BAMLET kills chemotherapy-resistant mesothelioma cells, holding oleic acid in an activated cytotoxic state

Our plain-English summary of BAMLET kills chemotherapy-resistant mesothelioma cells, holding oleic acid in an activated cytotoxic state, by E.M. Rath, Y.Y. Cheng, M. Pinese, et al (PloS One, 2018).

The study

• Authors: E.M. Rath, Y.Y. Cheng, M. Pinese, K.H. Sarun, A.L. Hudson, C. Weir, Y.D. Wang, A.P. Håkansson, V.M. Howell, G.J. Liu, G. Reid, R.B. Knott, A.P. Duff, W.B. Church
• Journal: PloS One
• Published: 2018;13(8):e0203003
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma is an aggressive cancer with poor prognosis. Here we have investigated in vitro efficacy of BAMLET and BLAGLET complexes (anti-cancer complexes consisting of oleic acid and bovine α-lactalbumin or β-lactoglobulin respectively) in killing mesothelioma cells, determined BAMLET and BLAGLET structures, and investigated possible biological mechanisms. We performed cell viability assays on 16 mesothelioma cell lines. BAMLET and BLAGLET having increasing oleic acid content inhibited human and rat mesothelioma cell line proliferation at decreasing doses. Most of the non-cancer primary human fibroblasts were more resistant to BAMLET than were human mesothelioma cells. BAMLET showed similar cytotoxicity to cisplatin-resistant, pemetrexed-resistant, vinorelbine-resistant, and parental rat mesothelioma cells, indicating the BAMLET anti-cancer mechanism may be different to drugs currently used to treat mesothelioma. Cisplatin, pemetrexed, gemcitabine, vinorelbine, and BAMLET, did not demonstrate a therapeutic window for mesothelioma compared with immortalised non-cancer mesothelial cells. We demonstrated by quantitative PCR that ATP synthase is downregulated in mesothelioma cells in response to regular dosing with BAMLET. We sought structural insight for BAMLET and BLAGLET activity by performing small angle X-ray scattering, circular dichroism, and scanning electron microscopy. Our results indicate the structural mechanism by which BAMLET and BLAGLET achieve increased cytotoxicity by holding increasing amounts of oleic acid in an active cytotoxic state encapsulated in increasingly unfolded protein. Our structural studies revealed similarity in the molecular structure of the protein components of these two complexes and in their encapsulation of the fatty acid, and differences in the microscopic structure and structural stability. BAMLET forms rounded aggregates and BLAGLET forms long fibre-like aggregates whose aggregation is more stable than that of BAMLET due to intermolecular disulphide bonds. The results reported here indicate that BAMLET and BLAGLET may be effective second-line treatment options for mesothelioma.

In plain English

This laboratory study used cells grown in dishes, not patients, and did not study asbestos exposure. The authors tested BAMLET and BLAGLET, which combine oleic acid with cow's-milk proteins. They used 11 human mesothelioma cell lines, a rat mesothelioma line and its chemotherapy-resistant versions, and non-cancer cells. The version developed for vinorelbine resistance was not consistently more resistant to that drug. Complexes containing more oleic acid killed mesothelioma cells at lower doses. A long-lived non-cancer mesothelial line was about as sensitive as the cancer cells. Three non-cancer skin fibroblast lines established months earlier contained a more-resistant portion of cells when serum was present, a window the authors called small. A fourth, grown for about four years, was as sensitive as the cancer cells. Cisplatin-resistant cells were as sensitive to BAMLET as the original cells. Pemetrexed-resistant cells were as sensitive in 22 out of 32 comparisons. Gemcitabine-resistant cells were more resistant. Regular high-dose BAMLET lowered expression of energy-production (ATP synthase) genes. Low doses sometimes raised some of them. The authors concluded that BAMLET may be a potential treatment option for mesothelioma that warrants testing in animals.

