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                                                                   EXHIBIT 10.44

                                 FIRST AMENDMENT

       THIS FIRST AMENDMENT (the "AMENDMENT") is made and entered into as of
March 9, 2006, by and between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE
LIMITED LIABILITY COMPANY ("LANDLORD") and COMBINATORX, INCORPORATED, A DELAWARE
CORPORATION ("TENANT").

                                    RECITALS

A.     Landlord and Tenant are parties to that certain lease dated October 18,
       2005 (the "LEASE"). Pursuant to the Lease, Landlord has leased to Tenant
       space currently containing approximately 40,130 rentable square feet (the
       "ORIGINAL PREMISES") consisting of approximately (i) 22,095 rentable
       square feet of lab space (the "ORIGINAL LAB SPACE") on the 4th floor
       (together with Tenant's proportionate share of the Ph Treatment Room on
       the 1st floor and Tenant's proportionate share of the 3A Annex Space) of
       the Science Building (as hereinafter defined); and (ii) 18,035 rentable
       square feet of office space described as suite number 1600 (the "OFFICE
       SPACE") on the 16th floor of the Office Building (as hereinafter defined)
       in the buildings located at 245 First Street, Cambridge, Massachusetts
       and commonly known as Cambridge Science Center and 245 First Street,
       comprised of two buildings, the first being the science building (the
       "SCIENCE BUILDING") and the second being the office building (the "OFFICE
       BUILDING").

B.     Tenant and Landlord mutually desire that the Lease be amended with
       respect to, among other things, the definition of the Premises and the
       Rentable Square Footage of the Premises, subject to the following terms
       and conditions.

C.     Tenant has requested that additional space containing approximately
       23,199 rentable square feet described as Suite No. 300 on the 3rd floor
       of the Science Building, which includes Tenant's proportionate share of
       the Ph Treatment Room on the 1st floor of the Science Building and
       Tenant's proportionate share of the 3A Annex Space in the Science
       Building, as more fully shown on EXHIBIT B hereto (the "EXPANSION SPACE")
       be added to the Premises and that the Lease be appropriately amended and
       Landlord is willing to do the same on the following terms and conditions.

D.     The Lease by its terms shall expire on November 30, 2016 ("PRIOR
       TERMINATION DATE"), and the parties desire to extend the Term of the
       Lease, all on the following terms and conditions.

       NOW, THEREFORE, in consideration of the above recitals which by this
reference are incorporated herein, the mutual covenants and conditions contained
herein and other valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, Landlord and Tenant agree as follows:

1.     PREMISES.

       A.     Effective as of the date hereof, Landlord and Tenant agree that
              Section 1.02 of the Lease shall be deleted in its entirety and
              replaced with the following:

              "1.02  "PREMISES" shall mean the area shown on EXHIBIT A to this
                     Lease. The Premises consists of (i) 22,095 rentable square
                     feet of space on the 4th floor of the Science Building and
                     known as suite number 400, which includes Tenant's
                     proportionate share of the Ph Treatment Room on the 1st
                     floor of the Science Building and Tenant's proportionate
                     share of the 3A Annex Space in the Science Building as more
                     fully identified on EXHIBIT A to this Lease (collectively,
                     the "LAB SPACE"), and (ii) 18,035 rentable square feet of
                     office space on the 16th floor of the Office Building and
                     known as suite number 1600 (the "OFFICE SPACE"). If the
                     Premises include one or more floors in their entirety, all
                     corridors and restroom facilities located on such full
                     floor(s) shall be considered part of the Premises. The
                     "RENTABLE SQUARE FOOTAGE OF THE PREMISES" is deemed to be
                     40,130 square feet. Landlord and Tenant stipulate and agree
                     that the Rentable Square Footage of the Buildings and the
                     Rentable Square Footage of the Premises are correct."

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       B.     Effective as of the date hereof, Landlord and Tenant agree that
              Section 1.11 of the Lease shall be deleted in its entirety and
              replaced with the following:

              "1.11  "PERMITTED USE": (a) with respect to the Office Space,
                     general office use, (b) with respect to the Lab Space,
                     technical office for research and development, laboratory
                     and research facility, (c) with respect to the portion of
                     the Lab Space consisting of the Ph Treatment Room,
                     wastewater treatment in compliance with applicable Laws,
                     and (d) with respect to the portion of the Lab Space
                     consisting of the 3A Annex Space, storage facilities for
                     Tenant's equipment and materials."

       C.     Effective as of the date hereof, EXHIBIT A to the Lease shall be
              deleted in its entirety and replaced with EXHIBIT A attached to
              this Amendment.

2.     LAB SPACE. Effective as of the date hereof Landlord and Tenant agree that
       notwithstanding the provisions of Section 1 of this Amendment, the term
       "Lab Space" as used in the following provisions of the Lease shall be
       deemed to mean only the 22,095 rentable square feet of lab space on the
       4th floor of the Science Building, and shall not be deemed to include
       either the Common Ph Treatment Room on the 1st floor of the Science
       Building, or the 3A Annex Space in the Science Building:

       2.01.  All references to "Lab Space" or "lab space" in the paragraphs
              titled "Air Handling Units" and "Distribution" in Section 7.02 of
              the Lease.

