Enhanced Therapeutic Efficacy of the Nanoscale Fluoropyrimidine Polymer CF10 in a Rat Colorectal Cancer Liver Metastasis Model

Combination chemotherapy regimens that include fluoropyrimidine (FP) drugs, e.g., 5-fluorouracil (5-FU), are central to the treatment of colorectal cancer liver metastases (CRLMs), a major cause of cancer mortality. We tested a second-generation FP polymer, CF10, in a CC531/WAGRij syngeneic orthotopic rat model of liver metastasis to determine if CF10 improved response relative to 5-FU. CF10 displayed increased potency relative to 5-FU in CC531 rat colorectal cancer cells based on clonogenic assay results and caused increased apoptosis, as shown using a live/dead assay. The increased potency of CF10 to CC531 cells was associated with increased replication stress, as assessed by Western blot for biomarkers of ATR/Chk1 and ATM/Chk2 pathway activation. CF10 dosed to deliver equivalent FP content as an established dose of 5-FU in rats (50 mg/kg) did not cause weight loss in WAGRij rats even when combined with ethynyl uracil (EU), an inhibitor of dihydropyrimidine dehydrogenase, the enzyme primarily responsible for 5-FU degradation in the liver. In contrast, 5-FU caused significant weight loss that was exacerbated in combination with EU. Importantly, CF10 was significantly more effective than 5-FU at inhibiting tumor progression (~90% reduction) in the CC531/WAG/Rij CRLM model. Our results reveal strong potential for CF10 to be used for CRLM treatment.

Synthesis and Biological Evaluation of Telmisartan Alkylamine Derivatives as Potential Anticancer Agents

BACKGROUND/AIM

Telmisartan is an angiotensin II receptor type 1 (AT1) antagonist with anticancer properties against solid and hematological cancer cell lines. Using telmisartan as a template, we developed alkylamine derivatives with reduced AT1 activity but increased anticancer activity.

MATERIALS AND METHODS

Synthesis of candidate compounds was carried out via hexafluorophosphate benzotriazole tetramethyl uronium coupling reaction, then their inhibition of cell proliferation was determined via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and colony-formation assay was carried out on the lead candidate compound 8 Cell death via apoptosis or necrosis by compound 8 was determined by flow cytometry using annexin V and propidium iodide, tolerability dosing was carried out in ICR mice, and tumor-reduction properties were determined in an MDA-MB-231 xenograft model.

RESULTS

Some of the synthesized candidates exhibited good inhibition of cell proliferation with low micromolar half maximal effective concentrations in triple-negative breast cancer cell lines MDA-MB-231 and 4T1. Compound 8 exhibited lower affinity towards AT1 than parent telmisartan, inhibition of colony formation, and cell-cycle analysis revealed apoptosis as potentially important in causing cell death. In vivo evaluation with compound 8 indicated that it was well tolerated at high concentrations in healthy mice. Additionally, compound 8 showed higher growth inhibition in the MDA-MB-231 tumor xenograft mouse model compared to telmisartan.

CONCLUSION

Our study indicated that alkylamine derivatives of telmisartan exhibited good solubility and higher inhibition of cancer cell proliferation than telmisartan. Compound 8 was found to be a good lead compound, with potential for development as an anticancer agent.

Synthesis and biological evaluation of benzofuran piperazine derivatives as potential anticancer agents

This work describes about the synthesis and evaluation of substituted benzofuran piperazines as potential anticancer agents. The synthesized candidates have been evaluated for their cell proliferation inhibition properties in six murine and human cancer cell lines. In vitro evaluation of apoptosis and cell cycle analysis with the lead candidate 1.19 reveals that necrosis might be an important pathway for the candidate compounds to cause cell death. Further, in vivo evaluation of the lead compound shows that this candidate is well tolerated in healthy mice. Additionally, an in vivo anticancer efficacy study in mice using a MDA-MB-231 xenograft model with the lead compound provides good anti-cancer efficacy.

Racial differences in RAD51 expression are regulated by miRNA-214-5P and its inhibition synergizes with olaparib in triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) affects young women and is the most aggressive subtype of breast cancer (BC). TNBCs disproportionally affect women of African-American (AA) descent compared to other ethnicities. We have identified DNA repair gene RAD51 as a poor prognosis marker in TNBC and its posttranscriptional regulation through microRNAs (miRNAs). This study aims to delineate the mechanisms leading to RAD51 upregulation and develop novel therapeutic combinations to effectively treat TNBCs and reduce disparity in clinical outcomes.

METHODS

Analysis of TCGA data for BC cohorts using the UALCAN portal and PrognoScan identified the overexpression of RAD51 in TNBCs. miRNA sequencing identified significant downregulation of RAD51-targeting miRNAs miR-214-5P and miR-142-3P. RT-PCR assays were used to validate the levels of miRNAs and RAD51, and immunohistochemical and immunoblotting techniques were used similarly for RAD51 protein levels in TNBC tissues and cell lines. Luciferase assays were performed under the control of RAD51 3'-UTR to confirm that miR-214-5P regulates RAD51 expression. To examine the effect of miR-214-5P-mediated downregulation of RAD51 on homologous recombination (HR) in TNBC cells, Dr-GFP reporter assays were performed. To assess the levels of olaparib-induced DNA damage responses in miR-214-5P, transfected cells, immunoblots, and immunofluorescence assays were used. Furthermore, COMET assays were used to measure DNA lesions and colony assays were performed to assess the sensitivity of BRCA-proficient TNBC cells to olaparib.

RESULTS

In-silico analysis identified upregulation of RAD51 as a poor prognostic marker in TNBCs. miRNA-seq data showed significant downregulation of miR-214-5P and miR-142-3P in TNBC cell lines derived from AA women compared to Caucasian-American (CA) women. miR-214-5P mimics downregulated RAD51 expression and induces HR deficiency as measured by Dr-GFP assays in these cell lines. Based on these results, we designed a combination treatment of miR-214-5P and olaparib in HR-proficient AA TNBC cell lines using clonogenic survival assays. The combination of miR-214-5P and olaparib showed synergistic lethality compared to individual treatments in these cell lines.

CONCLUSIONS

Our studies identified a novel epigenetic regulation of RAD51 in TNBCs by miR-214-5P suggesting a novel combination therapies involving miR-214-5P and olaparib to treat HR-proficient TNBCs and to reduce racial disparity in therapeutic outcomes.

Abstract 5496: Glutaminase inhibition induces replication stress in ovarian cancer cells and inhibition of replication checkpoint causes synthetic lethality

Ovarian cancer (OC) is a highly aggressive disease and the most lethal gynecologic malignancy in women. Although the majority of OC patients respond to chemotherapeutic drugs, more than 70% of the patients relapse and die as a result of chemoresistance. Therefore, novel therapeutics are warranted to prevent chemoresistance and treat the relapsed disease to improve prognosis. Many cancer cells depend on Glutamine as major carbon source and these cells have high Glutaminase (GLS) expression, an enzyme that converts Glutamine to Glutamate. Chemo-resistant OC cells have elevated levels of GLS, which confirms their increased dependency on glutamine metabolism. Based on these observations, we postulated that GLS inhibition may attenuate the aggressive growth of GLS high OC cells and may sensitize to the agents that can further potentiate these effects. Interestingly, GLS inhibition using a clinical-stage drug CB839 caused replication stress and activated DNA damage checkpoint protein 1 (CHK1) mediated cell cycle arrest. These novel findings suggested a role for CHK1 in protecting GLS inhibition-induced DNA damage by facilitating the timely repair of DNA breaks. Based on these observations, we hypothesized that GLS inhibition in combination with CHK1 inhibition may cause synergistic lethality in chemo-resistant and GLShigh OC cells. We evaluated the combination of GLS inhibitor CB839 and CHK1 inhibitor Prexasertib. Our results demonstrate that GLS inhibition-induced CHK1 phosphorylation is significantly attenuated by Prexasertib treatment. Similarly, combined treatment of CB839 and Prexasertib showed significantly elevated levels of DNA damage as measured by COMET assays, replication stress-mediated DNA damage responses, and synergistic OC cell lethality compared to individual drug treatments. Furthermore, CB839 and Prexasertib combination was more synergistic in cells that expressed high GLS compared to low GLS-expressing OC cells indicating the specificity of the combination of these drugs. Together, our studies identified a novel connection between metabolic and DNA damage checkpoint pathways in OC and propose a novel synergistic lethality-based combination therapy to treat chemo-resistant and aggressive OC.

Citation Format: Pamela Luna, Ganesh Acharya, Damieanus Ochola, Swetha Peddibhotla, Chinnadurai Mani, Mark B. Reedy, Komaraiah Palle. Glutaminase inhibition induces replication stress in ovarian cancer cells and inhibition of replication checkpoint causes synthetic lethality. [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 5496.

