CDK9-55 guides the anaphase-promoting complex/cyclosome (APC/C) in choosing the DNA repair pathway choice

DNA double-strand breaks (DSBs) contribute to genome instability, a key feature of cancer. DSBs are mainly repaired by homologous recombination (HR) and non-homologous end-joining (NHEJ). We investigated the role of an isoform of the multifunctional cyclin-dependent kinase 9, CDK9-55, in DNA repair, by generating CDK9-55-knockout HeLa clones (through CRISPR-Cas9), which showed potential HR dysfunction. A phosphoproteomic screening in these clones treated with camptothecin revealed that CDC23 (cell division cycle 23), a component of the E3-ubiquitin ligase APC/C (anaphase-promoting complex/cyclosome), is a new substrate of CDK9-55, with S588 being its putative phosphorylation site. Mutated non-phosphorylatable CDC23(S588A) affected the repair pathway choice by impairing HR and favouring error-prone NHEJ. This CDK9 role should be considered when designing CDK-inhibitor-based cancer therapies.

The hydrophilic extract from a new tomato genotype (named DHO) kills cancer cell lines through the modulation of the DNA damage response induced by Campthotecin treatment

Introduction

DNA double-strand breaks are the most toxic lesions repaired through the non-homologous and joining (NHEJ) or the homologous recombination (HR), which is dependent on the generation of single-strand tails, by the DNA end resection mechanism. The resolution of the HR intermediates leads to error-free repair (Gene Conversion) or the mutagenic pathways (Single Strand Annealing and Alternative End-Joining); the regulation of processes leading to the resolution of the HR intermediates is not fully understood.

Methods

Here, we used a hydrophilic extract of a new tomato genotype (named DHO) in order to modulate the Camptothecin (CPT) DNA damage response.

Results

We demonstrated increased phosphorylation of Replication Protein A 32 Serine 4/8 (RPA32 S4/8) protein in HeLa cells treated with the CPT in combination with DHO extract with respect to CPT alone. Moreover, we pointed out a change in HR intermediates resolution from Gene Conversion to Single Strand Annealing through the modified DNA repair protein RAD52 homolog (RAD52), DNA excision repair protein ERCC-1 (ERCC1) chromatin loading in response to DHO extract, and CPT co-treatment, with respect to the vehicle. Finally, we showed an increased sensitivity of HeLa cell lines to DHO extract and CPT co-treatment suggesting a possible mechanism for increasing the efficiency of cancer therapy.

Discussion

We described the potential role of DHO extract in the modulation of DNA repair, in response to Camptothecin treatment (CPT), favoring an increased sensitivity of HeLa cell lines to topoisomerase inhibitor therapy.

RBL1/p107 Expression Levels Are Modulated by Multiple Signaling Pathways

The members of the retinoblastoma (RB) protein family, RB1/p105, retinoblastoma-like (RBL)1/p107 and RBL2/p130 are critical modulators of the cell cycle and their dysregulation has been associated with tumor initiation and progression. The activity of RB proteins is regulated by numerous pathways including oncogenic signaling, but the molecular mechanisms of these functional interactions are not fully defined. We previously demonstrated that RBL2/p130 is a direct target of AKT and it is a key mediator of the apoptotic process induced by AKT inhibition. Here we demonstrated that RBL1/p107 levels are only minorly modulated by the AKT signaling pathway. In contrast, we discovered that RBL1/p107 levels are regulated by multiple pathways linked directly or indirectly to Ca²⁺-dependent signaling. Inhibition of the multifunctional calcium/calmodulin-dependent kinases (CaMKs) significantly reduced RBL1/p107 expression levels and phosphorylation, increased RBL1/p107 nuclear localization and led to cell cycle arrest in G0/G1. Targeting the Ca²⁺-dependent endopeptidase calpain stabilized RBL1/p107 levels and counteracted the reduction of RBL1/p107 levels associated with CaMKs inhibition. Thus, these novel observations suggest a complex regulation of RBL1/p107 expression involving different components of signaling pathways controlled by Ca²⁺ levels, including CaMKs and calpain, pointing out a significant difference with the mechanisms modulating the close family member RBL2/p130.

