Extracellular stiffness induces contractile dysfunction in adult cardiomyocytes via cell-autonomous and microtubule-dependent mechanisms.

The mechanical environment of the myocardium has a potent effect on cardiomyocyte form and function, yet an understanding of the cardiomyocyte responses to extracellular stiffening remains incomplete. We therefore employed a cell culture substrate with tunable stiffness to define the cardiomyocyte responses to clinically relevant stiffness increments in the absence of cell-cell interactions. When cultured on substrates magnetically actuated to mimic the stiffness of diseased myocardium, isolated rat adult cardiomyocytes exhibited a time-dependent reduction of sarcomere shortening, characterized by slowed contraction and relaxation velocity, and alterations of the calcium transient. Cardiomyocytes cultured on stiff substrates developed increases in viscoelasticity and microtubule detyrosination in association with early increases in the α-tubulin detyrosinating enzyme vasohibin-2 (Vash2). We found that knockdown of Vash2 was sufficient to preserve contractile performance as well as calcium transient properties in the presence of extracellular substrate stiffening. Orthogonal prevention of detyrosination by overexpression of tubulin tyrosine ligase (TTL) was also able to preserve contractility and calcium homeostasis. These data demonstrate that a pathologic increment of extracellular stiffness induces early, cell-autonomous remodeling of adult cardiomyocytes that is dependent on detyrosination of α-tubulin.

Truncated titin proteins in dilated cardiomyopathy.

Truncating variants in TTN (TTNtvs) are the most common known cause of nonischemic dilated cardiomyopathy (DCM), but how TTNtvs cause disease has remained controversial. Efforts to detect truncated titin proteins in affected human DCM hearts have failed, suggesting that disease is caused by haploinsufficiency, but reduced amounts of titin protein have not yet been demonstrated. Here, we leveraged a collection of 184 explanted posttransplant DCM hearts to show, using specialized electrophoretic gels, Western blotting, allelic phasing, and unbiased proteomics, that truncated titin proteins can quantitatively be detected in human DCM hearts. The sizes of truncated proteins corresponded to that predicted by their respective TTNtvs; the truncated proteins were encoded by the TTNtv-bearing allele; and no degradation fragments from protein encoded by either allele were detectable. In parallel, full-length titin was less abundant in TTNtv+ than in TTNtv− DCM hearts. Disease severity or need for transplantation did not correlate with TTNtv location. Transcriptomic profiling revealed few differences in splicing or allelic imbalance of the TTN transcript between TTNtv+ and TTNtv− DCM hearts. Studies with isolated human adult cardiomyocytes revealed no defects in contractility in cells from TTNtv+ compared to TTNtv− DCM hearts. Together, these data demonstrate the presence of truncated titin protein in human TTNtv+ DCM, show reduced amounts of full-length titin protein in TTNtv+ DCM hearts, and support combined dominant-negative and haploinsufficiency contributions to disease.

Genetic and Phenotypic Landscape of Peripartum Cardiomyopathy.