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) study: cell viability assays, gene-expression measurement (RT-qPCR), a bioinformatics comparison of bacterial genes, and structural studies (small angle X-ray scattering, circular dichroism, scanning electron microscopy)
• Who was studied: Cell lines, not people. There were 16 mesothelioma cell lines: 11 human (MM05, MSTO, REN, H28, H226, H2452, H2052, VMC20, VMC23, VMC33, VMC40), plus the rat line IL45 and four chemotherapy-resistant versions of it. Controls were an immortalised non-cancer human mesothelial line (MeT5A), a non-cancer rat mesothelial line (4/4RM.4), and four primary non-cancer human dermal fibroblast lines from biopsies taken during abdomen reduction surgery at Concord Hospital, Australia.
• Exposure: Treatment compounds, not asbestos. These were BAMLET and BLAGLET (oleic acid combined with bovine alpha-lactalbumin or beta-lactoglobulin) at low, medium and high oleic acid content, alpha-lactalbumin alone, and the chemotherapy drugs cisplatin, pemetrexed, gemcitabine and vinorelbine.
• Main results:
  • In the human mesothelioma cell lines, the dose killing half the cells (TC50) was 0.3 to 0.8 mg/ml for BAMLET-medium and 0.4 to 1.0 mg/ml for BLAGLET-medium. Higher oleic acid content gave lower TC50 values.
  • The immortalised non-cancer human mesothelial line MeT5A was about as sensitive as the mesothelioma lines. Its TC50 was 0.3 (plus or minus 0.04) mg/ml for BAMLET-medium and 0.2 (plus or minus 0.04) mg/ml for BLAGLET-medium.
  • With serum present, three of the four non-cancer primary fibroblast lines (HOFF, HOFM01, HOFM02) had a portion of cells that were more resistant than mesothelioma cells. The higher TC50 values were 2.4, 1.8 and 1.7 mg/ml, and the resistant portions were 71%, 51% and 43% of cells respectively.
  • The three resistant fibroblast lines had been established only months earlier. The fourth, established about four years before the others, was as sensitive as the mesothelioma cells.
  • Mesothelioma cells were about 7 to 10 times more sensitive to BAMLET when serum was removed before dosing.
  • Rat mesothelioma cells resistant to pemetrexed or cisplatin remained as sensitive to BAMLET as the original (parental) cells.
  • Pemetrexed-resistant rat cells matched the parental cells' sensitivity to BAMLET in 22 of 32 experiment comparisons.
  • Gemcitabine-resistant rat mesothelioma cells were more resistant to BAMLET than the parental cells.
  • The chemotherapy drugs pemetrexed and cisplatin also showed no window of difference between immortalised non-cancer cells and mesothelioma cells.
  • With regular high BAMLET dosing (0.3 mg/ml), 23 of 24 tested combinations of ATP synthase gene and cell line showed lower expression. Seven of these were statistically significant.
  • With regular low BAMLET dosing, some ATP synthase subunit c isoforms showed increased expression in the H28 and REN mesothelioma lines.
  • Structural studies showed that features typical of these protein and oleic acid complexes became more pronounced as oleic acid content increased.
  • Under the electron microscope, BLAGLET-high powder formed long, thin fibre-like protein aggregates (25 micrometres and longer). BAMLET-high powder formed spheres.
• The authors' conclusion: The authors concluded that BAMLET may be a potential treatment option for mesothelioma. They suggested giving it directly into the pleural cavity and said this approach warrants further investigation in animal (in vivo) models.
• Limitations the authors state:
  • The difference in resistance between primary non-cancer cells and mesothelioma cells was small.
  • The authors did not achieve consistently higher vinorelbine resistance in the line developed for vinorelbine resistance.
  • TC50 results in the rat chemotherapy-resistant experiments varied from week to week.
  • The immortalised MeT5A line was chosen as the non-cancer control for practical reasons.
  • Removing serum for the treatment period may have removed growth factors needed by the non-cancer fibroblasts, which could affect the comparison.

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: Chemotherapy, Mesothelioma, Pleural Mesothelioma, Prognosis, Fibroblast, Cisplatin, Pemetrexed (Alimta), Vinorelbine.

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