The Options line may be optional or it may be required. It depends on how your host set up your server. Sometimes you must remove it for anything to work.
The [L] makes this the Last rule if THIS rule matched.
Not using underscore has SEO value. Also underscore "disappears" in underlined links. Avoid it.
In your character group, the hyphen should be listed last.
Are you really using mixed cased URLs? That will be a problem. If you insist in doing so, replace a-zA-Z with a-z and the [NC] flag.
It would be far better to use all lower case URLs.