Significant augmentation of pro-apoptotic gene therapy by pharmacologic bcl-xl down-regulation in mesothelioma

Our plain-English summary of Significant augmentation of pro-apoptotic gene therapy by pharmacologic bcl-xl down-regulation in mesothelioma, by I. Mohiuddin, X. Cao, B. Fang, et al (Cancer Gene Therapy, 2001).

The study

• Authors: I. Mohiuddin, X. Cao, B. Fang, M. Nishizaki, W.R. Smythe
• Journal: Cancer Gene Therapy
• Published: 2001;8(8):547-54
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The ratio of pro-apoptotic (PAP) and anti-apoptotic (AAP) bcl-2 proteins is important in apoptosis regulation. We sought to determine if inhibition of the AAP bcl-xl by sodium butyrate (SB) would augment apoptotic cellular death in mesothelioma when combined with adenoviral pro-apoptotic gene therapy (PAGT) by simultaneously increasing PAP and decreasing AAP in these cells. Human mesothelioma cell lines were exposed to AdBax, AdBak, Adp53, and SB alone as well as all vectors combined with SB at varying doses and time points. Cell death was assessed, and apoptosis evaluated by morphology and FACS. Isobologram analysis evaluated additive or synergistic effect. Cellular death and apoptosis were augmented by PAGT/SB combinations compared to monotherapy. Following AdBax/SB and AdBak/SB, a decrease of the AAP bcl-xl was noted in combination with increases in PAP bax and bak. By isobologram analysis, additive or synergistic cell killing was noted with both combinations. SB treatment did not significantly augment cell killing or apoptosis in combination with Adp53. PAGT/SB was more effective than monotherapy in induction of apoptotic cell death. Synergy may be due to the ability of SB to decrease bcl-xl with marked increases in PAP engendered by PAGT. Combination therapy with agents that down-regulate AAP in addition to PAGT may prove useful clinically.

In plain English

This laboratory study used two human mesothelioma cell lines, REN and I-45, originally taken from patients with pleural tumors. The authors tested whether sodium butyrate, which lowers the cell-survival protein bcl-xl, would increase killing of these cells by gene therapy viruses carrying the cell-death genes bax, bak or p53. The study did not examine asbestos exposure. In I-45 cells, 28% were apoptotic (dying) after AdBax alone, 12% after AdBak alone and 3% after butyrate alone, versus 32% after AdBax plus butyrate and 59% after AdBak plus butyrate. At 72 hours, 38% to 39% of REN cells survived single treatments, versus 5% with AdBak plus butyrate and 20% with AdBax plus butyrate. Mathematical analysis found additive, and at some doses synergistic, killing for the bax and bak combinations. It found no synergy for p53 plus butyrate. The authors concluded that such combination therapy may prove useful clinically. They noted that butyrate's short half-life makes it unlikely to be useful in living organisms, though this may matter less for body-cavity tumors where it can be placed directly, and called for animal studies.

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 (in vitro) experiment on human mesothelioma cell lines
• Who was studied: Two human mesothelioma cell lines, both originally derived from patients with pleural tumors: REN (inflammatory epithelial subtype, p53 mutant) and I-45 (sarcomatous subtype, p53 wild type)
• Exposure: No asbestos exposure was studied. The cells were treated with sodium butyrate (2.5 mM or 3 mM), with adenoviral gene therapy vectors carrying bax, bak or p53 (AdBax, AdBak, Adp53) at varying doses, or with combinations of the two
• Main results:
  • I-45 cells, apoptotic (sub-G1) fraction: 28% with AdBax alone, 12% with AdBak alone and 3% with sodium butyrate alone, versus 59% with AdBak plus butyrate and 32% with AdBax plus butyrate
  • REN cells, apoptotic (sub-G1) fraction: 16% with AdBax alone, 18% with AdBak alone and 2% with butyrate alone, versus 34% with AdBak plus butyrate and 48% with AdBax plus butyrate
  • I-45 cells, viability at 72 hours: 45% with AdBax, 51% with AdBak and 52% with butyrate alone, versus 20% with AdBak plus butyrate and 15% with AdBax plus butyrate
  • REN cells, viability at 72 hours: 38% with AdBax, 39% with AdBak and 39% with butyrate alone, versus 5% with AdBak plus butyrate and 20% with AdBax plus butyrate
  • In both cell lines, isobologram analysis of the AdBax and AdBak combinations with butyrate showed additive and, at some doses, synergistic cell killing
  • In both cell lines, the combination treatments raised BAX or BAK protein and lowered bcl-xl protein
  • Sodium butyrate did not change how efficiently the viral vector got into the cells
  • Adp53 plus butyrate: adding butyrate did not significantly change cell viability compared with Adp53 alone (39% in REN, 51% in I-45), and there was no evidence of synergy
• The authors' conclusion: The authors concluded that combining pro-apoptotic gene therapy with agents that lower anti-apoptotic proteins may prove useful clinically
• Limitations the authors state:
  • Sodium butyrate's short half-life makes it unlikely to be useful in vivo, though the authors suggested this may matter less in body cavity tumors, where it can be placed directly into the cavity
  • The work was done only in cell lines; the authors called for animal studies and for studies of how butyrate lowers bcl-xl

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Apoptosis, Synergistic Effect.

Related studies

• Antisense therapy for malignant mesothelioma with oligonucleotides targeting the bcl-xl gene product — W.R. Smythe, I. Mohuiddin, et al. (2002)
• Manumycin A induces apoptosis in malignant pleural mesothelioma through regulation of Sp1 and activation of the mitochondria-related apoptotic pathway — K.H. Kim, J.I. Chae, et al. (2016)
• Downregulation of Bcl-xL and Mcl-1 is sufficient to induce cell death in mesothelioma cells highly refractory to conventional chemotherapy — E. Varin, C. Denoyelle, et al. (2010)
• Resveratrol and clofarabine induces a preferential apoptosis-activating effect on malignant mesothelioma cells by Mcl-1 down-regulation and caspase-3 activation — Y.J. Lee, Y.J. Lee, et al. (2015)
• Regression of AK7 malignant mesothelioma established in immunocompetent mice following intratumoral gene transfer of interferon gamma — L. Cordier Kellerman, L. Valeyrie, et al. (2003)
• Chemotherapy delivered after viral immunogene therapy augments antitumor efficacy via multiple immune-mediated mechanisms — Z.G. Fridlender, J. Sun, et al. (2010)

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