Abstract 3304: Targeting Cripto in breast cancer plasticity

The ability of cancer cells to adapt to various extrinsic challenges such as nutrient deprivation, hypoxia and chemotherapy may underlie their tumorigenicity as well as their ability to disseminate to distant organs. Therefore, identifying molecular mechanisms that govern such cellular plasticity may be critical to the development of anti-cancer therapies that target situationally defined tumor stem cells in metastasis, resistance, dormancy and recurrence. We considered the GPI-anchored/secreted Cripto protein to be an excellent target in this regard, as it regulates cellular plasticity during normal development including promotion of EMT, the embryonic stem cell state, and reacquisition of the stem cell state in cellular reprogramming. Cripto also regulates tissue specific stem cells including those of the mammary gland as we recently demonstrated. Due to the rarity of tissue stem cells under homeostasis, Cripto protein is generally low or undetectable in normal adult tissues but it is highly expressed in a wide variety of human tumors including breast cancers where its levels correlate with tumor aggressiveness and poor patient outcomes. Furthermore, inhibition of Cripto expression at the transcript level was recently reported to block metastasis in a mouse mammary tumor model. We have used xenograft assays to demonstrate that the requirement for Cripto function during metastasis, and to a lesser extent in primary tumor growth is conserved in human triple negative breast cancer cells. Critically, we demonstrate this through the use of a biologic/recombinant therapeutic protein specifically engineered to target Cripto. This recombinant protein, ALK4L75A-Fc, is comprised of an Fc-domain fused to a mutant extracellular domain of the natural Cripto binding partner and activin/Nodal type I signaling receptor, ALK4. The relatively modest effect of Cripto blockade on bulk primary tumors relative to metastasis and our inability to identify significant inhibitory effects of ALK4L75A-Fc on these cells in standard in vitro assays suggests that Cripto may only be critical for a subset of cancer cells and/or in specific microenvironmental contexts in the course of tumor progression. Consistent with this, we previously reported that Cripto signaling depends on its cell surface interaction with the stress inducible HSP70 family member and ER chaperone, GRP78 (glucose regulated protein, 78 kDa). Stresses including nutrient deprivation and chemotherapy strongly induce GR