Htaccess Problem Url Friendly

I have problem with this htaccess in STATIC URL

RewriteEngine On    
RewriteRule ^readlex/(.*)$/?$          readlex.php?slug=$1 [NC,L]

DINAMIC URL work fine only with defined CONSTANT: Example

<a href="<?php echo BASE_URL.READ_LEX ?>Le-mura-di-Lucca">Lucca</a>

Result = localhost/mysite/readlex/Le-mura-di-Lucca

STATIC URL not work (??)

<a href="localhost/mysite/readlex.php?slug=Le-mura-di-Lucca">Lucca</a>

Result = localhost/mysite/readlex.php?slug=Le-mura-di-Lucca">Lucca

***Unfortunately I can't insert the php CONSTANTS in mysql varchar/text