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Biological importance of Gab1 in HNSCC cells

Preclinical and clinical studies have evidenced that effective targeted therapy treatment designed against receptor tyrosine kinases (RTKs) in different solid tumor paradigms is predicated on simultaneous inhibition of both the PI3K and MEK intracellular signaling pathways. Indeed, reactivation of either pathway results in resistance to these therapies. Recently, oncogenic phosphatase SHP2 inhibitors have been developed with some now reaching clinical trials. To expand on possible indications for SHP099, we screened over 800 cancer cell lines covering over 25 subsets of cancer. We found head and neck squamous cell carcinoma (HNSCC) was the most sensitive adult subtype of cancer to SHP099. We found that, in addition to the MEK pathway, SHP2 inhibition blocks the PI3K pathway in sensitive HNSCCs, resulting in downregulation of mTORC signaling and antitumor effects across several HNSCC mouse models, including an human papillomavirus (HPV+) patient-derived xenograft. Importantly, we found low levels of the RTK ligand epiregulin identified HNSCCs that were sensitive to SHP2 inhibitor, and, adding exogenous epiregulin mitigated SHP099 efficacy. Mechanistically, epiregulin maintained SHP2–GAB1 complexes in the presence of SHP2 inhibition, preventing downregulation of the MEK and PI3K pathways. In the presence of SHP2 inhibitor, HNSCCs are highly dependent on GAB1 for their survival and knockdown of GAB1 is sufficient to block the ability of epiregulin to rescue MEK and PI3K signaling. These data connect the sensitivity of HNSCC to SHP2 inhibitors and to a broad reliance on GAB1-SHP2, revealing an important and druggable signaling axis. Overall, SHP2 inhibitors are being heavily developed and may have activity in HNSCCs, and in particular those with low levels of epiregulin.Significance:This work identifies a novel role of SHP2 inhibitor by dual downregulation of PI3K and MEK pathways, through loss of GAB1 activation and disruption of GAB1 complexes in low-epiregulin HNSCC.

Cell line information and SHP099 screen data

Supplemental Table 1 shows venetoclax screen data (AUC and IC50) across 791 solid tumor cell lines.

Supplemental legend

EWS-FLI1 increases BCL-2 expression in EWFT.

ZEB1 binding sites found in 1975R2 cells compared to 1975 parental cells

Figure S4. SLC40A1 promoter and first exon are highly methylated in the MYCN overexpressing NBs.

Supplemental Figure 1. Venetoclax sensitivity and BCL-2 mRNA correlation analysis; Supplemental Figure 2. Cell viability assays of border line venetoclax-sensitive and - resistant SCLC cell lines and combination of venetoclax with chemotherapy; Supplemental Figure 3. Correlation analysis of BCL-2 family members to venetoclax sensitivity in SCLC cell lines; Supplemental Figure 4. Comparison of BCL-2 family members to venetoclax sensitivity in SCLC cell lines; Supplemental Figure 5. BCL-2 mRNA expression is increased in SCLC compared to other cancer types; Supplemental Figure 6. Cell viability of venetoclax-sensitive and -resistant SCLC cell lines; Supplemental Figure 7. Weight profiles of xenograft and PDX models treated with venetoclax; Supplemental Figure 8. The PDX models from this study express high levels of BCL-2.

Purpose:It was recently demonstrated that the EWSR1-FLI1 t(11;22)(q24;12) translocation contributes to the hypersensitivity of Ewing sarcoma to PARP inhibitors, prompting clinical evaluation of olaparib in a cohort of heavily pretreated Ewing sarcoma tumors. Unfortunately, olaparib activity was disappointing, suggesting an underappreciated resistance mechanism to PARP inhibition in patients with Ewing sarcoma. We sought to elucidate the resistance factors to PARP inhibitor therapy in Ewing sarcoma and identify a rational drug combination capable of rescuing PARP inhibitor activity.Experimental Design:We employed a pair of cell lines derived from the same patient with Ewing sarcoma prior to and following chemotherapy, a panel of Ewing sarcoma cell lines, and several patient-derived xenograft (PDX) and cell line xenograft models.Results:We found olaparib sensitivity was diminished following chemotherapy. The matched cell line pair revealed increased expression of the antiapoptotic protein BCL-2 in the chemotherapy-resistant cells, conferring apoptotic resistance to olaparib. Resistance to olaparib was maintained in this chemotherapy-resistant model in vivo, whereas the addition of the BCL-2/XL inhibitor navitoclax led to tumor growth inhibition. In 2 PDXs, olaparib and navitoclax were minimally effective as monotherapy, yet induced dramatic tumor growth inhibition when dosed in combination. We found that EWS-FLI1 increases BCL-2 expression; however, inhibition of BCL-2 alone by venetoclax is insufficient to sensitize Ewing sarcoma cells to olaparib, revealing a dual necessity for BCL-2 and BCL-XL in Ewing sarcoma survival.Conclusions:These data reveal BCL-2 and BCL-XL act together to drive olaparib resistance in Ewing sarcoma and reveal a novel, rational combination therapy that may be put forward for clinical trial testing.

Figure legends for Supplementary Figures S1-S8.

MYCN is amplified in 20% to 25% of neuroblastoma, and MYCN-amplified neuroblastoma contributes to a large percent of pediatric cancer–related deaths. Therapy improvements for this subtype of cancer are a high priority. Here we uncover a MYCN-dependent therapeutic vulnerability in neuroblastoma. Namely, amplified MYCN rewires the cell through expression of key receptors, ultimately enhancing iron influx through increased expression of the iron import transferrin receptor 1. Accumulating iron causes reactive oxygen species (ROS) production, and MYCN-amplified neuroblastomas show enhanced reliance on the system Xc- cystine/glutamate antiporter for ROS detoxification through increased transcription of this receptor. This dependence creates a marked vulnerability to targeting the system Xc-/glutathione (GSH) pathway with ferroptosis inducers. This reliance can be exploited through therapy with FDA-approved rheumatoid arthritis drugs sulfasalazine (SAS) and auranofin: in MYCN-amplified, patient-derived xenograft models, both therapies blocked growth and induced ferroptosis. SAS and auranofin activity was largely mitigated by the ferroptosis inhibitor ferrostatin-1, antioxidants like N-acetyl-L-cysteine, or by the iron scavenger deferoxamine (DFO). DFO reduced auranofin-induced ROS, further linking increased iron capture in MYCN-amplified neuroblastoma to a therapeutic vulnerability to ROS-inducing drugs. These data uncover an oncogene vulnerability to ferroptosis caused by increased iron accumulation and subsequent reliance on the system Xc-/GSH pathway.Significance:This study shows how MYCN increases intracellular iron levels and subsequent GSH pathway activity and demonstrates the antitumor activity of FDA-approved SAS and auranofin in patient-derived xenograft models of MYCN-amplified neuroblastoma.