       2.02.  All references to "Lab Space" in Section 7.03 of the Lease.

       2.03.  All references to "Lab Space" in the second paragraph of Section
              9.03 of the Lease.

       2.04.  The reference to "Lab Space" in the second sentence of Section 10
              of the Lease.

3.     EXPANSION.

       3.01.  Effective as of February 1, 2007 (the "EXPANSION EFFECTIVE DATE"),
              the Premises, as defined in the Lease, is increased from 40,130
              rentable square feet to 63,329 rentable square feet consisting of
              (i) 23,199 rentable square feet of expansion lab space on the 3rd
              floor of the Science Building, which includes Tenant's
              proportionate share of the Ph Treatment Room on the 1st floor of
              the Science Building and Tenant's proportionate share of the 3A
              Annex Space in the Science Building with respect to such expansion
              lab space as more fully identified on EXHIBIT B, (ii) 22,095
              rentable square feet of original lab space on the 4th floor of the
              Science Building, which includes Tenant's proportionate share of
              the Ph Treatment Room on the 1st floor of the Science Building and
              Tenant's proportionate share of the 3A Annex Space in the Science
              Building with respect to such original lab space as more fully
              identified on EXHIBIT A, and (iii) 18,035 rentable square feet on
              the 16th floor of the Office Building as more fully identified on
              EXHIBIT A, by the addition of the Expansion Space, and from and
              after the Expansion Effective Date, the Original Premises and the
              Expansion Space, collectively, shall be deemed the Premises, as
              defined in the Lease. The Term for the Expansion Space shall
              commence on the Expansion Effective Date and end on the Extended
              Termination Date (as hereinafter defined). The Expansion Space is
              subject to all the terms and conditions of the Lease except as
              expressly modified herein and except that Tenant shall not be
              entitled to receive any allowances, abatements or other financial
              concessions granted with respect to the Original Premises unless
              such concessions are expressly provided for herein with respect to
              the Expansion Space.

       3.02.  The Expansion Effective Date shall be delayed to the extent that
              Landlord fails to deliver possession of the Expansion Space for
              any reason. Any such delay in the Expansion Effective Date shall
              not subject Landlord to any liability for any loss or damage
              resulting therefrom. If the Expansion Effective Date is delayed,
              the Extended Termination Date (as hereinafter defined) shall not
              be similarly extended.

4.     EXTENSION. The Term of the Lease is hereby extended for a period of 2
       months and shall expire on January 31, 2017 ("EXTENDED TERMINATION
       DATE"), unless sooner terminated in accordance with the terms of the
       Lease. That portion of the Term commencing the day

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       immediately following the Prior Termination Date ("EXTENSION DATE") and
       ending on the Extended Termination Date shall be referred to herein as
       the "EXTENDED TERM".

5.     BASE RENT.

       5.01.  OFFICE BASE RENT.

              A.     OFFICE SPACE THROUGH PRIOR TERMINATION DATE. The Office
                     Base Rent, Additional Rent applicable to the Office Space
                     and all other charges under the Lease applicable to the
                     Office Space shall be payable as provided therein with
                     respect to the Office Space through and including the Prior
                     Termination Date.

              B.     OFFICE SPACE FROM AND AFTER EXTENSION DATE. As of the
                     Extension Date, the schedule of Office Base Rent payable
                     with respect to the Office Space during the Extended Term
                     is the following:

<Table>
<Caption>
                                 ANNUAL RATE PER SQUARE   MONTHLY OFFICE BASE
                    PERIOD                FOOT                    RENT
              ---------------------------------------------------------------
              <S>                        <C>                  <C>
              12/1/16 - 1/31/17          $ 35.00              $ 52,602.08
</Table>

                     All such Office Base Rent shall be payable by Tenant in
                     accordance with the terms of the Lease.

       5.02.  LAB BASE RENT.

              A.     ORIGINAL LAB SPACE THROUGH PRIOR TERMINATION DATE. The Lab
                     Base Rent, Additional Rent applicable to the Original Lab
                     Space and all other charges under the Lease applicable to
                     the Original Lab Space shall be payable as provided therein
                     with respect to the Original Lab Space through and
                     including the Prior Termination Date.

              B.     ORIGINAL LAB SPACE FROM AND AFTER EXTENSION DATE. As of the
                     Extension Date, the schedule of Lab Base Rent payable with
                     respect to the Original Lab Space during the Extended Term
                     is the following:

<Table>
<Caption>
                                 ANNUAL RATE PER SQUARE    MONTHLY LAB BASE
                    PERIOD                FOOT                   RENT
              -------------------------------------------------------------
              <S>                        <C>                 <C>
              12/1/16 - 1/31/17          $ 53.00             $ 97,586.25
</Table>

                     All such Lab Base Rent shall be payable by Tenant in
                     accordance with the terms of the Lease.

