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Supplementary Tables 1 and 2. Supplementary Table 1: Fold de-repression of miR-21 target genes after anti-miR-21 treatment. Supplementary Table 2: Taqman Primer and Probes

Supplementary Figure Legends. Figure legends for Supplementary Figures 1, 2, 3, and 4.

Supplementary Data 1. Excel sheet with fold change in gene expression following anti-miR-21 treatment.

Supplementary Figure 1. miR-21 mimic suppresses expression of ANKRD46, DDAH1 and RECK. SKHep1 cells were transfected with miR-21 or negative mimic. RNA was isolated and expression of ANKRD46, DDAH1 and RECK was assessed by qPCR. (Mean, {plus minus} SD, n=3).

Supplementary Figure 3. HMBG1 and LDH are induced upon miR-21 inhibition. SKHep1, HepG2 and Hep3B cells were treated with anti-miR-21 or MM control and extracellular HMBG1 and LDH activity was quantified. (Mean, {plus minus} SEM, n=3)

Supplementary Figure 4. Pathway analysis of gene expression changes following anti-miR-21 treatment. SKHep1 cells treated with anti-miR-21 were subjected to microarray gene expression analysis. Changes in cellular processes (top) and pathways (bottom) upon anti-miR-21 treatment are shown.

Supplementary Figure 2. Anti-miR-21 treatment causes limited caspase 3/7 activation in non-transformed cell lines. Caspase 3/7 activation after treatment of SKHep1, IMR-90, and WI-38 cells with MM control or anti-miR-21 for 72 hours. (Mean, {plus minus} SEM, n=3).

Supplementary Table

Supplementary Figures

Purpose: Estrogen receptor–positive (ER+) breast cancers are typically treated with endocrine agents, and dependence on the ER pathway is often retained even after multiple rounds of antiestrogen therapy. Selective estrogen receptor degraders (SERD) are being developed as a strategy to more effectively target ER and exploit ER dependence in these cancers, which includes inhibiting both wild-type and mutant forms of ER. The purpose of this study was to evaluate the efficacy of a novel orally bioavailable SERD, elacestrant (RAD1901), in preclinical models of ER+ breast cancer.Experimental Design: Elacestrant was evaluated as a single agent and in combination with palbociclib or everolimus in multiple ER+ breast cancer models, including several patient-derived xenograft models.Results: Elacestrant induces the degradation of ER, inhibits ER-mediated signaling and growth of ER+ breast cancer cell lines in vitro and in vivo, and significantly inhibits tumor growth of multiple PDX models. Furthermore, we demonstrate that elacestrant in combination with palbociclib or everolimus can lead to greater efficacy in certain contexts. Finally, elacestrant exhibits significant antitumor activity both as a single agent and in combination with palbociclib in two patient-derived breast cancer xenograft models harboring ESR1 mutations.Conclusions: These data underscore the potential clinical utility of elacestrant as a single agent and as a combination therapy, for both early- and late-stage ER+ disease. Clin Cancer Res; 23(16); 4793–804. ©2017 AACR.

Purpose: Metastatic HR+ breast cancer initially responds to serial courses of endocrine therapy but ultimately becomes refractory Elacestrant, a new generation oral selective estrogen receptor degrader (SERD) and antagonist, has demonstrated efficacy in a subset of women with advanced HR+ breast cancer (Bidard FC, et al J Clin Oncol 2022;40:3246-3256), but there are few patient-derived models to characterize its effect in advanced cancers with diverse treatment histories and acquired mutations In this translational study, we tested the efficacy of elacestrant on ex vivo circulating tumor cells (CTCs) and patient-derived xenograft (PDX) mouse models with serial exposures to fulvestrant and conducted a reanalysis of the EMERALD trial to evaluate the efficacy of elacestrant vs standard endocrine therapy among patients who had received prior fulvestrant. Methods: Using PDX models and cultured CTCs isolated from metastatic breast cancer patients, we analyzed sensitivity to elacestrant, compared with the currently approved SERD, fulvestrant We further analyzed clinical responses to elacestrant, compared with endocrine therapy, among women who had previously been treated with a fulvestrant-containing regimen from the recent phase 3 EMERALD Study (NCT03778931), Results: In a patient-derived HR+ breast cancer PDX model, we demonstrate that elacestrant, at a clinically relevant dose, is highly effective in tumors extensively pretreated with fulvestrant In cultured CTCs isolated from HR+ breast cancer patients who had received multiple prior treatments, including fulvestrant, elacestrant is active, independent of mutations in the estrogen receptor (ESR1) or Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha (PIK3CA) genes In these cells, elacestrant suppresses estrogen-receptor (ER) signaling at concentrations below those required for protein degradation Post-hoc analysis of the EMERALD clinical trial confirms that elacestrant is effective in patient populations previously treated with fulvestrant-containing regimens, irrespective of ESR1 mutation status. Conclusion: In the EMERALD study, elacestrant showed significantly prolonged PFS compared with SOC (including fulvestrant) Using a PDX model and CTCs isolated from patients with MBC from the EMERALD study, this translational investigation demonstrates that elacestrant retains efficacy in breast cancer cells that have acquired resistance to currently available ER-targeting therapies Elacestrant may be an option for patients with HR+/HER2- breast cancer whose disease progressed while receiving fulvestrant in the metastatic setting. Citation Format: Taronish D. Dubash, Aditya Bardia, Brian Chirn, Brittany A. Reeves, Joseph A. LiCausi, Risa Burr, Ben S. Wittner, Sumit Rai, Hitisha Patel, Teeru Bihani, Heike Arlt, Francois-Clement Bidard, Virginia G. Kaklamani, Philippe Aftimos, Javier Cortés, Simona Scartoni, Monica Binaschi, Nassir Habboubi, A. John Iafrate, Mehmet Toner, Daniel A. Haber, Shyamala Maheswaran. Efficacy of novel oral SERD elacestrant in fulvestrant-refractory hormone receptor-positive (HR+) breast cancer: a translational investigation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT073.

