Low-grade Serous Ovarian Cancer Research Articles

An open-label, single-arm, prospective, multi-center, tandem two-stage designed phase II study to evaluate the efficacy of fulvestrant in women with recurrent/metastatic estrogen receptor-positive gynecological malignancies (FUCHSia study)

ObjectiveThis study aimed to evaluate fulvestrant efficacy in women with estrogen receptor-positive low-grade gynecological cancers. The primary objective was to determine the response rate. Secondary objectives were progression-free survival, clinical...

Clinical and genomic landscape of RAS mutations in gynecologic cancers.

We aimed to describe RAS mutations in gynecologic cancers as they relate to clinicopathologic and genomic features, survival, and therapeutic implications. Gynecologic cancers with available somatic molecular profiling data at our institution between February 2010 and August 2022 were included and grouped by RAS mutation status. Overall survival was estimated by Kaplan-Meier method, and multivariable analysis was performed using Cox proportional-hazards model. Of 3328 gynecologic cancers, 523 (15.7%) showed any RAS mutation. Patients with RAS-mutated tumors were younger (57 vs 60 years non-mutated), had higher prevalence of endometriosis (27.3% vs 16.9%), and lower grades (grade 1/2, 43.2% vs 8.1%, all p<0.0001). Highest prevalence of KRAS mutation was in mesonephric-like endometrial (100%, n=9/9), mesonephric-like ovarian (83.3%, n=5/6), mucinous ovarian (60.4%), and low-grade serous ovarian (44.4%) cancers. After adjustment for age, cancer type, and grade, RAS mutation was associated with worse overall survival (HR=1.3, p=0.001). Specific mutations were in KRAS (13.5%), NRAS (2.0%), and HRAS (0.51%), most commonly KRAS G12D (28.4%) and G12V (26.1%). Common co-mutations were PIK3CA (30.9%), PTEN(28.8%), ARID1A (28.0%), and TP53 (27.9%), of which 64.7% were actionable. RAS+MAPK pathway-targeted therapies were administered to 62 patients with RAS-mutated cancers. While overall survival was significantly higher with therapy (8.4 years [95%CI 5.5-12.0] vs 5.5 years [95%CI 4.6-6.6], HR=0.67, p=0.031), this effect did not persist in multivariable analysis. RAS mutations in gynecologic cancers have a distinct histopathologic distribution and may impact overall survival. PIK3CA, PTEN, and ARID1A are potentially actionable co-alterations. RAS pathway-targeted therapy should be considered.

Advances in precision therapy of low-grade serous ovarian cancer: A review.

Low-grade serous ovarian carcinoma (LGSOC) is a rare subtype of ovarian cancer that accounts for approximately 6% to 10% of serous ovarian cancers. The clinical treatment of LGSOC is similar to that of high-grade serous ovarian carcinoma, however, its clinical and molecular characteristics are different from those of high-grade serous ovarian carcinoma. This article reviews the research on gene diagnosis, surgical treatment, chemotherapy, and biological therapy of LGSOC, providing reference for clinical diagnosis and treatment of LGSOC. Surgery is the cornerstone of LGSOC treatment and maximum effort must be made to achieve R0 removal. Although LGSOC is not sensitive to chemotherapy, postoperative platinum-based combination chemotherapy remains the first-line treatment option for LGSOC. Additional clinical trials are needed to confirm the clinical benefits of chemotherapy and explore new chemotherapy protocols. Hormone and targeted therapies may also play important roles. Some patients, particularly those with residual lesions after treatment, may benefit from hormone maintenance therapy after chemotherapy. Targeted therapies, such as MEKi, show good application prospects and are expected to change the treatment pattern of LGSOC. Continuing to further study the genomics of LGSOC, identify its specific gene changes, and combine traditional treatment methods with precision targeted therapy based on second-generation sequencing may be the direction for LGSOC to overcome the treatment bottleneck. In future clinical work, comprehensive genetic testing should be carried out for LGSOC patients to accumulate data for future scientific research, in order to find more effective methods and drugs for the treatment of LGSOC.

The prognostic value of MEK pathway-associated estrogen receptor signaling activity for female cancers.