Supplemental data

Top 10 correlated genes to BIM (BCL2L11)

Purpose: Epithelial-to-mesenchymal transition (EMT) confers resistance to a number of targeted therapies and chemotherapies. However, it has been unclear why EMT promotes resistance, thereby impairing progress to overcome it.Experimental Design: We have developed several models of EMT-mediated resistance to EGFR inhibitors (EGFRi) in EGFR-mutant lung cancers to evaluate a novel mechanism of EMT-mediated resistance.Results: We observed that mesenchymal EGFR-mutant lung cancers are resistant to EGFRi-induced apoptosis via insufficient expression of BIM, preventing cell death despite potent suppression of oncogenic signaling following EGFRi treatment. Mechanistically, we observed that the EMT transcription factor ZEB1 inhibits BIM expression by binding directly to the BIM promoter and repressing transcription. Derepression of BIM expression by depletion of ZEB1 or treatment with the BH3 mimetic ABT-263 to enhance “free” cellular BIM levels both led to resensitization of mesenchymal EGFR-mutant cancers to EGFRi. This relationship between EMT and loss of BIM is not restricted to EGFR-mutant lung cancers, as it was also observed in KRAS-mutant lung cancers and large datasets, including different cancer subtypes.Conclusions: Altogether, these data reveal a novel mechanistic link between EMT and resistance to lung cancer targeted therapies. Clin Cancer Res; 24(1); 197–208. ©2017 AACR.

Purpose: Small-cell lung cancer (SCLC) is an often-fatal neuroendocrine carcinoma usually presenting as extensive disease, carrying a 3% 5-year survival. Despite notable advances in SCLC genomics, new therapies remain elusive, largely due to a lack of druggable targets.Experimental Design: We used a high-throughput drug screen to identify a venetoclax-sensitive SCLC subpopulation and validated the findings with multiple patient-derived xenografts of SCLC.Results: Our drug screen consisting of a very large collection of cell lines demonstrated that venetoclax, an FDA-approved BCL-2 inhibitor, was found to be active in a substantial fraction of SCLC cell lines. Venetoclax induced BIM-dependent apoptosis in vitro and blocked tumor growth and induced tumor regressions in mice bearing high BCL-2–expressing SCLC tumors in vivo. BCL-2 expression was a predictive biomarker for sensitivity in SCLC cell lines and was highly expressed in a subset of SCLC cell lines and tumors, suggesting that a substantial fraction of patients with SCLC could benefit from venetoclax. Mechanistically, we uncover a novel role for gene methylation that helped discriminate high BCL-2–expressing SCLCs.Conclusions: Altogether, our findings identify venetoclax as a promising new therapy for high BCL-2–expressing SCLCs. Clin Cancer Res; 24(2); 360–9. ©2017 AACR.

Preclinical and clinical studies have evidenced that effective targeted therapy treatment designed against receptor tyrosine kinases (RTKs) in different solid tumor paradigms is predicated on simultaneous inhibition of both the PI3K and MEK intracellular signaling pathways. Indeed, reactivation of either pathway results in resistance to these therapies. Recently, oncogenic phosphatase SHP2 inhibitors have been developed with some now reaching clinical trials. To expand on possible indications for SHP099, we screened over 800 cancer cell lines covering over 25 subsets of cancer. We found head and neck squamous cell carcinoma (HNSCC) was the most sensitive adult subtype of cancer to SHP099. We found that, in addition to the MEK pathway, SHP2 inhibition blocks the PI3K pathway in sensitive HNSCCs, resulting in downregulation of mTORC signaling and antitumor effects across several HNSCC mouse models, including an human papillomavirus (HPV+) patient-derived xenograft. Importantly, we found low levels of the RTK ligand epiregulin identified HNSCCs that were sensitive to SHP2 inhibitor, and, adding exogenous epiregulin mitigated SHP099 efficacy. Mechanistically, epiregulin maintained SHP2–GAB1 complexes in the presence of SHP2 inhibition, preventing downregulation of the MEK and PI3K pathways. In the presence of SHP2 inhibitor, HNSCCs are highly dependent on GAB1 for their survival and knockdown of GAB1 is sufficient to block the ability of epiregulin to rescue MEK and PI3K signaling. These data connect the sensitivity of HNSCC to SHP2 inhibitors and to a broad reliance on GAB1-SHP2, revealing an important and druggable signaling axis. Overall, SHP2 inhibitors are being heavily developed and may have activity in HNSCCs, and in particular those with low levels of epiregulin. Significance: This work identifies a novel role of SHP2 inhibitor by dual downregulation of PI3K and MEK pathways, through loss of GAB1 activation and disruption of GAB1 complexes in low-epiregulin HNSCC.

Triple negative breast cancer (TNBC) accounts for over 30% of all breast cancer (BC)-related deaths, despite accounting for only 10% to 15% of total BC cases. Targeted therapy development has largely stalled in TNBC, underlined by a lack of traditionally druggable addictions like receptor tyrosine kinases (RTKs). Here, through full genome CRISPR/Cas9 screening of TNBC models, we have uncovered the sensitivity of TNBCs to the depletion of the ubiquitin-like modifier activating enzyme 1 (UBA1). Targeting UBA1 with the first-in-class UBA1 inhibitor TAK-243 induced unresolvable endoplasmic reticulum (ER)-stress and activating transcription factor 4 (ATF4)-mediated upregulation of proapoptotic NOXA, leading to cell death. c-MYC expression correlates with TAK-243 sensitivity and cooperates with TAK-243 to induce a stress response and cell death. Importantly, there was an order of magnitude greater sensitivity of TNBC lines to TAK-243 compared to normal tissue-derived cells. In five patient derived xenograft models (PDXs) of TNBC, TAK-243 therapy led to tumor inhibition or frank tumor regression. Moreover, in an intracardiac metastatic model of TNBC, TAK-243 markedly reduced metastatic burden, indicating UBA1 is a potential new target in TNBC expressing high levels of c-MYC.

