Inhibition of CAMKK2 impairs autophagy and castration-resistant prostate cancer via suppression of AMPK-ULK1 signaling

Previous work has suggested androgen receptor (AR) signaling mediates prostate cancer progression in part through the modulation of autophagy. However, clinical trials testing autophagy inhibition using chloroquine derivatives in men with castration-resistant prostate cancer (CRPC) have yet to yield promising results, potentially due to the side effects of this class of compounds. We hypothesized that identification of the upstream activators of autophagy in prostate cancer could highlight alternative, context-dependent targets for blocking this important cellular process during disease progression. Here, we used molecular, genetic, and pharmacological approaches to elucidate an AR-mediated autophagy cascade involving Ca2+/calmodulin-dependent protein kinase kinase 2 (CAMKK2; a kinase with a restricted expression profile), 5'-AMP-activated protein kinase (AMPK), and Unc-51 like autophagy activating kinase 1 (ULK1), but independent of canonical mechanistic target of rapamycin (mTOR) activity. Increased CAMKK2-AMPK-ULK1 signaling correlated with disease progression in genetic mouse models and patient tumor samples. Importantly, CAMKK2 disruption impaired tumor growth and prolonged survival in multiple CRPC preclinical mouse models. Similarly, an inhibitor of AMPK-ULK1 blocked autophagy, cell growth, and colony formation in prostate cancer cells. Collectively, our findings converge to demonstrate that AR can co-opt the CAMKK2-AMPK-ULK1 signaling cascade to promote prostate cancer by increasing autophagy. Thus, this pathway may represent an alternative autophagic target in CRPC.

Abstract 4083: Crizotinib improves the therapeutic efficacy of olaparib in ovarian cancer

Despite improvements in treatment, ovarian cancer still proves lethal in >60% of cases. One of the most important factors contributing to poor patient outcomes is the ability of dormant ovarian cancer cells to survive following primary surgery and chemotherapy. Poly (ADP) ribose polymerase inhibitors (PARPi) are promising agents for treating both primary and recurrent ovarian cancers. However, acquired drug resistance to PARPi decreases the clinical efficacy of these agents. We have previously found that olaparib induces autophagy in ovarian cancer and the addition of drugs that inhibit autophagy, such as chloroquine, can overcome drug resistance and enhance the anti-cancer activity of PARP inhibitors in ovarian cancer cells, cell line-derived xenograft and patient-derived xenograft models.

Building upon this work, our group has sought drugs that are selectively toxic for autophagic ovarian cancer cells and that might enhance sensitivity to PARP inhibitors. In a previous study, our laboratory had found that knockdown of the anaplastic lymphoma kinase (ALK) significantly reduced survival of ovarian cancer cells that were undergoing autophagy. The FDA-approved ALK inhibitor, crizotinib, exhibited significantly greater toxicity for autophagic ovarian cancer cells in culture and cured a fraction of mice with dormant, autophagic ovarian cancer xenografts. As olaparib induces autophagy in ovarian cancer cells and crizotinib selectively targets autophagic cancer cells, we 1) explored the vulnerability of autophagic cells to the combination treatment of olaparib and crizotinib both in vitro and in vivo; and 2) the mechanism by which the combination of olaparib and crizotinib regulates cell proliferation and programmed cell death.

Enhancement of olaparib activity was observed in 4 ovarian cancer cell lines (OVCAR8, OVCAR3, HEY and SKOV3). Moreover, a combination of olaparib and crizotinib proved more effective than either single agent in a xenograft model of the OVCAR8 ovarian cancer cell line. Mechanistically, a combination of olaparib and crizotinib induces DNA damage and accumulation of γ-H2AX. A combination of olaparib and crizotinib increased reactive oxygen species, while decreasing the phosphorylation of AKT. This decrease in p-AKT was associated with a decrease in p-mTOR, all of which contributed to an increase in autophagy, documented by western blot analysis, LC3 puncta and electron microscopy. Decreased p-AKT also correlated with a decrease in its downstream effector, survivin, leading to apoptosis.

Together, our data suggest that crizotinib can enhance the therapeutic efficacy of olaparib in ovarian cancer by modulating autophagy and apoptosis. Moreover, we have identified a unique combination of therapy with olaparib and crizotinib that could improve the therapeutic efficacy of olaparib and outcomes for ovarian cancer patients.

Citation Format: Janice M. Santiago-O'Farrill, Alicia M. Blessing, Sarah E. Becker, Zhen Lu, Robert C. Bast. Crizotinib improves the therapeutic efficacy of olaparib in ovarian cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4083.

Elimination of dormant, autophagic ovarian cancer cells and xenografts through enhanced sensitivity to anaplastic lymphoma kinase inhibition

BACKGROUND

Poor outcomes for patients with ovarian cancer relate to dormant, drug-resistant cancer cells that survive after primary surgery and chemotherapy. Ovarian cancer (OvCa) cells persist in poorly vascularized scars on the peritoneal surface and depend on autophagy to survive nutrient deprivation. The authors have sought drugs that target autophagic cancer cells selectively to eliminate residual disease.

METHODS

By using unbiased small-interfering RNA (siRNA) screens, the authors observed that knockdown of anaplastic lymphoma kinase (ALK) reduced the survival of autophagic OvCa cells. Small-molecule ALK inhibitors were evaluated for their selective toxicity against autophagic OvCa cell lines and xenografts. Autophagy was induced by reexpression of GTP-binding protein Di-Ras3 (DIRAS3) or serum starvation and was evaluated with Western blot analysis, fluorescence imaging, and transmission electron microscopy. Signaling pathways required for crizotinib-induced apoptosis of autophagic cells were explored with flow cytometric analysis, Western blot analysis, short-hairpin RNA knockdown of autophagic proteins, and small-molecule inhibitors of STAT3 and BCL-2.

RESULTS

Induction of autophagy by reexpression of DIRAS3 or serum starvation in multiple OvCa cell lines significantly reduced the 50% inhibitory concentration of crizotinib and other ALK inhibitors. In 2 human OvCa xenograft models, the DIRAS3-expressing tumors treated with crizotinib had significantly decreased tumor burden and long-term survival in 67% to 79% of mice. Crizotinib treatment of autophagic cancer cells further enhanced autophagy and induced autophagy-mediated apoptosis by decreasing phosphorylated STAT3 and BCL-2 signaling.

CONCLUSIONS

Crizotinib may eliminate dormant, autophagic, drug-resistant OvCa cells that remain after conventional cytoreductive surgery and combination chemotherapy. A clinical trial of ALK inhibitors as maintenance therapy after second-look operations should be seriously considered.

Abstract 4263: Autophagic ovarian cancer cells exhibit substantially enhanced sensitivity to ALK inhibition

One of the major factors contributing to poor outcomes for patients with ovarian cancer is the persistence of dormant, drug resistant cancer cells after primary surgery and chemotherapy. The persistent cancer found in positive second look operations is poorly vascularized and autophagy is widespread in more than 80% of cases. Consequently, drugs that regulate survival in autophagic cancer cells may be much more active when administered as maintenance therapy than when used to treat gross recurrent disease. Using unbiased siRNA screens, we have identified target genes that regulate the survival of ovarian cancer cells that are undergoing autophagy-induced by the re-expression of DIRAS3 (ARHI) or by serum starvation. Knockdown of the anaplastic lymphoma kinase (ALK) significantly reduced survival of ovarian cancer cells that were undergoing autophagy. Importantly, FDA-approved ALK inhibitors, including crizotinib, exhibited significantly greater toxicity after induction of autophagy by upregulation of DIRAS3 or serum starvation in 5 ovarian cancer cell lines. Induction of autophagy by upregulation of DIRAS3 or serum starvation in ovarian cancer cells reduced the IC50 of crizotinib and other ALK inhibitors ranging from 1.5 to 20-fold (all p-values <0.05). Crizotinib treatment in autophagic cancer cells enhanced autophagy and apoptosis via a decrease in p-STAT3 and BCL-2 signaling. Selective targeting of p-STAT3 or BCL-2 also resulted in significantly greater toxicity after induction of autophagy by upregulation of DIRAS3 or serum starvation in multiple ovarian cancer cells. Inducible upregulation of DIRAS3 by doxycycline in the first 6 weeks prompted autophagy and dormancy in two separate xenograft models (SKOV3 and OVCAR8). Crizotinib treatment of dormant autophagic SKOV3 xenografts prolonged median survival by 9.7 weeks (p<0.0032) and cured a subset of mice. Thirteen of fifteen mice (87%) bearing SKOV3 xenografts and nine of eleven mice (82%) bearing OVCAR8 xenografts, were tumor free at 200 days compared to the other three control arms (overall survival, p<0.0001 and p<0.05, respectively). Our studies suggest that ALK inhibitors might provide an effective agent to eliminate autophagic, dormant, drug resistant ovarian cancer cells that remain after conventional cytoreductive surgery and combination chemotherapy.

Citation Format: Alicia M. Blessing, Weiqun Mao, Lan Pang, Philip Rask, Zhen Lu, Robert C. Bast. Autophagic ovarian cancer cells exhibit substantially enhanced sensitivity to ALK inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4263.

Abstract 3313: Autophagic ovarian cancer cells exhibit substantially enhanced sensitivity to Crizotinib

One of the major factors contributing to poor outcomes for patients with ovarian cancer is the persistence of dormant, drug resistant cancer cells after primary surgery and chemotherapy. Recurrent, progressively growing ovarian cancer metastases are generally well vascularized and may only have a small fraction of cancer cells undergoing autophagy. By contrast, the persistent, drug resistant, dormant cancer cells that remain on the peritoneal cavity after conventional treatment tend to be poorly vascularized. In this nutrient-poor, avascular microenvironment autophagy is widespread and can be found in more than 80% of cases. Drugs that regulate survival in autophagic cancer cells may be much more active when administered as maintenance therapy than when used to treat gross primary or recurrent disease. Using unbiased siRNA screens, we have identified target genes that regulate the survival of ovarian cancer cells that are undergoing autophagy that has been induced by the re-expression of DIRAS3 or by amino acid starvation. Knockdown of the anaplastic lymphoma kinase (ALK) significantly reduced survival of ovarian cancer cells that were undergoing autophagy. Importantly, the FDA-approved ALK inhibitor, Crizotinib, exhibited significantly greater toxicity after induction of autophagy by upregulation of DIRAS3 (ARHI) in OVCAR8, CAOV3, and SKOv3 ovarian cancer cells. Induction of autophagy by upregulation of DIRAS3 in SKOv3 ovarian cancer cells reduced the IC50 of Crizotinib from 7.44µM ± 0.04708 to 2.129µM ± 0.06152 (P<0.05). Conversely, siRNA knockdown of DIRAS3 in CAOV3 cells with endogenously high DIRAS3 expression and baseline autophagy increased the IC50 of Crizotinib from 204 nM ± 0.01265 to 267 nM ± 0.01715 (P<0.05). Our studies in cell culture suggest that Crizotinib might provide an effective agent to eliminate autophagic, dormant drug resistant ovarian cancer cells that remain after conventional cytoreductive surgery and combination chemotherapy. Subsequent studies will evaluate the effect of Crizotinib in xenograft models of DIRAS3-induced ovarian cancer dormancy.

Citation Format: Alicia M. Blessing, Yan Wang, Weiqun Mao, Lan Pang, Zhen Lu, Robert C. Bast. Autophagic ovarian cancer cells exhibit substantially enhanced sensitivity to Crizotinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3313. doi:10.1158/1538-7445.AM2017-3313

Transcriptional regulation of core autophagy and lysosomal genes by the androgen receptor promotes prostate cancer progression