Abstract 6178: A novel second-generation nano-fluoropyrimidine to treat metastatic colorectal cancer and overcome 5-fluorouracil resistance

Colorectal cancer (CRC) is the 3rd leading cause of cancer-related mortality. The mortality associated with colon cancer results notably from metastatic disease (mCRC), with a 5-year survival rate for patients with stage IV CRC being < 14%. Despite extensive efforts towards developing personalized therapies, limited success has been achieved and chemotherapeutic regimens that include the fluoropyrimidine (FP) drug 5-fluorouracil (5-FU) are central to patient management. While using 5-FU-based regimens such as FOLFOX and FOLFIRI in combination with biologics confer a survival benefit, their ineffectiveness at promoting long-term survival in a substantial fraction of mCRC patients and associated toxicities limits their use. This underscores the pressing need to develop improved FP drugs. To overcome the limitations of 5-FU that include resistance due to elevated expression of thymidylate synthase (TS) and inefficient anabolic metabolism to FdUMP, the TS-inhibitory/active metabolite, we are developing FP polymers consisting of single-stranded DNA with FdUMP (only active metabolite) as the repeating nucleotide unit. Our therapeutic objective is to initiate a Phase I clinical trial with a new 2nd generation nanoscale FP polymer (CF10) that demonstrates promising anticancer effects in several preclinical models and significantly lower systemic toxicity. We observed that CF10 displayed significantly higher anti-tumor activity than 5-FU in flank and syngeneic tumor models. Additionally, CF10 treatment improved survival (84.5 days vs 32 days; P < 0.0001) relative to 5-FU in an orthotopic HCT-116-luc colorectal cancer mice model that spontaneously metastasized to the liver. Interestingly, a reduction in metastatic tumor burden in the CF10 treatment group led us to hypothesize that CF10 could inhibit the TS-mediated EMT phenotype and pro-metastatic activities in colorectal cancer cells (CRCs). This was supported by increased vimentin, decreased E-cadherin expression, and increased cell migration and invasion in TS-overexpressing CRC cells (“Tet-on” system). Alkaline comet assay, immunofluorescence imaging, and immunoblot identified significantly higher replication stress with CF10 treatment than 5-FU in mouse, rat, and human-established CRC cell lines and primary CRC cells. Strikingly, we also discovered that CF10 attenuates the growth of TS-overexpressing primary colonoids. In conclusion, CF10 induces increased replication stress compared to a similar concentration of conventional drugs. Our findings suggest the significance of elevated TS in CRC metastatic progression and 5-FU resistance and demonstrate that CF10 may be effective at inhibiting CRC metastatic progression. CF10 may be a successful candidate for early-phase clinical trials to treat mCRC.

Citation Format: Naresh Sah, Pamela Luna, Chinnadurai Mani, William Gmeiner, Komaraiah Palle. A novel second-generation nano-fluoropyrimidine to treat metastatic colorectal cancer and overcome 5-fluorouracil resistance [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 6178.

Abstract PO-131: RAD51 is a biomarker for aggressive disease and racial disparities in triple-negative breast cancer

Breast cancer (BC) is the second most diagnosed malignant disease in women, and one of the leading causes of cancer-related deaths. Triple-negative breast cancer (TNBC) is the most aggressive and difficult to treat subtype of BC because it is highly metastatic and lacks targeted therapies. African American (AA) women have a higher death rate from BC than women of other races and ethnicities. The higher incidences of TNBCs and their aggressive growth in young AA women contributing to higher death rates indicate a biological basis for this difference. Thus, it is imperative to understand the molecular mechanisms that contribute to aggressive tumor growth in AA women, identify biomarkers to select patients who will respond to existing therapies, and develop effective therapeutics to reduce this disparity. Our studies identified that multiple TNBC cells derived from AA women are inherently chemoresistant and exhibit aggressive growth behavior compared to TNBC cells derived from European American (EA) patients. Our preliminary screenings showed that the DNA repair protein, RAD51, is overexpressed in AA TNBC patients and correlates a poor prognosis relative to EA TNBC patients. Analysis of AA and EA TNBC tumor specimens indicated the epigenetic regulation of RAD51 by promoter methylations and microRNAs. Furthermore, AA women diagnosed with TNBC, have a considerably lower incidence of germline BRCA1 mutations than women of other racial or ethnic groups. This indicates most TNBC tumors in AA patients are DNA repair proficient and have intact cell cycle checkpoint mechanisms that protect them from chemotherapy-induced DNA damage and promote therapeutic resistance. Our drug screenings identified CHK1 inhibitor, Prexasertib caused DNA repair deficiency in BRCA wild-type TNBC cells by promoting proteasome-mediated degradation of BRCA1 and RAD51 proteins. Therefore, we designed a synthetic lethality-based drug combination of Prexasertib with PARP inhibitors (PARPi) in DNA repair proficient TNBC cells. Data from our preclinical evaluations show Prexasertib and Olaparib cause increased DNA strand breaks, mitotic catastrophe, and synergistic TNBC cell lethality compared to individual drug treatments. Additionally, computational analysis of TCGA data revealed a RAD51 upregulation in TNBC tumors compared to normal breast tissues and other subtypes of BC which renders as a poor prognostic marker for these patients. Remarkably, there was an interesting discrepancy in RAD51 expression levels between different racial groupings, with AA and Asian BC patients having higher levels of RAD51 expression than Caucasian BC patients. Consistent with these observations, AA and Asian TNBC patients showed decreased survival probability. Together, our data indicate that RAD51 and its epigenetic regulators could be biomarkers for aggressive TNBC and racial disparity in BC therapeutic outcomes and suggests a novel combination therapy involving Prexasertib and Olaparib may improve prognosis and reduce racial disparity in TNBC.

Citation Format: Ganesh N. Acharya, Chinnadurai Mani, Upender Manne, Komaraiah Palle. RAD51 is a biomarker for aggressive disease and racial disparities in triple-negative breast cancer [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PO-131.

Case Report: Intra-Tumoral Vaccinations of Quadrivalent HPV-L1 Peptide Vaccine With Topical TLR-7 Agonist Following Recurrence: Complete Resolution of HPV-HR-Associated Gynecologic Squamous Cell Carcinomas in Two Patients

The human papilloma virus (HPV) high-risk variants (HPV-HR) such as HPV16 and HPV18 are responsible for most HPV related cancers, including anogenital and head and neck cancers. Here, we present two patients with HPV-HR-associated gynecological malignancies who, after failing radiation therapy, were treated with experimental salvage immunotherapy regimen resulting in complete, durable responses in both patients. Each patient was diagnosed with recurrent, radiation-refractory, HPV-HR positive, squamous cell carcinoma of the lower genital tract. Patient A was a 90-year-old, African American, with metastatic vulvar cancer to the right inguinal-femoral triangle and pulmonary metastases. Patient B was a 41-year-old, Caucasian, with a central-recurrence of cervix cancer. Each patient received at least two intratumoral quadrivalent HPV-L1 vaccine (Gardasil™) injections and daily topical TLR-7 agonist (imiquimod) to the tumor surface 2 weeks apart. This combination of intratumoral vaccinations and topical TLR-7 agonist produced unexpected complete resolution of disease in both patients. The importance of radiation therapy, despite being considered a treatment failure by current definitions, cannot be understated. Radiation therapy appears to have offered a therapeutic immune advantage by modifying the tumor microenvironment. This immune protocol has potential to help patients with advanced HPV-HR-related malignancies previously considered incurable.

A Novel Role for BRIP1/FANCJ in Neuronal Cells Health and in Resolving Oxidative Stress-Induced DNA Lesions

BACKGROUND

DNA damage accumulation and mitochondrial abnormalities are elevated in neurons during aging and may contribute to neurodegenerative pathologic conditions such as Alzheimer's disease. BRCA1 interacting protein 1 or BRIP1 is a 5' to 3' DNA helicase that catalyzes many abnormal DNA structures during DNA replication, gene transcription, and recombination, and contribute to genomic integrity.

OBJECTIVE

BRIP1 functions were reasonably well studied in DNA repair; however, there is limited data on its role and regulation during aging and neurodegenerative diseases.

METHODS

We used immunohistochemistry, western blot, and qRT-PCR assays to analyze the expression of BRIP1. Immunofluorescence studies were performed to study the formation of R-loops, reactive oxygen species (ROS) generation, and mitochondrial morphology. Flow cytometry and transmission electron microscopy were used to evaluate mitochondrial ROS and mitochondrial structures, respectively. Oxygen consumption rate was measured using Seahorse, and the Presto Blue™ assays were used to evaluate cell viability.

RESULTS

Our results demonstrate the expression of BRIP1 in mouse and human brain tissues and in neuronal cell lines. BRIP1 levels were elevated in the hippocampal regions of the brains, specifically in the dentate gyrus. BRIP1 downregulation in neuronal cells caused increased R-loop formation basally and in response to H2O2 treatment. Furthermore, BRIP1 deficient cells exhibited elevated levels of excitotoxicity induced by L-Glutamic acid exposure as evidenced by (mitochondrial) ROS levels, deteriorated mitochondrial health, and cell death compared to BRIP1 proficient neuronal cells.

CONCLUSION

Overall, our results indicate an important role for BRIP1 in maintaining neuronal cell health and homeostasis by suppressing cellular oxidative stress.

GLI1-targeting drugs induce replication stress and homologous recombination deficiency and synergize with PARP-targeted therapies in triple negative breast cancer cells

Triple negative breast cancer (TNBC), an aggressive and highly metastatic subtype of breast cancer. Glioma-associated oncogene 1 (GLI1) is a transcription factor and effector of the Hedgehog (Hh) signaling pathway, and is predictive of poor survival for TNBC patients. A nanostring DNA Damage Response (DDR) mRNA panel was used to identify GLI1-induced regulation of DDR genes. Western blots, immunohistochemistry and immunofluorescence were used to evaluate protein expression. Colony assays and mammosphere formation assays were utilized to assess survival of cancer cells. Flow cytometry analyses were employed to evaluate changes in the cell cycle profile, and DNA fiber assays were used to analyze alterations in replication dynamics in TNBC cells. The UALCAN portal and Ensemble programs were used for computational analysis of TCGA data. CompuSyn software was used to calculate combination index (CI) values to assess synergism in drug combination experiments. Inhibition of GLI1 in TNBC cells transcriptionally downregulate expression of FANCD2 and its foci formation, and causes a homologous recombination repair (HR) deficiency. As HR-deficient cancer cells are sensitive to PARP-targeted therapies, we evaluated a combination of the GLI1 inhibitor, GANT61, and a PARP inhibitor (olaparib) in TNBC cells. Combination of GANT61 and olaparib elevated DNA damage levels and these drug combinations caused synergistic lethality to TNBC cells. Aberrantly activated GLI1 regulates HR-mediated DNA repair by transcriptionally regulating FANCD2 to overcome chemotherapy-induced replication stress and DNA damage, and it contributes to resistance of TNBC cells to therapeutics.