Other than for breast cancer, endocrine therapy has not been highly effective for gynecologic cancers. Endocrine therapy resistance in estrogen receptor positive gynecologic cancers is still poorly understood. In this retrospective study, we examined the estrogen receptor (ER) signaling pathway activities of breast, ovarian, endometrial, and cervical cancers to identify those that may predict endocrine therapy responsiveness. Clinical and genomic data of women with breast and gynecological cancers were downloaded from cBioPortal for Cancer Genomics. Estrogen receptor alpha (ESR1) expression level and sample-level pathway enrichment scores (EERES) were calculated to classify patients into four groups (low/high ESR1 and low/high EERES). Correlation between ESR1/EERES score and survival was further validated with RNAseq data from low-grade serous ovarian cancer. Pathway analyses were performed among different ESR1/EERES groups to identify genes that correlate with endocrine resistance, which are validated using Cancer Cell Line Encyclopedia gene expression and Genomics of Drug Sensitivity in Cancer data. We identified a novel combined prognostic value of ESR1 expression and the corresponding estrogen response signaling (EERES score) for breast cancer. The combined prognostic value (ESR1/EERES) may be applicable to other gynecologic cancers. More importantly, we discovered that ER signaling can cross-regulate MEK pathway activation. We identified downstream genes in the MEK pathway (EPHA2, INAVA, MALL, MPZL2, PCDH1, and TNFRSF21) that are potential endocrine therapy response biomarkers. This study demonstrated that targeting both the ER and the ER signaling activity related MEK pathway may aid the development of endocrine therapy strategies for personalized medicine.

Abstract 6279: Estrogen signaling in low-grade serous ovarian carcinoma

Abstract High level of estrogen in the blood of women has been linked to the progression and possibly development of ovarian cancer. Almost all low-grade serous ovarian cancer (LGSOC) expresses estrogen receptor alpha (ERα protein encoded by the gene ESR1) and develops during reproductive age of women. However, recent studies suggested that a higher expression of ERα correlates with better survival. In a phase II clinical trial, hormonal therapies have been shown to be associated with a clinical benefit rate of 61% for recurrent ER-positive LGSOC patients. The study also indicated that women with recurrent LGSOC who received hormonal therapies had a significantly longer progression-free survival but not overall survival. Endocrine therapies have proven to be effective in treating breast cancer. Unfortunately, in ovarian cancer clinical trials (GOG0281 and PARAGON), these treatments have not achieved comparable results, with an objective response rate of only approximately 14%. To understand the ESR1 regulation in LGSOC, we have performed RNAseq and ChIPseq analyses of LGSOC tumor tissues. We also forced over-expression of ESR1 in LGSOC cell lines. Using RNAseq data, we aligned the sequencing reads to all the known ESR1 transcript variants. We found that ESR1 transcript variant 1, 2, 3 and X11 were the major transcripts expressed. Variants 1, 2 and 3 encode the regular 66 kDa ESR1 protein, while the X11 variant encodes a 52 kDa ESR1 protein. Both 66 kDa and 52 kDa ESR1 proteins were also detected in LGSOC tumor tissues by western blots. To further explore the function of ESR1 66kDa in LGSOC, we over-expressed ESR1 variant 1 in two LGSOC cell lines (HOC-7 and HCC5075) by transfecting with an expression plasmid. Total proteins were extracted from the mock control and transfected cells for functional proteomic analysis by reverse phase protein arrays (RPPA). From the RPPA data, overexpressing ESR1 in LGSOC cell lines suppressed DNA repair pathways but activated cell cycle and mitosis pathways. To further delineate the ESR1 DNA binding sites in LGSOC, we performed ChIPseq analysis of these tumor samples as well as two ovarian cancer cell lines that express ESR1 protein. Our results demonstrated that ESR1 regulated “cistromes” in ER positive ovarian carcinoma is very different from that in ER positive breast cancer as much less ESR1 binding sites were found in LGSOC. There are ESR1 binding sites common to both types of cancers, but we found quite a few unique ESR1 binding sites. We are trying to integrate the ChIPseq and RNAseq data and hopefully identify, for the first time, an ovarian cancer specific ERα cistrome. ER expression may not always correlate with activation of ESR1 signaling pathways, which may be one of the reasons underlying endocrine therapy resistance in ovarian cancer. The results of an integrated analyses will also give us insight on the management of ER positive LGSOC by identifying new genetic targets that may be used in combination with endocrine therapy. Citation Format: Yvonne TM Tsang, Chun Wai Oscar Ng, David Gershenson, K-Kwok wong. Estrogen signaling in low-grade serous ovarian carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6279.

