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Palladium-spermine complex (Pd2Spm) triggers autophagy and caspase-independent cell death in triple-negative breast cancer cells
* 1 , 2, 3 , 2 , 4 , 5 , * 1
1  LAQV/REQUIMTE, Laboratory of Pharmacology, Department of Drug Sciences, Faculty of Pharmacy, University of Porto, 4050-313 Porto, Portugal
2  “Molecular Physical-Chemistry” R&D Unit, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
3  Department of Life Sciences, University of Coimbra, 3000-456 Coimbra, Portugal
4  iMed.ULisboa, Faculty of Pharmacy, University of Lisbon, 1649-003 Lisbon, Portugal
5  LAQV/REQUIMTE, Laboratory of Bromatology and Hydrology, Department of Chemical Sciences, Faculty of Pharmacy, University of Porto, 4050-313 Porto, Portugal
Academic Editor: Alfredo Berzal-Herranz


Triple-negative breast cancer (TNBC) is an aggressive breast carcinoma with a poor prognosis. Current treatment options with platinum-(Pt)-based chemotherapeutics are limited by toxicity/acquired resistance, which prompted the search for novel metal-based compounds. The dinuclear palladium(II)-spermine chelate (Pd2Spm) has previously shown promising pharmacokinetics and in vivo antitumor effects. However, its impact towards chemotherapy-resistant TNBC is still to be addressed. This work developed a cell model of cisplatin resistance and compared the anticancer/antiproliferative effects of cisplatin (reference Pt-based drug) and Pd2Spm in TNBC cells sensitive (MDA-MB-231) and resistant to cisplatin (MDA-MB-231/R). Pd2Spm displayed a similar antiproliferative potency in MDA-MB-231 and MDA-MB-231/R cells, while cisplatin showed ca. 18-fold lower potency towards MDA-MB-231/R cells. When focusing on cell death, incubation of Pd2Spm with either Necrostatin-1 (necroptosis inhibitor), Z-VAD (apoptosis inhibitor) or 3-Methyladenine (3-MA, autophagy inhibitor) showed that 3-MA can rescue Pd2Spm-induced growth inhibition in MDA-MB-231 and MDA-MB-231/R cells. Furthermore, in MDA-MB-231 cells, Pd2Spm triggered higher LC3-II levels and more profound Beclin-1 inhibition than cisplatin. Regarding apoptosis, Pd2Spm did not induce the cleavage of caspase-3 and co-incubation with both Pd2Spm and Z-VAD yielded only marginal effects in preventing the phosphatidylserine externalization compared to cisplatin. Thus, the present data provided more evidence on Pd2Spm’s cell death mechanisms, triggering a caspase-independent cell death with autophagy involvement. In addition, the potential of Pd2Spm to overcome chemotherapy resistance is promising.

Keywords: breast cancer; TNBC; cisplatin; Pd2Spm; Pd(II)-based drugs