BACKGROUND: Peripartum cardiomyopathy (PPCM) occurs in ≈1:2000 deliveries in the United States and worldwide. The genetic underpinnings of PPCM remain poorly defined. Approximately 10% of women with PPCM harbor truncating variants in TTN (TTNtvs). Whether mutations in other genes can predispose to PPCM is not known. It is also not known if the presence of TTNtvs predicts clinical presentation or outcomes. Nor is it known if the prevalence of TTNtvs differs in women with PPCM and preeclampsia, the strongest risk factor for PPCM. METHODS: Women with PPCM were retrospectively identified from several US and international academic centers, and clinical information and DNA samples were acquired. Next-generation sequencing was performed on 67 genes, including TTN, and evaluated for burden of truncating and missense variants. The impact of TTNtvs on the severity of clinical presentation, and on clinical outcomes, was evaluated. RESULTS: Four hundred sixty-nine women met inclusion criteria. Of the women with PPCM, 10.4% bore TTNtvs (odds ratio=9.4 compared with 1.2% in the reference population; Bonferroni-corrected P [P*]=1.2×10-46). We additionally identified overrepresentation of truncating variants in FLNC (odds ratio=24.8, P*=7.0×10-8), DSP (odds ratio=14.9, P*=1.0×10-8), and BAG3 (odds ratio=53.1, P*=0.02), genes not previously associated with PPCM. This profile is highly similar to that found in nonischemic dilated cardiomyopathy. Women with TTNtvs had lower left ventricular ejection fraction on presentation than did women without TTNtvs (23.5% versus 29%, P=2.5×10-4), but did not differ significantly in timing of presentation after delivery, in prevalence of preeclampsia, or in rates of clinical recovery. CONCLUSIONS: This study provides the first extensive genetic and phenotypic landscape of PPCM and demonstrates that predisposition to heart failure is an important risk factor for PPCM. The work reveals a degree of genetic similarity between PPCM and dilated cardiomyopathy, suggesting that gene-specific therapeutic approaches being developed for dilated cardiomyopathy may also apply to PPCM, and that approaches to genetic testing in PPCM should mirror those taken in dilated cardiomyopathy. Last, the clarification of genotype/phenotype associations has important implications for genetic counseling.

PPT1 Promotes Tumor Growth and Is the Molecular Target of Chloroquine Derivatives in Cancer.

Clinical trials repurposing lysosomotropic chloroquine (CQ) derivatives as autophagy inhibitors in cancer demonstrate encouraging results, but the underlying mechanism of action remains unknown. Here, we report a novel dimeric CQ (DC661) capable of deacidifying the lysosome and inhibiting autophagy significantly better than hydroxychloroquine (HCQ). Using an in situ photoaffinity pulldown strategy, we identified palmitoyl-protein thioesterase 1 (PPT1) as a molecular target shared across monomeric and dimeric CQ derivatives. HCQ and Lys05 also bound to and inhibited PPT1 activity, but only DC661 maintained activity in acidic media. Knockout of PPT1 in cancer cells using CRISPR/Cas9 editing abrogates autophagy modulation and cytotoxicity of CQ derivatives, and results in significant impairment of tumor growth similar to that observed with DC661. Elevated expression of PPT1 in tumors correlates with poor survival in patients in a variety of cancers. Thus, PPT1 represents a new target in cancer that can be inhibited with CQ derivatives. SIGNIFICANCE: This study identifies PPT1 as the previously unknown lysosomal molecular target of monomeric and dimeric CQ derivatives. Genetic suppression of PPT1 impairs tumor growth, and PPT1 levels are elevated in cancer and associated with poor survival. These findings provide a strong rationale for targeting PPT1 in cancer. This article is highlighted in the In This Issue feature, p. 151.

ALDH1A1 and HLTF modulate the activity of lysosomal autophagy inhibitors in cancer cells.

Lysosomal autophagy inhibitors (LAI) such as hydroxychloroquine (HCQ) have significant activity in a subset of cancer cell lines. LAIs are being evaluated in cancer clinical trials, but genetic determinants of sensitivity to LAIs are unknown, making it difficult to predict which tumors would be most susceptible. Here we characterize differentially expressed genes in HCQ-sensitive (-S) and -resistant (-R) cancer cells. Notably, expression of canonical macroautophagy/autophagy genes was not associated with sensitivity to HCQ. Expression patterns of ALDH1A1 (aldehyde dehydrogenase 1 family member A1) and HLTF (helicase like transcription factor) identified HCQ-S (ALDH1A1high HLTFlow; ALDH1A1low HLTFlow) and HCQ-R (ALDH1A1low HLTFhigh) cells. ALDH1A1 overexpression was found to enhance LAI cell entry and cytotoxicity without directly affecting lysosome function or autophagic flux. Expression of HLTF allows repair of DNA damage caused by LAI-induced reactive oxygen species, leading to HCQ resistance. Sensitivity to HCQ is increased in cells where HLTF is silenced by promoter methylation. HLTF overexpression blunted the antitumor efficacy of chloroquine derivatives in vitro and in vivo. Analysis of tumor RNA sequencing data from >700 patients in the Cancer Genome Atlas identified cancers including colon cancer, renal cell carcinoma, and gastric cancers, that were enriched for the HCQ-S or HCQ-R signature. These results provide mechanistic insights into LAI efficacy, and guidance for LAI clinical development.

