Intermolecular biparatopic trapping of ErbB2 prevents compensatory activation of PI3K/AKT via RAS–p110 crosstalk

Abstract

Compensatory mechanisms, such as relief of AKT-ErbB3-negative feedback, are known to desensitize ErbB2-dependent tumours to targeted therapy. Here we describe an adaptation mechanism leading to reactivation of the PI3K/AKT pathway during trastuzumab treatment, which occurs independently of ErbB3 re-phosphorylation. This signalling bypass of phospho-ErbB3 operates in ErbB2-overexpressing cells via RAS-PI3K crosstalk and is attributable to active ErbB2 homodimers. As demonstrated by dual blockade of ErbB2/RAS and ErbB3 by means of pharmacological inhibition, RNA interference or by specific protein binders obstructing the RAS–p110α interaction, both routes must be blocked to prevent reactivation of the PI3K/AKT pathway. Applying these general principles, we developed biparatopic designed ankyrin repeat proteins (DARPins) trapping ErbB2 in a dimerization-incompetent state, which entail pan-ErbB inhibition and a permanent OFF state in the oncogenic signalling, thereby triggering extensive apoptosis in ErbB2-addicted tumours. Thus, these novel insights into mechanisms underlying network robustness provide a guide for overcoming adaptation response to ErbB2/ErbB3-targeted therapy.

Genetic and Epigenetic Alterations in Bladder Cancer

“…Moreover, upregulation of PIK3CA , AKT1/2/3 , and PDK1 expression, as well as loss-of-function mutations in TSC1/2 (tuberous sclerosis 1/2) and PTEN occur in MIBC and NMIBC bladder tumors [31]. Overexpression of EGFR or ERBB2 leads to RAS activation, which in turn activates the PI3K pathway [32]. As a result, the mTOR pathway is activated by the inactivation of the TSC1/TSC2 complex [31], thereby increasing cell proliferation.…”

High-Throughput Functional Evaluation of Variants of Unknown Significance in ERBB2

“…Erb-B2 receptor tyrosine kinase 2 (ERBB2) is a member of the ErbB tyrosine receptor family, which also includes EGFR, ERBB3, and ERBB4. ERBB2 dimerizes with itself or other ErbB members to activate two major downstream signaling pathways: PI3K-AKT and MEK-ERK (1). ERBB2 gene amplification occurs in a wide variety of human cancers (2)(3)(4).…”

Non-invasive in vivo imaging of tumour-associated cathepsin B by a highly selective inhibitory DARPin

“…7 b). Although this approach has found substantial use in developing extremely selective binders to various receptors, including for potential therapeutic applications 57 , 58 , it has not been used in cellular or non-invasive diagnostic imaging of proteases. Moreover, the only protease-targeting DARPins were developed as selective inhibitors of a tobacco virus protease 59 or caspases 35 , 60 to help elucidate the molecular basis of their specificity.…”