Background: PDPN is a transmembrane receptor that promotes cell migration, but modifications that regulate its effects are not known. Results: PKA can phosphorylate PDPN, nonphosphorylatable PDPN promotes cell migration, and phosphomimetic PDPN fails to promote cell migration. Conclusion: PKA can phosphorylate PDPN to decrease cell migration. Significance: PDPN effects on cell motility are important for processes including embryonic development and cancer progression.

Cancer is a leading cause of death of men and women worldwide. Tumor cell motility contributes to metastatic invasion that causes the vast majority of cancer deaths. Extracellular receptors modified by α2,3-sialic acids that promote this motility can serve as ideal chemotherapeutic targets. For example, the extracellular domain of the mucin receptor podoplanin (PDPN) is highly O-glycosylated with α2,3-sialic acid linked to galactose. PDPN is activated by endogenous ligands to induce tumor cell motility and metastasis. Dietary lectins that target proteins containing α2,3-sialic acid inhibit tumor cell growth. However, anti-cancer lectins that have been examined thus far target receptors that have not been identified. We report here that a lectin from the seeds of Maackia amurensis (MASL) with affinity for O-linked carbohydrate chains containing sialic acid targets PDPN to inhibit transformed cell growth and motility at nanomolar concentrations. Interestingly, the biological activity of this lectin survives gastrointestinal proteolysis and enters the cardiovascular system to inhibit melanoma cell growth, migration, and tumorigenesis. These studies demonstrate how lectins may be used to help develop dietary agents that target specific receptors to combat malignant cell growth.

Podoplanin (PDPN) is a unique transmembrane receptor that promotes tumor cell motility. Indeed, PDPN may serve as a chemotherapeutic target for primary and metastatic cancer cells, particularly oral squamous cell carcinoma (OSCC) cells that cause most oral cancers. Here, we studied how a monoclonal antibody (NZ-1) and lectin (MASL) that target PDPN affect human OSCC cell motility and viability. Both reagents inhibited the migration of PDPN expressing OSCC cells at nanomolar concentrations before inhibiting cell viability at micromolar concentrations. In addition, both reagents induced mitochondrial membrane permeability transition to kill OSCC cells that express PDPN by caspase independent nonapoptotic necrosis. Furthermore, MASL displayed a surprisingly robust ability to target PDPN on OSCC cells within minutes of exposure, and significantly inhibited human OSCC dissemination in zebrafish embryos. Moreover, we report that human OSCC cells formed tumors that expressed PDPN in mice, and induced PDPN expression in infiltrating host murine cancer associated fibroblasts. Taken together, these data suggest that antibodies and lectins may be utilized to combat OSCC and other cancers that express PDPN.

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Oral cancer is diagnosed in over 300 thousand people, and kills over 100 thousand people, around the world each year. Current treatments rely on radiation and surgery procedures that often decrease the quality of life for oral cancer survivors. There is a clear need to improve treatments for these patients. Over 90% of oral cancers are formed by oral squamous cell carcinoma (OSCC). Most OSCC cells express the transmembrane receptor podoplanin (PDPN), which has emerged as a promising target for OSCC treatment. The PDPN receptor promotes tumor cell invasion and metastasis which leads to the vast majority of cancer deaths. Here, we describe efforts to target PDPN intracellularly and extracellularly in order to prevent and treat oral cancer. PDPN contains intracellular serine residues that can be phosphorylated by protein kinases including CDK5 and PKA to decrease cell migration. Additionally, the extracellular portion of PDPN can be targeted with Maackia amurensis seed lectin (MASL) to inhibit tumor cell migration and viability. Previous studies suggest that PDPN induces RhoA GTPase activity to promote cell migration. However, we show here that MASL dynamically binds PDPN to downregulate Cdc42 GTPase activity, but not RhoA or Rac1 GTPase activity. These data suggest that MASL suppresses Cdc42 GTPase activity to disrupt cell polarity and inhibit cell migration. Taken together, these data indicate that PDPN can serve as a functionally relevant target to prevent and combat oral cancer. Citation Format: Edward P. Retzbach, Harini Krishnan, Jhon A. Ochoa-Alvarez, Yongquan Shen, Evan Nevel, David J. Kephart, Evelyne Kalyoussef, Soly Baredes, Mahnaz Fatahzadeh, Maria I. Rameriz, Kingsley Yin, Mary Ann Young, Lisa Deluca-Rapone, Alan J. Shienbaum, Lasse D. Jensen, Gary S. Goldberg. Utilization of podoplanin as a chemotherapeutic target for oral squamous cell carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1215.

