A small molecule inhibitor of inducible heat shock protein 70.

The multifunctional, stress-inducible molecular chaperone HSP70 has important roles in aiding protein folding and maintaining protein homeostasis. HSP70 expression is elevated in many cancers, contributing to tumor cell survival and resistance to therapy. We have determined that a small molecule called 2-phenylethynesulfonamide (PES) interacts selectively with HSP70 and leads to a disruption of the association between HSP70 and several of its cochaperones and substrate proteins. Treatment of cultured tumor cells with PES promotes cell death that is associated with protein aggregation, impaired autophagy, and inhibition of lysosomal function. Moreover, this small molecule is able to suppress tumor development and enhance survival in a mouse model of Myc-induced lymphomagenesis. The data demonstrate that PES disrupts actions of HSP70 in multiple cell signaling pathways, offering an opportunity to better understand the diverse functions of this molecular chaperone and also to aid in the development of new cancer therapies.

Defining D-irAEs: consensus-based disease definitions for the diagnosis of dermatologic adverse events from immune checkpoint inhibitor therapy.

With an increasing number of patients eligible for immune checkpoint inhibitors, the incidence of immune-related adverse events (irAEs) is on the rise. Dermatologic immune-related adverse events (D-irAEs) are the most common and earliest to manifest, often with important downstream consequences for the patient. Current guidelines lack clarity in terms of diagnostic criteria for D-irAEs. The goal of this project is to better define D-irAE for the purposes of identification, diagnosis, and future study of this important group of diseases.The objectives of this project were to develop consensus guidance for an approach to D-irAEs including disease definitions and severity grading. Knowing that consensus among oncologists, dermatologists, and irAE subspecialists would be critical for usability, we formed a Dermatologic irAE Disease Definition Panel. The panel was composed of 34 experts, including oncologists, dermatologists, a rheumatologist, and an allergist/immunologist from 22 institutions across the USA and internationally. A modified Delphi consensus process was used, with two rounds of anonymous ratings by panelists and two virtual meetings to discuss areas of controversy. Panelists rated content for usability, appropriateness, and accuracy on 9-point scales in electronic surveys and provided free text comments. A working group aggregated survey responses and incorporated them into revised definitions. Consensus was based on numeric ratings using the RAND/UCLA Appropriateness Method with prespecified definitions.Following revisions based on panelist feedback, all items received consensus in the second round of ratings. Consensus definitions were achieved for 10 core D-irAE diagnoses: ICI-vitiligo, ICI-lichen planus, ICI-psoriasis, ICI-exanthem, ICI-bullous pemphigoid, ICI-Grover's, ICI-eczematous, ICI-eruptive atypical squamous proliferation, ICI-pruritus without rash, and ICI-erosive mucocutaneous. A standard evaluation for D-irAE was also found to reach consensus, with disease-specific exceptions detailed when necessary. Each disorder's description includes further details on disease subtypes, symptoms, supportive exam findings, and three levels of diagnostic certainty (definite, probable, and possible).These consensus-driven disease definitions standardize D-irAE classification in a useable framework for multiple disciplines and will be the foundation for future work. Given consensus on their accuracy and usability from a representative panel group, we anticipate that they can be used broadly across clinical and research settings.

ARF stimulates XPC to trigger nucleotide excision repair by regulating the repressor complex of E2F4.

The tumour suppressor ARF (alternative reading frame), which is mutated or silenced in various tumours, has a crucial role in tumour surveillance to suppress unwarranted cell growth and proliferation. ARF has also been linked to the DNA-damage-induced response of p53 because of its ability to inhibit murine double minute 2 (MDM2). Here, however, we provide genetic evidence for a role of ARF in nucleotide excision repair (NER) that is independent of p53. Cells lacking ARF are deficient in NER. Expression of ARF restores the repair activity, which coincides with increased expression of the damaged-DNA recognition protein xeroderma pigmentosum, complementation group C (XPC). We provide evidence that, by disrupting the interaction between E2F transcription factor 4 (E2F4) and DRTF polypeptide 1 (DP1), ARF reduces the interaction of the E2F4-p130 repressor complex with the promoter of XPC to ensure high-level expression of XPC. Together, our results point to an important 'care-taker'-type tumour-suppression function for ARF in NER through the increased expression of XPC.

Methylseleninic acid sensitizes prostate cancer cells to TRAIL-mediated apoptosis.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytotoxic agent that preferentially induces apoptosis in a variety of human cancer cells. Unfortunately, some tumor cells remain resistant to TRAIL. Therefore, agents that sensitize malignant cells to TRAIL-mediated cell death might be of particular importance for the development of novel antitumor therapeutic regimens. Recent studies establish a critical role of selenium in prostate cancer prevention in vitro and in vivo. Here, we demonstrate that concomitant administration of TRAIL and methylseleninic acid (MSA) produces synergistic effects on the induction of apoptosis in androgen-dependent LNCaP and androgen-independent DU-145 prostate cancer cells. MSA rapidly and specifically downregulates expression of the cellular FLICE inhibitory protein, a negative regulator of death receptor signaling. In addition, we demonstrate that the synergistic effects of MSA and TRAIL result from the activation of the mitochondrial pathway-mediated amplification loop. Addition of MSA effectively blocked TRAIL-mediated BAD phosphorylation at Ser112 and Ser136 in DU-145 cells and was accompanied by induction of the mitochondrial permeability transition and release of apoptogenic cytochrome c and Smac/DIABLO proteins from the mitochondria and into the cytosol. These results suggest that selenium-based dietary compounds may help to overcome resistance to TRAIL-mediated apoptosis in prostate cancer cells.

