Ruthenium-based assemblies containing tetrapyridylporphyrins (TPyP) in their structure have been evaluated as photosensitizers (PS) to treat rheumatoid arthritis (RA) by photodynamic therapy (PDT). TPyP is useless by itself as a PS due to its low solubility in biological media, however, incorporated in metallacages it can be internalized in cells. The study shows a cellular antiproliferative activity in fibroblast-like synoviocyte (FLS) in the lower nanomolar range in the presence of light, and no dark toxicity at 1 μM concentration, thus having an excellent photoactivity index. The presence of diamagnetic (Zn2+) and paramagnetic (Co2+) metals in the center of TPyP impairs the effectiveness of PDT, showing no (Co) or reduced (Zn) photoactivity. A total of five metallacages with different structural characteristics have been evaluated, and our results suggest that the incorporation of PS in metalla-assemblies is not only an elegant method to increase solubility in biological media for TPyP but also appears to be an efficient hybrid system to treat RA by PDT.