Triple negative breast cancer (TNBC) accounts for over 30% of all breast cancer-related deaths, despite accounting for only 10%–15% of total breast cancer cases. Targeted therapy development has largely stalled in TNBC, underlined by a lack of traditionally druggable addictions like receptor tyrosine kinases (RTKs). Here, through full genome CRISPR/Cas9 screening of TNBC models, we have uncovered the sensitivity of TNBCs to the depletion of the Ubiquitin-Like Modifier Activating Enzyme 1 (UBA1). Targeting UBA1 with the first in-class UBA1 inhibitor TAK-243 induced unresolvable ER-stress and activating transcription factor 4 (ATF4)-mediated upregulation of pro-apoptotic NOXA, leading to cell death. In five patient derived xenograft models (PDXs) of TNBC, TAK-243 therapy led to tumor inhibition or frank tumor regression. In an intracardiac metastatic model of TNBC, TAK-243 markedly reduced metastatic burden. Importantly, there was an order of magnitude greater sensitivity of TNBC lines to TAK-243 compared to normal tissue-derived cells. Lastly, c-MYC expression correlates with TAK-243 sensitivity and cooperates with TAK-243 to induce a stress response and cell death. We posit UBA1 is an important new target in TNBC expressing high levels of c-MYC.SignificanceGenomic screening of TNBC cell lines revealed broad sensitivity to depletion of the E1 ubiquitin enzyme, UBA1. Disrupting UBA1 with the first in-class inhibitor TAK-243 in TNBC models induces ER-stress through an ATF4-NOXA axis that is dependent on c-MYC, leading to apoptosis, in vitro and in vivo, primary tumor growth inhibition and metastatic inhibition.

MYCN is amplified in 20% to 25% of neuroblastoma, and MYCN-amplified neuroblastoma contributes to a large percent of pediatric cancer–related deaths. Therapy improvements for this subtype of cancer are a high priority. Here we uncover a MYCN-dependent therapeutic vulnerability in neuroblastoma. Namely, amplified MYCN rewires the cell through expression of key receptors, ultimately enhancing iron influx through increased expression of the iron import transferrin receptor 1. Accumulating iron causes reactive oxygen species (ROS) production, and MYCN-amplified neuroblastomas show enhanced reliance on the system Xc- cystine/glutamate antiporter for ROS detoxification through increased transcription of this receptor. This dependence creates a marked vulnerability to targeting the system Xc-/glutathione (GSH) pathway with ferroptosis inducers. This reliance can be exploited through therapy with FDA-approved rheumatoid arthritis drugs sulfasalazine (SAS) and auranofin: in MYCN-amplified, patient-derived xenograft models, both therapies blocked growth and induced ferroptosis. SAS and auranofin activity was largely mitigated by the ferroptosis inhibitor ferrostatin-1, antioxidants like N-acetyl-L-cysteine, or by the iron scavenger deferoxamine (DFO). DFO reduced auranofin-induced ROS, further linking increased iron capture in MYCN-amplified neuroblastoma to a therapeutic vulnerability to ROS-inducing drugs. These data uncover an oncogene vulnerability to ferroptosis caused by increased iron accumulation and subsequent reliance on the system Xc-/GSH pathway. Significance: This study shows how MYCN increases intracellular iron levels and subsequent GSH pathway activity and demonstrates the antitumor activity of FDA-approved SAS and auranofin in patient-derived xenograft models of MYCN-amplified neuroblastoma.

Ferroptosis is an iron-dependent, oxidative form of cell death that is countered mainly by glutathione peroxidase 4 (GPX4) and the production of glutathione (GSH), which is formed from cysteine. The identification of the cancers that may benefit from pharmacological ferroptotic induction is just emerging. We recently demonstrated that inducing ferroptosis genetically or pharmacologically in

Purpose: It was recently demonstrated that the EWSR1-FLI1 t(11;22)(q24;12) translocation contributes to the hypersensitivity of Ewing sarcoma to PARP inhibitors, prompting clinical evaluation of olaparib in a cohort of heavily pretreated Ewing sarcoma tumors. Unfortunately, olaparib activity was disappointing, suggesting an underappreciated resistance mechanism to PARP inhibition in patients with Ewing sarcoma. We sought to elucidate the resistance factors to PARP inhibitor therapy in Ewing sarcoma and identify a rational drug combination capable of rescuing PARP inhibitor activity. Experimental Design: We employed a pair of cell lines derived from the same patient with Ewing sarcoma prior to and following chemotherapy, a panel of Ewing sarcoma cell lines, and several patient-derived xenograft (PDX) and cell line xenograft models. Results: We found olaparib sensitivity was diminished following chemotherapy. The matched cell line pair revealed increased expression of the antiapoptotic protein BCL-2 in the chemotherapy-resistant cells, conferring apoptotic resistance to olaparib. Resistance to olaparib was maintained in this chemotherapy-resistant model in vivo, whereas the addition of the BCL-2/XL inhibitor navitoclax led to tumor growth inhibition. In 2 PDXs, olaparib and navitoclax were minimally effective as monotherapy, yet induced dramatic tumor growth inhibition when dosed in combination. We found that EWS-FLI1 increases BCL-2 expression; however, inhibition of BCL-2 alone by venetoclax is insufficient to sensitize Ewing sarcoma cells to olaparib, revealing a dual necessity for BCL-2 and BCL-XL in Ewing sarcoma survival. Conclusions: These data reveal BCL-2 and BCL-XL act together to drive olaparib resistance in Ewing sarcoma and reveal a novel, rational combination therapy that may be put forward for clinical trial testing.

MYCN is amplified in 20% to 25% of neuroblastoma, and MYCN-amplified neuroblastoma contributes to a large percent of pediatric cancer-related deaths. Therapy improvements for this subtype of cancer are a high priority. Ferroptosis is an iron-dependent, oxidative form of cell death that is counteracted mainly by the production of Glutathione Peroxidase 4 (GPX4), a phospholipid hydroperoxidase that is produced through the glutathione pathway. The identification of cancers that may benefit from ferroptosis inducers are just emerging. Here we uncover a MYCN-dependent therapeutic vulnerability in neuroblastoma. Namely, amplified MYCN rewires the cell through expression of key receptors, ultimately enhancing iron influx through increased expression of the iron import transferrin receptor 1 (TFR1). Accumulating iron causes reactive oxygen species (ROS) production, and MYCN-amplified neuroblastomas show enhanced reliance on the system Xc- cystine/glutamate antiporter for ROS detoxification through increased transcription of this receptor. By performing metabolomics, we demonstrate that the transsulfuration pathway is also activated by MYCN. The increased activation of both pathways leads to cysteine accumulation that results in inhibition of lipid peroxidation. Utilizing drugs that target the main components of the glutathione and transsulfuration pathway we sensitize the MYCN neuroblastomas to ferroptotic cell death. These data provide novel insights into how MYCN alters the transcriptome in neuroblastoma to confer growth and survival advantages and simultaneously sheds light on the mechanism of action of ferroptosis inducers with potential application in other types of cancer. Citation Format: Konstantinos V. Floros, Mia O. Johnson-Berro, Richard Kurupi, Carter K. Fairchild, Krista Dalton, Bin Hu, Madhavi Puchalapalli, Mikhail G. Dozmorov, Jennifer E. Koblinski, James A. Olzmann, Lauren A. Cowart, Anthony C. Faber. MYCN-amplified neuroblastoma is addicted to iron and vulnerable to ferroptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 362.

