•One-tissue format enables multiple tissue combinations on chip without design changes.•Tilting-based perfusion eliminates any tubing and ensures device robustness.•Perfusion leads to improved liver function on chip.•On-chip activation of the pro-drug cyclophosphamide leads to reduced tumor growth.•Chip design allows for biochemical and optical assays to assess drug response. Rational development of more physiologic in vitro models includes the design of robust and flexible 3D-microtissue-based multi-tissue devices, which allow for tissue–tissue interactions. The developed device consists of multiple microchambers interconnected by microchannels. Pre-formed spherical microtissues are loaded into the microchambers and cultured under continuous perfusion. Gravity-driven flow is generated from on-chip reservoirs through automated chip-tilting without any need for additional tubing and external pumps. This tilting concept allows for operating up to 48 devices in parallel in order to test various drug concentrations with a sufficient number of replicates. For a proof of concept, rat liver and colorectal tumor microtissues were interconnected on the chip and cultured during 8 days in the presence of the pro-drug cyclophosphamide. Cyclophosphamide has a significant impact on tumor growth but only after bio-activation by the liver. This effect was only observed in the perfused and interconnected co-cultures of different microtissue types on-chip, whereas the discontinuous transfer of supernatant via pipetting from static liver microtissues that have been treated with cyclophosphamide did not significantly affect tumor growth. The results indicate the utility and multi-tissue functionality of this platform. The importance of continuous medium circulation and tissue interaction is highlighted.