Renal Lipid Metabolism Abnormalities in Obesity and Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma is the most common and deadly type of cancer affecting the kidney, and is characterized histologically by large intracellular lipid deposits. These deposits are thought to result from lipid metabolic reprogramming occurring in tumor cells, but the exact mechanisms and implications of these metabolic alterations are incompletely understood. Obesity is an independent risk factor for clear cell renal cell carcinoma, and is also associated with lipid accumulation in noncancerous epithelial cells of the proximal tubule, where clear cell renal cell carcinoma originates. This article explores the potential link between obesity-associated renal lipid metabolic disturbances and lipid metabolic reprogramming in clear cell renal cell carcinoma, and discusses potential implications for future research.

Disparities in Breast Cancer Survivors in Rural West Texas

Objectives

Breast cancer is the second highest female mortality rate in Texas for all races and ethnicities, except for Hispanics. Interestingly, Hale County is a rural underserved county in West Texas which experiences a lower rate of cancer, has higher age-adjusted mortality rates (26.2/100 000), on average, compared to all of Texas (23.1/100 000). The purpose of this study was to determine the relationship between sociodemographic variables and breast cancer outcomes in underserved Hale County which contributed to the highest mortality rate in Texas.

Methods

Hale County breast cancer data (1995–2014) were obtained from the Texas Cancer Registry. Statistical methods independent samples t-test, Kaplan–Meier curve, and Cox proportional hazard were used to describe the significant relationship between survival time, sociodemographic, and prognostic variables.

Results

Women with breast cancer in Hale County were more likely to be White non-Hispanics (n = 266, 65.5%) and had the highest longevity (2753.6 ± 2073.5 days). White Hispanics experienced the worst survival (2369.6 ± 2060.2 days) and were more likely to develop a serious grade of cancer. Significant relationships were found between the stage of cancer and insurance status with survival time for both White non-Hispanics and White Hispanics (P < .001). Patients in grades II and III were found to be significantly (P < .01) associated with breast cancer death, and grades II and III which had around five-fold and eleven-fold increased risk of death, respectively, compared with the referent group, grade I.

Conclusion

Determining the impact of sociodemographic variables on breast cancer outcome is essential to addressing issues of geographic disparities and integrating such variables may guide relevant policy interventions to reduce breast cancer’s incidence in rural underserved communities in West Texans.

Hedgehog/GLI1 Transcriptionally Regulates FANCD2 in Ovarian Tumor Cells: Its Inhibition Induces HR-Deficiency and Synergistic Lethality with PARP Inhibition

Ovarian cancer (OC) is one of the most lethal type of cancer in women due to a lack of effective targeted therapies and high rates of treatment resistance and disease recurrence. Recently Poly (ADP-ribose) polymerase inhibitors (PARPi) have shown promise as chemotherapeutic agents; however, their efficacy is limited to a small fraction of patients with BRCA mutations. Here we show a novel function for the Hedgehog (Hh) transcription factor Glioma associated protein 1 (GLI1) in regulation of key Fanconi anemia (FA) gene, FANCD2 in OC cells. GLI1 inhibition in HR-proficient OC cells induces HR deficiency (BRCAness), replication stress and synergistic lethality when combined with PARP inhibition. Treatment of OC cells with combination of GLI1 and PARP inhibitors shows enhanced DNA damage, synergy in cytotoxicity, and strong in vivo anticancer responses.

Abstract 2111: RAD6-mediated epigenetic reprogramming contributes to therapy-induced chemo-resistance in ovarian cancer

Epithelial Ovarian Cancer (EOC) is the fifth leading cause of cancer-related deaths in women in the USA, gets diagnosed at an advanced stage (stage III-IV) with local or distant metastasis. The primary therapeutic regimen of EOC involves surgical removal of all the visible tumor mass followed by platinum-based chemotherapy either as a single agent or in combination with a taxane. Despite initial responses, over 70% of EOC patients develop recurrent disease and they are often resistant to available chemotherapeutic drugs, contributing to poor survival. This appalling situation emphasizes the critical need to identify the molecular mechanisms involving recurrence of these tumors' aggressive growth and developing therapeutic resistance. Our analysis from chemo naïve and recurrent tumors from the same patients' samples, and isogenic ovarian cancer cell lines data showed recurrent tumors and resistant cell lines several upregulated cancer stem cell markers including ALDH1A1, SOX2 and altered expression of DNA damage response and repair genes that are involved in the processing of platinum adducts and crosslink repair. Prominently, RAD6, an E2ubiquitin-conjugating enzyme, is significantly (&gt; 6 folds) overexpressed in recurrent ovarian tumors and associated with aggressive tumor cell growth, stemness, chemoresistance to platinum drugs, and poor prognosis. Our studies validated that, chemotherapy induced upregulated RAD6 reprograms epigenetic milieu in tumor cells through ubiquitination of histone variants H2A, H2AX, and H2B, which further recruits additional epigenetic modifiers to these regions and regulates genes involved in DNArepair, cell survival, stemness, and chemoresistance. Additionally, our mechanistic studies demonstrate RAD6 dependent recruitment of several epigenetic modifiers such as histone methylases and demethylases to regions of ubiquitylated histones and their crosstalk. Collectively, our study presents novel chemotherapy induced epigenetic modulator contributing to therapeutic recurrence of EOC and could be an important therapeutic target to treat chemo-resistant EOC and improve the progression-free survival of patients suffering from this deadly disease.

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Citation Format: Tasmin Rahman Omy, Shirisha Jonnalagadda, Mark Reedy, Komaraiah Palle. RAD6-mediated epigenetic reprogramming contributes to therapy-induced chemo-resistance in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2111.

Sex Differences in Cardiovascular Disease and Cognitive Dysfunction in Rural West Elderly Texans

BACKGROUND

The prevalence of cognitive dysfunction increases in elderly due to cardiovascular disease related risk factors in rural communities like West Texas.

OBJECTIVE

The purpose of this study was to find risk factors of cardiovascular disease (CVD) related to cognitive dysfunction and their impact on elderly adults in rural West Texans.

METHODS

Statistical methods such as Pearson's chi-squared and a multinomial logistic regression were utilized to analyze data. We used SPSS software to detect and understand the nature of the risk factors.

RESULTS

A summary of statistics was obtained by using Pearson's chi-squared test for categorical variables. CVD, diabetes mellitus, and depression were significantly associated with cognitive dysfunction for both males and females (p = 0.0001), whereas anxiety was found to be significantly associated with cognitive dysfunction for females (p = 0.0001). Age group and race/ethnicity were significantly associated with cognitive dysfunction for both males and females (p = 0.0001). By performing a multinomial logistic regression method and controlling for confounders, the significant risk factors (p <  0.05)- age (65- 84 years), diabetes, and memory loss for age-associated cognitive impairment; diabetes for cognitive impairment no dementia; age (65- 84, ≥85 years), CVD, diabetes, depression, memory loss, non-Hispanic Whites, and Black/African-Americans for mild cognitive impairment; and age, memory loss, non-Hispanic Whites, Black/African-Americans, and male gender were found for dementia.

CONCLUSION

CVD related risk factors in developing cognitive dysfunction exist and integrating such risk variables may guide relevant policy interventions to reduce Alzheimer's incidence or dementia in rural communities in West Texans.

AraC-FdUMP[10] Is a Next-Generation Fluoropyrimidine with Potent Antitumor Activity in PDAC and Synergy with PARG Inhibition

AraC-FdUMP[10] (CF10) is a second-generation polymeric fluoropyrimidine that targets both thymidylate synthase (TS), the target of 5-fluorouracil (5-FU), and DNA topoisomerase 1 (Top1), the target of irinotecan, two drugs that are key components of FOLFIRNOX, a standard-of-care regimen for pancreatic ductal adenocarcinoma (PDAC). We demonstrated that F10 and CF10 are potent inhibitors of PDAC cell survival (in multiple cell lines including patient-derived lines) with IC₅₀s in the nanomolar range and are nearly 1,000-fold more potent than 5-FU. The increased potency of CF10 relative to 5-FU correlated with enhanced TS inhibition and strong Top1 cleavage complex formation. Furthermore, CF10 displayed single-agent activity in PDAC murine xenografts without inducing weight loss. Through a focused drug synergy screen, we identified that combining CF10 with targeting the DNA repair enzyme, poly (ADP-ribose) glycohydrolase, induces substantial DNA damage and apoptosis. This work moves CF10 closer to a clinical trial for the treatment of PDAC. IMPLICATIONS: CF10 is a promising polymeric fluoropyrimidine with dual mechanisms of action (i.e., TS and Top1 inhibition) for the treatment of PDAC and synergizes with targeting of DNA repair. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/4/565/F1.large.jpg.

Improved Antitumor Activity of the Fluoropyrimidine Polymer CF10 in Preclinical Colorectal Cancer Models through Distinct Mechanistic and Pharmacologic Properties

Chemotherapy regimens that include 5-fluorouracil (5-FU) are central to colorectal cancer treatment; however, risk/benefit concerns limit 5-FU's use, necessitating development of improved fluoropyrimidine (FP) drugs. In our study, we evaluated a second-generation nanoscale FP polymer, CF10, for improved antitumor activity. CF10 was more potent than the prototype FP polymer F10 and much more potent than 5-FU in multiple colorectal cancer cell lines including HCT-116, LS174T, SW480, and T84D. CF10 displayed improved stability to exonuclease degradation relative to F10 and reduced susceptibility to thymidine antagonism due to extension of the polymer with arabinosyl cytidine. In colorectal cancer cells, CF10 strongly inhibited thymidylate synthase (TS), induced Top1 cleavage complex formation and caused replication stress, while similar concentrations of 5-FU were ineffective. CF10 was well tolerated in vivo and invoked a reduced inflammatory response relative to 5-FU. Blood chemistry parameters in CF10-treated mice were within normal limits. In vivo, CF10 displayed antitumor activity in several colorectal cancer flank tumor models including HCT-116, HT-29, and CT-26. CF10's antitumor activity was associated with increased plasma levels of FP deoxynucleotide metabolites relative to 5-FU. CF10 significantly reduced tumor growth and improved survival (84.5 days vs. 32 days; P < 0.0001) relative to 5-FU in an orthotopic HCT-116-luc colorectal cancer model that spontaneously metastasized to liver. Improved survival in the orthotopic model correlated with localization of a fluorescent CF10 conjugate to tumor. Together, our preclinical data support an early-phase clinical trial of CF10 for treatment of colorectal cancer.

