When a synonymous mutation breaks the silence in a thalassaemia patient

Synonymous mutations were considered to lack functional roles in human diseases; however, distinguishing deleterious synonymous mutations from benign ones is still a challenge. In this article, we identified a deleterious synonymous mutation β-codon 16 (C>T). HBB: c.51C>T, in compound heterozygous form with known β-thalassaemia mutation patients who clinically presented as non-transfusion-dependent thalassaemia (NTDT). A total of 9 families with 11 compound heterozygous index cases were reported. In the heterozygous state, codon 16 (C>T) mutation results in borderline HbA2 (3.18 ± 0.36%) and slightly reduced RBC indices (RBCs: 4.73 ± 0.75 × 106 /μL, Hb: 12.26 ± 2.60 g/dL, MCV: 79.48 ± 8.40 fL, MCH: 25.95 ± 4.15 pg). The compound heterozygous patients showed elevated HbA2 (5.98 ± 1.17%) and HbF (12.75 ± 7.51%) and presented clinically as NTDT with a mean Hb of 6.95 ± 1.29 g/dL. Many of them were dependent on few transfusions and had mild splenomegaly. Of the 11 patients, 5 (45.4%) were treated with hydroxyurea. This study highlights the clinical significance of synonymous mutation, when inherited with other β-thalassaemia mutations leading to the phenotype of NTDT. Thus, the study would help to improve screening protocols for β-thalassaemia carriers, which will ultimately improve the prevention programme.

A phase III, multicenter, randomized study of olvimulogene nanivacirepvec followed by platinum-doublet chemotherapy and bevacizumab compared with platinum-doublet chemotherapy and bevacizumab in women with platinum-resistant/refractory ovarian cancer

BACKGROUND

Treatment options for patients with platinum-resistant/refractory ovarian cancers are limited and only marginally effective. The development of novel, more effective therapies addresses a critical unmet medical need. Olvimulogene nanivacirepvec (Olvi-Vec), with its strong immune modulating effect on the tumor microenvironment, may provide re-sensitization to platinum and clinically reverse platinum resistance or refractoriness in platinum-resistant/refractory ovarian cancer.

PRIMARY OBJECTIVE

The primary objective is to evaluate the efficacy of intra-peritoneal Olvi-Vec followed by platinum-based chemotherapy and bevacizumab in patients with platinum-resistant/refractory ovarian cancer.

STUDY HYPOTHESIS

This phase III study investigates Olvi-Vec oncolytic immunotherapy followed by platinum-based chemotherapy and bevacizumab as an immunochemotherapy evaluating the hypothesis that such sequential combination therapy will prolong progression-free survival (PFS) and bring other clinical benefits compared with treatment with platinum-based chemotherapy and bevacizumab.

TRIAL DESIGN

This is a multicenter, prospective, randomized, and active-controlled phase III trial. Patients will be randomized 2:1 into the experimental arm treated with Olvi-Vec followed by platinum-doublet chemotherapy and bevacizumab or the control arm treated with platinum-doublet chemotherapy and bevacizumab.

MAJOR INCLUSION/EXCLUSION CRITERIA

Eligible patients must have recurrent, platinum-resistant/refractory, non-resectable high-grade serous, endometrioid, or clear-cell ovarian, fallopian tube, or primary peritoneal cancer. Patients must have had ≥3 lines of prior chemotherapy.

PRIMARY ENDPOINT

The primary endpoint is PFS in the intention-to-treat population.

SAMPLE SIZE

Approximately 186 patients (approximately 124 patients randomized to the experimental arm and 62 to the control arm) will be enrolled to capture 127 PFS events.

ESTIMATED DATES FOR COMPLETING ACCRUAL AND PRESENTING RESULTS

Expected complete accrual in 2024 with presentation of primary endpoint results in 2025.

TRIAL REGISTRATION

NCT05281471.

