Analysis of transcriptomic responses to SARS-CoV-2 reveals plausible defective pathways responsible for increased susceptibility to infection and complications and helps to develop fast-track repositioning of drugs against COVID-19

Background

To understand the transcriptomic response to SARS-CoV-2 infection, is of the utmost importance to design diagnostic tools predicting the severity of the infection.

Methods

We have performed a deep sampling analysis of the viral transcriptomic data oriented towards drug repositioning. Using different samplers, the basic principle of this methodology the biological invariance, which means that the pathways altered by the disease, should be independent on the algorithm used to unravel them.

Results

The transcriptomic analysis of the altered pathways, reveals a distinctive inflammatory response and potential side effects of infection. The virus replication causes, in some cases, acute respiratory distress syndrome in the lungs, and affects other organs such as heart, brain, and kidneys. Therefore, the repositioned drugs to fight COVID-19 should, not only target the interferon signalling pathway and the control of the inflammation, but also the altered genetic pathways related to the side effects of infection. We also show via Principal Component Analysis that the transcriptome signatures are different from influenza and RSV. The gene COL1A1, which controls collagen production, seems to play a key/vital role in the regulation of the immune system. Additionally, other small-scale signature genes appear to be involved in the development of other COVID-19 comorbidities.

Conclusions

Transcriptome-based drug repositioning offers possible fast-track antiviral therapy for COVID-19 patients. It calls for additional clinical studies using FDA approved drugs for patients with increased susceptibility to infection and with serious medical complications.

Artificial intelligence: a disruptive tool for a smarter medicine

OBJECTIVE

Although highly successful, the medical R&D model is failing at improving people's health due to a series of flaws and defects inherent to the model itself. A new collective intelligence, incorporating human and artificial intelligence (AI) could overcome these obstacles. Because AI will play a key role in this new collective intelligence, it is necessary that those involved in healthcare have a general knowledge of how these technologies work. With this comprehensive review, we intend to provide it.

MATERIALS AND METHODS

A broad-ranging search has been undertaken on institutional and non-institutional websites in order to identify relevant papers, comments and reports.

RESULTS

We firstly describe the flaws and defects of the current R&D biomedical model and how the generation of a new collective intelligence will result in a better and wiser medicine through a truly personalized and holistic approach. We, then, discuss the new forms of data collection and data processing and the different types of artificial learning and their specific algorithms. Finally, we review the current uses and applications of AI in the biomedical field and how these can be expanded, as well as the limitations and challenges of applying these new technologies in the medical field.

CONCLUSIONS

This colossal common effort based on a new collective intelligence will exponentially improve the quality of medical research, resulting in a radical change for the better in the healthcare model. AI, without replacing us, is here to help us achieve the ambitious goal set by the WHO in the Alma Ata declaration of 1978: "Health for All".

Deep Neural Frameworks Improve the Accuracy of General Practitioners in the Classification of Pigmented Skin Lesions

This study evaluated whether deep learning frameworks trained in large datasets can help non-dermatologist physicians improve their accuracy in categorizing the seven most common pigmented skin lesions. Open-source skin images were downloaded from the International Skin Imaging Collaboration (ISIC) archive. Different deep neural networks (DNNs) (n = 8) were trained based on a random dataset constituted of 8015 images. A test set of 2003 images was used to assess the classifiers' performance at low (300 × 224 RGB) and high (600 × 450 RGB) image resolution and aggregated data (age, sex and lesion localization). We also organized two different contests to compare the DNN performance to that of general practitioners by means of unassisted image observation. Both at low and high image resolution, the DNN framework differentiated dermatological images with appreciable performance. In all cases, the accuracy was improved when adding clinical data to the framework. Finally, the least accurate DNN outperformed general practitioners. The physician's accuracy was statistically improved when allowed to use the output of this algorithmic framework as guidance. DNNs are proven to be high performers as skin lesion classifiers and can improve general practitioner diagnosis accuracy in a routine clinical scenario.

Why we do what we do. A brief analysis of cancer therapies

The goal of all medical activity is to preserve health in fit people, and to restore the sick into a state of complete physical, mental and social wellbeing. In an effort to determine whether we are achieving this last goal in oncology, herein we review the biological and clinical framework that has led to the foundations of the current anticancer treatment paradigm. Currently, cancer therapy is still based on the ancient axiom that states that the complete eradication of the tumor burden is the only way to achieve a cure. This strategy has led to a substantial improvement in survival rates as cancer mortality rates have dropped in an unprecedented way. Despite this progress, more than 9 million people still die from cancer every year, indicating that the current treatment strategy is not leading to a cancer cure, but to a cancer remission, that is "the temporary absence of manifestations of a particular disease"; after months or years of remission, in most patients, cancer will inevitably recur. Our critical analysis indicates that it is time to discuss about the new key challenges and future directions in clinical oncology. We need to generate novel treatment strategies more suited to the current clinical reality.

Lessons from Hippocrates: Time to Change the Cancer Paradigm

The ultimate goal of all medical activity is to restore patients to a state of complete physical, mental, and social wellbeing. In cancer, it is assumed that this can only be obtained through the complete eradication of the tumor burden. So far, this strategy has led to a substantial improvement in cancer survival rates. Despite this, more than 9 million people die from cancer every year. Therefore, we need to accept that our current cancer treatment paradigm is obsolete and must be changed. The new paradigm should reflect that cancer is a systemic disease, which affects an individual patient living in a particular social reality, rather than an invading organism or a mere cluster of mutated cells that need to be eradicated. This Hippocratic holistic view will ultimately lead to an improvement in health and wellbeing in cancer patients. They deserve nothing less.

The Antitumor Drugs Trabectedin and Lurbinectedin Induce Transcription-Dependent Replication Stress and Genome Instability

R-loops are a major source of replication stress, DNA damage, and genome instability, which are major hallmarks of cancer cells. Accordingly, growing evidence suggests that R-loops may also be related to cancer. Here we show that R-loops play an important role in the cellular response to trabectedin (ET743), an anticancer drug from marine origin and its derivative lurbinectedin (PM01183). Trabectedin and lurbinectedin induced RNA-DNA hybrid-dependent DNA damage in HeLa cells, causing replication impairment and genome instability. We also show that high levels of R-loops increase cell sensitivity to trabectedin. In addition, trabectedin led to transcription-dependent FANCD2 foci accumulation, which was suppressed by RNase H1 overexpression. In yeast, trabectedin and lurbinectedin increased the presence of Rad52 foci, a marker of DNA damage, in an R-loop-dependent manner. In addition to providing new insights into the mechanisms of action of these drugs, our study reveals that R-loops could be targeted by anticancer agents. Given the increasing evidence that R-loops occur all over the genome, the ability of lurbinectedin and trabectedin to act on them may contribute to enhance their efficacy, opening the possibility that R-loops might be a feature shared by specific cancers. IMPLICATIONS: The data presented in this study provide the new concept that R-loops are important cellular factors that contribute to trabectedin and lurbinectedin anticancer activity.

Multicenter Phase II Study of Lurbinectedin in BRCA-Mutated and Unselected Metastatic Advanced Breast Cancer and Biomarker Assessment Substudy

PURPOSE

This multicenter phase II trial evaluated lurbinectedin (PM01183), a selective inhibitor of active transcription of protein-coding genes, in patients with metastatic breast cancer. A unicenter translational substudy assessed potential mechanisms of lurbinectedin resistance.

PATIENTS AND METHODS

Two arms were evaluated according to germline BRCA1/2 status: BRCA1/2 mutated (arm A; n = 54) and unselected ( BRCA1/2 wild-type or unknown status; arm B; n = 35). Lurbinectedin starting dose was a 7-mg flat dose and later, 3.5 mg/m² in arm A. The primary end point was objective response rate (ORR) per Response Evaluation Criteria in Solid Tumors (RECIST). The translational substudy of resistance mechanisms included exome sequencing (n = 13) and in vivo experiments with patient-derived xenografts (n = 11) from BRCA1/2-mutated tumors.

RESULTS

ORR was 41% (95% CI, 28% to 55%) in arm A and 9% (95% CI, 2% to 24%) in arm B. In arm A, median progression-free survival was 4.6 months (95% CI, 3.0 to 6.0 months), and median overall survival was 20.0 months (95% CI, 11.8 to 26.6 months). Patients with BRCA2 mutations showed an ORR of 61%, median progression-free survival of 5.9 months, and median overall survival of 26.6 months. The safety profile improved with lurbinectedin dose adjustment to body surface area. The most common nonhematologic adverse events seen at 3.5 mg/m² were nausea (74%; grade 3, 5%) and fatigue (74%; grade 3, 21%). Neutropenia was the most common severe hematologic adverse event (grade 3, 47%; grade 4, 10%). Exome sequencing showed mutations in genes related to the nucleotide excision repair pathway in four of seven tumors at primary or acquired resistance and in one patient with short-term stable disease. In vivo, sensitivity to cisplatin and lurbinectedin was evidenced in lurbinectedin-resistant (one of two) and cisplatin-resistant (two of three) patient-derived xenografts.

CONCLUSION

Lurbinectedin showed noteworthy activity in patients with BRCA1/2 mutations. Response and survival was notable in those with BRCA2 mutations. Additional clinical development in this subset of patients with metastatic breast cancer is warranted.

ATLANTIS: a Phase III study of lurbinectedin/doxorubicin versus topotecan or cyclophosphamide/doxorubicin/vincristine in patients with small-cell lung cancer who have failed one prior platinum-containing line

Lurbinectedin is an inhibitor of active transcription of protein-coding genes, causing DNA-break accumulation, apoptosis and modulation of the tumor microenvironment. Early-phase clinical trials indicate promising activity of lurbinectedin in small-cell lung cancer. Here, we describe the rationale and design of ATLANTIS (NCT02566993), an open-label, randomized, multicenter Phase III study to compare the efficacy of lurbinectedin and doxorubicin combination with standard-of-care chemotherapy, investigator's choice of cyclophosphamide/doxorubicin/vincristine or topotecan, in patients with small-cell lung cancer that has progressed following one line of platinum-based chemotherapy. Patients are randomized in a 1:1 ratio. The primary end point is overall survival and key secondary end points include progression-free survival, best tumor response and duration of response, each assessed by independent review committee.

Multicenter Phase II Study of Lurbinectedin in BRCA-Mutated and Unselected Metastatic Advanced Breast Cancer and Biomarker Assessment Substudy

Purpose

This multicenter phase II trial evaluated lurbinectedin (PM01183), a selective inhibitor of active transcription of protein-coding genes, in patients with metastatic breast cancer. A unicenter translational substudy assessed potential mechanisms of lurbinectedin resistance.

