Amide- and ester-linked kinase inhibitor-cytotoxin conjugates were rationally designed and synthesised as prototype hypoxia-activated anticancer mutual prodrugs. Chemical reduction of an aryl nitro trigger moiety was shown to initiate a spontaneous cyclisation/fragmentation reaction that simultaneously released the kinase inhibitor semaxanib (SU5416) and the amine- or alcohol-linked cytotoxin from the prodrugs. Preliminary cell testing and reduction potential measurements support optimisation of the compounds towards tumour-selective mutual prodrugs.