flanked by two fluidic media channels, was used to develop the model. A collagen hydrogel (2.5 mg/mL) was injected into the central region of the 3D chip, incubated in sterile humidity chambers, and channels were hydrated with RPMI. 50 µL of 3x106 cells/mL human umbilical vein endothelial cells (HUVECs) suspension was injected twice on the fluidic channel, and the chip was rotated twice to create a confluent hollow-lumen 3D macrovessel. Then, 2x105 cells/mL ALCL cells were added inside the 3D macrovessel. Medium was refreshed daily, supplemented +/- 300 nM crizotinib (ALK TKI). Image analysis was performed using a confocal microscope. The model consisted of a well-formed perfusable macrovessel with ALCL cells flowing inside and interacting with HUVECs. ALCL viability was evaluated with a luminescent readout assay after 3 days of interactions with HUVECs. Strikingly, ALCL cells cultivated within the vasculature showed marked resistance to treatment with ALK TKI compared to cells cultivated in the absence of vessels. CCR7 KO cells showed decreased viability and decreased perivascular localization compared to wild-type control cells. The results suggest that the 3D ALCL-vascular microphysiologic model is a feasible platform with great potential to unveil the molecular mechanisms of drug resistance in a complex TME. The presence of macrovessels was sufficient to induce resistance to ALK TKI, which was decreased in CCR7 KO cells. These data indicate that CCL19/21 and possibly other cytokines produced by vessels generate survival signals in ALCL cells treated with ALK TKI. This physiologically relevant ALCL-vascular model offers a tool to genetically dissect the TME contribution to drug resistance, predict more reliably therapeutic vulnerabilities, and recapitulate patient-specific cell-cell interactions.

Citation Format: Marco Campisi, Claudia Voena, Ines Mota, Enrico Patrucco, Roger Dale Kamm, Roberto Chiarle. Microphysiologic model of ALK+ anaplastic large cell lymphoma and vascular interactions predicts drug efficacy in a 3D microfluidic chip [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-17.

Complete and prolonged response to anti-PD1 therapy in an ALK rearranged lung adenocarcinoma

OBJECTIVE

Immune checkpoint inhibitors (ICI) have become a major treatment in advanced non small cell lung cancer (NSCLC). However, some patients do not benefit from ICI, especially those harboring an ALK rearrangement. Here, we report a case of prolonged complete tumor response to immunotherapy in an ALK-rearranged NSCLC patient.

MATERIALS AND METHODS

We verify ALK expression and rearrangement on formalin-fixed paraffin-embedded tumor samples of the patient by Immunohistochemistry and Fluorescence In Situ Hybridization analysis. The patient provided written informed consent authorizing publication of clinical case.

RESULTS

We report the case of 48 years old man with a ALK-rearranged NSCLC. This patient displayed a complete response for 16 months under nivolumab therapy in third line setting after ceritinib and platin based chemotherapy.

CONCLUSION

This is the first case of complete and prolonged response to ICI in ALK rearranged NSCLC. This case supports the idea that some ALK rearranged NSCLC could durably benefit from immunotherapy.

Comment on "ALK is a therapeutic target for lethal sepsis"

Physiologically relevant ALK (anaplastic lymphoma kinase) expression was not detected in human and mouse monocytes and macrophages, suggesting that the effects of bioactive compounds on stimulator of interferon genes (STING) activation may not depend on ALK.

Tumor Resistance against ALK Targeted Therapy-Where It Comes From and Where It Goes

Anaplastic lymphoma kinase (ALK) is a validated molecular target in several ALK-rearranged malignancies, particularly in non-small-cell lung cancer (NSCLC), which has generated considerable interest and effort in developing ALK tyrosine kinase inhibitors (TKI). Crizotinib was the first ALK inhibitor to receive FDA approval for ALK-positive NSCLC patients treatment. However, the clinical benefit observed in targeting ALK in NSCLC is almost universally limited by the emergence of drug resistance with a median of occurrence of approximately 10 months after the initiation of therapy. Thus, to overcome crizotinib resistance, second/third-generation ALK inhibitors have been developed and received, or are close to receiving, FDA approval. However, even when treated with these new inhibitors tumors became resistant, both in vitro and in clinical settings. The elucidation of the diverse mechanisms through which resistance to ALK TKI emerges, has informed the design of novel therapeutic strategies to improve patients disease outcome. This review summarizes the currently available knowledge regarding ALK physiologic function/structure and neoplastic transforming role, as well as an update on ALK inhibitors and resistance mechanisms along with possible therapeutic strategies that may overcome the development of resistance.