Abstract 4688: EC359, A new therapeutic drug for the treatment of low grade serous ovarian cancer

Abstract Background: Ovarian cancer (OCa) is the deadliest of all gynecologic cancers in the United States. About 10% of all cases of serous ovarian cancer have the unusual histology named low-grade serous carcinomas (LGSOC), that has a distinct clinical behavior with a unique molecular landscape. LGSOC is characterized by a younger age at diagnosis, indolent progression, and chemotherapy resistance. BRAF and KRAS mutations occur in 33% and 35% of LGSOC cases, respectively. LGSOC is frequently detected when the malignancy is in advanced stage and LGSOC relapses in about 70% of patients with advanced disease. Therefore, new targeted therapies are required. Since LGSOC uniquely expresses mutations of either BRAF or KRAS, and because Leukemia Inhibitor Factor (LIF) expression is induced by oncogenes such as KRAS, we reason that the LIF/LIFR axis represents a unique target for treating LGSOC. The objective of this study is to test the utility of blocking LIF/LIFR axis using LIFR inhibitor EC359 in treating LGSOC. Methods: The expression of LIF and its receptor LIFR was profiled using multiple established LGSOC cells and primary LGSOC model cells. The effects of EC359 on LGSOC cells were evaluated using cell viability, colony formation, and apoptosis assays. Mechanistic investigations were conducted with Western blotting, reporter assays and RT-qPCR analysis. The in vivo efficacy of LIFR inhibitor EC359 as a targeted therapy was investigated using LGSOC cell-based xenografts. Results: Western blot analysis confirmed expression of LIFR and LIF in established LGSOC and primary LGSOC cells and functional autocrine loop of LIF/LIFR signaling. The treatment with the LIFR inhibitor EC359 significantly reduced LGSOC cell viability, cell survival, and increased apoptosis. The activation of downstream LIFR signaling including STAT3, mTOR, AKT, and p42/44 MAPKs markedly decreased by EC359 treatment. EC359 enhanced the efficacy of trametinib, a currently used medication of LGSOC. EC359+trametinib as a combination therapy showed more efficacy over monotherapy of EC359 or trametinib in reducing cell viability and colony formation. Using cell-based xenograft and PDX models, we demonstrated that the EC359 at 5mg/kg dose significantly reduced the LGSOC xenograft growth compared to the vehicle control. Conclusions: Together, our findings support the existence of LIF/LIFR autocrine loops, and EC359 is a viable treatment option for LGSOC. Citation Format: Yasmin Lyons, William Cole Arnold, Behnam Ebrahimi, Bindu Santhamma, Edward R. Kost, Hareesh B. Nair, Suryavathi Viswanadhapalli, Ratna K. Vadlamudi. EC359, A new therapeutic drug for the treatment of low grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4688.

Abstract 952: Ex vivo drug testing identifies a potentially effective drug in 94% of cases for 403 patients in 42 tumor types

Abstract Objective: To determine whether patient derived tumor cells (PDTC) could be derived from a variety of solid tumors and used to select effective therapies, we developed a CLIA certified assay, the PARIS® test, to quantify drug sensitivities using PDTCs. Methods: Oncologists referred patients for the PARIS® test and patients had the option to consent to SEngine Precision Medicine’s IRB protocol. Samples were obtained from multiple cancer centers across the US and abroad. Patients were at all stages in their clinical journey ranging from treatment naïve to late stage, recurrent/refractory disease settings. Fresh specimens obtained from surgical resections, core biopsies, or body fluids arrived at our CLIA laboratory within 48 hrs from collection. Tumor origin and driver mutations were confirmed by IHC or DNA sequence in 88% of the cases. Results: PDTCs derived from 403 patients diagnosed with 42 different solid tumor types, including both common and rare tumors, were subjected to the PARIS® assay. An average of 67 oncology drugs (ranging from 6-307), including chemotherapies and targeted agents, were tested for each patient sample. A report ranking drug sensitivities was provided to the oncologist with an average turnaround time of less than 3 weeks. Drug sensitivity was classified as exceptional/good, moderate/low and no responses. Remarkably, 94.2% of the PDTCs exhibited selective exceptional/good responses to at least one, and typically several drugs, despite the majority of PDTCs being derived from patients with drug resistant, metastatic disease. The drug sensitivity profiles showed highly individualized responses as well as tumor type specificity. While known biomarkers/drug sensitivity associations were confirmed, many samples exhibited sensitivity to targeted agents in the absence of known biomarkers. For example, HER2+ breast cancers demonstrated sensitivity to HER2/EGFR inhibitor and a subset of luminal B and triple negative breast cancers demonstrated HER2/EGFRi responses without underlying genetic alterations. Functional testing was also useful in the rare tumor types. For example, low grade serous ovarian cancer (LGSOC) cells, differentiated from high grade by their response to specific receptor tyrosine kinase inhibitors and estrogen antagonists, but a poor response to standard of care, as is observed in the clinic. Three patients with LGSOC that were treated with the PARIS test top scoring drugs had a positive clinical response and cases from other tumor types will be presented. Conclusions: Functional testing of PDTCs from both common and rare tumor types is feasible, even for those that have failed standard of care. We provide an unprecedented view of patient-specific, actionable vulnerabilities to current oncology drugs. Personalization of cancer care will require improved access to off-label drugs. Citation Format: Rachele Rosati, Alex C. Rajevski, Payel Chatterjee, Lauren R. Appleyard, Ana Cristina Cordero Schmidt, Shalini Pereira, Robert L. Diaz, Brady Bernard, Brady Bernard, Carla Grandori, Christopher J. Kemp. Ex vivo drug testing identifies a potentially effective drug in 94% of cases for 403 patients in 42 tumor types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 952.

