The CHK1 inhibitor prexasertib in BRCA wild-type platinum-resistant recurrent high-grade serous ovarian carcinoma: a phase 2 trial

The multi-cohort phase 2 trial NCT02203513 was designed to evaluate the clinical activity of the CHK1 inhibitor (CHK1i) prexasertib in patients with breast or ovarian cancer. Here we report the activity of CHK1i in platinum-resistant high-grade serous ovarian carcinoma (HGSOC) with measurable and biopsiable disease (cohort 5), or without biopsiable disease (cohort 6). The primary endpoint was objective response rate (ORR). Secondary outcomes were safety and progression-free survival (PFS). 49 heavily pretreated patients were enrolled (24 in cohort 5, 25 in cohort 6). Among the 39 RECISTv1.1-evaluable patients, ORR was 33.3% in cohort 5 and 28.6% in cohort 6. Primary endpoint was not evaluable due to early stop of the trial. The median PFS was 4 months in cohort 5 and 6 months in cohort 6. Toxicity was manageable. Translational research was an exploratory endpoint. Potential biomarkers were investigated using pre-treatment fresh biopsies and serial blood samples. Transcriptomic analysis revealed high levels of DNA replication-related genes (POLA1, POLE, GINS3) associated with lack of clinical benefit [defined post-hoc as PFS < 6 months]. Subsequent preclinical experiments demonstrated significant cytotoxicity of POLA1 silencing in combination with CHK1i in platinum-resistant HGSOC cell line models. Therefore, POLA1 expression may be predictive for CHK1i resistance, and the concurrent POLA1 inhibition may improve the efficacy of CHK1i monotherapy in this hard-to-treat population, deserving further investigation.

Dual-inhibition of NAMPT and PAK4 induces anti-tumor effects in 3D-spheroids model of platinum-resistant ovarian cancer

Ovarian cancer follows a characteristic progression pattern, forming multiple tumor masses enriched with cancer stem cells (CSCs) within the abdomen. Most patients develop resistance to standard platinum-based drugs, necessitating better treatment approaches. Targeting CSCs by inhibiting NAD+ synthesis has been previously explored. Nicotinamide phosphoribosyltransferase (NAMPT), which is the rate limiting enzyme in the salvage pathway for NAD+ synthesis is an attractive drug target in this pathway. KPT-9274 is an innovative drug targeting both NAMPT and p21 activated kinase 4 (PAK4). However, its effectiveness against ovarian cancer has not been validated. Here, we show the efficacy and mechanisms of KPT-9274 in treating 3D-cultured spheroids that are resistant to platinum-based drugs. In these spheroids, KPT-9274 not only inhibited NAD+ production in NAMPT-dependent cell lines, but also suppressed NADPH and ATP production, indicating reduced mitochondrial function. It also downregulated of inflammation and DNA repair-related genes. Moreover, the compound reduced PAK4 activity by altering its mostly cytoplasmic localization, leading to NAD+-dependent decreases in phosphorylation of S6 Ribosomal protein, AKT, and β-Catenin in the cytoplasm. These findings suggest that KPT-9274 could be a promising treatment for ovarian cancer patients who are resistant to platinum drugs, emphasizing the need for precision medicine to identify the specific NAD+ producing pathway that a tumor relies upon before treatment.

NOS2 and COX2 Provide Key Spatial Targets that Determine Outcome in ER- Breast Cancer

Estrogen receptor-negative (ER-) breast cancer is an aggressive breast cancer subtype with limited therapeutic options. Upregulated expression of both inducible nitric oxide synthase (NOS2) and cyclo-oxygenase (COX2) in breast tumors predicts poor clinical outcomes. Signaling molecules released by these enzymes activate oncogenic pathways, driving cancer stemness, metastasis, and immune suppression. The influence of tumor NOS2/COX2 expression on the landscape of immune markers using multiplex fluorescence imaging of 21 ER- breast tumors were stratified for survival. A powerful relationship between tumor NOS2/COX2 expression and distinct CD8+ T cell phenotypes was observed at 5 years post-diagnosis. These results were confirmed in a validation cohort using gene expression data showing that ratios of NOS2 to CD8 and COX2 to CD8 are strongly associated with poor outcomes in high NOS2/COX2-expressing tumors. Importantly, multiplex imaging identified distinct CD8+ T cell phenotypes relative to tumor NOS2/COX2 expression in Deceased vs Alive patient tumors at 5-year survival. CD8+NOS2-COX2- phenotypes defined fully inflamed tumors with significantly elevated CD8+ T cell infiltration in Alive tumors expressing low NOS2/COX2. In contrast, two distinct phenotypes including inflamed CD8+NOS2+COX2+ regions with stroma-restricted CD8+ T cells and CD8-NOS2-COX2+ immune desert regions with abated CD8+ T cell penetration, were significantly elevated in Deceased tumors with high NOS2/COX2 expression. These results were supported by applying an unsupervised nonlinear dimensionality-reduction technique, UMAP, correlating specific spatial CD8/NOS2/COX2 expression patterns with patient survival. Moreover, spatial analysis of the CD44v6 and EpCAM cancer stem cell (CSC) markers within the CD8/NOS2/COX2 expression landscape revealed positive correlations between EpCAM and inflamed stroma-restricted CD8+NOS2+COX2+ phenotypes at the tumor/stroma interface in deceased patients. Also, positive correlations between CD44v6 and COX2 were identified in immune desert regions in deceased patients. Furthermore, migrating tumor cells were shown to occur only in the CD8-NOS2+COX2+ regions, identifying a metastatic hot spot. Taken together, this study shows the strength of spatial localization analyses of the CD8/NOS2/COX2 landscape, how it shapes the tumor immune microenvironment and the selection of aggressive tumor phenotypes in distinct regions that lead to poor clinical outcomes. This technique could be beneficial for describing tumor niches with increased aggressiveness that may respond to clinically available NOS2/COX2 inhibitors or immune-modulatory agents.

Spatial analysis of NOS2 and COX2 interaction with T-effector cells reveals immunosuppressive landscapes associated with poor outcome in ER- breast cancer patients

Multiple immunosuppressive mechanisms exist in the tumor microenvironment that drive poor outcomes and decrease treatment efficacy. The co-expression of NOS2 and COX2 is a strong predictor of poor prognosis in ER- breast cancer and other malignancies. Together, they generate pro-oncogenic signals that drive metastasis, drug resistance, cancer stemness, and immune suppression. Using an ER- breast cancer patient cohort, we found that the spatial expression patterns of NOS2 and COX2 with CD3+CD8+PD1- T effector (Teff) cells formed a tumor immune landscape that correlated with poor outcome. NOS2 was primarily associated with the tumor-immune interface, whereas COX2 was associated with immune desert regions of the tumor lacking Teff cells. A higher ratio of NOS2 or COX2 to Teff was highly correlated with poor outcomes. Spatial analysis revealed that regional clustering of NOS2 and COX2 was associated with stromal-restricted Teff, while only COX2 was predominant in immune deserts. Examination of other immunosuppressive elements, such as PDL1/PD1, Treg, B7H4, and IDO1, revealed that PDL1/PD1, Treg, and IDO1 were primarily associated with restricted Teff, whereas B7H4 and COX2 were found in tumor immune deserts. Regardless of the survival outcome, other leukocytes, such as CD4 T cells and macrophages, were primarily in stromal lymphoid aggregates. Finally, in a 4T1 model, COX2 inhibition led to a massive cell infiltration, thus validating the hypothesis that COX2 is an essential component of the Teff exclusion process and, thus, tumor evasion. Our study indicates that NOS2/COX2 expression plays a central role in tumor immunosuppression. Our findings indicate that new strategies combining clinically available NOS2/COX2 inhibitors with various forms of immune therapy may open a new avenue for the treatment of aggressive ER-breast cancers.

A Single-Arm, Open-Label Phase II Study of ONC201 in Recurrent/Refractory Metastatic Breast Cancer and Advanced Endometrial Carcinoma

BACKGROUND

ONC201 is a small molecule that can cause nonapoptotic cell death through loss of mitochondrial function. Results from the phase I/II trials of ONC201 in patients with refractory solid tumors demonstrated tumor responses and prolonged stable disease in some patients.

METHODS

This single-arm, open-label, phase II clinical trial evaluated the efficacy of ONC201 at the recommended phase II dose (RP2D) in patients with recurrent or refractory metastatic breast or endometrial cancer. Fresh tissue biopsies and blood were collected at baseline and at cycle 2 day 2 for correlative studies.

RESULTS

Twenty-two patients were enrolled; 10 patients with endometrial cancer, 7 patients with hormone receptor-positive breast cancer, and 5 patients with triple-negative breast cancer. The overall response rate was 0%, and the clinical benefit rate, defined by complete response (CR) + partial response (PR) + stable disease (SD), was 27% (n = 3/11). All patients experienced an adverse event (AE), which was primarily low grade. Grade 3 AEs occurred in 4 patients; no grade 4 AEs occurred. Tumor biopsies did not show that ONC201 consistently induced mitochondrial damage or alterations in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or the TRAIL death receptors. ONC201 treatment caused alterations in peripheral immune cell subsets.

CONCLUSION

ONC201 monotherapy did not induce objective responses in recurrent or refractory metastatic breast or endometrial cancer at the RP2D dose of 625 mg weekly but had an acceptable safety profile (ClinicalTrials.gov Identifier: NCT03394027).

Opportunities for Achieving the Cancer Moonshot Goal of a 50% Reduction in Cancer Mortality by 2047

On February 2, 2022, President Biden and First Lady Dr. Biden reignited the Cancer Moonshot, setting a new goal to reduce age-standardized cancer mortality rates by at least 50% over the next 25 years in the United States. We estimated trends in U.S. cancer mortality during 2000 to 2019 for all cancers and the six leading types (lung, colorectum, pancreas, breast, prostate, liver). Cancer death rates overall declined by 1.4% per year from 2000 to 2015, accelerating to 2.3% per year during 2016 to 2019, driven by strong declines in lung cancer mortality (-4.7%/year, 2014 to 2019). Recent declines in colorectal (-2.0%/year, 2010-2019) and breast cancer death rates (-1.2%/year, 2013-2019) also contributed. However, trends for other cancer types were less promising. To achieve the Moonshot goal, progress against lung, colorectal, and breast cancer deaths needs to be maintained and/or accelerated, and new strategies for prostate, liver, pancreatic, and other cancers are needed. We reviewed opportunities to prevent, detect, and treat these common cancers that could further reduce population-level cancer death rates and also reduce disparities.

SIGNIFICANCE

We reviewed opportunities to prevent, detect, and treat common cancers, and show that to achieve the Moonshot goal, progress against lung, colorectal, and breast cancer deaths needs to be maintained and/or accelerated, and new strategies for prostate, liver, pancreatic, and other cancers are needed. See related commentary by Bertagnolli et al., p. 1049. This article is highlighted in the In This Issue feature, p. 1027.

Phase I Study and Cell-Free DNA Analysis of T-DM1 and Metronomic Temozolomide for Secondary Prevention of HER2-Positive Breast Cancer Brain Metastases

PURPOSE

Preclinical data showed that prophylactic, low-dose temozolomide (TMZ) significantly prevented breast cancer brain metastasis. We present results of a phase I trial combining T-DM1 with TMZ for the prevention of additional brain metastases after previous occurrence and local treatment in patients with HER2+ breast cancer.