Patients and Methods

Two arms were evaluated according to germline BRCA1/2 status: BRCA1/2 mutated (arm A; n = 54) and unselected (BRCA1/2 wild-type or unknown status; arm B; n = 35). Lurbinectedin starting dose was a 7-mg flat dose and later, 3.5 mg/m² in arm A. The primary end point was objective response rate (ORR) per Response Evaluation Criteria in Solid Tumors (RECIST). The translational substudy of resistance mechanisms included exome sequencing (n = 13) and in vivo experiments with patient-derived xenografts (n = 11) from BRCA1/2-mutated tumors.

Results

ORR was 41% (95% CI, 28% to 55%) in arm A and 9% (95% CI, 2% to 24%) in arm B. In arm A, median progression-free survival was 4.6 months (95% CI, 3.0 to 6.0 months), and median overall survival was 20.0 months (95% CI, 11.8 to 26.6 months). Patients with BRCA2 mutations showed an ORR of 61%, median progression-free survival of 5.9 months, and median overall survival of 26.6 months. The safety profile improved with lurbinectedin dose adjustment to body surface area. The most common nonhematologic adverse events seen at 3.5 mg/m² were nausea (74%; grade 3, 5%) and fatigue (74%; grade 3, 21%). Neutropenia was the most common severe hematologic adverse event (grade 3, 47%; grade 4, 10%). Exome sequencing showed mutations in genes related to the nucleotide excision repair pathway in four of seven tumors at primary or acquired resistance and in one patient with short-term stable disease. In vivo, sensitivity to cisplatin and lurbinectedin was evidenced in lurbinectedin-resistant (one of two) and cisplatin-resistant (two of three) patient-derived xenografts.

Conclusion

Lurbinectedin showed noteworthy activity in patients with BRCA1/2 mutations. Response and survival was notable in those with BRCA2 mutations. Additional clinical development in this subset of patients with metastatic breast cancer is warranted.

Abstract 2906: eEF1A2 interacts with and inhibits PKR to enhance cancer cell survival

Human translation elongation factor 1α2, encoded by the eEF1A2 gene, is a pro-oncogenic protein absent from the majority of body tissues (with exception of brain, heart and skeletal muscle1), but expressed in many cancers1-3, where it provides tumor cells with improved fitness and survival. Though its canonical function is delivering aminoacyl-tRNAs to the ribosome, other “moonlighting” functions such as enhancing sphingosine kinase4,5 or antioxidant (most probably through peroxiredoxin-1 stimulation) activities6 have been described for the elongation factor. Recently, we have reported that eEF1A2 is the target for plitidepsin, a marine-derived cyclic depsipeptide currently under development for the treatment of relapsed or refractory multiple myeloma patients7. We have also confirmed that eEF1A2 interacted with previously described partners as PRDX1 and SPHK and enhanced their pro-survival activities8. Here we investigated the role of new “moonlighting functions” of eEF1A2 in the maintenance of the tumor phenotype and survival of cancer cells. Through co-immunoprecipitation and HPLC/MS we have uncovered the interaction between eEF1A2 and dsRNA-activated protein kinase (PKR, EIF2AK2). We have analyzed the kinase activity of PKR in the presence of eEF1A2, demonstrating that PKR activity is inhibited when complexed with eEF1A2. This complex is disrupted after plitidepsin binding to eEF1A2, rendering PKR active. Once activated, the kinase triggers a MAPK cascade and the NF-κB signaling pathway, leading to the activation of the extrinsic apoptotic pathway and the death of the tumor cell. Taken together, these results show that the fitness boost that the moonlighting functions of eEF1A2 provide to cancer cells, which are important for their growth and survival, constitutes an Achilles heel that can be purposely exploited in anticancer therapy. 1 Abbas, W., Kumar, A. & Herbein, G. Front Oncol 5, 75 (2015). 2 Anand, N. et al. Nature genetics 31, 301-305 (2002). 3 Li, Z. et al. PloS one 5, e10755 (2010). 4 Leclercq, T. M., Moretti, P. A., Vadas, M. A. & Pitson, S. M. J Biol Chem 283, 9606-9614 (2008). 5 Leclercq, T. M., Moretti, P. A. & Pitson, S. M. Oncogene 30, 372-378 (2011). 6 Chang, R. & Wang, E. J Cell Biochem 100, 267-278 (2007). 7 Losada, A. et al. Sci Rep 6, 35100 (2016) 8 Losada, A. et al. Abstract #1165, AACR Annual Meeting (2017)

Citation Format: Juan F. Martínez-Leal, Alejandro Losada, Maria Jose Muñoz, Marta Martinez-Diez, Juan Manuel Dominguez, Carlos M. Galmarini. eEF1A2 interacts with and inhibits PKR to enhance cancer cell survival [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 2906.

MI130004, a Novel Antibody-Drug Conjugate Combining Trastuzumab with a Molecule of Marine Origin, Shows Outstanding In Vivo Activity against HER2-Expressing Tumors

In the search for novel payloads to design new antibody-drug conjugates (ADC), marine compounds represent an interesting opportunity given their unique chemical features. PM050489 is a marine compound that binds β-tubulin at a new site and disrupts the microtubule network, hence leading to mitotic aberrations and cell death. PM050489 has been conjugated to trastuzumab via Cys residues through a noncleavable linker, and the resulting ADC, named MI130004, has been studied. Analysis of MI130004 delivered data consistent with the presence of two molecules of PM050489 per antibody molecule, likely bound to both sides of the intermolecular disulfide bond connecting the antibody light and heavy chains. The antitumor activity of MI130004 was analyzed in vitro and in vivo in different cell lines of diverse tumor origin (breast, ovary, and gastric cancer) expressing different levels of HER2. MI130004 showed very high in vitro potency and good selectivity for tumor cells that overexpressed HER2. At the cellular level, MI130004 impaired tubulin polymerization, causing disorganization and disintegration of the microtubule network, which ultimately led to mitotic failure, mirroring the effect of its payload. Treatment with MI130004 in mice carrying histologically diverse tumors expressing HER2 induced a long-lasting antitumor effect with statistically significant inhibition of tumor growth coupled with increases in median survival time compared with vehicle or trastuzumab. These results strongly suggest that MI130004 is endowed with remarkable anticancer activity and confirm the extraordinary potential of marine compounds for the design of new ADCs. Mol Cancer Ther; 17(4); 786-94. ©2018 AACR.

Plocabulin, a novel tubulin-binding agent, inhibits angiogenesis by modulation of microtubule dynamics in endothelial cells

BACKGROUND

Vascular supply of tumors is one of the main targets for cancer therapy. Here, we investigated if plocabulin (PM060184), a novel marine-derived microtubule-binding agent, presents antiangiogenic and vascular-disrupting activities.

METHODS

The effects of plocabulin on microtubule network and dynamics were studied on HUVEC endothelial cells. We have also studied its effects on capillary tube structures formation or destabilization in three-dimensional collagen matrices. In vivo experiments were performed on different tumor cell lines.

RESULTS

In vitro studies show that, at picomolar concentrations, plocabulin inhibits microtubule dynamics in endothelial cells. This subsequently disturbs the microtubule network inducing changes in endothelial cell morphology and causing the collapse of angiogenic vessels, or the suppression of the angiogenic process by inhibiting the migration and invasion abilities of endothelial cells. This rapid collapse of the endothelial tubular network in vitro occurs in a concentration-dependent manner and is observed at concentrations lower than that affecting cell survival. The in vitro findings were confirmed in tumor xenografts where plocabulin treatment induced a large reduction in vascular volume and induction of extensive necrosis in tumors, consistent with antivascular effects.

CONCLUSIONS

Altogether, these data suggest that an antivascular mechanism is contributing to the antitumor activities of plocabulin.

Phase II randomized study of PM01183 versus topotecan in patients with platinum-resistant/refractory advanced ovarian cancer

Background

PM01183 is a new compound that blocks active transcription, produces DNA breaks and apoptosis, and affects the inflammatory microenvironment. PM01183 showed strong antitumor activity in preclinical models of cisplatin-resistant epithelial ovarian cancer.

Patients and methods

Patients with platinum-resistant/refractory ovarian cancer were included in a two-stage, controlled, randomized (in a second stage), multicenter, phase II study. Primary endpoint was overall response rate (ORR) by RECIST and/or GCIG criteria. The exploratory first stage (n = 22) confirmed the activity of PM01183 as a single agent at 7.0 mg flat dose every 3 weeks (q3wk). The second stage (n = 59) was randomized and controlled with topotecan on days 1-5 q3wk or weekly (every 4 weeks, q4wk).

Results

ORR was 23% (95% CI, 13%-37%) for 52 PM01183-treated patients. Median duration of response was 4.6 months (95% CI, 2.5-6.9 months), and 23% (95% CI, 0%-51%) of responses lasted 6 months or more. Ten of the 12 confirmed responses were reported for 33 patients with platinum-resistant disease [ORR = 30% (95% CI, 16%-49%)]; for the 29 patients treated with topotecan in the second stage, no responses were found. Median PFS for all PM01183-treated patients was 4.0 months (95% CI, 2.7-5.6 months), and 5.0 months (95% CI, 2.7-6.9 months) for patients with platinum-resistant disease. Grade 3/4 neutropenia in 85% of patients; febrile neutropenia in 21% and fatigue (grade 3 in 35%) were the principal safety findings for PM01183.

Conclusion

PM01183 is an active drug in platinum-resistant/refractory ovarian cancer and warrants further development. The highest activity was observed in platinum-resistant disease. Its safety profile indicates the dose should be adjusted to body surface area (mg/m2).

Trial code

EudraCT 2011-002172-16.

Dynamic cellular maps of molecular species: Application to drug-target interactions

The design of living cell studies aimed at deciphering the mechanism of action of drugs targeting proteins with multiple functions, expressed in a wide range of concentrations and cellular locations, is a real challenge. We recently showed that the antitumor drug plitidepsin (APL) localizes sufficiently close to the elongation factor eEF1A2 so as to suggest the formation of drug-protein complexes in living cells. Here we present an extension of our previous micro-spectroscopy study, that combines Generalized Polarization (GP) images, with the phasor approach and fluorescence lifetime imaging microscopy (FLIM), using a 7-aminocoumarin drug analog (APL*) as fluorescence tracer. Using the proposed methodology, we were able to follow in real time the formation and relative distribution of two sets of APL-target complexes in live cells, revealing two distinct patterns of behavior for HeLa-wt and APL resistant HeLa-APL-R cells. The information obtained may complement and facilitate the design of new experiments and the global interpretation of the results obtained with other biochemical and cell biology methods, as well as possibly opening new avenues of study to decipher the mechanism of action of new drugs.

