Shuttle Pharmaceuticals Holdings, Inc. is a discovery and development stage specialty pharmaceutical company. The Company is focused on improving the outcomes of cancer patients treated with radiation therapy (RT). It is developing a pipeline of products designed to address cancer therapies as well as to extend to the new applications of radiation therapy. Its product candidates include Ropidoxuridine (IPdR), Ropidoxuridine and Tipracil (IPdR/TPI), SP-1-161, SP-2-225, and SP-1-303. Ropidoxuridine (IPdR) is its lead candidate radiation sensitizer for use in combination with RT to treat brain tumors (glioblastoma) and sarcomas. Ropidoxuridine and Tipracil (IPdR/TPI) is undergoing preclinical development for use as a radiation sensitizer for rectal cancers. SP-1-161 is a pre-clinical candidate lead histone deacetylase (HDAC) inhibitor, a radiation sensitizing candidate product. SP-2-225 is a pre-clinical class II b selective HDAC inhibitor that affects histone deacetylase HDAC6.