PATIENTS AND METHODS

Eligible patients had HER2+ breast cancer with brain metastases and were within 12 weeks of whole brain radiation therapy (WBRT), stereotactic radiosurgery, and/or surgery. Standard doses of T-DM1 were administered intravenously every 21 days (3.6 mg/kg) and TMZ was given orally daily in a 3+3 phase I dose escalation design at 30, 40, or 50 mg/m2, continuously. DLT period was one 21-day cycle. Primary endpoint was safety and recommended phase II dose. Symptom questionnaires, brain MRI, and systemic CT scans were performed every 6 weeks. Cell-free DNA sequencing was performed on patients' plasma and CSF.

RESULTS

Twelve women enrolled, nine (75%) with prior SRS therapy and three (25%) with prior WBRT. Grade 3 or 4 AEs included thrombocytopenia (1/12), neutropenia (1/12), lymphopenia (6/12), and decreased CD4 (6/12), requiring pentamidine for Pneumocystis jirovecii pneumonia prophylaxis. No DLT was observed. Four patients on the highest TMZ dose underwent dose reductions. At trial entry, 6 of 12 patients had tumor mutations in CSF, indicating ongoing metastatic colonization despite a clear MRI. Median follow-up on study was 9.6 m (2.8-33.9); only 2 patients developed new parenchymal brain metastases. Tumor mutations varied with patient outcome.

CONCLUSIONS

Metronomic TMZ in combination with standard dose T-DM1 shows low-grade toxicity and potential activity in secondary prevention of HER2+ brain metastases.

Abstract 957: Prediction of patient response to targeted and immunotherapies from the tumor transcriptome in a wide set of indications and clinical trials

Background: Precision oncology is gradually advancing into mainstream clinical practice, demonstrating significant survival benefits. However, eligibility and response rates remain limited in many cases, calling for better predictive biomarkers.

Methods: We present ENLIGHT, a transcriptomics-based computational approach that identifies clinically relevant genetic interactions and uses them to predict a patient’s response to a variety of therapies in multiple cancer types, importantly, without training on previous treatment response data. Consequently, in addition to its ability to predict patients' response to approved and well-studied therapies, ENLIGHT can predict the response to new treatments in early development, even before clinical data has accumulated. Accordingly, we study ENLIGHT in two translationally relevant scenarios: Personalized Oncology (PO), aimed at prioritizing approved treatments to a given patient, and Clinical Trial Design (CTD), selecting the subset of most likely responders in a patient cohort.

Results: Evaluating ENLIGHT’s performance on 21 blinded clinical trial datasets spanning 11 indications and 15 different drugs in the PO setting, we show that it can effectively predict a patient’s treatment response across multiple therapies and cancer types, with an overall odds ratio of 2.59 (p=3.41e-8), and a 36% increase in response rate over the baseline (p=3.30e-13). Its prediction accuracy is better than other state-of-the-art transcriptomics-based signatures. Unlike most signatures that are prognostic or provide insights for only very few, specific treatments, ENLIGHT provides matching scores to a broad range of treatments. Quite strikingly, its performance is comparable to that of supervised predictors developed for specific indications and drugs. In combination with the IFN-γ signature, ENLIGHT achieves an odds ratio larger than 4 in predicting response to immune checkpoint therapy. In the CTD scenario, our results show that by excluding non-responders ENLIGHT can enhance clinical trial success for immunotherapies and other monoclonal antibodies, achieving &gt; 90% of the response rate attainable under an optimal exclusion strategy.

Conclusion: ENLIGHT is a powerful transcriptomics-based precision oncology pipeline developed by Pangea Biomed that broadly predicts response to both extant and novel targeted and immune therapies, going beyond context-specific biomarkers.

Citation Format: Gal Dinstag, Eldad D. Shulman, Efrat Elis, Doreen S. Ben-Zvi, Omer Tirosh, Eden Maimon, Isaac Meilijson, Emmanuel Elalouf, Boris Temkin, Philipp Vitkovsky, Eyal Schiff, Danh-Tai Hoang, Sanju Sinha, Nishanth Ulhas Nair, Joo Sang-Lee, Alejandro A. Schäffer, Ze'ev Ronai, Dejan Juric, Andrea B. Apolo, William L. Dahut, Stanley Lipkowitz, Raanan Berger, Razelle Kurzrock, Antonios Papanicolau-Sengos, Fatima Karzai, Mark R. Gilbert, Kenneth Aldape, Padma S. Rajagopal, Tuvik Beker, Eytan Ruppin, Ranit Aharonov. Prediction of patient response to targeted and immunotherapies from the tumor transcriptome in a wide set of indications and clinical trials [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 957.

Multi-omics analyses reveal ClpP activators disrupt essential mitochondrial pathways in triple-negative breast cancer

ClpP activators ONC201 and related small molecules (TR compounds, Madera Therapeutics), have demonstrated significant anti-cancer potential in vitro and in vivo studies, including clinical trials for refractory solid tumors. Though progress has been made in identifying specific phenotypic outcomes following ClpP activation, the exact mechanism by which ClpP activation leads to broad anti-cancer activity has yet to be fully elucidated. In this study, we utilized a multi-omics approach to identify the ClpP-dependent proteomic, transcriptomic, and metabolomic changes resulting from ONC201 or the TR compound TR-57 in triple-negative breast cancer cells. Applying mass spectrometry-based methods of proteomics and metabolomics, we identified ∼8,000 proteins and 588 metabolites, respectively. From proteomics data, 113 (ONC201) and 191 (TR-57) proteins significantly increased and 572 (ONC201) and 686 (TR-57) proteins significantly decreased in this study. Gene ontological (GO) analysis revealed strong similarities between proteins up- or downregulated by ONC201 or TR-57 treatment. Notably, this included the downregulation of many mitochondrial processes and proteins, including mitochondrial translation and mitochondrial matrix proteins. We performed a large-scale transcriptomic analysis of WT SUM159 cells, identifying ∼7,700 transcripts (746 and 1,100 significantly increasing, 795 and 1,013 significantly decreasing in ONC201 and TR-57 treated cells, respectively). Less than 21% of these genes were affected by these compounds in ClpP null cells. GO analysis of these data demonstrated additional similarity of response to ONC201 and TR-57, including a decrease in transcripts related to the mitochondrial inner membrane and matrix, cell cycle, and nucleus, and increases in other nuclear transcripts and transcripts related to metal-ion binding. Comparison of response between both compounds demonstrated a highly similar response in all -omics datasets. Analysis of metabolites also revealed significant similarities between ONC201 and TR-57 with increases in α-ketoglutarate and 2-hydroxyglutaric acid and decreased ureidosuccinic acid, L-ascorbic acid, L-serine, and cytidine observed following ClpP activation in TNBC cells. Further analysis identified multiple pathways that were specifically impacted by ClpP activation, including ATF4 activation, heme biosynthesis, and the citrulline/urea cycle. In summary the results of our studies demonstrate that ONC201 and TR-57 induce highly similar and broad effects against multiple mitochondrial processes required for cell proliferation.

First-in-human phase 1 clinical trial of anti-core 1 O-glycans targeting monoclonal antibody NEO-201 in treatment-refractory solid tumors

BACKGROUND

NEO201 is a humanized IgG1 monoclonal antibody (mAb) generated against tumor-associated antigens from patients with colorectal cancer. NEO-201 binds to core 1 or extended core 1 O-glycans expressed by its target cells. Here, we present outcomes from a phase I trial of NEO-201 in patients with advanced solid tumors that have not responded to standard treatments.

METHODS

This was a single site, open label 3 + 3 dose escalation clinical trial. NEO-201 was administered intravenously every two weeks in a 28-day cycle at dose level (DL) 1 (1 mg/kg), DL 1.5 (1.5 mg/kg) and DL 2 (2 mg/kg) until dose limiting toxicity (DLT), disease progression, or patient withdrawal. Disease evaluations were conducted after every 2 cycles. The primary objective was to assess the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of NEO-201. The secondary objective was to assess the antitumor activity by RECIST v1.1. The exploratory objectives assessed pharmacokinetics and the effect of NEO-201 administration on immunologic parameters and their impact on clinical response.

RESULTS

Seventeen patients (11 colorectal, 4 pancreatic and 2 breast cancers) were enrolled; 2 patients withdrew after the first dose and were not evaluable for DLT. Twelve of the 15 patients evaluable for safety discontinued due to disease progression and 3 patients discontinued due to DLT (grade 4 febrile neutropenia [1 patient] and prolonged neutropenia [1 patient] at DL 2, and grade 3 prolonged (> 72 h) febrile neutropenia [1 patient] at DL 1.5). A total of 69 doses of NEO-201 were administered (range 1-15, median 4). Common (> 10%) grade 3/4 toxicities occurred as follows: neutropenia (26/69 doses, 17/17 patients), white blood cell decrease (16/69 doses, 12/17 patients), lymphocyte decrease (8/69 doses, 6/17 patients). Thirteen patients were evaluable for disease response; the best response was stable disease (SD) in 4 patients with colorectal cancer. Analysis of soluble factors in serum revealed that a high level of soluble MICA at baseline was correlated with a downregulation of NK cell activation markers and progressive disease. Unexpectedly, flow cytometry showed that NEO-201 also binds to circulating regulatory T cells and reduction of the quantities of these cells was observed especially in patients with SD.

CONCLUSIONS

NEO-201 was safe and well tolerated at the MTD of 1.5 mg/kg, with neutropenia being the most common adverse event. Furthermore, a reduction in the percentage of regulatory T cells following NEO-201 treatment supports our ongoing phase II clinical trial evaluating the efficiency of the combination of NEO-201 with the immune checkpoint inhibitor pembrolizumab in adults with treatment-resistant solid tumors.

TRIAL REGISTRATION

NCT03476681 . Registered 03/26/2018.

Targeting Mitochondria with ClpP Agonists as a Novel Therapeutic Opportunity in Breast Cancer

Breast cancer is the most frequently diagnosed malignancy worldwide and the leading cause of cancer mortality in women. Despite the recent development of new therapeutics including targeted therapies and immunotherapy, triple-negative breast cancer remains an aggressive form of breast cancer, and thus improved treatments are needed. In recent decades, it has become increasingly clear that breast cancers harbor metabolic plasticity that is controlled by mitochondria. A myriad of studies provide evidence that mitochondria are essential to breast cancer progression. Mitochondria in breast cancers are widely reprogrammed to enhance energy production and biosynthesis of macromolecules required for tumor growth. In this review, we will discuss the current understanding of mitochondrial roles in breast cancers and elucidate why mitochondria are a rational therapeutic target. We will then outline the status of the use of mitochondria-targeting drugs in breast cancers, and highlight ClpP agonists as emerging mitochondria-targeting drugs with a unique mechanism of action. We also illustrate possible drug combination strategies and challenges in the future breast cancer clinic.

Intraperitoneal Monocytes plus IFNs as a Novel Cellular Immunotherapy for Ovarian Cancer: Mechanistic Characterization and Results from a Phase I Clinical Trial

PURPOSE

Ovarian cancer is the most lethal gynecologic cancer and intrinsically resistant to checkpoint immunotherapies. We sought to augment innate immunity, building on previous work with IFNs and monocytes.

PATIENTS AND METHODS

Preclinical experiments were designed to define the mechanisms of cancer cell death mediated by the combination of IFNs α and γ with monocytes. We translated these preclinical findings into a phase I trial of autologous IFN-activated monocytes administered intraperitoneally to platinum-resistant or -refractory ovarian cancer patients.

RESULTS

IFN-treated monocytes induced caspase 8-dependent apoptosis by the proapoptotic TRAIL and mediated by the death receptors 4 and 5 (DR4 and DR5, respectively) on cancer cells. Therapy was well tolerated with evidence of clinical activity, as 2 of 9 evaluable patients had a partial response by RECIST criteria, and 1 additional patient had a CA-125 response. Upregulation of monocyte-produced TRAIL and cytokines was confirmed in peripheral blood. Long-term responders had alterations in innate and adaptive immune compartments.

