Unsymmetric Cisplatin-Based Pt(IV) Conjugates Containing a PARP-1 Inhibitor Pharmacophore Tested on Malignant Pleural Mesothelioma Cell Lines

Our plain-English summary of Unsymmetric Cisplatin-Based Pt(IV) Conjugates Containing a PARP-1 Inhibitor Pharmacophore Tested on Malignant Pleural Mesothelioma Cell Lines, by E. Gabano, G. Pinton, C. Balzano, et al (Molecules, 2021).

The study

• Authors: E. Gabano, G. Pinton, C. Balzano, S. Boumya, D. Osella, L. Moro, M. Ravera
• Journal: Molecules
• Published: 2021;26(16)
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Cisplatin is widely employed as a first-line chemotherapeutic agent for many solid tumors, including malignant pleural mesothelioma (MPM). However, its clinical use is limited by heavy side effects and acquired resistance, the latter being mainly related to enhanced DNA repair. Many clinical trials using combinations of platinum drugs and PARP-1 inhibitors (PARPis) have been carried out, with the hope that such combinations might lead to improved therapeutic efficacy against tumors. Here, the synthesis and efficacy in reducing MPM cell viability of four cisplatin-based Pt(IV) prodrugs containing the PARPi 3-aminobenzamide (3-ABA) fragment are described. The most promising conjugate is more effective than cisplatin or cisplatin/3-ABA combination, administered in equimolar doses, in inhibiting PARP-1 activity and inducing apoptosis in BRCA1/2 wild type MPM cells, grown as monolayer or as multicellular spheroids.

In plain English

This laboratory study from the Università del Piemonte Orientale in Italy made four new platinum compounds (numbered 6 to 9). Each is a platinum(IV) "prodrug" built from cisplatin, a standard chemotherapy drug for malignant pleural mesothelioma, and carries a fragment based on 3-aminobenzamide (3-ABA), a substance that blocks the DNA-repair enzyme PARP-1. The compounds were tested on four human mesothelioma cell lines grown in the laboratory, not on patients or animals. No asbestos exposure was studied. Compound 6 was slightly more toxic to the cells than cisplatin on all four cell lines, at roughly twice the potency. Compounds 8 and 9 were much weaker. In further tests on one cell line, MSTO-211H, compound 6 entered the cells, lowered PARP-1 levels and inhibited PARP-1 activity. It also damaged DNA and showed signs of triggering cell death, including in three-dimensional cell clusters called spheroids. The authors concluded that linking PARP inhibitors to platinum could be a workable approach for developing possible mesothelioma drugs. They noted that they could not rule out a role for a chemical protecting group in compound 6's effect.