Abstract 4682: Influence of PI3K/AKT pathway on imatinib mesylate treatment outcome in chronic myeloid leukemia patients

Chronic myeloid leukemia (CML) is a common myeloproliferative disorder characterized by cytogenetic abnormality [t(9;22)(q34;q11)] that generates BCR-ABL oncogene with aberrant tyrosine kinase activity, the driver event in CML origin. Tyrosine kinase inhibitors (TKIs) are remarkably effective; yet, treatment failure is common in some cases due to the accumulation of mutations in BCR-ABL itself and other genes causing drug resistance/relapse, which indicates that BCR-ABL inhibition alone may not be sufficient to combat CML. The PI3K/Akt/mTOR signaling pathway downstream of BCR-ABL has been proven to be an important survival mechanism in leukemias. In vitro studies demonstrated that targeting this pathway could be a viable strategy, but needs further validation in CML patients. In this study, we examined the critical PI3K/AKT/mTOR pathway genes (PIK3CA, PTEN, AKT1, SHIP1, mTOR, and FOXO3A) in CML patients (n=51) using qPCR method at diagnosis and after treatment, and analyzed with respect to BCR-ABL status, and JAK2, STAT5, and STAT3 levels. Interestingly, significant upregulation of AKT1 (p=0.012) and PIK3CA (p=0.026) and downregulation of PTEN (P=0.06) and SHIP1 (p=0.039) was observed in samples at diagnosis compared to their post imatinib treated. Remarkably, these elevated AKT1 and PI3KCA transcript levels were significantly associated with increased BCR-ABL and JAK2 transcript levels, but not STAT3 and STAT5 suggesting PI3K pathway as a prominent target in CML. However, with respect to the clinical phase and imatinib response, none of the genes showed significant differences except for PTEN, which was significantly downregulated in advanced phase (p&lt;0.042) and in cases with poor imatinib response. Overall, these results indicate a critical role for PI3K pathway in CML and its maintenance.

Citation Format: Swathi Banapuram, Manjula Gorre, Raghunadha Rao Digumarti, Vishnupriya Satti, Komaraiah Palle, Sandhya Annamaneni. Influence of PI3K/AKT pathway on imatinib mesylate treatment outcome in chronic myeloid leukemia patients [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 4682.

Abstract 2380: A novel role for PACS-1 in suppression of oncogenic replication stress in cancer cells

PACS-1 is a protein involved in trafficking, especially transport of proteins like furin and Mannose-6-phosphate into the trans-golgi network. Intriguingly, our studies identified dynamic translocation of PACS-1 during cell division and its association with chromatin in tumor cells. Downregulation of PACS-1 in cancer cell lines attenuated cell growth, induced replication stress mediated DNA damage response (DDR), such as ATM/ATR-mediated checkpoint activation, and formation RPA, FANCD2 and pH2AX foci. Consistent with these observations, live-cell imaging revealed increased nuclear translocation of PACS-1 during S-phase and until the complete cell division. These results point to a novel role for PACS-1 during normal replication or in the suppression of oncogenic replication in tumor cells. However, a direct role for PACS-1 in cancer development or progression is not clear. Analysis of the cancer genome atlas (TCGA) data revealed occurrence of PACS-1 amplifications, mutations and deletions in cancers of different tissues. PACS-1 depletion leads to proteasome-mediated degradation of HDAC2 and HDAC3, compromised chromatin maturation, leads to replication stress and genomic instability. Intriguingly, stable overexpression of PACS-1 in MDA-MB-231 cells enhanced malignant behavior of tumor cells in their ability to form soft agar colonies and matrigel invasion compared to the cells that are expressing vector control. PACS-1 downregulation promotes replication stress in tumor cells suggesting that its upregulation in tumors may be important for replication stress recovery in cancer cells and for an efficient response to chemotherapy induced DNA damage. Furthermore, Prognoscan analysis indicated that PACS-1 expression levels correlates with poor survival in multiple studies, including breast, ovarian and lung cancers, suggesting a role for PACS-1 in tumorigenesis and a biomarker for poor prognosis.

Citation Format: Chinnadurai Mani, Kaushlendra Tripathi, David W. Clark, Gary Thomas, Komaraiah Palle. A novel role for PACS-1 in suppression of oncogenic replication stress in cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2380.

The multifunctional protein PACS-1 is required for HDAC2- and HDAC3-dependent chromatin maturation and genomic stability

Phosphofurin acidic cluster sorting protein-1 (PACS-1) is a multifunctional membrane traffic regulator that plays important roles in organ homeostasis and disease. In this study, we elucidate a novel nuclear function for PACS-1 in maintaining chromosomal integrity. PACS-1 progressively accumulates in the nucleus during cell cycle progression, where it interacts with class I histone deacetylases 2 and 3 (HDAC2 and HDAC3) to regulate chromatin dynamics by maintaining the acetylation status of histones. PACS-1 knockdown results in the proteasome-mediated degradation of HDAC2 and HDAC3, compromised chromatin maturation, as indicated by elevated levels of histones H3K9 and H4K16 acetylation, and, consequently, increased replication stress-induced DNA damage and genomic instability.

Abstract DP-015: BIOTINYLATED ESTROGENS A NOVEL TOOL FOR EARLY DETECTION OF ADDUCT IN OVARIAN CANCER

Elevated estrogens exert their carcinogenic effects by at least three different mechanisms; they promote cell proliferation by transcriptional regulation of estrogen responsive genes, cause generation of reactive oxygen species and other free radicals, and directly react with DNA and form potentially mutagenic adducts. However, unbalanced estrogen metabolism has been linked to development of several malignant diseases including breast, endometrial and ovarian cancer and has been identified as a risk factor for these cancers. The metabolic breakdown of estogens is regulated by a series of reactions mediated by hepatic and peripheral enzymes that balances the induction and reduction of cellular stress. An imbalance in this enzymes and processes can lead to highly reactive catechol estrogen metabolites that can react with DNA, form carcinogenic DAN-adducts and lesions. Although several studies established a connection between estrogen-induced DNA damage and carcinogenesis, the underlying molecular mechanisms have been difficult to study because of the technical challenges in detecting and analyzing the variety of different DNA lesions that are formed by estrogen compounds. Moreover, detection and analysis of these adducts are important to directly monitor estrogen metabolites induced cellular responses in the cells. Towards this, we developed a novel method using biotinylated-estrogens that allows immunodetection of estrogen-induced DNA adducts by Slot-blot and single-cell molecular combing and proximity ligation assays. Using these modified estrogens we first time quantitatively detected these adducts on DNA by immune Slot-blot techniques and on DNA fibers. Furthermore, similar to other environmental carcinogens estrogens activates replication associated DNA damage responses and induces chromosomal instability. Hence, first time our studies demonstrate that biotin-labeled estrogens could be a powerful tool to detect estrogen adducts and to probe associated DNA damage responses and cellular responses.

Citation Format: Kaushlendra Tripathi, Chinnadurai Mani, David W. Clark, Komaraiah Palle. BIOTINYLATED ESTROGENS A NOVEL TOOL FOR EARLY DETECTION OF ADDUCT IN OVARIAN CANCER [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr DP-015.

Prexasertib treatment induces homologous recombination deficiency and synergizes with olaparib in triple-negative breast cancer cells

Background

Breast cancer remains as one of the most lethal types of cancer in women. Among various subtypes, triple-negative breast cancer (TNBC) is the most aggressive and hard to treat type of breast cancer. Mechanistically, increased DNA repair and cell cycle checkpoint activation remain as the foremost reasons behind TNBC tumor resistance to chemotherapy and disease recurrence.

Methods

We evaluated the mechanism of prexasertib-induced regulation of homologous recombination (HR) proteins using 20S proteasome inhibitors and RT-PCR. HR efficiency and DNA damages were evaluated using Dr-GFP and comet assays. DNA morphology and DNA repair focus studies were analyzed using immunofluorescence. UALCAN portal was used to evaluate the expression of RAD51 and survival probability based on tumor stage, subtype, and race in breast cancer patients.

Results

Our results show that prexasertib treatment promotes both post-translational and transcriptional mediated regulation of BRCA1 and RAD51 proteins. Additionally, prexasertib-treated TNBC cells revealed over 55% reduction in HR efficiency compared to control cells. Based on these results, we hypothesized that prexasertib treatment induced homologous recombination deficiency (HRD) and thus should synergize with PARP inhibitors (PARPi) in TNBC cells. As predicted, combined treatment of prexasertib and PARPi olaparib increased DNA strand breaks, γH2AX foci, and nuclear disintegration relative to single-agent treatment. Further, the prexasertib and olaparib combination was synergistic in multiple TNBC cell lines, as indicated by combination index (CI) values. Analysis of TCGA data revealed elevated RAD51 expression in breast tumors compared to normal breast tissues, especially in TNBC subtype. Interestingly, there was a discrepancy in RAD51 expression in racial groups, with African-American and Asian breast cancer patients showing elevated RAD51 expression compared to Caucasian breast cancer patients. Consistent with these observations, African-American and Asian TNBC patients show decreased survival.

Conclusions

Based on these data, RAD51 could be a biomarker for aggressive TNBC and for racial disparity in breast cancer. As positive correlation exists between RAD51 and CHEK1 expression in breast cancer, the in vitro preclinical data presented here provides additional mechanistic insights for further evaluation of the rational combination of prexasertib and olaparib for improved outcomes and reduced racial disparity in TNBC.

