Pharmacological targeting of p53 through RITA is an effective antitumoral strategy for malignant pleural mesothelioma

Our plain-English summary of Pharmacological targeting of p53 through RITA is an effective antitumoral strategy for malignant pleural mesothelioma, by D. Di Marzo, I.M. Forte, P. Indovina, et al (Cell Cycle, 2014).

The study

• Authors: D. Di Marzo, I.M. Forte, P. Indovina, E. Di Gennaro, V. Rizzo, F. Giorgi, E. Mattioli, C.A. Iannuzzi, A. Budillon, A. Giordano, F. Pentimalli
• Journal: Cell Cycle
• Published: 2014;13(4):652-65
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant mesothelioma, a very aggressive tumor associated to asbestos exposure, is expected to increase in incidence, and unfortunately, no curative modality exists. Reactivation of p53 is a new attractive antitumoral strategy. p53 is rarely mutated in mesothelioma, but it is inactivated in most tumors by the lack of p14(ARF). Here, we evaluated the feasibility of this approach in pleural mesothelioma by testing RITA and nutlin-3, two molecules able to restore p53 function through a different mechanism, on a panel of mesothelioma cell lines representing the epithelioid (NCI-H28, NCI-H2452, IST-MES 2), biphasic (MSTO-211H), and sarcomatoid (NCI-H2052) histotypes compared with the normal mesothelial HMC-hTERT. RITA triggered robust caspase-dependent apoptosis specifically in epithelioid and biphasic mesothelioma cell lines, both through wild-type and mutant p53, concomitant to p21 downregulation. Conversely, nutlin-3 induced a p21-dependent growth arrest, rather than apoptosis, and was slightly toxic on HMC-hTERT. Interestingly, we identified a previously undetected point mutation of p53 (p.Arg249Ser) in IST-MES 2, and showed that RITA is also able to reactivate this p53 mutant protein and its apoptotic function. RITA reduced tumor growth in a MSTO-211H-derived xenograft model of mesothelioma and synergized with cisplatin, which is the mainstay of treatment for this tumor. Our data indicate that reactivation of p53 and concomitant p21 downregulation effectively induce cell death in mesothelioma, a tumor characterized by a high intrinsic resistance to apoptosis. Altogether, our findings provide the preclinical framework supporting the use of p53-reactivating agents alone, or in combination regimens, to improve the outcome of patients with mesothelioma.

In plain English

This was a laboratory study of cancer cells and mice, not of people or of asbestos exposure. The authors tested two drugs meant to restore p53, a protein that can make cancer cells die: RITA and nutlin-3. They used five malignant pleural mesothelioma cell lines (three epithelioid, one biphasic, one sarcomatoid) and one normal mesothelial cell line. RITA caused programmed cell death (apoptosis) in all the mesothelioma lines except the sarcomatoid one, and showed no toxic effects on the normal cells. Nutlin-3 only moderately reduced mesothelioma cell survival and was slightly toxic to the normal cells. The mice carried tumors grown from the biphasic cell line. In the 10 given RITA, tumors grew significantly more slowly than in the 10 given the drug solvent alone, and 4 RITA-treated tumors regressed completely. The authors described the difference in final tumor weight as approaching statistical significance (P = 0.059). RITA combined with cisplatin acted synergistically in four cell lines. The authors said further experiments are needed to learn whether RITA works the same way in animals and whether resistance may arise.

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: Laboratory experiments on human cell lines, plus a pilot experiment in mice carrying transplanted human mesothelioma tumors (xenografts)
• Who was studied: Five human malignant pleural mesothelioma cell lines: epithelioid (NCI-H28, NCI-H2452, IST-MES 2), biphasic (MSTO-211H) and sarcomatoid (NCI-H2052). These were compared with a normal mesothelial cell line (HMC-hTERT). The study also used 20 female nude mice, 6 to 7 weeks old, injected with MSTO-211H cells, with xenograft work done at the Biogem Institute in Ariano Irpino, Italy. A human colon cancer cell line lacking p53 (HCT116 p53-/-) was used for some experiments.
• Exposure: Asbestos exposure was not studied. Cells were treated with two p53-reactivating drugs, RITA and nutlin-3, and with RITA combined with cisplatin. Mice received RITA at 1 mg/kg (controls received the solvent DMSO) by injection into the tumor for 5 consecutive days a week, over 3 weeks.
• Main results:
  • RITA was toxic to all the mesothelioma cell lines except the sarcomatoid line NCI-H2052.
  • RITA showed no toxic effects on the normal mesothelial cell line HMC-hTERT.
  • Nutlin-3 was slightly toxic to the normal mesothelial cells and only moderately reduced mesothelioma cell viability at 10 to 20 micromolar doses.
  • In the mesothelioma cell lines that responded to RITA, RITA activated molecular markers of apoptosis (PARP and caspase 3 cleavage).
  • Blocking p53 with the inhibitor pifithrin-alpha strongly reduced RITA's effect in all susceptible mesothelioma cell lines, which the authors took as evidence that p53 at least partly mediates RITA's effect.
  • The authors found a p53 mutation (p.Arg249Ser) in the IST-MES 2 cell line. They state it had not been described in mesothelioma before.
  • In mice with MSTO-211H tumors, RITA (10 mice) significantly reduced tumor growth rate compared with solvent-only controls (10 mice).
  • In the RITA-treated mouse group, 4 tumors regressed completely. Two RITA-treated xenografts seemed not to respond.
  • The difference in final tumor weight between the RITA-treated and solvent-treated mice was described as approaching statistical significance (P = 0.059).
  • RITA combined with cisplatin gave combination index values always below 1, indicating synergy, in the mesothelioma cell lines tested (NCI-H28, NCI-H2452, IST-MES 2, MSTO-211H).
• The authors' conclusion: The authors concluded that, although the mechanisms need further investigation, their study provides a preclinical basis for possibly using RITA in the most common forms of mesothelioma, alone or combined with other therapies.
• Limitations the authors state:
  • The authors stated that further experiments are needed to determine whether RITA acts in living animals through the same mechanisms seen in cell cultures, and whether resistance may arise.
  • The authors' attempts to switch off p53 in mesothelioma cells failed, so they could not definitively show that RITA-induced cell death is mediated by p53.
  • The authors stated that the molecular mechanisms behind RITA's effects in mesothelioma require further investigation, and that RITA might have effects that do not depend on p53.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Malignant Mesothelioma, Asbestos Exposure, Mesothelioma, Epithelioid, Biphasic Mesothelioma, Sarcomatoid, Apoptosis.

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