Intermittent administration of PTH type 1 receptor (PTH1R) agonists increases bone remodeling, with greater stimulation of bone formation relative to bone resorption causing net gains in bone mass. This pharmacodynamic feature underlies the bone-building effects of teriparatide and abaloparatide, the only PTH1R agonists approved to reduce osteoporotic fracture risk in postmenopausal women. This study in 8-week-old female mice compared bone resorption and formation responses to these agents delivered at the same 10 μg/kg dose, and a 40 μg/kg abaloparatide dose was also included to reflect its 4-fold higher approved clinical dose. Peptides or vehicle were administered by daily supra-calvarial subcutaneous injection for 12 days, and local (calvarial) and systemic (L5 vertebral and tibial) responses were evaluated by histomorphometry. Terminal bone histomorphometry data indicated that calvarial resorption cavities were similar in both abaloparatide groups versus vehicle controls, whereas the teriparatide group had more calvarial resorption cavities compared with the vehicle or abaloparatide 40 μg/kg groups. The bone resorption marker serum CTX was significantly lower in the abaloparatide 40 μg/kg group and similar in the other two active treatment groups compared with vehicle controls. Both peptides increased trabecular bone formation rate (BFR) in L5 and proximal tibia versus vehicle, and L5 BFR was higher with abaloparatide 40 μg/kg versus teriparatide. At the tibial diaphysis, periosteal BFR was higher with abaloparatide 40 μg/kg versus vehicle or teriparatide, and endocortical BFR was higher with teriparatide but not with abaloparatide 10 or 40 μg/kg versus vehicle. Few differences in structural or microarchitectural bone parameters were observed with this brief duration of treatment. In summary, calvarial bone resorption cavity counts were higher in the teriparatide group versus the vehicle and abaloparatide 40 μg/kg groups, and the abaloparatide 40 μg/kg group had lower serum CTX versus vehicle. L5 and tibial trabecular bone formation indices were higher in all three active treatment groups versus vehicle. The abaloparatide 40 μg/kg group had higher L5 trabecular BFR and tibial periosteal BFR versus teriparatide, whereas tibial endocortical BFR was higher with teriparatide but not abaloparatide. Together, these findings in female mice indicate that an improved balance of bone formation versus bone resorption is established shortly after initiating treatment with abaloparatide., Highlights • PTH receptor (PTH-R) agonists increase bone density by stimulating bone formation. • PTH-R agonists differ in their propensity to increase bone resorption. • Female mice were treated for 12 d with PTH-R agonists abaloparatide or teriparatide. • The systemic resorption marker serum CTX was lower with abaloparatide vs vehicle. • Calvarial resorption cavities were higher with teriparatide but not abaloparatide.

