LCK facilitates DNA damage repair by stabilizing RAD51 and BRCA1 in the nucleus of chemoresistant ovarian cancer

Poly-ADP Ribose Polymerase (PARP) targeted therapy is clinically approved for the treatment of homologous recombination (HR) repair deficient tumors. The remarkable success of this therapy in the treatment of HR repair deficient cancers has not translated to HR-proficient cancers. Our studies identify the novel role of non-receptor lymphocyte-specific protein tyrosine kinase (LCK) in the regulation of HR repair in endometrioid epithelial ovarian cancer (eEOC) model. We show that DNA damage leads to direct interaction of LCK with the HR repair proteins RAD51 and BRCA1 in a kinase dependent manner RAD51 and BRCA1 stabilization. LCK expression is induced and activated in the nucleus in response to DNA damage insult. Disruption of LCK expression attenuates RAD51, BRCA1, and BRCA2 protein expression by hampering there stability and results in inhibition of HR-mediated DNA repair including suppression of RAD51 foci formation, and augmentation of γH2AX foci formation. In contrast LCK overexpression leads to increased RAD51 and BRCA1 expression with a concomitant increase in HR DNA damage repair. Importantly, attenuation of LCK sensitizes HR-proficient eEOC cells to PARP inhibitor in cells and pre-clinical mouse studies. Collectively, our findings identify a novel therapeutic strategy to expand the utility of PARP targeted therapy in HR proficient ovarian cancer.

The Microbiome and Gynecologic Cancer: Current Evidence and Future Opportunities

PURPOSE OF REVIEW

We review the emerging evidence regarding the relationship between the microbiota of the gastrointestinal and female reproductive tracts and gynecologic cancer.

RECENT FINDINGS

The microbiome has essential roles in maintaining health. In recent years, the microbiota of the gastrointestinal and female reproductive tracts have been linked to many diseases, including gynecologic cancer. Alterations to the bacterial populations in a microbiota, or dysbiosis, have been shown to favor a pro-carcinogenic state through altered immune responses, dysregulated hormone metabolism, and modulation of the cell cycle. Pre-clinical and clinical studies have emerged, demonstrating that specific bacteria or microbial communities may be associated with increased risk for uterine, ovarian, and cervical cancers. Notably, numerous studies have linked a non-Lactobacillus-dominant vaginal microbiota, composed of anaerobic bacteria, with HPV infection, persistence, and development of invasive cervical cancer. Similarly, next-generation high-throughput sequencing techniques have enabled the characterization of unique microbiotas in patients with malignant and benign gynecologic conditions, shedding light on new associations between bacterial species and gynecologic cancers. Harnessing the power of the microbiome for early diagnosis, therapeutic intervention and modulation creates tremendous potential to optimize gynecologic cancer outcomes in the future.

Islet Dysfunction in a Novel Transgenic Model of T Cell Insulitis

The newly established CD3FLAG-mIR transgenic mouse model on a C57Bl/6 background has a FLAG tag on the mouse Insulin Receptor (mIR), specifically on T cells, as the FLAG-tagged mIR gene was engineered behind CD3 promoter and enhancer. The IR is a chemotactic molecule for insulin and the Flag-tagged mIR T cells in the BL/6-CD3FLAGmIR transgenic mice can migrate into the pancreas, as shown by immunofluorescent staining. While the transgenic mice do not become diabetic, there are phenotypic and metabolic changes in the islets. The transgenic islets become enlarged and disorganized by 15 weeks and those phenotypes continue out to 35 weeks of age. We examined the islets by RT-PCR for cell markers, ER stress markers, beta cell proliferation markers, and cytokines, as well as measuring serum insulin and insulin content in the pancreas at 15, 25, and 35 weeks of age. In transgenic mice, insulin in serum was increased at 15 weeks of age and glucose intolerance developed by 25 weeks of age. Passage of transgenic spleen cells into C57Bl/6 RAG⁻/⁻ mice resulted in enlarged and disorganized islets with T infiltration by 4 to 5 weeks post-transfer, replicating the transgenic mouse studies. Therefore, migration of non-antigen-specific T cells into islets has ramifications for islet organization and function.