CONCLUSIONS

Given the mechanism of cancer cell death, and the acceptable tolerability of the clinical regimen, this platform presents a possibility for future combination therapies to augment anticancer immunity. See related commentary by Chow and Dorigo, p. 299.

Clinically oriented prediction of patient response to targeted and immunotherapies from the tumor transcriptome

BACKGROUND

Precision oncology is gradually advancing into mainstream clinical practice, demonstrating significant survival benefits. However, eligibility and response rates remain limited in many cases, calling for better predictive biomarkers.

METHODS

We present ENLIGHT, a transcriptomics-based computational approach that identifies clinically relevant genetic interactions and uses them to predict a patient's response to a variety of therapies in multiple cancer types without training on previous treatment response data. We study ENLIGHT in two translationally oriented scenarios: personalized oncology (PO), aimed at prioritizing treatments for a single patient, and clinical trial design (CTD), selecting the most likely responders in a patient cohort.

FINDINGS

Evaluating ENLIGHT's performance on 21 blinded clinical trial datasets in the PO setting, we show that it can effectively predict a patient's treatment response across multiple therapies and cancer types. Its prediction accuracy is better than previously published transcriptomics-based signatures and is comparable with that of supervised predictors developed for specific indications and drugs. In combination with the interferon-γ signature, ENLIGHT achieves an odds ratio larger than 4 in predicting response to immune checkpoint therapy. In the CTD scenario, ENLIGHT can potentially enhance clinical trial success for immunotherapies and other monoclonal antibodies by excluding non-responders while overall achieving more than 90% of the response rate attainable under an optimal exclusion strategy.

CONCLUSIONS

ENLIGHT demonstrably enhances the ability to predict therapeutic response across multiple cancer types from the bulk tumor transcriptome.

FUNDING

This research was supported in part by the Intramural Research Program, NIH and by the Israeli Innovation Authority.

Photochemical Dimerization of Plakinidine B Leads to Potent Inhibition of the E3 Ubiquitin-Protein Ligase CBL-B

A new dimeric alkaloid plakoramine A [(±)-1] was identified from a marine sponge Plakortis sp. Chiral-phase HPLC separation of (±)-1 led to the purified enantiomers (+)-1 and (-)-1 which both potently inhibited CBL-B E3 ubiquitin ligase activities. The absolute configurations of the enantiomers were determined by quantum chemical calculations. Scrutinization of the purification conditions revealed a previously undescribed, nonenzymatic route to form (±)-1 via photochemical conversion of its naturally occurring monomeric counterpart, plakinidine B (2).

Flotillin-2 regulates epidermal growth factor receptor activation, degradation by Cbl-mediated ubiquitination, and cancer growth

Epidermal growth factor receptor (EGFR) signaling is frequently dysregulated in various cancers. The ubiquitin ligase Casitas B-lineage lymphoma proto-oncogene (Cbl) regulates degradation of activated EGFR through ubiquitination and acts as an adaptor to recruit proteins required for trafficking. Here, we used stable isotope labeling with amino acids in cell culture mass spectrometry to compare Cbl complexes with or without epidermal growth factor (EGF) stimulation. We identified over a hundred novel Cbl interactors, and a secondary siRNA screen found that knockdown of Flotillin-2 (FLOT2) led to increased phosphorylation and degradation of EGFR upon EGF stimulation in HeLa cells. In PC9 and H441 cells, FLOT2 knockdown increased EGF-stimulated EGFR phosphorylation, ubiquitination, and downstream signaling, reversible by EGFR inhibitor erlotinib. CRISPR knockout (KO) of FLOT2 in HeLa cells confirmed EGFR downregulation, increased signaling, and increased dimerization and endosomal trafficking. Furthermore, we determined that FLOT2 interacted with both Cbl and EGFR. EGFR downregulation upon FLOT2 loss was Cbl dependent, as coknockdown of Cbl and Cbl-b restored EGFR levels. In addition, FLOT2 overexpression decreased EGFR signaling and growth. Overexpression of wildtype (WT) FLOT2, but not the soluble G2A FLOT2 mutant, inhibited EGFR phosphorylation upon EGF stimulation in HEK293T cells. FLOT2 loss induced EGFR-dependent proliferation and anchorage-independent growth. Lastly, FLOT2 KO increased tumor formation and tumor volume in nude mice and NSG mice, respectively. Together, these data demonstrated that FLOT2 negatively regulated EGFR activation and dimerization, as well as its subsequent ubiquitination, endosomal trafficking, and degradation, leading to reduced proliferation in vitro and in vivo.

Systemic Nos2 Depletion and Cox inhibition limits TNBC disease progression and alters lymphoid cell spatial orientation and density

Antitumor immune polarization is a key predictor of clinical outcomes to cancer therapy. An emerging concept influencing clinical outcome involves the spatial location of CD8+ T cells, within the tumor. Our earlier work demonstrated immunosuppressive effects of NOS2 and COX2 tumor expression. Here, we show that NOS2/COX2 levels influence both the polarization and spatial location of lymphoid cells including CD8+ T cells. Importantly, elevated tumor NOS2/COX2 correlated with exclusion of CD8+ T cells from the tumor epithelium. In contrast, tumors expressing low NOS2/COX2 had increased CD8+ T cell penetration into the tumor epithelium. Consistent with a causative relationship between these observations, pharmacological inhibition of COX2 with indomethacin dramatically reduced tumor growth of the 4T1 model of TNBC in both WT and Nos2- mice. This regimen led to complete tumor regression in ∼20-25% of tumor-bearing Nos2- mice, and these animals were resistant to tumor rechallenge. Th1 cytokines were elevated in the blood of treated mice and intratumoral CD4+ and CD8+ T cells were higher in mice that received indomethacin when compared to control untreated mice. Multiplex immunofluorescence imaging confirmed our phenotyping results and demonstrated that targeted Nos2/Cox2 blockade improved CD8+ T cell penetration into the 4T1 tumor core. These findings are consistent with our observations in low NOS2/COX2 expressing breast tumors proving that COX2 activity is responsible for limiting the spatial distribution of effector T cells in TNBC. Together these results suggest that clinically available NSAID's may provide a cost-effective, novel immunotherapeutic approach for treatment of aggressive tumors including triple negative breast cancer.

Mitochondrial Matrix Protease ClpP Agonists Inhibit Cancer Stem Cell Function in Breast Cancer Cells by Disrupting Mitochondrial Homeostasis

Mitochondria are multifaceted organelles which are important for bioenergetics, biosynthesis and signaling in metazoans. Mitochondrial functions are frequently altered in cancer to promote both the energy and the necessary metabolic intermediates for biosynthesis required for tumor growth. Cancer stem cells (CSCs) contribute to chemotherapy resistance, relapse, and metastasis. Recent studies have shown that while non-stem, bulk cancer cells utilize glycolysis, breast CSCs are more dependent on oxidative phosphorylation (OxPhos) and therefore targeting mitochondria may inhibit CSC function. We previously reported that small molecule ONC201, which is an agonist for the mitochondrial caseinolytic protease (ClpP), induces mitochondrial dysfunction in breast cancer cells. In this study, we report that ClpP agonists inhibit breast cancer cell proliferation and CSC function in vitro and in vivo. Mechanistically, we found that OxPhos inhibition downregulates multiple pathways required for CSC function, such as the mevalonate pathway, YAP, Myc, and the HIF pathway. ClpP agonists showed significantly greater inhibitory effect on CSC functions compared with other mitochondria-targeting drugs. Further studies showed that ClpP agonists deplete NAD(P)+ and NAD(P)H, induce redox imbalance, dysregulate one-carbon metabolism and proline biosynthesis. Downregulation of these pathways by ClpP agonists further contribute to the inhibition of CSC function. In conclusion, ClpP agonists inhibit breast CSC functions by disrupting mitochondrial homeostasis in breast cancer cells and inhibiting multiple pathways critical to CSC function.

Significance

ClpP agonists disrupt mitochondrial homeostasis by activating mitochondrial matrix protease ClpP. We report that ClpP agonists inhibit cell growth and cancer stem cell functions in breast cancer models by modulating multiple metabolic pathways essential to cancer stem cell function.

Late-onset Proteus syndrome with cerebriform connective tissue nevus and subsequent development of intraductal papilloma

Proteus syndrome (PS) is a rare segmental overgrowth disorder caused by a mosaic activating variant in AKT1. The features of PS are often not present at birth but develop during the first few years of life. We describe a 55-year-old female, whose first symptom of overgrowth, a cerebriform connective tissue nevus, occurred at 19 years of age. We report the identification of the AKT1 c.49G > A p.(Glu17Lys) variant in this progressive lesion, the bony overgrowth, and recurrence after surgical intervention. In the sixth decade of life, this individual developed intraductal papillomas within her right breast which were confirmed to contain the same activating AKT1 variant as the connective tissue nevus. While similar neoplasms have been described in an individual with Proteus syndrome, none has been evaluated for the presence of the AKT1 variant. The tumor also contained two likely pathogenic variants in PIK3R1, c.1392_1403dupTAGATTATATGA p.(Asp464_Tyr467dup) and c.1728_1730delGAG p.(Arg577del). The finding of additional genetic variation putatively affecting the PI3K/AKT pathway in the neoplastic tissue may provide preliminary evidence of a molecular mechanism for tumorigenesis in PS. The late onset of symptoms and molecular characterization of the breast tumor expand the clinical spectrum of this rare disorder.

Characterization of TR-107, a novel chemical activator of the human mitochondrial protease ClpP

We recently described the identification of a new class of small‐molecule activators of the mitochondrial protease ClpP. These compounds synthesized by Madera Therapeutics showed increased potency of cancer growth inhibition over the related compound ONC201. In this study, we describe chemical optimization and characterization of the next generation of highly potent and selective small‐molecule ClpP activators (TR compounds) and demonstrate their efficacy against breast cancer models in vitro and in vivo. We selected one compound (TR‐107) with excellent potency, specificity, and drug‐like properties for further evaluation. TR‐107 showed ClpP‐dependent growth inhibition in the low nanomolar range that was equipotent to paclitaxel in triple‐negative breast cancer (TNBC) cell models. TR‐107 also reduced specific mitochondrial proteins, including OXPHOS and TCA cycle components, in a time‐, dose‐, and ClpP‐dependent manner. Seahorse XF analysis and glucose deprivation experiments confirmed the inactivation of OXPHOS and increased dependence on glycolysis following TR‐107 exposure. The pharmacokinetic properties of TR‐107 were compared with other known ClpP activators including ONC201 and ONC212. TR‐107 displayed excellent exposure and serum t_1/2 after oral administration. Using human TNBC MDA‐MB‐231 xenografts, the antitumor response to TR‐107 was investigated. Oral administration of TR‐107 resulted in a reduction in tumor volume and extension of survival in the treated compared with vehicle control mice. ClpP activation in vivo was validated by immunoblotting for TFAM and other mitochondrial proteins. In summary, we describe the identification of highly potent new ClpP agonists with improved efficacy against TNBC, through targeted inactivation of OXPHOS and disruption of mitochondrial metabolism.

