ABSTRACT
BACKGROUND: Agarose encapsulated murine renal adenocarcinoma cells (RENCA macrobeads) are currently being investigated in clinical trials as a treatment for therapy-resistant metastatic colorectal cancer. We have previously demonstrated the capacity of RENCA macrobeads to produce diffusible substances that markedly inhibit the proliferation of epithelial-derived tumor cells outside the macrobead environment. This study examined the molecular mechanisms underlying the observed inhibition in targeted tumor cells exposed to RENCA macrobeads. METHODS: We evaluated changes in transcription factor responses, participating intracellular signaling pathways and the involvement of specific cellular receptors in targeted tumor cells exposed to RENCA macrobeads. RESULTS: Factors secreted by RENCA macrobeads significantly up-regulated the activity of the MEF2 transcription factor as well as altered the transcription of MEF2b and MEF2d isoforms in targeted tumor cells. Suppression of individual or multiple MEF2 isoforms in target tumor cells markedly reduced the growth inhibitory effects of RENCA macrobeads. Furthermore, these effects were linked to the activation of the EGF receptor as attenuation of EGFR resulted in a substantial reduction of the cancer cell growth-inhibitory effect. CONCLUSIONS: Since interruption of the EGFR signaling cascade did not eliminate RENCA macrobead-induced growth control, our data suggests that RENCA macrobeads exert their full growth inhibitory effects through the simultaneous activation of multiple signaling pathways. In contrast to a precision medicine approach targeting single molecular abnormalities, the RENCA macrobead functions as a biological-systems therapy to re-establish regulation in a highly dysfunctional and dysregulated cancer system.