Insulin Receptor-Expressing T Cells Appear in Individuals at Risk for Type 1 Diabetes and Can Move into the Pancreas in C57BL/6 Transgenic Mice

Insulin receptor (IR) expression on the T cell surface can indicate an activated state; however, the IR is also chemotactic, enabling T cells with high IR expression to physically move toward insulin. In humans with type 1 diabetes (T1D) and the NOD mouse model, a T cell-mediated autoimmune destruction of insulin-producing pancreatic β cells occurs. In previous work, when purified IR⁺ and IR^- T cells were sorted from diabetic NOD mice and transferred into irradiated nondiabetic NOD mice, only those that received IR⁺ T cells developed insulitis and diabetes. In this study, peripheral blood samples from individuals with T1D (new onset to 14 y of duration), relatives at high-risk for T1D, defined by positivity for islet autoantibodies, and healthy controls were examined for frequency of IR⁺ T cells. High-risk individuals had significantly higher numbers of IR⁺ T cells as compared with those with T1D (p < 0.01) and controls (p < 0.001); however, the percentage of IR⁺ T cells in circulation did not differ significantly between T1D and control subjects. With the hypothesis that IR⁺ T cells traffic to the pancreas in T1D, we developed a (to our knowledge) novel mouse model exhibiting a FLAG-tagged mouse IR on T cells on the C57BL/6 background, which is not susceptible to developing T1D. Interestingly, these C57BL/6-CD3FLAGmIR/mfm mice showed evidence of increased IR⁺ T cell trafficking into the islets compared with C57BL/6 controls (p < 0.001). This transgenic animal model provides a (to our knowledge) novel platform for investigating the influence of IR expression on T cell trafficking and the development of insulitis.

Abstract 2450: Methyl CpG Binding Protein 2 suppresses Myc targeting miRNAs to promote context dependent tumor proliferation

Background: Epigenetic reader proteins maintain an imbalance between differentiation and self-renewal in cancer. Genetic alterations in the DNA methylation machinery (e.g., TET, DNMTs) and chromatin remodelers (e.g., KDMs, EZH1/2) are a hallmark of cancer. Methyl CpG binding domain protein 2 (MBD2) is an epigenetic reader protein which modulates regional gene transcription by recruiting co-repressor complexes to sites of CpG methylation. Our goal is to develop a novel class of anti-neoplastic epigenetic therapies targeting MBD2 to selectively reprogram tumor cells towards a terminally differentiated state and sensitize them to chemotherapy, radiation, and immunotherapy.

Methods: To explore conserved mediators of MBD2 function in cancer, we used MBD2 targeting shRNA lentivirus to stably knockdown MBD2 in prostate cancer (PC3, DU145, LnCap), leukemia (SigM5, TET2WTK562 or TET2KOK562) and triple negative breast cancer (MDA-MB231-nanog-GFP) cell lines. Inhibition of MBD2 expression was confirmed by qRT-PCR and Western Blot. Proliferative potential was determined by cell counting and clonogenic potential was determined by methylcellulose-based colony forming assays. RNAseq analysis was performed on prostate cancer and leukemia cell lines. miRNA expression was analyzed using miScript miRNA PCR (Qiagen). In vivo tumor initiation capacity was analyzed using orthotropic and heterotopic xenografts in athymic NSG mice.

Results: Our results show that MBD2 is required for the proliferation of triple negative breast cancer (TNBC), prostate cancer (PCa), and TET mutant leukemias (TML), in vitro. The functional mediators of MBD2's growth promoting effects were tissue/tumor context dependent. In leukemias, MBD2's growth promoting and tumor initiating effects were most pronounced in TET2 null cells (which accumulate 5mC). In TNBC, nanog-GFP reporter positive cells were more sensitive to MBD2 knockdown than reporter negative cells. In PCa and TNBC, RNAseq analysis revealed that knockdown of MBD2 led to downregulation of Myc pathway genes and increased the expression of Myc targeting microRNAs, miR33-5, miR34a, miR148a and miR363. Western blot analysis confirmed that MBD2 knockdown coordinately downregulated cMyc expression and activated p27 expression. We further demonstrated that inhibition of MBD2 diminished the tumor initiating capacity of TNBC and PCa in xenograft models and the in vivo engraftment rate of patient derived TET-/- AML.

Conclusions: MBD2 knockdown diminished the proliferative capacity of PCa, TNBC and primary TET2 mutant leukemia cells in a genetic (TET2) and phenotypic (nanog+ stem/progenitor) context dependent manner. Delayed peak effect and altered differentiation markers after MBD2 inhibition suggest epigenetic reprogramming as the mechanism of growth suppression. MBD2 targets miRNA's upstream of cMyc in PCa and TNBC. MBD2 murine knockout models are developmentally normal, suggesting an acquired function in cancer with a favorable therapeutic window for targeting.

Citation Format: Aysegul Balyimez, Yihong Guan, Emily Esakov, Shinjini Ganguly, Ofer Reizes, Daniel J. Lindner, Jaroslaw Maciejewski, Babal Jha, Omar Y. Mian. Methyl CpG Binding Protein 2 suppresses Myc targeting miRNAs to promote context dependent tumor proliferation [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 2450.

