Merck & Co., Inc. to Acquire Sirna Therapeutics, Inc.

  
    
  
  
    
      Merck & Co., Inc. (NYSE: MRK), one of the world's leading research-based 
      pharmaceutical companies, and Sirna Therapeutics, Inc. (NASDAQ: RNAI), a 
      publicly held biotechnology company and a leader in developing a new 
      class of medicines based on RNA interference (RNAi) technology, today 
      announced that they have entered into a definitive agreement under which 
      Merck will acquire Sirna.
    
    
      Under the terms of the agreement, Merck will acquire through a merger 
      100 percent of the equity of Sirna at a price of $13 per share in cash, 
      making Sirna a wholly owned subsidiary of Merck & Co., Inc. The 
      transaction has a cash value of approximately $1.1 billion.
    
    
      Sirna Therapeutics has been at the forefront of efforts to create 
      RNAi-based therapeutics, medicines which could significantly alter the 
      treatment of disease. RNAi-based therapeutics selectively catalyze the 
      destruction of the RNA transcribed from an individual gene. This enables 
      an entirely novel approach to discovering drugs with the potential to 
      produce highly specific, potent, and long-lasting effects.
    
    
      The acquisition of Sirna complements the cutting-edge research on RNA 
      expression that Merck has been doing since the 2001 acquisition of 
      Rosetta Inpharmatics, Inc. “That research has 
      led to a deeper understanding of the biological circuits that control 
      the activity of cells, and thus the identification of many novel targets 
      which can now be approached through the use of RNAi-based treatments,” 
      said Alan Sachs, M.D., Ph.D., vice president at Merck's Rosetta 
      laboratories.
    
    
      “We are delighted about our agreement to 
      acquire Sirna Therapeutics, a company that has established a leading 
      presence in the critically important area of RNAi,” 
      said Peter S. Kim, Ph.D., president, Merck Research Laboratories. “We 
      believe that RNAi could significantly change the way in which we go 
      about discovering and developing drugs, and could become a new way to 
      treat patients with unmet medical needs.”
    
    
      One area in which RNAi shows great promise is in cancer research.
    
    
      “RNAi is a powerful enabler of drug discovery 
      in cells, in animals, and in humans. We can potentially use this 
      technology to target the activity of genes which control the activity of 
      cancer cells, and so produce their destruction without damaging normal 
      cells,” said Stephen H. Friend, M.D., Ph.D., 
      executive vice president and franchise head, Oncology and Neuroscience, 
      Merck Research Laboratories.
    
    
      Sirna's lead clinical development candidate, Sirna-027, is a chemically 
      optimized, short interfering RNA (siRNA) currently moving into Phase II 
      development for the treatment of the wet-form of age related macular 
      degeneration (AMD) as part of a broad collaboration with Allergan, Inc. 
      in the area of ophthalmic diseases. In addition to the collaboration 
      with Allergan, Sirna has established a strategic alliance with 
      GlaxoSmithKline for the development of siRNA compounds for the treatment 
      of respiratory diseases. Besides its external collaborations, Sirna has 
      several programs covering a broad range of therapeutic areas, including 
      infectious diseases, metabolism, CNS and dermatology.
    
    
      “We are extremely pleased to be joining 
      forces with one of the world’s premier 
      pharmaceutical companies. Merck’s decision to 
      acquire Sirna speaks volumes about Sirna’s 
      expertise in the field of RNAi-based therapeutics, the breadth of our 
      intellectual property estate and talent of our scientific and management 
      team,” said Howard W. Robin, president and 
      chief executive officer of Sirna Therapeutics. “Combining 
      the expertise of both companies will significantly accelerate the 
      development of RNAi-based therapeutics.”
    
    
      “We are excited about the opportunity to 
      undertake the discovery and development of therapeutic siRNAs with 
      Merck, a company that clearly recognizes the potential of this 
      breakthrough technology,” said Sirna Senior 
      Vice President of Research and Chief Scientific Officer Barry Polisky. “Merck’s 
      commitment to the development of RNAi-based therapeutics will ensure 
      that this novel therapeutic modality will achieve its full potential.”
    
    
      Sirna stockholders owning approximately 36 percent of Sirna's 
      outstanding shares have committed to support the transaction and have 
      entered into voting agreements. The acquisition is subject to clearance 
      under the Hart-Scott-Rodino Antitrust Improvements Act and approval by 
      the stockholders of Sirna and other customary closing conditions. The 
      two companies expect to complete the acquisition in the first quarter of 
      2007.
    
