Effects of Alpha-Connexin Carboxyl-Terminal Peptide (aCT1) and Bowman-Birk Protease Inhibitor (BBI) on Canine Oral Mucosal Melanoma (OMM) Cells

Abstract

Oral mucosal melanomas (OMM) are aggressive cancers in dogs, and are good models for human OMM. Gap junctions are composed of connexin units, which may have altered expression patterns and/or subcellular localization in cancer cells. Cell-to-cell communication by gap junctions is often impaired in cancer cells, including in melanomas. Meanwhile, the upregulated expression of the gap junction protein connexin 43 (Cx43) inhibits melanoma progression. The α-connexin carboxyl-terminal (aCT1) peptide reportedly maintains Cx43 expression and cell-cell communication in human mammary cells and increases the communication activity through gap junctions in functional assays, therefore causing decreased cell proliferation. The Bowman-Birk protease inhibitor (BBI), a component of soybeans, induces Cx43 expression in several tumor cells as a trypsin–chymotrypsin inhibition function, with antineoplastic effects. This study investigated the effect of aCT1 peptide and BBI treatment, alone or in combination, on TLM1 canine melanoma cell viability. Cell viability after treatment with aCT1, the reverse sequence peptide (R-pep), and/or BBI for 5 days was analyzed by PrestoBlue assay. Immunofluorescence was used to observe Cx43 localization and expression. aCT1 (200 μM) alone did not significantly decrease cell viability in TLM1 cells, whereas BBI (400 μg/ml) alone significantly decreased the TLM1 viability. Combined treatment with both aCT1 (200 μM) and BBI (400 μg/ml) significantly decreased cell viability in TLM1 cells. Cx43 expression, as identified by immunostainings in TLM1 cells, was increased in the cell membrane after the combination treatment with BBI and aCT1. This dual treatment can be combined to achieve the anticancer activity, possibly by increasing Cx 43 expression and affecting Cx43 migration to the cell membrane. In conclusion, a treatment strategy targeting Cx43 with BBI and aCT1 may possibly lead to new effective therapies for canine OMM.

Mapping the Anti-Cancer Activity of α-Connexin Carboxyl-Terminal (aCT1) Peptide in Resistant HER2+ Breast Cancer

“…Application of aCT1 was shown to increase gap junction size and GJIC [12,44]. Prior work shows the anti-cancer effects of aCT1 in the brain, melanoma, and breast cancer [12,45,46]. These reports suggest that aCT1 may have anti-cancer effects of its own and is quite effective at boosting the impact of other anti-cancer agents when added in combination, consistent with the concept of the bystander effect.…”

“…Numerous studies have evaluated Cx43 in breast cancer or other human cancers but fewer have looked at targeting Cx43 with a targeted agent [39,41]. Only a handful of prior studies evaluated the agent aCT1 for use in cancer [12,46,70]. Prior reports have indicated that the mechanism of action for aCT1 is the binding of ZO-1, leading to gap junction accretion, which promotes GJIC [44].…”

Degradation of the α-Carboxyl Terminus 11 Peptide: In Vivo and Ex Vivo Impacts of Time, Temperature, Inhibitors, and Gender in Rat

“…4-year later, one of its variants, αCT11, was found to have the same or similar properties (e.g., membrane permeable) and biological functions (e.g., modulating Cx43 or ZO-1) as αCT1 . In recent years, numerous studies, especially with αCT1, have been conducted to investigate αCT1′s roles in wound healing, , cardiovascular protection, ,, and as an adjunct therapy for cancer. − In terms of αCT­(1/11)’s therapeutic benefits for MI and HF, only a few studies using animal or isolated organs have been reported. In the cryo-injured ventricular model of mouse heart, O’Quinn et al found that methylcellulose patches containing αCT1 adhered to injured heart tissue reduced colocalization of Cx43 and ZO-1, increased intercalated disk association of Cx43 at the injury border zone (IBZ), and showed reductions in cardiac arrhythmias and an increase in depolarization rates in treated hearts relative to controls .…”

Resveratrol can induce differentiating phenotypes in canine oral mucosal melanoma cells

“…Notably, in mouse melanoma models, resveratrol enhances cisplatin’s therapeutic effect through the upregulation of connexin 43 (Cx43) expression [ 4 ]. Previously, we have reported [ 15 ] that Cx43 function is impaired in canine OMM cells. Further research is therefore required to explore the influence of resveratrol on the upregulation of Cx43 in canine OMM cells and consequently an enhancement in cisplatin chemosensitivity.…”