MYCN-amplified neuroblastoma is a lethal subset of pediatric cancer. MYCN drives numerous effects in the cell, including metabolic changes that are critical for oncogenesis. The understanding that both compensatory pathways and intrinsic redundancy in cell systems exists implies that the use of combination therapies for effective and durable responses is necessary. Additionally, the most effective targeted therapies exploit an “Achilles’ heel” and are tailored to the genetics of the cancer under study. We performed an unbiased screen on select metabolic targeted therapy combinations and correlated sensitivity with over 20 subsets of cancer. We found that MYCN-amplified neuroblastoma is hypersensitive to the combination of an inhibitor of the lactate transporter MCT1, AZD3965, and complex I of the mitochondrion, phenformin. Our data demonstrate that MCT4 is highly correlated with resistance to the combination in the screen and lowly expressed in MYCN-amplified neuroblastoma. Low MCT4 combines with high expression of the MCT2 and MCT1 chaperone CD147 in MYCN-amplified neuroblastoma, altogether conferring sensitivity to the AZD3965 and phenformin combination. The result is simultaneous disruption of glycolysis and oxidative phosphorylation, resulting in dramatic disruption of adenosine triphosphate (ATP) production, endoplasmic reticulum stress, and cell death. In mouse models of MYCN-amplified neuroblastoma, the combination was tolerable at concentrations where it shrank tumors and did not increase white-blood-cell toxicity compared to single drugs. Therefore, we demonstrate that a metabolic combination screen can identify vulnerabilities in subsets of cancer and put forth a metabolic combination therapy tailored for MYCN-amplified neuroblastoma that demonstrates efficacy and tolerability in vivo.

MYCN-amplified neuroblastoma is a lethal subset of pediatric cancer. MYCN drives numerous effects in the cell, including metabolic changes that are critical for oncogenesis. The understanding that both compensatory pathways and intrinsic redundancy in cell systems exists implies that the use of combination therapies for effective and durable responses is necessary. Additionally, the most effective targeted therapies exploit an "Achilles' heel" and are tailored to the genetics of the cancer under study. We performed an unbiased screen on select metabolic targeted therapy combinations and correlated sensitivity with over 20 subsets of cancer. We found that MYCN-amplified neuroblastoma is hypersensitive to the combination of an inhibitor of the lactate transporter MCT1, AZD3965, and complex I of the mitochondrion, phenformin. Our data demonstrate that MCT4 is highly correlated with resistance to the combination in the screen and lowly expressed in MYCN-amplified neuroblastoma. Low MCT4 combines with high expression of the MCT2 and MCT1 chaperone CD147 in MYCN-amplified neuroblastoma, altogether conferring sensitivity to the AZD3965 and phenformin combination. The result is simultaneous disruption of glycolysis and oxidative phosphorylation, resulting in dramatic disruption of adenosine triphosphate (ATP) production, endoplasmic reticulum stress, and cell death. In mouse models of MYCN-amplified neuroblastoma, the combination was tolerable at concentrations where it shrank tumors and did not increase white-blood-cell toxicity compared to single drugs. Therefore, we demonstrate that a metabolic combination screen can identify vulnerabilities in subsets of cancer and put forth a metabolic combination therapy tailored for MYCN-amplified neuroblastoma that demonstrates efficacy and tolerability in vivo.

Simple Summary Synovial sarcoma is a soft-tissue sarcoma that lacks effective systemic therapy and carries poor prognosis due to frequent late local recurrence and metastases. The cancer is known to be driven in part by increased expression of the pro-survival protein BCL-2. Surprisingly, synovial sarcoma proved resistant to BCL-2 inhibitors in pre-clinical trials. We identified increased activity of a second pro-survival protein, MCL-1, as responsible for this resistance. We showed that co-targeting both BCL-2 and MCL-1 proves to be an effective therapeutic approach both in cell culture and animal models of synovial sarcoma, supporting translation into clinical trials. Abstract Synovial sarcoma (SS) is frequently diagnosed in teenagers and young adults and continues to be treated with polychemotherapy with variable success. The SS18-SSX gene fusion is pathognomonic for the disease, and high expression of the anti-apoptotic BCL-2 pathologically supports the diagnosis. As the oncogenic SS18-SSX fusion gene itself is not druggable, BCL-2 inhibitor-based therapies are an appealing therapeutic opportunity. Venetoclax, an FDA-approved BCL-2 inhibitor that is revolutionizing care in some BCL-2-expressing hematological cancers, affords an intriguing therapeutic possibility to treat SS. In addition, there are now dozens of venetoclax-based combination therapies in clinical trials in hematological cancers, attributing to the limited toxicity of venetoclax. However, preclinical studies of venetoclax in SS have demonstrated an unexpected ineffectiveness. In this study, we analyzed the response of SS to venetoclax and the underlying BCL-2 family biology in an effort to understand venetoclax treatment failure and find a therapeutic strategy to sensitize SS to venetoclax. We found remarkably depressed levels of the endogenous MCL-1 inhibitor, NOXA, in SS compared to other sarcomas. Expressing NOXA led to sensitization to venetoclax, as did the addition of the MCL-1 BH3 mimetic, S63845. Importantly, the venetoclax/S63845 combination induced tumor regressions in SS patient-derived xenograft (PDX) models. As a very close analog of S63845 (S64315) is now in clinical trials with venetoclax in AML (NCT03672695), the combination of MCL-1 BH3 mimetics and venetoclax should be considered for SS patients as a new therapy.

Human epidermal growth factor receptor 2 gene (HER2) is focally amplified in approximately 20% of breast cancers. HER2 inhibitors alone are not effective, and sensitizing agents will be necessary to move away from a reliance on heavily toxic chemotherapeutics. We recently demonstrated that the efficacy of HER2 inhibitors is mitigated by uniformly low levels of the myeloid cell leukemia 1 (MCL-1) endogenous inhibitor, NOXA. Emerging clinical data have demonstrated that clinically advanced cyclin-dependent kinase (CDK) inhibitors are effective MCL-1 inhibitors in patients, and, importantly, well tolerated. We, therefore, tested whether the CDK inhibitor, dinaciclib, could block MCL-1 in preclinical HER2-amplified breast cancer models and therefore sensitize these cancers to dual HER2/EGFR inhibitors neratinib and lapatinib, as well as to the novel selective HER2 inhibitor tucatinib. Indeed, we found dinaciclib suppresses MCL-1 RNA and is highly effective at sensitizing HER2 inhibitors both in vitro and in vivo. This combination was tolerable in vivo. Mechanistically, liberating the effector BCL-2 protein, BAK, from MCL-1 results in robust apoptosis. Thus, clinically advanced CDK inhibitors may effectively combine with HER2 inhibitors and present a chemotherapy-free therapeutic strategy in HER2-amplified breast cancer, which can be tested immediately in the clinic.

