These days I noticed that Youtube API which I'm using on my project is no longer available, e.g.
https://gdata.youtube.com/feeds/api/videos/dLEk9yiXVQs?v=2
returns HTTP 410 response code which means that requested resource is no longer available and will not be available again.
What should I use instead?
If I'm understanding your question correctly then you should be using https://www.googleapis.com/youtube/v3/videos?id=<video_id>&key=<YOUR_API_KEY>&part=snippet
from now on.
Google shutdown the old API effective April 20th, 2015.
Take a look at the newest v3 API getting started.