Disuse osteoporosis (bone loss resulted from a reduction in mechanical loading) occurs in patients due to prolonged bed rest, paralysis and application of braces. Abaloparatide (ABL) is a synthetic peptide analog of PTHrP that has been shown to promote bone formation with limited bone resorption. ABL was approved by the FDA in 2017 to treat osteoporosis in postmenopausal women at high fracture risk. Yet, the ability of ABL to prevent bone loss in disuse is unknown. We hypothesized that ABL would prevent bone loss in the hindlimb unloading (HLU) rat model of disuse osteoporosis. Adult male Wistar rats, 13–14 weeks of age, were assigned to 1 of 4 groups (10 rats/group): ambulatory + vehicle (CON-VEH), ambulatory + ABL (CON-ABL), HLU + vehicle (HLU-VEH) or HLU + ABL (HLU-ABL). The rats received a daily subcutaneous injection of ABL (25µg/kg/day) or vehicle for 28 days. Blood serum was collected on day 0, 7, 14 and 28 to examine the expression of bone markers such as osteocalcin (OCN) and TRAcP5b. pQCT scans were acquired at the proximal tibia at day 0 and 28 to measure changes in the total and trabecular vBMD. Following euthanasia, trabecular (Tb) and cortical (Ct) bone microarchitecture from femurs, tibias and L4 vertebrae were assessed using µCT. Femurs were mechanically tested to failure in 3-point bending to determine ultimate load (N) and stiffness (N/mm). Treatment effects were evaluated using 2-way ANOVA. Effects were considered significant at p < 0.05. Data reported as mean±SD. HLU led to loss of bone density and structure that were prevented by ABL. Longitudinal pQCT revealed significant increases in total vBMD in ABL-CON (52±17%) vs. VEH-CON (20±5%); and in HLU-ABL (24±6%) vs. HLU-VEH (-2±3%) (p We demonstrated positive effects of ABL on BMD, trabecular bone mass and structure in both ambulating and unloaded rats. These results are consistent with prior studies showing positive effects of ABL on bone mass, structure and strength in OVX and ORX rats. Limits include only male rats and 1 dose of ABL. However, the results observed in this study provide a strong rationale for investigating the ability of ABL to prevent disuse bone loss in humans.

Purpose: Estrogen receptor–positive (ER+) breast cancers are typically treated with endocrine agents, and dependence on the ER pathway is often retained even after multiple rounds of antiestrogen therapy. Selective estrogen receptor degraders (SERD) are being developed as a strategy to more effectively target ER and exploit ER dependence in these cancers, which includes inhibiting both wild-type and mutant forms of ER. The purpose of this study was to evaluate the efficacy of a novel orally bioavailable SERD, elacestrant (RAD1901), in preclinical models of ER+ breast cancer. Experimental Design: Elacestrant was evaluated as a single agent and in combination with palbociclib or everolimus in multiple ER+ breast cancer models, including several patient-derived xenograft models. Results: Elacestrant induces the degradation of ER, inhibits ER-mediated signaling and growth of ER+ breast cancer cell lines in vitro and in vivo, and significantly inhibits tumor growth of multiple PDX models. Furthermore, we demonstrate that elacestrant in combination with palbociclib or everolimus can lead to greater efficacy in certain contexts. Finally, elacestrant exhibits significant antitumor activity both as a single agent and in combination with palbociclib in two patient-derived breast cancer xenograft models harboring ESR1 mutations. Conclusions: These data underscore the potential clinical utility of elacestrant as a single agent and as a combination therapy, for both early- and late-stage ER+ disease. Clin Cancer Res; 23(16); 4793–804. ©2017 AACR.

Osteoporosis is characterized by low bone mass associated with bone fragility and high fracture risk resulting in reduced quality of life and a higher mortality rate. Osteoporosis is a result of unbalanced bone remodeling with increased catabolic actions of osteoclasts. To date, mechanisms of coupling bone resorption to bone formation are not well understood limiting treatment for osteoporotic patients. Abaloaratide (ABL), a synthetic analog of PTHrP, has been recently approved by the FDA for the treatment of postmenopausal women with osteoporosis at high risk for fracture. ABL exhibits anabolic functions on bone with only limited effects on bone resorption when compared to hPTH(1-34). Noteworthy, in vitro studies suggest that certain PTH or PTHrP ligand analogs can distinguish between two high-affinity PTHR1 conformations resulting in different signaling responses, one possibility to explain the distinct effects on bone resorption. To compare the effects of ABL and PTH(1-34) on calvarial bone resorption in vitro and in vivo mouse models were used. Mice were subcutaneously injected once daily with 10µg/kg of either peptide for 5 and 12 consecutive days. Our data demonstrate that in peptide-treated mice numbers of TRAP+ cells and bone marrow filled cavities within the calvariae are significantly increased compared to controls. Intriguingly, ABL-treated mice exhibit ~50% less TRAP+ cells compared to PTH(1-34). The markedly reduced ratio of marrow cavity/region of interest in response to ABL correlates with lower serum Rankl levels. Besides, in vitro formation of pits and trails, a general hallmark of osteoclastic activity, was increased when bone-marrow derived osteoclasts were treated with conditioned media from peptide-treated osteoblasts. Similarly to in vivo data, the total resorbing area was 3-fold less in ABL- than in PTH(1-34) treated osteoclasts, and the numbers of long trenches representing continuous resorption were reduced when using conditioned medium from ABL treated cells. Moreover, osteoclastogenesis assays with Ocy454 cells co-cultured for seven days with primary bone marrow-derived macrophages and treated intermittently for 6hr/day with ABL, or PTH(1-34) resulted in more osteoclast numbers compared to vehicle controls. Consistent with our in vivo results, in PTH-treated cells, the increase in osteoclast number and size was 1.6-fold and 2-fold greater, respectively, than in ABL- treated cells. These data imply differences in the extent of induction of osteoclastogenesis by ABL and PTH(1-34)-dependent signaling, which might manifest in different amounts of bone resorption. Our studies comparing the effects of ABL and PTH (1-34) on bone resorption provide mechanistic explanation for the net bone gain observed in the ACTIVE trial indicating that increased bone mass is, at least partly, the consequence of reduced osteoclastogenesis in ABL-treated patients.

