AstraZeneca takeover: 'Opportunistic bid' from Pfizer risks R&D disruption
* Pfizer hints at improved offer if AstraZeneca engages
* Read says can't commit to specific research spend
* AstraZeneca says "opportunistic" bid risks R&D disruption
* But AZ CEO says cannot rule accepting compelling offer
* Head of Unite union says members "very, very concerned"
British drugs company AstraZeneca said its bigger U.S. rival Pfizer was making an "opportunistic attempt" to buy the company for a price that didn't reflect the value of its "exciting pipeline" of new drugs.
In response to an appeal from Pfizer for it to enter negotiations, AstraZeneca said Pfizer's announcement on Tuesday contained no new proposal nor substantive new information