Abstract P1-21-06: Phase I study of T-DM1 and metronomic temozolomide in secondary prevention of HER2+ breast cancer brain metastases following local radiation therapy

Background: The incidence of breast cancer brain metastases is rising, and, these lesions in the central nervous system (CNS) and their treatments cause physical and neurocognitive impairment. Only modest incremental advances in progression free survival have been achieved with drugs to treat CNS lesions, while nearly half of the patients who receive SRS will develop new brain metastases within 1 year. In murine models of breast cancer, we demonstrated that low doses of temozolomide (TMZ) administered in a prophylactic, metronomic fashion significantly prevented development of brain metastases. No effect, however, was seen in established brain metastases or systemic breast cancer metastases. We hypothesize that low dose, metronomic TMZ will prevent the outgrowth of brain lesions in HER2+ patients, when added to an active anti-HER2 treatment. We present here the results of the phase I trial combining T-DM1 to TMZ for the prevention of additional brain metastases after their first occurrence and local treatment. Methods: Eligible patients had HER2+ breast cancer with brain metastases and were within 12 weeks of local brain metastases therapy (WBRT, SRS and or surgery), with PS 0-2 and adequate end organ function. Standard doses of T-DM1 were administered IV every 21 days (3.6 mg/kg) and TMZ was given PO daily in a 3+3 design at 30, 40 or 50 mg/m2, continuously. The DLT period was one 21d cycle. Safety was assessed by CTCAEv4.0 and response by RECISTv1.1 and RANO-BM. Brain MRI and systemic CT scans were performed every 6 weeks. Blood samples for correlatives evaluation were collected at baseline and every cycle while on trial. CSF was collected at baseline and C3D1 for all patients. Questionnaires (MDASI-BT and PROMIS®) for evaluation of symptoms and quality of life were completed every 6 weeks. Results: Twelve women with median age 55.5yr (44-67) were enrolled. Only 3 (25%) patients had HR+/HER2+ tumors at initial diagnosis. Nine (75%) patients presented stages II and III disease at initial diagnosis, and developed brain metastases at the diagnosis of first recurrence. Nine (75%) patients received SRS therapy and 3 (25%) received WBRT prior to trial enrollment. Grade 3 or 4 AEs included thrombocytopenia (1/12), neutropenia (1/12), lymphopenia (6/12) and decreased CD4 (6/12), requiring pentamidine for PCP prophylaxis. No DLT was observed. Four patients underwent dose reductions (thrombocytopenia, fatigue and peripheral neuropathy), all of them enrolled on the highest TMZ dose. Median follow-up on study is now 9.6m (1.2-32) and no patient developed new parenchymal brain metastases. Five patients remain on study, while 7 are off study due to progression at previously irradiated CNS lesion (2), progression of systemic disease (2), focal leptomeningeal involvement (1), new cancer (1) and persistent thrombocytopenia (1). Completion rates for the questionnaires were 99% by Cycle 15 (81 completed out of expected 82) and 90% by Cycle 41 (123/137), and will be reported at presentation. Conclusion: Metronomic TMZ in combination with standard dose T-DM1 is tolerable and shows promising activity in secondary prevention of HER2+ brain metastases. Systematic longitudinal symptom assessments in breast cancer patients with brain metastasis are feasible. A randomized phase II expansion of this trial with T-DM1 or T-Dxd +/- TMZ is planned.

Citation Format: Alexandra S Zimmer, Seth Steinberg, Mark Gilbert, Terri Armstrong, Eric Burton, Nicole Houston, Dee Dee Smart, Nadia Biassou, John Butman, Priscilla K Brastianos, Carey K Anders, Stanley Lipkowitz, Patricia S Steeg. Phase I study of T-DM1 and metronomic temozolomide in secondary prevention of HER2+ breast cancer brain metastases following local radiation therapy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-21-06.

Abstract P127: Mitochondrial matrix protease ClpP agonists suppress breast cancer stem cell function by downregulating multiple stem cell regulatory mechanisms

Background: We previously reported that small molecule ONC201 induces mitochondrial structural and functional damage, leading to death in breast cancer cells. Subsequent studies demonstrated that ONC201 and the related analogs TR compounds are agonists of mitochondrial caseinolytic protease P (ClpP), an essential protein for maintenance of mitochondrial protein homeostasis. Recent studies have shown that cancer stem cells (CSCs) preferentially use mitochondrial oxidative metabolism for energy production. Here, we report that ClpP agonists inhibit breast CSCs by unique mechanisms targeting pathways vital to maintain CSC function. Methods: ONC201 and other ClpP agonists (TR-57, 65), other mitochondria-targeting drugs, such as oligomycin, metformin, CPI-613 were used. MDA-MB231 cell line was used as a primary in vitro model system. CLPP knockout (KO) cells were generated by CRISPR/Cas9 technology. Seahorse XF analyzer was used for cellular respiration analysis. Luminescence-based assays were used for cell viability and metabolism assays. Protein expression was examined by Western blotting. Aldefluor assay and SORE6 (OCT4/SOX2 response element)-reporter gene were used to monitor CSC fraction. Mammosphere formation assay was used to evaluate CSC function in vitro. In vivo limiting dilution analysis was used to evaluate tumor initiation capability of cells injected into mammary fat pad of athymic nude female mice. Results: Seahorse XF analyzer showed that mammospheres are more dependent on OxPhos than glycolysis compared with cells grown in 2D, supporting the hypothesis that breast CSCs rely on OxPhos. ClpP agonists reduced the CSC fraction in both Aldefluor and SORE6 reporter assays. ClpP agonists inhibited mammosphere formation in CLPP WT, but not in CLPP KO cells, demonstrating the on-target effects on CSC function. In in vivo assays, tumor formation was significantly (p&lt;0.001) inhibited in the ClpP agonist-treated group compared with the control group, and the effect was CLPP-dependent. Altogether, these findings support that ClpP agonists inhibit CSC in breast cancers. We found that ClpP agonists downregulate multiple pathways and proteins critical for CSC maintenance including mevalonate pathway, HIF1a, EPAS1, YAP, and Myc. We also observed that other mitochondria targeting drugs such as oligomycin, metformin downregulate these signaling pathways and proteins to some extent. Importantly, however, ClpP agonists showed significantly greater impact in mammosphere formation and cell growth assays, compared with other mitochondria-targeting drugs. Further studies revealed that ClpP agonists uniquely deplete NAD+/NADH and promote reactive oxygen species, both of which are shown as key factors to maintain pluripotency of stem cells. Moreover, ClpP agonists uniquely inhibited enzymes involved with glutamine catabolism and proline biosynthesis, vital to amino acids and nucleotide synthesis. Conclusion: ClpP agonists inhibit cell growth and tumor initiation in breast cancer cells by targeting multiple pathways essential to maintain CSC function.

Citation Format: Yoshimi E. Greer, Lidia Hernandez, Donna Voeller, Raj Chari, Binwu Tang, Christina M. Annunziata, Sam Gilbert, Lalage Wakefield, Edwin Iwanowicz, Lee M. Graves, Stanley Lipkowitz. Mitochondrial matrix protease ClpP agonists suppress breast cancer stem cell function by downregulating multiple stem cell regulatory mechanisms [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P127.

Acute eosinophilic pneumonia: a fatal reaction to ado-trastuzumab

Ado-trastuzumab emtansine (T-DM1) is a monoclonal antibody drug conjugate approved for the treatment of HER2-positive breast cancers. Presented here is a case report of a patient who developed fatal pulmonary toxicity in the form of acute eosinophilic pneumonia while undergoing treatment with T-DM1. Prior to beginning T-DM1 therapy, this patient had been treated with two HER2-targeted agents (trastuzumab, pertuzumab) per National Comprehensive Cancer Network (NCCN) guidelines. This case represents a novel presentation of toxicity associated with T-DM1 while perhaps demonstrating additive toxicity associated with multiple lines of HER2 targeted therapies.

In Vitro Ubiquitination Platform Identifies Methyl Ellipticiniums as Ubiquitin Ligase Inhibitors

The transfer of the small protein ubiquitin to a target protein is an intricately orchestrated process called ubiquitination that results in modulation of protein function or stability. Proper regulation of ubiquitination is essential, and dysregulation of this process is implicated in several human diseases. An example of a ubiquitination cascade that is a central signaling node in important disease-associated pathways is that of CBLB [a human homolog of a viral oncogene Casitas B-lineage lymphoma (CBL) from the Cas NS-1 murine retrovirus], a RING finger ubiquitin ligase (E3) whose substrates include a number of important cell-signaling kinases. These include kinases important in immune function that act in the T cell receptor and costimulatory pathways, the Tyro/Axl/MerTK (TAM) receptor family in natural killer (NK) cells, as well as growth factor receptor kinases like epidermal growth factor receptor (EGFR). Loss of CBLB has been shown to increase innate and adaptive antitumor immunity. This suggests that small-molecule modulation of CBLB E3 activity could enhance antitumor immunity in patients. To explore the hypothesis that enzymatic inhibition of E3s may result in modulation of disease-related signaling pathways, we established a high-throughput screen of >70,000 chemical entities for inhibition of CBLB activity. Although CBLB was chosen as a proof-of-principle target for inhibitor discovery, we demonstrate that our assay is generalizable to monitoring the activity of other ubiquitin ligases. We further extended our observed in vitro inhibition with additional cell-based models of CBLB activity. From these studies, we demonstrate that a class of natural product-based alkaloids, known as methyl ellipticiniums (MEs), is capable of inhibiting ubiquitin ligases intracellularly.

Abstract 1977: Combined inhibition of EGFR and PI3Kinase signaling in EGFR amplified triple negative breast cancer cells induces apoptosis and reduces cancer stem cells

Signaling from the Epidermal Growth Factor Receptor (EGFR) family is commonly dysregulated in various cancer types by amplification or activating mutations. For example, HER2 amplification occurs in 15-20% of breast cancers, and is a well-defined driver of tumorigenesis. EGFR is amplified in approximately 2% of breast cancer patients with unknown significance. It is amplified more frequently in TNBC (5.7-6.7%) and ER-/HER2+ cancers (5.8-6.5%). Basal (4.3-8.1%) and HER2 enriched (3.9-45.4%) molecular subtypes show the highest amplification than other molecular subtypes. EGFR amplification leads to shorter overall survival among breast cancer patients compared to those without amplified EGFR. Approximately 71% of EGFR amplified tumors have activated PI3K signaling, indicating a possible dual-inhibition therapeutic approach targeting both EGFR and PI3K. In order to study the role of EGFR amplification and PI3K aberrations in TNBC, we used the TNBC cell lines BT20 (amplified EGFR, PIK3CA activating mutation), MDA-MB-468 (amplified EGFR, PTEN deletion), and MDA-MB-231 (no amplification of EGFR or PI3K pathway mutations). EGFR amplification in both MDA-MB-468 and BT20 cell lines was confirmed by western blotting and Fluorescent in situ Hybridization; MDA-MB-231 did not have EGFR amplification. Activating mutations in both alleles of PIK3CA in BT20 was confirmed by sequencing. Loss of PTEN in MDA-MB-468 was confirmed by immunoblotting. Inhibition of EGFR with erlotinib resulted in decreased ERK signaling in BT20 and MDA-MB-468, but not in MDA-MB-231. Inhibition of the PI3K with Ly294002 or BKM120 decreased activation of AKT and mTOR signaling in BT20 and MDA-MB-468, but not in MDA-MB-231. The combination of erlotinib and PI3K inhibitors more dramatically reduced mTOR and AKT signaling in the BT20 and MDA-MB-468 cells. Combination of erlotinib and PI3K inhibitors reduced cell viability in these 3 cell lines, but inhibition was greater in MDA-MB-468 and BT20 compared to MDA-MB-231, and only MDA-MB-468 and BT20 cells had an increased fraction of apoptotic cells, signifying that combination therapy is most effective in cells with amplified EGFR and aberrant PI3K. It has been previously shown that HER2/HER3 activation plays a role in self renewal of tumor initiating cells. We demonstrate that the combination of erlotinib and BKM120 reduced the cancer stem cell population as measured by an aldeflour assay and by mammosphere formation. In summary, these data demonstrate that EGFR amplification in TNBC drives cell viability through EGFR and PI3K signaling, and EGFR/PI3K inhibitor combination causes apoptosis as well as reduction in the cancer stem cell population. We present evidence therefore that dual inhibition of EGFR/PI3K presents as a potential targetable pathway in TNBC with EGFR amplification and aberrant PI3K signaling.