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 study: chemical synthesis of new compounds followed by experiments on human cancer cell lines (in vitro)
• Who was studied: Four human malignant pleural mesothelioma cell lines: MSTO-211H (biphasic), REN (epithelioid), BR95 (epithelioid) and MM98 (sarcomatoid). MM98 and BR95 were derived from pleural effusions of untreated patients. Mechanistic tests used MSTO-211H cells, including cells grown as multicellular spheroids. Work was done at the Università del Piemonte Orientale, Italy.
• Exposure: No asbestos exposure was studied. The exposures were treatments of cells with four new cisplatin-based platinum(IV) compounds (6 to 9). Each carries a 3-ABA-based PARP-1 inhibitor fragment at the end of a chain attached to the platinum; compounds 6 and 7 still carry an Fmoc protecting group. These were compared with cisplatin, with the compound SAA1, with 3-ABA alone, and with cisplatin plus 3-ABA (5 µM, 1:1 ratio).
• Main results:
  • After 72 h, compound 6 was slightly more cytotoxic than cisplatin on all four cell lines (cisplatin IC50 divided by compound IC50 was around 2). Compound 7 surpassed it only on the sarcomatoid MM98 line. IC50 for compound 6 versus cisplatin: MSTO-211H 0.69 ± 0.03 vs 1.14 ± 0.07 µM; REN 1.59 ± 0.07 vs 3.07 ± 0.43 µM; BR95 0.83 ± 0.04 vs 2.15 ± 0.29 µM; MM98 0.98 ± 0.03 vs 1.75 ± 0.09 µM.
  • The deprotected compounds 8 and 9 were much less active than 6 and 7. Their IC50 values ranged from 28.9 to 58.4 µM (compound 8) and from 38.9 to 54.9 µM (compound 9) across the four cell lines.
  • 3-ABA alone had negligible antiproliferative activity on MSTO-211H cells, with an IC50 of 5412 ± 28 µM.
  • Platinum uptake in MSTO-211H cells after 4 h, in ng Pt per million cells: compound 6, 10.64 ± 1.77; compound 7, 10.86 ± 1.17; cisplatin, 9.23 ± 0.96; compound 8, 2.50 ± 1.16; compound 9, 3.12 ± 0.78.
  • In MSTO-211H cells treated at their IC50 for 72 h, compound 6 lowered PARP-1 expression the most, followed by 7. Compounds 8 and 9 were similar to untreated control cells.
  • At 5 µM for 72 h in MSTO-211H cells, cisplatin increased PARP-1 activity (parylation), and cisplatin plus 3-ABA did so to a lesser extent. No PARP-1 self-parylation was seen in cells treated with compound 6 or with 3-ABA. Compound 6, but not cisplatin, caused PARP-1 cleavage, which the authors took as suggesting apoptosis.
  • MSTO-211H cells treated with compound 6 showed more γH2AX foci, a marker of DNA damage.
  • In MSTO-211H multicellular spheroids treated with compound 6, apoptotic death was shown by altered spheroid shape, PARP-1 cleavage, and switching on of the pro-apoptotic genes for BIM and PUMA.
  • In a heat-stability test (cellular thermal shift assay), PARP-1 from cells treated with compound 6 was more heat-stable than PARP-1 from control cells or 3-ABA-treated cells. The authors interpreted this as binding of 6 to PARP-1.
• The authors' conclusion: The authors concluded that attaching PARP inhibitors to a platinum(IV) centre could be an applicable approach to developing new metal-based anticancer compounds as potential drug candidates for malignant pleural mesothelioma therapy.
• Limitations the authors state:
  • The authors could not rule out that the Fmoc chemical protecting group itself contributed to the PARP-inhibiting properties of compound 6, rather than only the improved cell accumulation.
  • The three-dimensional spheroid cultures share many of the limitations of standard flat (2D) cell cultures.
  • The cell-counting method chosen (dye exclusion) may explain minor differences from previously published IC50 values for cisplatin.

Topics

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

Medical terms in this study, explained in our Lexicon: Cisplatin, Pleural Mesothelioma, Clinical Trial, Apoptosis.

Related studies

• PARP1 inhibition affects pleural mesothelioma cell viability and uncouples AKT/mTOR axis via SIRT1 — G. Pinton, A.G. Manente, et al. (2013)
• Interaction and cross-resistance of cisplatin and pemetrexed in malignant pleural mesothelioma cell lines — M. Kitazono-Saitoh, Y. Takiguchi, et al. (2012)
• Resistance to caspase-8 and -9 fragments in a malignant pleural mesothelioma cell line with acquired cisplatin-resistance — V. Janson, A. Johansson, et al. (2010)
• ADP sensitizes ZL55 cells to the activity of cisplatin — A. Muscella, L.G. Cossa, et al. (2019)
• Mechanisms of cisplatin-induced cell death in malignant mesothelioma cells: role of inhibitor of apoptosis proteins (IAPs) and caspases — I.L. Cregan, A.M. Dharmarajan, et al. (2013)
• Synthetic lethality in malignant pleural mesothelioma with PARP1 inhibition — G. Srinivasan, G.S. Sidhu, et al. (2017)

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