The reaction of aqueous cis-[Pt(NH 3 ) 2 (H 2 O) 2 ](NO 3 ) 2 with Na + HMEL − (H 2 MEL, meloxicam, 4-hydroxy-2-methyl-N-(5-methyl-1,3-thiazol-2-yl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide), and Na + HISO − (H 2 ISO, isoxicam, 4-hydroxy-2-methyl-N-(5-methylisoxazol-3-yl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide) at pH 7 produced micro-crystalline cis-[Pt(NH 3 ) 2 (N 1′ -HMEL) 2 ], 5 and cis-[Pt(NH 3 ) 2 (N 1′ -HISO) 2 ], 6. The X-ray diffraction structure of 5 shows two HMEL − anions donating through the thiazole nitrogen atoms and adopting a head-to-tail (HT) conformation. The 1 H NMR spectrum for 5 from DMSO-d 6 shows inertness of the complex up to at least 24h. Delivery studies for 5 and 6 from vinyl hydrogel based on l-phenylalanine (pH 6.5, 25°C) show that concentrations of complexes ranging between 2.5 and 5μM can be reached after a day. Compounds 5 and 6 show strong anti-proliferative effects on CH1 cells (ovarian carcinoma, human) in vitro, IC 50 values being 0.60 and 0.37μM, respectively (0.16μM for reference, cis-diamminodichloridoplatinum(II), cisplatin). ESI-MS measurements clearly documented that both 5 and 6 form adducts with the three model proteins ubiquitin (UBI), cytochrome c (CYT C) and superoxide dismutase (SOD), the HISO − complex being significantly more effective than the HMEL − one. Density functional methods help in finding rationale for the easiest dissociation of Pt–H 2 ISO/HISO bonds when compared to the Pt–N 1 ′ –H 2 MEL/N 1 ′ –HMEL linkages.