Beta-adrenergic regulation of the heart expressing the Ser1700A/Thr1704A mutated Cav1.2 channel

Beta-adrenergic stimulation of the heart increases I_Ca. PKA dependent phosphorylation of several amino acids (among them Ser 1700 and Thr 1704 in the carboxy-terminus of the Cav1.2 α₁c subunit) has been implicated as decisive for the β-adrenergic up-regulation of cardiac I_Ca. Mutation of Ser 1700 and Thr 1704 to alanine results in the Cav1.2PKA_P2^-/- mice. Cav1.2PKA_P2^-/- mice display reduced cardiac L-type current. Fractional shortening and ejection fraction in the intact animal and I_Ca in isolated cardiomyocytes (CM) are stimulated by isoproterenol. Cardiac specific expression of the mutated Cav1.2PKA_P2^-/- gene reduces Cav1.2 α₁c protein concentration, I_Ca, and the β-adrenergic stimulation of L-type I_Ca in CMs. Single channels were not detected on the CM surface of the cCav1.2PKA_P2^-/- hearts. This outcome supports the notion that S1700/1704 is essential for expression of the Cav1.2 channel and that isoproterenol stimulates I_Ca in Cav1.2PKA_P2^-/- CMs.

cAMP-specific phosphodiesterases 8A and 8B, essential regulators of Leydig cell steroidogenesis

Phosphodiesterase (PDE) 8A and PDE8B are high-affinity, cAMP-specific phosphodiesterases that are highly expressed in Leydig cells. PDE8A is largely associated with mitochondria, whereas PDE8B is broadly distributed in the cytosol. We used a new, PDE8-selective inhibitor, PF-04957325, and genetically ablated PDE8A(-/-), PDE8B(-/-) and PDE8A(-/-)/B(-/-) mice to determine roles for these PDEs in the regulation of testosterone production. PF-04957325 treatment of WT Leydig cells or MA10 cells increased steroid production but had no effect in PDE8A (-/-)/B(-/-) double-knockout cells, confirming the selectivity of the drug. Moreover, under basal conditions, cotreatment with PF-04957325 plus rolipram, a PDE4-selective inhibitor, synergistically potentiated steroid production. These results suggest that the pool(s) of cAMP regulating androgen production are controlled by PDE8s working in conjunction with PDE4. Likewise, PDE8A (-/-)/B(-/-) cells had higher testosterone production than cells from either PDE8A(-/-) or PDE8B(-/-) mice, suggesting that both PDE8s work in concert to regulate steroid production. We further demonstrate that combined inhibition of PDE8s and PDE4 greatly increased PKA activity including phosphorylation of cholesterol-ester hydrolase (CEH)/hormone-sensitive lipase (HSL). CEH/HSL phosphorylation also was increased in PDE8A(-/-)/B(-/-) cells compared with WT cells. Finally, combined inhibition of PDE8s and PDE4 increased the expression of steroidogenic acute regulatory (StAR) protein. Together these findings suggest that both PDE8A and PDE8B play essential roles to maintain low cAMP levels, thereby suppressing resting steroidogenesis by keeping CEH/HSL inactive and StAR protein expression low. They also suggest that in order for PDE inhibitor therapy to be an effective stimulator of steroidogenesis, both PDE8 isozymes and PDE4 need to be simultaneously targeted.

Sildenafil reverses cardiac dysfunction in the mdx mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive and fatal genetic disorder of muscle degeneration. Patients with DMD lack expression of the protein dystrophin as a result of mutations in the X-linked dystrophin gene. The loss of dystrophin leads to severe skeletal muscle pathologies as well as cardiomyopathy, which manifests as congestive heart failure and arrhythmias. Like humans, dystrophin-deficient mice (mdx mice) show cardiac dysfunction as evidenced by a decrease in diastolic function followed by systolic dysfunction later in life. We have investigated whether sildenafil citrate (Viagra), a phosphodiesterase 5 (PDE5) inhibitor, can be used to ameliorate the age-related cardiac dysfunction present in the mdx mice. By using echocardiography, we show that chronic sildenafil treatment reduces functional deficits in the cardiac performance of aged mdx mice, with no effect on normal cardiac function in WT controls. More importantly, when sildenafil treatment was started after cardiomyopathy had developed, the established symptoms were rapidly reversed within a few days. It is recognized that PDE5 inhibitors can have cardioprotective effects in other models of cardiac damage, but the present study reports a prevention and reversal of pathological cardiac dysfunction as measured by functional analysis in a mouse model of DMD. Overall, the data suggest that PDE5 inhibitors may be a useful treatment for the cardiomyopathy affecting patients with DMD at early and late stages of the disease.