The Genomic Landscape of Vulvar Squamous Cell Carcinoma

Vulvar squamous cell cancer (VSC) accounts for 90% of vulvar cancers. Next-generation sequencing studies of VSC imply human papillomavirus (HPV) and p53 status play separate roles in carcinogenesis and prognosis. We sought to describe the genomic landscape and analyze the immunologic profiles of VSC with respect to HPV and p53 status. A total of 443 VSC tumors underwent tumor profiling. Next-generation sequencing was performed on genomic DNA isolated from formalin-fixed paraffin-embedded tumor samples. PD-L1, microsatellite instability were tested by fragment analysis, IHC, and next-generation sequencing. Tumor mutational burden-high was defined as >10 mutations per MB. HPV 16/18 positive (HPV+) status was determined using whole exome sequencing on 105 samples. Three cohorts were identified from 105 samples with known HPV: HPV+, HPV-/p53wt, and HPV-/p53mt. Where HPV and p53 status were examined, TP53 mutations were exclusive of HPV+ tumors. In all, 37% of samples were HPV+. Among the 66 HPV- tumors, 52 (78.8%) were HPV-/p53mt and 14 (21.2%) were HPV-/p53wt. The HPV-/p53wt cohort had a higher rate of mutations in the PI3KCA gene (42.9% HPV-/p53wt vs 26.3% HPV+ vs. 5.8% HPV-/p53mt, q =0.028) and alterations in the PI3K/AkT/mTOR pathway (57.1% HPV-/p53wt vs. 34.2% HPV+ vs. 7.7% HPV-/p53mt, q =0.0386) than the other 2 cohorts. Ninety-eight VSC tumors with HPV16/18 information underwent transcriptomic analysis and immune deconvolution method. No differences were observed in immune profiles. The HPV-/p53wt VSC tumors had significantly higher rates of mutations in the PI3KCA gene and alterations in the PI3K/AkT/mTOR pathway, a potential target that merits further investigation in this subgroup.

Well-being and stress vulnerability in ovarian cancer survivors during the COVID-19 pandemic

OBJECTIVE

This study was designed to examine (1) whether ovarian cancer (OC) survivors would have greater well-being vs. elevated distress compared to community members during a universal health stressor (COVID-19) and (2) how resources and risk factors at diagnosis predicted vulnerability to a subsequent health-related stressor.

METHODS

One hundred seventeen OC survivors were recruited from two academic medical centers and compared to a community-based sample on COVID-related distress and disruption. Latent class analysis identified differentially impacted groups of survivors.

RESULTS

Survivors reported lower distress than community members. Predictors of higher distress included shorter-term survivorship, greater disruption, and poorer emotional well--being (EWB) at diagnosis. Survivors were divided into high- and low-COVID-19-impact subgroups; high-impact individuals endorsed higher perceived stress and lower EWB at diagnosis.

CONCLUSION

Survivors reported lower COVID-related distress than community participants. While depression at diagnosis did not predict later distress, EWB was a strong predictor of response to a novel health-related stressor.

Abstract 5702: Ovarian cancer tumor microenvironment and atezolizumab (atezo) clinical activity: IMagyn050 sub-study

Background: Tumor biomarkers such as CD8 density and location (i.e., immune inflamed phenotype) and immune rich molecular subtype have been linked to immune checkpoint blockade (ICB) overall survival (OS) in different cancers. The IMagyn050 trial (NCT03038100), which evaluated the efficacy of Atezo vs placebo (Pla) with carboplatin, paclitaxel and bevacizumab (CPB) in front line ovarian cancer patient (pts), did not meet its co-primary endpoints of PFS in ITT or PD-L1+ (Moore et al. JCO 2021). In the current IMagyn050 substudy we assessed potential predictive tumor immune biomarkers for Atezo clinical benefit.

Methods: FFPE tumors from the biomarker evaluable population were tested for PD-L1 IHC, CD8/PanCK IHC (total CD8 T cells and immune location phenotypes [inflamed, excluded, desert]) and RNA-seq (to derive molecular subtypes, biological pathways and cellular components [xCELL]) in tissue from baseline (n=860), on-treatment (OT, 9 weeks, n=233), intra- (n=8) and inter-lesion (n=12) matched samples. Hazard ratio (HR) interaction test from multivariate adjusted Cox-regression analysis for PFS and OS was performed to test predictive biomarkers.

