Shuttle Pharmaceuticals Holdings, Inc. is a discovery and development stage specialty pharmaceutical company focused on improving the outcomes for cancer patients treated with radiation therapy (RT). Its product candidates include Ropidoxuridine, a Phase II, clinical-stage radiation sensitizer, a platform of HDAC inhibitors (SP-1-161, SP-2-225 and SP-1-303), and two preclinical, prostate cancer-oriented diagnostics assets: PC-RAD Test, a blood test to predict clinical response to radiation therapy and PSMA-B ligand for potential use as a theranostic agent. Ropidoxuridine (IPdR) is for use in combination with RT to treat brain tumors (glioblastoma) and sarcomas. SP-1-161 is a candidate lead of compounds demonstrating activation of the ATM gene product (mutated in Ataxia-Telangiectasia). SP-2-225 is a candidate lead of compounds demonstrating Class II (HDAC6) selective inhibition. SP-1-303 is a candidate Class I HDAC inhibitor with preferential efficacy against ER positive cancers.