Citation Format: David John Wisniewski, Donna Voeller, Stanley Lipkowitz. Combined inhibition of EGFR and PI3Kinase signaling in EGFR amplified triple negative breast cancer cells induces apoptosis and reduces cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1977.

Sinularamides A-G, Terpenoid-Derived Spermidine and Spermine Conjugates with Casitas B-Lineage Lymphoma Proto-Oncogene B (Cbl-b) Inhibitory Activities from a Sinularia sp. Soft Coral

An extract of a Sinularia sp. soft coral showed inhibitory activity against the E3-ubiquitin ligase casitas B-lineage lymphoma proto-oncogene B (Cbl-b). Subsequent bioassay-guided separation of the extract provided a series of terpenoid-derived spermidine and spermine amides that were named sinularamides A-G (1-7). Compounds 1-7 represent new natural products; however, sinularamide A (1) was previously reported as a synthetic end product. The structures of sinularamides A-G (1-7) were elucidated by analysis of spectroscopic and spectrometric data from NMR, IR, and HRESIMS experiments and by comparison with literature data. All of the isolated compounds showed Cbl-b inhibitory activities with IC₅₀ values that ranged from approximately 6.5 to 33 μM.

Rare Breast Cancer Subtypes

PURPOSE OF REVIEW

Breast cancer is a collection of diseases including the more common invasive ductal and lobular carcinomas and rarer subtypes of breast cancer. This review summarizes the features of rare breast cancers.

RECENT FINDINGS

Each of the rare tumors has defined pathological and clinical features that impact treatment recommendations. In this review, we summarize these for each rare type of breast cancer and where available we include molecular features of each tumor. Rare subtypes of breast cancer each have unique features. In many cases, data is limited for the optimal treatment approaches.

Improving the Odds in Advanced Breast Cancer With Combination Immunotherapy: Stepwise Addition of Vaccine, Immune Checkpoint Inhibitor, Chemotherapy, and HDAC Inhibitor in Advanced Stage Breast Cancer

Breast tumors commonly harbor low mutational burden, low PD-L1 expression, defective antigen processing/presentation, and an immunosuppressive tumor microenvironment (TME). In a malignancy mostly refractory to checkpoint blockade, there is an unmet clinical need for novel combination approaches that increase tumor immune infiltration and tumor control. Preclinical data have guided the development of this clinical trial combining 1) BN-Brachyury (a poxvirus vaccine platform encoding the tumor associated antigen brachyury), 2) bintrafusp alfa (a bifunctional protein composed of the extracellular domain of the TGF-βRII receptor (TGFβ "trap") fused to a human IgG1 anti-PD-L1), 3), entinostat (a class I histone deacetylase inhibitor), and 4) T-DM1 (ado-trastuzumab emtansine, a standard of care antibody-drug conjugate targeting HER2). We hypothesize that this tetratherapy will induce a robust immune response against HER2+ breast cancer with improved response rates through 1) expanding tumor antigen-specific effector T cells, natural killer cells, and immunostimulatory dendritic cells, 2) improving antigen presentation, and 3) decreasing inhibitory cytokines, regulatory T cells, and myeloid-derived suppressor cells. In an orthotopic HER2+ murine breast cancer model, tetratherapy induced high levels of antigen-specific T cell responses, tumor CD8+ T cell/Treg ratio, and augmented the presence of IFNγ- or TNFα-producing CD8+ T cells and IFNγ/TNFα bifunctional CD8+ T cells with increased cytokine production. Similar effects were observed in tumor CD4+ effector T cells. Based on this data, a phase 1b clinical trial evaluating the stepwise addition of BN-Brachyury, bintrafusp alfa, T-DM1 and entinostat in advanced breast cancer was designed. Arm 1 (TNBC) receives BN-Brachyury + bintrafusp alfa. Arm 2 (HER2+) receives T-DM1 + BN-Brachyury + bintrafusp alfa. After safety is established in Arm 2, Arm 3 (HER2+) will receive T-DM1 + BN-Brachyury + bintrafusp alfa + entinostat. Reimaging will occur every 2 cycles (1 cycle = 21 days). Arms 2 and 3 undergo research biopsies at baseline and after 2 cycles to evaluate changes within the TME. Peripheral immune responses will be evaluated. Co-primary objectives are response rate and safety. All arms employ a safety assessment in the initial six patients and a 2-stage Simon design for clinical efficacy (Arm 1 if ≥ three responses of eight then expand to 13 patients; Arms 2 and 3 if ≥ four responses of 14 then expand to 19 patients per arm). Secondary objectives include progression-free survival and changes in tumor infiltrating lymphocytes. Exploratory analyses include changes in peripheral immune cells and cytokines. To our knowledge, the combination of a vaccine, an anti-PD-L1 antibody, entinostat, and T-DM1 has not been previously evaluated in the preclinical or clinical setting. This trial (NCT04296942) is open at the National Cancer Institute (Bethesda, MD).

Sequential ubiquitination of NLRP3 by RNF125 and Cbl-b limits inflammasome activation and endotoxemia

Aberrant NLRP3 inflammasome activation contributes to the development of endotoxemia. The importance of negative regulation of NLRP3 inflammasomes remains poorly understood. Here, we show that the E3 ubiquitin ligase Cbl-b is essential for preventing endotoxemia induced by a sub-lethal dose of LPS via a caspase-11/NLRP3-dependent manner. Further studies show that NLRP3 undergoes both K63- and K48-linked polyubiquitination. Cbl-b binds to the K63-ubiquitin chains attached to the NLRP3 leucine-rich repeat domain (LRR) via its ubiquitin-associated region (UBA) and then targets NLRP3 at K496 for K48-linked ubiquitination and proteasome-mediated degradation. We also identify RNF125 as an additional E3 ubiquitin ligase that initiates K63-linked ubiquitination of the NLRP3 LRR domain. Therefore, NLRP3 is sequentially ubiquitinated by K63- and K48-linked ubiquitination, thus keeping the NLRP3 inflammasomes in check and restraining endotoxemia.

Suberitamides A-C, Aryl Alkaloids from a Pseudosuberites sp. Marine Sponge that Inhibit Cbl-b Ubiquitin Ligase Activity

Three new aryl alkaloids named suberitamides A-C (1-3), were isolated from an extract of the marine sponge Pseudosuberites sp. collected along the coast of North Carolina. Their planar structures were established by extensive nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis. To assign the challenging relative configuration of the saturated five-membered ring in suberitamide A (1), a simple and efficient NMR protocol was applied that is based on the analysis of 2- and 3-bond 1H-13C spin-spin coupling constants using a PIP (pure in-phase) HSQMBC (heteronuclear single quantum multiple bond correlation) IPAP (in-phase and anti-phase) experiment. Suberitamides A (1) and B (2) inhibited Cbl-b, an E3 ubiquitin ligase that is an important modulator of immune cell function, with IC50 values of approximately 11 μM.

Abstract 4794: Mitochondrial matrix protease ClpP agonists inhibit cell growth and cancer stem cell function in breast cancer cells

Background: We previously reported that ONC201, a novel anti-tumor drug currently being tested in early phase clinical trials, impairs mitochondrial structure and function in breast cancer cells (Greer et al., 2018). Recent studies demonstrated that ONC201 and the related TR compounds are agonists of mitochondrial caseinolytic protease P (ClpP), an essential protein to mitochondrial protein homeostasis (Graves et al. 2019). Cancer stem cells (CSCs) preferentially use mitochondrial oxidative metabolism for energy production. Here, we tested the impact of ClpP agonists-mediated mitochondrial dysregulation on breast CSCs.

Methods: Mitochondrial DNA (mtDNA)-depleted (rho0) MDA-MB231 (MB231) cells were generated by ethidium bromide treatment. MtDNA copy numbers were measured by qPCR. Mitochondrial respiration was monitored by Seahorse XF analyzer. Cell viability was analyzed by CellTiter-Glo 2.0 and RealTime-Glo assay. Protein expression was examined by Western blotting. ClpP knockout (KO) cells were generated by CRISPR/Cas9 technology. Mammosphere formation assay was performed to evaluate CSC function. MB231 cells stably expressing SORE6 (OCT4/SOX2 response element)-mCherry reporter gene were used to monitor CSC numbers. In vivo limiting dilution analysis was performed to examine the effect of ClpP agonists on MB231 mammary fat pad tumor initiation capability in athymic nude female mice.

Results: We observed that mammospheres formed by MB231were enriched in mtDNA compared to cells grown in 2D culture while rho0 cells lacking functional mitochondria failed to form mammospheres. This suggested that mitochondria are required for CSC function. The effects of ONC201 and TR compounds in breast cancer cells were tested. First, we confirmed that TR compounds (TR-65, TR-57) had ~60-250 fold higher potency compared to ONC201 in cell viability assays. Both ONC201 and TR-57 impaired mitochondrial structure, function, inhibited cell growth in 2D, and significantly inhibited mammosphere formation in multiple breast cancer cell lines. Importantly, ONC201 and TR-57 did not affect mitochondrial function, cell growth in 2D, nor mammosphere formation in CLPP KO cell lines, confirming ClpP is the target of these drugs. Flow cytometry analysis of MB231-SORE6-mCherry expressing cells demonstrated that ONC201 treatment significantly reduced the fraction of cells that were positive for the SORE6-mCherry activity, consistent with loss of CSCs. Finally, using in vivo limiting dilution experiments, CSC frequency was significantly lower (p&lt;0.05) in the ONC201-treated group compared with the control group, indicating that ONC201 inhibits tumor initiation capability in breast cancers.

Conclusion: Our studies suggest that targeting mitochondria by ClpP agonists inhibit cell growth and tumor initiation in breast cancer cells.

Citation Format: Yoshimi E. Greer, Lidia Hernandez, Voeller Donna, Raj Chari, Sam Gilbert, Binwu Tang, Christina Annunziata, Lalage Wakefield, Edwin Iwanowicz, Lee M. Graves, Stanley Lipkowitz. Mitochondrial matrix protease ClpP agonists inhibit cell growth and cancer stem cell function in breast cancer cells [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 4794.

Combination of PARP Inhibitor Olaparib, and PD-L1 Inhibitor Durvalumab, in Recurrent Ovarian Cancer: a Proof-of-Concept Phase II Study

PURPOSE

Preclinical studies suggest PARP inhibition (PARPi) induces immunostimulatory micromilieu in ovarian cancer thus complementing activity of immune checkpoint blockade. We conducted a phase II trial of PARPi olaparib and anti-PD-L1 durvalumab and collected paired fresh core biopsies and blood samples to test this hypothesis.

PATIENTS AND METHODS

In a single-center, proof-of-concept phase II study, we enrolled women aged ≥18 with recurrent ovarian cancer. All patients were immune checkpoint inhibitor-naïve and had measurable disease per RECISTv1.1, ECOG performance status 0-2, and adequate organ and marrow function. Patients received olaparib 300 mg twice daily and durvalumab 1,500 mg intravenously every 4 weeks until disease progression, unacceptable toxicity, or withdrawal of consent. Primary endpoint was overall response rate (ORR). Secondary objectives were safety and progression-free survival (PFS). Translational objectives included biomarker evaluation for relationships with clinical response and immunomodulatory effects by treatment.