Identification of potentially actionable genetic variants in epithelial ovarian cancer: a retrospective cohort study

Ovarian cancer is the most lethal gynecologic malignancy, mainly due to late-stage diagnosis, frequent recurrences, and eventually therapy resistance. To identify potentially actionable genetic variants, sequencing data of 351 Belgian ovarian cancer patients were retrospectively captured from electronic health records. The cohort included 286 (81%) patients with high-grade serous ovarian cancer, 17 (5%) with low-grade serous ovarian cancer, and 48 (14%) with other histotypes. Firstly, an overview of the prevalence and spectrum of the BRCA1/2 variants highlighted germline variants in 4% (11/250) and somatic variants in 11% (37/348) of patients. Secondly, application of a multi-gene panel in 168 tumors revealed a total of 214 variants in 28 genes beyond BRCA1/2 with a median of 1 (IQR, 1–2) genetic variant per patient. The ten most often altered genes were (in descending order): TP53, BRCA1, PIK3CA, BRCA2, KRAS, ERBB2 (HER2), TERT promotor, RB1, PIK3R1 and PTEN. Of note, the genetic landscape vastly differed between the studied histotypes. Finally, using ESCAT the clinical evidence of utility for every genetic variant was scored. Only BRCA1/2 pathogenic variants were classified as tier-I. Nearly all patients (151/168; 90%) had an ESCAT tier-II variant, most frequently in TP53 (74%), PIK3CA (9%) and KRAS (7%). In conclusion, our findings imply that although only a small proportion of genetic variants currently have direct impact on ovarian cancer treatment decisions, other variants could help to identify novel (personalized) treatment options to address the poor prognosis of ovarian cancer, particularly in rare histotypes.

Abstract A107: Characterizing the genomic and immunologic landscape of serous borderline tumors and low-grade serous ovarian cancer

Abstract A107: Characterizing the genomic and immunologic landscape of serous borderline tumors and low-grade serous ovarian cancer

Abstract A026: Identifying mechanisms to target in combination with trametinib to improve therapeutic efficacy in low-grade serous ovarian cancer

Abstract A026: Identifying mechanisms to target in combination with trametinib to improve therapeutic efficacy in low-grade serous ovarian cancer

Abstract B054: Defective STING signaling in low-grade serous ovarian cancer: an opportunity for oncolytic viruses therapy