Introduction: Recurrence of Cushing’s disease (CD) caused by benign pituitary microadenomas are challenging clinical problems. Mechanisms underlying adenoma formation and recurrence remain unknown. PMAIP1 gene codes for Noxa, a Bcl-2 homology 3 (BH3) pro-apoptotic protein frequently downregulated in malignant human tumors.1-6 The role of dysregulated apoptosis remains largely unknown in benign tumors and in CD. We hypothesized that altered expression of Noxa protein is a pro-survival adaptation employed by CD adenomas. Methods: Syngeneic human pituitary adenoma and adjacent normal gland pairs (n=2), and an additional CD adenoma were analyzed with RNAseq. 10 CD, 1 growth hormone (GH) and 1 non-functioning adenoma (NFPA) underwent immunohistochemical (IHC) analysis for Noxa expression, which was graded by a neuropathologist as 0=none, 1=light, 2=medium, 3=strong. Staining grade represents relative protein expression. Results: Compared to adjacent normal pituitary tissue, we found that adenomas (n = 3) had a 3.76 fold increase in PMAIP1 mRNA. However, there was attenuated Noxa IHC staining in adenomas compared to normal pituitary in 8 of 10 CD patients (2:3, respectively), but similar staining in 2 of 10 CD patients (2:2 and 2-3:2-3). In GH and NFPA, we found similar patterns of Noxa suppression in the adenomas compared to the normal gland. Conclusion: Despite elevated PMAIP1 (Noxa) gene expression in adenomas compared to adjacent normal gland in CD, protein expression was reduced in adenomas. This downregulation of Noxa protein expression may contribute to reduced apoptosis of tumor cells. These findings suggest that CD adenomas gain pro-survival advantage by downregulating Noxa protein at post-transcriptional or post-translational level. References 1. Escobar, D. et al. Cell Death Dis.6, 1-14 (2015).2. Brinkmann, K. et al. Cell Rep.3, 881-891 (2013).3. Liu, Y. L. et al. Oncotarget5, 11237-11251 (2014).4. Dengler, M. A. et al. Cell Death Dis.5, 1-10 (2014).5. Liang, L. et al. J. Oral Pathol. Med.48, 52-59 (2019).6. Tahir, S. K. et al. Cancer Res.67, 1176-1183 (2007).

Purpose: Epithelial-to-mesenchymal transition (EMT) confers resistance to a number of targeted therapies and chemotherapies. However, it has been unclear why EMT promotes resistance, thereby impairing progress to overcome it. Experimental Design: We have developed several models of EMT-mediated resistance to EGFR inhibitors (EGFRi) in EGFR-mutant lung cancers to evaluate a novel mechanism of EMT-mediated resistance. Results: We observed that mesenchymal EGFR-mutant lung cancers are resistant to EGFRi-induced apoptosis via insufficient expression of BIM, preventing cell death despite potent suppression of oncogenic signaling following EGFRi treatment. Mechanistically, we observed that the EMT transcription factor ZEB1 inhibits BIM expression by binding directly to the BIM promoter and repressing transcription. Derepression of BIM expression by depletion of ZEB1 or treatment with the BH3 mimetic ABT-263 to enhance “free” cellular BIM levels both led to resensitization of mesenchymal EGFR-mutant cancers to EGFRi. This relationship between EMT and loss of BIM is not restricted to EGFR-mutant lung cancers, as it was also observed in KRAS-mutant lung cancers and large datasets, including different cancer subtypes. Conclusions: Altogether, these data reveal a novel mechanistic link between EMT and resistance to lung cancer targeted therapies. Clin Cancer Res; 24(1); 197–208. ©2017 AACR.

Targeted therapies have revolutionized treatment of several different types of cancers. However, in almost an invariable fashion, cancers eventually regrow in the presence of the targeted therapy, a phenomenon referred to as acquired resistance. In this issue of Cancer Research, Finn and colleagues demonstrate that modeling acquired resistance to MET tyrosine kinase inhibition in a MET-amplified gastric cancer cell line by a single, high exposure of the targeted therapy reveals clinically relevant acquired resistant mechanisms, which may be more faithful and comprehensive than the ones revealed through traditional ramp-up approaches. See related article by Finn et al., p. 79

MYCN-amplified neuroblastoma is responsible for ~10% of all cancer-related deaths in the pediatric population. MYCN drives numerous effects in the cell, including metabolic changes that are critical for oncogenesis. The understanding that both compensatory pathways and intrinsic redundancy in cell systems exists implies that the use of combination therapies for effective and durable responses is necessary. Additionally, the most effective targeted therapies exploit an “Achilles’ heels” and are tailored to the genetics of the cancer under study. We performed an unbiased screen on select metabolic targeted therapy combinations and correlated sensitivity with over 20 subsets of cancer. We found that MYCN-amplified neuroblastoma are hypersensitive to the combination of AZD3965, an inhibitor of the lactate transporter MCT1, and phenformin, an inhibitor of complex I of the mitochondrion. Our data demonstrate MCT4 is highly correlated with resistance to the combination of AZD3965 and phenformin through the screen, is heavily methylated, and lowly expressed in MYCN-amplified neuroblastoma. Low MCT4 combines with high expression of the MCT2 and MCT1 chaperone CD147 in MYCN-amplified neuroblastoma, altogether conferring sensitivity to AZD3965 and phenformin combination. Metabolomic analysis showed that the result is simultaneous disruption of glycolysis and oxidative phosphorylation, resulting in dramatic disruption of adenosine triphosphate (ATP) production, endoplasmic reticulum (ER) stress, and apoptosis, which was seen through cell viability assays and protein analysis. In mouse models of MYCN-amplified neuroblastoma, the combination was tolerable at concentrations where it shrank tumors and did not increase white blood cell toxicity compared to single-drugs. Therefore, we demonstrate a metabolic combination screen can identify vulnerabilities in subsets of cancer and put forth a metabolic combination therapy tailored for MYCN-amplified neuroblastoma that demonstrates efficacy and tolerability in vivo. Citation Format: Krista M. Powell, Timonthy L. Lochmann, Konstantinos V. Floros, Marissa L. Calbert, Richard Kurupi, Giovanna T. Stein, Joseph McClanaghan, Ellen Murchie, Regina K. Egan, Patricia Greninger, Mikhail Dozmorov, Sivapriya Ramamoorthy, Madhavi Puchalapalli, Bin Hu, Lisa Shock, Jennifer Koblisnski, John Glod, Sosipatros A. Boikos, Cyril H. Benes, Anthony C. Faber. Catastrophic ATP loss underlines a metabolic combination therapy tailored for MYCN-amplified neuroblastoma [abstract]. In: Abstracts: AACR Special Virtual Conference on Epigenetics and Metabolism; October 15-16, 2020; 2020 Oct 15-16. Philadelphia (PA): AACR; Cancer Res 2020;80(23 Suppl):Abstract nr PO-024.

