Most destitute are born and expire on street (8)

'most destitute' is the definition.
('needy' can be a synonym of 'destitute')

'born and expire on street' is the wordplay.
'born' becomes 'nee' (I've seen this before).
'and' means one lot of letters go next to another.
'expire' becomes 'die' ('die' can be a synonym of 'expire').
'on street' becomes 'st' (I've seen this in other clues).
'nee'+'die'+'st'='NEEDIEST'

'are' acts as a link.