Abstract There are two serous ovarian cancer histotypes, low and high grade (LGSOC and HGSOC), which are distinct clinical and biological entities. LGSOC is a rare histotype with a relatively stable genome, while HGSC is more common and genomically unstable. Surprisingly LGSOC expresses high levels of the stimulator of the interferon genes (STING). The STING pathway recognizes cytoplasmic double-stranded DNA and mounts innate cellular immunity through interferon-beta type I production. Our objective is to investigate the aberrant STING signaling in LGSOC and test the effectiveness of oncolytic viruses against LGSOC. We used immunohistochemistry on tissue microarrays (TMAs) to assess STING protein expression in different ovarian cancer histotypes. Whole proteome analysis was applied to identify differentially expressed proteins in LGSOC and HGSOC patient samples (both n=9). Further, a semi-targeted proteomics approach was used to evaluate the expression levels of the STING pathway-related proteins in LGSOC, HGSOC, and LGSOC precursor tumors (each subtype, n=20). To evaluate the key transcription, phosphorylation, and translocation events in STING signaling, we treated LGSOC cell lines with an agonist (dsDNA90) and performed qPCR, immunoblotting, and immunofluorescence experiments, respectively. We tested the viability of the LGSOC cell lines in response to Vaccinia Virus (VV), and Vesicular Stomatitis Virus (VSV) based oncolytic vectors with or without immunostimulatory transgenes. Our results show that STING protein levels were consistently higher in LGSOC TMAs relative to other histotypes. Proteomics analysis showed that the half of the 16 most differentially expressed proteins were the effectors of STING signaling with unexpectedly lower expression in LGSOC, suggesting that despite the robust levels of STING in LGSOC tumors, the pathway is not fully active. Attenuated STING translocation and expression of IFNB1 and other cytokines in LGSOC cell lines confirm the aberrancy in the STING pathway. Semi-targeted proteomics revealed the considerable overexpression of STIM1 in LGSOC patient tumors, which has previously been shown to sequester STING in the endoplasmic reticulum. The treatment with VV and VSV oncolytic viruses significantly reduced the proliferation of LGSOC cell lines. In summary, we find attenuated STING signaling in LGSOC, possibly due to overexpression of STIM1 preventing STING translocation. Although oncolytic viruses show promising results in LGSOC cell lines, more research is needed to determine the optimal treatment strategy, testing oncolytic viruses expressing various transgenes and combination therapies. Citation Format: Almira Zhantuyakova, Dawn Cochrane, Gian Luca Negri, Sandra Spencer Miko, Taha Azad, Marta Llaurado Fernandez, Mark Carey, Gregg B. Morin, John Bell, David D. Huntsman. Defective STING signaling in low-grade serous ovarian cancer: an opportunity for oncolytic viruses therapy [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B054.

Abstract A038: Epigenetic compound library screen of ovarian clear cell carcinoma cell line models identifies decreased cell viability following treatment with the Bruton tyrosine kinase inhibitor ibrutinib

Abstract Ovarian clear cell carcinoma (OCCC) is a difficult to treat histological subtype of ovarian cancer, demonstrating resistance to standard chemotherapy. New approaches are required in order to identify compounds with the potential to target this tumor. OCCC are characterized by mutations in ARID1A and/or ARID1B (AT-rich interactive domain-containing proteins) that encode for members of the mammalian SWI/SNF (SWItch/Sucrose Non-Fermentable) chromatin remodeling complex. We have used an epigenetic library consisting of 160 compounds that targets epigenetic readers, writers, erasers, and transcriptional modulators, to screen seven OCCC cell line models (RMG1, JHOC5, OVTOKO, OVMANA, OVISE, OV207 and TOV21G) and three non-OCCC ovarian cancer cell line models (A2780, COV434 and OVCAR8). Cell lines were seeded in triplicate into 96-well plates and treated with all 160 compounds at both 5 µM and 0.5 µM, as well as with a DMSO vehicle control, for 72 hours. Following treatment, cell viability was determined using a MTS assay and each data point normalized to the DMSO control. Based on the results of viability assays, drugs were sought that preferentially targeted OCCC relative to non-OCCC cell lines. Drugs that increased cell proliferation in two or more of the OCCC lines were removed from the analysis, as were drugs that did not impact upon viability. Drug 152, ibrutinib, inhibited cell viability between 53 to 78% in 6 of the 7 OCCC cell lines at 5 µM, with an average inhibition of 64%. In non-OCCC cell lines, the average cell viability after treatment with 5 µM ibrutinib was 91% (range, 84 – 103%). Ibrutinib is a small molecule inhibitor of Bruton tyrosine kinase (BTK) that has been approved by the FDA for treatment of a number of hematological malignancies including mantle cell lymphoma, small lymphocytic lymphoma and chronic lymphocytic leukemia. BTK functions in B-cell receptor signaling, regulating B cell proliferation and survival. Ibrutinib works by irreversibly blocking the kinase activity of BTK. Interestingly, ibrutinib binding sites are also present in other tyrosine kinases, including EGFR, raising the possibility of off-target effects that can function to decrease tumor cell viability. In addition to hematological malignancies, ibrutinib is being investigated in clinical trials for the potential to impact on solid tumors including non-small cell lung cancer, certain oesophagogastric carcinoma, advanced carcinoid and pancreatic neuroendocrine tumors, squamous cell carcinoma of the head and neck, renal cell carcinoma and glioblastoma, including in some cases in combination with other therapeutic drugs including cisplatin, temozolomide and nivolumab. Following organoid drug testing, off-label use of ibrutinib in a patient with low-grade serous ovarian cancer has recently shown promising results. Research is on-going to determine the effectiveness of ibrutinib in pre-clinical models of OCCC, including analyses of the effectiveness of ibrutinib in ARID1A and ARID1B wild-type and mutant CRISPR-engineered isogenic cell line panels of OCCC. Citation Format: Yue Ma, Kristie Ann Dickson, Natisha Field, Tao Xie, Nham Tran, Deborah Joy Marsh. Epigenetic compound library screen of ovarian clear cell carcinoma cell line models identifies decreased cell viability following treatment with the Bruton tyrosine kinase inhibitor ibrutinib [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr A038.