              C.     EXPANSION SPACE FROM EXPANSION EFFECTIVE DATE THROUGH
                     EXTENDED TERMINATION DATE. As of the Expansion Effective
                     Date, the schedule of Lab Base Rent payable with respect to
                     the Expansion Space for the balance of the original Term
                     and the Extended Term is the following:

<Table>
<Caption>
                                 ANNUAL RATE PER SQUARE    MONTHLY LAB BASE
                    PERIOD                FOOT                   RENT
              --------------------------------------------------------------
              <S>                        <C>                 <C>
              2/1/07 - 1/31/12           $ 48.00             $  92,796.00
              2/1/12 - 1/31/17           $ 53.00             $ 102,462.25
</Table>

                     All such Lab Base Rent shall be payable by Tenant in
                     accordance with the terms of the Lease.

6.     LETTER OF CREDIT. Concurrently with Tenant's execution of this Amendment,
       Tenant shall provide Landlord with an additional letter of credit (the
       "ADDITIONAL LETTER OF CREDIT") in the amount of $1,500,000.00. The
       Additional Letter of Credit shall be in addition to, and not in
       substitution of, the original Letter of Credit identified in the Lease.
       Except for the Letter of Credit Amount (as hereinafter defined), the
       Additional Letter of Credit shall be in form substantially identical to
       that of the original Letter of Credit, a copy of which is attached hereto
       as EXHIBIT E. The Additional Letter of Credit shall be subject to and in
       conformance

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       with the terms and provisions of Section 1 of Exhibit E to the Lease
       except that for purposes of the Additional Letter of Credit, (i) the
       "LETTER OF CREDIT AMOUNT" shall be $1,500,000.00, and (ii) provided
       Tenant satisfies each of the Contingency Requirements (as defined in
       Section 1.06 of Exhibit E to the Lease) as of each applicable reduction
       date described below, the Letter of Credit Amount for the Additional
       Letter of Credit shall reduce as follows: (i) $1,200,000.00 effective as
       of the third anniversary of the Lab Space Commencement Date; (ii)
       $975,000.00 effective as of the fourth anniversary of the Lab Space
       Commencement Date; (iii) $750,000.00 effective as of the fifth
       anniversary of the Lab Space Commencement Date; (iv) $525,000.00
       effective as of the sixth anniversary of the Lab Space Commencement Date;
       and (v) $300,000.00 effective as of the seventh anniversary of the Lab
       Space Commencement Date.

7.     TENANT'S PRO RATA SHARE.

       7.01.  For the period commencing with the Expansion Effective Date and
              ending on the Extended Termination Date Tenant's Pro Rata Share
              for the Science Building for the Expansion Space is 17.7754%.

       7.02.  For the period commencing with the Expansion Effective Date and
              ending on the Extended Termination Date, Tenant's Pro Rata Share
              for the Buildings is amended from 14.3802% to 22.6934%.

8.     EXPENSES AND TAXES.

       8.01.  OFFICE SPACE FOR THE EXTENDED TERM. For the period commencing with
              the Extension Date and ending on the Extended Termination Date,
              Tenant shall pay for Tenant's Pro Rata Share of Office Expenses
              and Office Taxes applicable to the Office Space in accordance with
              the terms of the Lease.

       8.02.  ORIGINAL LAB SPACE FOR THE EXTENDED TERM. For the period
              commencing with the Extension Date and ending on the Extended
              Termination Date, Tenant shall pay for Tenant's Pro Rata Share of
              Lab Expenses and Lab Taxes applicable to the Original Lab Space in
              accordance with the terms of the Lease.

       8.03.  EXPANSION SPACE FROM EXPANSION EFFECTIVE DATE THROUGH EXTENDED
              TERMINATION DATE. For the period commencing with the Expansion
              Effective Date and ending on the Extended Termination Date, Tenant
              shall pay for Tenant's Pro Rata Share of Lab Expenses and Lab
              Taxes applicable to the Expansion Space in accordance with the
              terms of the Lease.

9.     IMPROVEMENTS TO EXPANSION SPACE.

       9.01.  CONDITION OF EXPANSION SPACE. Tenant has inspected the Expansion
              Space and agrees to accept the same "as is" without any
              agreements, representations, understandings or obligations on the
              part of Landlord to perform any alterations, repairs or
              improvements.

       9.02.  RESPONSIBILITY FOR IMPROVEMENTS TO EXPANSION SPACE. Tenant may
              perform improvements to the Expansion Space in accordance with the
              Work Letter attached hereto as EXHIBIT C and Tenant shall be
              entitled to an improvement allowance in connection with such work
              as more fully described in EXHIBIT C.

10.    EARLY ACCESS TO EXPANSION SPACE. If Tenant occupies the Expansion Space
       for the conduct of its business therein before the Expansion Effective
       Date (the "EXPANSION SPACE OCCUPANCY"), during the period commencing on
       the first day of the Expansion Space Occupancy and ending on the day
       preceding the Expansion Effective Date, (the "EXPANSION SPACE OCCUPANCY
       PERIOD"), Tenant shall not be required to pay Rent with respect to the
       Expansion Space, provided however, during the Expansion Space Occupancy
       Period, Tenant shall be subject to the terms and conditions of the Lease
       and this Amendment, and Tenant shall pay the actual costs of the Science
       Building Services with respect to the Expansion Space, together with the
       cost of any special services requested by Tenant (e.g. freight elevator
       usage). Except for he cost of services requested by Tenant with respect
       to the Expansion Space, Tenant shall not be required to pay Rent or the
       cost of Science Building Services with respect to the Expansion Space for
       any days of possession before the Expansion Effective Date during which
       Tenant, with the approval of Landlord, is in possession of the Expansion
       Space for the

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       sole purpose of performing improvements or installing furniture,
       equipment or other personal property.

