Human Immunodeficiency virus (HIV) and cancer are a globalpublic health problem. Despite the stabilization of the HIV epidemicin most regions, 2.6 million people were newly infected in 2009. Inthe western world the leading cause of death is cancer and thenumber of cancer deaths will rise by 2030 to 12 million accordingthe WHO. Despite the tremendous success of the actual antiretroviraltreatment, the severe side effects, the associated lack ofadherence and virological failure lead to the emergency of drugresistant virus strains. The development of new anti-retroviralmolecules facilitating the treatment compliance and active againstmultidrug resistant strains will reduce the selection of drugresistance mutations and will offer new and optimized treatmentoptions to naïve and treatment experienced HIV patients. In thefield of cancer research, metastatic processes are responsible formore than 90% of the cancer related deaths. The G protein coupledreceptor CXCR4 and CXCR7 are implicated in cancer metastasisand are expressed on numerous types of cancer cells. To date,drugs targeting metastasis development are not yet available butwill significantly improve cancer treatments and reduce cancerrelated mortality. The current proposal aims to tackle both cancerand HIV, two global health priorities. Indeed, this project will focuson the identification and full characterization of protein leadmolecules inhibiting CXCR4 interactions implicated in cancermetastasis and HIV.