Abstract A066: The cytotoxic effects of oxaliplatin and 5-fluorouracil against low-grade serous ovarian cancer cells

Abstract A066: The cytotoxic effects of oxaliplatin and 5-fluorouracil against low-grade serous ovarian cancer cells

Abstract A065: High throughput drug screening to decipher the mechanisms of trametinib adaptive resistance in low-grade serous ovarian cancer cell lines

Abstract Low Grade Serous Ovarian Cancer (LGSOC) is a rare disease but accounts for a significant percentage of epithelial ovarian cancers in young women. Targeted therapy with trametinib, a MEK inhibitor (MEKi), has emerged as a new treatment option for women with recurrent LGSOC from a recent clinical trial. Initial tumor shrinkage was observed in approximately 26% patients treated with trametinib but most patient eventually died of the disease because the tumor became trametinib adaptive resistance. Thus, further investigation to overcome trametinib resistance is necessary to improve the survival of patients with LGSOC. To understand how LGSOC patients develop adaptive resistance to trametinib, we generated several trametinib adaptive resistant LGSOC cell lines. By comparing the expression of over 400 signaling proteins with reverse phase protein array (RPPA) between an adaptive resistant cell (HOC-7R) to the parental cells (HOC-7), we discovered several proteins that were up-regulated in the adaptive resistant cell lines such as plasminogen activator inhibitor-1 (PAI-1 or SERPINE1), p-Rb, p-ERK1/2, MEK1, p-S6, p-Yb1, p-YAP, p-Chk1, and histone H3. By over-expressing SERPINE1 in cell line HOC-7, we were able to show that HOC-7-SERPINE1 (a stable clone of HOC-7 overexpressing SERPINE1) became more resistant to trametinib. By high-throughput drug screening with 555 drugs from libraries with targeted molecules, approved drugs, investigational agents, and bioactive molecules, HOC-7-SERPINE1 cells were confirmed to have increased resistance to other MEK inhibitors in comparison to the parental cell HOC-7. The fold increase in IC50 for MEKi for HOC-7-SERPINE1 were 3.46 (18.65 nM/5.39 nM), 3.74 (28.74 nM/7.68 nM), 2.65 (52.2 nM/19.68 nM) and 1.66 (22.79 nM/13.73 nM) for trametinib, binimetinib, selumetinib and cobimetinib respectively. In addition, overexpression of SERPINE1 in HOC-7 cells also enhanced their resistance to an SRC inhibitor (saracatinib; about 1.7 folds increase in IC50), histone deacetylases inhibitor (belinostat; about 1.2 folds increase in IC50) and Bcl-2 inhibitor (obatoclax; about 2.38 folds increase in IC50). On the other hand, HOC-7-SERPINE1 became more sensitive to farnesyltransferase inhibitor (lonafarnib; about 36.8 folds decrease in IC50), PARP (Poly ADP Ribose Polymerase) inhibitor (talazoparib; about 2.69 folds decrease in IC50). These results suggest that HOC-7-SERPINE1 cells become less dependent on SRC, histone deacetylases, and Bcl-2 than the parental HOC-7 cells but become more dependent on signaling through farnesyltransferase and PARP. The combination of MEKi and PARPi (PARP inhibitor) has previously been shown to be a promising combination and is in clinical trial. It is possible that combinations of trametinib and lonafarnib treatment could overcome trametinib adaptive resistance. In conclusion, high-throughput drug screening allows us to discover potential mechanisms of trametinib adaptive resistance and potential drugs for treatment of LGSOC patients who have developed trametinib resistance. Citation Format: Kwong-Kwok Wong, Chun Wai Ng, Yvonne Tsang, David M. Gershenson. High throughput drug screening to decipher the mechanisms of trametinib adaptive resistance in low-grade serous ovarian cancer cell lines [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr A065.