Abstract 2087: Mechanistic studies reveal novel molecular insights on anticancer properties of F10 compound in human colon cancer cells

Fluoropyrimidine (FP) drugs, mainly 5-Fluorouracil (5-FU), constitute the backbone of combination chemotherapy regimens (e.g. FOLFOX and FOLFIRI) for treating colorectal cancer (CRC) and provide a survival benefit for patients with stage II, III, and IV colorectal cancer. However, 5 year survival rate for CRC patients with metastatic disease is less than 10%. This dreadful situation suggests urgent need for novel and more potent FPs to improve the outcomes of these patients. We have developed novel fluoropyrimidine drug polymers (e.g. F10) that show promising antitumor activity in multiple pre-clinical models even while displaying reduced systemic toxicities. F10 is taken up by malignant cells via active transport compared to 5-Fluorouracil, which is taken up by diffusion in malignant and non-malignant cells. Additionally, F10 compound is primarily incorporated into DNA, and produced thymidylate synthase and topoisomerase toxic metabolites at greater levels, whereas 5-Fluorouracil is primarily incorporated into RNA, and only has about 5-10% production of active form of thymidylate synthase toxic metabolites. MMR is involved in repairing the DNA mismatches and FP drugs induced DNA damage. Interestingly, our studies show that F10 acts by different mechanisms compared to 5-FU. Particularly, F10 treated CRC cells exhibit replication stress as evidenced by paused and slow progression of replication forks and R-loops formation at the active transcriptional regions, suggesting replication and transcription dependent generation of DNA lesions in these cells. F10 treatment induced several fold increased DNA double strand breaks (DSB) as measured by COMET assays and about 1000 folds more cytotoxicity to CRC cells compared to 5-FU. Similarly, F10 treatment activated distinctive DNA damage responses in MMR proficient CRC cells compared MMR deficient cells. Additionally, our studies suggest F10 as a promising therapeutic agent for CRC therapy either alone or in combination with CHK1 and PARP inhibitors.

Citation Format: Chinnadurai Mani, William Gmeiner, Komaraiah Palle. Mechanistic studies reveal novel molecular insights on anticancer properties of F10 compound in human colon cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2087.

DNA repair fidelity in stem cell maintenance, health, and disease

Stem cells are a sub population of cell types that form the foundation of our body, and have the potential to replicate, replenish and repair limitlessly to maintain the tissue and organ homeostasis. Increased lifetime and frequent replication set them vulnerable for both exogenous and endogenous agents-induced DNA damage compared to normal cells. To counter these damages and preserve genetic information, stem cells have evolved with various DNA damage response and repair mechanisms. Furthermore, upon experiencing irreparable DNA damage, stem cells mostly prefer early senescence or apoptosis to avoid the accumulation of damages. However, the failure of these mechanisms leads to various diseases, including cancer. Especially, given the importance of stem cells in early development, DNA repair deficiency in stem cells leads to various disabilities like developmental delay, premature aging, sensitivity to DNA damaging agents, degenerative diseases, etc. In this review, we have summarized the recent update about how DNA repair mechanisms are regulated in stem cells and their association with disease progression and pathogenesis.

Thymineless Death by the Fluoropyrimidine Polymer F10 Involves Replication Fork Collapse and Is Enhanced by Chk1 Inhibition

We are developing the fluoropyrimidine polymer F10 to overcome limitations of 5-fluorouracil (5-FU) that result from inefficient metabolism to 5-fluoro-2′-deoxyuridine-5′-mono- and tri-phosphate, the deoxyribonucleotide metabolites that are responsible for 5-FU's anticancer activity. F10 is much more cytotoxic than 5-FU to colorectal cancer (CRC) cells; however, the mechanism of enhanced F10 cytotoxicity remains incompletely characterized. Using DNA fiber analysis, we establish that F10 decreases replication fork velocity and causes replication fork collapse, while 1000-fold excess of 5-FU is required to achieve similar endpoints. Treatment of HCT-116 cells with F10 results in Chk1 phosphorylation and activation of intra–S-phase checkpoint. Combining F10 with pharmacological inhibition of Chk1 with either PF-477736 or prexasertib in CRC cells enhanced DNA damage relative to single-agent treatment as assessed by γH2AX intensity and COMET assay. PF-477736 or prexasertib co-treatment also inhibited upregulation of Rad51 levels in response to F10, resulting in reduced homologous repair. siRNA knockdown of Chk1 also increased F10-induced DNA damage assessed and sensitized CRC cells to F10. However, Chk1 knockdown did not inhibit Rad51 upregulation by F10, indicating that the scaffolding activity of Chk1 imparts activity in DNA repair distinct from Chk1 enzymatic activity. Our results indicate that F10 is cytotoxic to CRC cells in part through DNA damage subsequent to replication fork collapse. F10 is ~1000-fold more potent than 5-FU at inducing replication-mediated DNA damage which correlates with the increased overall potency of F10 relative to 5-FU. F10 efficacy can be enhanced by pharmacological inhibition of Chk1.

Abstract 2828: MMR status affects efficiency of homologous recombination repair of F10-induced DNA DSBs

Background: DNA mismatch repair (MMR) is an important stratification factor in colorectal cancer (CRC). 10-20% of sporadic CRC cases display high microsatellite instability (MSI-H) due to DNA mismatch repair (MMR) deficiency, and these are refractory to current fluoropyrimidine (FP) chemotherapy. Our studies with DNA-directed FP polymers, such as F10, indicate they are highly effective regardless of MMR-deficiency consistent with inducing MMR-independent cell death. We investigate the role of MMR-status on potency of F10 and induction of DNA damage and activation of the DNA damage response as part of an overall effort to determine if fluoropyrimidine polymers can be used effectively in the treatment of MMR-deficient CRC.

Methods: Studies were conducted using MMR-deficient HCT-116 CRC cells and HCT-116 3-6 cells. Potency was assessed by cell-titer glo and clonogenic assays. Replication stress was evaluated by DNA fiber combing. DNA damage and activation of the DNA damage response was evaluated by Western blots for gH2AX, Chk1 activation, and proteins important for homologous recombination repair.

Results: F10 is highly potent to CRC cells regardless of MMR status and is ~1,000-fold more potent than 5-FU to MMR-deficient HCT-116 cells. The increased potency of F10 parallels increased efficiency at causing replication fork slowing as assessed by DNA fiber analysis. F10 causes DNA double strand breaks (DSBs) and activates Chk1 consistent with causing replication fork collapse. DNA DSBs, Chk1 activation, and upregulation of FANCD2, which mediates HR-repair of DNA DSBs all show a marked MMR-dependence consistent with hMLH1 being a factor in HR-mediated repair of F10-induced DNA DSBs.

Conclusions: F10 is highly potent to CRC cells regardless of MMR status via a mechanism involving replication fork slowing and increased replication stress. MMR status affects basal levels of proteins involved in HR and the upregulation of these proteins in response to F10 treatment. Our studies indicate FP polymers are likely to be generally effective in CRC regardless of MMR status however MMR status may be an important factor in a personalized medicine approach to their use as combination with Chk1 inhibitors and other drugs modulating the DNA damage response may depend on MMR status.

Citation Format: William H. Gmeiner, Chinnadurai Mani, Komaraiah Palle. MMR status affects efficiency of homologous recombination repair of F10-induced DNA DSBs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2828.

Rad18 is required for functional interactions between FANCD2, BRCA2, and Rad51 to repair DNA topoisomerase 1-poisons induced lesions and promote fork recovery

Camptothecin (CPT) and its analogues are chemotherapeutic agents that covalently and reversibly link DNA Topoisomerase I to its nicked DNA intermediate eliciting the formation of DNA double strand breaks (DSB) during replication. The repair of these DSB involves multiple DNA damage response and repair proteins. Here we demonstrate that CPT-induced DNA damage promotes functional interactions between BRCA2, FANCD2, Rad18, and Rad51 to repair the replication-associated DSB through homologous recombination (HR). Loss of any of these proteins leads to equal disruption of HR repair, causes chromosomal aberrations and sensitizes cells to CPT. Rad18 appears to function upstream in this repair pathway as its downregulation prevents activation of FANCD2, diminishes BRCA2 and Rad51 protein levels, formation of nuclear foci of all three proteins and recovery of stalled or collapsed replication forks in response to CPT. Taken together this work further elucidates the complex interplay of DNA repair proteins in the repair of replication-associated DSB.

RAD6 promotes chemoresistance in ovarian cancer

Mortality in ovarian cancer is predominantly due to acquired chemoresistance and tumor recurrence. UBIQUITIN CONJUGATING ENZYME E2 or RAD6 expression increases in cell lines and patient tumors in response to platinum-based chemotherapy and promotes both activation of DNA damage response pathways and expression of stemness genes and a stem cell-like phenotype driving ovarian cancer chemoresistance.

Synthesis, anti-angiogenic and DNA cleavage studies of novel N-(4-methyl-3-((4-(pyridin-3-yl)pyrimidin-2-yl)amino)phenyl)piperidine-4-carboxamide derivatives

A series of novel N-(4-methyl-3-((4-(pyridin-3-yl)pyrimidin-2-yl)amino)phenyl)piperidine-4-carboxamide derivatives 10(a-f), 12(a-c) and 14(a-c) were synthesized and characterized by FTIR, ¹H-NMR, mass spectral and elemental analysis. The efficacy of these derivatives to inhibit in vivo angiogenesis was evaluated using chick chorioallantoic membrane (CAM) model and their DNA cleavage abilities were evaluated after incubating with calf thymus DNA followed by gel electrophoresis. These novel piperidine analogues efficiently blocked the formation of blood vessels in vivo in CAM model and exhibited differential migration and band intensities in DNA binding/cleavage assays. Among the tested compounds 10a, 10b, 10c, 12b, 14b and 14c showed significant anti-angiogenic and DNA cleavage activities compared to their respective controls and the other derivatives used in this study. These observations suggest that the presence of electron donating and withdrawing groups at positions 2, 3 and 4 of the phenyl ring of the side chain may determine their potency and as anticancer agents by exerting both anti-angiogenic and cytotoxic effects .

