CA9 and cancer: In order to test our working hypothesis, we designed five different PEGylated bis-sulfonamides bearing PEG 1K, PEG 2K, PEG 3.4K, PEG 5K, and PEG 20K polymeric backbones, which were synthesized via our standard procedure and were tested in vitro for their ability to kill cancer cells expressing CA IX and CA XII.