Protein Synthesis Inhibition Activity of Mesothelin Targeting Immunotoxin LMB-100 Decreases Concentrations of Oncogenic Signaling Molecules and Secreted Growth Factors
Salma El-Behaedi,
Rebekah Landsman,
Michael Rudloff,
Emily Kolyvas,
Rakan Albalawy,
Xianyu Zhang,
Tapan Bera,
Keith Collins,
Serguei Kozlov,
Christine Alewine
Affiliations
Salma El-Behaedi
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
Rebekah Landsman
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
Michael Rudloff
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
Emily Kolyvas
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
Rakan Albalawy
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
Xianyu Zhang
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
Tapan Bera
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
Keith Collins
Center for Advanced Preclinical Research, National Cancer Institute at Frederick, National Institutes of Health, Frederick, MD 21702, USA
Serguei Kozlov
Center for Advanced Preclinical Research, Frederick National Laboratory for Cancer Research sponsored by the National Cancer Institute, P.O. Box B, Frederick, MD 21702, USA
Christine Alewine
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
LMB-100 is a mesothelin-targeted recombinant immunotoxin (iTox) that carries a modified Pseuodomonas exotoxin A (PE) payload. PE kills cells by inhibiting synthesis of new proteins. We found that treatment of pancreatic cancer cells with LMB-100 for 24⁻48 h did not change total protein level despite inducing protein synthesis inhibition (PSI). Further, increased levels of ubiquitinated proteins were detected, indicating that cells may have limited ability to compensate for PSI by reducing protein degradation. Together, these data suggest that PE depletes concentrations of a minority of cellular proteins. We used reverse phase protein array and Luminex assay to characterize this subset. LMB-100 decreased the abundance of 24 of 32 cancer-related proteins (including Bcl-x, Her2, Her3 and MUC16) without compensatory increases in other analytes. Further, cancer cells failed to maintain extracellular concentrations of cancer cell secreted growth factors (CCSGFs), including Vascular Endothelial Growth Factor (VEGF) following treatment with cytostatic LMB-100 doses both in culture and in mouse tumors. Decreased VEGF concentration did not change tumor vasculature density, however, LMB-100 caused tissue-specific changes in concentrations of secreted factors made by non-cancer cells. In summary, our data indicate that PSI caused by cytostatic LMB-100 doses preferentially depletes short-lived proteins such as oncogenic signaling molecules and CCSGFs.