RAD6 promotes DNA repair and stem cell signaling in ovarian cancer and is a promising therapeutic target to prevent and treat acquired chemoresistance

Ovarian cancer (OC) is the most deadly gynecological cancer and unlike most other neoplasms, survival rates for OC have not significantly improved in recent decades. We show that RAD6, an ubiquitin-conjugating enzyme, is significantly overexpressed in ovarian tumors and its expression increases in response to carboplatin chemotherapy. RAD6 expression correlated strongly with acquired chemoresistance and malignant behavior of OC cells, expression of stem cell genes and poor prognosis of OC patients, suggesting an important role for RAD6 in ovarian tumor progression. Upregulated RAD6 enhances DNA damage tolerance and repair efficiency of OC cells and promotes their survival. Increased RAD6 levels cause histone 2B ubiquitination-mediated epigenetic changes that stimulate transcription of stem cell genes, including ALDH1A1 and SOX2, leading to a cancer stem cell phenotype, which is implicated in disease recurrence and metastasis. Downregulation of RAD6 or its inhibition using a small molecule inhibitor attenuated DNA repair signaling and expression of cancer stem cells markers and sensitized chemoresistant OC cells to carboplatin. Together, these results suggest that RAD6 could be a therapeutic target to prevent and treat acquired chemoresistance and disease recurrence in OC and enhance the efficacy of standard chemotherapy.

BRIP1/FANCJ Mutation Analysis in a Family with History of Male and Female Breast Cancer in India

Male breast cancer (MBC) is a rare and poorly studied disease that is a growing global health problem. Interestingly, both the molecular basis of MBC and its histological profile are often quite distinct from the far more prevalent female breast cancer, emphasizing the need for increased focus on MBC. Here, we present a case report of an MBC patient from India with a strong familial history of breast cancer. This patient was normal for BRCA1/2 and many other common breast cancer-associated genes. However, upon further analysis, the individual was found to possess two mutations in the DNA helicase and tumor suppressor gene BRIP1, including a silent mutation at residue 879 as well as a P919S variant. Other family members were also screened for these mutations. To the best of our knowledge, this is the first report of BRIP1 mutation in MBC in the Indian population.

Aldehyde dehydrogenases in cancer stem cells: potential as therapeutic targets

Resistance to current chemotherapeutic or radiation-based cancer treatment strategies is a serious concern. Cancer stem cells (CSCs) are typically able to evade treatment and establish a recurrent tumor or metastasis, and it is these that lead to the majority of cancer deaths. Therefore, a major current goal is to develop treatment strategies that eliminate the resistant CSCs as well as the bulk tumor cells in order to achieve complete disease clearance. Aldehyde dehydrogenases (ALDHs) are important for maintenance and differentiation of stem cells as well as normal development. There is expanding evidence that ALDH expression increases in response to therapy and promotes chemoresistance and survival mechanisms in CSCs. This perspective will discuss a paper by Cojoc and colleagues recently published in Cancer Research, that indicates ALDHs play a key role in resistance to radiation therapy and tumor recurrence in prostate cancer. The authors suggest that ALDHs are a potential therapeutic target for treatment prostate cancer patients to limit radiation resistance and disease recurrence. The findings are consistent with work from other cancers showing ALDHs are major contributors of CSC signaling and resistance to anti-cancer treatments. This perspective will address representative work concerning the validity of ALDH and the associated retinoic acid signaling pathway as chemotherapeutic targets for prostate as well as other cancers.

FANCJ protein is important for the stability of FANCD2/FANCI proteins and protects them from proteasome and caspase-3 dependent degradation

Fanconi anemia (FA) is a rare genome instability syndrome with progressive bone marrow failure and cancer susceptibility. FANCJ is one of 17 genes mutated in FA-patients, comprises a DNA helicase that is vital for properly maintaining genomic stability and is known to function in the FA-BRCA DNA repair pathway. While exact role(s) of FANCJ in this repair process is yet to be determined, it is known to interact with primary effector FANCD2. However, FANCJ is not required for FANCD2 activation but is important for its ability to fully respond to DNA damage. In this report, we determined that transient depletion of FANCJ adversely affects stability of FANCD2 and its co-regulator FANCI in multiple cell lines. Loss of FANCJ does not significantly alter cell cycle progression or FANCD2 transcription. However, in the absence of FANCJ, the majority of FANCD2 is degraded by both the proteasome and Caspase-3 dependent mechanism. FANCJ is capable of complexing with and stabilizing FANCD2 even in the absence of a functional helicase domain. Furthermore, our data demonstrate that FANCJ is important for FANCD2 stability and proper activation of DNA damage responses to replication blocks induced by hydroxyurea.

Abstract 3734: Preclinical evaluation of Rad6 inhibition to overcome platinum resistance in ovarian cancer

Ovarian cancer (OC) is the most lethal gynecological cancer in women in the United States. Advances in surgery and chemotherapy have not significantly changed the overall survival rate of OC for the last few decades, which highlights the need for new therapeutic strategies. Platinum drug resistance and refractory disease pose major challenges in treating this disease and are major factors contributing to the poor survival rate of OC patients. Although most patients initially respond to platinum based chemotherapy, about 80% of cases present with recurrent disease, develop platinum resistance, and die with the advanced disease. Considering the heterogeneity, small fractions of the cells could be inherently resistant to chemotherapy and/or dormant and exhibit stem-like cell properties, contributing to the resistant phenotype and disease recurrence. Although the Cancer stem cell (CSC) theory of therapeutic resistance proposes that the proportion of CSCs correlate to enhanced chemoresistance and early disease recurrence, the specific molecular mechanisms that regulate tumor cell behavior (stemness) and integrate signaling networks with aberrant oncogenic signaling in OC cells are not known. Our analysis of clinical samples revealed upregulation of Rad6, an E2 ubiquitin conjugating enzyme, in more than 80% of ovarian tumors compared to normal ovarian tissues. Upregulation of Rad6 also correlated well with tumor progression. Further analysis of molecular pathways in OC cells revealed a strong correlation between Rad6 upregulation and increased β-catenin and hedgehog signaling, stem cell like characteristics and platinum resistance. Downregulation of Rad6 using siRNAs or inhibition of its catalytic activity by a small molecule inhibitor, attenuated carboplatin induced monoubiquitination of its target proteins such as histone 2B, PCNA and proteins of the Fanconi anemia pathway thereby sensitizing OC cells to carboplatin. Interestingly, inhibition of Rad6 alone in OC cells induced replication stress and reduced cell survival and proliferation by arresting cells in the G2/M phase. Moreover, inhibition of Rad6 in various OC cell lines reduced expression of β-catenin, Gli1 and several OC stem cell markers. Moreover, Rad6 plays an important role in the activation of the trans-lesion synthesis (TLS) pathway by monoubiquitinating PCNA and in the activation of the Fanconi Anemia (FA) DNA repair pathway. These are critical mechanisms for cells to repair DNA crosslinks induced by platinum drugs. Together with these observations, our data suggest that inhibition of Rad6 could be a viable therapeutic target for overcoming platinum resistance and disease recurrence in ovarian cancer.

Citation Format: Sebastian M. Spencer, Ranganatha R. Somasagara, Kaushlendra Tripathi, David W. Clark, Hend Kothayer, Andrew D. Westwell, Rodney P. Rocconi, Komaraiah Palle. Preclinical evaluation of Rad6 inhibition to overcome platinum resistance in ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3734.

Synthesis and in vitro anticancer evaluation of some 4,6-diamino-1,3,5-triazine-2-carbohydrazides as Rad6 ubiquitin conjugating enzyme inhibitors

Series of 4-amino-6-(arylamino)-1,3,5-triazine-2-carbohydrazides (3a-e) and N'-phenyl-4,6-bis(arylamino)-1,3,5-triazine-2-carbohydrazides (6a-e), for ease of readership, we will abbreviate our compound names as 'new triazines', have been synthesized, based on the previously reported Rad6B-inhibitory diamino-triazinylmethyl benzoate anticancer agents TZ9 and 4-amino-N'-phenyl-6-(arylamino)-1,3,5-triazine-2-carbohydrazides. Synthesis of the target compounds was readily accomplished in two steps from either bis-aryl/aryl biguanides via reaction of phenylhydrazine or hydrazinehydrate with key 4-amino-6-bis(arylamino)/(arylamino)-1,3,5-triazine-2-carboxylate intermediates. These new triazine derivatives were evaluated for their abilities to inhibit Rad6B ubiquitin conjugation and in vitro anticancer activity against several human cancer cell lines: ovarian (OV90 and A2780), lung (H1299 and A549), breast (MCF-7 and MDA-MB231) and colon (HT29) cancer cells by MTS assays. All the 10 new triazines exhibited superior Rad6B inhibitory activities in comparison to selective Rad6 inhibitor TZ9 that was reported previously. Similarly, new triazines also showed better IC50 values in survival assays of various tumor cell lines. Particularly, new triazines 6a-c, exhibited lower IC50 (3.3-22 μM) values compared to TZ9.

Oxidative stress and metabolic disorders: Pathogenesis and therapeutic strategies

Increased body weight and metabolic disorder including insulin resistance, type 2 diabetes and cardiovascular complications together constitute metabolic syndrome. The pathogenesis of metabolic syndrome involves multitude of factors. A number of studies however indicate, with some conformity, that oxidative stress along with chronic inflammatory condition pave the way for the development of metabolic diseases. Oxidative stress, a state of lost balance between the oxidative and anti-oxidative systems of the cells and tissues, results in the over production of oxidative free radicals and reactive oxygen species (ROS). Excessive ROS generated could attack the cellular proteins, lipids and nucleic acids leading to cellular dysfunction including loss of energy metabolism, altered cell signalling and cell cycle control, genetic mutations, altered cellular transport mechanisms and overall decreased biological activity, immune activation and inflammation. In addition, nutritional stress such as that caused by high fat high carbohydrate diet also promotes oxidative stress as evident by increased lipid peroxidation products, protein carbonylation, and decreased antioxidant system and reduced glutathione (GSH) levels. These changes lead to initiation of pathogenic milieu and development of several chronic diseases. Studies suggest that in obese person oxidative stress and chronic inflammation are the important underlying factors that lead to development of pathologies such as carcinogenesis, obesity, diabetes, and cardiovascular diseases through altered cellular and nuclear mechanisms, including impaired DNA damage repair and cell cycle regulation. Here we discuss the aspects of metabolic disorders-induced oxidative stress in major pathological conditions and strategies for their prevention and therapy.

