Selected polyoxopalladates as promising and selective antitumor drug candidates

Polyoxo-noble-metalates (PONMs), a class of molecular noble metal-oxo nanoclusters that combine features of both polyoxometalates and noble metals, are a promising platform for the development of next-generation antitumor metallodrugs. This study aimed to evaluate the antitumor potential against human neuroblastoma cells (SH-SY5Y), as well as toxicity towards healthy human peripheral blood cells (HPBCs), of five polyoxopalladates(II): (Na 8 [Pd 13 As 8 O 34 (OH) 6 ]·42H 2 O ( Pd 13 ), Na 4 [SrPd 12 O 6 (OH) 3 (PhAsO 3 ) 6 (OAc) 3 ]·2NaOAc·32H 2 O ( SrPd 12 ), Na 6 [Pd 13 (AsPh) 8 O 32 ]·23H 2 O ( Pd 13 L ), Na 12 [SnO 8 Pd 12 (PO 4 ) 8 ]·43H 2 O ( SnPd 12 ) , and Na 12 [PbO 8 Pd 12 (PO 4 ) 8 ]·38H 2 O ( PbPd 12 )), as the largest subset of PONMs. A pure inorganic, Pd 13 , was found as the most potent and selective antineuroblastoma agent with IC 50 values (µM) of 7.2 ± 2.2 and 4.4 ± 1.2 for 24 and 48 h treatment, respectively, even lower than cisplatin (28.4 ± 7.4 and 11.6 ± 0.8). The obtained IC 50 values (µM) for 24/48 h treatment with SrPd 12 and Pd 13 L were 75.8 ± 6.7/76.7 ± 22.9 and 63.8 ± 3.6/21.4 ± 10.8, respectively, whereas SnPd 12 and PbPd 12 did not remarkably affect the SH-SY5Y viability ( IC 50 > > 100 µM). Pd 13 caused depolarisation of inner mitochondrial membrane prior to superoxide ion hyperproduction, followed by caspase activation, DNA fragmentation and cell cycle arrest, all hallmarks of apoptotic cell death, and accompanied by an increase in acidic vesicles content, suggestive of autophagy induction. Importantly, Pd 13 demonstrated the antitumor effect at concentrations not cytogenotoxic for normal HPBCs. On the contrary, SrPd 12 and Pd 13 L at concentrations ≥ 1/3 IC 50 (24 h) decreased HPBC viability and increased % tail DNA up to 42% and 3.05 times, respectively, related to control. SnPd 12 and PbPd 12, previously confirmed promising antileukemic agents, did not exhibit cytogenotoxicity to HPBCs, and thus could be regarded as tumor cell specific and selective drug candidates. Graphic abstract