Preclinical evaluation of CDK4 phosphorylation predicts high sensitivity of pleural mesotheliomas to CDK4/6 inhibition

Our plain-English summary of Preclinical evaluation of CDK4 phosphorylation predicts high sensitivity of pleural mesotheliomas to CDK4/6 inhibition, by S. Paternot, E. Raspé, C. Meiller, et al (Molecular Oncology, 2024).

The study

• Authors: S. Paternot, E. Raspé, C. Meiller, M. Tarabichi, J.B. Assié, F. Libert, M. Remmelink, X. Bisteau, P. Pauwels, Y. Blum, N. Le Stang, S. Tabone-Eglinger, F. Galateau-Sallé, C. Blanquart, J.P. Van Meerbeeck, T. Berghmans, D. Jean, P.P. Roger
• Journal: Molecular Oncology
• Published: 2024;18(4):866-894
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive cancer with limited therapeutic options. We evaluated the impact of CDK4/6 inhibition by palbociclib in 28 MPM cell lines including 19 patient-derived ones, using various approaches including RNA-sequencing. Palbociclib strongly and durably inhibited the proliferation of 23 cell lines, indicating a unique sensitivity of MPM to CDK4/6 inhibition. When observed, insensitivity to palbociclib was mostly explained by the lack of active T172-phosphorylated CDK4. This was associated with high p16INK4A (CDKN2A) levels that accompany RB1 defects or inactivation, or (unexpectedly) CCNE1 overexpression in the presence of wild-type RB1. Prolonged palbociclib treatment irreversibly inhibited proliferation despite re-induction of cell cycle genes upon drug washout. A senescence-associated secretory phenotype including various potentially immunogenic components was irreversibly induced. Phosphorylated CDK4 was detected in 80% of 47 MPMs indicating their sensitivity to CDK4/6 inhibitors. Its absence in some highly proliferative MPMs was linked to very high p16 (CDKN2A) expression, which was also observed in public datasets in tumours from short-survival patients. Our study supports the evaluation of CDK4/6 inhibitors for MPM treatment, in monotherapy or combination therapy.

© 2022 The Authors. Molecular Oncology published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.

In plain English

This laboratory study tested palbociclib, a drug that blocks the cell-growth enzymes CDK4 and CDK6, on a panel of 28 cell lines. Most were malignant pleural mesothelioma lines, 19 of them derived from patients. The panel also included MeT-5A, which is not a mesothelioma line but mesothelial cells immortalized by the SV40 virus, which inactivates the cells' pRb protein. The study did not examine asbestos exposure. Palbociclib prevented cell-cycle progression in 23 of the 28 lines. The resistant lines that lacked the activated (phosphorylated) form of CDK4 had strongly elevated levels of the protein p16. The effect lasted at least 2 weeks. After a 10-day treatment, growth arrest was mostly irreversible in colony-forming tests. The activated form of CDK4 was found in 39 of 47 tumour samples and was absent in normal pleura. In combined datasets, patients with very high expression of the CDKN2A gene (which encodes p16) had shorter survival than patients with intermediate expression (7.88 vs. 23.10 months). The authors concluded that their study supports further clinical evaluation of CDK4/6 inhibitors for pleural mesothelioma.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Preclinical laboratory study of mesothelioma cell lines and frozen tumour samples, combined with analysis of publicly available RNA-sequencing and survival data
• Who was studied: 28 cell lines: commercial and patient-derived malignant pleural mesothelioma (MPM) lines, plus MeT-5A, SV40-immortalized mesothelial cells used as a model of pRb-deficient cells (pRb inactivated by SV40). Also 47 frozen MPM tumours and normal pleura samples from biobanks in Belgium (Erasme Hospital, Antwerp University Hospital) and France (MESOBANK, Lyon). Public RNA-seq data came from TCGA-Meso (n = 86) and Bueno et al. (n = 211). Collection dates were not given.
• Exposure: Treatment with the CDK4/6 inhibitor palbociclib (mainly at 1 micromolar, for 24 hours up to 1 month, with or without drug washout), and in some tests ribociclib or abemaciclib. Asbestos exposure was not studied.
• Main results:
  • A 24-hour palbociclib treatment prevented cell-cycle progression, in a concentration-dependent way, in 23 of 28 cell lines.
  • In the majority of the sensitive lines, 1 micromolar palbociclib reduced the number of DNA-replicating cells by more than 90%.
  • Four MPM cell lines and the immortalized MeT-5A cells were completely insensitive to palbociclib.
  • In MeT-5A, pRb is inactivated by SV40; the authors suggest this could explain the high p16 levels and the impaired CDK4 phosphorylation in these cells.
  • Across the cell lines, the presence or absence of phosphorylated CDK4 matched the response to palbociclib in 27 of 28 lines.
  • Insensitive cell lines lacking phosphorylated CDK4 had strongly elevated p16 levels.
  • The effect of palbociclib on cell-cycle progression lasted at least 2 weeks.
  • In colony-forming (clonogenic) assays, the effect of a 10-day palbociclib treatment was mostly irreversible after the drug was removed.
  • Phosphorylated CDK4 was detected in 39 of 47 MPM tumours and was absent in normal pleura.
  • Phosphorylated CDK4 was undetectable in six proliferative tumours; in four of these, this went with extremely high p16 expression.
  • In the merged public and study RNA-seq data, high CDKN2A levels were seen in 17 of 141 (12%) MPMs expressing CDKN2A, which the authors state was 5% of the overall 331 patients.
  • Patients with very high CDKN2A expression had shorter survival than those with intermediate expression: 7.88 vs. 23.10 months in the combined cohort. The article prints this as HR = 0.31, CI = 0.05 to 0.28.
  • Patients with CCNE1 overexpression also had shorter overall survival.
• The authors' conclusion: The authors concluded that their study supports further clinical evaluation of CDK4/6 inhibitors for treating pleural mesotheliomas, including in combination with standard therapies. They added that a minority of insensitive tumours lacking CDK4 phosphorylation might have to be identified.
• Limitations the authors state:
  • The authors could not fully exclude that CDK4 phosphorylation was lost during sample processing in two tumours.
  • Cell lines with normal levels of wild-type p16 grew too slowly to be evaluated in detail, and two patient-derived lines had to be excluded.
  • Detecting phosphorylated CDK4 in routine formalin-fixed paraffin-embedded (FFPE) samples would be complicated by its extremely low abundance.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, CDKN2A.

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