The Role of Systematic Lymphadenectomy in Low-Grade Serous Ovarian Cancer: A Systematic Review and Meta-Analysis.

To evaluate the role of systematic lymphadenectomy in low-grade serous ovarian cancer (LGSOC) and determine its impact on clinical outcomes in overall survival (OS) and disease-free survival (DFS) terms. A comprehensive, systematic computer literature search on PubMed was performed using the following Medical Subject Headings (MeSH) terms: "low grade serous ovarian cancer" AND/OR "lymphadenectomy" AND/OR "staging" AND/OR "ovarian cancer" AND/OR "cytoreduction". Separate searches were performed with MeSH terms on MEDLINE and EMBASE to extract all the relevant literature available. We included only patients with histologically confirmed LGSOC. Three studies were considered in the quantitative analysis. Systematic lymphadenectomy in LGSOC failed to provide a significant OS or PFS benefit in LGSOC when compared to no lymphadenectomy in the entire (all the stages) population (for OS: HR = 1.15, 95% CI [0.42, 3.18] I2 = 84% and for PFS: HR = 1.46, 95% CI [0.63, 3.41], I2 = 71%), nor did it in the subtype analysis regarding FIGO stages. For FIGO early-stage I-II LGSOC, the DFS data were pooled (HR = 1.48, 95% CI [0.58, 3.78], I2 = 75%). In patients with advanced-stage (FIGO II-IV), we also failed to prove survival benefit for lymphadenectomy in OS (HR = 1.74, 95% CI [0.87, 3.48], I2 = 11%) or DFS (HR = 1.48, 95% CI [0.58, 3.78], I2 = 75%) compared to no lymphadenectomy. More extensive prospective research is mandatory to understand the real impact of lymphadenectomy on survival in LGSOC. The existing literature does not provide strong evidence.

Low-grade serous ovarian cancer with BRAFV600E mutation treated with metronomic chemotherapy — a case report and literature review

Low-grade serous ovarian cancer with BRAFV600E mutation treated with metronomic chemotherapy — a case report and literature review

Efficacy and safety of bevacizumab in patients with low-grade serous ovarian cancer.

Aim: To investigate the efficacy and safety of bevacizumab in patients with recurrent low-grade serous ovarian carcinoma. Materials & methods: The data of patients who received at least two cycles of bevacizumab in combination with chemotherapy were retrospectively recorded. Results: The median age of 51 patients was 56 (range: 33-75) years. The complete response rate was 10.4%and thepartial response rate was 43.7%. The objective response rate was 54.1%. Median progression-free survival was 15.9months (95% CI: 9.1-22.6)and median overall survival was 42.5months (95% CI: 37.2-47.8). Conclusion: Bevacizumab with chemotherapy is an effective option for treating recurrent ovarian low-grade serous carcinoma.

Abstract A091: The RAF/MEK clamp avutometinib as the backbone of therapy for pancreatic cancer: Novel combinations with standard of care chemotherapy, FAK inhibitors, KRAS G12D inhibitors and/or autophagy inhibitors