Summary Fewer than half of children with high-risk neuroblastoma survive. Many of these tumors harbor high-level amplification of MYCN, which correlates with poor disease outcome. Using data from our large drug screen we predicted, and subsequently demonstrated, that MYCN-amplified neuroblastomas are sensitive to the BCL-2 inhibitor ABT-199. This sensitivity occurs in part through low anti-apoptotic BCL-xL expression, high pro-apoptotic NOXA expression, and paradoxical, MYCN-driven upregulation of NOXA. Screening for enhancers of ABT-199 sensitivity in MYCN-amplified neuroblastomas, we demonstrate that the Aurora Kinase A inhibitor MLN8237 combines with ABT-199 to induce widespread apoptosis. In diverse models of MYCN-amplified neuroblastoma, including a patient-derived xenograft model, this combination uniformly induced tumor shrinkage, and in multiple instances led to complete tumor regression., Graphical Abstract, Highlights • Amplified MYCN is synthetic lethal with the BCL-2 inhibitor ABT-199 in neuroblastoma • MYCN upregulates the MCL-1 inhibitor, NOXA • MYCN-amplified neuroblastomas are further sensitized to ABT-199 with MLN8237 • ABT-199 with MLN8237 induce tumor regressions in MYCN-amplified neuroblastoma mice, Ham et al. show that MYCN-amplified neuroblastomas are sensitive to treatment with the BCL-2 inhibitor ABT-199 due to MYCN-driven increase of NOXA. Combination treatment with the Aurora Kinase A inhibitor MLN8237 and ABT-199 is synergistic in xenograft models of this tumor type, in part via reducing MCL-1.

e23561 Background: While Synovial Sarcoma (SS) only accounts for about 10% of soft tissue sarcomas (STS), or ~10,000 cases/year, ~4,000 of these will be fatal. Little benefit has been seen with newer combination chemotherapies and immune checkpoint inhibitors. SS is a transcription factor-driven cancer characterized by an t(X;18) chromosomal translocation resulting in the SS18-SSX fusion gene. SS is also known to overexpress the anti-apoptotic protein BCL-2, which has been used as a diagnostic marker for SS. Venetoclax, the FDA approved BH3 mimetic which specifically inhibits BCL-2, has been used to treat BCL-2-driven hematological cancers. Yet, preclinical studies of venetoclax, currently in clinical use for BCL-2 related hematologic malignancies, have failed in SS, raising the possibility of other BCL-2 family members playing a role in resistance. Methods: Publicly available gene expression databases of SS were queried for expression of BCL-2 family member expression, including the endogenous MCL-1 inhibitor, NOXA. Six SS cell lines, including ASKA, HS-SY-II, Yamato, SW982, SYO.1, and an ex vivo line from a SS patient-derived xenograft (PDX) were tested in vitro with combinations of venetoclax and the MCL-1 inhibitor S63845, using cell viability assays. In vivo testing employed both a patient-derived xenograft (PDX) model of SS and a cell line derived (SYO.1) xenograft model. Results: Queries of published gene expression data for SS demonstrated that SS expresses low levels of the endogenous MCL-1 inhibitor, NOXA, nominating a mechanism for intrinsic venetoclax resistance in these tumors, and suggesting rational combination of venetoclax and the MCL-1 inhibitor, S63845. In vitro, SS all cell lines possessing the SS18-SSX fusion gene demonstrated synergistic sensitivity to combined S63845 and venetoclax, despite generally insensitivity to either drug as monotherapy. Importantly, in an SS PDX, we demonstrated S63845 and venetoclax synergize to induce tumor regression. In the SYO.1 xenograft model, combination therapy significantly reduced tumor growth compared to no treatment or single agent groups. Conclusions: These findings provide the preclinical rationale for translation of the rational combination of BCL-2 and MCL-1 inhibitors into clinical trials for SS.

Pharmaceutical inhibition of the Human Epidermal growth factor Receptor 2 (HER2) oncogene has dramatically improved outcomes in HER2-amplified breast cancers. However, monotherapy HER2 inhibitors are not effective. We have recently reported that a co-amplified microRNA within the HER2 amplicon, leads to activation of the oncogene Myeloid Cell Leukemia-1 (MCL-1), tempering cell death responses to HER2 inhibitors. Importantly, HER2 inhibitors are sensitized to cell death by the addition of pharmacological MCL-1 inhibitors, which are entering clinical trials.

Significance In HER2-amplified breast cancers, HER2 inhibitors have been very successful as adjuvant therapy but not as monotherapy. Here, we demonstrate that coamplification of a HER2 intronic miRNA causes intrinsic resistance to HER2 inhibitors by indirectly down-regulating the pro-apoptotic NOXA. Importantly, coinhibition with MCL-1 inhibitors overcomes this resistance., HER2 (ERBB2) amplification is a driving oncogenic event in breast cancer. Clinical trials have consistently shown the benefit of HER2 inhibitors (HER2i) in treating patients with both local and advanced HER2+ breast cancer. Despite this benefit, their efficacy as single agents is limited, unlike the robust responses to other receptor tyrosine kinase inhibitors like EGFR inhibitors in EGFR-mutant lung cancer. Interestingly, the lack of HER2i efficacy occurs despite sufficient intracellular signaling shutdown following HER2i treatment. Exploring possible intrinsic causes for this lack of response, we uncovered remarkably depressed levels of NOXA, an endogenous inhibitor of the antiapoptotic MCL-1, in HER2-amplified breast cancer. Upon investigation of the mechanism leading to low NOXA, we identified a micro-RNA encoded in an intron of HER2, termed miR-4728, that targets the mRNA of the Estrogen Receptor α (ESR1). Reduced ESR1 expression in turn prevents ERα-mediated transcription of NOXA, mitigating apoptosis following treatment with the HER2i lapatinib. Importantly, resistance can be overcome with pharmacological inhibition of MCL-1. More generally, while many cancers like EGFR-mutant lung cancer are driven by activated kinases that when drugged lead to robust monotherapeutic responses, we demonstrate that the efficacy of targeted therapies directed against oncogenes active through focal amplification may be mitigated by coamplified genes.