RESULTS

Thirty-five patients with ovarian cancer [median, four prior therapies (IQR, 2-5.5), predominantly platinum-resistant (86%), BRCA wild-type (77%)] received at least one full cycle of treatment. ORR was 14% [5/35; 95% confidence interval (CI), 4.8%-30.3%]. Disease control rate (PR+SD) was 71% (25/35; 95% CI, 53.7%-85.4%). Treatment enhanced IFNγ and CXCL9/CXCL10 expression, systemic IFNγ/TNFα production, and tumor-infiltrating lymphocytes, indicating an immunostimulatory environment. Increased IFNγ production was associated with improved PFS [HR, 0.37 (95% CI, 0.16-0.87), P = 0.023], while elevated VEGFR3 levels were associated with worse PFS (HR, 3.22 (95% CI, 1.23-8.40), P = 0.017].

CONCLUSIONS

The PARPi and anti-PD-L1 combination showed modest clinical activity in recurrent ovarian cancer. Our correlative study results suggest immunomodulatory effects by olaparib/durvalumab in patients and indicate that VEGF/VEGFR pathway blockade would be necessary for improved efficacy of the combination.

A Phase II Single Arm Pilot Study of the CHK1 Inhibitor Prexasertib (LY2606368) in BRCA Wild-Type, Advanced Triple-Negative Breast Cancer

LESSONS LEARNED

Monotherapy with prexasertib demonstrated modest activity in BRCA wild-type, recurrent triple-negative breast cancer, highlighting the unmet need for combination treatment strategies. Neutropenia, anemia, and thrombocytopenia are common with the use of prexasertib but are manageable with supportive care measures. Prophylactic use of granulocyte colony stimulating factor should be considered to avoid dose reductions or treatment delays. Pharmacodynamic studies showed prexasertib treatment induced DNA damage in peripheral immune cells.

BACKGROUND

Cell cycle checkpoint kinase 1 (CHK1) is a major G2/M cell cycle regulator in tumors with p53 dysfunction, such as triple-negative breast cancer (TNBC). We hypothesized the second-generation CHK1 inhibitor, prexasertib, would yield clinical activity in sporadic TNBC.

METHODS

This single arm, phase II trial evaluated prexasertib at 105 mg/m² IV every 2 weeks in patients with metastatic/recurrent TNBC. The primary endpoint was overall response rate (ORR).

RESULTS

All nine patients enrolled were germline BRCA wild-type (BRCAwt) and had at least one prior treatment. One partial response (PR) was observed (ORR of 11.1%). Four patients experienced stable disease. The median progression-free survival (PFS) was 86 days (range 17 to 159 days). Grade 3/4 treatment-related adverse events included afebrile neutropenia (n = 8; 88.9%), anemia (n = 3; 33.3%), and thrombocytopenia (n = 1; 11.1%). Pharmacodynamic studies showed prexasertib treatment induced DNA damage in peripheral immune cells and demonstrated a decrease in activated/reinvigorated CD8 T cells; however, the one patient with a PR showed evidence of T-cell recovery.

CONCLUSION

Prexasertib monotherapy had modest clinical efficacy in BRCAwt TNBC. Further studies of prexasertib in combination with other agents are needed.

Phase I/II study of T-DM1 alone versus T-DM1 and metronomic temozolomide in secondary prevention of HER2-positive breast cancer brain metastases following stereotactic radiosurgery

TPS2572

Background: We demonstrated that low doses of temozolomide (TMZ) administered in a prophylactic, metronomic fashion significantly prevented development of brain metastases in murine models of breast cancer. Based on these findings, we developed a secondary-prevention clinical trial. Methods: Phase I is a standard 3+3 design: T-DM1 3.6mg/kg IV every 21 days plus TMZ 30, 40 or 50 mg/m2 daily, to identify the maximum tolerated dose (MTD) of the combination, and is completing accrual, with 9 patients accrued, currently on the third and last dose level. Phase II will randomize patients to T-DM1 3.6mg/kg versus T-DM1 3.6mg/kg plus TMZ at recommended phase 2 dose (RP2D), to evaluate if addition of TMZ improves the recurrence-free incidence from distant new brain metastases at one year from 50% to 65%. Patients will undergo radiology guided lumbar puncture at baseline and after 6 weeks of treatment (C3D1) for correlative studies, brain MRI, systemic restaging CTs, and questionnaires for evaluation of symptoms and quality of life. Eligibility: HER2+ breast cancer with brain metastases (up to 10 lesions), treated with SRS and/or resection ≤12 weeks before enrollment, no leptomeningeal metastases, no previous WBRT, ECOG ≤2 and adequate organ and marrow function. Biomarkers, including cell free DNA from CSF, serum and tumor block, exosomal DNA, serum markers for neuroinflammation, and patient reported outcomes, will be analyzed in an exploratory fashion. Target accrual: up to 18 patients in phase I and 98 in phase II. Clinical trial information: NCT03190967 .

Correlation of clinical activity of NEO201 mAb with the expression of NK activation markers and levels of soluble factors

e15002

Background: NEO-201 is a humanized IgG1 mAb that targets tumor-associated variants of CEACAM-5/6. NEO201 exerts anti-tumor activity by (NK)-mediated ADCC, CDC, and by enhancing NK cell cytotoxicity through blockade of CEACAM5-CEACAM1 interaction. The first in human phase I clinical trial is ongoing. Neutropenia caused DLT and was observed at 2mg/kg (DL 2). At DL2, 2/6 patients with colorectal cancers had stable disease. In the present study we evaluated the correlation between response, NK status, and profiles of soluble factors. Methods: This is a classic 3+3 dose escalation. NEO-201 is administered intravenously every 2 weeks, with 4 dose levels planned (DL1 = 1mg/kg, DL2 = 2mg/kg, DL3 = 4mg/kg and DL4 = 6mg/kg). So far, 3 patients received DL1 and 6 patients DL2. Safety is evaluated according to CTCAEv5.0, and response according to RECISTv1.1. Biological samples are collected at baseline, at 4, 24 and 72 hours after the first dose, and before C1D15 dose to understand NEO-201 pharmacokinetics (PK), effects on immune profile and correlation with treatment toxicity and response. CD56+/CD16+ NK cells were evaluated for modulation of NKG2D, CD107a, NKp46 (activation markers), and CEACAM1 (inhibitory marker) by flow cytometry. Soluble factors (cytokines, sMICA and sCEACAM5) were evaluated by ELISA. Results: Among the 3 patients achieving radiological SD, one (DL1) had clinical progression (PD) without radiological progression after 2 cycles due to mucous producing disease, a second patient (DL2) went off study after 2 cycles for drug unrelated issues, and the third patient (DL2) has stable disease (SD) for 6 months without significant toxicity. All other patients had radiologic PD after 2 cycles. Interestingly, baseline CD56+/CD16+ NK cells from the two patients with SD showed an increase in NKG2D, CD107a and NKp46, and a low expression of CEACAM1. They also had low serum levels of sMICA, sCEACAM5 and IL-6. On contrary, CD56+/CD16+ NK cells from patients with PD had low expression of NKG2D and CD107a, high expression of CEACAM1, and high levels of sMICA. Conclusions: High expression of activating markers and low expression of CEACAM1 on CD56+/CD16+ NK cells, as well as low levels of sMICA and sCEACAM5 correlate with clinical response to NEO-201. Thus, the activity of NK cells may serve as predictors for efficacy of tumor-targeting antibody therapy. Further correlation of these biomarkers with PK and CEACAM1/5/6 expression in patients’ tissue samples will provide further support for optimizing the use of NEO201. Clinical trial information: NCT03476681 .

Prexasertib, a cell cycle checkpoint kinase 1 inhibitor, in BRCA mutant recurrent high-grade serous ovarian cancer (HGSOC): A proof-of-concept single arm phase II study

6038

Background: Preclinical data suggest cell cycle checkpoint inhibition induces greater cell death in BRCA mutant HGSOC by causing replication stress and dysregulation of DNA damage responses. We hypothesized that prexasertib, a cell cycle checkpoint kinase 1 (CHK1) inhibitor, would be active in BRCA mutated HGSOC patients. Methods: We conducted a single center, two-stage phase II study of prexasertib (105mg/m2 IV every 2 weeks) in HGSOC patients with known germline or somatic BRCA mutations. The primary endpoint was RECIST response rate (RR). Progression-free survival (PFS) and safety (CTCAE v4) were secondary endpoints. Baseline research biopsies and blood samples were collected for exploratory biomarker endpoints. Results: Between February 2015 and July 2019, 22 heavily pretreated (median 5 prior systemic therapies [1-12]) women with BRCA mutant HGSOC (median age 58.7 [44-74.8]) received at least one dose of prexasertib. 13 (59%) patients were secondary platinum-resistant (median 8 [3-12] prior therapies) and 9 (41%) maintained platinum-sensitivity (median 4 [1-5] prior therapies). All but one received prior PARP inhibitor (PARPi) either in combination (10 [48%]) or as monotherapy (11 [52%]), with a median 5 month [mo; 1-29] PARPi-free interval prior to study entry. There was one complete response (41+mo, platinum-sensitive, no prior PARPi) and one partial response (9+mo, platinum-sensitive, 13.5mo PARPi-free interval) yielding an 11% RR (2/18 evaluable). No response was seen in platinum-resistant patients with prior PARPi. Median duration on study treatment was 4mo [1-9] among 21 patients with prior PARPi and 4mo [1.5-9] among 17 evaluable patients with prior PARPi. Common (>10%) grade 3/4 adverse events were neutropenia (82%), leukopenia (64%), and thrombocytopenia (14%); only one patient had grade 3 febrile neutropenia. 16 of 18 (89%) patients with grade 3/4 neutropenia received prophylactic growth factors for subsequent treatments. Conclusions: Prexasertib is tolerable and has modest activity in heavily pretreated BRCA mutant HGSOC patients. Further evaluation of predictive biomarkers for exceptional responders is ongoing. Clinical trial information: NCT02203513.

Temozolomide in secondary prevention of HER2-positive breast cancer brain metastases

Brain metastases occur in up to 25-55% of patients with metastatic HER2-positive breast cancer. Standard treatment has high rates of recurrence or progression, limiting survival and quality of life in most patients. Temozolomide (TMZ) is known to penetrate the blood-brain barrier and is US FDA approved for treatment of glioblastoma. Our group has demonstrated that low doses of TMZ administered in a prophylactic, metronomic fashion can significantly prevent development of brain metastases in murine models of breast cancer. Based on these findings, we initiated a secondary-prevention clinical trial with oral TMZ given to HER2-positive breast cancer patients with brain metastases after recent local treatment in combination with T-DM1 for systemic control of disease. Primary end point is freedom from new brain metastases at 1 year. (NCT03190967).

Novel Apoptosis-Inducing Agents for the Treatment of Cancer, a New Arsenal in the Toolbox

Evasion from apoptosis is an important hallmark of cancer cells. Alterations of apoptosis pathways are especially critical as they confer resistance to conventional anti-cancer therapeutics, e.g., chemotherapy, radiotherapy, and targeted therapeutics. Thus, successful induction of apoptosis using novel therapeutics may be a key strategy for preventing recurrence and metastasis. Inhibitors of anti-apoptotic molecules and enhancers of pro-apoptotic molecules are being actively developed for hematologic malignancies and solid tumors in particular over the last decade. However, due to the complicated apoptosis process caused by a multifaceted connection with cross-talk pathways, protein–protein interaction, and diverse resistance mechanisms, drug development within the category has been extremely challenging. Careful design and development of clinical trials incorporating predictive biomarkers along with novel apoptosis-inducing agents based on rational combination strategies are needed to ensure the successful development of these molecules. Here, we review the landscape of currently available direct apoptosis-targeting agents in clinical development for cancer treatment and update the related biomarker advancement to detect and validate the efficacy of apoptosis-targeted therapies, along with strategies to combine them with other agents.