Phosphodiesterase 8A (PDE8A) regulates excitation-contraction coupling in ventricular myocytes

In ventricular myocytes, activation of protein kinase A (PKA) by 3'-5' cyclic adenosine monophosphate (cAMP) increases the force of contraction by increasing L-type Ca(2+) channel currents (I(Ca)) and sarcoplasmic reticulum (SR) Ca(2+) release during excitation-contraction coupling. Cyclic-nucleotide phosphodiesterases (PDEs) comprise a large family of enzymes whose role in the cell is to regulate the spatial and temporal profile of cAMP signals by controlling the degradation of this second messenger. At present, however, the molecular identity and functional roles of the PDEs expressed in ventricular myocytes are incompletely understood. Here, we tested the hypothesis that PDE8A plays a critical role in the modulation of at least one compartment of cAMP and hence PKA activity during beta-adrenergic receptor (betaAR) activation in ventricular myocytes. Consistent with this hypothesis, we found that PDE8A transcript and protein are expressed in ventricular myocytes. Our data indicate that evoked [Ca(2+)](i) transients and I(Ca) increased to a much larger extent in PDE8A null (PDE8A(-/-)) than in wild-type (WT) myocytes during beta-adrenergic signaling activation. In addition, Ca(2+) spark activity was higher in PDE8A(-/-) than in WT myocytes. Our data indicate that PDE8A is a novel cardiac PDE that controls one or more pools of cAMP implicated in regulation of Ca(2+) movement through cardiomyocyte.

Negative feedback regulation of Rac in leukocytes from mice expressing a constitutively active phosphatidylinositol 3-kinase gamma

Polarization of chemotaxing cells depends on positive feedback loops that amplify shallow gradients of chemoattractants into sharp intracellular responses. In particular, reciprocal activation of phosphatidylinositol 3-kinases (PI3Ks) and small GTPases like Rac leads to accumulation, at the leading edge, of the PI3K product phosphatidylinositol 3,4,5-trisphosphate (PIP3). Mice carrying a "knockin" allele of the G protein-coupled receptor (GPCR)-activated PI3Kgamma, encoding a plasma membrane-targeted protein appeared normal, but their leukocytes showed GPCR-uncoupled PIP3 accumulation. In vivo, the mutation increased proliferation and decreased apoptosis, leading to leukocytosis and delayed resolution of inflammation in wound healing. Mutant leukocytes showed significantly impaired directional cell migration in response to chemoattractants. Stimulated mutant macrophages did not polarize PIP3 and showed a shortened Rac activation because of enhanced PI3K-dependent activation of RacGAPs. Together with the finding that chemoattractants stimulate a PIP3-dependent GAP activation in wild-type macrophages, these results identify a molecular mechanism involving PI3K- and RacGAP-dependent negative control of Rac that limits and fine-tunes feedback loops promoting cell polarization and directional motility.

Lack of phosphoinositide 3-kinase-gamma attenuates ventilator-induced lung injury

OBJECTIVE

G protein-coupled receptors may up-regulate the inflammatory response elicited by ventilator-induced lung injury but also regulate cell survival via protein kinase B (Akt) and extracellular signal regulated kinases 1/2 (ERK1/2). The G protein-sensitive phosphoinositide-3-kinase gamma (PI3Kgamma) regulates several cellular functions including inflammation and cell survival. We explored the role of PI3Kgamma on ventilator-induced lung injury.

DESIGN

Prospective, randomized, experimental study.

SETTING

University animal research laboratory.

SUBJECTS

Wild-type (PI3Kgamma), knock-out (PI3Kgamma ), and kinase-dead (PI3Kgamma) mice.

INTERVENTIONS

Three ventilatory strategies (no stretch, low stretch, high stretch) were studied in an isolated, nonperfused model of acute lung injury (lung lavage) in PI3Kgamma, PI3Kgamma, and PI3Kgamma mice.

MEASUREMENTS AND MAIN RESULTS

Reduction in lung compliance, hyaline membrane formation, and epithelial detachment with high stretch were more pronounced in PI3Kgamma than in PI3Kgamma and PI3Kgamma (p < .01). Inflammatory cytokines and IkBalpha phosphorylation with high stretch did not differ among PI3Kgamma, PI3Kgamma, and PI3Kgamma. Apoptotic index (terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling) and caspase-3 (immunohistochemistry) with high stretch were larger (p < .01) in PI3Kgamma and PI3Kgamma than in PI3Kgamma. Electron microscopy showed that high stretch caused apoptotic changes in alveolar cells of PI3Kgamma mice whereas PI3Kgamma mice showed necrosis. Phosphorylation of Akt and ERK1/2 with high stretch was more pronounced in PI3Kgamma than in PI3Kgamma and PI3Kgamma (p < .01).

