This excerpt taken from the NLST 8-K filed Apr 6, 2007.
SECTION 21.5. AMENDMENTS. No amendment or termination of this Lease shall be effective unless in writing signed by authorized signatories of Tenant and Landlord, or by their respective successors in interest. No actions, policies, oral or informal arrangements, business dealings or other course of conduct by or between the parties shall be deemed to modify this Lease in any respect.