    
      Richard N. Kender, vice president of Business Development and Corporate 
      Licensing at Merck, noted that Merck's acquisition of Sirna “is 
      another example of Merck delivering on its strategy of aggressively 
      pursuing biotechnology companies that complement our considerable 
      internal research capabilities.”
    
    
      About Sirna Therapeutics, Inc.
    
    
      Sirna Therapeutics is a clinical-stage biotechnology company developing 
      RNAi-based therapies for serious diseases and conditions, including 
      age-related macular degeneration (AMD), hepatitis C, dermatology, 
      asthma, respiratory syncytial virus (RSV) and Huntington's disease. 
      Sirna Therapeutics completed its Phase I clinical trial for Sirna-027 in 
      AMD in 2005 and with its strategic partner, Allergan, Inc., is moving 
      Sirna-027 forward into Phase II clinical trials. Sirna has selected a 
      clinical candidate for hepatitis C virus, Sirna-034. Sirna has 
      established an exclusive multi-year strategic alliance with 
      GlaxoSmithKline for the development of siRNA compounds for the treatment 
      of respiratory diseases. Sirna has a leading intellectual property 
      portfolio in RNAi covering over 250 mammalian gene and viral targets and 
      over 200 issued or pending patents covering other major aspects of RNAi 
      technology, including the microRNA technology. More information on Sirna 
      Therapeutics is available on the Company's web site at http://www.sirna.com.
    
    
      Sirna Forward-Looking Statement
    
    
      Statements in this press release which are not strictly historical are 
      "forward-looking" statements which are subject to many risks and 
      uncertainties. These include the failure to satisfy the closing 
      conditions set forth in the merger agreement between Sirna and Merck, 
      the termination of the merger agreement, the failure of the proposed 
      acquisition to close or a significant delay in the closing for any 
      reason, and business uncertainty and contractual restrictions before 
      closing. Additionally, all of Sirna's programs are still at a relatively 
      early stage of development and are subject to significant risks and 
      unknowns. In addition, patent applications may not result in issued 
      patents, and issued patents may not be enforceable or could be 
      invalidated. Risk factors are identified in Sirna's Securities and 
      Exchange Commission filings, including Forms 10-K and 10-Q and in other 
      SEC filings. Sirna undertakes no obligation to revise or update any 
      forward-looking statements in order to reflect events or circumstances 
      that may arise after the date of this release.
    
    
      About Merck
    
    
      Merck & Co., Inc. is a global research-driven pharmaceutical company 
      dedicated to putting patients first. Established in 1891, Merck 
      discovers, develops, manufactures and markets vaccines and medicines to 
      address unmet medical needs. The Company devotes extensive efforts to 
      increase access to medicines through far-reaching programs that not only 
      donate Merck medicines but help deliver them to the people who need 
      them. Merck also publishes unbiased health information as a 
      not-for-profit service. For more information, visit www.merck.com.
    
    
      Merck Forward-Looking Statement
    
    
      This press release contains "forward-looking statements" as that term is 
      defined in the Private Securities Litigation Reform Act of 1995. These 
      statements are based on management's current expectations and involve 
      risks and uncertainties, which may cause results to differ materially 
      from those set forth in the statements. The forward-looking statements 
      may include statements regarding product development, product potential 
      or financial performance. No forward-looking statement can be 
      guaranteed, and actual results may differ materially from those 
      projected. Merck undertakes no obligation to publicly update any 
      forward-looking statement, whether as a result of new information, 
      future events, or otherwise. Forward-looking statements in this press 
      release should be evaluated together with the many uncertainties that 
      affect Merck's business, particularly those mentioned in the cautionary 
      statements in Item 1 of Merck's Form 10-K for the year ended Dec. 31, 
      2005, and in its periodic reports on Form 10-Q and Form 8-K, which the 
      Company incorporates by reference.
    
    
      Participants in the Solicitation and Additional Information
    
    
      This communication may be deemed to be solicitation material regarding 
      the proposed acquisition of Sirna by Merck. In connection with the 
      proposed acquisition, Sirna intends to file relevant documents with the 
      SEC, including Sirna’s proxy statement on 
      Schedule 14A. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ ALL 
      RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING SIRNA’S 
      PROXY STATEMENT, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT 
      SIRNA AND THE PROPOSED ACQUISITION. Investors and security holders may 
      obtain free copies of these documents and other documents filed with the 
      SEC at the SEC’s website at www.sec.gov 
      or at Sirna’s website at www.sirna.com. 
      Such information is currently not available.
    
    
      Sirna and its directors and executive officers may be deemed to be 
      participants in the solicitation of proxies from Sirna’s 
      stockholders in connection with the proposed acquisition. Such 
      individuals have interests in the proposed acquisition, including as a 
      result of holding options to purchase or shares of Sirna stock or 
      affiliation with large stockholders of Sirna. Certain information 
      regarding Sirna’s directors and executive 
      officers and their interests in the solicitation is set forth in the 
      proxy statement for Sirna’s 2006 annual 
      meeting of stockholders filed with the SEC on May 1, 2006, and will be 
      included in the proxy statement relating to the proposed acquisition 
      when it becomes available.
    
  
Merck & Co., Inc. (NYSE: MRK), one of the world's leading
research-based pharmaceutical companies, and Sirna Therapeutics, Inc.
(NASDAQ: RNAI), a publicly held biotechnology company and a leader in
developing a new class of medicines based on RNA interference (RNAi)
technology, today announced that they have entered into a definitive
agreement under which Merck will acquire Sirna.

   Under the terms of the agreement, Merck will acquire through a
merger 100 percent of the equity of Sirna at a price of $13 per share
in cash, making Sirna a wholly owned subsidiary of Merck & Co., Inc.
The transaction has a cash value of approximately $1.1 billion.

   Sirna Therapeutics has been at the forefront of efforts to create
RNAi-based therapeutics, medicines which could significantly alter the
treatment of disease. RNAi-based therapeutics selectively catalyze the
destruction of the RNA transcribed from an individual gene. This
enables an entirely novel approach to discovering drugs with the
potential to produce highly specific, potent, and long-lasting
effects.

   The acquisition of Sirna complements the cutting-edge research on
RNA expression that Merck has been doing since the 2001 acquisition of
Rosetta Inpharmatics, Inc. "That research has led to a deeper
understanding of the biological circuits that control the activity of
cells, and thus the identification of many novel targets which can now
be approached through the use of RNAi-based treatments," said Alan
Sachs, M.D., Ph.D., vice president at Merck's Rosetta laboratories.

   "We are delighted about our agreement to acquire Sirna
Therapeutics, a company that has established a leading presence in the
critically important area of RNAi," said Peter S. Kim, Ph.D.,
president, Merck Research Laboratories. "We believe that RNAi could
significantly change the way in which we go about discovering and
developing drugs, and could become a new way to treat patients with
unmet medical needs."

   One area in which RNAi shows great promise is in cancer research.

   "RNAi is a powerful enabler of drug discovery in cells, in
animals, and in humans. We can potentially use this technology to
target the activity of genes which control the activity of cancer
cells, and so produce their destruction without damaging normal
cells," said Stephen H. Friend, M.D., Ph.D., executive vice president
and franchise head, Oncology and Neuroscience, Merck Research
Laboratories.

   Sirna's lead clinical development candidate, Sirna-027, is a
chemically optimized, short interfering RNA (siRNA) currently moving
into Phase II development for the treatment of the wet-form of age
related macular degeneration (AMD) as part of a broad collaboration
with Allergan, Inc. in the area of ophthalmic diseases. In addition to
the collaboration with Allergan, Sirna has established a strategic
alliance with GlaxoSmithKline for the development of siRNA compounds
for the treatment of respiratory diseases. Besides its external
collaborations, Sirna has several programs covering a broad range of
therapeutic areas, including infectious diseases, metabolism, CNS and
dermatology.

   "We are extremely pleased to be joining forces with one of the
world's premier pharmaceutical companies. Merck's decision to acquire
Sirna speaks volumes about Sirna's expertise in the field of
RNAi-based therapeutics, the breadth of our intellectual property
estate and talent of our scientific and management team," said Howard
W. Robin, president and chief executive officer of Sirna Therapeutics.
"Combining the expertise of both companies will significantly
accelerate the development of RNAi-based therapeutics."

   "We are excited about the opportunity to undertake the discovery
and development of therapeutic siRNAs with Merck, a company that
clearly recognizes the potential of this breakthrough technology,"
said Sirna Senior Vice President of Research and Chief Scientific
Officer Barry Polisky. "Merck's commitment to the development of
RNAi-based therapeutics will ensure that this novel therapeutic
modality will achieve its full potential."

   Sirna stockholders owning approximately 36 percent of Sirna's
outstanding shares have committed to support the transaction and have
entered into voting agreements. The acquisition is subject to
clearance under the Hart-Scott-Rodino Antitrust Improvements Act and
approval by the stockholders of Sirna and other customary closing
conditions. The two companies expect to complete the acquisition in
the first quarter of 2007.

