Efficacy of CDK4/6 inhibitors in preclinical models of malignant pleural mesothelioma

[Recent Advances in Medical Treatment of Malignant Pleural Mesothelioma]

Malignant pleural mesothelioma (MPM) is a highly aggressive malignancy originating from mesothelial cells of the pleura, primarily associated with asbestos exposure, and is often characterized by poor prognosis. Due to the lack of specific clinical manifestations in the early stages, the diagnosis of MPM presents a significant challenge, leading to most patients being diagnosed at an advanced stage, which limits the effectiveness of surgical treatment. Consequently, systemic therapies are commonly required. Although Pemetrexed in combination with Platinum-based chemotherapy remains the first-line standard treatment for unresectable MPM, its therapeutic efficacy is limited, and more effective treatment strategies are urgently needed. In recent years, immune checkpoint inhibitors have made significant progress in the treatment of MPM, markedly improving patient survival outcomes. With the increasing depth of molecular biological research on MPM, targeted therapies offer promising personalized treatment options. Additionally, the therapeutic potential of novel strategies such as cell therapy and oncolytic virus therapy is beginning to emerge. This review summarizes the latest advancements in the medical treatment of MPM and looks forward to future therapeutic directions, aiming to provide insights for clinical practice.
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Diagnosis of Pleural Mesothelioma: Is Everything Solved at the Present Time?

Ranked high in worldwide growing health issues, pleural diseases affect approximately one million people globally per year and are often correlated with a poor prognosis. Among these pleural diseases, malignant pleural mesothelioma (PM), a neoplastic disease mainly due to asbestos exposure, still remains a diagnostic challenge. Timely diagnosis is imperative to define the most suitable therapeutic approach for the patient, but the choice of diagnostic modalities depends on operator experience and local facilities while bearing in mind the yield of each diagnostic procedure. Since the analysis of pleural fluid cytology is not sufficient in differentiating historical features in PM, histopathological and morphological features obtained via tissue biopsies are fundamental. The quality of biopsy samples is crucial and often requires highly qualified expertise. Since adequate tissue biopsy is essential, medical or video-assisted thoracoscopy (MT or VATS) is proposed as the most suitable approach, with the former being a physician-led procedure. Indeed, MT is the diagnostic gold standard for malignant pleural pathologies. Moreover, this medical or surgical approach can allow diagnostic and therapeutic procedures: it provides the possibility of video-assisted biopsies, the drainage of high volumes of pleural fluid and the administration of sterile calibrated talcum powder under visual control in order to achieve pleurodesis, placement of indwelling pleural catheters if required and in a near future potential intrapleural therapy. In this context, dedicated diagnostic pathways remain a crucial need, especially to quickly and properly diagnose PM. Lastly, the interdisciplinary approach and multidisciplinary collaboration should always be implemented in order to direct the patient to the best customised diagnostic and therapeutic pathway. At the present time, the diagnosis of PM remains an unsolved problem despite MDT (multidisciplinary team) meetings, mainly because of the lack of standardised diagnostic work-up. This review aims to provide an overview of diagnostic procedures in order to propose a clear strategy.

Pharmacological inhibition of CDK4/6 impairs diffuse pleural mesothelioma 3D spheroid growth and reduces viability of cisplatin-resistant cells

Introduction

Diffuse pleural mesothelioma (DPM) of the pleura is a highly aggressive and treatment-resistant cancer linked to asbestos exposure. Despite multimodal treatment, the prognosis for DPM patients remains very poor, with an average survival of 2 years from diagnosis. Cisplatin, a platinum-based chemotherapy drug, is commonly used in the treatment of DPM. However, the development of resistance to cisplatin significantly limits its effectiveness, highlighting the urgent need for alternative therapeutic strategies. New selective inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) have shown promise in various malignancies by inhibiting cell cycle progression and suppressing tumor growth. Recent studies have indicated the potential of abemaciclib for DPM therapy, and a phase II clinical trial has shown preliminary encouraging results.

Methods

Here, we tested abemaciclib, palbociclib, and ribociclib on a panel of DPM cell lines and non-tumor mesothelial(MET-5A) cells.

Results

Specifically, we focused on abemaciclib, which was the mosteffective cytotoxic agent on all the DPM cell lines tested. Abemaciclib reduced DPM cell viability, clonogenic potential, and ability to grow as three-dimensional (3D) spheroids. In addition, abemaciclib induced prolonged effects, thereby impairing second-generation sphere formation and inducing G0/G1 arrest and apoptosis/ necrosis. Interestingly, single silencing of RB family members did not impair cell response to abemaciclib, suggesting that they likely complement each other in triggering abemaciclib's cytostatic effect. Interestingly, abemaciclib reduced the phosphorylation of AKT, which is hyperactive in DPM and synergized with the pharmacological AKT inhibitor (AKTi VIII). Abemaciclib also synergized with cisplatin and reduced the viability of DPM cells with acquired resistance to cisplatin.