Results: While tumors with CD8 T cells, immunoreactive molecular subtypes or immune inflamed phenotype were enriched for PD-L1+, only pts with immune inflamed tumors showed improved OS Atezo benefit (HR 0.67). Improved Atezo PFS/OS benefit was also observed in pts with whose tumors had high oxidative phosphorylation (OXPHOS, HR: 0.72/0.65) and UV Response (UV, HR: 0.64/0.58) but not IFNγ response. Plasma B cells were linked to improved OS Atezo benefit vs Pla (HR 0.53). We leveraged OT samples from pts in the neoadjuvant cohort to assess treatment effect on the tumor microenvironment. Analyses showed that CPB reduced tumor proliferation and increased tumor immune inflammation (CD8 T cells, PD-L1 and IFNα/IFNγ response), further increased by Atezo. Immune inflammation is challenging in ovarian cancer due to extensive tumor heterogeneity. Prevalence of tumor biomarkers varied by anatomic locations: total CD8, CD8 localization and molecular subtypes. Inter- and intra-lesion biomarker status within the same pt showed PD-L1 and plasma B cells as most consistent. Molecular subtypes and immune phenotypes had moderate intra-lesion agreement but discordant between lesions. PD-L1 and OXPHOS were the only biomarkers linked to Atezo benefit regardless of anatomical location.

Conclusion: This comprehensive exploratory study suggests that DNA damage, OXPHOS, plasma B cells and immune inflamed tumors, but not molecular subtypes or total CD8 T cells, may predict Atezo + CPB OS. This treatment promotes immune inflammation in OC tumors. Notably, we found that several biomarkers are highly heterogeneous. Our findings highlight the challenges of achieving durable clinical benefit from targeted immunotherapy in ovarian cancer pts.

Citation Format: Venkatesh Krishnan, Ching-Wei Chang, Habib Hamidi, Michael A. Bookman, Charles Landen, Tashanna Myers, Hiroaki Kajiyama, Sakari Hietanen, Lyndsay Willmott, Premal Thaker, Cagatay Taskiran, Jalid Sehouli, Victor Khor, Yvonne Lin Liu, Sandro Pignata, Kathleen Moore, Luciana Molinero. Ovarian cancer tumor microenvironment and atezolizumab (atezo) clinical activity: IMagyn050 sub-study. [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 5702.

Abstract 4877: Mutant or overexpressed SF3B1 facilitates endometrial cancer tumorigenesis

Aberrant expression or mutations in core splicing factors including U2AF1, SRSF2, ZRSR2, and SF3B1 found to drive tumorigenesis of various malignant tumors e.g., myelodysplastic syndromes, chronic lymphocytic leukemia, uveal melanoma, and breast cancer. Importantly, the amplifications and mutations in SF3B1, the pioneer splicing factor, are reportedly far more common than those in other splicing factors. However, the functional relevance and underlying mechanisms of dysregulated SF3B1 in endometrial cancer are not investigated. Endometrial cancer is the fourth most common cancer in women in the United States and there will be about 65,950 new endometrial cancer cases in the current year alone with 12,550 estimated cancer deaths in the United States. In this study, we thus investigated the role of SF3B1 in endometrial adenocarcinoma. We found SF3B1 is one of the most frequently amplified or mutated splicing factors in endometrial cancer. Specifically, analysis of The Cancer Genome Atlas (TCGA) uterine pan-cancer dataset revealed that up to 9% of endometrial cancers have SF3B1 mutations or amplification. Additionally, we showed that the SF3B1 protein is overexpressed in human as well as mouse endometrial tumor samples. Further analysis found elevated SF3B1 protein in multiple endometrial cancer cell lines even in the absence of SF3B1 mutations. However, we did not observe any altered expression at the transcript level. Further, we identified a correlation between the over-expressed SF3B1 levels and the tumorigenicity/invasive potential of cancer cell lines. For instance, endometrial cancer cell lines (Ishikawa, AN3CA, KLE) with over-expressed SF3B1 levels were much more tumorigenic and invasive than those with low endogenous SF3B1 levels (normal human endometrial epithelial cells, RL-95-2 cells). Moreover, cell viability assays revealed that Ishikawa, AN3CA, and KLE cells were more susceptible to the loss of SF3B1 or treatment with the SF3B1 inhibitor Pladienolide-B (PLAD-B) than RL-95-2 cells. To further ensure that overexpressed or mutated SF3B1 drives endometrial tumorigenesis, we transiently transfected an empty vector or a vector expressing FLAG-tagged wild-type SF3B1 or vector with mutated SF3B1 construct R957Q into RL-95-2 cells which have minimal endogenous SF3B1. Analysis of proliferation assays revealed that cells overexpressing SF3B1 proliferated significantly more than cells expressing empty vector. Intriguingly, we observed that RL-95-2 cells over-expressing R957Q mutants were even more proliferative than the cells expressing wild-type SF3B1. Together, this data suggest that SF3B1 over-expression and mutation play a crucial oncogenic role in endometrial cancer, and these findings may support the development of SF3B1 inhibitors to treat this disease.