AR (androgen receptor) signaling is crucial for the development and maintenance of the prostate as well as the initiation and progression of prostate cancer. Despite the AR's central role in prostate cancer progression, it is still unclear which AR-mediated processes drive the disease. Here, we identified 4 core autophagy genes: ATG4B, ATG4D, ULK1, and ULK2, in addition to the transcription factor TFEB, a master regulator of lysosomal biogenesis and function, as transcriptional targets of AR in prostate cancer. These findings were significant in light of our recent observation that androgens promoted prostate cancer cell growth in part through the induction of autophagy. Expression of these 5 genes was essential for maximal androgen-mediated autophagy and cell proliferation. In addition, expression of each of these 5 genes alone or in combination was sufficient to increase prostate cancer cell growth independent of AR activity. Further, bioinformatic analysis demonstrated that the expression of these genes correlated with disease progression in 3 separate clinical cohorts. Collectively, these findings demonstrate a functional role for increased autophagy in prostate cancer progression, provide a mechanism for how autophagy is augmented, and highlight the potential of targeting this process for the treatment of advanced prostate cancer.

Chitosan nanoparticle-mediated delivery of miRNA-34a decreases prostate tumor growth in the bone and its expression induces non-canonical autophagy

While several new therapies are FDA-approved for bone-metastatic prostate cancer (PCa), patient survival has only improved marginally. Here, we report that chitosan nanoparticle-mediated delivery of miR-34a, a tumor suppressive microRNA that downregulates multiple gene products involved in PCa progression and metastasis, inhibited prostate tumor growth and preserved bone integrity in a xenograft model representative of established PCa bone metastasis. Expression of miR-34a induced apoptosis in PCa cells, and, in accord with downregulation of targets associated with PCa growth, including MET and Axl and c-Myc, also induced a form of non-canonical autophagy that is independent of Beclin-1, ATG4, ATG5 and ATG7. MiR-34a-induced autophagy is anti-proliferative in prostate cancer cells, as blocking apoptosis still resulted in growth inhibition of tumor cells. Thus, combined effects of autophagy and apoptosis are responsible for miR-34a-mediated prostate tumor growth inhibition, and have translational impact, as this non-canonical form of autophagy is tumor inhibitory. Together, these results provide a new understanding of the biological effects of miR-34a and highlight the clinical potential for miR-34a delivery as a treatment for bone metastatic prostate cancer.

Alcohol Regulates Genes that Are Associated with Response to Endocrine Therapy and Attenuates the Actions of Tamoxifen in Breast Cancer Cells

Hereditary, hormonal, and behavioral factors contribute to the development of breast cancer. Alcohol consumption is a modifiable behavior that is linked to increased breast cancer risks and is associated with the development of hormone-dependent breast cancers as well as disease progression and recurrence following endocrine treatment. In this study we examined the molecular mechanisms of action of alcohol by applying molecular, genetic, and genomic approaches in characterizing its effects on estrogen receptor (ER)-positive breast cancer cells. Treatments with alcohol promoted cell proliferation, increased growth factor signaling, and up-regulated the transcription of the ER target gene GREB1 but not the canonical target TFF1/pS2. Microarray analysis following alcohol treatment identified a large number of alcohol-responsive genes, including those which function in apoptotic and cell proliferation pathways. Furthermore, expression profiles of the responsive gene sets in tumors were strongly associated with clinical outcomes in patients who received endocrine therapy. Correspondingly, alcohol treatment attenuated the anti-proliferative effects of the endocrine therapeutic drug tamoxifen in ER-positive breast cancer cells. To determine the contribution and functions of responsive genes, their differential expression in tumors were assessed between outcome groups. The proto-oncogene BRAF was identified as a novel alcohol- and estrogen-induced gene that showed higher expression in patients with poor outcomes. Knock-down of BRAF, moreover, prevented the proliferation of breast cancer cells. These findings not only highlight the mechanistic basis of the effects of alcohol on breast cancer cells and increased risks for disease incidents and recurrence, but may facilitate the discovery and characterization of novel oncogenic pathways and markers in breast cancer research and therapeutics.