Discussion

Overall, our results suggest that CDK4/6 inhibitors alone or in combination with standard of care should be further explored for DPM therapy.

Targeted Therapy in Mesotheliomas: Uphill All the Way

Mesothelioma (MM) is an aggressive and lethal disease with few therapeutic opportunities. Platinum-pemetrexed chemotherapy is the backbone of first-line treatment for MM. The introduction of immunotherapy (IO) has been the only novelty of the last decades, allowing an increase in survival compared to standard chemotherapy (CT). However, IO is not approved for epithelioid histology in many countries. Therefore, therapy for relapsed MM remains an unmet clinical need, and the prognosis of MM remains poor, with an average survival of only 18 months. Increasing evidence reveals MM complexity and heterogeneity, of which histological classification fails to explain. Thus, scientific focus on possibly new molecular markers or cellular targets is increasing, together with the search for target therapies directed towards them. The molecular landscape of MM is characterized by inactivating tumor suppressor alterations, the most common of which is found in CDKN2A, BAP1, MTAP, and NF2. In addition, cellular targets such as mesothelin or metabolic enzymes such as ASS1 could be potentially amenable to specific therapies. This review examines the major targets and relative attempts of therapeutic approaches to provide an overview of the potential prospects for treating this rare neoplasm.

[Advances in Targeted Therapy for Malignant Pleural Mesothelioma]

Malignant pleural mesothelioma (MPM) is a rare cancer with high malignancy and aggressiveness on the pleural, caused by the following risk factors including asbestos inhalation, genetic factors, and genetic mutation. The present chemotherapy, antiangiogenic therapy, and immunotherapy methods are ineffective and the survival time of patients is very short. There is an urgent need to find potential therapeutic targets for MPM. At present, it has been found the following types of targets: gene mutation targets such as BRCA associated protein 1 (BAP1) and cyclin-dependent kinase 2A (CDKN2A); epigenetic targets such as lysine (K)-specific demethylase 4A (KDM4A) and lysine-specific demethylase 1 (LSD1), and signal protein targets such as glucose-regulated protein 78 (GRP78) and signal transducer and activator of transcription 3 (STAT3). So far, available clinical trials include phase II clinical trials of histone methyltransferase inhibitor Tazemetostat, poly (ADP-ribose) polymerase (PARP) inhibitor Rucaparib and cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitor Abemaciclib, as well as phase I clinical trials of mesothelin-targeting chimeric antigen receptor T-cell immunotherapy (CAR-T) cell injection in the thoracic cavity and TEA domain family member (TEAD) inhibitor VT3989 and IK-930, and the results of these trials have showed certain clinical efficacy.
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Emerging New Targets in Systemic Therapy for Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a heterogeneous cancer composed of distinct molecular and pathologic subtypes. Unfortunately, MPM is aggressive, and current therapies for advanced, unresectable disease remain limited to cytotoxic chemotherapy and immunotherapy. Our understanding of the genomic landscape of MPM is steadily growing, while the discovery of effective targeted therapies in MPM has advanced more slowly than in other solid tumors. Given the prevalence of alterations in tumor suppressor genes in MPM, it has been challenging to identify actionable targets. However, efforts to characterize the genetic signatures in MPM over the last decade have led to a range of novel targeted therapeutics entering early-phase clinical trials. In this review, we discuss the advancements made thus far in targeted systemic therapies in MPM and the future direction of targeted strategies in patients with advanced MPM.

Targeted Approaches to Treatment of Pleural Mesothelioma: A Review

Pleural mesothelioma is an aggressive disease that is enriched for inactivating alterations in tumor suppressor genes. Systemic therapeutic strategies for pleural mesothelioma generally involve chemotherapies and immunotherapies that are chosen without consideration of the tumor's molecular profile. As this generalized approach to treatment rarely yields durable responses, alternative therapeutic regimens are urgently indicated. Preclinical studies have identified synthetic lethal protein and metabolic interactions, recurrently overexpressed proteins, and frequent pathway perturbations that may be therapeutically exploited in mesothelioma. This review discusses the mechanism of action of emerging investigational therapies and summarizes findings from phase I-II clinical trials exploring selective, biomarker-driven therapeutic strategies for mesothelioma, with a focus on five common targets. Finally, using lessons learned from these clinical trials, imperatives for successful implementation of targeted therapy in mesothelioma are discussed.

