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Towards cancer cell-specific phototoxic organometallic rhenium(I) complexes

Anna Leonidova1, Vanessa Pierroz, Riccardo Rubbiani

  • 1Institute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse 190, CH 8057 Zurich, Switzerland. gilles.gasser@aci.uzh.ch.

Dalton Transactions (Cambridge, England : 2003)
|August 29, 2013
PubMed

Insights

This study explores rhenium (Re) complexes as photodynamic therapy (PDT) agents. Conjugating a Re complex to peptides enhanced its cancer cell targeting and light-activated toxicity, showing promise for new cancer treatments.

Area of Science:

  • Organometallic Chemistry
  • Photodynamic Therapy (PDT)
  • Cancer Research

Background:

  • Rhenium (Re) organometallic compounds show anticancer activity but lack selectivity.
  • Existing Re(I) complexes require improved targeting for effective cancer chemotherapy.
  • Photodynamic therapy (PDT) offers a targeted approach to cancer treatment.

Purpose of the Study:

  • To evaluate two N,N-bis(quinolinoyl) Re(I) tricarbonyl complex derivatives (Re-NH₂ and Re-COOH) as PDT photosensitizers.
  • To enhance the selectivity of Re-COOH by conjugating it with a nuclear localization signal (NLS) and a bombesin peptide derivative.
  • To assess the photocytotoxicity and DNA-damaging capabilities of the Re complexes and their bioconjugates.

Main Methods:

  • Synthesis and characterization of Re(I) tricarbonyl complexes (Re-NH₂, Re-COOH) and their peptide conjugates (Re-NLS, Re-Bombesin).
  • Measurement of singlet oxygen generation quantum yields.
  • Fluorescent microscopy to track cellular uptake and localization in HeLa cervical cancer cells.
  • Assessment of photocytotoxicity upon light irradiation.
  • DNA photo-cleavage assays to determine the mechanism of DNA damage.

Main Results:

  • Re-NH₂ and Re-COOH exhibited high singlet oxygen generation (quantum yield ~75%) in lipophilic environments.
  • Conjugation of Re-COOH to NLS significantly improved its nuclear and nucleoli accumulation in HeLa cells.
  • Photocytotoxicity increased substantially upon light irradiation for all Re complexes and bioconjugates.
  • Re-Bombesin demonstrated at least a 20-fold increase in toxicity after light activation.
  • All tested compounds induced DNA damage primarily through singlet oxygen and secondarily via superoxide production.

Conclusions:

  • Re(I) tricarbonyl complexes are effective singlet oxygen generators for PDT applications.
  • Peptide conjugation, particularly with NLS and bombesin, enhances cellular targeting and photocytotoxicity of Re complexes.
  • Re-Bombesin shows significant potential as a targeted PDT agent for cancer therapy due to its enhanced photo-induced toxicity.

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