A phase I study of the PD-L1 inhibitor, durvalumab, in combination with a PARP inhibitor, olaparib, and a VEGFR1-3 inhibitor, cediranib, in recurrent women's cancers with biomarker analyses

BACKGROUND

Strategies to improve activity of immune checkpoint inhibitors are needed. We hypothesized enhanced DNA damage by olaparib, a PARP inhibitor, and reduced VEGF signaling by cediranib, a VEGFR1-3 inhibitor, would complement anti-tumor activity of durvalumab, a PD-L1 inhibitor, and the 3-drug combination would be tolerable.

METHODS

This phase 1 study tested the 3-drug combination in a 3 + 3 dose escalation. Cediranib was taken intermittently (5 days on/2 days off) at 15 or 20 mg (dose levels 1 and 2, respectively) with durvalumab 1500 mg IV every 4 weeks, and olaparib tablets 300 mg twice daily. The primary end point was the recommended phase 2 dose (RP2D). Response rate, pharmacokinetic (PK), and correlative analyses were secondary endpoints.

RESULTS

Nine patients (7 ovarian/1 endometrial/1 triple negative breast cancers, median 3 prior therapies [2-6]) were treated. Grade 3/4 adverse events include hypertension (1/9), anemia (1/9) and lymphopenia (3/9). No patients experienced dose limiting toxicities. The RP2D is cediranib, 20 mg (5 days on/2 days off) with full doses of durvalumab and olaparib. Four patients had partial responses (44%) and 3 had stable disease lasting ≥6 months, yielding a 67% clinical benefit rate. No significant effects on olaparib or cediranib PK parameters from the presence of durvalumab, or the co-administration of cediranib or olaparib were identified. Tumoral PD-L1 expression correlated with clinical benefit but cytokines and peripheral immune subsets did not.

CONCLUSIONS

The RP2D is tolerable and has preliminary activity in recurrent women's cancers. A phase 2 expansion study is now enrolling for recurrent ovarian cancer patients.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02484404. Registered June 29, 2015.

HER3-Targeted Affibodies with Optimized Formats Reduce Ovarian Cancer Progression in a Mouse Xenograft Model

Expression of the receptor tyrosine kinase HER3 is negatively correlated with survival in ovarian cancer, and HER3 overexpression is associated with cancer progression and therapeutic resistance. Thus, improvements in HER3-targeted therapy could lead to significant clinical impact for ovarian cancer patients. Previous work from our group established multivalency as a potential strategy to improve the therapeutic efficacy of HER3-targeted ligands, including affibodies. Others have established HER3 affibodies as viable and potentially superior alternatives to monoclonal antibodies for cancer therapy. Here, bivalent HER3 affibodies were engineered for optimized production, specificity, and function as evaluated in an ovarian cancer xenograft model. Enhanced inhibition of HER3-mediated signaling and increased HER3 downregulation associated with multivalency could be achieved with a simplified construct, potentially increasing translational potential. Additionally, functional effects of affibodies due to multivalency were found to be specific to HER3 targeting, suggesting a unique molecular mechanism. Further, HER3 affibodies demonstrated efficacy in ovarian cancer xenograft mouse models, both as single agents and in combination with carboplatin. Overall, these results reinforce the potential of HER3-targeted affibodies for cancer therapy and establish treatment of ovarian cancer as an application where multivalent HER3 ligands may be useful. Further, this work introduces the potential of HER3 affibodies to be utilized as part of clinically relevant combination therapies (e.g., with carboplatin).

MEDI3039, a novel highly potent tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptor 2 agonist, causes regression of orthotopic tumors and inhibits outgrowth of metastatic triple-negative breast cancer

Background

TNF-related apoptosis-inducing ligand (TRAIL) receptor agonists are attractive anti-tumor agents because of their capability to induce apoptosis in cancer cells by activating death receptors (DR) 4 and 5 with little toxicity against normal cells. Despite an attractive mechanism of action, previous clinical efforts to use TRAIL receptor agonists have been unsuccessful. In this study, we examined MEDI3039, a highly potent multivalent DR5 agonist, in breast cancer cell lines and in vivo models.

Methods

As in vitro model systems, we used 19 breast cancer cell lines that are categorized into four subtypes: ER+, HER2 amplified, basal A (triple-negative breast cancer) TNBC, and basal B TNBC. Cell viability was analyzed by MTS and RealTime live/dead assays. As in vivo model systems, MDA-MB231T orthotopic primary tumor growth in the mammary fat pad (MFP) and two experimental lung metastasis models were used. The effect of MEDI3039 on MFP tumors was assessed with immunohistochemical analysis. Lung metastases were analyzed with Bouin’s and H&E staining.

Results

MEDI3039 killed multiple breast cancer cell lines, but the sensitivity varied among different subtypes. Sensitivity was basal B TNBC >> basal A TNBC > HER2 amplified > ER+ (average IC₅₀ = 1.4, 203, 314, 403 pM, respectively). While the pattern of relative sensitivity was similar to GST-TRAIL in most cell lines, MEDI3039 was at least two orders of magnitude more potent compared with GST-TRAIL. In the MFP model, weekly treatment with 0.1 or 0.3 mg/kg MEDI3039 for 5 weeks inhibited tumor growth by 99.05% or 100% (median), respectively, compared with the control group, and extended animal survival (p = 0.08 or p = 0.0032 at 0.1 or 0.3 mg/kg, respectively). MEDI3039-induced caspase activation was confirmed in tumors grown in MFP (p < 0.05). In an experimental pulmonary metastasis model, MEDI3039 significantly suppressed outgrowth of surface (p < 0.0001) and microscopic metastases (p < 0.05). In an established lung metastasis model, MEDI3039 significantly inhibited growth of metastases (p < 0.01 in surface [> 4 mm], p < 0.01 in tumor percentage) and extended animal survival (p < 0.0001).

Conclusion

MEDI3039 is a potent DR5 agonist in breast cancer cells in vitro and in vivo and has potential as a cancer drug in breast cancer patients, especially those with basal B TNBC.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1116-1) contains supplementary material, which is available to authorized users.

First-in-human phase 0 study of 111In-CHX-A"-DTPA trastuzumab for HER2 tumor imaging

Introduction:

Tumors over-expressing the human epithelial receptor 2 (HER2) or exhibiting amplification or mutation of its proto-oncogene have a poorer prognosis. Using trastuzumab and/or other HER2 targeted therapies can increase overall survival in patients with HER2(+) tumors making it critical to accurately identify patients who may benefit. We report on a Phase 0 study of the imaging agent, ¹¹¹In-CHX-A”-DTPA trastuzumab, in patients with known HER2 status to evaluate its safety and biodistribution and to obtain preliminary data regarding its ability to provide an accurate, whole-body, non-invasive means to determine HER2 status.

Methods:

¹¹¹In-CHX-A”-DTPA trastuzumab was radiolabeled on-site and slowly infused into 11 patients who underwent single (n=5) or multiple (n=6) ɣ-camera (n=6) and/or SPECT (n=8) imaging sessions.

Results:

No safety issues were identified. Visual and semi-quantitative imaging data were concordant with tissue HER2 expression profiling in all but 1 patient. The biodistribution showed intense peak liver activity at the initial imaging timepoint (3.3h) and a single-phase clearance fit of the average time-activity curve (TAC) estimated t_1/2=46.9h (R²=0.97; 95%CI 41.8 to 53h). This was followed by high gastrointestinal (GI) tract activity peaking by 52h. Linear regression predicted GI clearance by 201.2h (R² =0.96; 95%CI 188.5 to 216.9h). Blood pool had lower activity with its maximum on the initial images. Non-linear regression fit projected a t_1/2=34.2h (R² =0.96; 95%CI 25.3 to 46.3h). Assuming linear whole-body clearance, linear regression projected complete elimination (x-intercept) at 256.5hr (R²=0.96; 95%CI 186.1 to 489.2h).

Conclusion:

¹¹¹In-CHX-A”-DTPA trastuzumab can be safely imaged in humans. The biodistribution allowed for visual and semiquantitative analysis with results concordant with tissue expression profiling in 10 of 11 patients. Advances in Knowledge and Implications for Patient Care Using readily available components and on-site radiolabeling ¹¹¹In-CHX-A”-DTPA trastuzumab SPECT imaging may provide an economical, non-invasive means to detect HER2 over-expression.

Abstract 555: Loss of function Cbl-c mutations in solid tumors

Receptor Tyrosine Kinase (RTK) signaling, which is essential for cellular growth and proliferation, can lead to malignant transformation and tumorigenesis when aberrantly activated. Cbl proteins (Cbl, Cbl-b, and Cbl-c) are a conserved family of RING finger (RF) ubiquitin ligases (E3) that negatively regulate the activity of several tyrosine kinases such as the EGFR. Cbl mutations have recently been identified in 5% of human myeloid neoplasms, with a majority of mutations clustered within the RF and linker domains. Cbl-c is the most recently identified Cbl protein and is exclusively expressed in epithelial cells. We recently identified a novel cDNA isolated from a mouse mammary tumor in the C3(1) Large T Antigen transgenic mouse model. This mutant cDNA encodes a protein that has a deletion in the RF domain of Cbl-c, thereby resembling known Cbl family mutations associated with myeloid neoplasias. Genomic analyses of both parental and transgenic lines show no evidence of germline mutation, suggesting that this mutation is most likely somatic. The mutant Cbl-c protein enhances transformation of NIH 3T3 cells when co-transfected with SV40 Large T Antigen. In overexpression studies, this mutant Cbl-c fails to mediate ubiquitination of activated EGFR and acts in a dominant negative manner to prevent ubiquitination of activated EGFR by wildtype Cbl proteins. Datamining also reveals Cbl-c mutations associated with human solid tumors. Cell-based analyses demonstrate a similar loss of E3 function in some of these human mutations. These data collectively suggest that, like Cbl mutations in myeloid neoplasms, loss of function Cbl-c mutants may also contribute to the pathogenesis of solid tumors in murine models and in humans.

Citation Format: Silvano R. Daniels, Stephen C. Kales, Mariya Liyasova, Marion M. Nau, Phil E. Ryan, Jeffrey E. Green, Stanley Lipkowitz. Loss of function Cbl-c mutations in solid tumors [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 555.

