Exhibit 4.3


 


SECOND AMENDMENT TO

SECURED PROMISSORY NOTE


 


This Second Amendment to Secured Promissory
Note (“Amendment”) is made and entered into as of December 13, 2016, by and between CASI Pharmaceuticals, Inc.
(the “Debtor”), and Talon Therapeutics, Inc. (the “Holder”).


 


BACKGROUND


 


WHEREAS, the Debtor and the Holder
are parties to that certain Secured Promissory note, dated as of September 17, 2014 (the “Note”), and amended
on September 28, 2015;


 


WHEREAS, the Debtor and the Holder
desire to further amend the Note as set forth below;


 


WHEREAS, pursuant to paragraph 11
of the Note, the Note may be amended by an agreement in writing signed by the party against whom enforcement of any waiver, change,
modification or discharge is sought; and


 


WHEREAS, the Debtor and the Holder
represent all parties to the Note and agree to amend the Note as set forth below.


 


AGREEMENT


 


NOW, THEREFORE, intending to be legally
bound hereby, the parties hereto agree as follows:


 


1.           Existing
Definitions. All capitalized terms used and not otherwise defined herein shall have their respective meanings as set forth
in the Note.


 


2.           Amendment.
Paragraph 2 of the Note is hereby amended and restated in full as follows:


 


“ Interest Rate; Maturity Date. Interest
shall accrue on the outstanding balance of the principal sum evidenced hereby at the rate of 0.50% per annum from the date hereof.
Interest shall be payable in arrears to the Holder on the date that is twelve (12) months after the date of this Note. The entire
unpaid principal balance of this Secured Promissory Note (the “Note”), together with all accrued but unpaid interest,
shall be and become due and payable in full on the date that is forty-two (42) months after the date of this Note (the “Maturity
Date”). Any amount of principal and/or interest hereon which is not paid when due, whether at stated maturity, by acceleration
or otherwise, shall bear interest from the date when due until said principal and/or interest amount is paid in full, at the lesser of
(a) an interest rate equal to two percent (2%) per annum in excess of the interest rate set forth above, and (b) the highest rate
of interest allowable under applicable law.”


 


3.           No
Other Amendments. Except for the amendment specified in Section 2 of this Amendment, this Amendment shall not be deemed
to effect any amendment, modification or waiver of any provision of the Note.


 


4.           Governing
Law. This Amendment is to be construed and governed by the Laws of the State of Delaware (without giving effect to principles
of conflicts of laws).


 






     


     


    

 


5.           Counterparts.
This Amendment may be executed in two or more counterparts, all of which shall be considered one and the same agreement and shall
become effective when one or more counterparts have been signed by each of the parties hereto and delivered to the other parties,
including delivery by facsimile or other electronic means, it being understood that all parties need not sign the same counterpart.


 


 



    [signature pages follow]


     


    


 


IN WITNESS WHEREOF, each of the parties
hereto has executed this Amendment as of the date first set forth above.


 


	 	DEBTOR:	 
	 	 	 
	 	CASI PHARMACEUTICALS, INC.
	 	 	 
	 	 	 
	 	By: 	/s/ Ken K. Ren	 
	 	Name:
Title:	Ken K. Ren
Chief Executive Officer



 


 



    Signature page to Second Amendment to
Promissory Note


     


    


 


IN WITNESS WHEREOF, each of the parties
hereto has executed this Amendment as of the date first set forth above.


 





	 	HOLDER:	 
	 	 	 
	 	TALON THERAPEUTICS, INC.
	 	 	 
	 	 	 
	 	By: 	/s/ Kurt A. Gustafson	 
	 	Name:
Title:	Kurt A. Gustafson
Chief Financial Officer



 


 



    Signature page to Second Amendment to
Promissory Note