Abstract B057: Plitidepsin inhibits autophagy, the main mechanism of acquired resistance to bortezomib

Background: Plitidepsin (APL), an antitumor agent isolated from the marine tunicate Aplidium albicans, has been tested with positive results in multiple myeloma (MM) patients in a phase III pivotal trial in combination with dexamethasone (clinicaltrials.gov identifier: NCT01102426) and in a phase I trial in combination with bortezomib and dexamethasone (clinicaltrials.gov identifier: NCT02100657). Plitidepsin targets eEF1A2, one of two isoforms of the alpha subunit of the eEF1 complex. In mammals, eEF1A2 has a selective pattern of expression in those tissues that do not express the A1 isoform, namely brain and muscle. Nonetheless, eEF1A2 is aberrantly expressed in many cancers, including solid tumors (1-3) and MM (4), and has been shown to hold oncogenic properties (5). We have previously demonstrated through several means the interaction of plitidepsin with its target, eEF1A2 and calculated a Kd of around 80 nM for this interaction (6). Indeed, we have found that plitidepsin exclusively binds to the GTP-bound form of eEF1A2 Aims: Here we investigated whether eEF1A2 levels had any effect on the sensitivity of MM cells to both plitidepsin and bortezomib, to better understand the synergistic effect these two drugs yield when combined (7). Methods: RPMI-8226, OPM1, U266-B1, MM1S and NCI-NH929 multiple myeloma cells were cultured in optimal conditions. eEF1A2 (GTX102326) and autophagy (L7543) were followed by Western blot. Dose-response experiments were performed in 96 well plates, treating cells with increasing doses of the compounds for 24 hours and measuring cell growth with MTT. Curves were then fitted with GraphPad Prism5 software. For combination experiments, the Chou-Talalay procedure was used. Results: We first analyzed the level of eEF1A2 protein in a panel of multiple myeloma cell lines. Then, we selected a cell line with low expression, MM-1S, and one with high expression, OPM-1, of the elongation factor and checked the sensitivity to both, bortezomib and plitidepsin through dose-response experiments. Interestingly, the overexpression of eEF1A2, the target of plitidepsin, seems to be related to an increased resistance to bortezomib, a phenomenon usually related to enhanced autophagy since this latter pathway compensates the inhibition of proteasome. eEF1A, in its GTP-bound form, has been shown to inhibit chaperone-mediated autophagy (CMA), essential for the degradation of unfolded proteins (8). Since plitidepsin binds to the GTP-bound eEF1A2, probably stabilizing this form of the elongation factor, it seems likely that, in such a way, it may inhibit CMA. We explored this possibility and, indeed, we observed that plitidepsin inhibited autophagy in MM cells. Summary/Conclusion: Plitidepsin treatment presumably counteracts the main mechanism of acquired resistance to bortezomib, namely autophagy. (1)Sun et al., 2014, Biochem Biophys Res Commun 450:1-6. (2)Xu et al., 2013, Clin Exp Metastasis 30:933-44. (3)Anand et al., 2002, Nat Genet 31:301-5. (4)Li et al., 2010, PLOS One 5, e10755. (5)Lee and Surh, 2009, Ann N Y Acad Sci 1171:87-93. (6)Losada et al., 2004, Br J Cancer 91:1405-13. (7)Mitsiades et al., 2008, Cancer Res 68:5216-25. (8)Bandyopadhyay et al., 2010, Mol Cel 39:535-47.

Citation Format: Juan F. Martínez-Leal, Gaëlle Quiniou, Alejandro Losada, María José Muñoz, Rafael Sanchez-Mesa, Patricia Martinez-Rivas, Juan Manuel Dominguez, Carlos M. Galmarini. Plitidepsin inhibits autophagy, the main mechanism of acquired resistance to bortezomib [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B057.

Lurbinectedin reduces tumour-associated macrophages and the inflammatory tumour microenvironment in preclinical models

Background:

Lurbinectedin is a novel anticancer agent currently undergoing late-stage (Phase II /III) clinical evaluation in platinum-resistant ovarian, BRCA1/2-mutated breast and small-cell lung cancer. Lurbinectedin is structurally related to trabectedin and it inhibits active transcription and the DNA repair machinery in tumour cells.

Methods:

In this study we investigated whether lurbinectedin has the ability to modulate the inflammatory microenvironment and the viability of myeloid cells in tumour-bearing mice.

Results:

Administration of lurbinectedin significantly and selectively decreased the number of circulating monocytes and, in tumour tissues, that of macrophages and vessels. Similar findings were observed when a lurbinectedin-resistant tumour variant was used, indicating a direct effect of lurbinectedin on the tumour microenviroment. In vitro, lurbinectedin induced caspase-8-dependent apoptosis of human purified monocytes, whereas at low doses it significantly inhibited the production of inflammatory/growth factors (CCL2, CXCL8 and VEGF) and dramatically impaired monocyte adhesion and migration ability. These findings were supported by the strong inhibition of genes of the Rho-GTPase family in lurbinectedin-treated monocytes.

Conclusions:

The results illustrate that lurbinectedin affects at multiple levels the inflammatory microenvironment by acting on the viability and functional activity of mononuclear phagocytes. These peculiar effects, combined with its intrinsic activity against cancer cells, make lurbinectedin a compound of particular interest in oncology.

Abstract 1211: Lurbinectedin reverses platinum dependent IRF1 overexpression and nuclear localization, partially responsible for resistance to platinum drugs in ovarian cancer

Lurbinectedin (PM1183) is a new synthetic compound from the tetrahydroisoquinoline family, which has demonstrated a strong antiproliferative activity against a panel of human tumor models in preclinical assays and is currently being evaluated in phase III clinical trials in platinum-resistant ovarian cancer and small cell lung cancer. Lurbinectedin binds to DNA, inhibits trans-activated transcription, induces the degradation of elongating RNA Pol II and fools nucleotide excision repair to produce dsDNA breaks that need to be repaired mainly by homologous recombination (HR)1,2. Nearly 70% of patients diagnosed with ovarian cancer are in advanced stage, and the vast majority of them will eventually relapse after a primary cytoreductive surgery and several cycles of standard adjuvant chemotherapy including a platinum drug and a taxane. After a period of treatment with platinum drugs, patients will finally develop resistance, usually mediated by mechanisms such as drug detoxification or efflux and enhanced DNA repair. IRF-1 transcription factor expression has been shown to be up-regulated by cisplatin (CDDP) in ovarian cancer cells and might be limiting the response to the drug, likely by inhibiting cell proliferation3. Here we took advantage of the A2780/A2780cis human ovarian cancer cell lines, the second being a cisplatin resistant derivative, to investigate the role of IRF1 in the response of human ovarian cancer cells to cisplatin and lurbinectedin. A2780cis cells are, indeed, more resistant to cisplatin that their parental cell line but they do not differ in their resistance to lurbinectedin. Basal IRF-1 protein levels were actually higher in A2780cis cells than in their parental cell line, contributing to their resistance to cisplatin. Furthermore, cisplatin treatment induced the overexpression and nuclear localization of IRF-1 both, in A2780 and A2780cis cell lines. Contrarily, lurbinectedin did not induce the overexpression of IRF-1 neither in A2780 nor in A2780cis, explaining why this latter cell line is not resistant to the compound. Furthermore, lurbinectedin co-treatment with cisplatin reduced the expression of IRF-1 in A2780 and, more importantly, in A2780cis cells, explaining the synergism the combination has on these tumor cell lines. Thus, lurbinectedin not only did not activate the same mechanisms of resistance as cisplatin in ovarian cancer cells, but even reversed the resistance of these resistant cells to platinum drugs. 1 Santamaría Nuñez et al, 2016. Mol Cancer Ther 15(10):2399-2412 2 Romano et al, 2013. Int J Cancer. 2013 Nov;133(9):2024-33 3 Pavan et al, 2013. Eur J Cancer 49(4):964-973

Citation Format: Gema Santamaria Nuñez, Maria Jose Guillén, Juan F. Martínez-Leal, Pablo Avilés, Carlos M. Galmarini. Lurbinectedin reverses platinum dependent IRF1 overexpression and nuclear localization, partially responsible for resistance to platinum drugs in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1211. doi:10.1158/1538-7445.AM2017-1211

Abstract 1165: Plitidepsin targets the moonlighting functions of eEF1A2 in cancer cells

Plitidepsin, a cyclic depsipeptide of marine origin, has shown potent anticancer activity in preclinical assays and recently finished with positive results a pivotal phase III trial (clinicaltrials.gov identifier: NCT01102426) for the treatment of multiple myeloma patients. We have recently found that eukaryotic elongation factor 1A2 (eEF1A2), one of the two isoforms of the alpha subunit of eEF1, is the pharmacological target of plitidepsin. Although it shares 96% homology with eEF1A1 (the other isoform), they display an exclusive pattern of expression, being eEF1A2 solely expressed in brain and muscle in healthy individuals. However, it has been found that many tumors abnormally overexpress this protein, including multiple myeloma, prostate, pancreatic, ovarian, breast, lung and liver cancers. Furthermore, although eEF1A2 canonical function consists in the delivery of aminoacyl-tRNAs to the A site in the ribosome, it has been shown to have pro-oncogenic moonlighting activities, including inhibition of apoptosis, protein degradation by the proteasome, heat shock response, cytoskeleton organization and regulation of oxidative stress. We now investigated several of the pro-oncogenic activities of eEF1A2 to analyze the impact that plitidepsin could have preventing them. Indeed, we observed that plitidepsin interfered with the interaction between eEF1A2 and Peroxiredoxin 1 (PRDX1), a complex that allosterically enhances the enzymatic activity of PRDX1. This way, plitidepsin would diminish PRDX1 antioxidant activity, possibly originating the oxidative stress that has been described in the bibliography as one of the first effects triggered by the drug in cancer cells. PRDX1 only interacts with the GDP-bound form of eEF1A2, while plitidepsin exclusively binds to the GTP-bound form, most probably sequestering this protein from the pool that could interact with and activate PRDX1. Furthermore, we have confirmed that eEF1A2 interacts with Sphingosine kinase 1 (SPHK1), a complex that has been described in the bibliography as having enhanced SPHK1 activity. SPHK1 phosphorylates sphingosine producing sphingosine-1-P, second messenger that binds to its receptors in the cell membrane and conveys growth and survival signals to the cell. We could see that plitidepsin treatment reduced the production of sphingosine-1-P in HeLa cells, destabilizing the equilibrium towards the pro-apoptotic ceramide/sphingosine side and promoting cell death. Thus, through its binding to eEF1A2, plitidepsin derails a series of its moonlighting functions that are essential for the survival of tumor cells, driving them into apoptosis.

Citation Format: Alejandro Losada, Maria Jose Muñoz, Juan F. Martínez-Leal, Juan M. Domínguez, Carlos M. Galmarini. Plitidepsin targets the moonlighting functions of eEF1A2 in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1165. doi:10.1158/1538-7445.AM2017-1165

Mechanism of action of trabectedin in desmoplastic small round cell tumor cells

Background

Desmoplastic small round cell tumor (DSRCT) is a rare and highly aggressive disease, that can be described as a member of the family of small round blue cell tumors. The molecular diagnostic marker is the t(11;22)(p13;q12) translocation, which creates an aberrant transcription factor, EWS-WT1, that underlies the oncogenesis of DSRCT. Current treatments are not very effective so new active drugs are needed. Trabectedin, now used as a single agent for the treatment of soft tissue sarcoma, was reported to be active in some pre-treated DSRCT patients. Using JN-DSRCT-1, a cell line derived from DSRCT expressing the EWS-WT1 fusion protein, we investigated the ability of trabectedin to modify the function of the chimeric protein, as in other sarcomas expressing fusion proteins. After detailed characterization of the EWS-WT1 transcripts structure, we investigated the mode of action of trabectedin, looking at the expression and function of the oncogenic chimera.

