Abstract C100: Evaluation of pyriplatin, a monofunctional cationic platinum(II) compound, in human cancer cells
Authors: Lovejoy Katherine S. , Serova Maria , Emami Shahin , Bieche Ivan , Gespach Christian , Cvitkovic Esteban , Faivre Sandrine , Raymond Eric , Lippard Stephen J. 
Published: June 2012

Background: We evaluated pyriplatin (cis-diammine(pyridine)chloroplatinum(II) or cDPCP), a platinum-based antitumor drug candidate, in vitro using an established cancer cell line panel (Ref. 1) with direct comparison to cisplatin and oxaliplatin. Pyriplatin is a monofunctional, cationic compound with proven anticancer properties in mice (Ref. 2) and recently rediscovered as a substrate for the organic cation transporters, hOCT1 and hOCT2 (Ref. 3).

Methods: Antiproliferative effects of pyriplatin given as a single agent for 24 h were evaluated in a panel of 10 human cancer cell lines. Flow cytometry was used to record cell cycle effects after staining cells with propidium iodide and to study apopotosis as imaged with FITC-conjugated annexin V. Effects of combinations of pyriplatin with either taxol, gemcitabine, SN38, cisplatin or 5-fluorouracil were evaluated in parallel with corresponding combinations of either cisplatin or oxaliplatin. Gene expression was determined by quantitative RT-PCR. The formation of platinum-DNA adducts over time was determined by ICP-MS.

Results: Pyriplatin exhibited cytotoxic effects against human cell lines after 24 h of treatment (IC50 values: 171 – 443 µM). Pyriplatin continued to be effective over time, with IC50 values decreasing to 24 µM after 72 h in HOP-62 cells, the most sensitive cell line. Antiproliferative effects were also observed at short time points, with IC50 values ranging from 230 to 450 µM at 1, 2 and 5 h. Combinations of pyriplatin with either taxol or cisplatin showed better than additive antiproliferative effects. These results were obtained both for pretreatment of cells with taxol prior to pyriplatin and for simultaneous treatment of cells with cisplatin and pyriplatin. The effects of pyriplatin on cell cycle revealed an accumulation of cells in a sub-G1, or apoptotic phase, after only 24 hours of treatment, which was a result unique from that of either cisplatin or oxaliplatin. Increased apoptosis induction after 24 h relative to cisplatin was confirmed by staining cells with FITC-conjugated Annexin-V. Quantitative RT-PCR results indicated that cells with high levels of RAD50 mRNA are more resistant to pyriplatin, suggesting a role of double-strand breaks and homologous recombination repair in the cellular response to pyriplatin damage.

Conclusions: The antiproliferative effects of pyriplatin are unique from those of either cisplatin or oxaliplatin, although the potency of pyriplatin is roughly one order of magnitude lower than either cisplatin or oxaliplatin. Pyriplatin induces apoptosis earlier than either oxaliplatin or cisplatin and the downstream effects of DNA double strand breaks are more evident for pyriplatin than for either oxaliplatin or cisplatin.

Support: This work was supported in part by a grant from the U. S. National Cancer Institute.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C100.