The Requirement for Neutrality

The anion is clearly not as active as the neutral compound but the result is noteworthy. In principle, the trend in activities in this series may be related to differing cellular absorption with subsequent different intracellular concentrations or to different reactivity with the proposed target molecule. Studies have shown that some of these complexes such as K2PtCl4 [12], rran5-[PtCl2(NH3)2] [13] and [Pt(dien)Cl]+ [14] do inhibit DNA synthesis, and indeed all bind to DNA (see Chapter 1) they are not unreactive but the inhibition does not lead to an antitumour effect. Biodistribution data in vivo have correlated the activity and toxicity of 

Antitumour and toxicity data for the general series [PtCl (am)4 ](2 ,  

Complex % Dose Retained (Rel. Ret n) Relative Order of Partition Coefficient (Kjf 1/2(6) days  

Recently, antitumour effects with PtCl salts of large, planar aromatic molecules such as ethidium [14] and rhodamine 123 [15] have been reported. These 2 1 salts show enhanced antitumour activity and reduced toxicity compared to the simple dyes that constitute the cations. The structure of the rhodamine species confirms the ionic nature [15]. The mechanism of action, and particularly the means whereby the acute toxicity of the parent dyes is reduced, is of some interest. 

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