A conserved domain in exon 2 coding for the human and murine ARF tumor suppressor protein is required for autophagy induction.

The ARF tumor suppressor, encoded by the CDKN2A gene, has a well-defined role regulating TP53 stability; this activity maps to exon 1ß of CDKN2A. In contrast, little is known about the function(s) of exon 2 of ARF, which contains the majority of mutations in human cancer. In addition to controlling TP53 stability, ARF also has a role in the induction of autophagy. However, whether the principal molecule involved is full-length ARF, or a small molecular weight variant called smARF, has been controversial. Additionally, whether tumor-derived mutations in exon 2 of CDKN2A affect ARF's autophagy function is unknown. Finally, whereas it is known that silencing or inhibiting TP53 induces autophagy, the contribution of ARF to this induction is unknown. In this report we used multiple autophagy assays to map a region located in the highly conserved 5' end of exon 2 of CDKN2A that is necessary for autophagy induction by both human and murine ARF. We showed that mutations in exon 2 of CDKN2A that affect the coding potential of ARF, but not p16INK4a, all impair the ability of ARF to induce autophagy. We showed that whereas full-length ARF can induce autophagy, our combined data suggest that smARF instead induces mitophagy (selective autophagy of mitochondria), thus potentially resolving some confusion regarding the role of these variants. Finally, we showed that silencing Tp53 induces autophagy in an ARF-dependent manner. Our data indicated that a conserved domain in ARF mediates autophagy, and for the first time they implicate autophagy in ARF's tumor suppressor function.

Interaction of the ARF tumor suppressor with cytosolic HSP70 contributes to its autophagy function.

The p14/p19 (ARF) (ARF) tumor suppressor gene is frequently mutated in human cancer. Recently ARF has been shown to localize to mitochondria and to induce autophagy. However the controls that regulate the trafficking of ARF to mitochondria remain unknown. We recently reported that 2-phenylethynesulfonamide (PES) selectively interacts with cytosolic heat shock protein 70 (HSP70) and inhibits its function; we further showed that PES promotes the death of tumor cells, and that this is associated with an impairment of lysosome function and an inhibition of autophagy. In the present work we used a mass spectrometry-based approach to identify mitochondrial ARF-binding proteins. We report that mitochondrial ARF interacts with HSP70. We show that treatment of cells with PES blocks the trafficking of ARF to mitochondria, indicating that interaction with HSP70 mediates the mitochondrial localization of ARF. We also show that PES inhibits the ability of ARF to induce autophagy, supporting the premise that localization to this organelle is critical for ARF-induced autophagy. Finally, we report that cells expressing high levels of ARF are more sensitive to PES than counterparts with ARF silenced. High levels of ARF are characteristic of tumor cells with enhanced MAPK signaling and advanced stage; therefore, these data support the premise that PES may show preferential cytotoxicity to advanced stage cancers.

HSP70 inhibition by the small-molecule 2-phenylethynesulfonamide impairs protein clearance pathways in tumor cells.

The evolutionarily conserved stress-inducible HSP70 molecular chaperone plays a central role in maintaining protein quality control in response to various forms of stress. Constitutively elevated HSP70 expression is a characteristic of many tumor cells and contributes to their survival. We recently identified the small-molecule 2-phenylethyenesulfonamide (PES) as a novel HSP70 inhibitor. Here, we present evidence that PES-mediated inhibition of HSP70 family proteins in tumor cells results in an impairment of the two major protein degradation systems, namely, the autophagy-lysosome system and the proteasome pathway. HSP70 family proteins work closely with the HSP90 molecular chaperone to maintain the stability and activities of their many client proteins, and PES causes a disruption in the HSP70/HSP90 chaperone system. As a consequence, many cellular proteins, including known HSP70/HSP90 substrates, accumulate in detergent-insoluble cell fractions, indicative of aggregation and functional inactivation. Overall, PES simultaneously disrupts several cancer critical survival pathways, supporting the idea of targeting HSP70 as a potential approach for cancer therapeutics.

Tumor suppression by ARF: gatekeeper and caretaker.

ARF is a vital tumor suppressor and its loss contributes significantly to cancer. The frequency in which ARF is mutated, deleted or silenced is second to the loss of p53. The most documented and widely accepted activity of ARF is mediated through its activation of the p53 transcriptional program by inhibiting MDM2 function. However, several lines of evidence have surfaced demonstrating that ARF possesses p53-independent functions. One of these p53-independent functions is ARF's regulation of the E2F family. The E2F/DP transcription factor is critical for cell cycle progression. The balance between activator and repressor E2Fs regulates the expression of E2F target genes and thus cell proliferation as well as other cellular functions such as checkpoint, chromosome assembly and repair. Through its ability to bind directly to DP1, ARF can cause dissociation of both activator and repressor E2Fs. While the regulation of the activator E2Fs is related to cell cycle arrest, there is evidence that the regulation of the repressors, E2F4 and E2F5, is significant in maintaining genomic stability.

