Targeting the tumor microenvironment with chemically modified tetracyclines: Inhibition of laminin 5 γ2 chain promigratory fragments and vasculogenic mimicry

The laminin 5 (Ln-5) γ2 chain and matrix metalloproteinases (MMPs) MMP-2 and membrane type 1 (MT1)-MMP act cooperatively and are required for highly aggressive melanoma cells to engage in vasculogenic mimicry when cultured on a three-dimensional matrix. Furthermore, generation of Ln-5 γ2 chain promigratory fragments by MMP-2 and MT1-MMP proteolysis is necessary for an aggressive tumor cell-preconditioned matrix to induce vasculogenic mimicry in poorly aggressive tumor cells. These observations suggest that treatment regimes that specifically target aggressive tumor cells may fail to take into account changes in the extracellular microenvironment that persist after removal or destruction of an aggressive tumor and could result in a recurrence or continuance of the tumor. As a potential therapeutic approach to address this concern, the work presented here measured the molecular consequences of adding a chemically modified tetracycline (CMT-3; COL-3) that inhibits MMP activity to aggressive metastatic melanoma cells in three-dimensional culture. COL-3 inhibited vasculogenic mimicry and the expression of vasculogenic mimicry-associated genes in aggressive cells, as well as the induction of vasculogenic mimicry in poorly aggressive cells seeded onto an aggressive cell-preconditioned matrix. Furthermore, molecular analysis revealed that COL-3 not only inhibited the generation of Ln-5 γ2 chain promigratory fragments in the aggressive cell-preconditioned matrix but also inhibited the induction of Ln-5 γ2 chain gene expression in poorly aggressive cells by the aggressive cell-preconditioned matrix. These results suggest that COL-3 (and related chemically modified tetracyclines) may be useful in targeting molecular cues in the microenvironment of aggressive tumors and could potentially be used in a combinatorial manner with other therapies that specifically target and kill aggressive tumor cells.