您可以使用以下 regex*（使用capturing group和positive lookahead）*：

input        >>  2017 - Alpha Romeo United kingdom : New vehicle (by abc)
regex search >>  (?=:):(.*)
replace with >>  " "
output       >>  2017 - Alpha Romeo United kingdom

参见demo / explanation

聪明

{
    assign
    var = "articleTitle"
    value = "2017 - Alpha Romeo United kingdom : New vehicle (by abc)"
} {
    $articleTitle | regex_replace: "/(?=:):(.*)/": " "
}

private void Form1_Load(object sender, EventArgs e)
    {
        string str = "2017 - Alpha Romeo United kingdom : New vehicle (by abc)";
        str = Regex.Replace(str, @":+(.*)", "");
        MessageBox.Show(str);

    }