Monobodies can be engineered to displayexceptionally high affinity for difficult-to-inhibit proteins,44,45 are 20–25% more compact than nanobodies,45 and are not themselves cell-permeant.46,47 In particular, we focused on NS1 (Figure 4a), a small (12 kDa), cationic (pI = 9.2when conjugated to ZF5.3) monobody that binds HRAS and KRAS with highaffinity (KD values of 15 and 65 nM, respectively)and inhibits KRAS-driven tumor growth when expressed in vivo.47 Here, HRAS is linked to neoplasm.