A series of porphyrazines (Pzs) with chiral bis-acetal moieties in the β-pyrrole positions ((2R,3R)-2,3-dimethyl-2,3-dimethoxy-1,4-diox-2-ene) have been synthesized and screened as antitumor agents in MDA-MB-231 breast tumor cellsin vitro. The leadPz 285was further tested in a mouse tumor xenograft model with Td-tomato-luc2 fluorescent breast tumor cells (MDA-MB-231 LM24 Her2+) that are highly metastatic to the lungs.Pz 285shows marked antitumor effectsin vivo, with treated mice exhibiting longer median survival that we attribute to smaller primary tumor regrowth after resection and less occurrence of metastasis when compared to vehicle control groups.Pz 285is further compared to the clinically approved chemotherapeutic doxorubicin (Dox). This report lays the groundwork for development of an understudied class of compounds for classical chemotherapy.