Cancer is a leading cause of death. In fact, cancer killed over 8 million people around the world in 2012. Over 90% of these cancer deaths are due to metastasis, which results from tumor cell migration and invasion. Specific cancer biomarkers need to be identified in order to effectively target these motile cells. The transmembrane glycoprotein receptor podoplanin (PDPN) promotes tumor cell motility and metastasis in many aggressive cancers. Indeed, PDPN has emerged as a prime cancer biomarker and chemotherapeutic target. Here, we describe how PDPN can be targeted to inhibit the growth and motility of melanoma and oral cancer cells. PDPN has a short intracellular domain of 9 amino acids which include two conserved serine residues. PDPN also has a large extracellular domain that is extensively O-glycosylated with α2,3-sialic acid linked to galactose. We are developing novel methods to target the intracellular and extracellular domains of PDPN to combat cancer progression. For example, we have found that some activators of protein kinase A can induce phosphorylation of the intracellular serine residues of PDPN to inhibit tumor cell migration. In addition, we have found that Maackia amurensis seed lectin (MASL) can target the extracellular domain of PDPN to inhibit tumor cell growth, migration, and tumor progression in cell culture and animal models. Furthermore, we utilized live cell imaging to find that PDPN expression can be modulated in cancer associated fibroblasts to inhibit neighboring tumor cell migration and survival. Thus, reagents can be used to target PDPN from inside of the cell and outside of the cell to inhibit tumor cell migration and combat cancer progression. This work illuminates novel strategies designed to exploit PDPN as a functionally relevant biomarker and chemotherapeutic target. Citation Format: Harini Krishnan, Jhon Ochoa-alvarez, Yongquan Shen, Evan Nevel, David Kephart, Angels Nguyen, Min Han, Nimish Acharya, Robert Nagele, Maria Ramirez, W. Todd Miller, Evelyne Kalyoussef, Soly Baredes, Mahnaz Fatahzadeh, Lasse Jensen, Alan Shienbaum, Gary Goldberg. Podoplanin (PDPN): novel biomarker and chemotherapeutic target. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4375. doi:10.1158/1538-7445.AM2015-4375

No abstract

Oral cancer is diagnosed in over 300 thousand people, and kills over 100 thousand people, around the world each year. Current treatments rely on radiation and surgery procedures that often decrease the quality of life for oral cancer survivors. There is a clear need to improve treatments for these patients. Over 90% of oral cancers are oral squamous cell carcinoma (OSCC). Most OSCC cells express the transmembrane receptor podoplanin (PDPN), which has emerged as a promising target for OSCC treatment. The PDPN receptor promotes tumor cell invasion and metastasis which leads to the vast majority of cancer deaths. Here, we describe efforts to target PDPN in order to prevent and treat oral cancer. PDPN can be targeted with Maackia amurensis seed lectin (MASL) to inhibit tumor cell migration and viability. Recent evidence also suggests that PDPN may undergo cancer specific changes, which indicates another potential route for targeting PDPN in oral cancer. Taken together, these data indicate that PDPN can serve as a functionally relevant target to prevent and combat oral cancer. Citation Format: Edward P. Retzbach, Harini Krishnan, Jhon A. Ochoa-Alvarez, Yongquan Shen, Evan Nevel, David J. Kephart, Evelyne Kalyoussef, Soly Baredes, Mahnaz Fatahzadeh, Kingsley Yin, Alan J. Shienbaum, Yukinari Kato, Lasse Jensen, Gary S. Goldberg. Podoplanin's diverse potential as a chemotherapeutic target for oral squamous cell carcinom [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 968. doi:10.1158/1538-7445.AM2017-968