Disuse osteoporosis can result from prolonged bed rest, paralysis, casts, braces, fractures and other conditions. Abaloparatide (ABL) is a PTHrP analog that increases bone density and strength by stimulating osteogenesis with limited effects on bone resorption. We examined skeletal responses to abaloparatide in young adult male rats with normal weight-bearing and with hindlimb unloading via a pelvic harness. Rats were allocated to four groups (10–12 per group): normal weight-bearing plus vehicle treatment (CON-VEH), normal weight-bearing plus ABL treatment (CON-ABL), hindlimb-unloading plus vehicle (HLU-VEH), or hindlimb-unloading plus ABL (HLU-ABL). Rats received ABL (25 μg/kg/day, s.c.) or vehicle throughout the 28-day unloading period and were then sacrificed, at which time HLU-VEH rats exhibited reduced bone formation and significant deficits in tibial, femoral, and vertebral bone mass compared with CON-VEH. ABL treatment increased serum osteocalcin in CON and HLU animals while having no effect on the osteoclast marker TRACP-5b. Longitudinal peripheral quantitative computed tomography (pQCT) indicated that ABL increased trabecular and cortical bone mass in the tibia. ABL was also associated with improved trabecular and cortical bone mass and architectural parameters at the femur, tibia, and vertebrae by μCT. Tibial histomorphometry indicated increased trabecular and endocortical bone formation with HLU-ABL versus HLU-VEH and with CON-ABL versus CON-VEH, and ABL was also associated with lower trabecular and endocortical osteoclast surfaces. Vertebral finite element analysis indicated higher ultimate load and stiffness for CON-ABL versus CON-VEH and for HLU-ABL versus HLU-VEH. In summary, ABL was associated with improved trabecular and cortical bone density and architecture in normal weight-bearing and hindlimb-unloaded rats, with higher bone formation and no difference in bone resorption. ABL was also associated with improved bone biomechanical parameters. These results provide rationale for investigating the ability of abaloparatide to prevent or treat disuse osteoporosis in humans.

Background: Recurrence after standard-of-care estrogen receptor α (ER)-targeted therapy presents challenges in management of metastatic ER positive (ER+) breast cancer (BC). The high prevalence of androgen receptor (AR) in ER+ BC, along with preclinical and clinical evidence showing anti-tumor activity of AR agonists in AR+/ER+ BC, suggest an opportunity to address resistance to ER-targeted agents by targeting AR. Significant anti-tumor activity has been reported with RAD140, an oral selective AR modulator (SARM), in estrogen-dependent and -independent AR+/ER+ BC models. Mechanistic investigation revealed that inhibition of tumor growth by RAD140 was in part through AR-mediated reduction of ESR1 mRNA and subsequent suppression of ER signaling, independent of ESR1 alterations. Here, we present new observations on RAD140 mechanisms of action in in vitro and in vivo models of endocrine-independent BC models. Methods: HCC1428-long term estrogen deprived (LTED) line was established by passaging cells in steroid-depleted media for > 6 months. HCC1428-LTED-palbociclib resistant (-palboR) BC cell line was generated from LTED by long-term passaging in the presence of 500 nM palbociclib. Fluorescence-microscopy was used to assess annexin V/propidium iodide (PI) and phospho- H2A.X expression. The endocrine-independent BC PDX model was established in nude mice without supplemental estradiol. Prior anti-cancer therapy of the donor patient included tamoxifen, exemestane, fulvestrant and multiple lines of chemotherapy. RAD140 (3 mg/kg twice daily), elacestrant (30 mg/kg once daily), and palbociclib (10 mg/kg once daily) were administered via oral gavage for the duration of study. Fulvestrant (3 mg/mouse) was given once weekly subcutaneously. Results: In a hormone-independent BC PDX model harboring the ESR1 D538G mutation, RAD140 treatment led to 80% tumor growth inhibition (TGI) compared to the vehicle. The selective ER degrader (SERD) fulvestrant had TGI of 7%, while the oral SERD elacestrant (RAD1901) had TGI of 60%. The combination of RAD140 with elacestrant exhibited enhanced anti-tumor activity greater than that of each agent alone (93% TGI). These in vivo findings suggest the activity of the AR-targeting RAD140 may be mediated through mechanisms beyond its AR-mediated inhibition of ER signaling. We then sought to identify additional mechanisms of action of RAD140 in two hormone-independent AR+/ER+ BC cell line models, HCC1428-LTED and HCC1428-LTED-palboR. After prolonged treatment (2 weeks) at 100 nM, RAD140 induced morphological changes related to apoptosis, along with increased number of annexin V/PI-positive cells. This was further supported by increases in cleaved PARP/caspase3/caspase7 proteins by western blot analysis. A decrease in the pro-survival protein BCL-2 was also seen. These results collectively suggest that RAD140 induced apoptosis in endocrine-resistant BC cells. In line with these findings, an increase in phospho-H2A.X, a sensitive marker for DNA damage, was also observed in RAD140-treated cells. Similar changes were observed with the positive control AR agonist dihydrotestosterone (DHT), but not with fulvestrant. The AR antagonist apalutamide was found to partially reverse the apoptosis induced by RAD140 and DHT, further supporting the on-target effect. Conclusion: Our data suggest the anti-tumor activity of RAD140 may be mediated through suppression of ER signaling as well as additional mechanisms. The effect of RAD140 on DNA damage and apoptosis implies the potential for combination therapy with agents targeting cell survival and DNA damage repair pathways. RAD140 is being studied in a Phase 1, first-in-human trial in postmenopausal women with hormone receptor positive BC (NCT03088527). Citation Format: Suqin He, Maureen G Conlan, Heike Arlt, Charles Morris, Ziyang Yu. Novel mechanisms of action of selective androgen receptor modulator RAD140 in AR+/ER+ breast cancer models [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-05-01.

