Malignant Pleural Mesothelioma: Is Tailoring the Second-Line Therapy Really "Raising the Bar?"

The two sides of chromosomal instability: drivers and brakes in cancer

Chromosomal instability (CIN) is a hallmark of cancer and is associated with tumor cell malignancy. CIN triggers a chain reaction in cells leading to chromosomal abnormalities, including deviations from the normal chromosome number or structural changes in chromosomes. CIN arises from errors in DNA replication and chromosome segregation during cell division, leading to the formation of cells with abnormal number and/or structure of chromosomes. Errors in DNA replication result from abnormal replication licensing as well as replication stress, such as double-strand breaks and stalled replication forks; meanwhile, errors in chromosome segregation stem from defects in chromosome segregation machinery, including centrosome amplification, erroneous microtubule-kinetochore attachments, spindle assembly checkpoint, or defective sister chromatids cohesion. In normal cells, CIN is deleterious and is associated with DNA damage, proteotoxic stress, metabolic alteration, cell cycle arrest, and senescence. Paradoxically, despite these negative consequences, CIN is one of the hallmarks of cancer found in over 90% of solid tumors and in blood cancers. Furthermore, CIN could endow tumors with enhanced adaptation capabilities due to increased intratumor heterogeneity, thereby facilitating adaptive resistance to therapies; however, excessive CIN could induce tumor cells death, leading to the "just-right" model for CIN in tumors. Elucidating the complex nature of CIN is crucial for understanding the dynamics of tumorigenesis and for developing effective anti-tumor treatments. This review provides an overview of causes and consequences of CIN, as well as the paradox of CIN, a phenomenon that continues to perplex researchers. Finally, this review explores the potential of CIN-based anti-tumor therapy.

Establishment and Characterization of Patient-Derived Xenografts (PDXs) of Different Histology from Malignant Pleural Mesothelioma Patients

Simple Summary

Malignant pleural mesothelioma (MPM) is a rare tumor with unfavorable prognosis for which new therapeutic interventions are urgently needed. The aim of our study was to develop a preclinical model representative of the different histotypes found in human tumors that can be used as models for the discovery of new treatments and combinations. We successfully generated patient-derived xenografts (PDXs) from MPM, which strongly resembled the tumors of origin in terms of morphology and immunohistochemistry. These tumors, when growing in mice, poorly respond to cisplatin, a finding that aligned with the clinical results. From one of the PDXs, we generated 2D and 3D cultures maintaining the phenotypical characteristics of human tumors and PDXs. Altogether, these preclinical models represent a useful tool for the discovery of new targets and drug combinations.

Abstract

Background: Malignant pleural mesothelioma (MPM) is a very aggressive tumor originating from mesothelial cells. Although several etiological factors were reported to contribute to MPM onset, environmental exposure to asbestos is certainly a major risk factor. The latency between asbestos (or asbestos-like fibers) exposure and MPM onset is very long. MPM continues to be a tumor with poor prognosis despite the introduction of new therapies including immunotherapy. One of the major problems is the low number of preclinical models able to recapitulate the features of human tumors. This impacts the possible discovery of new treatments and combinations. Methods: In this work, we aimed to generate patient-derived xenografts (PDXs) from MPM patients covering the three major histotypes (epithelioid, sarcomatoid, and mixed) occurring in the clinic. To do this, we obtained fresh tumors from biopsies or pleurectomies, and samples were subcutaneously implanted in immunodeficient mice within 24 h. Results: We successfully isolated different PDXs and particularly concentrated our efforts on three covering the three histotypes. The tumors that grew in mice compared well histologically with the tumors of origin, and showed stable growth in mice and a low response to cisplatin, as was observed in the clinic. Conclusions: These models are helpful in testing new drugs and combinations that, if successful, could rapidly translate to the clinical setting.

PD-L1 and prognosis in patients with malignant pleural mesothelioma: a meta-analysis and bioinformatics study

BACKGROUND

The prognostic value of programmed death-ligand 1 (PD-L1) expression in patients with malignant pleural mesothelioma (MPM) has been controversial according to previous investigations. Therefore, we conducted a meta-analysis to assess the potential prognostic significance of PD-L1 expression in MPM.

METHODS

PubMed, Embase, Web of Science, Scopus, and the Cochrane Library were thoroughly searched for relevant original articles published before 9 April 2020. The pooled hazard ratios (HRs) and 95% confidence intervals (CIs) of overall survival (OS) and progression-free survival (PFS) were calculated. The results of the meta-analysis were verified using The Cancer Genome Atlas (TCGA) dataset.

RESULTS

In total 16 studies were included in our meta-analysis. A high PD-L1 expression was associated with a poor OS (HR = 1.53, 95% CI = 1.28-1.83, p < 0.001), but not a grave PFS (HR = 1.07, 95% CI = 0.82-1.39, p = 0.643) in MPM. Furthermore, the PD-L1 expression correlated with the sarcomatoid + biphasic type of MPM (odds ratio = 4.32, 95% CI = 2.16-8.64, p < 0.001). TCGA data indicated that PD-L1 was a significant prognostic factor for OS (HR = 2.069, 95% CI = 1.136-3.769, p = 0.0175), but not for PFS (HR = 1.205, 95% CI = 0.572-2.539, p = 0.624), which was in accordance with the results of the meta-analysis.

CONCLUSION

A high PD-L1 expression is a significant prognostic factor for poor OS of patients with MPM. We therefore suggest that PD-L1 expression levels can be used to predict the clinical outcomes of patients with MPM in the future.

A phase II study of the combination of gemcitabine and imatinib mesylate in pemetrexed-pretreated patients with malignant pleural mesothelioma

OBJECTIVES

Second-line chemotherapy is not a standard of care in patients with malignant pleural mesothelioma (MPM) that progresses after first-line treatment with cisplatin and pemetrexed. In pre-clinical models, the combination of gemcitabine (GEM) and imatinib mesylate (IM), compared with GEM alone, led to a further tumor growth inhibition and improved survival. This phase II study evaluates the antitumor activity of a combination of IM and GEM in platinum-pemetrexed-pretreated MPM patients expressing PDGFR-β and/or cKIT by immunohistochemistry (IHC).

PATIENTS AND METHODS

GEM (1000 mg/m²) was given on days 3 and 10; IM (400 mg) was taken orally on days 1-5 and 8-12 of a 21-day cycle. The primary endpoint was the 3-month progression-free survival (PFS) rate. The study follows the optimal two-stage design of Simon. A 3-month PFS target of 75 % was required. With a probability error α = 10 % and a power of 80 %, the calculated sample size was 22 patients. In particular, in the first step, six out of nine patients and globally 14/22 patients free from progressive disease at 3 months were required. Secondary endpoints included response rate, duration of response, toxicity and overall survival (OS).

RESULTS

In total, 23 patients were enrolled (ECOG PS 0-1/2: 9/13; one previous line/≥two previous lines: 10/13). Partial response was achieved in four patients (17.4 %) and stable disease in 11 (47.8 %) with a disease control rate of 65.3 %. After a median follow-up of 34.5 months, median PFS and OS were 2.8 and 5.7 months, respectively. The 3-month PFS rate was 39.1 % (9/23 patients). All-grade drug-related adverse events occurred in 17 (73.9 %) patients. Grade 3 treatment-related adverse events were observed in four (17 %) patients.

CONCLUSIONS

The combination of IM and GEM is well tolerated in platinum-pemetrexed-pretreated MPM patients expressing PDGFR-β and/or cKIT by IHC, but it does not show a significant PFS benefit.