11.    OTHER PERTINENT PROVISIONS. Landlord and Tenant agree that, effective as
       of the date of this Amendment (unless different effective dates are
       specifically referenced in this Section), the Lease shall be amended in
       the following additional respects:

       11.01. PARKING.

              A.     Effective as of the Expansion Effective Date, the first
                     sentence of Section 2.01 of EXHIBIT E of the Lease shall be
                     deleted in its entirety and replaced with the following:

                     "During the initial Term, Tenant agrees to lease from
                     Landlord and Landlord agrees to lease to Tenant a total of
                     76 unreserved parking spaces and 2 reserved spaces
                     (collectively, the "SPACES"), for the use of Tenant and its
                     employees, in the parking facility owned by Landlord that
                     serves the Building (the "PARKING FACILITY"), and if the
                     Parking Facility includes a garage, then such Spaces may be
                     in, or on the roof of, such garage."

              B.     Effective as of the Expansion Effective Date, Section 2.02
                     of EXHIBIT E of the Lease shall be deleted in its entirety
                     and replaced with the following:

                     "During the initial Term, Tenant shall pay Landlord, as
                     Additional Rent in accordance with Section 4 of the Lease,
                     the sum of $210.00 per month, plus applicable tax thereon,
                     if any, for each unreserved Space leased by Tenant
                     hereunder, and the sum of $260.00 per month, plus
                     applicable tax thereon, if any, for each reserved Space
                     leased by Tenant hereunder, as such rates may be adjusted
                     from time-to-time to reflect the then current rate for
                     parking in the Parking Facility."

              C.     Effective as of the Expansion Effective Date, Section 2.03
                     of EXHIBIT E of the Lease shall be deleted in its entirety
                     and replaced with the following:

                     "Except for particular spaces and areas designated by
                     Landlord for reserved parking, all parking in the Parking
                     Facility shall be on an unreserved, first-come,
                     first-served basis. Landlord shall install a sign or other
                     notification as reasonably determined by Landlord to
                     designate the reserved Spaces provided to Tenant hereunder.
                     However, the Parking Facility shall always be managed by
                     Landlord (whether using valet parking or otherwise) so
                     that, subject to the provisions of this Section 2, the
                     Tenant will be always be able to utilize the number of
                     Spaces leased by Tenant hereunder."

              D.     Effective as of the Expansion Effective Date, the third
                     sentence of Section 2.06 of EXHIBIT E of the Lease shall be
                     deleted in its entirety and replaced with the following:

                     "If it is necessary for Tenant or its employees to leave an
                     automobile in the Parking Facility overnight, Tenant shall
                     use its reasonable efforts to provide Landlord with prior
                     notice thereof designating the license plate number and
                     model of such automobile."

       11.02. RIGHT OF FIRST OFFER.

              A.     GRANT OF OPTION; CONDITIONS. In addition to the Right of
                     First Offer set forth in Section 5 of EXHIBIT E of the
                     Lease, Tenant shall have the continuing right of first
                     offer (the "RIGHT OF FIRST OFFER") with respect to the
                     17,869 rentable square feet on the 10th floor of the Office
                     Building shown on the demising plan attached hereto as
                     EXHIBIT D and the 16,905 rentable square feet on the 18th
                     floor of the Office Building shown on the demising plan
                     attached hereto as EXHIBIT D (collectively, the "OFFERING
                     SPACE"). Tenant's Right of First Offer shall be exercised
                     as follows: at any time after Landlord has determined that
                     the existing tenant in any portion of the Offering Space
                     will not extend or renew the term of its lease for such
                     portion of the Offering Space (but prior to leasing such

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                     portion of the Offering Space to a party other than the
                     existing tenant), Landlord shall advise Tenant (the "ROFO
                     ADVICE") of the terms under which Landlord is prepared to
                     lease the applicable Offering Space to Tenant for the
                     remainder of the Term, which terms shall reflect the
                     Prevailing Market (hereinafter defined) rate for such
                     Offering Space as reasonably determined by Landlord. Tenant
                     may lease such Offering Space in its entirety only, under
                     such terms, by delivering written notice of exercise to
                     Landlord (the "ROFO NOTICE OF EXERCISE") within 5 Business
                     Days after the date the ROFO Advice is deemed to have been
                     received by Tenant (in accordance with Section 24 of the
                     Lease), except that Tenant shall have no such Right of
                     First Offer and Landlord need not provide Tenant with a
                     ROFO Advice, if:

                     1.     Tenant is in Default under the Lease beyond any
                            applicable cure periods at the time that Landlord
                            would otherwise deliver the ROFO Advice; or

                     2.     the Premises, or any portion thereof, is sublet
                            (other than pursuant to a Permitted Transfer, as
                            defined in Section 11 of the Lease) at the time
                            Landlord would otherwise deliver the ROFO Advice; or

                     3.     the Lease has been assigned (other than pursuant to
                            a Permitted Transfer, as defined in Section 11 of
                            the Lease) prior to the date Landlord would
                            otherwise deliver the ROFO Advice; or