Mechanisms of unassisted delivery of RNA therapeutics, including inhibitors of microRNAs, remain poorly understood. We observed that the hepatocellular carcinoma cell line SKHEP1 retains productive free uptake of a miR-21 inhibitor (anti-miR-21). Uptake of anti-miR-21, but not a mismatch (MM) control, induces expression of known miR-21 targets (DDAH1, ANKRD46) and leads to dose-dependent inhibition of cell growth. To elucidate mechanisms of SKHEP1 sensitivity to anti-miR-21, we conducted an unbiased shRNA screen that revealed tumor susceptibility gene 101 (TSG101), a component of the endosomal sorting complex required for transport (ESCRT-I), as an important determinant of anti-proliferative effects of anti-miR-21. RNA interference-mediated knockdown of TSG101 and another ESCRT-I protein, VPS28, improved uptake of anti-miR-21 in parental SKHEP1 cells and restored productive uptake to SKHEP1 clones with acquired resistance to anti-miR-21. Depletion of ESCRT-I in several additional cancer cell lines with inherently poor uptake resulted in improved activity of anti-miR-21. Finally, knockdown of TSG101 increased uptake of anti-miR-21 by cancer cells in vivo following systemic delivery. Collectively, these data support an important role for the ESCRT-I complex in the regulation of productive free uptake of anti-miRs and reveal potential avenues for improving oligonucleotide free uptake by cancer cells.

Tumor cells display fundamental changes in metabolism and nutrient uptake in order to utilize additional nutrient sources to meet their enhanced bioenergetic requirements. Glutamine (Gln) is one such nutrient that is rapidly taken up by tumor cells to fulfill this increased metabolic demand. A vital step in the catabolism of glutamine is its conversion to glutamate by the mitochondrial enzyme glutaminase (GLS). This study has identified GLS a potential therapeutic target in breast cancer, specifically in the basal subtype that exhibits a deregulated glutaminolysis pathway. Using inducible shRNA mediated gene knockdown, we discovered that loss of GLS function in triple-negative breast cancer (TNBC) cell lines with a deregulated glutaminolysis pathway led to profound tumor growth inhibition in vitro and in vivo. GLS knockdown had no effect on growth and metabolite levels in non-TNBC cell lines. We rescued the anti-tumor effect of GLS knockdown using shRNA resistant cDNAs encoding both GLS isoforms and by addition of an α-ketoglutarate (αKG) analog thus confirming the critical role of GLS in TNBC. Pharmacological inhibition of GLS with the small molecule inhibitor CB-839 reduced cell growth and led to a decrease in mammalian target of rapamycin (mTOR) activity and an increase in the stress response pathway driven by activating transcription factor 4 (ATF4). Finally, we found that GLS inhibition synergizes with mTOR inhibition, which introduces the possibility of a novel therapeutic strategy for TNBC. Our study revealed that GLS is essential for the survival of TNBC with a deregulated glutaminolysis pathway. The synergistic activity of GLS and mTOR inhibitors in TNBC cell lines suggests therapeutic potential of this combination for the treatment of vulnerable subpopulations of TNBC.

