To the surprise of scientists, the most dangerous cancers of the uterine lining closely resemble the worst ovarian and breast cancers, raising the tantalizing possibility that the three deadly cancers might respond to the same drugs. Another finding was that many endometrial cancers had a mutation in a gene that had been seen before only in colon cancers. The mutation disables a system for repairing DNA damage, resulting in 100 times more mutations than typically occur in cancer cells. Indeed, endometrial cancers with the mutation had better outcomes, perhaps because the accumulating DNA damage is devastating to cancer cells.

A new horizon of possibilities is possible for mesothelioma as well, after the recent finding that germline BAP1 mutations predispose to mesothelioma and uveal/cutaneous melanoma. Indeed, finding the connection to BAP1 is the best new discovery in mesothelioma in the last decade, with potential for being a game changer in diagnosis, prevention, and treatment.

These results open a new scenario for the interpretation of cancer, from the way we diagnose it to the way we treat it.

Since the gene ratio technique is binary, they used a sequential method similar to most clinical pathological diagnostic approaches. They developed sequential binary tests to differentiate MPM from all confounding diagnoses. Altogether, a 26-gene signature performed by the sequential gene-ratio tests diagnosed MPM with high sensitivity and specificity. This signature required fewer genes than the one identified by standard bioinformatics.

The overall sensitivity for the sequential diagnosis of MPM was 100% when both microarray and RT-PCR data were included, whereas the overall specificity was 99% using the microarray platform and 90% using the RT-PCR platform.

The authors used the same strategy to develop a test to differentiate the epithelioid from the sarcomatoid histological subtypes of MPM, a clinically important problem. The two subtypes clearly clustered into two separate branches in both the dendrogram and heat-map generated from the 172 genes differentially expressed between the two types.

Up-regulated pathways in the epithelioid group were related to transmembrane receptor protein tyrosine kinase signaling, germ cell development, and regulation of cell proliferation. The downregulated pathways in the epithelioid group were related to response to external stimulus, blood vessel development, cell adhesion, and regulation of secretion.

Finally, they used the same dataset to discover molecular features unique to mesothelioma.
The pathways up-regulated in mesotheliomas could be clustered into at least four main groups:

• extracellular organization
• development
• response to endogenous, mechanical, or hormonal stimuli
• immune response

Read more here.

BALB/c mice, injected with murine mesothelioma cells, with a control vaccination (left) and one with recombinant Fowlpox virus replicons encoding survivin (right).

Malignant Mesothelioma patients exhibiting antitumor immune responses have demonstrated improved survival. One of the most effective vaccination methods for generating potent-specific immune responses is based on recombinant viral vectors. Recent interest has focused on Fowlpox virus as a candidate mammalian vaccine due to its large cloning capacity, which can provide sustained expression of heterologous genes combined with an impeccable safety profile.

In this paper, P. Bertino et al. reveal that a variant of Fowlpox vector expressing the mesothelioma-relevant tumor associated antigen survivin (FP-surv) exerted a significant antitumor effect against experimental mesothelioma tumors in mice.

FP-surv induced an increased number of tumor-infiltrating CD8⁺ T cells that correlated with improved animal survival and slower tumor growth in subcutaneous and intraperitoneal mesothelioma mouse models. The increased number of tumor-infiltrating CD8⁺ T cells were comprised of survivin-specific T cells with high IFN-γ producing capacity as revealed by ELISPOT and intracellular cytokine analyses. Additional evidence of the generation of survivin-specific CTLs by FP-surv came from the staining of splenocytes and lymph node cells from immunized mice with survivin-specific pentamers. In addition, FP-surv vaccination altered the tumor microenvironment resulting in a significant increase in IFN-γ expression.

Survivin vaccination induced complete tumor regression in 33% of mice with EKKH5 mesothelioma cells. The remaining mice eventually died due to tumor mass growth, but tumor progression in vaccinated mice was significantly delayed compared to unvaccinated mice. In most cases, tumors in vaccinated mice contained both areas with signs of necrosis exhibiting complete cellular degradation and a small rim or viable tumor cells.

Importantly, fertility and histopathological analyses were performed to evaluate potential adverse effects arising from autoimmunity. Vaccination of mice against survivin neither affected fertility nor induced tissue damage in healthy organs.

Taken together, these results suggest that Fowlpox vectors expressing survivin induce specific immune responses that effectively suppress mesothelioma tumor progression in vivo without induction of autoimmune responses. This vaccination approach may serve as the basis for promising clinical applications.

Read more here.

Scheme of PARP1/SIRT1/Akt/mTOR signaling

The targeting of PARP1 is showing considerable potential for selectively killing tumor cells while sparing normal cells, and offers a scientifically rational clinical application.

In this paper, G. Pinton et al. investigate PARP1 expression in normal mesothelial and malignant mesothelioma tissue samples.

