The aim of the study is to evaluate the differences of protein binding
of NAMI-A, a new ruthenium drug endowed with selective antimetastatic
properties, and of cisplatin and to ascertain the possibility to use two
drugs based on heavy metals in combination to treat solid tumour
metastases. For this purpose, we have developed a technique that allows
the proteins, to which metal drugs bind, to be identified from real
protein mixtures. Following incubation with the drugs, the bands
containing platinum and/or ruthenium are separated by native PAGE,
SDS-PAGE and 2D gel electrophoresis, and identified using laser ablation
inductively coupled plasma mass spectrometry. Both drugs interact with
essentially the same proteins which, characterised by proteomics, are
human serum albumin precursor, macroglobulin alpha 2 and human
serotransferrin precursor. The interactions of NAMI-A are largely
reversible whereas cisplatin forms stronger interactions that are less
reversible. These data correlate well with the MCa mammary carcinoma
model on which full doses of NAMI-A combined with cisplatin show
additive effects as compared to each treatment taken alone,
independently of whether NAMI-A precedes or follows cisplatin.
Furthermore, the implication from this study is that the significantly
lower toxicity of NAMI-A, compared to cisplatin, could be a consequence
of differences in the mode of binding to plasma proteins, involving
weaker interactions compared to cisplatin.