Citation Format: Pooja Popli, Xinchao Deng, Premal Thaker, Ramakrishna Kommagani. Mutant or overexpressed SF3B1 facilitates endometrial cancer tumorigenesis. [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 4877.

Abstract 2331: Metabolic profiling of pre and post treatment ovarian cancer tissues using in situ mass spectrometry imaging

Chemotherapy resistance represents a major problem in ovarian cancer prognosis and reliable indicators of chemotherapy sensitivity remain an unmet need. Here, we examined metabolic profiles of pre- and post-neoadjuvant chemotherapy (NACT) tumor samples from patients with high-grade serous ovarian cancer (HGSC). We performed spatially resolved, desorption electrospray ionization-mass spectrometry (DESI-MS) on sections from clinically annotated HGSC samples collected according to a laparoscopic triage algorithm from patients pre- and post-NACT. Patients were considered to be either excellent (ER) if they presented complete response or only microscopic disease left at interval surgery, or poor responders (PR) if they presented stable or progressive disease after NACT. Tumor tissues from 50 patients (29 ER and 21 PR, 13 ER matched pre and post NACT, 13 PR matched pre and post-NACT) were eligible for the analyses Data relative to the detected metabolites, were collected from epithelium and stroma separately. We first identified differentially upregulated metabolites in ER and PR groups and performed pathway analysis. The over-represented pathways in the chemo-naïve PR tissues included the nucleotide metabolism pathway in epithelial areas, and degradation of cysteine and homocysteine, metabolism of amino acids and derivatives, as well as sulfur amino acids metabolism in the stromal areas (p values FDR adjusted 0.045). In general, both the epithelium and stroma of PR tissues of chemo-naïve tumors, contained a higher number and a higher variety of lipid species compared with ER tissues. In post-NACT tumor epithelial areas, there was global downregulation of metabolites across all patient samples, compared to the pre-chemo specimens; this was more evident in ER patients. In post-NACT tumors from PR patients, glutathione synthesis and recycling pathway, and sulfite oxidation to sulfate pathway and many glycerolipids species were upregulated in the epithelium, while phosphatidic acids were upregulated in the stroma. Lastly, we evaluated the predictive power of the metabolic data extracted by the epithelial areas of chemo-naïve tissues, in classifying patients as ER or PR. We used 10-fold cross-validation to create a ridge regression model for the classification of ER and PR samples from pre-NACT tumor tissues. This model, based on 78 differentially expressed metabolites (small molecules and lipids), correctly classified patients as ER or PR with an accuracy of 76.2% (sensitivity 84.6% and specificity 62.5%). Our findings indicate altered metabolic pathways in ovarian cancer tissues based on response to NACT. The identification of differentially activated pathways, such as sulfate metabolism and glutathione metabolism in tumors with poor response, suggest novel actionable targets to overcome chemotherapy resistance in patients with HGSC.

Citation Format: Sara Corvigno, Meredith Spraldin, Michael Keating, Sunil Badal, Igor Pereira, Elaine Stur, Nicholas Bateman, Waleed Barakat, Thomas Conrads, Sanghoon Lee, George Maxwell, Susan K. Lutgendorf, Premal Thaker, Jinsong Liu, Nicole Fleming, Katheleen Darcy, Livia S. Eberlin, Anil K. Sood. Metabolic profiling of pre and post treatment ovarian cancer tissues using in situ mass spectrometry imaging [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2331.

Overall survival in patients with FIGO stage IVA cervical cancer

OBJECTIVE

FIGO stage IVA cervical cancer is a unique diagnosis that conveys a poor prognosis. Despite the use of PET/CT for staging, concurrent chemotherapy, and image-guided brachytherapy, overall survival (OS) in these patients is low. Treatment requires aggressive use of radiotherapy and chemotherapy. We report results of a prospective observational cohort study for patients with de novo stage IVA cervical cancer treated at a single institution.