Methods

We characterized JN-DSRCT-1 cells using cellular approaches (FISH, Clonogenicity assay) and molecular approaches (Sanger sequencing, ChIP, GEP).

Results

JN-DSRCT-1 cells were sensitive to trabectedin at nanomolar concentrations. The cell line expresses different variants of EWS-WT1, some already identified in patients. EWS-WT1 mRNA expression was affected by trabectedin and chimeric protein binding on its target gene promoters was reduced. Expression profiling indicated that trabectedin affects the expression of genes involved in cell proliferation and apoptosis.

Conclusions

The JN-DSRCT-1 cell line, in vitro, is sensitive to trabectedin: after drug exposure, EWS-WT1 chimera expression decreases as well as binding on its target promoters. Probably the heterogeneity of chimera transcripts is an obstacle to precisely defining the molecular mode of action of drugs, calling for further cellular models of DSRCT, possibly growing in vivo too, to mimic the biological complexity of this disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3091-1) contains supplementary material, which is available to authorized users.

Antitumour activity of trabectedin in myelodysplastic/myeloproliferative neoplasms

BACKGROUND

Juvenile myelomonocytic leukaemia (JMML) and chronic myelomonocytic leukaemia (CMML) are myelodysplastic myeloproliferative (MDS/MPN) neoplasms with unfavourable prognosis and without effective chemotherapy treatment. Trabectedin is a DNA minor groove binder acting as a modulator of transcription and interfering with DNA repair mechanisms; it causes selective depletion of cells of the myelomonocytic lineage. We hypothesised that trabectedin might have an antitumour effect on MDS/MPN.

METHODS

Malignant CD14+ monocytes and CD34+ haematopoietic progenitor cells were isolated from peripheral blood/bone marrow mononuclear cells. The inhibition of CFU-GM colonies and the apoptotic effect on CD14+ and CD34+ induced by trabectedin were evaluated. Trabectedin's effects were also investigated in vitro on THP-1, and in vitro and in vivo on MV-4-11 cell lines.

RESULTS

On CMML/JMML cells, obtained from 20 patients with CMML and 13 patients with JMML, trabectedin - at concentration pharmacologically reasonable, 1-5 nM - strongly induced apoptosis and inhibition of growth of haematopoietic progenitors (CFU-GM). In these leukaemic cells, trabectedin downregulated the expression of genes belonging to the Rho GTPases pathway (RAS superfamily) having a critical role in cell growth and cytoskeletal dynamics. Its selective activity on myelomonocytic malignant cells was confirmed also on in vitro THP-1 cell line and on in vitro and in vivo MV-4-11 cell line models.

CONCLUSIONS

Trabectedin could be good candidate for clinical studies in JMML/CMML patients.

Translation Elongation Factor eEF1A2 is a Novel Anticancer Target for the Marine Natural Product Plitidepsin

eEF1A2 is one of the isoforms of the alpha subunit of the eukaryotic Elongation Factor 1. It is overexpressed in human tumors and is endowed with oncogenic properties, favoring tumor cell proliferation while inhibiting apoptosis. We demonstrate that plitidepsin, an antitumor agent of marine origin that has successfully completed a phase-III clinical trial for multiple myeloma, exerts its antitumor activity by targeting eEF1A2. The drug interacts with eEF1A2 with a K_D of 80 nM and a target residence time of circa 9 min. This protein was also identified as capable of binding [¹⁴C]-plitidepsin in a cell lysate from K-562 tumor cells. A molecular modelling approach was used to identify a favorable binding site for plitidepsin at the interface between domains 1 and 2 of eEF1A2 in the GTP conformation. Three tumor cell lines selected for at least 100-fold more resistance to plitidepsin than their respective parental cells showed reduced levels of eEF1A2 protein. Ectopic expression of eEF1A2 in resistant cells restored the sensitivity to plitidepsin. FLIM-phasor FRET experiments demonstrated that plitidepsin localizes in tumor cells sufficiently close to eEF1A2 as to suggest the formation of drug-protein complexes in living cells. Altogether, our results strongly suggest that eEF1A2 is the primary target of plitidepsin.

Abstract 3039: Lurbinectedin specifically targets transcription in cancer cells, triggering DNA breaks and degradation of phosphorylated Pol II

Cancer cells are characterized for their avid demand for active transcription, which reaches the level of a real addiction in solid tumors as small cell lung cancer (SCLC) or triple-negative breast cancer. Pharmacological modulation of transcription may thus provide a therapeutic approach to treat tumor types that depend on deregulated transcription for the maintenance of their oncogenic state. Lurbinectedin, currently under evaluation in a Phase III clinical trial for platinum-resistant ovarian cancer patients, and with very promising activity in combination with doxorubicin in SCLC, inhibits active transcription. Here we demonstrate that, after binding to specific DNA triplets highly represented in the CG-rich region surrounding the promoter of genes, this drug induces a rapid degradation of RNA Polymerase II (Pol II). Our results show that the hyperphosphorylated form of Pol II, already engaged in transcription elongation and likely blocked during this process by the lurbinectedin-DNA adduct, is then specifically submitted to the ubiquitin/proteasome degradation process, which finally removes the majority of the Pol II protein pool in treated cells. Disappearance of Pol II is followed by the formation of DNA breaks, process in which the nucleotide excision repair (NER) machinery, specifically the endonuclease XPF, has an important role. Pol II degradation and subsequent DNA damage were not only abrogated by inhibitors of CDK7 and CDK9 cyclin dependent kinases (DRB and flavopyridol), ubiquitin ligation (PYR-41), or proteasome activity (MG132), but also correlated with the antiproliferative activity of lurbinectedin in different cancer cell line models. In summary, lurbinectedin exemplifies a prototype drug for targeting transcriptional dependency in tumor cells and, thus, it could represent a new therapeutic alternative for solid tumors with this addiction.

Citation Format: Gema Santamaria-Nunez, Carlos M. Genes-Robles, Juan F. Martínez-Leal, Carlos M. Galmarini, Jean Marc Egly. Lurbinectedin specifically targets transcription in cancer cells, triggering DNA breaks and degradation of phosphorylated Pol II. [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 3039.

Abstract 3015: Plitidepsin targets the GTP-bound form of eEF1A2 in cancer cells

Plitidepsin (APL), an antitumor agent originally isolated from the marine tunicate Aplidium albicans, is being tested in multiple myeloma (MM) patients in a phase III pivotal trial in combination with dexamethasone and a phase I trial in combination with bortezomib and dexamethasone. eEF1A2 is one of two isoforms of the alpha subunit of the eEF1 complex. In mammals, eEF1A2 has a selective pattern of expression in those tissues that do not express the A1 isoform, namely brain and muscle. Nonetheless, eEF1A2 is aberrantly expressed in many cancers, including solid tumors (1-3) and MM (4), and has been shown to hold pro-oncogenic activities (5). Here we analyze the interaction of plitidepsin with its target, eEF1A2. DARTS assays, either with whole cell extracts or with purified eEF1A2 protein, indicate that plitidepsin binds to eEF1A2 and protects it from digestion by subtilisin (EC 3.4.21.62). Moreover, a [14C]-APL binding-guided fractionation of K562 cell extracts through differential centrifugation and three chromatographic steps demonstrated that eEF1A2 is the only cellular protein that can be retrieved through specific binding to plitidepsin. A saturation binding experiment with [14C]-APL and purified GTP-bound eEF1A2 (from rabbit muscle) allowed us to calculate a Kd of around 80 nM for the interaction, while a dissociation experiment revealed a residence time of around 9 minutes. Indeed, we have found that plitidepsin exclusively binds to the GTP-bound form of eEF1A2. HeLa-APL-R cells, ≥1000 fold more resistant to plitidepsin than parental HeLa wt cells (6), are now shown to have lower eEF1A2 mRNA and protein levels than parental cells. Furthermore, when eEF1A2 levels were restored to normal in HeLa-APL-R cells through ectopic expression of an eEF1A2-GFP construct, they were rendered partially sensitive to plitidepsin. Interestingly, transfected cells recovered most of the signaling events typically induced by the drug in HeLa wt cells. NCI-H460 (lung) and HGC-27 (stomach) cancer cell lines were rendered resistant to plitidepsin following the same procedure described in (6) for HeLa-APL-R cells. When we analyzed the levels of eEF1A2 in this two new cell lines we observed that both of them were lacking eEF1A2. Altogether, our results demonstrate that plitidepsin targets the pro-oncogenic eEF1A2 protein, a new druggable target for anticancer therapy.

(1)Sun et al, 2014, Biochem Biophys Res Commun 450:1-6

(2)Xu et al, 2013, Clin Exp Metastasis 30:933-44

(3)Anand et al, 2002, Nat Genet 31:301-5

(4)Li et al, 2010, PLOS One 5, e10755

(5)Lee and Surh, 2009, Ann N Y Acad Sci 1171:87-93

(6)Losada et al., 2004, Br J Cancer 91:1405-13

Citation Format: Alejandro Losada, Maria J. Munoz-Alonso, Juan F. Martínez-Leal, Juan M. Dominguez, Carlos M. Galmarini. Plitidepsin targets the GTP-bound form of eEF1A2 in cancer cells. [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 3015.

Abstract 1284: Lurbinectedin reduces tumor-associated macrophages and the production of inflammatory cytokines, chemokines, and angiogenic factors in preclinical models

Lurbinectedin, currently undergoing clinical evaluation in ovarian, breast and small-cell lung cancer patients, inhibits active transcription. The drug is structurally related to trabectedin containing the same pentacyclic skeleton of the fused tetrahydroisoquinoline rings, but differing by the presence of a tetrahydro-B-carboline replacing the additional tetrahydroisoquinoline of trabectedin. We investigated whether lurbinectedin has the ability to regulate the inflammatory tumor microenvironment in vitro and in vivo. Human purified monocytes were highly sensitive to lurbinectedin (IC50: 5-10 nM) and, after drug treatment, underwent caspase-8-dependent apoptosis. Furthermore, in vitro, lurbinectedin significantly inhibited the production of selected inflammatory chemokines (CCL2, CXCL8) and VEGF by stimulated monocytes and liposarcoma cell lines. Administration of lurbinectedin to mice bearing a murine fibrosarcoma -resistant to this compound in vitro- resulted in significant anti-tumor activity (T/C value around 50%). The analysis of immune cells of blood spleen and tumor tissues during treatment with lurbinectedin revealed a significant and selective decrease in the subset of monocytes and macrophages, including tumor-associated macrophages (TAM). A gene expression analysis of monocytes treated with lurbinectedin indicated a modulation of the transcriptional program in LPS-stimulated human monocytes. Overall, these results indicate that lurbinectedin affects the inflammatory micro-environment, with a selective apoptotic-inducing effect on mononuclear phagocytes and a specific inhibition of production of inflammatory cytokines.