Triple-Negative Breast Cancer Comparison With Canine Mammary Tumors From Light Microscopy to Molecular Pathology

Many similar characteristics in human and dog cancers including, spontaneous development, clinical presentation, tumor heterogeneity, disease progression, and response to standard therapies have promoted the approval of this comparative model as an alternative to mice. Breast cancer represents the second most frequent neoplasm in humans after lung cancer. Triple-negative breast cancers (TNBC) constitute around 15% of all cases of breast cancer and do not express estrogen receptor (ER), progesterone receptor (PR), and do not overexpress human epidermal growth factor receptor 2 (HER2). As a result, they do not benefit from hormonal or trastuzumab-based therapy. Patients with TNBC have worse overall survival than patients with non-TNBC. Lehmann and collaborators described six different molecular subtypes of TNBC which further demonstrated its transcriptional heterogeneity. This six TNBC subtype classification has therapeutic implications. Breast cancer is the second most frequent neoplasm in sexually intact female dogs after skin cancer. Canine mammary tumors are a naturally occurring heterogeneous group of cancers that have several features in common with human breast cancer (HBC). These similarities include etiology, signaling pathway activation, and histological classification. Molecularly CMTs are more like TNBCs, and therefore dogs are powerful spontaneous models of cancer to test new therapeutic approaches, particularly for human TNBCs. More malignant tumors of the breast are more often ER and PR negative in both humans and dogs. Promising breast cancer biomarkers in both humans and canines are cancer-associated stroma (CAS), circulating tumor cells and tumor DNA (ctDNA), exosomes and miRNAs, and metabolites.

Virotherapy: From single agents to combinatorial treatments

Virotherpay is emerging as a promising strategy against cancer, and three oncolytic viruses (OVs) have gained approval in different countries for the treatment of several cancer types. Beyond the capability to selectively infect, replicate and lyse cancer cells, OVs act through a multitude of events, including modification of the tumour micro/macro-environment as well as a complex modulation of the anti-tumour immune response by activation of danger signals and immunogenic cell death pathways. Most OVs show limited effects, depending on the viral platform and the interactions with the host. OVs used as monotherapy only in a minority of patients elicited a full response. Better outcomes were obtained using OVs in combination with other treatments, such as immune therapy or chemotherapy, suggesting that the full potential of OVs can be unleashed in combination with other treatment modalities. Here, we report the main described combination of OVs with conventional chemotherapeutic agents: platinum salts, mitotic inhibitors, anthracyclines and other antibiotics, anti-metabolites, alkylating agents and topoisomerase inhibitors. Additionally, our work provides an overview of OV combination with targeted therapies: histone deacetylase inhibitors, kinase inhibitors, monoclonal antibodies, inhibitors of DNA repair, inhibitors of the proteasome complex and statins that demonstrated enhanced OV anti-neoplastic activity. Although further studies are required to assess the best combinations to translate the results in the clinic, it is clear that combined therapies, acting with complementary mechanisms of action might be useful to target cancer lesions resistant to currently available treatments.

The Oncolytic Virus dl922-947 Triggers Immunogenic Cell Death in Mesothelioma and Reduces Xenograft Growth

Background: Malignant pleural mesothelioma (MPM) is an aggressive cancer associated with asbestos exposure that urgently requires effective therapeutic strategies. Current treatments are unable to increase significantly patient survival, which is often limited to <1 year from diagnosis. Virotherapy, based on the use of oncolytic viruses that exert anti-cancer effects by direct cell lysis and through the induction of anti-tumor immune response, represents an alternative therapeutic option for rare tumors with limited life expectancy. In this study, we propose the use of the adenovirus dl922-947, engineered to allow selective replication in cancer cells, to counteract MPM.