METHODS

Patients with a new diagnosis of stage IVA cervical cancer treated at an academic institution between 1997 and 2020 were prospectively monitored. Staging was retroactively assigned using the 2018 FIGO staging system. All patients had a PET/CT prior to treatment and were treated with definitive intent radiotherapy with or without chemotherapy. The primary outcome of interest was OS. Secondary outcomes were local control, progression-free survival (PFS), and disease-specific survival (DSS).

RESULTS

32 patients with de novo stage IVA cervical cancer were treated with definitive intent radiotherapy. Median follow-up time was 4.27 years (1.31-10.35). 22/32 (69%) of patients received brachytherapy as a part of their definitive treatment, and 28/32 (88%) received chemotherapy concurrently with radiotherapy. 14/32 (44%) of patients had no evidence of disease at last follow-up. The 5-year local control, PFS, DFS, and OS estimates were 79%, 49%, 53%, and 48%, respectively. On multivariate analysis, complete metabolic response was associated with a statistically significant improvement in PFS (HR = 0.256, 95% CI = 0.078-0.836, p = 0.024) and OS (HR = 0.273, 95% CI 0.081-0.919).

CONCLUSIONS

These data demonstrate a robust OS in patients with stage IVA cervical cancer when treated with definitive chemoradiotherapy.

Prognostic significance of ethnicity and age in advanced stage epithelial ovarian cancer: An NRG oncology/gynecologic oncology group study

BACKGROUND

Age and ethnicity are among several factors that influence overall survival (OS) in ovarian cancer. The study objective was to determine whether ethnicity and age were of prognostic significance in women enrolled in a clinical trial evaluating the addition of bevacizumab to front-line therapy.

METHODS

Women with advanced stage ovarian, primary peritoneal, or fallopian tube cancer were enrolled in a phase III clinical trial. All women had surgical staging and received adjuvant chemotherapy with one of three regimens. Cox proportional hazards models were used to evaluate the relationship between OS with age and race/ethnicity among the study participants.

RESULTS

One-thousand-eight-hundred-seventy-three women were enrolled in the study. There were 280 minority women and 328 women over the age of 70. Women age 70 and older had a 34% increase risk for death when compared to women under 60 (HR = 1.34; 95% CI 1.16-1.54). Non-Hispanic Black women had a 54% decreased risk of death with the addition of maintenance bevacizumab (HR = 0.46, 95% CI:0.26-0.83). Women of Asian descent had more hematologic grade 3 or greater adverse events and a 27% decrease risk of death when compared to non-Hispanic Whites (HR = 0.73; 95% CI: 0.59-0.90).

CONCLUSIONS

Non-Hispanic Black women showed a decreased risk of death with the addition of bevacizumab and patients of Asian ancestry had a lower death rate than all other minority groups, but despite these clinically meaningful improvements there was no statistically significant difference in OS among the groups.

Phase I Trial of Stereotactic MRI-Guided Online Adaptive Radiation Therapy (SMART) for the Treatment of Oligometastatic Ovarian Cancer

PURPOSE

Stereotactic body radiation therapy is increasingly used to treat a variety of oligometastatic histologies, but few data exist for ovarian cancer. Ablative stereotactic body radiation therapy dosing is challenging in sites like the abdomen, pelvis, and central thorax due to proximity and motion of organs at risk. A novel radiation delivery method, stereotactic magnetic-resonance-guided online-adaptive radiation therapy (SMART), may improve the therapeutic index of stereotactic body radiation therapy through enhanced soft-tissue visualization, real-time nonionizing imaging, and ability to adapt to the anatomy-of-the-day, with the goal of producing systemic-therapy-free intervals. This phase I trial assessed feasibility, safety, and dosimetric advantage of SMART to treat ovarian oligometastases.

METHODS AND MATERIALS

Ten patients with recurrent oligometastatic ovarian cancer underwent SMART for oligometastasis ablation. Initial plans prescribed 35 Gy/5 fractions with goal 95% planning target volume coverage by 95% of prescription, with dose escalation permitted, subject to strict organ-at-risk dose constraints. Daily adaptive planning was used to protect organs-at-risk and/or increase target dose. Feasibility (successful delivery of >80% of fractions in the first on-table attempt) and safety of this approach was evaluated, in addition to efficacy, survival metrics, quality-of-life, prospective timing and dosimetric outcomes.