Tumor cells display enhanced requirements for energy and building blocks such as amino acids, nucleic acids and lipids to sustain their proliferation. Metabolic demands of cancer cells are often met in the context of limited access to nutrients and the need to maintain redox balance. Glutamine catabolism is considered critical to cancer cell survival by not only delivering carbon and nitrogen atoms needed for nucleic acid and amino acid precursors but also by serving as the source of antioxidants such as NADPH and glutathione. A vital step in the catabolism of glutamine is its conversion to glutamate by the mitochondrial enzyme glutaminase (GLS).In this study, we confirmed the significance of GLS and enhanced glutamine utilization in the basal subtype of breast cancer as evidenced by higher GLS to GLUL (Glutamine synthetase) ratio in a panel of breast cancers in The Cancer Genome Atlas (TCGA) database. Using inducible shRNA mediated gene knockdown, we discovered that loss of GLS function in triple-negative breast cancer (TNBC) cell lines led to profound tumor growth inhibition in vitro and in vivo. This anti-tumor effect of GLS knockdown was rescued either using shRNA resistant cDNAs encoding both GLS isoforms or by addition of an a-ketoglutarate analog thus confirming the critical role of GLS in TNBC. Along with these observations, we have found that pharmacological inhibition of GLS with the small molecule inhibitor CB-839 reduced cell growth and led to a decrease in mammalian target of rapamycin (mTOR) coupled with an increase in the stress response pathway driven by activating transcription factor 4 (ATF4). In line with the observed impact on mTOR pathway we found that GLS inhibition synergizes with mTOR inhibition. In conclusion, our preliminary investigation revealed that glutaminolysis is deregulated in a majority of TNBC cancer patients. Our target credentialing studies confirmed that GLS is essential for the survival of TNBC cell lines and xenografts tumors. The synergistic activity of GLS and mTOR inhibitors in this specific breast cancer subtype suggests a new therapeutic modality that may bring benefit to TNBC patients with high unmet need. Citation Format: Christophe Henry, Michael Lampa, Timothy He, Beatriz Ospina, Bailin Zhang, Gejing Deng, Claude Barberis, Dietmar Hoffmann, Jack Pollard, Adrian Francisco, Heike Arlt, Jason Reeves, Joshua Murtie, Christopher Winter, Victoria Richon, Hong Cheng, Carlos Garcia-Echeverria, Dmitri Wiederschain, Lakshmi Srinivasan. Basal-like breast cancer subtype is characterized by deregulated glutamine metabolism and is sensitive to GLS inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5472.

Monoacylglycerol lipase (MAGL) represents a primary degradation enzyme of the endogenous cannabinoid (eCB), 2-arachidonoyglycerol (2-AG). This study reports a potent covalent MAGL inhibitor, SAR127303. The compound behaves as a selective and competitive inhibitor of mouse and human MAGL, which potently elevates hippocampal levels of 2-AG in mice. In vivo, SAR127303 produces antinociceptive effects in assays of inflammatory and visceral pain. In addition, the drug alters learning performance in several assays related to episodic, working and spatial memory. Moreover, long term potentiation (LTP) of CA1 synaptic transmission and acetylcholine release in the hippocampus, two hallmarks of memory function, are both decreased by SAR127303. Although inactive in acute seizure tests, repeated administration of SAR127303 delays the acquisition and decreases kindled seizures in mice, indicating that the drug slows down epileptogenesis, a finding deserving further investigation to evaluate the potential of MAGL inhibitors as antiepileptics. However, the observation that 2-AG hydrolysis blockade alters learning and memory performance, suggests that such drugs may have limited value as therapeutic agents.

Hepatocellular carcinoma (HCC) remains a significant clinical challenge with few therapeutic options available to cancer patients. MicroRNA 21-5p (miR-21) has been shown to be upregulated in HCC, but the contribution of this oncomiR to the maintenance of tumorigenic phenotype in liver cancer remains poorly understood. We have developed potent and specific single-stranded oligonucleotide inhibitors of miR-21 (anti-miRNAs) and used them to interrogate dependency on miR-21 in a panel of liver cancer cell lines. Treatment with anti–miR-21, but not with a mismatch control anti-miRNA, resulted in significant derepression of direct targets of miR-21 and led to loss of viability in the majority of HCC cell lines tested. Robust induction of caspase activity, apoptosis, and necrosis was noted in anti–miR-21-treated HCC cells. Furthermore, ablation of miR-21 activity resulted in inhibition of HCC cell migration and suppression of clonogenic growth. To better understand the consequences of miR-21 suppression, global gene expression profiling was performed on anti–miR-21-treated liver cancer cells, which revealed striking enrichment in miR-21 target genes and deregulation of multiple growth-promoting pathways. Finally, in vivo dependency on miR-21 was observed in two separate HCC tumor xenograft models. In summary, these data establish a clear role for miR-21 in the maintenance of tumorigenic phenotype in HCC in vitro and in vivo. Implications: miR-21 is important for the maintenance of the tumorigenic phenotype of HCC and represents a target for pharmacologic intervention. Mol Cancer Res; 13(6); 1009–21. ©2015 AACR.