   Richard N. Kender, vice president of Business Development and
Corporate Licensing at Merck, noted that Merck's acquisition of Sirna
"is another example of Merck delivering on its strategy of
aggressively pursuing biotechnology companies that complement our
considerable internal research capabilities."

   About Sirna Therapeutics, Inc.

   Sirna Therapeutics is a clinical-stage biotechnology company
developing RNAi-based therapies for serious diseases and conditions,
including age-related macular degeneration (AMD), hepatitis C,
dermatology, asthma, respiratory syncytial virus (RSV) and
Huntington's disease. Sirna Therapeutics completed its Phase I
clinical trial for Sirna-027 in AMD in 2005 and with its strategic
partner, Allergan, Inc., is moving Sirna-027 forward into Phase II
clinical trials. Sirna has selected a clinical candidate for hepatitis
C virus, Sirna-034. Sirna has established an exclusive multi-year
strategic alliance with GlaxoSmithKline for the development of siRNA
compounds for the treatment of respiratory diseases. Sirna has a
leading intellectual property portfolio in RNAi covering over 250
mammalian gene and viral targets and over 200 issued or pending
patents covering other major aspects of RNAi technology, including the
microRNA technology. More information on Sirna Therapeutics is
available on the Company's web site at http://www.sirna.com.

   Sirna Forward-Looking Statement

   Statements in this press release which are not strictly historical
are "forward-looking" statements which are subject to many risks and
uncertainties. These include the failure to satisfy the closing
conditions set forth in the merger agreement between Sirna and Merck,
the termination of the merger agreement, the failure of the proposed
acquisition to close or a significant delay in the closing for any
reason, and business uncertainty and contractual restrictions before
closing. Additionally, all of Sirna's programs are still at a
relatively early stage of development and are subject to significant
risks and unknowns. In addition, patent applications may not result in
issued patents, and issued patents may not be enforceable or could be
invalidated. Risk factors are identified in Sirna's Securities and
Exchange Commission filings, including Forms 10-K and 10-Q and in
other SEC filings. Sirna undertakes no obligation to revise or update
any forward-looking statements in order to reflect events or
circumstances that may arise after the date of this release.

   About Merck

   Merck & Co., Inc. is a global research-driven pharmaceutical
company dedicated to putting patients first. Established in 1891,
Merck discovers, develops, manufactures and markets vaccines and
medicines to address unmet medical needs. The Company devotes
extensive efforts to increase access to medicines through far-reaching
programs that not only donate Merck medicines but help deliver them to
the people who need them. Merck also publishes unbiased health
information as a not-for-profit service. For more information, visit
www.merck.com.

   Merck Forward-Looking Statement

   This press release contains "forward-looking statements" as that
term is defined in the Private Securities Litigation Reform Act of
1995. These statements are based on management's current expectations
and involve risks and uncertainties, which may cause results to differ
materially from those set forth in the statements. The forward-looking
statements may include statements regarding product development,
product potential or financial performance. No forward-looking
statement can be guaranteed, and actual results may differ materially
from those projected. Merck undertakes no obligation to publicly
update any forward-looking statement, whether as a result of new
information, future events, or otherwise. Forward-looking statements
in this press release should be evaluated together with the many
uncertainties that affect Merck's business, particularly those
mentioned in the cautionary statements in Item 1 of Merck's Form 10-K
for the year ended Dec. 31, 2005, and in its periodic reports on Form
10-Q and Form 8-K, which the Company incorporates by reference.

   Participants in the Solicitation and Additional Information

   This communication may be deemed to be solicitation material
regarding the proposed acquisition of Sirna by Merck. In connection
with the proposed acquisition, Sirna intends to file relevant
documents with the SEC, including Sirna's proxy statement on Schedule
14A. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ ALL RELEVANT
DOCUMENTS FILED WITH THE SEC, INCLUDING SIRNA'S PROXY STATEMENT,
BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT SIRNA AND THE
PROPOSED ACQUISITION. Investors and security holders may obtain free
copies of these documents and other documents filed with the SEC at
the SEC's website at www.sec.gov or at Sirna's website at
www.sirna.com. Such information is currently not available.

   Sirna and its directors and executive officers may be deemed to be
participants in the solicitation of proxies from Sirna's stockholders
in connection with the proposed acquisition. Such individuals have
interests in the proposed acquisition, including as a result of
holding options to purchase or shares of Sirna stock or affiliation
with large stockholders of Sirna. Certain information regarding
Sirna's directors and executive officers and their interests in the
solicitation is set forth in the proxy statement for Sirna's 2006
annual meeting of stockholders filed with the SEC on May 1, 2006, and
will be included in the proxy statement relating to the proposed
acquisition when it becomes available.