                     4.     Tenant is not occupying the Premises on the date
                            Landlord would otherwise deliver the ROFO Advice; or

                     5.     the applicable portion of the Offering Space is not
                            intended for the exclusive use of Tenant during the
                            Term; or

                     6.     the existing tenant in the applicable portion of the
                            Offering Space is interested in extending or
                            renewing its lease for such applicable portion of
                            the Offering Space or entering into a new lease for
                            such applicable portion of the Offering Space
                            regardless of whether such existing tenant has an
                            option to renew or extend its lease; provided,
                            however, that if Landlord reasonably determines that
                            such tenant's interest will not culminate in an
                            executed lease renewal, extension, new lease or
                            other similar document, then (i) such tenant shall
                            be conclusively considered as not being interested,
                            as aforesaid, and (ii) Landlord shall be
                            conclusively considered as having determined (under
                            subsection A hereof) that such existing tenant will
                            not extend or renew its lease. Accordingly, at the
                            time of such determination of non-interest as
                            aforesaid, Landlord shall send Tenant the ROFO
                            Advice, as aforesaid, to begin the process for
                            Tenant's exercise of its Right of First Offer under
                            this Section 11.02. Landlord shall respond to
                            Tenant's requests for information regarding any such
                            existing tenant's interest in the ROFO Space and the
                            status of negotiation and execution of the
                            documentation of any such lease renewal, extension,
                            new lease or other similar document with such
                            existing tenant.

              B.     TERMS FOR OFFERING SPACE.

                     1.     The term for each applicable portion of the Offering
                            Space shall commence upon the commencement date
                            stated in the ROFO Advice and thereupon each such
                            applicable portion of the Offering Space shall be
                            considered a part of the Premises, provided that all
                            of the terms stated in the ROFO Advice shall govern
                            Tenant's leasing of such applicable portion of the
                            Offering Space and only to the extent that they do
                            not conflict with the ROFO Advice, the terms and
                            conditions of the Lease shall apply to such
                            applicable portion of the Offering Space.

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                     2.     Tenant shall pay Base Rent and Additional Rent for
                            each applicable portion of the Offering Space in
                            accordance with the terms and conditions of the ROFO
                            Advice, which terms and conditions shall reflect the
                            Prevailing Market rate for such applicable portion
                            of the Offering Space as determined in Landlord's
                            reasonable judgment.

                     3.     Each applicable portion of the Offering Space
                            (including improvements and personalty, if any)
                            shall be accepted by Tenant in its condition and
                            as-built configuration existing on the earlier of
                            the date Tenant takes possession of the applicable
                            portion of the Offering Space or as of the date the
                            term for such applicable portion of the Offering
                            Space commences, unless the ROFO Advice specifies
                            any work to be performed by Landlord in such
                            applicable portion of the Offering Space, in which
                            case Landlord shall perform such work in the
                            applicable portion of the Offering Space. If
                            Landlord is delayed delivering possession of the
                            applicable portion of the Offering Space due to the
                            holdover or unlawful possession of such space by any
                            party, Landlord shall use reasonable efforts to
                            obtain possession of the space, and the commencement
                            of the term for such applicable portion of the
                            Offering Space shall be postponed until the date
                            Landlord delivers possession of the applicable
                            portion of the Offering Space to Tenant free from
                            occupancy by any party.

              C.     TERMINATION OF RIGHT OF FIRST OFFER. The rights of Tenant
                     hereunder with respect to each applicable portion of the
                     Offering Space shall terminate on the earlier to occur of:
                     (i) November 30, 2014; (ii) Tenant's failure to exercise
                     its Right of First Offer within the 5 Business Day period
                     provided in Section 11.02.A. above; and (iii) the date
                     Landlord would have provided Tenant a ROFO Advice if Tenant
                     had not been in violation of one or more of the conditions
                     set forth in Section 11.02.A. above. In addition, if
                     Landlord provides Tenant with a ROFO Advice for any portion
                     of the Offering Space that contains expansion rights
                     (whether such rights are described as an expansion option,
                     right of first refusal, right of first offer or otherwise)
                     with respect to any other portion of the Offering Space
                     (such other portion of the Offering Space subject to such
                     expansion rights is referred to herein as the "ENCUMBERED
                     OFFERING SPACE") and Tenant does not exercise its Right of
                     First Offer to lease the Offering Space described in the
                     ROFO Advice, Tenant's Right of First Offer with respect to
                     the Encumbered Offering Space shall be subject and
                     subordinate to all such expansion rights contained in the
                     ROFO Advice. Notwithstanding the foregoing, if (i) Tenant
                     was entitled to exercise its Right of First Offer, but
                     failed to provide Landlord with a ROFO Notice of Exercise
                     within the 5 Business Day period provided in Section
                     11.02.A. above, and (ii) Landlord does not enter into a
                     lease for the applicable portion of the Offering Space
                     within a period of 12 months following the date of the ROFO
                     Advice, Tenant shall once again have a Right of First Offer
                     with respect to such portion of the Offering Space. In
                     addition, subject to the provisions of sub-clauses (i) and
                     (iii) in the first sentence of this Section 11.02.C. above,
                     if Landlord does enter into a lease for the applicable
                     portion of the Offering Space with a third party tenant
                     (the "ROFO PROSPECT"), Tenant shall have a Right of First
                     Offer on such portion of the Offering Space (subject to the
                     terms hereof) upon the expiration of the lease (including
                     any renewals or extensions thereof) with the ROFO Prospect.