Methods: We performed a thorough preclinical assessment of dl922-947 effects in a set of MPM cell lines and xenografts. Cytotoxicity of dl922-947 alone and in combination assays was evaluated by sulforhodamine B assay. Cell cycle, calreticulin expression, and high mobility group box protein 1 (HMGB1) secretion were determined by flow cytometry, whereas ATP content was determined by a luminescence-based bioassay. The modulation of angiogenic factors in MPM-infected cells was evaluated through ELISA.

Results: We found that dl922-947 infection exhibits cytotoxic effects in MPM cell lines, affecting cell viability, cell cycle progression, and regulating main hallmarks of immunogenic cell death inducing calreticulin surface exposure, HMGB1 and ATP release. Our results also suggest that dl922-947 may affect angiogenic signals by regulation of VEGF-A and IL-8 secretion. Furthermore, dl922-947 shows anti-tumor efficacy in murine xenograft models reducing tumor growth and enhancing survival. Finally, the combination with cisplatin potentiated the cytotoxic effect of dl922-947.

Conclusions: Overall our data identify virotherapy, based on the use of dl922-947, as a new possible therapeutic strategy against MPM, which could be used alone, in combination with standard chemotherapy drugs, as shown here, or other approaches also aimed at enhancing the antitumoral immune response elicited by the virus.

Abstract 3747: Oncolytic viruses as a possible therapeutic strategy against malignant mesothelioma

Malignant mesothelioma (MM) is a very aggressive tumor associated to asbestos exposure, which is poorly responsive to the current therapeutic strategies, resulting in a dismal prognosis. So, considering also that various studies predict an increase in incidence, new effective therapeutic approaches are urgently needed. Here we investigated at the preclinical level a new possible therapeutic strategy for MM based on the use of oncolytic viruses. Oncolytic viruses show various benefits as anticancer agents: they can replicate selectively in tumor cells reaching 10,000-fold amplification of the input dose; they stimulate the antitumoral immune response; they can be used in combination with other cytotoxic agents; the pleural cavity in which pleural MM arises is easily accessible for such therapeutic approach. In particular, we focused on adenoviruses with a 24 bp deletion in the E1A-conserved region 2, which binds and inactivates the retinoblastoma protein, resulting in a virus (dl 922-947) that cannot trigger S phase entry in normal cells, but can still replicate in cells with an aberrant G1-S checkpoint, a defect observed in over 90% human cancers, including MM. We studied on a panel of mesothelioma cell lines representative of the main different histotypes — the epithelioid NCI-H28 and NCI-H2452, the biphasic MSTO-211H, the sarcomathoid NCI-H2052 — the effects of dl 922-947 treatment used both as a single agent or in combination with other strategies. At first, dl 922-947 cytotoxicity was evaluated through the sulforhodamine B (SRB) assay, which showed that all MM cell lines were susceptible to viral treatment, except NCI-H2052 cells, in which viral entry was not efficient, as shown through infection with a reporter adenovirus transducing GFP. Interestingly and consistently with the cytotoxic effect observed, FACS analysis showed that dl 922-947 treatment induced an increase of the subG1 cell fraction (suggestive of apoptosis induction) and of the hyperdiploid (4N) population (suggestive of mitotic defects). We also investigated by SRB the possible cytotoxic effects of dl922-947 in combination with other therapeutic strategies. In particular, we analyzed the effect of dl922-947 in combination with cisplatin, which is the first-line treatment against MM, and found that, by comparing different schedules of treatment, cisplatin increased the cytotoxic effect of the oncolytic virus. We also tested dl922-947 efficacy in combination with MK-1775, an efficient inhibitor of the WEE1 kinase, which is currently being tested in clinical trials. We found that MK-1775, at doses equal to or above its IC50value, is able to increase the cytotoxic effect of the oncolytic virus treatment.