Immunohistochemical analysis revealed low PARP1 staining in peri-tumoral normal mesothelium. In contrast, staining was found to be elevated in mesothelioma with a progressive increase from moderate staining in epithelioid mesotheliomas to the highest staining in the most aggressive sarcomatoid mesotheliomas. In mesothelioma-derived cell lines, increased PARP1 expression correlated with sensitivity to its inhibitor CO-338. As a single agent, CO-338 significantly reduced cell viability and, when combined with cisplatin, was synergistically active. The authors also described a pathway by which PARP inhibition led to activation of a deacetylase enzyme, SIRT1, which could modulate Akt activity. In conclusion, this study demonstrates that PARP1 overexpression defines increased responsiveness to its inhibition and that a substantial fraction of patients could be candidates for therapy with PARP1 inhibitors.

Read the article here.

(A) Formation of MPeMSCs with capsular covering and possible asymmetric and symmetric stem cell division. a, b, CSCs originate from the parental cells as dark bubble-like protrusions (arrows). Cells detach and float in the culture and MPeMSCs ‘hatch-out’ of the capsule (arrows). c, Asymmetric cell division in capsular stem cells. Asymmetrically dividing cells originate from the capsule (upper panel, arrows) or cells divide unequally along with the capsule generating two non-identical cells (lower panel). d, Symmetric cell division of a capsular stem cell. Scale bars: 100 px. e, f, Fluorescent images of asymmetric (e) and symmetric (f) cell division of encapsulated cells. Arrows indicate the outer capsular covering of the cell (B) a, MPeMSCs originate from the nucleus of a multinucleated cell; the newly formed cell moves through the cytoplasm and is released from the parental cell. b, Origin of multiple CSCs from a multinucleated cell. c, Fluorescent images of a multinucleated cell.

Recent studies in solid organ cancers have shown that cancer stem cells (CSCs) play a pivotal role in the initiation and progression of tumors. However, it is not known whether tumorigenic stem cells exist and whether they promote tumor growth in mesothelioma.

In this study, the authors developed and characterized a CSC model for mesothelioma using stably expandable tumorigenic stem cells derived from patient tumors. They found morphologically distinct populations of CSCs that divide asymmetrically or symmetrically in vitro cell culture.

Mesothelioma stem cells express stem cell markers c-MYC, NES and VEGFR2 and in the presence of matrix components cells form colony spheres. Mesothelioma stem cells are multipotent, differentiate into neuronal, vascular and adipose progeny upon defined induction and the differentiating cells express lineage-specific markers such as TUBB3, an early neuronal marker; vWF, VEGFA, VEGFC and IL-8, endothelial markers; and PPARγ and FABP4, adipose markers.

Xenotransplantation experiments using mesothelioma stem cells demonstrated early tumor growth compared with parental cells. Interestingly, by using mesothelioma stem cells and endothelial lineage-induced cells derived from a single stem cell resulted in early tumor growth in the latter group indicating that endothelial differentiation of ste cells is important for mesothelioma initiation.

This has important implications for understanding the cells of origin and tumor progression in mesothelioma and hence targeting stem cells may be a useful strategy to inhibit malignant progression.

Read article here.

Vorinostat abolishes multicellular resistance of spheroids.

September 29, 2011 (Stockholm, Sweden) — The largest randomized phase 3 study ever conducted in patients with advanced malignant pleural mesothelioma has failed; no survival benefit was seen with vorinostat (Zolinza, Merck & Co).
Sadly yes, out of 660 patients, there was no significant difference in median overall survival between the vorinostat and placebo groups. The latest article from Dr. Barbone and colleagues sheds some light on possible reasons for the unsuccessful outcome of the trial.
Interestingly Dr. Broaddus’ group has tested the activity of Vorinostat by using 3D spheroids, a model that has proven very effective in investigating chemoresistance. The authors have previously shown that when grown in 3D cultures as spheroids, mesothelioma cells acquire a multicellular resistance to apoptosis that resembles that of solid tumors. Also, previous data from the same lab showed that resistance in 3D can be explained by a lack of upregulation of Noxa, the pro-apoptotic BH3 sensitizer that acts via displacement of the Bak/Bax-activator BH3-only protein, Bim.
Dr. Barbone an colleagues hypothesized that the histone deacetylase inhibitor vorinostat might reverse this block to Noxa upregulation in 3D. Indeed, they found that vorinostat effectively restored upregulation of Noxa protein levels and message and abolished multicellular resistance to bortezomib in the 3D spheroids. These results support the evidence that the manipulation of the core apoptotic repertoire is key to improve the chemosensitivity of mesothelioma.Addition of vorinostat similarly increased the apoptotic response to bortezomib in another 3D model, the tumor fragment spheroid, which is grown from human mesothelioma ex vivo. In addition to its benefit when used with bortezomib, vorinostat also enhanced the response to cisplatin plus pemetrexed, as shown in both 3D models.
The biggest advance in mesothelioma treatment was the combination of two chemotherapeutics, cisplatin and pemetrexed so the authors believe that key to therapeutic efficacy lies in combinatorial strategies. Whereas neither vorinostat nor bortezomib alone had been clinically effective in mesothelioma, vorinostat may undermine chemoresistance to bortezomib and to other therapies thereby providing a rationale for combinatorial strategies.

