A new series of organometallic ruthenium(II)-arene compounds of the type RuCl₂(η⁶-arene)(phosphine) (phosphine = 1,3,5-triaza-7-phosphaadamantane, PTA, and 3,7-diacetly-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, DAPTA) with different potential hydrogen-bonding functionalities on the arene ligand have been prepared and studied for their antitumor activity. Cell viability studies using the TS/A mouse adenocarcinoma cancer cell line and the nontumorigenic HBL-100 human mammary cell line, combined with uptake determinations, are compared to the nonfunctionalized analogues, previously shown to be active on solid metastasizing tumors. The reactivity of the functionalized RAPTA compounds with a 14-mer oligonucleotide (established by mass spectrometry) has been rationalized by DFT calculations, which indicate that environmental factors are important.