              D.     OFFERING AMENDMENT. If Tenant exercises its Right of First
                     Offer, Landlord shall prepare an amendment (the "OFFERING
                     AMENDMENT") adding the applicable portion of the Offering
                     Space to the Premises on the terms set forth in the ROFO
                     Advice and reflecting the changes in the Base Rent,
                     Rentable Square Footage of the Premises, Tenant's Pro Rata
                     Share and other appropriate terms. A copy of the Offering
                     Amendment shall be sent to Tenant within a reasonable time
                     after Landlord's receipt of the ROFO Notice of Exercise
                     executed by Tenant, and Tenant shall execute and return the
                     Offering Amendment to Landlord within 15 days

                                        7
<Page>

                     thereafter, but an otherwise valid exercise of the Right of
                     First Offer shall be fully effective whether or not the
                     Offering Amendment is executed.

              E.     DEFINITION OF PREVAILING MARKET. For purposes of this Right
                     of First Offer provision, "PREVAILING MARKET" shall mean
                     the annual rental rate per square foot for space comparable
                     to the applicable portion of the Offering Space in the
                     Office Building and office buildings comparable to the
                     Office Building in the Cambridge, Massachusetts area under
                     leases and renewal and expansion amendments being entered
                     into at or about the time that Prevailing Market is being
                     determined, giving appropriate consideration to tenant
                     concessions, brokerage commissions, tenant improvement
                     allowances, existing improvements in the space in question,
                     and the method of allocating operating expenses and taxes.
                     Notwithstanding the foregoing, space leased under any of
                     the following circumstances shall not be considered to be
                     comparable for purposes hereof: (i) the lease term is for
                     less than the lease term of the applicable Offering Space,
                     (ii) the space is encumbered by the option rights of
                     another tenant, or (iii) the space has a lack of windows
                     and/or an awkward or unusual shape or configuration. The
                     foregoing is not intended to be an exclusive list of space
                     that will not be considered to be comparable.

       11.03. SIGNAGE.

              A.     During the Term, Tenant shall have (a) the exclusive right
                     to install up to two signs (the "ROOF SIGNS") on the
                     exterior roof or the facade of the Office Building, with
                     such dimensions and in a location to be reasonably
                     designated by Landlord, and (b) the non-exclusive right to
                     install one sign depicting Tenant's logo on each of the two
                     existing Building monument signs currently located outside
                     of the Buildings (the "TENANT MONUMENT SIGNS") with such
                     dimensions and in a location reasonably designated by
                     Landlord, provided (i) for each of the Roof Signs and the
                     Tenant Monument Signs, Tenant receives approval from the
                     City of Cambridge, Massachusetts to install each of the
                     Roof Signs and the Tenant Monument Signs and each of the
                     Roof Signs and the Tenant Monument Signs complies with all
                     applicable signage codes, laws, regulations and ordinances;
                     (ii) Tenant submits to Landlord, and Landlord approves,
                     detailed drawings of each of the Roof Signs and the Tenant
                     Monument Signs prior to installing such signs; (iii) all
                     materials to be incorporated into each of the Roof Signs
                     and the Tenant Monument Signs, as well as the methods of
                     affixing the Roof Signs and the Tenant Monument Signs to
                     the Building or the existing monument signs (as the case
                     may be) shall be subject to the prior written and
                     reasonable approval of Landlord, it being agreed that
                     Landlord reserves the right to withhold consent if any of
                     the Roof Signs or the Tenant Monument Signs, in the sole,
                     reasonable judgment of Landlord, are not harmonious with
                     the design standards of the Building; and (iv) Tenant shall
                     bear all responsibility for all costs associated with the
                     Roof Signs and the Monument Signs, including, without
                     limitation, the cost of design, government permit and
                     approval procurement, construction, installation,
                     maintenance, repair, replacement, insurance, and removal
                     and repair at the expiration of the Term. If Tenant fails
                     to promptly make appropriate repairs or replacements to any
                     of the Roof Signs or the Tenant Monument Signs, Landlord
                     may do so, and Tenant shall reimburse Landlord's cost plus
                     a reasonable administrative fee in doing so. Any such costs
                     incurred by Landlord shall be deemed to be Additional Rent
                     payable under the Lease.

              B.     Upon the expiration or earlier termination of the Term, or
                     upon the assignment by Tenant of Tenant's interest in the
                     Lease or the subleasing by Tenant of any portion of the
                     Premises, Landlord shall have the right to require that
                     Tenant, at Tenant's sole cost and expense, remove one or
                     more of the Roof Signs and the Tenant Monument Signs, using
                     a contractor approved in writing in advance by Landlord. In
                     such event, Tenant, at Tenant's sole cost and expense,
                     shall repair all damage and deterioration attributable to
                     the installation or removal of the Roof Signs and the
                     Tenant Monument Signs or their presence during the Term to
                     Landlord's satisfaction. If Tenant fails to promptly remove
                     the Roof Signs

                                        8
<Page>

                     and/or the Monument Signs and to make all repairs in
                     connection therewith, Landlord may do so, and Tenant shall
                     reimburse Landlord's cost plus a reasonable administrative
                     fee in doing so. Tenant acknowledges that the right to
                     maintain the Sign shall be personal to Tenant (i.e.,
                     CombinatoRX, Incorporated, a Delaware corporation).