Identification of a Novel Coregulator, SH3YL1, That Interacts With the Androgen Receptor N-Terminus

Nuclear receptor (NR)-mediated transcriptional activity is a dynamic process that is regulated by the binding of ligands that induce distinct conformational changes in the NR. These structural alterations lead to the differential recruitment of coregulators (coactivators or corepressors) that control the expression of NR-regulated genes. Here, we show that a stretch of proline residues located within the N-terminus of androgen receptor (AR) is a bona fide coregulator binding surface, the disruption of which reduces the androgen-dependent proliferation and migration of prostate cancer (PCa) cells. Using T7 phage display, we identified a novel AR-interacting protein, Src homology 3 (SH3)-domain containing, Ysc84-like 1 (SH3YL1), whose interaction with the receptor is dependent upon this polyproline domain. As with mutations within the AR polyproline domain, knockdown of SH3YL1 attenuated androgen-mediated cell growth and migration. RNA expression analysis revealed that SH3YL1 was required for the induction of a subset of AR-modulated genes. Notable was the observation that ubinuclein 1 (UBN1), a key member of a histone H3.3 chaperone complex, was a transcriptional target of the AR/SH3YL1 complex, correlated with aggressive PCa in patients, and was necessary for the maximal androgen-mediated proliferation and migration of PCa cells. Collectively, these data highlight the importance of an amino-terminal activation domain, its associated coregulator, and downstream transcriptional targets in regulating cellular processes of pathological importance in PCa.

Abstract 1136: Regulation of AMPK by androgen receptor signaling and its role in promoting prostate cancer through the use of autophagy

While we now know that the androgen receptor (AR) is important for progression to the deadly advanced stages of prostate cancer, it is poorly understood what AR-regulated processes drive this pathology. Autophagy, an enigmatic cellular recycling process, has received increased attention as of late due to its potential oncogenic role in late-stage cancers. One of the master regulators of autophagy is the 5′-AMP-activated protein kinase (AMPK). Previous work from several independent laboratories has suggested AR signaling promotes cancer progression through an AMPK-dependent signaling mechanism. Further, it was demonstrated this enzymatic cascade was specifically regulated by Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2). Given AMPK's known role as a regulator of autophagy, we hypothesized that AR-mediated CaMKK2-AMPK signaling could promote prostate cancer through increasing cellular rates of autophagy.

To test this hypothesis, we initially assessed whether AR signaling could regulate autophagy and if so, what effect(s) this had on prostate cancer cell growth and tumor formation. We then used a variety of pharmacological and molecular approaches to determine whether CaMKK2-AMPK signaling was required and sufficient to regulate autophagy and subsequent prostate cancer cell growth in vitro and in vivo.

Here, we have determined that 1) AR regulates cell metabolism and cell growth in part by increasing autophagy in prostate cancer cells, 2) functional autophagy was clinically detected in metastatic, castration-resistant cancers but not treatment-naïve, localized tumors and 3) autophagy is required for prostate cancer progression in preclinical animal models. Additionally, AR-mediated autophagy was mediated through the direct expression of CaMKK2 and subsequent phosphorylation/activation of AMPK. Correspondingly, levels of both CaMKK2 and phosphorylated/activated AMPK correlated with prostate cancer progression in genetic mouse models and patients. Mechanistically, AR-mediated autophagy appears to promote cell growth by augmenting intracellular lipid accumulation, a hallmark of prostate cancers.

Taken together, our findings converge to demonstrate that AR signaling can co-opt the AMPK signaling cascade, a known homeostatic mechanism, to promote prostate cancer by increasing autophagy. The current study points to the potential utility of developing metabolic-targeted therapies directed towards the CaMKK2-AMPK signaling axis for the treatment of prostate cancer. Further, an inhibitor of this signaling cascade could serve as an alternative, more specific therapeutic compared to existing inhibitors of autophagy that, to date, have demonstrated limited efficacy in clinical trials due to their toxicity and poor pharmacokinetics.

Citation Format: Yan Shi, Efrosini Tsouko, Alicia M. Blessing, Jayantha Tennakoon, Jenny J. Han, Michael M. Ittmann, Daniel E. Frigo. Regulation of AMPK by androgen receptor signaling and its role in promoting prostate cancer through the use of autophagy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1136. doi:10.1158/1538-7445.AM2015-1136