APC is not supported starting from PHP 5.5 (replaced by Zend OPcache), so Zend_Cache_Backend_Apc is not usable anymore.
Is there any easy alternative? (eg. Zend_Cache_Backend_OPcache?) besides memcached?
You can install APCu, which implements just the userland caching features of APC. Zend_Cache_Backend_Apc will then work exactly as it did before.