Investigating the Role of Proteases in Aggressiveness of Inflammatory Breast Cancer

Abstract

Inflammatory breast cancer (IBC) is the most lethal form of breast cancer with a three‐year survival rate of 42% versus 85% for other breast cancers. IBC is an aggressive, metastatic and highly angiogenic form of locally advanced breast cancer that invades into lymphatics where it forms large cellular aggregates. Here we performed live‐cell imaging using a SUM149 model of human inflammatory breast cancer. We hypothesize that the invasion of IBC is dependent on proteolytic activity at the tumor cell surface and that proteases contribute to the formation of tumor cell aggregates within the lymphatics. We assessed proteolytic activity using our functional assay for proteolysis. Quantification on a per cell basis throughout the volume of IBC structures was performed. Briefly, cells were grown in 3D reconstituted basement membrane (rBM) overlay cultures in which the lower layer of rBM is mixed with DQ‐collagen IV. Fluorescent cleavage products arising from the degradation of the collagen IV substrate were imaged on a Leica TCS SP5 laser scanning confocal microscope. Fluorescence intensities from 3D reconstructions of optical sections were quantified using Metamorph and Volocity software. Incubating the 3D rBM overlay cultures of SUM149 with inhibitors that target different classes of protease indicated that matrix metalloproteases and perhaps the cysteine protease cathepsin B play roles in the invasiveness of IBC.