Allyl isothiocyanate induces replication-associated DNA damage response in NSCLC cells and sensitizes to ionizing radiation

Allyl isothiocyanate (AITC), a constituent of many cruciferous vegetables exhibits significant anticancer activities in many cancer models. Our studies provide novel insights into AITC-induced anticancer mechanisms in human A549 and H1299 non-small cell lung cancer (NSCLC) cells. AITC exposure induced replication stress in NSCLC cells as evidenced by γH2AX and FANCD2 foci, ATM/ATR-mediated checkpoint responses and S and G2/M cell cycle arrest. Furthermore, AITC-induced FANCD2 foci displayed co-localization with BrdU foci, indicating stalled or collapsed replication forks in these cells. Although PITC (phenyl isothiocyanate) exhibited concentration-dependent cytotoxic effects, treatment was less effective compared to AITC. Previously, agents that induce cell cycle arrest in S and G2/M phases were shown to sensitize tumor cells to radiation. Similar to these observations, combination therapy involving AITC followed by radiation treatment exhibited increased DDR and cell killing in NSCLC cells compared to single agent treatment. Combination index (CI) analysis revealed synergistic effects at multiple doses of AITC and radiation, resulting in CI values of less than 0.7 at Fa of 0.5 (50% reduction in survival). Collectively, these studies identify an important anticancer mechanism displayed by AITC, and suggest that the combination of AITC and radiation could be an effective therapy for NSCLC.

Rad6 upregulation promotes stem cell-like characteristics and platinum resistance in ovarian cancer

Ovarian cancer is the fifth most deadly cancer in women in the United States and despite advances in surgical and chemotherapeutic treatments survival rates have not significantly improved in decades. The poor prognosis for ovarian cancer patients is largely due to the extremely high (80%) recurrence rate of ovarian cancer and because the recurrent tumors are often resistant to the widely utilized platinum-based chemotherapeutic drugs. In this study, expression of Rad6, an E2 ubiquitin-conjugating enzyme, was found to strongly correlate with ovarian cancer progression. Furthermore, in ovarian cancer cells Rad6 was found to stabilize β-catenin promoting stem cell-related characteristics, including expression of stem cell markers and anchorage-independent growth. Cancer stem cells can promote chemoresistance, tumor recurrence and metastasis, all of which are limiting factors in treating ovarian cancer. Thus it is significant that Rad6 overexpression led to increased resistance to the chemotherapeutic drug carboplatin and correlated with tumor cell invasion. These findings show the importance of Rad6 in ovarian cancer and emphasize the need for further studies of Rad6 as a potential target for the treatment of ovarian cancer.

GLI inhibitor GANT-61 diminishes embryonal and alveolar rhabdomyosarcoma growth by inhibiting Shh/AKT-mTOR axis

Rhabdomyosarcoma (RMS) typically arises from skeletal muscle. Currently, RMS in patients with recurrent and metastatic disease have no successful treatment. The molecular pathogenesis of RMS varies based on cancer sub-types. Some embryonal RMS but not other sub-types are driven by sonic hedgehog (Shh) signaling pathway. However, Shh pathway inhibitors particularly smoothened inhibitors are not highly effective in animals. Here, we show that Shh pathway effectors GLI1 and/or GLI2 are over-expressed in the majority of RMS cells and that GANT-61, a specific GLI1/2 inhibitor dampens the proliferation of both embryonal and alveolar RMS cells-derived xenograft tumors thereby blocking their growth. As compared to vehicle-treated control, about 50% tumor growth inhibition occurs in mice receiving GANT-61 treatment. The proliferation inhibition was associated with slowing of cell cycle progression which was mediated by the reduced expression of cyclins D1/2/3 & E and the concomitant induction of p21. GANT-61 not only reduced expression of GLI1/2 in these RMS but also significantly diminished AKT/mTOR signaling. The therapeutic action of GANT-61 was significantly augmented when combined with chemotherapeutic agents employed for RMS therapy such as temsirolimus or vincristine. Finally, reduced expression of proteins driving epithelial mesenchymal transition (EMT) characterized the residual tumors.

Abstract 3631: A novel combination of Hedgehog inhibitors with carboplatin exhibits synergy in ovarian cancer treatment by altered regulation of DNA repair networks

Ovarian cancer (OVCA) is the deadliest of all the reproductive cancers, affecting over 22,000 lives of women annually in the USA alone. In spite of their initial promising response rates to platinum drugs, more than 70% of patients relapse and die with the advanced disease. An important factor contributing to the poor outcomes in OVCA is platinum resistance (PR) and disease recurrence. Therefore, it is vital to understand the molecular mechanisms contributing to tumor resistance to platinum drugs and disease recurrence. Our preliminary studies identified aberrant activation of Hedgehog (Hh) signaling in advanced stage tumors and in OVCA cells, particularly those that are resistant to platinum agents. Further genetic and biochemical studies revealed altered expression of several cell cycle checkpoint and DNA repair genes involved in repair of platinum drug-induced DNA damage in these tumors and cell lines. Aberrant Hh signaling is implicated in the regulation of several signaling pathways including cell cycle, differentiation and DNA repair networks. Hence, we hypothesized that inhibition of Hh signaling could affect the expression of altered DNA damage response and repair networks and sensitize OVCA cells to platinum therapy. To this end, we evaluated two small molecule inhibitors of Hh signaling that target SMO (BMS-833923) and GLI transcription factors (GANT61) either alone or in combination with carboplatin in several OVCA cell lines by clonogenic and MTS cell survival assays. The therapeutic efficacy was assessed by calculating combination index (CI) values using CalcuSyn software. Simultaneously, we have also assessed the status of Hh signaling and several DNA damage response and repair networks that respond to platinum drugs. Interestingly, both the inhibitors of Hh signaling attenuated OVCA cells’ growth and their ability to form colonies. Consistent with this, inhibition of Hh signaling alone induced replication stress associated DNA damage responses (as evidenced by γH2AX foci) and compromised ATR-mediated cell cycle checkpoint responses. Similarly, combination treatment of Hh inhibitor (either SMO inhibitor or GLI inhibitor) with carboplatin potentiated the DNA damage induced by carboplatin and its cytotoxic effects in several ovarian cancer cell lines. Additionally, evaluation of combination treatments efficacies was confirmed in isogenic platinum sensitive (A2780) and resistant (A2780/CP70) OVCA cell lines. Moreover, analysis of combination therapeutic indexes revealed synergistic effects by demonstrating the CI values in the range of 0.3 to 0.49 (synergy defined as CI &lt;1) at multiple dosage combinations. Collectively, our studies suggest the combination of Hh signaling inhibitors with carboplatin could be an effective therapeutic modality in synergistic killing of ovarian cancer cells and overcoming platinum resistance.

Citation Format: Sebastian M. Spencer, Kaushlendra Tripathi, Erhong Meng, Jennifer Scalici, Rodney P. Rocconi, Komaraiah Palle. A novel combination of Hedgehog inhibitors with carboplatin exhibits synergy in ovarian cancer treatment by altered regulation of DNA repair networks. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3631. doi:10.1158/1538-7445.AM2015-3631

Abstract P5-06-07: A novel role for breast cancer associated protein 2 (BCA2) in regulation replication-stress mediated DNA damage responses

Breast cancer associated gene 2 (BCA2) has been originally identified from invasive breast cancer cells and shown to be overexpressed in over 50% of invasive breast cancers. Its expression is known to be highly associated with estrogen receptor-alpha (ER-α) status and promote cell proliferation and invasive properties. Importantly, expression of BCA2 is minimal or undetectable in most normal cells and tissues, which makes it as a valuable biomarker for ER-α positive breast cancers and a potential therapeutic target. BCA2 protein is a RING and ZINC-finger domain containing E3 ubiquitin ligase that has been shown to auto-ubiquitylate and interact with several proteins including Rab7, tetherin, ubiquitin, Ubc9 and p21, which are involved in different cellular processes. However, most of these studies have been focused on tumor progression, migration and invasive properties and almost no information on its role in carcinogenesis. Since many RING and ZINC-finger domain containing ubiquitin ligases are implicated in oncogenic signaling and DNA damage responses (DDR), in this study we examined the role of BCA2 in regulation of spontaneous and chemotherapeutics induced DDR in different breast cancer cell lines (ER-α positive versus triple negative). Interestingly, siRNA mediated down regulation of BCA2 induced spontaneous DDR, such as activation of replication checkpoint, slow cell cycle progression and double strand breaks (γH2AX foci). Exposure of BCA2 knockdown cells to DNA topoisomerase inhibitors (camptothecin and etoposide) potentiated DDR induced by these drugs. However, the molecular basis for this enhanced DDR is yet to be determined. Consistent with the previous studies, BCA2 knockdown attenuated cell proliferation, and compromised migration and invasion properties of these cells. Moreover, this novel role for BCA2 in DDR strongly suggests its status may also influence tumor response to chemo and radiation therapies and in carcinogenesis process. Further evaluation of breast cancer cell’s responses to different chemotherapeutic agents revealed distinct cellular responses based on the status of BCA2 and ER-α status. Taken together, our studies implicate a novel role for BCA2 in regulation of DDR and its influence on tumor response to chemotherapy. Additionally, we aim to present E3 ligase dependent and independent roles of BCA2 in these processes and tumor responses to different therapeutic agents.

Acknowledgment: This is work is supported by Abraham Mitchell Cancer Research Scholar Endowment grant.