Abstract 2506: Flotillin 2 negatively regulates EGFR phosphorylation and Cbl-mediated ubiquitination and degradation

EGF receptor (EGFR) signaling is dysregulated by gene amplification or activating mutations of the EGFR in a variety of human malignancies. Activation of the EGFR by EGF leads to recruitment of the ubiquitin ligase Cbl, which ubiquitinates EGFR targeting it for degradation and acts as an adaptor, recruiting additional proteins required for EGFR internalization and trafficking to the lysosome. However, the detailed molecular mechanisms remain elusive. Complete characterization of proteins involved in EGFR trafficking and degradation may uncover additional mechanisms of EGFR dysregulation in cancer. To characterize the EGFR degradative pathway, we investigated protein complexes formed on Cbl with Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC) mass spectrometry. By labeling proteins with stable isotopes in culture, we compared complexes in 3 groups: 1) complexes formed on Cbl without EGF stimulation (control), 2) complexes formed on Cbl with EGF stimulation for 30 min and 3) complexes formed on Cbl with EGF stimulation in the presence of YM201636, a trafficking inhibitor, which was added to prevent degradation of the Cbl/EGFR complex and to enrich it for other proteins important for EGFR trafficking. This approach identified over a hundred novel Cbl interactors, whose abundance in the complex with Cbl changed significantly with the treatments. Fifty of these proteins were selected for RNAi knockdown to examine their effects on EGFR degradation. We found that knockdown of Flotillin 2 (FLOT2) protein, a major scaffold protein within caveolar lipid rafts, led to increased phosphorylation and accelerated degradation of EGFR upon EGF stimulation compared to negative control siRNA in HeLa cells. Conversely, overexpression of FLOT2 in HEK293T inhibited EGFR phosphorylation and formation of the EGFR/Cbl complex upon EGF stimulation and led to decreased EGFR ubiquitination and degradation. CRISPR knockout of FLOT2 in HeLa cells led to decreased steady-state levels of EGFR, increased phosphorylation of EGFR and ERK1/2 compared to non-targeting CRISPR control. Stable overexpression of FLOT2 in HeLa cells increased steady-state levels of EGFR, but decreased EGFR phosphorylation and ubiquitination upon EGF stimulation. FLOT2 is frequently amplified and overexpressed in breast, endometrial and lung cancers. In a lung adenocarcinoma cell line H441, in which FLOT2 gene is amplified, knockdown of FLOT2 increased EGFR phosphorylation and ubiquitination, as well as EGFR signaling, as detected by the phosphorylation of ERK1/2. Our data indicate that FLOT2 negatively regulates EGFR phosphorylation, ubiquitination and degradation. Although it is not clear how FLOT2 amplification could contribute to cancer pathogenesis, we speculate that studying how FLOT2 regulates EGFR signaling could lead to a better understanding of its role in normal physiology and cancer.

Citation Format: Mariya Liyasova, Xu Zhang, Udayan Guha, Stanley Lipkowitz. Flotillin 2 negatively regulates EGFR phosphorylation and Cbl-mediated ubiquitination and degradation [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 2506.

Update on PARP Inhibitors in Breast Cancer

OPINION STATEMENT

The single agent activity of PARP inhibitors (PARPi) in germline BRCA mutated (gBRCAm) breast and ovarian cancer suggests untapped potential for this new class of drug in breast cancer. The US Food and Drug Administration has approved three PARPi (olaparib, rucaparib, and niraparib) so far to treat certain ovarian cancers, including those with gBRCAm and olaparib for treatment of gBRCAm breast cancers. Several PARPi are now under clinical development for breast cancer in the various treatment settings. Recently, two phase III trials of olaparib (OlympiaD) and talazoparib (EMBRACA) demonstrated 3-month progression-free survival improvement with PARPi compared to physician's choice single agent chemotherapy in metastatic gBRCAm breast cancer. To date, PARPi seems less efficacious in metastatic breast cancer patients than those with BRCA mutated platinum-sensitive recurrent ovarian cancer, perhaps reflecting the biologic heterogeneity and low somatic BRCA mutation rate in breast cancer. The use of PARPi is gradually evolving, including combination strategies with chemotherapy, targeted agents, radiotherapy, or immunotherapy in women with and without gBRCAm. The role of predictive biomarkers, including molecular signatures and homologous recombination repair deficiency scores based on loss of heterozygosity and other structural genomic aberrations, will be crucial to identify a subgroup of patients who may have benefit from PARPi. An improved understanding of the mechanisms underlying PARPi clinical resistance will also be important to enable the development of new approaches to increase efficacy. This is a field rich in opportunity, and the coming years should see a better understanding of which breast cancer patients we should treat with PARPi and where these agents should come in over the course of treatment.

ONC201 kills breast cancer cells in vitro by targeting mitochondria

We report a novel mechanism of action of ONC201 as a mitochondria-targeting drug in cancer cells. ONC201 was originally identified as a small molecule that induces transcription of TNF-related apoptosis-inducing ligand (TRAIL) and subsequently kills cancer cells by activating TRAIL death receptors. In this study, we examined ONC201 toxicity on multiple human breast and endometrial cancer cell lines. ONC201 attenuated cell viability in all cancer cell lines tested. Unexpectedly, ONC201 toxicity was not dependent on either TRAIL receptors nor caspases. Time-lapse live cell imaging revealed that ONC201 induces cell membrane ballooning followed by rupture, distinct from the morphology of cells undergoing apoptosis. Further investigation found that ONC201 induces phosphorylation of AMP-dependent kinase and ATP loss. Cytotoxicity and ATP depletion were significantly enhanced in the absence of glucose, suggesting that ONC201 targets mitochondrial respiration. Further analysis indicated that ONC201 indirectly inhibits mitochondrial respiration. Confocal and electron microscopic analysis demonstrated that ONC201 triggers mitochondrial structural damage and functional impairment. Moreover, ONC201 decreased mitochondrial DNA (mtDNA). RNAseq analysis revealed that ONC201 suppresses expression of multiple mtDNA-encoded genes and nuclear-encoded mitochondrial genes involved in oxidative phosphorylation and other mitochondrial functions. Importantly, fumarate hydratase deficient cancer cells and multiple cancer cell lines with reduced amounts of mtDNA were resistant to ONC201. These results indicate that cells not dependent on mitochondrial respiration are ONC201-resistant. Our data demonstrate that ONC201 kills cancer cells by disrupting mitochondrial function and further suggests that cancer cells that are dependent on glycolysis will be resistant to ONC201.

Abstract OT2-06-01: Phase I/II study of T-DM1 alone versus T-DM1 and metronomic temozolomide in secondary prevention of HER2-Positive breast cancer brain metastases following stereotactic radiosurgery

Background: Brain metastases occur in up to 25-40% of HER2+ breast cancer patients. Standard treatment is limited to surgery or stereotactic radiosurgery (SRS) and/or whole brain radiation therapy (WBRT), with high levels of recurrence or progression, limiting survival and quality of life in most patients. Our group has demonstrated that low doses of temozolomide (TMZ) administered in a prophylactic, metronomic fashion can significantly prevent development of brain metastases in murine models of breast cancer. Based on these findings, we propose a secondary-prevention clinical trial.

Trial Design: Phase I/II open label study. Phase I will follow a standard 3+3 design: T-DM1 3.6 mg/kg IV every 21 days plus TMZ 30, 40 or 50 mg/m2 daily. Phase II: randomization T-DM1 3.6 mg/kg versus T-DM1 3.6mg/kg plus TMZ at recommended phase 2 dose (RP2D). Patients will undergo radiology guided lumbar puncture at baseline and after 6 weeks of treatment (C3D1) for correlative studies, brain MRI, systemic restaging CTs, and questionnaires for evaluation of symptoms and quality of life (MDASI-BT and PROMIS®) every 6 weeks.

Eligibility: HER2+ breast cancer with ≤3 brain metastases, treated with SRS and/or resection ≤6 weeks before enrollment, no leptomeningeal metastases, no previous WBRT, able to complete brain MRI with contrast evaluations, willing to undergo lumbar puncture, ECOG ≤2 and adequate organ and marrow function. HBV, HCV or HIV-positive patients are ineligible.

Specific Aims: Phase I: to identify the maximum tolerated dose (MTD) of TMZ combined with T-DM1. Phase II: to determine if the combination regimen of T-DM1 and TMZ improves the recurrence-free incidence from distant new brain metastases at one year as compared to T-DM1 alone. Biomarkers, including cell free DNA sequencing from CSF, serum and tumor block, serum markers for neuroinflammation, and patient reported outcomes, will be analyzed in an exploratory fashion.

Statistical Methods: Phase I, MTD will be identified based on the dose level at which 0 or 1 patient in 6 has a DLT. Phase II, to test whether TMZ will increase RFS from 50% to 65% at 12 months. RFS Kaplan-Meier curves will be created for each of the randomized arms and compared using a one-tailed log-rank test, with a one-sided 0.10 significance level of interest to be detected. Patients will be stratified for number of brain lesions and status of systemic metastases (controlled or not).

Target Accrual: 49 evaluable patients per arm (total 98), plus 9 to 18 patients during phase I. Trial will open in Summer 2017, at NIH in Bethesda, MD.

Contact Information: Principal Investigator: Alexandra S Zimmer, MD alexandra.zimmer@nih.gov

Citation Format: Zimmer AS, Gril B, Steinberg S, Smart D, Gilbert M, Armstrong T, Xiao L, Houston N, Biassou N, Brastianos P, Carter S, Lyden DC, Lipkowitz S, Steeg P. Phase I/II study of T-DM1 alone versus T-DM1 and metronomic temozolomide in secondary prevention of HER2-Positive breast cancer brain metastases following stereotactic radiosurgery [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT2-06-01.

Abstract OT2-07-04: A phase 2 study of ONC201 in recurrent/refractory metastatic breast cancer and advanced endometrial carcinoma

Background: Advanced breast cancer (BC) and endometrial cancer (EC) have limited treatment options with no treatments improving survival. ONC201 is the founding member of a novel class of anticancer drugs called impiridones. The drug is orally bioavailable and crosses the blood brain barrier. Preclinical studies have demonstrated that ONC201 selectively kills various cancer cells, including all subtypes of BC and EC, while having little effect on normal cells. An on-going Phase 1 study of ONC201 has demonstrated clinical benefit in some solid tumors, including EC and glioblastomas.

Trial Design: Phase 2 single arm study of ONC201 with 3 cohorts: Cohort 1, female and male hormone receptor positive breast cancer (HR+BC); Cohort 2, female and male triple negative breast cancer (TNBC); and Cohort 3, EC. All patients will receive ONC201 at the recommended Phase 2 dose of 625mg by mouth q7 days (1 cycle = 28 days). Patients will undergo a baseline biopsy as well as a biopsy after 5 doses of ONC201 (C2D2). Patients will be evaluated for response every two cycles (8 weeks) by RECIST 1.1.

Eligibility Criteria: Measurable disease with &gt;1 biopsiable lesion, willing to undergo biopsies. Cohort 1 (HR+BC) requires prior treatment with &gt;2 lines of hormonal treatment. No prior treatment required for the other cohorts. Patients must have ECOG 0-1 and adequate organ function. Patients with asymptomatic or brain metastases treated &gt; 4 weeks from study entry are eligible. Exclusion criteria include: symptomatic CNS metastases, radiotherapy ≤ 4 weeks from study entry, HIV, Hepatitis B or Hepatitis C.

Specific Aims: Primary objectives for this study are progression free survival (PFS) at 8 months for Cohort 1 (HR+BC) and overall response rate (ORR) for Cohorts 2 and 3 (TNBC and EC). Secondary objectives include safety, clinical benefit rate (CBR = partial response + complete response + stable disease), and overall survival.

Statistical Methods: This study has been designed to pause prior to full accrual to allow for evaluation of futility prior to proceeding to full accrual. In Cohort 1, if &gt;1 of 5 patients is progression-free at 8 months, then we will recruit up to 24 patients. In Cohort 2, if &gt;2 of 10 patients has clinical benefit then we will recruit up to 29 patients. For Cohort 3, if 1 of 13 patients has clinical benefit, then we will recruit up to 25 patients. Additional evaluations of tumor or blood samples performed will be done in an exploratory fashion, with results presented without any formal adjustment for multiple comparisons.

Target Accrual: 24 patients with HR+BC, 29 patients with TNBC, and 25 patients with EC.This trial will open Summer 2017 at the National Institutes of Health (Bethesda, MD).

Contact Information: Principal Investigator Alexandra S Zimmer, MD; alexandra.zimmer@nih.gov

Citation Format: Gatti-Mays ME, Greer Y, Steinberg S, Soltani S, Collins J, Olson M, Ojemuyiwa M, Annunziata C, Lee J-M, Nunes A, Lipkowitz S, Zimmer A. A phase 2 study of ONC201 in recurrent/refractory metastatic breast cancer and advanced endometrial carcinoma [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT2-07-04.