RESULTS

Ten women with seventeen ovarian oligometastases were treated with SMART, and 100% of treatment fractions were successfully delivered. Online adaptive plans were selected at time of treatment for 58% of fractions, due to initial plan violation of organs-at-risk constraints (84% of adapted fractions) or observed opportunity for planning target volume dose escalation (16% of adapted fractions), with a median on-table time of 64 minutes. A single Grade ≥3 acute (within 6 months of SMART) treatment-related toxicity (duodenal ulcer) was observed. Local control at 3 months was 94%; median progression-free survival was 10.9 months. Median Kaplan-Meier estimated systemic-therapy-free survival after radiation completion was 11.5 months, with concomitant quality-of-life improvements.

CONCLUSIONS

SMART is feasible and safe for high-dose radiation therapy ablation of ovarian oligometastases of the abdomen, pelvis, and central thorax with minimal toxicity, high rates of local control, and prolonged systemic-therapy-free survival translating into improved quality-of-life.

Abstract PO045: Inhibition of GAS6/AXL improves efficacy of HER2 inhibitor trastuzumab in uterine serous cancer

Objectives: To determine whether inhibition of GAS6/AXL can improve efficacy to the humanized anti-HER2 monoclonal antibody trastuzumab by decreasing uterine serous cancer cell invasion and cell survival in vitro and tumor burden in vivo. Methods: We treated AXL-expressing and HER2-expressing uterine serous cancer cell lines (ARK1, ARK2) with trastuzumab, AVB-500, or trastuzumab plus AVB-500. Clonogenic cell survival assays were performed. Matrigel invasion assays were used to assess the invasive capacity of ARK2 cells after 24 hours of treatment with vehicle, AVB-500, trastuzumab, or trastuzumab plus AVB-500. A proximity ligation assay was used to examine colocalization of HER2/neu and AXL. Western blots were performed to assess the effects of the individual drugs and combination on phosphorylation of HER2/neu and AXL. An intraperitoneal tumor model with 10 million ARK1 cells was treated with vehicle, AVB-500, trastuzumab, or trastuzumab plus AVB-500 for 35 days. The number, size, and volume of tumor nodules were measured. GraphPad Prism was used for statistical analysis. Results: We found decreased cell survival by clonogenic assays in ARK1 and ARK2 cells treated with trastuzumab plus AVB-500 compared to trastuzumab alone (relative absorbance 0.155 nm vs 0.202 nm, P=0.015). There was significantly less invasion from treatment with trastuzumab plus AVB-500 than with trastuzumab alone (3.2 vs 17.8 invading tumor cells/hpf, P=0.0004). Western blot showed that cells treated with trastuzumab plus AVB-500 had reduced phospho-AXL compared to cells treated with AVB-500 or trastuzumab alone. Furthermore, the proximity ligation assay demonstrated co-localization of the AXL and HER2 receptors in both ARK1 and ARK2 cells indicating a physical closeness that could account for this co-regulation. We found that mice treated with trastuzumab plus AVB-500 developed significantly less tumor burden than mice treated with trastuzumab alone (0.03205 g vs 0.08316 g, P= 0.024), AVB-500 alone (0.0320 g vs 0.1638 g, P<0.0001), and vehicle alone (0.03205 g vs 0.1154 g, P= 0.0395). Conclusions: The GAS6/AXL inhibitor AVB-500 potentiated the effect of trastuzumab to decrease uterine serous cancer cell proliferation and invasion in vitro and tumor burden in vivo likely through AXL and HER2 complexes.

Citation Format: Joan Tankou, Michael Toboni, Hollie Noia, Alyssa Oplt, Daniel Wilke, Dineo Khabele, Lindsay Kuroki, Andrea Hagemann, Carolyn McCourt, Premal Thaker, David Mutch, Matthew Powell, Katherine Fuh. Inhibition of GAS6/AXL improves efficacy of HER2 inhibitor trastuzumab in uterine serous cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO045.