ARF, autophagy and tumor suppression.

Autophagy plays a critical role in the initiation and progression of tumors. The exact nature of this role, however, is complex. Autophagy is suppressive to tumor initiation, and reduces genomic instability. Genes with key roles in autophagy are mutated in human cancer, and knockout mice for certain autophagy genes are predisposed to cancer. Conversely, established tumors appear to utilize autophagy in order to survive periods of metabolic or hypoxic stress. Consistent with this, small molecule inhibitors of autophagy like chloroquine are effective anticancer agents for certain tumor types. The consensus appears to be that autophagy suppresses tumor initiation, but promotes the survival of established tumors. But this premise may be over-simplified. Several groups have recently shown that the ARF tumor suppressor can induce autophagy. While some groups have found that ARF-mediated autophagy is cytotoxic to tumor cells, we have shown that ARF's autophagy function may promote the survival and progression of certain tumors. We have previously shown that silencing ARF limits autophagy and the development of p53-null lymphomas. In this addendum, we show this is not true for primary p53-null sarcoma cells. Rather, ARF-silencing enhances sarcoma development. These data suggest that the survival-benefit of ARF, and possibly also of autophagy, may be restricted to certain tumor types.

A regulatory role of the Bateman domain of IMP dehydrogenase in adenylate nucleotide biosynthesis.

The Bateman domain (CBS subdomain) of IMP dehydrogenase (IMPDH), a rate-limiting enzyme of the de novo GMP biosynthesis, is evolutionarily conserved but has no established function. Deletion of the Bateman domain has no effect on the in vitro IMPDH activity. We report that in vivo deletion of the Bateman domain of IMPDH in Escherichia coli (guaB(DeltaCBS)) sensitizes the bacterium to growth arrest by adenosine and inosine. These nucleosides exert their growth inhibitory effect via a dramatic increase in the intracellular adenylate nucleotide pool, which results in the enhanced allosteric inhibition of PRPP synthetase and consequently a PRPP deficit. The ensuing starvation for pyrimidine nucleotides culminates in growth arrest. Thus, deletion of the Bateman domain of IMPDH derepresses the synthesis of AMP from IMP. The growth inhibitory effect of inosine can be rescued by second-site suppressor mutations in the genes responsible for the conversion of inosine to AMP (gsk, purA, and purB) as well as by the prsA1 allele, which encodes a PRPP synthetase that is insensitive to allosteric inhibition by adenylate nucleotides. Importantly, the guaB(DeltaCBS) phenotype can be complemented in trans by a mutant guaB allele, which encodes a catalytically disabled IMPDH(C305A) protein containing an intact Bateman domain. We conclude that the Bateman domain of IMPDH is a negative trans-regulator of adenylate nucleotide synthesis, and that this role is independent of the catalytic function of IMPDH in the de novo GMP biosynthesis.

ARF induces autophagy by virtue of interaction with Bcl-xl.

The ARF tumor suppressor controls a well-described p53/Mdm2-dependent oncogenic stress checkpoint. In addition, ARF has recently been shown to localize to mitochondria, and to induce autophagy; however, this has never before been demonstrated for endogenous ARF, and the molecular basis for this activity of ARF has not been elucidated. Using an unbiased mass spectrometry-based approach, we show that mitochondrial ARF interacts with the Bcl2 family member Bcl-xl, which normally protects cells from autophagy by inhibiting the Beclin-1/Vps34 complex, which is essential for autophagy. We find that increased expression of ARF decreases Beclin-1/Bcl-xl complexes in cells, thereby providing a basis for ARF-induced autophagy. Our data also indicate that silencing p53 leads to high levels of ARF and increased autophagy, thereby providing a possible basis for the finding by others that p53 inhibits autophagy. The combined data support the premise that ARF induces autophagy in a p53-independent manner in part by virtue of its interaction with Bcl-xl.

The ARF tumor suppressor can promote the progression of some tumors.

p14/p19ARF (ARF) is a tumor suppressor gene that is frequently mutated in human cancer. ARF has multiple tumor suppressor functions, some of which are mediated by signaling to p53. Surprisingly, a significant fraction of human tumors retain persistently high levels of ARF, suggesting that ARF may possess a prosurvival function. We show that ARF protein is markedly up-regulated in cells exposed to nutrient starvation. Cells with silenced ARF show reduced autophagy and reduced viability when placed under conditions of starvation. We show for the first time that ARF silencing can limit the progression of some tumors, such as lymphoma, but not others, such as E1A/Ras-induced tumors. Specifically, myc-driven lymphomas with mutant p53 tend to overexpress ARF; we show that silencing ARF in these tumors greatly impedes their progression. These data are the first to show that ARF can act in a p53-independent manner to promote the progression of some tumors.