PRP4 kinase is known for its roles in regulating pre-mRNA splicing and beyond. Therefore, a wider spectrum of PRP4 kinase substrates could be expected. The role of PRP4 kinase in cancer is also yet to be fully elucidated. Attaining specific and potent PRP4 inhibitors would greatly facilitate the study of PRP4 biological function and its validation as a credible cancer target. In this report, we verified the requirement of enzymatic activity of PRP4 in regulating cancer cell growth and identified an array of potential novel substrates through orthogonal proteomics approaches. The ensuing effort in structural biology unveiled for the first time unique features of PRP4 kinase domain and its potential mode of interaction with a low molecular weight inhibitor. These results provide new and important information for further exploration of PRP4 kinase function in cancer. Background: Little is known about the cancer dependence and druggability of PRP4. Results: Significance of PRP4 catalytic activity is demonstrated, novel substrates are identified, and features of kinase domain structure are revealed. Conclusion: PRP4 is required for cancer cell survival, displays substrate specificity, and is amenable to pharmacological inhibition. Significance: Our results indicate that PRP4 is a potential drug target to pursue in cancer.

ATP dependent proteolytic degradation of misfolded proteins in the mitochondrial matrix is mediated by the PIM1 protease and depends on the molecular chaperone proteins mt-hsp70 and Mdj1p. Chaperone function is essential to maintain misfolded proteins in a soluble state, a prerequisite for their degradation by PIM1 protease. In the absence of functional mt-hsp70 or Mdj1p misfolded proteins either remain associated with mt-hsp70 or form aggregates and thereby are no longer substrates for PIM1 protease. Mdj1p is shown to regulate the ATP dependent association of an unfolded polypeptide chain with mt-hsp70 affecting binding to as well as release from mt-hsp70. These findings establish a central role of molecular chaperone proteins in the degradation of misfolded proteins by PIM1 protease and thereby demonstrate a functional interrelation between components of the folding machinery and the proteolytic system within mitochondria.

Hepatocellular carcinoma (HCC) remains a significant unmet medical need with few therapeutic options available. Micro RNA 21 (miR-21) has been shown to be upregulated in HCC, however, contribution of this onco-miR to the maintenance of tumorigenic phenotype in liver cancer remains poorly understood. We have developed potent and specific single-stranded oligonucleotide inhibitors of miR-21 (anti-miR-21) and used them to interrogate dependency on miR-21 in a panel of 20 commercially available HCC cell lines in vitro. Upon lipid-mediated transfection, anti-miR-21, but not its mismatched (MM) control, caused significant de-repression of known direct targets of miR-21 (ANKRD46, DDAH1, RECK1) and inhibited survival of a large subset of HCC cell lines. Treatment of these sensitive HCC cell lines with anti-miR-21 resulted in dose- and time-dependent induction of caspase 3/7 activity. In contrast, non-responder HCC cell lines failed to significantly upregulate caspase activity and maintained viability in the presence of anti-miR compound. Further analysis of responder cell lines revealed robust induction of cell death, inhibition of cell migration and suppression of clonogenic growth upon treatment with miR-21 inhibitor. To better understand the consequences of miR-21 suppression in HCC, we carried out global gene expression profiling of anti-miR-21 treated sensitive liver cancer cells. Striking enrichment in miR-21 targets was noted among upregulated transcripts. Gene ontology analysis identified key cellular processes affected by miR-21 inhibition, including deregulation of metabolic pathways. In addition to the induction of direct miR-21 targets, cyclin H was found to be significantly downregulated upon miR-21 inhibition in the majority of responder cell lines. We hypothesize that inhibition of cyclin H expression, while an indirect effect of miR-21 suppression, could contribute to the activity of anti-miR-21 compounds. In summary, our data suggest that inhibition of miR-21 merits further investigation in the treatment of hepatocellular carcinoma. Citation Format: Sonya Zabludoff, Timothy Wagenaar, Francisco Adrian, Charles Allerson, Heike Arlt, Raffaele Baffa, Bal Bhat, Hui Cao, Scott Davis, Carlos Garcia-Echeverria, Kathrin Heermeier, Shih-Min Huang, Lan Jiang, Eric Marcusson, Christiane Metz-Weidmann, Adam Pavlicek, Jack Pollard, Jennifer Rocnik, Sabine Scheidler, Chaomei Shi, Fangxian Sun, Tatiana Tolstykh, Qunyan Yu, Gang Zheng, Dmitri Wiederschain. Targeting miR-21 in hepatocellular carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4787. doi:10.1158/1538-7445.AM2014-4787