       11.04. DELETED SECTIONS. Effective as of the Expansion Effective Date, in
              addition to the other Sections and provisions of the Lease
              modified herein, Section 6 (Right of First Refusal) of EXHIBIT E
              of the Lease shall be deleted in its entirety and shall be of no
              further force and effect.

12.    MISCELLANEOUS.

       12.01. This Amendment and the attached exhibits, which are hereby
              incorporated into and made a part of this Amendment, set forth the
              entire agreement between the parties with respect to the matters
              set forth herein. There have been no additional oral or written
              representations or agreements. Under no circumstances shall Tenant
              be entitled to any Rent abatement, improvement allowance,
              leasehold improvements, or other work to the Premises, or any
              similar economic incentives that may have been provided Tenant in
              connection with entering into the Lease, unless specifically set
              forth in this Amendment. Tenant agrees that neither Tenant nor its
              agents or any other parties acting on behalf of Tenant shall
              disclose any matters set forth in this Amendment or disseminate or
              distribute any information concerning the terms, details or
              conditions hereof to any person, firm or entity without obtaining
              the express written consent of Landlord, provided, however, that
              no such consent shall be required for any information required to
              be disclosed to any securities exchange, governmental agency or
              the like, or if otherwise required by law or court order to be
              disclosed.

       12.02. Except as herein modified or amended, the provisions, conditions
              and terms of the Lease shall remain unchanged and in full force
              and effect.

       12.03. In the case of any inconsistency between the provisions of the
              Lease and this Amendment, the provisions of this Amendment shall
              govern and control.

       12.04. Submission of this Amendment by Landlord is not an offer to enter
              into this Amendment but rather is a solicitation for such an offer
              by Tenant. Landlord shall not be bound by this Amendment until
              Landlord has executed and delivered the same to Tenant.

       12.05. The capitalized terms used in this Amendment shall have the same
              definitions as set forth in the Lease to the extent that such
              capitalized terms are defined therein and not redefined in this
              Amendment.

       12.06. Tenant hereby represents to Landlord that Tenant has dealt with no
              broker other than Richards Barry Joyce & Partners in connection
              with this Amendment. Tenant agrees to indemnify and hold Landlord,
              its trustees, members, principals, beneficiaries, partners,
              officers, directors, employees, mortgagee(s) and agents, and the
              respective principals and members of any such agents
              (collectively, the "LANDLORD RELATED PARTIES") harmless from all
              claims of any brokers other than Richards Barry Joyce & Partners
              claiming to have represented Tenant in connection with this
              Amendment. Landlord hereby represents to Tenant that Landlord has
              dealt with no broker in connection with this Amendment. Landlord
              agrees to indemnify and hold Tenant, its trustees, members,
              principals, beneficiaries, partners, officers, directors,
              employees, and agents, and the respective principals and members
              of any such agents (collectively, the "TENANT RELATED PARTIES")
              harmless from all claims of any brokers claiming to have
              represented Landlord in connection with this Amendment.

       12.07. Each signatory of this Amendment represents hereby that he or she
              has the authority to execute and deliver the same on behalf of the
              party hereto for which such signatory is acting.

                       [SIGNATURES ARE ON FOLLOWING PAGE]

                                        9
<Page>

       IN WITNESS WHEREOF, Landlord and Tenant have duly executed this Amendment
as of the day and year first above written.

<Table>
<S>                                 <C>
WITNESS/ATTEST:                     LANDLORD:

                                    MA-RIVERVIEW/245 FIRST STREET, L.L.C., A
                                    DELAWARE LIMITED LIABILITY COMPANY

                                    By:  Equity Office Management, L.L.C., a
                                         Delaware limited liability company,
                                         its non-member manager

                                         By:      /s/ Maryann Gilligan Suydam
--------------------------------                -------------------------------

Name (print):                            Name:     Maryann Gilligan Suydam
              ------------------                -----------------------------

                                         Title:  Senior Vice President Boston Region
--------------------------------                ------------------------------------

Name (print):
              ------------------


WITNESS/ATTEST:                     TENANT:

                                    COMBINATORX, INCORPORATED, A DELAWARE
                                    CORPORATION

   /s/ Jason F. Cole                By:       /s/ Robert Forrester
--------------------------------           ------------------------------------

Name (print):   Jason F. Cole       Name:         Robert Forrester
              ------------------           ------------------------------------

  /s/ Elizabeth Tibbetts            Title:    EVP and Chief Financial Officer
--------------------------------           ------------------------------------

Name (print): Elizabeth Tibbetts
              ------------------
</Table>

                                       10
<Page>

                                    EXHIBIT A

                    OUTLINE AND LOCATION OF ORIGINAL PREMISES

       This Exhibit is attached to and made a part of the Amendment by and
between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY
COMPANY ("LANDLORD") and COMBINATORX, INCORPORATED, A DELAWARE CORPORATION
("TENANT") for space in the Buildings located at 245 First Street, Cambridge,
Massachusetts.