Signaling within the epithelial ovarian cancer tumor microenvironment: the challenge of tumor heterogeneity

Epithelial ovarian cancer (EOC) is a leading cause of cancer death in women. Standard of care treatment has remained platinum-containing cytotoxic chemotherapy for over three decades. Among the central challenges in treating ovarian CA are disease recurrence and the development of chemoresistance. Survival is uniformly poor for patients with chemoresistant recurrent disease and effective therapeutic options are limited. As such, delineating the mechanisms of chemoresistance and developing targeted therapies to prevent chemoresistance from occurring are of vital importance to improving survival for patients with EOC. Attempts to characterize mechanisms of chemoresistance have implicated numerous cellular pathways, but a rift remains between pre-clinical findings and translation to improving patient survival. More recently, the interplay among different cell types within the tumor microenvironment has become central to understanding how chemoresistance may develop and may be sustained. An improved understanding of how tumor cell-intrinsic and -extrinsic pathways converge during the development of chemoresistance may improve the likelihood of successful clinical translation. This review focuses on the roles of the EOC tumor microenvironment and tumor cell heterogeneity in the development of chemoresistance. We review recent studies into mechanisms of chemoresistance as they relate to tumor microenvironment and development of novel therapeutic approaches that exploit these mechanisms to prevent or reverse chemoresistance. This review attempts to cast these latest discoveries in a clinical context by summarizing trends in ongoing clinical trials for patients with EOC.

Abstract B69: Gut microbiome attenuates epithelial ovarian cancer growth and sensitivity to cisplatin: New opportunities for ovarian cancer treatments

Epithelial ovarian cancer (EOC) is the second most common gynecologic malignancy in the United States, but the leading cause of gynecologic cancer death. Despite many women achieving remission with first-line therapy, which includes cytoreductive surgery and platinum-taxane chemotherapy, up to 80% of patients will recur and require additional treatment. The interval from last platinum chemotherapy to recurrence has important prognostic and therapeutic implications for patients. Patients with platinum-resistant EOC have fewer treatment options, worse prognosis, and their disease is seldom curable. Antibiotic therapy is frequently used during cancer treatments in patients with EOC for both prophylaxis and treatment of infections after surgery or through chemotherapy. While critical for the care of the patient, we now appreciate that the microbiome has many roles in maintenance of human health and is increasingly linked with many disease states including obesity, cardiovascular disease, and cancer. Recent evidence suggests the gut microbiome may modulate responses to cancer treatment, including traditional chemotherapy and immunotherapy. Given that antibiotics may lead to microbiome disruption for care of EOC patients and lack of understanding of the impact of these antibiotics on tumor progression, in preclinical models, we assessed the impact of microbiome disruption on EOC progression and cisplatin sensitivity. We established a necessary role for the microbiome in suppression of tumor growth and cisplatin response in two mouse models of EOC. Following treatment with antibiotics (ampicillin, neomycin, vancomycin, and metronidazole), murine ID8 or ID8-VEGF EOC that were injected intraperitoneally into C57Bl/6J mice exhibited accelerated tumor growth compared to non-antibiotic treated controls. Tumor growth was monitored by ultrasound weekly. ID8 and ID8-VEGF tumors in antibiotic-treated mice exhibited reduced sensitivity to cisplatin compared to non-antibiotic controls. Mice treated with antibiotics had significantly worse survival compared to non-antibiotic controls. We confirmed depletion of the gut microbiome based on dilated cecum and reduced microbial 16S rRNA concentration in stool of antibiotic-treated compared to control mice. The accelerated tumor growth and cisplatin resistance was not dependent on an intact immune system as we replicated the effect in immune-deficient mice. In mechanistic studies we determined that disruption of the microbiome led to increased cancer stem cells that was further augmented by cisplatin treatment. Collectively, these studies indicate an intact microbiome provides a tumor-suppressive microenvironment and enhances sensitivity to cisplatin. Future studies will assess whether individual microbial communities are sufficient to reverse the accelerated tumor growth and resistance to cisplatin observed in antibiotic-treated mice and use of selective antibiotics to target pathogenic bacteria while sparing beneficial microbes.

Citation Format: Laura Chambers, Emily Esakov, Chad Braley, Leila Edelman, Roberto Vargas, Justin Lathia, Chad Michener, Ofer Reizes. Gut microbiome attenuates epithelial ovarian cancer growth and sensitivity to cisplatin: New opportunities for ovarian cancer treatments [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 B69.