CONCLUSIONS

Silencing PI3Kgamma seems to attenuate functional and morphological consequences of ventilator-induced lung injury independently of inhibitory effects on cytokines release but through the enhancement of pulmonary apoptosis.

Protection from angiotensin II-mediated vasculotoxic and hypertensive response in mice lacking PI3Kgamma

Hypertension affects nearly 20% of the population in Western countries and strongly increases the risk for cardiovascular diseases. In the pathogenesis of hypertension, the vasoactive peptide of the renin-angiotensin system, angiotensin II and its G protein–coupled receptors (GPCRs), play a crucial role by eliciting reactive oxygen species (ROS) and mediating vessel contractility. Here we show that mice lacking the GPCR-activated phosphoinositide 3-kinase (PI3K)γ are protected from hypertension that is induced by administration of angiotensin II in vivo. PI3Kγ was found to play a role in angiotensin II–evoked smooth muscle contraction in two crucial, distinct signaling pathways. In response to angiotensin II, PI3Kγ was required for the activation of Rac and the subsequent triggering of ROS production. Conversely, PI3Kγ was necessary to activate protein kinase B/Akt, which, in turn, enhanced L-type Ca²⁺ channel–mediated extracellular Ca²⁺ entry. These data indicate that PI3Kγ is a key transducer of the intracellular signals that are evoked by angiotensin II and suggest that blocking PI3Kγ function might be exploited to improve therapeutic intervention on hypertension.

Phosphoinositide 3-kinase gamma controls autonomic regulation of the mouse heart through Gi-independent downregulation of cAMP level

Cardiac beta-adrenergic and the muscarinic receptors control contractility and heart rate by triggering multiple signaling events involving downstream targets like the phosphoinositide 3-kinase gamma (PI3Kgamma). We thus investigated whether the lack of PI3Kgamma could play a role in the autonomic regulation of the mouse heart. Contractility and ICaL of mutant cardiac preparations appeared increased in basal conditions and after beta-adrenergic stimulation. However, basal and beta-adrenergic stimulated heart rate were normal. Conversely, muscarinic inhibition of heart rate was reduced without alteration of the Gbetagamma-dependent stimulation of IK,ACh current. In addition, muscarinic-mediated anti-adrenergic effect on papillary muscle contractility and ICaL was significantly depressed. Consistently, cAMP level of PI3Kgamma-null ventricles was always higher than wild-type controls. Thus, PI3Kgamma controls the cardiac function by reducing cAMP concentration independently of Gi-mediated signaling.

Ablation of phosphoinositide 3-kinase-gamma reduces the severity of acute pancreatitis

In pancreatic acini, the G-protein-activated phosphoinositide 3-kinase-gamma (PI3K gamma) regulates several key pathological responses to cholecystokinin hyperstimulation in vitro. Thus, using mice lacking PI3K gamma, we studied the function of this enzyme in vivo in two different models of acute pancreatitis. The disease was induced by supramaximal concentrations of cerulein and by feeding mice a choline-deficient/ethionine-supplemented diet. Although the secretive function of isolated pancreatic acini was identical in mutant and control samples, in both models, genetic ablation of PI3K gamma significantly reduced the extent of acinar cell injury/necrosis. In agreement with a protective role of apoptosis in pancreatitis, PI3K gamma-deficient pancreata showed an increased number of apoptotic acinar cells, as determined by terminal dUTP nick-end labeling and caspase-3 activity. In addition, neutrophil infiltration within the pancreatic tissue was also reduced, suggesting a dual action of PI3K gamma, both in the triggering events within acinar cells and in the subsequent neutrophil recruitment and activation. Finally, the lethality of the choline-deficient/ethionine-supplemented diet-induced pancreatitis was significantly reduced in mice lacking PI3K gamma. Our results thus suggest that inhibition of PI3K gamma may be of therapeutic value in acute pancreatitis.

PI3Kgamma modulates the cardiac response to chronic pressure overload by distinct kinase-dependent and -independent effects

The G protein-coupled, receptor-activated phosphoinositide 3-kinase gamma (PI3Kgamma) mediates inflammatory responses and negatively controls cardiac contractility by reducing cAMP concentration. Here, we report that mice carrying a targeted mutation in the PI3Kgamma gene causing loss of kinase activity (PI3KgammaKD/KD) display reduced inflammatory reactions but no alterations in cardiac contractility. We show that, in PI3KgammaKD/KD hearts, cAMP levels are normal and that PI3Kgamma-deficient mice but not PI3KgammaKD/KD mice develop dramatic myocardial damage after chronic pressure overload induced by transverse aortic constriction (TAC). Finally, our data indicate that PI3Kgamma is an essential component of a complex controlling PDE3B phosphodiesterase-mediated cAMP destruction. Thus, cardiac PI3Kgamma participates in two distinct signaling pathways: a kinase-dependent activity that controls PKB/Akt as well as MAPK phosphorylation and contributes to TAC-induced cardiac remodeling, and a kinase-independent activity that relies on protein interactions to regulate PDE3B activity and negatively modulates cardiac contractility.