A Unified Approach to Targeting the Lysosome's Degradative and Growth Signaling Roles.

Lysosomes serve dual roles in cancer metabolism, executing catabolic programs (i.e., autophagy and macropinocytosis) while promoting mTORC1-dependent anabolism. Antimalarial compounds such as chloroquine or quinacrine have been used as lysosomal inhibitors, but fail to inhibit mTOR signaling. Further, the molecular target of these agents has not been identified. We report a screen of novel dimeric antimalarials that identifies dimeric quinacrines (DQ) as potent anticancer compounds, which concurrently inhibit mTOR and autophagy. Central nitrogen methylation of the DQ linker enhances lysosomal localization and potency. An in situ photoaffinity pulldown identified palmitoyl-protein thioesterase 1 (PPT1) as the molecular target of DQ661. PPT1 inhibition concurrently impairs mTOR and lysosomal catabolism through the rapid accumulation of palmitoylated proteins. DQ661 inhibits the in vivo tumor growth of melanoma, pancreatic cancer, and colorectal cancer mouse models and can be safely combined with chemotherapy. Thus, lysosome-directed PPT1 inhibitors represent a new approach to concurrently targeting mTORC1 and lysosomal catabolism in cancer.Significance: This study identifies chemical features of dimeric compounds that increase their lysosomal specificity, and a new molecular target for these compounds, reclassifying these compounds as targeted therapies. Targeting PPT1 blocks mTOR signaling in a manner distinct from catalytic inhibitors, while concurrently inhibiting autophagy, thereby providing a new strategy for cancer therapy. Cancer Discov; 7(11); 1266-83. ©2017 AACR.See related commentary by Towers and Thorburn, p. 1218This article is highlighted in the In This Issue feature, p. 1201.

A phase I/II trial of hydroxychloroquine in conjunction with radiation therapy and concurrent and adjuvant temozolomide in patients with newly diagnosed glioblastoma multiforme.

Preclinical studies indicate autophagy inhibition with hydroxychloroquine (HCQ) can augment the efficacy of DNA-damaging therapy. The primary objective of this trial was to determine the maximum tolerated dose (MTD) and efficacy of HCQ in combination with radiation therapy (RT) and temozolomide (TMZ) for newly diagnosed glioblastoma (GB). A 3 + 3 phase I trial design followed by a noncomparative phase II study was conducted in GB patients after initial resection. Patients received HCQ (200 to 800 mg oral daily) with RT and concurrent and adjuvant TMZ. Quantitative electron microscopy and immunoblotting were used to assess changes in autophagic vacuoles (AVs) in peripheral blood mononuclear cells (PBMC). Population pharmacokinetic (PK) modeling enabled PK-pharmacodynamic correlations. Sixteen phase I subjects were evaluable for dose-limiting toxicities. At 800 mg HCQ/d, 3/3 subjects experienced Grade 3 and 4 neutropenia and thrombocytopenia, 1 with sepsis. HCQ 600 mg/d was found to be the MTD in this combination. The phase II cohort (n = 76) had a median survival of 15.6 mos with survival rates at 12, 18, and 24 mo of 70%, 36%, and 25%. PK analysis indicated dose-proportional exposure for HCQ. Significant therapy-associated increases in AV and LC3-II were observed in PBMC and correlated with higher HCQ exposure. These data establish that autophagy inhibition is achievable with HCQ, but dose-limiting toxicity prevented escalation to higher doses of HCQ. At HCQ 600 mg/d, autophagy inhibition was not consistently achieved in patients treated with this regimen, and no significant improvement in overall survival was observed. Therefore, a definitive test of the role of autophagy inhibition in the adjuvant setting for glioma patients awaits the development of lower-toxicity compounds that can achieve more consistent inhibition of autophagy than HCQ.