Immunomodulatory effects of CDK4/6 inhibitors

The dysregulation of the cell cycle is one of the hallmarks of cancer. Cyclin-dependent kinase 4 (CDK4) and CDK6 play crucial roles in regulating cell cycle and other cellular functions. CDK4/6 inhibitors have achieved great success in treating breast cancers and are currently being tested extensively in other tumor types as well. Accumulating evidence suggests that CDK4/6 inhibitors exert antitumor effects through immunomodulation aside from cell cycle arrest. Here we outline the immunomodulatory activities of CDK4/6 inhibitors, discuss the immune mechanisms of drug resistance and explore avenues to harness their immunotherapeutic potential when combined with immune checkpoint inhibitors (ICIs) or chimeric antigen receptor (CAR) T-cell therapy to improve the clinical outcomes.

CDK4/6 Inhibition Enhances the Efficacy of Standard Chemotherapy Treatment in Malignant Pleural Mesothelioma Cells

BACKGROUND

The loss of the CDKN2A/ARF (cyclin-dependent kinase inhibitor 2A/alternative reading frame) gene is the most common alteration in malignant pleural mesothelioma (MPM), with an incidence of about 70%, thus representing a novel target for mesothelioma treatment. In the present study, we evaluated the antitumor potential of combining the standard chemotherapy regimen used for unresectable MPM with the CDK4/6 (cyclin-dependent kinase 4 or 6) inhibitor abemaciclib.

METHODS

Cell viability, cell death, senescence, and autophagy induction were evaluated in two MPM cell lines and in a primary MPM cell culture.

RESULTS

The simultaneous treatment of abemaciclib with cisplatin and pemetrexed showed a greater antiproliferative effect than chemotherapy alone, both in MPM cell lines and in primary cells. This combined treatment induced cellular senescence or autophagic cell death, depending on the cell type. More in detail, the induction of cellular senescence was related to the increased expression of p21, whereas autophagy induction was due to the impairment of the AKT/mTOR signaling. Notably, the effect of the combination was irreversible and no resumption in tumor cell proliferation was observed after drug withdrawal.

CONCLUSION

Our results demonstrated the therapeutic potential of CDK4/6 inhibitors in combination with chemotherapy for the treatment of MPM and are consistent with the recent positive results in the MiST2 arm in abemaciclib-treated patients.

Gilteritinib Enhances Anti-Tumor Efficacy of CDK4/6 Inhibitor, Abemaciclib in Lung Cancer Cells

Abemaciclib is a cyclin-dependent kinases 4/6 (CDK4/6) inhibitor approved for the treatment of metastatic breast cancer. Preclinical studies suggest that abemaciclib has the potential for lung cancer treatment. However, several clinical trials demonstrate that monotherapy with abemaciclib has no obvious superiority than erlotinib to treat lung cancer patients, limiting its therapeutic options for lung cancer treatment. Here, we show that the US Food and Drug Administration (FDA)-approved drug, gilteritinib, enhances the cytotoxicity of abemaciclib through inducing apoptosis and senescence in lung cancer cells. Interestingly, abemaciclib in combination with gilteritinib leads to excessive accumulation of vacuoles in lung cancer cells. Mechanistically, combined abemaciclib and gilteritinib induces complete inactivation of AKT and retinoblastoma (Rb) pathways in lung cancer cells. In addition, RNA-sequencing data demonstrate that combination of abemaciclib and gilteritinib treatment induces G2 phase cell-cycle arrest, inhibits DNA replication, and leads to reduction in homologous recombination associated gene expressions. Of note, abemaciclib-resistant lung cancer cells are more sensitive to gilteritinib treatment. In a mouse xenograft model, combined abemaciclib and gilteritinib is more effective than either drug alone in suppressing tumor growth and appears to be well tolerated. Together, our findings support the combination of abemaciclib with gilteritinib as an effective strategy for the treatment of lung cancer, suggesting further evaluation of their efficacy is needed in a clinical trial.

A Glimpse in the Future of Malignant Mesothelioma Treatment

Malignant mesothelioma (MMe) is a rare neoplasm with few therapeutic options available. The landscape of effective therapy for this disease remained unchanged in the last two decades. Recently, however, the introduction of Immune Checkpoint Inhibitors (ICIs) led to small, but nevertheless, promising improvements. However, many efforts are still needed to radically improve the prognosis of MMe. In this review, we analyze all those therapeutic strategies for MMe that are still in a preclinical or early clinical phase of development. In particular, we focus on novel antiangiogenic drugs and their possible combination with immunotherapy. Furthermore, we describe also more complex strategies such as microRNA-loaded vectors, oncolytic viruses, and engineered lymphocytes.