Citation Format: Paola Allavena, Cristina Belgiovine, Manuela Liguori, Ezia Bello, Roberta Frapolli, Carlos M. Galmarini, Maurizio D’Incalci. Lurbinectedin reduces tumor-associated macrophages and the production of inflammatory cytokines, chemokines, and angiogenic factors in preclinical models. [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 1284.

Abstract 3066: Anti-angiogenic properties of PM060184

Vascular supply of tumors is one of the main targets for cancer therapy. Different studies have shown that most of the microtubule-binding agents present antiangiogenic and vascular-disrupting effects. PM060184 is a new marine-derived drug that binds to a new site in β-tubulin inhibiting tubulin polymerization. The compound is currently being evaluated in phase 1/2 studies in patients with advanced malignancies. The present study describes the antiangiogenic and vascular-disrupting properties of PM060184. Treatment of HUVEC endothelial cells with PM060184 resulted in depolymerization of the microtubule network. Differently from untreated cells, PM060184-treated cells showed a rounded morphology with a well-developed actin filament structure and plasma membrane blebs. Using transwell chambers pre-coated with matrigel™ or collagen matrix, we showed that PM060184 inhibited migration and invasion of HUVEC endothelial cells. We finally found that PM060184 interfered with the correct formation of the HUVEC capillary network grown on matrigel™; moreover, drug treatment also resulted in a significant disruption of the previously formed capillary-like network. This rapid collapse of the endothelial tubular network in vitro occurred in a concentration-dependent manner and was observed at concentrations lower than those affecting cells survival. These in vitro findings were confirmed in nude mice bearing MDA-MB-231 (breast) xenografts: after the administration of a single dose of PM060184 (at its MTD, 16 mg/kg,) a very strong reduction in the number of vessels was quantified in serial tumor sections stained with H&E. Moreover, nude mice xenografted with H-460 (NSCLC) tumors and treated with a single dose of either 2 or 16 mg/kg of PM060184, experienced a strong and dose-dependent decrease of the intratumoral fluorescence after the administration of Angiosense™ 680, a fluorescence vascular imaging probe. Altogether, these data suggest that an anti-vascular mechanism is also contributing to the anti-tumor activities of PM060184.

Citation Format: Carlos M. Galmarini, Maria J. Guillen, Juan F. Martinez-Leal, Marta Martinez-Diez, Pablo Aviles. Anti-angiogenic properties of PM060184. [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 3066.

Synergistic Effect of Trabectedin and Olaparib Combination Regimen in Breast Cancer Cell Lines

Purpose

Trabectedin induces synthetic lethality in tumor cells carrying defects in homologous recombinant DNA repair. We evaluated the effect of concomitant inhibition of nucleotide-excision repair and poly (ADP-ribose) polymerase (PARP) activity with trabectedin and PARP inhibitors, respectively, and whether the synthetic lethality effect had the potential for a synergistic effect in breast cancer cell lines. Additionally, we investigated if this approach remained effective in BRCA1-positive breast tumor cells.

Methods

We have evaluated the in vitro synergistic effect of combinations of trabectedin and three different PARP inhibitors (veliparib, olaparib, and iniparib) in four breast cancer cell lines, each presenting a different BRCA1 genetic background. Antiproliferative activity, DNA damage, cell cycle perturbations and poly(ADP-ribosyl)ation were assessed by MTT assay, comet assay, flow cytometry and western blot, respectively.

Results

The combination of trabectedin and olaparib was synergistic in all the breast cancer cell lines tested. Our data indicated that the synergy persisted regardless of the BRCA1 status of the tumor cells. Combination treatment was associated with a strong accumulation of double-stranded DNA breaks, G2/M arrest, and apoptotic cell death. Synergistic effects were not observed when trabectedin was combined with veliparib or iniparib.

Conclusion

Collectively, our results indicate that the combination of trabectedin and olaparib induces an artificial synthetic lethality effect that can be used to kill breast cancer cells, independent of BRCA1 status.

Increased sensitivity to platinum drugs of cancer cells with acquired resistance to trabectedin

BACKGROUND

In order to investigate the mechanisms of acquired resistance to trabectedin, trabectedin-resistant human myxoid liposarcoma (402-91/T) and ovarian carcinoma (A2780/T) cell lines were derived and characterised in vitro and in vivo.

METHODS

Resistant cell lines were obtained by repeated exposures to trabectedin. Characterisation was performed by evaluating drug sensitivity, cell cycle perturbations, DNA damage and DNA repair protein expression. In vivo experiments were performed on A2780 and A2780/T xenografts.

RESULTS

402-91/T and A2780/T cells were six-fold resistant to trabectedin compared with parental cells. Resistant cells were found to be hypersensitive to UV light and did not express specific proteins involved in the nucleotide excision repair (NER) pathway: XPF and ERCC1 in 402-91/T and XPG in A2780/T. NER deficiency in trabectedin-resistant cells was associated with the absence of a G2/M arrest induced by trabectedin and with enhanced sensitivity (two-fold) to platinum drugs. In A2780/T, this collateral sensitivity, confirmed in vivo, was associated with an increased formation of DNA interstrand crosslinks.

CONCLUSIONS

Our finding that resistance to trabectedin is associated with the loss of NER function, with a consequent increased sensitivity to platinum drugs, provides the rational for sequential use of these drugs in patients who have acquired resistance to trabectedin.

Abstract A147: MI130004, a new ADC with a payload of marine origin shows outstanding activity against HER2-expressing tumors

PM050489 is a tubulin-binding agent originally isolated from the marine sponge Lithoplocamia lithistoides. This compound binds with very high affinity to β-tubulin at a new site, disrupting the microtubule network and impairing its function during divison, which leads to mitotic aberrations. MI130004 (a novel antibody-drug conjugate formed by PM050489, a non-hydrolysable linker and trastuzumab) was tested for its in vitro and in vivo activity against selected tumor cell lines with different levels of HER2 expression. In vitro MI130004 showed very high potency and good selectivity for tumor cells that overexpressed HER2, namely HCC-1954 (IC50, 0.036 μg/mL), SK-BR-3 (IC50, 0.017 μg/mL) and BT-474 (IC50, 0.156 μg/mL). At the cellular level, MI130004 impaired tubulin polymerization, causing disorganization and disintegration of the microtubule network which ultimately led to mitotic failure. Expressing HER2 cells of breast (BT-474 and JIMT-1), gastric (Gastric-008 and N87) and ovarian (SK-OV-3 and A2780cis) as well as negative HER2 breast (MDA-MB-231) and gastric (Hs748t) were subcutaneously implanted into immunosuppressed (SCID or athymic) mice. Tumor (ca. 115 mm3) bearing animals (N = 10/group) were randomly allocated to receive the ADC treatments (at different doses) or the appropriate control (placebo included). Treatments were administered weekly for 5

consecutive weeks. Tumor growth (as median/group) was calculated 2-3 times per week. Twenty-four hours after the first dose, representative tumors were dissected free and processed for HER2 expression (erb2) and chromatin organization (Hoescht 33258). The treatment with MI130004 induced a long lasting antitumor effect with statistically significant increases (P<0.05) in median survival time compared to placebo. The highest dose of MI130004 induced complete tumor remissions in mice bearing BT-474, JIMT-1, Gastric-008, N87, SK-OV-3 and A2780cis xenografts lasting up to 120, 60, 165, 63, 237 and 231 days, respectively. Also 24-h post-dosing, MI130004 induced a dose-dependent disappearance of HER2-expressing cells as well as mitotic aberrations, this last being consistent with the mechanism of action of PM050489. These results demonstrate that PM050489, a marine derived compound, is a novel and remarkable payload for the design of new ADCs with potential therapeutic anti-cancer properties.

Citation Format: Pablo Aviles, Maria Jose Guillen, Juan Manuel Dominguez, Carlos M. Galmarini, Carmen Cuevas. MI130004, a new ADC with a payload of marine origin shows outstanding activity against HER2-expressing tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A147.

Elisidepsin Interacts Directly with Glycosylceramides in the Plasma Membrane of Tumor Cells to Induce Necrotic Cell Death

Plasma membrane integrity is essential for cell life. Any major break on it immediately induces the death of the affected cell. Different molecules were described as disrupting this cell structure and thus showing antitumor activity. We have previously defined that elisidepsin (Irvalec^®, PM02734) inserts and self-organizes in the plasma membrane of tumor cells, inducing a rapid loss of membrane integrity, cell permeabilization and necrotic death. Here we show that, in sensitive HCT-116 colorectal cells, all these effects are consequence of the interaction of elisidepsin with glycosylceramides in the cell membrane. Of note, an elisidepsin-resistant subline (HCT-116-Irv) presented reduced levels of glycosylceramides and no accumulation of elisidepsin in the plasma membrane. Consequently, drug treatment did not induce the characteristic necrotic cell death. Furthermore, GM95, a mutant derivative from B16 mouse melanoma cells lacking ceramide glucosyltransferase (UGCG) activity and thus the synthesis of glycosylceramides, was also resistant to elisidepsin. Over-expression of UGCG gene in these deficient cells restored glycosylceramides synthesis, rendering them sensitive to elisidepsin, at a similar level than parental B16 cells. These results indicate that glycosylceramides act as membrane targets of elisidepsin, facilitating its insertion in the plasma membrane and the subsequent membrane permeabilization that leads to drug-induced cell death. They also indicate that cell membrane lipids are a plausible target for antineoplastic therapy.