Abstract PO047: AVB-500, a receptor tyrosine kinase AXL inhibitor, improves response to olaparib in uterine serous cancer

Objectives: We determined whether inhibition of GAS6/AXL with AVB-500 in combination with olaparib could improve response in HR-proficient (HRP) uterine serous cancer (USC). Methods: Two USC cell lines (ARK1 & ARK4) were radiated with 10Gy, and RAD51 foci were identified by immunofluorescence (IF). These were treated with AVB-500 (Aravive Biologics, Houston, TX) in combination with the poly ADP ribose polymerase (PARP) inhibitor, olaparib. Colony forming assays were assessed after 4 days of treatment with either AVB-500 alone, olaparib alone or combination treatment (olaparib + AVB-500). Colonies were stained and absorbance was obtained to calculate relative cell survival using Graph Pad Prism. In vivo studies were performed using NOD-SCID mice injected with 1 × 107 ARK1 cells intraperitoneally followed by treatment q3 days for 14-day treatment period. Treatment groups were vehicle control, AVB-500 alone, olaparib alone and olaparib with AVB-500. Results: ARK1 and ARK4 cells were found to have an increase in gamma-H2AX and RAD51 foci after radiation that was consistent with HRP. In clonogenic assays, colonies were stained and absorbance was obtained for each experimental arm. Olaparib + AVB-500 had significantly less absorbance than the olaparib only group for ARK1s (0.417nm vs 0.756nm, p=0.001) as well as in ARK4s (0.186nm vs 0.641nm, p=0.003). In an intraperitoneal model with ARK1 tumors, the olaparib + AVB-500 treated group had less tumor weight than those treated with olaparib alone (0.008g vs 0.138g, p=0.002) and AVB-500 alone (0.008g vs 0.145g, p=0.0006) after a 14-day treatment period. Conclusions: AVB-500 in combination with olaparib demonstrates an improved response than olaparib alone with a greater decrease in tumor burden. This was demonstrated in two HRP cell lines. Additional therapeutic and mechanistic experiments are ongoing.

Citation Format: Michael D. Toboni, Mary Mullen, Jo'an Tankou, Hollie Noia, Alyssa Oplt, Daniel Wilke, Dineo Khabele, Lindsay Kuroki, Andrea Hagemann, Carolyn McCourt, Premal Thaker, David Mutch, Matthew Powell, Katherine Fuh. AVB-500, a receptor tyrosine kinase AXL inhibitor, improves response to olaparib in uterine serous cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO047.

Abstract PR004: Multi-dimensional biomarker analyses identify pembrolizumab responders in advanced stage, high grade endometrial cancer

Objectives: The recent FDA approval of pembrolizumab for the treatment of recurrent, tissue agnostic cancers with Microsatellite Instability-High (MSI-H) or Mismatch Repair Deficient (dMMR) has led to the treatment of a selected cohort of endometrial cancer (EC) patients. Methods: We designed a study to ascertain tumor immune modulatory effects of pembrolizumab in the front-line setting for advanced stage III/IV surgically-resectable endometrial cancers regardless of MSI-H or dMMR status. The primary objectives were to determine the safety of treatment with pembrolizumab by radiographic imaging and to determine progression-free survival at 6 months. Exploratory objective was to compare the immune response before and after treatment. In an open label, single-arm Phase I trial, 8 EC patients were treated with 2 doses of preoperative pembrolizumab IV prior to surgery followed by carboplatin and paclitaxel and 4 doses of pembrolizumab 200mg/kg q3 weeks IV. Peripheral blood was collected from EC patients at baseline level before treatment and post 2 doses of pembrolizumab treatment. Blood from healthy controls (HC) was also collected. Both were processed for high-dimensional single-cell mass cytometry (CyTOF) using an optimized lymphoid and myeloid panel. Results: Patients who responded to therapy showed lower frequency of circulating CD8+ naïve T cells but higher frequency of CD8+ effector T cells after the treatment than the poor responders. We observed post-therapy expansion of populations of CD8+ and CD4+ T cells expressing co-stimulatory receptor ICOS in responders but not in poor responders. Granzyme+CD8+ and Granzyme+CD4+ T cell populations were expanded after pembrolizumab treatment in responders but were decreased in poor responders. Higher frequency of CD27+Fas- CD4+ T cells at baseline and increased frequency of CD27-Fas+CD4+ T cells post-treatment were observed in responders but not in the poor responders. Furthermore, we identified that circulating MDSCs were reduced after pembrolizumab treatment in responders. Conclusions: Our results suggest that peripheral blood analysis may provide valuable insights into responses to anti-PD-1-targeted therapies in patients with endometrial cancers.