Targeting ER stress-induced autophagy overcomes BRAF inhibitor resistance in melanoma.

Melanomas that result from mutations in the gene encoding BRAF often become resistant to BRAF inhibition (BRAFi), with multiple mechanisms contributing to resistance. While therapy-induced autophagy promotes resistance to a number of therapies, especially those that target PI3K/mTOR signaling, its role as an adaptive resistance mechanism to BRAFi is not well characterized. Using tumor biopsies from BRAF(V600E) melanoma patients treated either with BRAFi or with combined BRAF and MEK inhibition, we found that BRAFi-resistant tumors had increased levels of autophagy compared with baseline. Patients with higher levels of therapy-induced autophagy had drastically lower response rates to BRAFi and a shorter duration of progression-free survival. In BRAF(V600E) melanoma cell lines, BRAFi or BRAF/MEK inhibition induced cytoprotective autophagy, and autophagy inhibition enhanced BRAFi-induced cell death. Shortly after BRAF inhibitor treatment in melanoma cell lines, mutant BRAF bound the ER stress gatekeeper GRP78, which rapidly expanded the ER. Disassociation of GRP78 from the PKR-like ER-kinase (PERK) promoted a PERK-dependent ER stress response that subsequently activated cytoprotective autophagy. Combined BRAF and autophagy inhibition promoted tumor regression in BRAFi-resistant xenografts. These data identify a molecular pathway for drug resistance connecting BRAFi, the ER stress response, and autophagy and provide a rationale for combination approaches targeting this resistance pathway.

Autophagy inhibitor Lys05 has single-agent antitumor activity and reproduces the phenotype of a genetic autophagy deficiency.

Autophagy is a lysosome-dependent degradative process that protects cancer cells from multiple stresses. In preclinical models, autophagy inhibition with chloroquine (CQ) derivatives augments the efficacy of many anticancer therapies, but CQ has limited activity as a single agent. Clinical trials are underway combining anticancer agents with hydroxychloroquine (HCQ), but concentrations of HCQ required to inhibit autophagy are not consistently achievable in the clinic. We report the synthesis and characterization of bisaminoquinoline autophagy inhibitors that potently inhibit autophagy and impair tumor growth in vivo. The structural motifs that are necessary for improved autophagy inhibition compared with CQ include the presence of two aminoquinoline rings and a triamine linker and C-7 chlorine. The lead compound, Lys01, is a 10-fold more potent autophagy inhibitor than HCQ. Compared with HCQ, Lys05, a water-soluble salt of Lys01, more potently accumulates within and deacidifies the lysosome, resulting in impaired autophagy and tumor growth. At the highest dose administered, some mice develop Paneth cell dysfunction that resembles the intestinal phenotype of mice and humans with genetic defects in the autophagy gene ATG16L1, providing in vivo evidence that Lys05 targets autophagy. Unlike HCQ, significant single-agent antitumor activity is observed without toxicity in mice treated with lower doses of Lys05, establishing the therapeutic potential of this compound in cancer.

Measurements of tumor cell autophagy predict invasiveness, resistance to chemotherapy, and survival in melanoma.