Abstract 5430: eEF1A2 is a new target for anticancer therapy

Eukaryotic Elongation Factor 1A2 (eEF1A2) is an isoform of the alpha subunit of eEF1 complex. Differently from the A1 isoform, the expression of eEF1A2 is restricted to brain, heart and skeletal muscle. eEF1A2 is overexpressed in tumors, including multiple myeloma (MM) (Li et al, 2012, PLOS One 5, e10755), prostate (Sun et al, 2014, Biochem Biophys Res Commun 450:1-6), pancreas (Xu et al, 2013, Clin Exp Metastasis 30:933-44) and ovarian (Anand et al, 2002, Nat Genet 31:301-5), and has also an oncogenic behavior favoring tumor cell proliferation while inhibiting apoptosis (Lee and Surh, 2009, Ann N Y Acad Sci 1171:87-93). Thus, eEF1A2 is an interesting target for cancer treatment. Aplidin (plitidepsin) is an antitumor agent, originally isolated from the marine tunicate Aplidium albicans, which is being tested in MM patients in a phase III pivotal trial in combination with dexamethasone and a phase I trial in combination with bortezomib and dexamethasone. Herein we reveal the interaction of Aplidin with eEF1A2 using different methods; i) a DARTS assay showed that Aplidin protected eEF1A2 from digestion by the protease subtilisin (EC 3.4.21.62); ii) a saturation binding experiment using [14C]-Aplidin and eEF1A2 purified from rabbit muscle determined a Kd for the interaction of approximately 80 nM; iii) a fluorescence anisotropy test through two photon microscopy showed that Aplidin preferentially binds the GTP-bound form of eEF1A2. Furthermore, we performed a [14C]-Aplidin binding-guided fractionation of K562 cell extracts through differential centrifugation and several chromatographic steps, including ion-exchange and size-exclusion chromatography, demonstrating that eEF1A2 is the unique cellular protein that can be retrieved through specific binding to Aplidin. In addition, HeLa-APL-R cells, a HeLa subclone made extremely resistant to Aplidin, more than 1000 fold, (Losada et al., 2004, Br J Cancer 91:1405-13), are shown to express 8 fold less eEF1A2 than the parental cells both at the mRNA (determined with an Affimetryx HG-U133A Array) and protein (determined by iTRAQ) levels. When normal eEF1A2 levels were restored in HeLa-APL-R cells through ectopic expression of an eEF1A2-GFP construct, these cells were rendered partially sensitive to Aplidin. Interestingly, the transfected cells recovered most of the signaling events which are typically induced by the drug in HeLa wt cells. Altogether, our results demonstrate that eEF1A2, the oncogenic isoform of the alpha subunit of eEF1, is the primary target of Aplidin and a new suitable and druggable target for anticancer therapy.

Citation Format: Alejandro Losada, Maria José Muñoz, Carolina Garcia, Juan F. Martínez-Leal, Federico Gago, Carmen Cuevas, Luis F. Garcia-Fernández, Juan M. Dominguez, Pilar Lillo, Carlos M. Galmarini. eEF1A2 is a new target for anticancer therapy. [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 5430. doi:10.1158/1538-7445.AM2015-5430

Abstract 4472: Plitidepsin shows antitumor activity in patient-derived tumor xenografts and hematologic malignancies

Plitidepsin is a new marine-derived anti-tumor agent, originally isolated from the tunicate Aplidium albicans that is now fully obtained by total chemical synthesis. The compound is currently being evaluated in a pivotal phase III trial in patients with refractory/relapsed multiple myeloma. Previous in vitro studies in 26 hematological cell lines demonstrated that plitidepsin was more active in multiple myeloma and non-Hodgkin lymphoma compared to CML, AML and ALL derived cell lines as determined in a 4 day proliferation assay in suspension cultures. We have recently shown that plitidepsin interacts selectively with eEF1A2 (eukaryotic translation elongation factor 1 alpha 2) in tumor cells, which results in apoptotic cell death. To identify target tumor types for future clinical studies, the inhibition of colony formation of plitidepsin was assessed in vitro in 116 established patient derived xenografts tumor models from 23 different tumor types, including solid tumors and hematological malignancies such as myeloma, leukemia and lymphoma. The anti-tumor activity of plitidepsin varied depending on the concentration used, achieving a mean IC70 (inhibitory concentration of 70%) value of 3 nM (range between 0.03 nM and >1 μM), which can be also achieved in patients treated using the clinical recommended dose or less. 39 out of 116 tumors showed above average sensitivity (IC70 < 1nM) and IC70 values in these tumors were about 9-fold lower than the mean of all tumors as tested. Sensitive tumor types were seen among different tumor types, such as hematological malignancies, pleuramesothelioma, melanoma, small cell and non-small cell lung cancer (both adeno and large cell), as well as renal cancer. In conclusion plitidepsin showed a broad differential antitumor activity in vitro in hematological malignancies and in solid tumors. Bioinformatic analyses are currently underway to identify biomarkers and/or gene signatures that can predict sensitivity or resistance to plitidepsin for selecting patients being responsive to the drug.

Citation Format: Armin Maier, Gerhard Kelter, Vincent Vuaroquaux, Pablo M. Avilés Marin, Carmen Cuevas, Carlos M. Galmarini, Heinz H. Fiebig. Plitidepsin shows antitumor activity in patient-derived tumor xenografts and hematologic malignancies. [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 4472. doi:10.1158/1538-7445.AM2015-4472

Abstract 2520: Synergistic combination of lurbinectedin and PARP inhibitors in breast cancer tumor cell lines

Lurbinectedin (PM1183) is a new tetrahydroisoquinoline derivative currently evaluated in phase II trials in BRCA1-mutated breast cancer and NSCLC patients. Two pivotal trials (in platinum-resistant ovarian cancer and in SCLC) will be launched in 2015. PM1183 shows antitumor activity against a wide variety of tumor cells with mean IC50 values in the low nanomolar range. In living cells, PM1183 inhibits trans-activated transcription and blocks NER-dependent DNA repair inducing the formation of dsDNA breaks and the collapse of replication forks that need to be repaired by homologous recombination (HR). As expected, PM1183 is more active against homologous recombination (HR)-deficient cell lines. In this work, we evaluated the in vitro antitumor effect of PM1183 when combined with the PARP inhibitors ABT-88 (Veliparib, PARP-1 and -2), AZD-2281 (Olaparib, PARP-1), BSI-201 (Iniparib, PARP-1) and BMN-673 (PARP-1 and -2) (Selleck Chemicals, Houston, TX, USA) in a panel of human breast carcinoma cells with different BRCA1 status, including MCF-7 (BRCA1 +/+), MDA-MB-231 (BRCA1 +/-), HCC-1937 (BRCA1 -/-) and MDA-MB-436 (BRCA1 -/-). The combination index (CI) of each different drug-drug combination was calculated by applying the Chou and Talalay method. Different degrees of synergism (CI < 1) were recorded when PM1183 was combined with AZD-2281 (Olaparib) and BMN-673, depending on the tumor cell line and the conditions tested. The highest degree of synergism with Olaparib was observed in MDA-MB-436 cells followed by MDA-MB-231, MCF7 and HCC-1937 cells. The highest degree of synergism with BMN-673 was observed in MCF-7 cells followed by MDA-MB-231 and HCC-1937 cells. In MDA-MB-231 cells, both combinations led to a synergistic induction of γ-H2AX expression and PARP-1 cleavage, as analyzed by western blot. Collectively, our results indicate that the combination of PM1183 and PARP inhibitors (Olaparib and BMN673) induces an artificial synthetic lethality that can be advantageously used to kill several breast cancer cells, independently from their BRCA1 status.

Citation Format: Gema Santamaría, Sonia Avila, Victoria Moneo, Carmen Cuevas, Luis F. García-Fernández, Carlos M. Galmarini. Synergistic combination of lurbinectedin and PARP inhibitors in breast cancer tumor cell lines. [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 2520. doi:10.1158/1538-7445.AM2015-2520

Abstract 5467: Role of the eukaryotic elongation factor eEF1A in the mechanism of action of Aplidin

Aplidin is a cyclic depsipeptide of the family of didemnins, originally isolated from the colonial tunicate Aplidium albicans. Aplidin is being evaluated in a phase III clinical trial in patients with relapse or refractory multiple myeloma. As part of its antitumor activity, Aplidin induces rapid oxidative stress, activation of Rac1 and phosphorylation of p38 and JNK1 stress kinases, which together trigger the apoptotic death of tumor cells. Didemnin B (DB), a molecule closely related to Aplidin, has been previously shown to interact with the GTP-bound conformation of the eukaryotic elongation factor eEF1A, an interaction that was related to the didemnin's B ability to inhibit protein synthesis (J. Biol. Chem. 1994, 269:15411-14). A structural model for this interaction has been proposed (J. Med. Chem. 2004, 47:4439-52). We wanted to investigate whether eEF1A had any role in the mechanism of action of Aplidin. Using the DARTS technique, we observed that Aplidin treatment of tumor cells and subsequent digestion of the cellular extracts with different proteases, resulted in a significant increase in the stabililty of eEF1A against protease digestion, suggesting a direct effect of Aplidin on this protein. We previously generated, by continuous exposure to increasing concentrations of the drug, a HeLa derivative cell line (HeLa-APL-R) that showed specific resistance to Aplidin as well as to other related didemnins and tamandarins (Br. J. Cancer 2004, 91:1405-13). We investigated whether there was any difference in the expression levels of eEF1A between HeLa-wt and HeLa-APL-R cell lines. Since two isoforms of the elongation factor are expressed in tumor cells, eEF1A1 and eEF1A2, we checked the relative amount of both proteins at the mRNA and protein levels using DNA microarrays and iTRAQ, respectively. Remarkably, we observed that the mRNA and protein levels of eEF1A2 isoform were lower in HeLa-APL-R resistant cells as compared to their parental cell line. No significant changes were seen in the levels of eEF1A1. The reduced levels of eEF1A2 protein in HeLa-APL-R cells were further confirmed by western blotting using isoform-specific antibodies. To explore the effect of the restoration of the eEF1A2 levels in the HeLa resistant clone, we generated two cell lines stably overexpressing eEF1A1 or eEF1A2 and checked their sensitivity to Aplidin in dose-response cytotoxicity experiments. Both cell lines partially recovered the sensitivity to Aplidin, with the eEF1A2-overexpressing cell line having an even slightly higher sensitivity to the compound. In eEF1A overexpressing cells, Aplidin induced a robust cytostatic effect. At the molecular level, Aplidin induced the phosphorylation of p38 as well as ERK MAPKs, but not JNK phosphorylation or PARP cleavage, two key events in the cytotoxic signaling of the drug. These results could indicate a role of eEF1A in the biological activity of Aplidin in tumor cells.

Citation Format: Alejandro Losada, Juan F. Martínez-Leal, Federico Gago, Carmen Cuevas, Luis F. Garcia-Fernández, Carlos M. Galmarini. Role of the eukaryotic elongation factor eEF1A in the mechanism of action of Aplidin. [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 5467. doi:10.1158/1538-7445.AM2014-5467

Inhibitory effects of marine-derived DNA-binding anti-tumour tetrahydroisoquinolines on the Fanconi anaemia pathway

BACKGROUND AND PURPOSE

We have previously shown that cells with a defective Fanconi anaemia (FA) pathway are hypersensitive to trabectedin, a DNA-binding anti-cancer tetrahydroisoquinoline (DBAT) whose adducts functionally mimic a DNA inter-strand cross link (ICL). Here we expand these observations to new DBATs and investigate whether our findings in primary untransformed cells can be reproduced in human cancer cells.

EXPERIMENTAL APPROACH

Initially, the sensitivity of transformed and untransformed cells, deficient or not in one component of the FA pathway, to mitomycin C (MMC) and three DBATs, trabectedin, Zalypsis and PM01183, was assessed. Then, the functional interaction of these drugs with the FA pathway was comparatively investigated.