Use of Transabdominal Ultrasound for the detection of intra-peritoneal tumor engraftment and growth in mouse xenografts of epithelial ovarian cancer

OBJECTIVE

To evaluate intraperitoneal (IP) tumor engraftment, metastasis and growth in a pre-clinical murine epithelial ovarian cancer (EOC) model using both transabdominal ultrasound (TAUS) and bioluminescence in vivo imaging system (IVIS).

METHODS

Ten female C57Bl/6J mice at six weeks of age were included in this study. Five mice underwent IP injection of 5x106 ID8-luc cells (+ D- luciferin) and the remaining five mice underwent IP injection of ID8-VEGF cells. Monitoring of tumor growth and ascites was performed weekly starting at seven days post-injection until study endpoint. ID8-luc mice were monitored using both TAUS and IVIS, and ID8-VEGF mice underwent TAUS monitoring only. Individual tumor implant dimension and total tumor volume were calculated. Average luminescent intensity was calculated and reported per mouse abdomen. Tumor detection was confirmed by gross evaluation and histopathology. All data are presented as mean +/- standard deviation.

RESULTS

Overall, tumors were successfully detected in all ten mice using TAUS and IVIS, and tumor detection correlated with terminal endpoint histology/ H&E staining. For TAUS, the smallest confirmed tumor measurements were at seven days post-injection with mean long axis of 2.23mm and mean tumor volume of 4.17mm3. However, IVIS imaging was able to detect tumor growth at 14 days post-injection. Ascites formation was detected in mice at 21 days post-injection.

CONCLUSIONS

TAUS is highly discriminatory for monitoring EOC in pre-clinical murine model, allowing for detection of tumor dimension as small as 2 mm and as early as seven days post-injection compared to IVIS. In addition, TAUS provides relevant information for ascites development and detection of multiple small metastatic tumor implants. TAUS provides an accurate and reliable method to detect and monitor IP EOC growth in mouse xenografts.

Phosphorylation of the histone demethylase KDM5B and regulation of the phenotype of triple negative breast cancer

Epigenetic modifications are known to play critical roles in the expression of genes related to differentiation and dedifferentiation. Histone lysine demethylase KDM5B (PLU-1) catalyzes the demethylation of histone H3 on Lys 4 (H3K4), which results in the repression of gene expression. KDM5B is involved in regulation of luminal and basal cell specific gene expression in breast cancers. However, the mechanisms by which KDM5B is regulated in breast cancer, in particular in response to post-translational signals is not well-defined. Here, we demonstrate that KDM5B is phosphorylated at Ser1456 by the cyclin-dependent kinase 1 (CDK1). Phosphorylation of KDM5B at Ser1456 attenuated the occupancy of KDM5B on the promoters of pluripotency genes. Moreover, KDM5B inhibited the expression of pluripotency genes, SOX2 and NANOG, and decreased the stem cell population in triple-negative breast cancer cell lines (TNBC). We previously reported that the tumor suppressor HEXIM1 is a mediator of KDM5B recruitment to its target genes, and HEXIM1 is required for the inhibition of nuclear hormone receptor activity by KDM5B. Similarly, HEXIM1 is required for regulation of pluripotency genes by KDM5B.

T cell movement into the pancreas based on insulin receptor expression (BA14P.208)

In the nonobese diabetic (NOD) mouse, type 1 diabetes is an autoimmune disease characterized by insulitis and T cell-mediated beta cell destruction. The importance of insulin receptor (IR) expression in the pathogenesis of diabetes was examined since IR is a chemotactic molecule capable of directing cell movement in response to a gradient of insulin. Our published data shows that T cells, obtained from NOD diabetic mice, expressing a high density of IR can aggressively transfer insulitis and diabetes while T cells with low to negative amounts of IR, are capable of neither. Therefore, IR may function to deliver T cells to the islet where Ag specific cells within the population can recognize and destroy beta cells. Recently, it has been shown in NOD mice that benign insulitis can occur in the absence of T cell-MHC/Ag interactions. The object of this project was to test whether T cells expressing IR, can move into the pancreas based on insulin chemotaxis alone, in normal strains of mice. A transgenic C57Bl/6 mouse was made in which the mouse IR gene with a 3XFLAG tag was placed behind the CD3 promoter and enhancer to target IR expression on all T cells. In this transgenic model there is IR expression on all T cells and with age the transgenic mice exhibit insulitis, but not diabetes. Distinct areas of the IR mediate metabolic or chemotactic signaling indicating that a specific part of the IR may be selectively targeted for therapeutic intervention to block T cell movement.