In HER2 -amplified breast cancers, HER2 inhibitors have been very successful as adjuvant therapy but not as monotherapy. Here, we demonstrate that coamplification of a HER2 intronic miRNA causes intrinsic resistance to HER2 inhibitors by indirectly down-regulating the pro-apoptotic NOXA. Importantly, coinhibition with MCL-1 inhibitors overcomes this resistance. HER2 (ERBB2) amplification is a driving oncogenic event in breast cancer. Clinical trials have consistently shown the benefit of HER2 inhibitors (HER2i) in treating patients with both local and advanced HER2+ breast cancer. Despite this benefit, their efficacy as single agents is limited, unlike the robust responses to other receptor tyrosine kinase inhibitors like EGFR inhibitors in EGFR -mutant lung cancer. Interestingly, the lack of HER2i efficacy occurs despite sufficient intracellular signaling shutdown following HER2i treatment. Exploring possible intrinsic causes for this lack of response, we uncovered remarkably depressed levels of NOXA, an endogenous inhibitor of the antiapoptotic MCL-1, in HER2 -amplified breast cancer. Upon investigation of the mechanism leading to low NOXA, we identified a micro-RNA encoded in an intron of HER2, termed miR-4728, that targets the mRNA of the Estrogen Receptor α (ESR1). Reduced ESR1 expression in turn prevents ERα-mediated transcription of NOXA, mitigating apoptosis following treatment with the HER2i lapatinib. Importantly, resistance can be overcome with pharmacological inhibition of MCL-1. More generally, while many cancers like EGFR -mutant lung cancer are driven by activated kinases that when drugged lead to robust monotherapeutic responses, we demonstrate that the efficacy of targeted therapies directed against oncogenes active through focal amplification may be mitigated by coamplified genes.

It was recently demonstrated that theWe employed a pair of cell lines derived from the same patient with Ewing sarcoma prior to and following chemotherapy, a panel of Ewing sarcoma cell lines, and several patient-derived xenograft (PDX) and cell line xenograft models.We found olaparib sensitivity was diminished following chemotherapy. The matched cell line pair revealed increased expression of the antiapoptotic protein BCL-2 in the chemotherapy-resistant cells, conferring apoptotic resistance to olaparib. Resistance to olaparib was maintained in this chemotherapy-resistant modelThese data reveal BCL-2 and BCL-X

Targeted molecular agents have revolutionized cancer care in the adult population. Many of these drugs have been inhibitors of kinases. BCL-2 family members have long been understood to play key roles in mitochondrial integrity, serving as the key signaling nexus between kinase cascade-driven growth and survival signals, and they can also be found genetically altered in human cancers (e.g. IgG-BCL-2 translocations in follicular lymphoma). Indeed, the FDA-approval of the BCL-2 homology (BH)3 domain mimetic, venetoclax (AbbVie), is the first clinically approved BCL-2 family member targeted therapy of any kind, bringing BCL-2 family member inhibitors into the spotlight. This chapter will highlight the current state of affairs of this exciting time for BCL-2 family member targeted therapies, by focusing on three most advanced types of BCL-2 family inhibitors: the BCL-2 BH3 mimetic, venetoclax; the dual BCL-2/BCL-xL BH3 mimetic, navitoclax; and the recently developed MCL-1 BH3 mimetics. We will also discuss resistant mechanisms that have emerged from the intensification of preclinical and clinical studies of these compounds. The challenges understanding which cancers may most benefit from BH3 mimetics will also be discussed, as will the emergence of BH3 profling to address these challenges. Finally, we will discuss how these drugs may be combined with other currently available drugs to overcome resistance and induce robust clinical responses.

Proapoptotic BCL-2 proteins converge upon the outer mitochondrial membrane (OMM) to promote mitochondrial outer membrane permeabilization (MOMP) and apoptosis. Here we investigated the mechanistic relationship between mitochondrial shape and MOMP and provide evidence that BAX requires a distinct mitochondrial size to induce MOMP. We utilized the terminal unfolded protein response pathway to systematically define proapoptotic BCL-2 protein composition after stress and then directly interrogated their requirement for a productive mitochondrial size. Complementary biochemical, cellular, in vivo, and ex vivo studies reveal that Mfn1, a GTPase involved in mitochondrial fusion, establishes a mitochondrial size that is permissive for proapoptotic BCL-2 family function. Cells with hyperfragmented mitochondria, along with size-restricted OMM model systems, fail to support BAX-dependent membrane association and permeabilization due to an inability to stabilize BAXα9·membrane interactions. This work identifies a mechanistic contribution of mitochondrial size in dictating BAX activation, MOMP, and apoptosis.

High-risk neuroblastoma is often distinguished by amplification of MYCN and loss of differentiation potential. We performed high-throughput drug screening of epigenetic-targeted therapies across a large and diverse tumor cell line panel and uncovered the hypersensitivity of neuroblastoma cells to GSK-J4, a small-molecule dual inhibitor of lysine 27 of histone 3 (H3K27) demethylases ubiquitously transcribed tetratricopeptide repeat, X chromosome (UTX), and histone demethylase Jumonji D3 (JMJD3). Mechanistically, GSK-J4 induced neuroblastoma differentiation and endoplasmic reticulum (ER) stress, with accompanying up-regulation of p53 up-regulated modulator of apoptosis (PUMA) and induction of cell death. Retinoic acid (RA)–resistant neuroblastoma cells were sensitive to GSK-J4. In addition, GSK-J4 was effective at blocking the growth of chemorefractory and patient-derived xenograft models of high-risk neuroblastoma in vivo. Furthermore, GSK-J4 and RA combination increased differentiation and ER stress over GSK-J4 effects and limited the growth of neuroblastomas resistant to either drug alone. In MYCN-amplified neuroblastoma, PUMA induction by GSK-J4 sensitized tumors to the B cell lymphoma 2 (BCL-2) inhibitor venetoclax, demonstrating that epigenetic-targeted therapies and BCL-2 homology domain 3 mimetics can be rationally combined to treat this high-risk subset of neuroblastoma. Therefore, H3K27 demethylation inhibition is a promising therapeutic target to treat high-risk neuroblastoma, and H3K27 demethylation can be part of rational combination therapies to induce robust antineuroblastoma activity.