Yta10p (Afg3p) and Yta12p (Rcal1p), members of the conserved AAA family of ATPases, are subunits of the mitochondrial m-AAA protease, an inner membrane ATP-dependent metallopeptidase. Deletion of YTA10 or YTA12 impairs degradation of non-assembled inner membrane proteins and assembly of respiratory chain complexes. Mutations of the proteolytic sites in either YTA10 or YTA12 have been shown to inhibit proteolysis of membrane-integrated polypeptides but not the respiratory competence of the cells, suggesting additional activities of Yta10p and Yta12p. Here we demonstrate essential proteolytic functions of the m-AAA protease in the biogenesis of the respiratory chain. Cells harbouring proteolytically inactive forms of both Yta10p and Yta12p are respiratory deficient and exhibit a pleiotropic phenotype similar to Deltayta10 and Deltayta12 cells. They show deficiencies in expression of the intron-containing mitochondrial genes COX1 and COB. Splicing of COX1 and COB transcripts is impaired in mitochondria lacking m-AAA protease, whilst transcription and translation can proceed in the absence of Yta10p or Yta12p. The function of the m-AAA protease appears to be confined to introns encoding mRNA maturases. Our results reveal an overlapping substrate specificity of the subunits of the m-AAA protease and explain the impaired assembly of respiratory chain complexes by defects in expression of intron-containing genes in mitochondria lacking m-AAA protease.

The 86-kDa IE2 protein (IE86) of human cytomegalovirus (HCMV) has been described as a promiscuous transactivator of viral, as well as cellular, gene expression. Investigation of the mechanism used by IE86 to activate gene expression from the early UL112/113 promoter of HCMV revealed the existence of three binding sites for IE86 located between nucleotides -290 and -120 relative to the transcriptional start site (H. Arlt, D. Lang, S. Gebert, and T. Stamminger, J. Virol. 68:4117-4125, 1994). As shown previously, deletion of these target sites resulted in a reduction of IE86-mediated transactivation by approximately 70%. The remaining promoter, however, could still be stimulated about 40-fold, indicating the presence of an additional responsive element within these sequences. Here, we provide evidence that a binding site for the cellular transcription factor CREB can also act as a target for IE86 transactivation. By DNase I protection analysis, a binding sequence for CREB could be detected between nucleotides -78 and -56 within the respective promoter region. After in vitro mutagenesis of this CREB-binding site within the context of the entire UL112/113 promoter, a marked reduction in transactivation levels was evident. Moreover, when individual CREB-binding sites were positioned upstream of a minimal, TATA box-containing UL112/113 promoter, they were able to confer strong IE86 responsiveness, whereas a mutated sequence did not exert any effect. In far Western blot and pull-down experiments, a direct interaction of IE86 with the cellular transcription factor CREB could be observed. The in vivo relevance of this in vitro interaction was confirmed by using various GAL4 fusion proteins in the presence or absence of IE86 which revealed a strong activation only in the presence of both a GAL4-CREB fusion and IE86. This shows that at least one specific member of the ATF/CREB family of transcription factors is involved in mediating transactivation by the HCMV IE86 protein.

The 86-kDa IE2 protein (IE86) of human cytomegalovirus (HCMV) can act as both an activator and a repressor of gene expression. The mechanisms for both of these functions are not well defined. It has recently been demonstrated that this protein has sequence-specific DNA binding properties: it interacts directly with a target sequence that is located between the TATA box and the cap site of its own promoter. This sequence, termed the CRS (cis repression signal) element, is required for negative autoregulation of the IE1/IE2 enhancer/promoter by IE2. We demonstrate now that binding of this protein to DNA is not confined to this site but occurs also within an early promoter of HCMV that has previously been shown to be strongly IE2 responsive. By DNase I protection analysis using a purified, procaryotically expressed IE2 protein, we could identify three binding sites within the region of -290 to -120 of the UL112 promoter of HCMV. Competition in DNase I protection experiments as well as gel retardation experiments showed that the identified binding sites are specific and have high affinity. Deletion of IE2 binding sites from this promoter reduced the level of transactivation; however, the remaining promoter could still be stimulated about 40-fold. Constructs in which IE2 binding sites were fused directly to the TATA box of the UL112 promoter did not reveal a significant contribution of these sequences to transactivation. However, if an IE2 binding site was reinserted upstream of nucleotide -117 of the UL112 promoter, an increase in transactivation by IE2 was obvious, whereas a mutated sequence could not mediate this effect. This finding suggests that DNA-bound IE2 can contribute to transactivation but seems to require the presence of additional transcription factors. Moreover, a comparison of the detected IE2 binding sites could not detect a strong homology, suggesting that this protein may be able to interact with a broad spectrum of different target sequences.

The mitochondrial members of the highly conserved AAA family, Yta10p and Yta12p, constitute a membrane-embedded complex of about 850 kDa. As an ATP dependent metallopeptidase (AAA protease), the YTA10–12 complex mediates the degradation of nonassembled inner membrane proteins. In contrast to nucleotide-dependent complex formation and substrate binding, proteolysis of bound polypeptides depends on the hydrolysis of ATP and the metallopeptidase activity of both subunits. Independent of its proteolytic function, the chaperone-like activity of the YTA10–12 complex is required for assembly of the membrane-associated ATP synthase. We propose that proteolytic and chaperone-like activities in the YTA10–12 complex mediate assembly and degradation processes of membrane protein complexes and thereby exert key functions in the maintenance of membrane integrity.