KEY RESULTS

While untransformed FA-deficient haematopoietic cells were hypersensitive to both MMC and DBATs, the response of FA-deficient squamous cell carcinoma (SCC) cells to DBATs was similar to that of their respective FA-competent counterparts, even though these FA-deficient SCC cells were hypersensitive to MMC. Furthermore, while MMC always activated the FA pathway, the DBATs inhibited the FA pathway in the cancer cell lines tested and this enhanced their response to MMC.

CONCLUSIONS AND IMPLICATIONS

Our data show that although DBATs functionally interact with DNA as do agents that generate classical ICL, these drugs should be considered as FA pathway inhibitors rather than activators. Moreover, this effect was most significant in a variety of cancer cells. These inhibitory effects of DBATs on the FA pathway could be exploited clinically with the aim of 'fanconizing' cancer cells in order to make them more sensitive to other anti-tumour drugs.

PM060184, a new tubulin binding agent with potent antitumor activity including P-glycoprotein over-expressing tumors

PM060184 belongs to a new family of tubulin-binding agents originally isolated from the marine sponge Lithoplocamia lithistoides. This compound is currently produced by total synthesis and is under evaluation in clinical studies in patients with advanced cancer diseases. It was recently published that PM060184 presents the highest known affinities among tubulin-binding agents, and that it targets tubulin dimers at a new binding site. Here, we show that PM060184 has a potent antitumor activity in a panel of different tumor xenograft models. Moreover, PM060184 is able to overcome P-gp mediated resistance in vivo, an effect that could be related to its high binding affinity for tubulin. To gain insight into the mechanism responsible of the observed antitumor activity, we have characterized its molecular and cellular effects. We have observed that PM060184 is an inhibitor of tubulin polymerization that reduces microtubule dynamicity in cells by 59%. Interestingly, PM060184 suppresses microtubule shortening and growing at a similar extent. This action affects cells in interphase and mitosis. In the first case, the compound induces a disorganization and fragmentation of the microtubule network and the inhibition of cell migration. In the second case, it induces the appearance of multipolar mitosis and lagging chromosomes at the metaphase plate. These effects correlate with prometaphase arrest and induction of caspase-dependent apoptosis or appearance of cells in a multinucleated interphase-like state unrelated to classical apoptosis pathways. Taken together, these results indicate that PM060184 represents a new tubulin binding agent with promising potential as an anticancer agent.

Trabectedin and plitidepsin: drugs from the sea that strike the tumor microenvironment

The prevailing paradigm states that cancer cells acquire multiple genetic mutations in oncogenes or tumor suppressor genes whose respective activation/up-regulation or loss of function serve to impart aberrant properties, such as hyperproliferation or inhibition of cell death. However, a tumor is now considered as an organ-like structure, a complex system composed of multiple cell types (e.g., tumor cells, inflammatory cells, endothelial cells, fibroblasts, etc.) all embedded in an inflammatory stroma. All these components influence each other in a complex and dynamic cross-talk, leading to tumor cell survival and progression. As the microenvironment has such a crucial role in tumor pathophysiology, it represents an attractive target for cancer therapy. In this review, we describe the mechanism of action of trabectedin and plitidepsin as an example of how these specific drugs of marine origin elicit their antitumor activity not only by targeting tumor cells but also the tumor microenvironment.

Hypoxia reduces the efficiency of elisidepsin by inhibiting hydroxylation and altering the structure of lipid rafts

The mechanism of action of elisidepsin (PM02734, Irvalec^®) is assumed to involve membrane permeabilization via attacking lipid rafts and hydroxylated lipids. Here we investigate the role of hypoxia in the mechanism of action of elisidepsin. Culturing under hypoxic conditions increased the half-maximal inhibitory concentration and decreased the drug’s binding to almost all cell lines which was reversed by incubation of cells with 2-hydroxy palmitic acid. The expression of fatty acid 2-hydroxylase was strongly correlated with the efficiency of the drug and inversely correlated with the effect of hypoxia. Number and brightness analysis and fluorescence anisotropy experiments showed that hypoxia decreased the clustering of lipid rafts and altered the structure of the plasma membrane. Although the binding of elisidepsin to the membrane is non-cooperative, its membrane permeabilizing effect is characterized by a Hill coefficient of ~3.3. The latter finding is in agreement with elisidepsin-induced clusters of lipid raft-anchored GFP visualized by confocal microscopy. We propose that the concentration of elisidepsin needs to reach a critical level in the membrane above which elisidepsin induces the disruption of the cell membrane. Testing for tumor hypoxia or the density of hydroxylated lipids could be an interesting strategy to increase the efficiency of elisidepsin.

Mode of action of trabectedin in myxoid liposarcomas

To elucidate the mechanisms behind the high sensitivity of myxoid/round cell liposarcoma (MRCL) to trabectedin and the suggested selectivity for specific subtypes, we have developed and characterized three MRCL xenografts, namely ML017, ML015 and ML004 differing for the break point of the fusion gene FUS-CHOP, respectively of type I, II and III. FUS-CHOP binding to the promoters of some target genes such as Pentraxin 3 or Fibronectin 1, assessed by chromatin immunoprecipitation, was strongly reduced in the tumor 24 h after the first or the third weekly dose of trabectedin, indicating that the drug at therapeutic doses causes a detachment of the FUS-CHOP chimera from its target promoters as previously shown in vitro. Moreover, the higher sensitivity of MRCL types I and II appears to be related to a more prolonged block of the transactivating activity of the fusion protein. Doxorubicin did not affect the binding of FUS-CHOP to target promoters. Histologically, the response to trabectedin in ML017 and ML015 was associated with a marked depletion of non-lipogenic tumoral cells and vascular component, as well as lipidic maturation as confirmed by PPARγ2 expression in western Blot. By contrast, in ML004 no major changes either in the cellularity or in the amount of mature were found, and consistently PPARγ2 was null. In conclusion, the data support the view that the selective mechanism of action of trabectedin in MRCL is specific and related to its ability to cause a functional inactivation of the oncogenic chimera with consequent derepression of the adypocytic differentiation.

Nibrin is a marker of clinical outcome in patients with advanced serous ovarian cancer treated in the phase III OVA-301 trial

OBJECTIVE

This study investigated the relationship between 13 proteins involved in DNA damage and the outcomes of patients with recurrent ovarian cancer (ROC).

PATIENTS AND METHODS

Immunohistochemistry staining was performed in 114 diagnostic samples from patients with serous ROC who participated in the OVA-301 study, which compared pegylated liposomal doxorubicin (PLD) with a combination of trabectedin plus PLD. Percentage of positive cells for every marker was calculated and correlated with overall response rate (ORR), progression-free survival (PFS) and overall survival (OS).

RESULTS

A statistically significant correlation between high levels of nibrin and lower ORR (P=0.03), shorter PFS (P=0.007) and shorter OS (P=0.01) was observed. After stratification, in patients with platinum-sensitive disease treated with the combination of trabectedin plus PLD, high levels of nibrin correlated with lower ORR (P=0.01) and shorter PFS (P=0.02). A better clinical outcome (ORR, PFS and OS) was also associated to low levels of CHK2 in trabectedin plus PLD treated patients. No correlations were found in PLD-treated patients. According to the results of a multivariate analysis, there was a statistically significant correlation between high nibrin (P=0.001) and low BRCA2 levels (P=0.03) and a worse PFS, and between high nibrin levels and a worse OS (P=0.006).

CONCLUSION

Our results indicate that high nibrin expression seems to be associated with a worse clinical outcome in serous ROC, particularly in patients treated with the combination trabectedin plus PLD. Prospective studies to determine clinical usefulness of nibrin as a possible biomarker in other series of patients with ROC are warranted.

Abstract A177: Mode of action of PM060184, a new interfacial microtubule inhibitor of marine origin

PM060184 belongs to a new family of tubulin-binding agents originally isolated from the marine sponge Lithoplocamia lithistoides. This compound is currently produced by total chemical synthesis and is under evaluation in Phase I clinical studies in patients with advanced cancer diseases. Recently published results indicate that members of the PM060184 family are interfacial microtubule inhibitors that bind with nanomolar affinity to unassembled αβ-tubulin dimers at the beta tubulin plus end (Pera et al. 2013, ACS Chem. Biol.) In an attempt to shed light into the mechanism responsible of its antitumor activity, we have studied the effects of PM060184 in tumor cells including microtubule network structure, centrosome modifications and type of cell death induced by this compound. PM060184 rapidly internalizes into the tumor cells and shows a high intracellular retention rate, reflecting the high avidity for its cellular target. In addition, the antitumor activity of the compound seems to be rather irreversible after short (30 min) exposure times. At the cellular level, PM060184 inhibits tubulin polymerization. Interestingly, PM060184 affects interphase cells, where the compound induces disorganisation and fragmentation of the microtubule network and disturbing cell migration. PM060184 also affects mitotic cells, inducing the appearance of multipolar mitosis and lagging chromosomes at the metaphase plate. All these effects correlate with prometaphase arrest and induction of caspase-dependent apoptosis or appearance of cells in a multinucleated interphase-like state unrelated to classical apoptosis pathways. In summary, these results indicate that PM060184 represents a new tubulin binding agent with promising potential as an anticancer agent.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A177.

Citation Format: Marta Martínez-Diez, Juan Fernando Martínez-Leal, Luis F. Garcia-Fernandez, Carlos M. Galmarini. Mode of action of PM060184, a new interfacial microtubule inhibitor of marine origin. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A177.

Abstract A174: Comparison of the antitumor activity of Trabectedin, Lurbinectedin, Zalypsis and PM00128 in a panel of human cells deficient in transcription/NER repair factors

Trabectedin, Lurbinectedin, Zalypsis and PM00128 are marine-derived anticancer drugs. All these compounds contain a common pentacyclic skeleton which is responsible for the binding to the DNA minor groove. They differ in the additional chemical moiety attached to the pentacyclic skeleton that protrudes from the minor groove of the DNA. Trabectedin, Lurbinectedin and Zalypsis present a tetrahydroisoquinole, a tetrahydro β-carboline and a trifluorocinnamic groups, respectively, while PM00128 lacks such additional moiety. It is believed that the chemical structure of these groups could mediate compound specific interactions with proteins involved in different cellular functions, such as transcription or DNA repair. To gain insight into how the presence of those different chemical moieties could contribute to the specific activity of the compounds, we tested their cytotoxicity profiles against a panel of 24 fibroblast cell lines derived from patients with genetic diseases caused by mutations in the transcription/NER factors CSA, CSB, XPC, XPA, XPE, XPD and XPG. Four out of seven fibroblast cells lines carrying truncations in the XPG endonuclease gene were more resistant to Trabectedin than normal fibroblasts, with RI values ranging from 3.4 to 6.7. It was also observed that the cell line GM15754 was particularly resistant to both Trabectedin and Lurbinectedin, showing a RI of 41.0. This cell line presents a missense mutation (R112H) in the XPD helicase gene. The results indicated that the proper functionality of XPG and XPD factors in transcription and/or DNA repair may be important for the antiproliferative action of these compounds. Interestingly, no significant differences in the sensitivity of these cell lines were observed wih Zalypsis and PM00128. The sensitivity profiles obtained with standard DNA binders (cisplatin and mitomycin C) were completely opposed to those of Trabectedin and Lurbinectedin. These results indicate that i) the four compounds behave in a different way to other commonly used DNA binders such as cisplatin and mitomycin C and ii) the chemical groups attached to the common DNA binding scaffold in these compounds seem to be important for their specific biological activities against tumor cells.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A174.