Read the free article here.

Starvation selectively sensitizes human cancer cells to CDDP. In normal cells, serum starvation activates AMPK, which stabilizes p53 resulting in cell proliferation arrest. The processing of CDDP-DNA-adducts in proliferating cells results in DNA damage. Proliferation arrest may contribute to the inactivation of DNA damage response thus the tolerance of normal cells to CDDP. In cancer cells, serum starvation also activates ATM/Chk2/p53 signaling. The combination of CDDP with serum starvation results in the enhanced activation of the signaling and sensitizes cancer cells to CDDP

Starvation and possibly induction of authophagy have been suggested in many cancers as a possible support to chemotherapy, to enhance its efficacy. Group like the one of Dr. David Sabatini in Boston have clearly linked cancer to metabolic alterations, revolving around mTOR, and found ways to rewire metabolism therapeutically . Moreover, it is known that rapamycin mimics a starvation-like signal and that mTOR and its inhibitors are key targets for mesothelioma therapy both in vitro, ex vivo and in vivo.

The authors here investigated the effects of serum starvation on CDDP toxicity in normal and cancer cells by assessing proliferation, cell cycle distribution and activation of DNA-damage response and of AMPK, and compared them to the effects observed in cells grown in serum-containing medium. The effects of short-term food starvation on CDDP chemotherapy were assessed in xenografts-bearing mice and were compared to effects on tumor growth and/or regression determined in mice with no diet alteration.

They observed that serum starvation in vitro sensitizes cancer cells to CDDP while protecting normal cells. In detail, in normal cells, serum starvation resulted in a complete arrest of cellular proliferation, i.e. depletion of BrdU-incorporation during S-phase and accumulation of the cells in the G0/G1-phase of the cell cycle. In contrast to normal cells, serum starvation-induced p53 activation in cancer cells is both AMPK- and ATM-dependent. Combination of CDDP with serum starvation in vitro increased the activation of ATM/Chk2/p53 signaling pathway compared to either treatment alone resulting in an enhanced sensitization of cancer cells to CDDP.
Of note, short-term food starvation dramatically increased the sensitivity of human tumor xenografts to cisplatin as indicated not only by a significant growth delay, but also by the induction of complete remission in 60 % of the animals bearingmesothelioma xenografts, and in 40 % of the animals with lung carcinoma xenografts.

Read the article here.

Distribution of the 13 protein biomarkers by pathologic stage.

Early detection of mesothelioma is key for chemo-efficiency. The authors conducted a multi-center case-control studies in serum from 117 mesothelioma cases and 142 asbestos-exposed control individuals. Biomarker discovery, verification, and validation were performed using the SOMAmer proteomic technology, which simultaneously measures over 1000 proteins in unfractionated biologic samples. Using univariate and multivariate approaches they discovered 64 candidate protein biomarkers, consisting of both inflammatory and proliferative proteins, processes strongly associated with asbestos-induced malignancy. The author further selected a pool of 13 candidate proteins (classifiers) for distinguishing mesotheliomas from controls. The ability of the classifiers to detect mesothelioma was not compromised by neoadjuvant chemotherapy prior to blood draw or by histology. Overall 77% of Stage I, 93% of Stage II, 96% of Stage III and 96% of Stage IV cases were detected.

In sum, using the SOMAscan proteomic assay, a highly sensitive candidate 13-biomarker panel was discovered and validated for the detection of mesothelioma in the asbestos-exposed population with an accuracy of 92% and detection of 88% of Stage I and II disease.

SB-431542, an inhibitor of activin receptors, decreases cell growth and migration of mesothelioma cell lines in a dose-dependent way.

Activins are members of the transforming growth factor b (TGF-b) superfamily of growth and differentiation factors. Activin A has important physiological roles in cell differentiation, wound healing and inflammation and has the ability to either inhibit or promote growth, depending on the cell type. With respect to cancer, activin A was shown to inhibit cell proliferation in hepatocellular carcinoma, breast cancer or prostate cancer.

In this publication, the authors present activin A as a potential candidate for mesothelioma therapy. They show that activin A is highly expressed in mesothelioma cell lines and in a subset of mesothelioma tissue specimens. Furthermore, they demonstrate that inhibition of activin receptors or silencing of activin A gene expression impairs growth and migration of mesothelioma cells.

No previous reports have been published on the impact of activin A on mesothelioma cell behaviour. The authors also found that recombinant Activin A stimulated clonogenic growth and enhanced cell migration, possibly through the canonical SMAD pathway, similar to the findings described for activin A in oesophageal adenocarcinoma and lung adenocarcinoma. Collectively, these data suggest that in each of these thoracic malignancies activin A has a tumor promoting effect.

Read the article here.

Also, we would like to share some of the statistics related to the abstracts submissions and general attendance for the meeting. Here you can download a summary of the meeting statistics, including the country of origin.

Thanks to all the 506 delegates and the 282 Abstract submissions for having contributed to the most attended iMig meeting so far.

We look forward to seeing you in South Africa in 2014.