Potentiated Phospho-Protein Network Profiling of Multiple Myeloma Cell Lines and Primary Patient Samples by Multi-Parameter Flow Cytometry.
Authors: Li Zhi Hua , Bergsagel Peter Leif , Chow Sue , Hedley David , Trudel Suzanne 
Published: April 2020

Abstract
The importance of aberrant signal transduction in the development and progression of cancers including multiple myeloma (MM) is well recognized, although the detailed regulation of signaling networks in relation to oncogenic mutations remains incompletely understood. However, this subject is becoming increasing relevant to clinical oncology due the rapid development of biological-based therapies that can target signaling pathways. Analytical methods that can be applied to clinical samples to measure complex populations of cells and phenotype them for multiple activation states are now feasible due to the recent advances in intracellular signal techniques, flow cytometry and phospho-antibodies. Using multi-parameter flow cytometry, we monitored phospho-protein responses to activators/cytokines and signal transduction inhibitors in a panel of 14 extensively characterized human MM cell lines with heterogeneous molecular abnormalities. A panel of 4-phospho-specific antibodies: anti-pS6, anti-ERK1/2, anti-pAKT and anti-pSTAT3 that represent downstream target genes of signaling pathways known to play central roles in myelomagenesis were used in the initial analysis. Sixteen conditions (basal, inhibitor, activator alone, activator and inhibitor) were studied to generated 64 readouts designed to survey altered signal transduction in the 14 cell lines. We collected data on unstimulated cells and cells stimulated for 7–10 min with IL-6, IGF-1 or FGF or cells inhibited with the signal transduction inhibitors U0126 (MEK), rapamycin (mTOR) or LY294002 (PI3-K). Repeat measurements were collected and the technique and monoclonal antibodies displayed a high level of reproducibly. In contrast, the basal, cytokine and inhibitor responses between cell lines varied considerably reflecting the molecular heterogeneity at the level of signaling responses. The protocols that have been refined and validated in myeloma cell lines are now being applied to primary bone marrow samples from MM patients. Although the same size thus far is small, phospho-protein responses among primary CD138 positive myeloma cells show considerable induction and variance of AKT, MAPK, STAT3 and pS6 phosphorylation. In some MM tumor samples treatment with inhibitors suggest constitutive activation of these signaling pathways while in others the nodes remain activable with phosphorylation above the basal state following stimulation. The data further suggests that MAPK phosphorylation following aFGF stimulation displays significant variance among MM samples and correlates with the detection of t(4;14) translocation by FISH analysis. Additional samples are being assessed and correlation of phospho-protein responses with clinical parameters and cytogenetics will be reported. The data demonstrate that multi-parameter flow cytometry can be applied to myeloma tumor samples to study the phospho-proteome and that considerable heterogeneity exists at the level of signaling responses.