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.

Meta-analysis of the association between alcohol consumption and abdominal aortic aneurysm

Background

Alcohol is a possible risk factor for abdominal aortic aneurysm (AAA), but evidence from individual studies is weak and inconsistent. Existing narrative reviews suggest the possibility of non-linear associations. The aim here was to quantify any association using a systematic literature review, followed by dose–response meta-analysis of prospective studies.

Methods

MEDLINE, Embase and Web of Science were searched systematically to January 2017 for relevant prospective studies of alcohol consumption and AAA risk. Summary estimates of highest versus lowest levels of consumption, and linear and non-linear dose–response curves were quantified using random-effects models.

Results

Eleven relevant cohorts were identified describing results from 3580 individuals with among 473 092 participants. Data were extracted from ten cohorts for meta-analyses of high versus low levels of alcohol consumption (risk ratio for AAA 0·93, 95 per cent c.i. 0·78 to 1·11; P = 0·4, I2 = 47 per cent). The linear dose–response risk ratio for AAA, derived from 11 cohorts, was 1·00 (0·97 to 1·04) per 8 g alcohol per day (P = 0·9, I2 = 73 per cent). Non-linear dose–response results showed a tick-shaped curve with lower risk up to 2 units/day, but increasing risk beyond that (P = 0·05). The increase in risk beyond 2 units/day was stronger in men than in women.

Conclusion

Although the linear dose–response analysis revealed little evidence of an association between alcohol consumption and AAA risk, a tick-shaped trend in the association was observed. This non-linear dose–response analysis revealed reduced risks for alcohol consumption below 2 units/day, masking increased risks for 2 or more units/day.

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.

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.

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 <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

Concerns about breast cancer and relations to psychosocial well-being in a multiethnic sample of early-stage patients

Much work on psychosocial sequelae of breast cancer has been guided by the assumption that body image and partner reaction issues are focal. In a tri-ethnic sample of 223 women treated for early-stage breast cancer within the prior year, the authors assessed a wider range of concerns and relations to well-being. Strongest concerns were recurrence, pain, death, harm from adjuvant treatment, and bills. Body-image concerns were moderate; concern about rejection was minimal. Younger women had stronger sexual and partner-related concerns than older women. Hispanic women had many stronger concerns and more disruption than other women. Life and pain concerns and sexuality concerns contributed uniquely to predicting emotional and psychosexual disruption; life and pain concerns and rejection concerns contributed to predicting social disruption. In sum, adaptation to breast cancer is a process bearing on several aspects of the patient's life space.

Reovirus virion-like particles obtained by recoating infectious subvirion particles with baculovirus-expressed sigma3 protein: an approach for analyzing sigma3 functions during virus entry

Structure-function studies with mammalian reoviruses have been limited by the lack of a reverse-genetic system for engineering mutations into the viral genome. To circumvent this limitation in a partial way for the major outer-capsid protein sigma3, we obtained in vitro assembly of large numbers of virion-like particles by binding baculovirus-expressed sigma3 protein to infectious subvirion particles (ISVPs) that lack sigma3. A level of sigma3 binding approaching 100% of that in native virions was routinely achieved. The sigma3 coat in these recoated ISVPs (rcISVPs) appeared very similar to that in virions by electron microscopy and three-dimensional image reconstruction. rcISVPs retained full infectivity in murine L cells, allowing their use to study sigma3 functions in virus entry. Upon infection, rcISVPs behaved identically to virions in showing an extended lag phase prior to exponential growth and in being inhibited from entering cells by either the weak base NH4Cl or the cysteine proteinase inhibitor E-64. rcISVPs also mimicked virions in being incapable of in vitro activation to mediate lysis of erythrocytes and transcription of the viral mRNAs. Last, rcISVPs behaved like virions in showing minor loss of infectivity at 52 degrees C. Since rcISVPs contain virion-like levels of sigma3 but contain outer-capsid protein mu1/mu1C mostly cleaved at the delta-phi junction as in ISVPs, the fact that rcISVPs behaved like virions (and not ISVPs) in all of the assays that we performed suggests that sigma3, and not the delta-phi cleavage of mu1/mu1C, determines the observed differences in behavior between virions and ISVPs. To demonstrate the applicability of rcISVPs for genetic studies of protein functions in reovirus entry (an approach that we call recoating genetics), we used chimeric sigma3 proteins to localize the primary determinants of a strain-dependent difference in sigma3 cleavage rate to a carboxy-terminal region of the ISVP-bound protein.

Concerns about breast cancer and relations to psychosocial well-being in a multiethnic sample of early-stage patients

Much work on psychosocial sequelae of breast cancer has been guided by the assumption that body image and partner reaction issues are focal. In a tri-ethnic sample of 223 women treated for early-stage breast cancer within the prior year, the authors assessed a wider range of concerns and relations to well-being. Strongest concerns were recurrence, pain, death, harm from adjuvant treatment, and bills. Body-image concerns were moderate; concern about rejection was minimal. Younger women had stronger sexual and partner-related concerns than older women. Hispanic women had many stronger concerns and more disruption than other women. Life and pain concerns and sexuality concerns contributed uniquely to predicting emotional and psychosexual disruption; life and pain concerns and rejection concerns contributed to predicting social disruption. In sum, adaptation to breast cancer is a process bearing on several aspects of the patient's life space.

IRIS explorer software for radial-depth cueing reovirus particles and other macromolecular structures determined by cryoelectron microscopy and image reconstruction

Structures of biological macromolecules determined by transmission cryoelectron microscopy (cryo-TEM) and three-dimensional image reconstruction are often displayed as surface-shaded representations with depth cueing along the viewed direction (Z cueing). Depth cueing to indicate distance from the center of virus particles (radial-depth cueing, or R cueing) has also been used. We have found that a style of R cueing in which color is applied in smooth or discontinuous gradients using the IRIS Explorer software is an informative technique for displaying the structures of virus particles solved by cryo-TEM and image reconstruction. To develop and test these methods, we used existing cryo-TEM reconstructions of mammalian reovirus particles. The newly applied visualization techniques allowed us to discern several new structural features, including sites in the inner capsid through which the viral mRNAs may be extruded after they are synthesized by the reovirus transcriptase complexes. To demonstrate the broad utility of the methods, we also applied them to cryo-TEM reconstructions of human rhinovirus, native and swollen forms of cowpea chlorotic mottle virus, truncated core of pyruvate dehydrogenase complex from Saccharomyces cerevisiae, and flagellar filament of Salmonella typhimurium. We conclude that R cueing with color gradients is a useful tool for displaying virus particles and other macromolecules analyzed by cryo-TEM and image reconstruction.