Citation Format: Katherine Fuh, Elena Lomonosova, Russell Pachynski, Olga Malkova, Stephen Oh, Andrea Hagemann, Carolyn McCourt, Matthew Powell, Wendy Fantl, Premal Thaker. Multi-dimensional biomarker analyses identify pembrolizumab responders in advanced stage, high grade endometrial cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PR004.

Abstract A13: Therapeutic AXL inhibition with AVB-S6-500 improves response to chemotherapy and induces a homologous recombination deficiency in ovarian cancer

Background: Over 80% of patients with advanced ovarian cancer will develop chemoresistance and die within 5 years. Biomarkers to predict chemoresponse and novel therapies to target chemoresistance would be practice changing. We aim to establish serum and tissue GAS6 as predictive biomarkers of chemoresponse and to determine if AXL inhibition through sequestration of its ligand, GAS6, with AVB-S6-500 (AVB) can improve chemoresponse. Further, we desired to understand the affect AVB has on DNA damage response (DDR).

Methods: AVB was supplied by Aravive Biologics. High-grade serous ovarian cancer (HGSOC) tumor samples were obtained pre- and post-neoadjuvant chemotherapy. AXL and GAS6 expression were evaluated by immunohistochemistry and serum concentration. In vitro viability and clonogenic assays were performed on chemoresistant tumor cells (OVCAR8, OVCAR5, COV62, and POV71-hTERT) treated with chemotherapy +/- AVB. Mouse models (OVCAR8, PDX, OVCAR5) were used to determine if the combination of chemotherapy + AVB reduced tumor burden. Immunofluorescent (IF) assays targeting γH2AX were used to evaluate DNA damage and additional assays targeting 53BP1, RAD51, BRCA1, and BRCA2 were used to evaluate DNA damage response in cells treated with AVB, carboplatin, and/or AVB+carboplatin. Flow cytometry was used to evaluate RPA binding and cell cycle.

Results: Patients with high pretreatment tumor GAS6 expression (>85%, n=7) or serum GAS6 concentrations (>25ng/mL, n=13) were more likely to be resistant to neoadjuvant chemotherapy than those with low tumor GAS6 expression (<45%, n=4) (P=0.010) or low serum GAS6 concentrations (<15ng/mL, n=5) (P=0.002). Carboplatin plus AVB (2μM, 5μM) and paclitaxel plus AVB (1μM) resulted in decreased cell viability and clonogenic growth compared to chemotherapy alone (p<0.05) in all tumor cell lines. In vivo tumor mouse models treated with chemotherapy+AVB had significantly smaller subcutaneous and intraperitoneal (IP) tumors than those treated with chemotherapy alone (P<0.001). Increased DNA damage occurred in tumor cells treated with AVB than controls and in tumor cells treated with carboplatin+AVB than carboplatin alone (OVCAR8, COV362, CAOV3, OVCAR3-TPMES P<0.001). Cells treated with AVB either alone or in combination with carboplatin demonstrated decreased binding of protein involved in homologous recombination including RPA, RAD51, BRCA1, and BRCA2 (P<0.05). Conversely, these same cells demonstrated increased binding of the nonhomologous end joining protein 53BP1 (P<0.05). There were no differences in cell cycle among the treatment groups.

Conclusions: High GAS6 is associated with poor neoadjuvant chemoresponse in HGSOC patients. The combination of chemotherapy with AVB decreases tumor cell viability and tumor growth. AVB imparts a homologous recombination deficiency through downregulation of homology-directed DNA repair with an associated upregulation of nonhomologous end joining.

Citation Format: Mary Margaret Mullen, Elena Lomonosova, Hollie Noia, Daniel Wilke, Alyssa Oplt, Lei Guo, Lindsay Kuroki, Andrea Hagemann, Carolyn McCourt, Premal Thaker, David Mutch, Matthew Powell, Katherine Fuh. Therapeutic AXL inhibition with AVB-S6-500 improves response to chemotherapy and induces a homologous recombination deficiency in ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A13.