This work describes synthesis at the nanoscale of the isoreticular metal-organic framework (MOF) series ZnBDP_X, based on the assembly of Zn(II) metal ions and the functionalized organic spacers 1,4-bis(1H-pyrazol-4-yl)-2-X-benzene (H2BDP_X; X = H, NO2, NH2, OH). The colloidal stability of these systems was evaluated under different relevant intravenous and oral-simulated physiological conditions, showing that ZnBDP_OH nanoparticles exhibit good structural and colloidal stability probably because of the formation of a protein corona on their surface that prevents their aggregation. Furthermore, two antitumor drugs (mitroxantrone and [Ru(p-cymene)Cl2(pta)] (RAPTA-C) where pta = 1,3,5-triaza-7-phospaadamantane) were encapsulated within the pores of the ZnBDP_X series in order to investigate the effect of the framework functionalization on the incorporation/delivery of bioactive molecules. Thus, the loading capacity of both drugs within the ZnBDP_X series seems to directly depend on the surface area of the solids. Moreover, ligand functionalization significantly affects both the delivery kinetics and the total amount of released drug. In particular, ZnBDP_OH and ZnBDP_NH2 matrixes show a slower rate of delivery and higher percentage of release than ZnBDP_NO2 and ZnBDP_H systems. Additionally, RAPTA-C delivery from ZnBDP_OH is accompanied by a concomitant and progressive matrix degradation due to the higher polarity of the BPD_OH ligand, highlighting the impact of functionalization of the MOF cavities over the kinetics of delivery.