In conclusion our data indicate that treatment with the dl922-947 oncolytic virus might be a promising new approach against mesothelioma and warrants further investigation both as single agent and in combination strategies.

Citation Format: Carmelina Antonella Iannuzzi, Carmela Passaro, Silvia Boffo, Iris Maria Forte, Paola Indovina, Marcella Macaluso, Giuseppe Portella, Antonio Giordano, Francesca Pentimalli. Oncolytic viruses as a possible therapeutic strategy against malignant mesothelioma. [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 3747.

SRC Family Kinase Inhibition in Ewing Sarcoma Cells Induces p38 MAP Kinase-Mediated Cytotoxicity and Reduces Cell Migration

Ewing sarcoma (ES) is a highly aggressive bone and soft tissue cancer, representing the second most common primary malignant bone tumor in children and adolescents. Although the development of a multimodal therapy, including both local control (surgery and/or radiation) and systemic multidrug chemotherapy, has determined a significant improvement in survival, patients with metastatic and recurrent disease still face a poor prognosis. Moreover, considering that ES primarily affects young patients, there are concerns about long-term adverse effects of the therapy. Therefore, more rational strategies, targeting specific molecular alterations underlying ES, are required. Recent studies suggest that SRC family kinases (SFKs), which are aberrantly activated in most cancer types, could represent key therapeutic targets also for ES. Here, we challenged ES cell lines with a recently developed selective SFK inhibitor (a pyrazolo[3,4-d]pyrimidine derivative, called SI221), which was previously shown to be a valuable proapoptotic agent in other tumor types while not affecting normal cells. We observed that SI221 significantly reduced ES cell viability and proved to be more effective than the well-known SFK inhibitor PP2. SI221 was able to induce apoptosis in ES cells and also reduced ES cell clonogenic potential. Furthermore, SI221 was also able to reduce ES cell migration. At the molecular level, our data suggest that SFK inhibition through SI221 could reduce ES cell viability at least in part by hindering an SFK-NOTCH1 receptor-p38 mitogen-activated protein kinase (MAPK) axis. Overall, our study suggests a potential application of specific SFK inhibition in ES therapy. J. Cell. Physiol. 232: 129-135, 2017. © 2016 Wiley Periodicals, Inc.

Abstract LB-080: Reactivating RBL2/p130 oncosuppressive function as a new, possible antitumoral strategy

Deregulation of cell cycle control is the leading cause of cancer. The retinoblastoma (Rb) family members, including RB1/p105, RBL1/p107 and RBL2/p130, are crucial to restrain cell cycle progression and their inactivation, either direct or indirect, is a hallmark of most human tumors. In particular, RBL2/p130 emerging role in senescence and apoptosis, seems to contribute importantly to its tumor suppressor function. Furthermore, many studies largely contributed to establish RBL2/p130 as an important cancer target, which is inactivated by cell cycle kinases and whose deregulation underlies various cancer types. In this regard, we set out to restore RBL2/p130 function in tumors and exploit its tumor suppressive potential for cancer therapy. In particular, we have identified, through computational chemistry and molecular modeling studies, a small molecule able to act as a specific inhibitor of the CDK2-CycA complex and to reactivate the tumor suppressive function of RBL2/p130 in cancer.

We analyzed by MTS assay the cytotoxic effect of our compound on a panel of different tumor cell lines and determined its IC50 values. We evaluated its effects on cell cycle and apoptosis by FACS and dissected its molecular mechanism of action by Western blot and RT-PCR.

We found that our compound effectively inhibited proliferation of lung cancer and mesothelioma cell lines by specifically inhibiting CDK2-CycA activity towards RBL2/p130. The decrease in RBL2/p130 phosphorylation led to stabilization of its complex with the E2F4 transcriptional factor and consequent repression of their targets necessary for cell cycle progression, including CDK2 itself. Consistently, our compound arrested cell cycle and triggered apoptosis. Interestingly, apoptosis seemed to be mediated by RBL2/p130 itself because it was repressed in RBL2/p130-silenced cells. Furthermore, our compound proved to be active in an A549 xenograft model of lung cancer.