Purpose: Small-cell lung cancer (SCLC) is an often-fatal neuroendocrine carcinoma usually presenting as extensive disease, carrying a 3% 5-year survival. Despite notable advances in SCLC genomics, new therapies remain elusive, largely due to a lack of druggable targets. Experimental Design: We used a high-throughput drug screen to identify a venetoclax-sensitive SCLC subpopulation and validated the findings with multiple patient-derived xenografts of SCLC. Results: Our drug screen consisting of a very large collection of cell lines demonstrated that venetoclax, an FDA-approved BCL-2 inhibitor, was found to be active in a substantial fraction of SCLC cell lines. Venetoclax induced BIM-dependent apoptosis in vitro and blocked tumor growth and induced tumor regressions in mice bearing high BCL-2–expressing SCLC tumors in vivo. BCL-2 expression was a predictive biomarker for sensitivity in SCLC cell lines and was highly expressed in a subset of SCLC cell lines and tumors, suggesting that a substantial fraction of patients with SCLC could benefit from venetoclax. Mechanistically, we uncover a novel role for gene methylation that helped discriminate high BCL-2–expressing SCLCs. Conclusions: Altogether, our findings identify venetoclax as a promising new therapy for high BCL-2–expressing SCLCs. Clin Cancer Res; 24(2); 360–9. ©2017 AACR.

Objectives BCL2L12 is a recently discovered and cloned gene from members of our research team. It is a novel member of the BCL2 gene family, members of which are implicated in different hematological malignancies. In the present study, we investigated and studied the expression profile of BCL2L12 in acute myeloid leukemia (AML). Design and methods Total RNA was isolated from peripheral blood of 67 AML patients and healthy donors. The expression profile of BCL2L12 was studied using real-time PCR methodology (SYBR Green chemistry). We also evaluated the association of the BCL2L12 mRNA expression level with clinical and pathological disease parameters, as well with disease-free survival (DFS) and overall survival (OS), using the chi-square ( χ 2 ) test or the Fisher's exact test, where appropriate. Results Leukemia patients expressing high level of BCL2L12 were 3 times more likely to relapse ( p = 0.004) or die ( p = 0.007) than patients with low level of BCL2L12 expression. Additionally, statistically significant relationships were revealed between BCL2L12 expression level and CD117 expression, the presence of splenomegaly and chemotherapy response. Conclusions Our results suggest that BCL2L12 can be considered as a new independent prognostic and chemotherapy response marker in AML.

KRAS is frequently mutated in lung cancer. Whereas MAPK is a well-known effector pathway of KRAS, blocking this pathway with clinically available MAPK inhibitors is relatively ineffective. Here, we report that epithelial-to-mesenchymal transition rewires the expression of receptor tyrosine kinases, leading to differential feedback activation of the MAPK pathway following MEK inhibition. In epithelial-like KRAS-mutant lung cancers, this feedback was attributed to ERBB3-mediated activation of MEK and AKT. In contrast, in mesenchymal-like KRAS-mutant lung cancers, FGFR1 was dominantly expressed but suppressed by the negative regulator Sprouty proteins; MEK inhibition led to repression of SPRY4 and subsequent FGFR1-mediated reactivation of MEK and AKT. Therapeutically, the combination of a MEK inhibitor (MEKi) and an FGFR inhibitor (FGFRi) induced cell death in vitro and tumor regressions in vivo. These data establish the rationale and a therapeutic approach to treat mesenchymal-like KRAS-mutant lung cancers effectively with clinically available FGFR1 and MAPK inhibitors. Significance: Adaptive resistance to MEKi is driven by receptor tyrosine kinases specific to the differentiation state of the KRAS-mutant non–small cell lung cancer (NSCLC). In mesenchymal-like KRAS-mutant NSCLC, FGFR1 is highly expressed, and MEK inhibition relieves feedback suppression of FGFR1, resulting in reactivation of ERK; suppression of ERK by MEKi/FGFRi combination results in tumor shrinkage. Cancer Discov; 6(7); 754–69. ©2016 AACR. This article is highlighted in the In This Issue feature, p. 681

The purpose of this study is the development of a novel combination therapy that targets HER2-amplified breast cancer. About one quarter of breast cancers harbor amplification of HER2. HER2 is a transmembrane receptor tyrosine kinase (RTK) belonging to the ERBB family of receptors (ERBB1-4). Upon hetero- and homo-dimerization, HER2 activates several key intracellular pathways, regulating many cellular functions including proliferation and survival. HER2 inhibitors (HER2i) (e.g. the receptor tyrosine kinase (RTK) inhibitor, lapatinib) are now part of standard care for treating HER2-amplified breast cancers. However, despite their anti-cancer benefit, these drugs have limited efficacy as monotherapies, which contrasts to other RTK inhibitors in other RTK-driven cancers. To better understand this apparent dichotomy, in the present study, we evaluated potential modifiers of HER2i therapy. Here, we found that the pro-apoptotic NOXA, a member of the B-cell CLL/lymphoma 2 (BCL2) family which acts mainly via inhibitory binding of the pro-survival MCL-1, was markedly down-regulated in breast cancers compared to other cancers, and this was largely attributed to the HER2-amplified subset. Experimentally, overexpressing NOXA or silencing MCL-1 dramatically sensitizes HER2 amplified breast cancer cell lines to lapatinib via apoptosis. Consistently, pharmaceutical inhibition of MCL-1 sensitizes HER2-amplified breast cancers to lapatinib in vitro and in vivo. Mechanistically, disruption of MCL-1:BIM complexes and MCL-1:BAK underlie dual HER2i/MCL-1i therapy. Therefore, deficient NOXA expression constitutes a bonafide apoptotic block in HER2 amplified breast cancers, contributes to mitigated HER2i responses, and presents a rational combination therapy that may improve HER2i responses. Citation Format: Konstantinos V. Floros, Kyung-A Song, Timothy L. Lochmann, Mark T. Hughes, Daniel A. Heisey, Hisashi Harada, Bin Hu, Jennifer Koblinski, Andrew J. Souers, Joel D. Leverson, Anthony C. Faber. Deficient NOXA in HER2-amplified breast cancer drives kinase inhibitor resistance [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 3082. doi:10.1158/1538-7445.AM2017-3082

The mitochondrial pathway of apoptosis proceeds when the outer mitochondrial membrane (OMM) is compromised by the pro-apoptotic BCL-2 family members, BAK and BAX. Once activated, BAK and BAX form proteolipid pores in the OMM leading to mitochondrial outer membrane permeabilization (MOMP), and the release of inner membrane space proteins, such as cytochrome c, which promotes caspase activation. The use of isolated mitochondria has been instrumental to understanding the key interactions necessary to engage BAK and BAX activation, MOMP, and apoptosis. Furthermore, it is possible to biochemically define the relationships between BCL-2 family function and mitochondrial physiology using isolated systems. Our laboratory uses freshly isolated mitochondria from numerous sources to better understand BCL-2 family function and requirements for BAK and BAX activation. Here, we will discuss commonly used in vitro techniques to perform MOMP and cytochrome c release assays; and provide several key methodologies to implicate BAK and BAX activity in these processes.