Citation Format: Victoria Moneo, Patricia Martínez, Beatriz de Castro, Sofía Cascajares, Sonia Avila, Luis F. Garcia-Fernandez, Carlos M. Galmarini. Comparison of the antitumor activity of Trabectedin, Lurbinectedin, Zalypsis and PM00128 in a panel of human cells deficient in transcription/NER repair factors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A174.

Abstract A173: The new marine derived tubulin binding agent PM060184 shows potent antitumor activity in vivo against multidrug resistant, Pgp expressing tumors

PM060184 is new marine derived tubulin-binding agent originally isolated from the sponge Lithoplocamia lithistoides. The compound is currently under evaluation in Phase I clinical studies in patients with advanced cancer diseases. PM060184 showed potent antitumor activity in vitro and also in vivo against a panel of different tumor xenografted models. As the overexpression of P-gp pumps is generally related to resistance to tubulin binding agents, we have analyzed whether the expression of this efflux pump could also confer resistance to PM060184. In vitro, PM060184 showed potent antiproliferative activity against tumor cells over-expressing the P-gp multidrug efflux pump (LoVo/Dox, A2780/Dox and IGROV-1/ET), with IC50s values in the low nanomolar range. In vivo, the activity of PM060184 was evaluated in mice xenografted with LoVo (wild-type) or LoVo/DX (P-gp overexpressing) subcutaneous tumors. Tumor bearing (ca. 150-200 mm3) animals were randomly allocated into the following groups (N = 10/group): i) PM060184 (16 mg/kg); ii) paclitaxel (25 mg/kg); iii) vinorelbine (16 mg/kg); and, iv) placebo. Treatments were intravenously administered once per week for 3 consecutive weeks (q7dx3). Tumor dimensions were recorded 3 times per week starting from the first day of treatment (Day 0). Tumor volume was calculated using the equation (a·b2)/2, where a and b were the longest and shortest diameters, respectively. The antitumor effect obtained following paclitaxel, vinorelbine or PM060184 administration was calculated by using T/C (%), which was defined as the percentage of the change in tumor volume for each treated (T) and placebo (C) group during the surviving period for placebo-treated animals. In mice bearing LoVo xenografted tumors paclitaxel and vinorelbine treatments induced lowest T/C values of 23.3 % (Day 26) and 18.3% (Day 23), respectively. Also, PM060184 was highly active in this model, with a lowest T/C calculated as 8.1 % (Day 26). In LoVo/DX xenografted mice, paclitaxel and vinorelbine treatments resulted in no antitumor effect. However, LoVo/DX tumors were highly susceptible to PM060184 treatment (lowest T/C = 6.7%, on Day 28) demonstrating that a strong antitumor PM060184-related effect regardless of the P-gp status in this model.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A173.

Citation Format: Pablo M. Aviles, Maria José Guillen, Mandy Palomares, Praxedes Nuñez, Marta Martinez-Diez, Juan Fernando Martínez-Leal, Luis Francisco García-Fernández, Carlos M. Galmarini. The new marine derived tubulin binding agent PM060184 shows potent antitumor activity in vivo against multidrug resistant, Pgp expressing tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A173.

New interfacial microtubule inhibitors of marine origin, PM050489/PM060184, with potent antitumor activity and a distinct mechanism

We have investigated the target and mechanism of action of a new family of cytotoxic small molecules of marine origin. PM050489 and its dechlorinated analogue PM060184 inhibit the growth of relevant cancer cell lines at subnanomolar concentrations. We found that they are highly potent microtubule inhibitors that impair mitosis with a distinct molecular mechanism. They bind with nanomolar affinity to unassembled αβ-tubulin dimers, and PM050489 binding is inhibited by known Vinca domain ligands. NMR TR-NOESY data indicated that a hydroxyl-containing analogue, PM060327, binds in an extended conformation, and STD results define its binding epitopes. Distinctly from vinblastine, these ligands only weakly induce tubulin self-association, in a manner more reminiscent of isohomohalichondrin B than of eribulin. PM050489, possibly acting like a hinge at the association interface between tubulin heterodimers, reshapes Mg(2+)-induced 42 S tubulin double rings into smaller 19 S single rings made of 7 ± 1 αβ-tubulin dimers. PM060184-resistant mutants of Aspergillus nidulans map to β-tubulin Asn100, suggesting a new binding site different from that of vinblastine at the associating β-tubulin end. Inhibition of assembly dynamics by a few ligand molecules at the microtubule plus end would explain the antitumor activity of these compounds, of which PM060184 is undergoing clinical trials.

Comparison of in vitro and in vivo biological effects of trabectedin, lurbinectedin (PM01183) and Zalypsis® (PM00104)

This study: (i) investigated the in vitro cytotoxicity and mode of action of lurbinectedin (PM01183) and Zalypsis® (PM00104) compared with trabectedin in cell lines deficient in specific mechanisms of repair, (ii) evaluated their in vivo antitumor activity against a series of murine tumors and human xenografts. The antiproliferative activity, the DNA damage and the cell cycle perturbations induced by the three compounds on tumor lines were very similar. Nucleotide Excision Repair (NER) deficient cells were approximately fourfold more resistant to trabectedin, lurbinectedin and Zalypsis®. Cells deficient in non-homologous end joining (NHEJ), MRN complex and translesion synthesis (TLS) were slightly more sensitive to the three compounds (approximately fivefold) while cells deficient in homologous recombination (HR) were markedly more sensitive (150-200-fold). All three compounds showed a good antitumor activity in several in vivo models. Lurbinectedin and trabectedin had a similar pattern of antitumor activity in murine tumors and in xenografts, whereas Zalypsis® appeared to have a distinct spectrum of activity. The fact that no relationship whatsoever was found between the in vitro cytotoxic potency and the in vivo antitumor activity, suggests that in addition to direct cytotoxic mechanisms other host-mediated effects are involved in the in vivo pharmacological effects.

Abstract 2129: Aplidin triggers the activation of molecular components of the UPR as part of its pro-apoptotic program in tumor cells

Aplidin (APL), a cyclic depsipeptide originally isolated from the marine tunicate Aplidium albicans and currently under phase II/III clinical trials for cancer therapy, induces oxidative stress, activation of Rac1 and phosphorylation of JNK1, which together trigger a rapid apoptotic program in tumor cells. A previously generated APL-resistant HeLa cell line (APL-R) allowed us to find out differences in protein expression with the parental HeLa cells. Among the proteins differentially expressed, several endoplasmic reticulum (ER) stress-related proteins were observed. We found decreased basal levels of BiP in HeLa APL-R, while the levels of Ero1a and phospho-eIF2a were slightly increased when compared to parental HeLa cells, indicative of a higher basal ER stress. In this work, we investigated if APL was inducing a bona fide ER stress in HeLa cells and whether this process was essential in the mechanism of action of the compound. Similarly to that observed with thapsigargin and tunicamycin, two well known ER stress inducing agents, APL triggered the activation of several key molecular components of a classical ER stress induced unfolded protein response (UPR), including the phosphorylation of eIF2a and JNK1, the proteolitic processing of ATF6 and the alternative splicing of XBP1, but not others, such as the accumulation of noxa or the proteolitic activation of caspase 4. Interestingly, although the eIF2a phosphorylation induced by APL in HeLa wt cells correlated with a strong inhibition of protein synthesis, it did not elicit an increased expression of CHOP, a transcription factor involved in the launch of UPR mediated apoptosis. Actually, it was observed a clear reduction of CHOP protein levels after the treatment of HeLa cells with APL, most probably due to its rapid degradation by the proteasome machinery. In summary, as a part of the proapoptotic program triggered by APL in HeLa cells, we observed the induction of ER stress and the activation of several endpoint executioners of the UPR apoptotic branch.

Citation Format: Alejandro Losada, Juan F. Martínez-Leal, Alberto Bejarano, Carmen Cuevas, Luis F. Garcia-Fernández, Carlos M. Galmarini. Aplidin triggers the activation of molecular components of the UPR as part of its pro-apoptotic program in tumor cells. [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 2129. doi:10.1158/1538-7445.AM2013-2129

Abstract 5558: Lurbinectedin (PM01183) specifically targets RNA Pol II for degradation via the proteasome pathway in a TC-NER-dependent fashion

Lurbinectedin (PM01183), a new synthetic tetrahydroisoquinoline alkaloid, is a minor groove specific DNA binder that interacts directly with specific factors involved in DNA repair and transcription pathways. In living cells, PM01183-DNA adducts stall replication and transcription giving rise to double strand breaks, inducing accumulation of cells in the S-phase of the cell cycle and triggering apoptosis. In both the ongoing phase II trials (pancreas and platinum-resistant ovarian cancer) the first stage was concluded with positive results in clinical activity, ensuring the continuity of the studies. Also, phase I trials in combination with doxorubicin and gemcitabine as well as in advanced acute leukemia are ongoing. Here, we examined the effects of PM01183 on the activity and stability of the RNAPol II as well as on other factors of the transcriptional machinery, including TBP (TFIID), p62 (TFIIH), XPG and XPF. Our results showed that PM01183 induced a rapid, time- and concentration-dependent degradation of RNA Pol II in a panel of different human tumor cell lines, including HCT-116 (colon), A549 (NSCLC), HeLa (cervix) and A763 (sarcoma). This degradative process was efficiently abrogated in the presence of transcriptional (DRB or Actinomycin D) or proteasome inhibitors (MG132), demonstrating that PM01183 specifically targets the transcriptionally active RNA Pol II for degradation via the proteasome pathway. In addition, it was also shown that the effect of PM01183 on the RNA Pol II was dependent on the presence of a functional TC NER repair machinery. PM01183 induced degradation of RNA Pol II in global NER (XPC) deficient cells, but failed to do it in TC NER (CSB, XPD and XPG) deficient cells. Importantly, these effects were confirmed to be specific for the RNA Pol II, since other factors of the transcriptional machinery, such as TBP (TFIID), p62 (TFIIH), XPG or XPF or the RPA194 subunit of the RNA Pol I were not affected. Together, these results show up the complex mechanism of action of the drug on tumor cells.

Citation Format: Gema Santamaria, Juan F. Martinez-Leal, Carmen Cuevas, Luis F. Garcia-Fernandez, Carlos M. Galmarini. Lurbinectedin (PM01183) specifically targets RNA Pol II for degradation via the proteasome pathway in a TC-NER-dependent fashion. [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 5558. doi:10.1158/1538-7445.AM2013-5558