Overall our findings indicate that the pharmacological reactivation of RBL2/p130 induces its cell-cycle restraining and pro-apoptotic functions, the latter being still largely unexplored, and identify a new possible therapeutic strategy for cancer treatment.

Citation Format: Francesca Pentimalli, Luca Esposito, Iris Maria Forte, Carmelina Antonella Iannuzzi, Flavio Rizzolio, Tiziano Tuccinardi, Paola Indovina, Silvia Boffo, Antonio Giordano. Reactivating RBL2/p130 oncosuppressive function as a new, possible antitumoral strategy. [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 LB-080. doi:10.1158/1538-7445.AM2015-LB-080

p53 status as effect modifier of the association between pre-treatment fasting glucose and breast cancer outcomes in non diabetic, HER2 positive patients treated with trastuzumab

Mounting evidence supports the role of p53 in metabolic processes involved in breast carcinogenesis. We investigated whether p53 status affects the association of pre-treatment fasting glucose with treatment outcomes in 106 non diabetic, HER2 positive breast cancer patients treated with trastuzumab. p53 status was validated against gene sequencing of selected codons in 49 patients. The Kaplan-Meier method and log rank test were used to compare survival by categories of fasting glucose in the overall population and separate settings. Cox models included age and body mass index. Direct sequencing confirmed the lack of mutations in 73.7% of p53 negative patients and their presence in 53.3% of p53 positive cases. At 66 months, 88.3% of patients with glucose ≤ 89.0 mg/dl (median value) did not experiment disease progression compared with 70.0% in the highest category (p=0.034), with glucose being an independent predictor (p=0.046). Stratified analysis confirmed this association in p53 negative patients only (p=0.01). In the early setting, data suggested longer disease free survival in p53 negative patients in the lowest glucose category (p=0.053). In our study, p53 status acted as effect modifier of the investigated association. This may help differentiate target sub-groups and affect outcomes interpretation in similarly characterized patients.

Pharmacological targeting of p53 through RITA is an effective antitumoral strategy for malignant pleural mesothelioma

Malignant mesothelioma, a very aggressive tumor associated to asbestos exposure, is expected to increase in incidence, and unfortunately, no curative modality exists. Reactivation of p53 is a new attractive antitumoral strategy. p53 is rarely mutated in mesothelioma, but it is inactivated in most tumors by the lack of p14(ARF). Here, we evaluated the feasibility of this approach in pleural mesothelioma by testing RITA and nutlin-3, two molecules able to restore p53 function through a different mechanism, on a panel of mesothelioma cell lines representing the epithelioid (NCI-H28, NCI-H2452, IST-MES 2), biphasic (MSTO-211H), and sarcomatoid (NCI-H2052) histotypes compared with the normal mesothelial HMC-hTERT. RITA triggered robust caspase-dependent apoptosis specifically in epithelioid and biphasic mesothelioma cell lines, both through wild-type and mutant p53, concomitant to p21 downregulation. Conversely, nutlin-3 induced a p21-dependent growth arrest, rather than apoptosis, and was slightly toxic on HMC-hTERT.   Interestingly, we identified a previously undetected point mutation of p53 (p.Arg249Ser) in IST-MES 2, and showed that RITA is also able to reactivate this p53 mutant protein and its apoptotic function. RITA reduced tumor growth in a MSTO-211H-derived xenograft model of mesothelioma and synergized with cisplatin, which is the mainstay of treatment for this tumor. Our data indicate that reactivation of p53 and concomitant p21 downregulation effectively induce cell death in mesothelioma, a tumor characterized by a high intrinsic resistance to apoptosis. Altogether, our findings provide the preclinical framework supporting the use of p53-reactivating agents alone, or in combination regimens, to improve the outcome of patients with mesothelioma.