Abstract KRAS mutations (mt) occur in up to 98% of pancreatic ductal adenocarcinoma (PDAC) and represent a key initiating event in PDAC carcinogenesis. Therapeutic efforts targeting the RAS/RAF/MEK/ERK (MAPK) pathway with MEK-only inhibitors have been unsuccessful in substantially modifying PDAC prognosis. Thus, novel strategies are needed to overcome putative mechanisms of resistance to MEK inhibition such as focal adhesion kinase (FAK) pathway activation. Another hallmark of PDAC is its high stromal density, which is thought to limit the penetration of cytotoxic drugs and T cells into the tumor and has been shown to be correlated with FAK hyperactivation, altogether supporting co-targeting the MAPK and FAK pathways to achieve deep and durable responses for patients with PDAC. Avutometinib is a RAF/MEK clamp that potently inhibits MEK kinase activity and induces dominant negative RAF-MEK complexes preventing phosphorylation of MEK by ARAF, BRAF and CRAF. This unique mechanism allows avutometinib to block MEK signaling without the compensatory re-activation of MEK that appears to limit the efficacy of MEK-only inhibitors. Preclinically, avutometinib has shown strong anti-proliferative potency across tumor cell lines carrying KRAS mt including PDAC cell lines. Clinically, avutometinib in combination with the FAK inhibitor (FAKi) defactinib received breakthrough therapy designation for the treatment of patients with recurrent low-grade serous ovarian cancer. Here, we tested the combination of avutometinib and FAK inhibition with standard of care chemotherapy in PDAC mouse models. In a KRAS/p53 pancreatic cancer mouse model, we found that whereas the combination of avutometinib + FAKi induced tumor inhibition and increased survival, addition of chemotherapy (gemcitabine + paclitaxel as a surrogate for nab-paclitaxel) to avutometinib/FAKi induced tumor regression. These results support the ongoing clinical study of avutometinib and defactinib in combination with standard of care chemotherapy (gemcitabine/nab-paclitaxel) for patients with front-line metastatic PDAC (NCT05669482). Other combinations being explored preclinically include avutometinib with G12D inhibition (G12Di) in KRAS G12D PDAC, which accounts for 28% of patients with PDAC. In 3D culture, avutometinib was synergistic with the G12Di MRTX1133 in reducing viability of a panel of KRAS G12D PDAC cell lines. In mouse models, avutometinib enhanced anti-tumor efficacy of MRTX1133 in a KRAS G12D pancreatic cancer patient-derived xenograft model. Furthermore, in KRAS mt PDAC cell lines, avutometinib was synergistic with the autophagy inhibitors chloroquine or apilimod. Indeed, dual treatment with avutometinib + MRTX1333 synergistically decreased proliferation and increased autophagic flux in KRAS G12D PDAC cell lines, supporting testing the triple combination of avutometinib + G12Di + autophagy inhibitor in patients with KRAS G12D pancreatic cancers. In conclusion, we show that avutometinib is a unique RAF/MEK clamp with the potential to become the backbone of therapy for pancreatic cancers. Citation Format: Silvia Coma, Xiuting Liu, Noah L. Pieper, Wen-Hsuan Chang, Kirsten L. Bryant, Channing J. Der, David G. DeNardo, Jonathan A. Pachter. The RAF/MEK clamp avutometinib as the backbone of therapy for pancreatic cancer: Novel combinations with standard of care chemotherapy, FAK inhibitors, KRAS G12D inhibitors and/or autophagy inhibitors [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A091.

DIRAS3 induces autophagy and enhances sensitivity to anti-autophagic therapy in KRAS-driven pancreatic and ovarian carcinomas

ABSTRACT Pancreatic ductal adenocarcinoma (PDAC) and low-grade ovarian cancer (LGSOC) are characterized by the prevalence of KRAS oncogene mutations. DIRAS3 is the first endogenous non-RAS protein that heterodimerizes with RAS, disrupts RAS clustering, blocks RAS signaling, and inhibits cancer cell growth. Here, we found that DIRAS3-mediated KRAS inhibition induces ROS-mediated apoptosis in PDAC and LGSOC cells with KRAS mutations, but not in cells with wild-type KRAS, by downregulating NFE2L2/Nrf2 transcription, reducing antioxidants, and inducing oxidative stress. DIRAS3 also induces cytoprotective macroautophagy/autophagy that may protect mutant KRAS cancer cells from oxidative stress, by inhibiting mutant KRAS, activating the STK11/LKB1-PRKAA/AMPK pathway, increasing lysosomal CDKN1B/p27 localization, and inducing autophagic gene expression. Treatment with chloroquine or the novel dimeric chloroquine analog DC661 significantly enhances DIRAS3-mediated inhibition of mutant KRAS tumor cell growth in vitro and in vivo. Taken together, our study demonstrates that DIRAS3 plays a critical role in regulating mutant KRAS-driven oncogenesis in PDAC and LGSOC. Abbreviations: AFR: autophagic flux reporter; ATG: autophagy related; CQ: chloroquine; DCFDA: 2’-7’-dichlorodihydrofluorescein diacetate; DIRAS3: DIRAS family GTPase 3; DOX: doxycycline; KRAS: KRAS proto-oncogene, LGSOC: low-grade serous ovarian cancer; MiT/TFE: microphthalmia family of transcription factors; NAC: N-acetylcysteine; PDAC: pancreatic ductal adenocarcinoma; ROS: reactive oxygen species; TFEB: transcription factor EB

Targeting BRAF pathway in low-grade serous ovarian cancer

Targeting BRAF pathway in low-grade serous ovarian cancer