EXHIBIT 10.20

SEPTEMBER 21, 2011

FIRST AMENDMENT TO LEASE AGREEMENT

Re: Lease Agreement dated December 28, 2010, by and between STONECLIFF OFFICE,
L.P., as Lessor, and PAIN THERAPEUTICS, INC., as Lessee, (herein after referred
to as the “Lease Agreement”), demising 5,679 rentable square feet of space
locally known as Suite 260 in the StoneCliff building, located at 7801 Capital
of Texas Highway, Austin, Travis County, Texas, 78731.

This First Amendment shall amend and modify the Lease Agreement as follows:

 

1. Lease Term. Lessor and Lessee acknowledge and agree that Lessee’s lease term
shall be extended twenty-eight (28) months from the current expiration of
March 31, 2012 to July 31, 2014.

 

2. Base Rent. Effective April 1, 2012, Lessee shall pay to Lessor Base Rent as
set forth in the rent schedule below:

 

Term

   Monthly Rent      Term Rent      Annual Rent psf  

04/01/2012 to 05/31/2012

   $ 0.00       $ 0.00       $ 0.00   

06/01/2012 to 05/31/2013

   $ 11,358.00       $ 136,296.00       $ 24.00   

06/01/2013 to 07/31/2013

   $ 0.00       $ 0.00       $ 0.00   

08/01/2013 to 07/31/2014

   $ 11,594.63       $ 139,135.50       $ 24.50   

 

3. Additional Rents. Effective April 1, 2012 Lessee’s expense stop shall adjust
to a 2012 Base Year.

Except as provided to the contrary herein, all the remaining terms, covenants,
and provisions of the Lease Agreement shall remain in full force and effect and
unmodified hereby. Each party hereby acknowledges that the other is not in
default under the Lease Agreement in any respect. Each signatory hereto
represents and warrants that he or she is authorized to execute this document
and that upon said execution by both parties, this document will constitute the
binding obligation of the party on behalf of whom such person has signed,
without the necessity of joinder of any other person or entity.

EXECUTED on the dates set forth below our respective signatures.

 

LESSOR:

   LESSEE:

STONECLIFF OFFICE, L.P.

  

PAIN THERAPEUTICS, INC.

By:                                                                 
                                                 

   By:                                                                     
                                                           

Darrell R. Spaulding

  

Executive Vice President

   Name:                                                                     
                                                      

Kucera Management, Inc.

  

As Authorized Managing Agent

   Title:                                                                    
                                                         

Date:                                                                 
                                              

   Date: