PI3K\u03b4 and PI3K\u03b3 isoforms have distinct functions in regulating pro-tumoural signalling in the multiple myeloma microenvironment

R E Piddock,S Yu,S Yu,G E Pillinger,S A Rushworth,Z Zhou,Z Zhou,L Zaitseva,L Zaitseva,D R Edwards,K M Bowles,N Loughran,N Loughran,C R Marlein,M J Auger,S D Robinson

doi:10.1038/bcj.2017.16

R E Piddock, S Yu + Show 14 more

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https://doi.org/10.1038/bcj.2017.16

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Abstract

Phosphoinositide-3-kinase and protein kinase B (PI3K-AKT) is upregulated in multiple myeloma (MM). Using a combination of short hairpin RNA (shRNA) lentivirus-mediated knockdown and pharmacologic isoform-specific inhibition we investigated the role of the PI3K p110γ (PI3Kγ) subunit in regulating MM proliferation and bone marrow microenvironment-induced MM interactions. We compared this with inhibition of the PI3K p110δ (PI3kδ) subunit and with combined PI3kδ/γ dual inhibition. We found that MM cell adhesion and migration were PI3Kγ-specific functions, with PI3kδ inhibition having no effect in MM adhesion or migration assays. At concentration of the dual PI3Kδ/γ inhibitor duvelisib, which can be achieved in vivo we saw a decrease in AKT phosphorylation at s473 after tumour activation by bone marrow stromal cells (BMSC) and interleukin-6. Moreover, after drug treatment of BMSC/tumour co-culture activation assays only dual PI3kδ/γ inhibition was able to induce MM apoptosis. shRNA lentiviral-mediated targeting of either PI3Kδ or PI3Kγ alone, or both in combination, increased survival of NSG mice xeno-transplanted with MM cells. Moreover, treatment with duvelisib reduced MM tumour burden in vivo. We report that PI3Kδ and PI3Kγ isoforms have distinct functions in MM and that combined PI3kδ/γ isoform inhibition has anti-MM activity. Here we provide a scientific rationale for trials of dual PI3kδ/γ inhibition in patients with MM.

Highlights

Multiple Myeloma (MM), is presently incurable with o50% of patients surviving over 5 years post diagnosis.[1]
To verify that PI3Kδ and PI3Kγ subunits are expressed in MM cells we examined protein expression of both isoforms using Western blotting in primary MM samples and MM cell lines
To understand the significance of PI3Kδ and/or PI3Kγ in MM we investigated the effects of PI3K inhibitors (idelalisib (PI3Kδ), CZC24832 (PI3Kγ) and duvelisib (PI3Kδ/γ)) on MM cell death assays

Summary

Introduction

Multiple Myeloma (MM), is presently incurable with o50% of patients surviving over 5 years post diagnosis.[1] MM is characterised by the accumulation of monoclonal plasma cells that are primarily contained within the bone marrow. Phosphoinositide-3-kinases (PI3K) are an enzyme group that generate phosphatidylinositol 3,4, 5-triphosphate (PIP3). PIP3 provides a membrane docking site for the tyrosine kinase AKT ( known as protein kinase B), which on binding upregulates cell survival and proliferation signals. PI3Kδ is usually activated by receptor tyrosine kinase signalling, PI3Kγ is most commonly found downstream of G protein-coupled receptors.[5,6,7] PI3K α/β catalytic subunits are expressed in a wide variety of tissues, whereas PI3Kδ/γ have been shown to be enriched in the haematopoietic system.[8]

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