Citation Format: Yuan-Hao Lee, Kaushlendra Tripathi, David Clark, Komaraiah Palle. A novel role for breast cancer associated protein 2 (BCA2) in regulation replication-stress mediated DNA damage responses [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-06-07.

Abstract 2405: Rad18 regulates epistatic relationship between FA-BRCA and homologous recombination pathways to repair camptothecin induced DSB

DNA topoisomerase 1 (Top1) inhibiting anticancer agents such as camptothecin (CPT) show broad spectrum antitumor activity. The therapeutic activities of CPT and its analogues are attributed to prolonged stabilization of Top1-DNA covalent complexes and converting them into replication mediated double strand breaks (DSB). In spite of their therapeutic success, acquired tumor resistance poses major challenges for their therapeutic efficacy. Combination therapies using DNA repair inhibitors can increase the cytotoxic effects of these drugs and aid in overcoming such problems. Homologous recombination (HR) is the predominant DNA repair pathway involved in the repair of CPT induced DSB. Therefore, inhibition of either HR or tumors that are defective in HR could be effectively killed by Top1 inhibitors. In the same way, cells deficient in HR (ex. Rad51) or its associated proteins (such as Rad18, Fanconi anemia (FA) and breast cancer associated (BRCA1, BRCA2) proteins) are known to exhibit hypersensitivity to CPT. Specifically, FA proteins are known to associate with replication forks and implicated in repair of fork stalling lesions by HR in association with BRCA proteins. Thus, an epistatic relationship between FA and BRCA pathway has been suggested in repair of fork stalling lesions, but molecular basis for this cross-talk is not known. We previously shown that Rad18 regulates FANCD2 monoubiquitination (a key step in FA pathway) to promote HR mediated repair of CPT-induced DSB and cell survival. To further characterize the molecular interactions between Rad18 and FA-BRCA pathway in regulating HR, we have assessed their role in HR by DR-GFP reporter assays by downregulating Rad18 and FANCD2 proteins by siRNAs either alone or in combination. Consistent with survival data, cells deficient in Rad18 or FANCD2 exhibited reduced level of HR. Likewise, cells deficient in both the genes also exhibited similar results of single gene deficient cells, suggesting these two proteins work in a common pathway that promotes HR. Further biochemical and biophysical studies in Rad18 and FANCD2 deficient cells revealed dramatic decrease in nuclear localization of Rad51 and its CPT induced foci formation. Since, FANCD2 is required for BRCA2 recruitment to the sites of DSB, and BRCA2 known to associate with Rad51 and stabilize it on single stranded DNA, we further analyzed BRCA2 foci formation and its colocalization with Rad51 in response to CPT. Interestingly, our studies revealed reduced BRCA2 and Rad51 foci and their colocalization in response to CPT in Rad18 and FANCD2 deficient cells. Consistent with their role in HR, cells deficient in either of these genes exhibited chromosomal aberrations, implicating their role in accurate repair of replication coupled DSB. Together these data support that Rad18 regulates epistatic relationship between FA-BRCA and HR pathways in response to replication coupled DSB induced by CPT.

Citation Format: Kaushlendra Tripathi, Chinnadurai Mani, David Clark, Reagan Barnett, Komaraiah Palle. Rad18 regulates epistatic relationship between FA-BRCA and homologous recombination pathways to repair camptothecin induced DSB. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2405. doi:10.1158/1538-7445.AM2014-2405

Gli1 protein regulates the S-phase checkpoint in tumor cells via Bid protein, and its inhibition sensitizes to DNA topoisomerase 1 inhibitors

Aberrant expression of hedgehog molecules, particularly Gli1, is common in cancers of many tissues and is responsible for their aggressive behavior and chemoresistance. Here we demonstrate a novel and tumor-specific role for aberrant Gli1 in the regulation of the S-phase checkpoint that suppresses replication stress and resistance to chemotherapy. Inhibition of Gli1 in tumor cells induced replication stress-mediated DNA damage response, attenuated their clonogenic potential, abrogated camptothecin (CPT)-induced Chk1 phosphorylation, and potentiated its cytotoxicity. However, in normal fibroblasts, Gli1 siRNAs showed no significant changes in CPT-induced Chk1 phosphorylation. Further analysis of ataxia telangiectasia and Rad3-related protein (ATR)/Chk1 signaling cascade genes in tumor cells revealed an unexpected mechanism whereby Gli1 regulates ATR-mediated Chk1 phosphorylation by transcriptional regulation of the BH3-only protein Bid. Consistent with its role in DNA damage response, Bid down-regulation in tumor cells abolished CPT-induced Chk1 phosphorylation and sensitized them to CPT. Correspondingly, Gli1 inhibition affected the expression of Bid and the association of replication protein A (RPA) with the ATR- interacting protein (ATRIP)-ATR complex, and this compromised the S-phase checkpoint. Conversely, complementation of Bid in Gli1-deficient cells restored CPT-induced Chk1 phosphorylation. An in silico analysis of the Bid promoter identified a putative Gli1 binding site, and further studies using luciferase reporter assays confirmed Gli1-dependent promoter activity. Collectively, our studies established a novel connection between aberrant Gli1 and Bid in the survival of tumor cells and their response to chemotherapy, at least in part, by regulating the S-phase checkpoint. Importantly, our data suggest a novel drug combination of Gli1 and Top1 inhibitors as an effective therapeutic strategy in treating tumors that expresses Gli1.

ALDH1A1 maintains ovarian cancer stem cell-like properties by altered regulation of cell cycle checkpoint and DNA repair network signaling

Objective

Aldehyde dehydrogenase (ALDH) expressing cells have been characterized as possessing stem cell-like properties. We evaluated ALDH+ ovarian cancer stem cell-like properties and their role in platinum resistance.

Methods

Isogenic ovarian cancer cell lines for platinum sensitivity (A2780) and platinum resistant (A2780/CP70) as well as ascites from ovarian cancer patients were analyzed for ALDH+ by flow cytometry to determine its association to platinum resistance, recurrence and survival. A stable shRNA knockdown model for ALDH1A1 was utilized to determine its effect on cancer stem cell-like properties, cell cycle checkpoints, and DNA repair mediators.

Results

ALDH status directly correlated to platinum resistance in primary ovarian cancer samples obtained from ascites. Patients with ALDH^HIGH displayed significantly lower progression free survival than the patients with ALDH^LOW cells (9 vs. 3 months, respectively p<0.01). ALDH1A1-knockdown significantly attenuated clonogenic potential, PARP-1 protein levels, and reversed inherent platinum resistance. ALDH1A1-knockdown resulted in dramatic decrease of KLF4 and p21 protein levels thereby leading to S and G2 phase accumulation of cells. Increases in S and G2 cells demonstrated increased expression of replication stress associated Fanconi Anemia DNA repair proteins (FANCD2, FANCJ) and replication checkpoint (pS317 Chk1) were affected. ALDH1A1-knockdown induced DNA damage, evidenced by robust induction of γ-H2AX and BAX mediated apoptosis, with significant increases in BRCA1 expression, suggesting ALDH1A1-dependent regulation of cell cycle checkpoints and DNA repair networks in ovarian cancer stem-like cells.

Conclusion

This data suggests that ovarian cancer cells expressing ALDH1A1 may maintain platinum resistance by altered regulation of cell cycle checkpoint and DNA repair network signaling.

Abstract 2475: Design and development of combretastatin based unsymmetrical terphenyls as small molecule antimitotic agents

The microtubule system of the eukaryotic cell plays indispensable role in the process of separating duplicated chromosomes before the cell division. Due to this essential function, they have been an important target for the development of cancer therapeutics. Several natural products such as Taxol, Vinca alkaloids, colchicine and their synthetic analogues that target microtubules have been used to treat several malignancies. However, cancer cells develop resistance to several of these agents by altering drug transporters and signaling pathways. Recently, combretastatins (CA) a group of diarylstilbenes isolated originally from stem wood of the South African tree Combretum caffrum have received much attention due to their potent anticancer activity against wide variety of human cancers including those that are multidrug resistant. These molecules specifically bind to the colchicine-binding site of the tubulins and prevent their polymerization required for the mitotic tubule formation thus possesses anti-proliferative and antivascular activities. A water soluble disodium phosphate derivative of CA has shown promising results in clinical trials of several malignancies, thus stimulating significant interest in a variety of CA analogues. However, the cis configuration of CA favors to form thermodynamically more stable trans isomer during storage and administration, producing a dramatic reduction in both tubulin binding and antiproliferative activities. Considering these limitations, we designed and synthesized a series of 3′,4′,5′-trimethoxy-2-phenylbiphenyl derivatives as cis-restricted CA analogues and evaluated for their antiproliferative activity, inhibitory effects on tubulin polymerization, cell cycle effects and apoptosis induction. Moreover, we adopted a novel strategy to synthesize these low molecular weight unsymmetrical terphenyls by a new synthetic methodology using Suzuki coupling in a one pot operation without isolating the biaryls intermediate. A majority of these compounds demonstrated significant anti-proliferative activity against most of the cell lines tested including that are multi-drug resistant. Interestingly, some of these compounds elicited DNA damage response in a dose dependent manner. Specifically, the compounds with acetamido and acetyl functional groups exhibited significant inhibitory activities in tubulin polymerization and growth inhibition. Consistent with their FACS profiles, Immunocytochemistry and biochemical analysis revealed loss of intact microtubule structure, up regulation of cyclin B1 and aurora kinase B mRNA levels, corresponding to growth arrest in the G2/M. More importantly, our one pot synthesis strategy of unsymmetrical terphenyls of this structural class paves the way for design and development of novel anticancer agents.

Citation Format: Surendra Reddy Punganuru, Sadanandam Palle, Kaushlendra Tripathi, Komaraiah Palle. Design and development of combretastatin based unsymmetrical terphenyls as small molecule antimitotic agents. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2475. doi:10.1158/1538-7445.AM2013-2475