Regeneron Pharmaceuticals will partner with Parabilis Medicines to discover and develop an initial five candidates encompassing a new form of antibody-drug conjugates aimed at challenging and historically undruggable targets, through a strategic research collaboration that could generate up to $2.3 billion-plus for the Cambridge, MA, biotech. Regeneron will marry its antibody capabilities with Parabilis’ stabilized helical peptide or Helicon pla…