Analysis of the murine phosphoinositide 3-kinase gamma gene

Phosphoinositide 3-kinase gamma is preferentially expressed in leukocytes. PI3Kgamma is activated by betagamma subunits of heterotrimeric G-proteins, which thus link seven transmembrane helix receptor activation to phosphatidylinositol (3,4,5)-trisphosphate production. Here we describe the molecular cloning of the murine PI3Kgamma cDNA, the PI3Kgamma gene structure, its chromosomal assignment and the analysis of promoter activity. The mouse cDNA shares 86% identity to its pig and human orthologues at the nucleotide level. The MmPI3Kgamma gene spans approximately 30kb and comprises 11 exons. RACE-PCR indicated the presence of multiple start sites generating 5' UTRs with different lengths, the longest being 874bp. The putative promoter region contains no TATA box but several putative binding sites for hematopoietic specific transcription factors. A 1200bp long sequence upstream the first transcription start site was found to possess tissue specific promoter activity. Deletion constructs revealed two contiguous regions, with activator function, ranging from positions -139 to -557, and with inhibitory function, ranging from positions -557 to -892. FISH analysis revealed that the MmPI3Kgamma is located on chromosome 12 band B and that the human orthologue is positioned on chromosome 7q22.2-22.3. In spite of some differences in the ATP-binding site, recombinant murine PI3Kgamma protein is equally sensitive to wortmannin as its human counterpart. This suggests that mouse models will provide reliable results in the assessments of novel PI3Kgamma inhibitors.

Defective recovery and severe renal damage after acute hemolysis in hemopexin-deficient mice

Hemopexin (Hx) is a plasma glycoprotein mainly expressed in liver and, less abundantly, in the central and peripheral nervous systems. Hx has a high binding affinity with heme and is considered to be a major transport vehicle of heme into the liver, thus preventing both heme-catalyzed oxidative damage and heme-bound iron loss. To determine the physiologic relevance of heme-Hx complex formation, Hx-deficient mice were generated by homologous recombination in embryonic stem (ES) cells. The Hx-deficient mice were viable and fertile. Their plasma iron level and blood parameters were comparable to those of control mice and they showed no evidence of tissue lesions caused by oxidative damage or abnormal iron deposits. Moreover, they were sensitive to acute hemolysis, as are wild-type mice. Nevertheless, Hx-null mice recovered more slowly after hemolysis and were seen to have more severe renal damage than controls. After hemolytic stimulus, Hx-deficient mice presented prolonged hemoglobinuria with a higher kidney iron load and higher lipid peroxidation than control mice. Moreover, Hx-null mice showed altered posthemolysis haptoglobin (Hp) turnover in as much as Hp persisted in the circulation after hemolytic stimulus. These data indicate that, although Hx is not crucial either for iron metabolism or as a protection against oxidative stress under physiologic conditions, it does play an important protective role after hemolytic processes.

Multiple transcription start sites of the carrot dihydrofolate reductase-thymidylate synthase gene, and sub-cellular localization of the bifunctional protein

The analysis of clones obtained by rapid amplification of the 5' end and by primer extension of the mRNA for carrot bifunctional dihydrofolate reductase-thymidylate synthase showed transcripts of differing lengths that belonged to two sub-populations. The longer transcripts were found to contain a translation start site 147 nt upstream of, and in frame with, the one which is present in the shorter transcripts. The ORF that begins at this ATG codes for a protein of 64714 Da, which is much larger than mature DHFR-TS subunit. The N-terminus region of this polypeptide shows features typical of plant transit peptides. Immunogold labelling studies and immunorecognition of the plastid-containing sub-cellular fraction suggested a plastidial localisation of the bifunctional protein. Although plant cells were shown to contain folate pools in plastids, in mitochondria and in the cytosol, few enzymes of the folate pathway have been associated with any sub-cellular compartment. Thus, this is the first indication for the presence of an enzyme of the folate biosynthetic pathway in plastids. The longer transcripts revealed the presence of a TC microsatellite at the 5'-untranslated end.