PURPOSE: Autophagy consists of lysosome-dependent degradation of cytoplasmic contents sequestered by autophagic vesicles (AV). The role of autophagy in determining tumor aggressiveness and response to therapy in melanoma was investigated in this study. EXPERIMENTAL DESIGN: Autophagy was measured in tumor biopsies obtained from metastatic melanoma patients enrolled on a phase II trial of temozolomide and sorafenib and correlated to clinical outcome. These results were compared with autophagy measurements in aggressive and indolent melanoma cells grown in two- and three-dimensional (3D) culture and as xenograft tumors. The effects of autophagy inhibition with either hydroxychloroquine or inducible shRNA (short hairpin RNA) against the autophagy gene ATG5 were assessed in three-dimensional spheroids. RESULTS: Patients whose tumors had a high autophagic index were less likely to respond to treatment and had a shorter survival compared with those with a low autophagic index. Differences in autophagy were less evident in aggressive and indolent melanoma cells grown in monolayer culture. In contrast, autophagy was increased in aggressive compared with indolent melanoma xenograft tumors. This difference was recapitulated when aggressive and indolent melanoma cells were grown as spheroids. Autophagy inhibition with either hydroxychloroquine or inducible shRNA against ATG5 resulted in cell death in aggressive melanoma spheroids, and significantly augmented temozolomide-induced cell death. CONCLUSIONS: Autophagy is a potential prognostic factor and therapeutic target in melanoma. Three dimensional culture mimics the tumor microenvironment better than monolayer culture and is an appropriate model for studying therapeutic combinations involving autophagy modulators. Autophagy inhibition should be tested clinically in patients with melanoma.

Identification, regulation and anti-proliferative role of the NPR-C receptor in gastric epithelial cells.

Evidence suggests that functional atrial natriuretic peptide (ANP) receptors occur in surface gastric mucosal epithelial cells. To evaluate functional aspects of ANP in a model of these cells we examined the expression of natriuretic peptide receptors (NPR) subtypes A and C in the non-transformed rat gastric mucosal epithelial cell line RGM1. Transcripts for NPR-A and NPR-C were detected in RGM1 cells by RT-PCR. However, only NPR-C protein was detected by Western blot and immunohistochemical analyses. Specific saturable binding of (125)I-ANP to RGM1 cells revealed a single class of high affinity binding sites (K (d) = 208 +/- 71pM, B (max) = 110,000 +/- 14,000 sites/cell, Hill coefficient = 0.97 +/- 0.05). ANP (IC(50) 130 +/- 47pM), BNP (IC(50) 716 +/- 26 pM), CNP (IC(50) 356 +/- 85pM) and C-ANP (IC(50) 134 +/- 13pM), a specific ligand for NPR-C, effectively displaced (125)I-ANP binding. Cross-linking of (125)I-ANP to cells labeled predominantly a protein of 66,000 Da. These data suggest that (125)I-ANP binding was primarily to NPR-C. ANP and C-ANP inhibited forskolin- and prostaglandin E(2) (PGE(2))-stimulated cAMP in a PTx-sensitive fashion. PGE(2), transforming growth factor-+/-1 (TGF-+/-1), forskolin, 8-bromo-cyclic AMP, and phorbol-12-myristate-13-acetate (PMA) caused a dose-dependent decrease in specific (125)I-ANP binding, whereas epidermal growth factor (EGF), 8-bromo-cyclic GMP and 4+/--phorbol didecanoate had no effect. PGE(2), forskolin, TGF-+/-1 and PMA significantly decreased (125)I-ANP B (max) values, NPR-C protein and steady-state NPR-C transcript levels. H89, a protein kinase A inhibitor, blocked the reduction of NPR-C mRNA produced by both forskolin and PGE(2.) GF109203X, a protein kinase C inhibitor, abolished the PMA-induced decrease in NPR-C transcripts but only partially blocked that produced by TGF-+/-1. RGM1 cells exhibited a dose-dependent decrease in both DNA synthesis and cell proliferation when cultured in the presence of ANP or C-ANP. These findings indicate that RGM1 cells express functional NPR-C receptors that can influence RGM1 cell proliferation and are down-regulated by PGE(2) and TGF-+/-1.