                           [Diagram of space omitted]

                                       11
<Page>

                                    EXHIBIT B

                     OUTLINE AND LOCATION OF EXPANSION SPACE

       This Exhibit is attached to and made a part of the Amendment by and
between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY
COMPANY ("LANDLORD") and COMBINATORX, INCORPORATED, A DELAWARE CORPORATION
("TENANT") for space in the Buildings located at 245 First Street, Cambridge,
Massachusetts.

                           [Diagram of space omitted]

                                       12
<Page>

                                    EXHIBIT C

                                   WORKLETTER

       This Exhibit is attached to and made a part of the Amendment by and
between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY
COMPANY ("LANDLORD") and COMBINATORX, INCORPORATED, A DELAWARE CORPORATION
("TENANT") for space in the Buildings located at 245 First Street, Cambridge,
Massachusetts.

As used in this Work Letter, the "PREMISES" shall be deemed to mean the
Expansion Space, as defined in the attached Amendment.

I.     ALTERATIONS AND ALLOWANCE.

       A.     Tenant, following the delivery of the Premises by Landlord and the
              full and final execution and delivery of the Amendment to which
              this Exhibit is attached and all prepaid rental and security
              deposits required under such agreement, shall have the right to
              perform alterations and improvements in the Premises (the "INITIAL
              ALTERATIONS"). Notwithstanding the foregoing, Tenant and its
              contractors shall not have the right to perform Initial
              Alterations in the Premises unless and until Tenant has complied
              with all of the terms and conditions of Section 9 of the Lease,
              including, without limitation, approval by Landlord of the final
              plans for the Initial Alterations and the contractors to be
              retained by Tenant to perform such Initial Alterations. Tenant
              shall be responsible for all elements of the design of Tenant's
              plans (including, without limitation, compliance with law,
              functionality of design, the structural integrity of the design,
              the configuration of the Premises and the placement of Tenant's
              furniture, appliances and equipment), and Landlord's approval of
              Tenant's plans shall in no event relieve Tenant of the
              responsibility for such design. Landlord's approval of the
              contractors to perform the Initial Alterations shall not be
              unreasonably withheld. Landlord hereby approves of The Richmond
              Group as Tenant's general contractor to perform the Initial
              Alterations. If Tenant does not elect to utilize The Richmond
              Group as its general contractor for the Initial Alterations, then
              the parties agree that Landlord's approval of any other general
              contractor to perform the Initial Alterations shall not be
              considered to be unreasonably withheld if any such general
              contractor (i) does not have trade references reasonably
              acceptable to Landlord, (ii) does not maintain insurance as
              required pursuant to the terms of the Lease, (iii) does not have
              the ability to be bonded for the work in an amount of no less than
              150% of the total estimated cost of the Initial Alterations, (iv)
              does not provide current financial statements reasonably
              acceptable to Landlord, or (v) is not licensed as a contractor in
              the state/municipality in which the Premises is located. Tenant
              acknowledges the foregoing is not intended to be an exclusive list
              of the reasons why Landlord may reasonably withhold its consent to
              a general contractor other than The Richmond Group.

       B.     Provided Tenant is not in default, Landlord agrees to contribute
              the sum of $2,899,875.00 (the "ALLOWANCE") toward the cost of
              performing the Initial Alterations in preparation of Tenant's
              occupancy of the Premises. The Allowance may only be used for the
              cost of preparing design and construction documents and mechanical
              and electrical plans for the Initial Alterations and for hard
              costs in connection with the Initial Alterations. The Allowance,
              less a 10% retainage (which retainage shall be payable as part of
              the final draw), shall be paid to Tenant or, at Landlord's option,
              to the order of the general contractor that performs the Initial
              Alterations, in periodic disbursements within 30 days after
              receipt of the following documentation: (i) an application for
              payment and sworn statement of contractor substantially in the
              form of AIA Document G-702 covering all work for which
              disbursement is to be made to a date specified therein; (ii) a
              certification from an AIA architect substantially in the form of
              the Architect's Certificate for Payment which is located on AIA
              Document G702, Application and Certificate of Payment; (iii)
              Contractor's, subcontractor's and material supplier's waivers of
              liens which shall cover all Initial Alterations for which
              disbursement is being requested and all other statements and forms
              required for compliance with the mechanics' lien laws of the state
              in which the Premises is located, together with all such invoices,
              contracts, or other supporting data as Landlord or Landlord's
              Mortgagee may reasonably require; (iv) a cost breakdown for each
              trade or subcontractor performing the Initial Alterations; (v)
              plans and specifications for the Initial Alterations, together
              with a

                                       13
<Page>

              certificate from an AIA architect that such plans and
              specifications comply in all material respects with all laws
              affecting the Building, Property and Premises; (vi) copies of all
              construction contracts for the Initial Alterations, together with
              copies of all change orders, if any; and (vii) a request to
              disburse from Tenant containing an approval by Tenant of the work
              done and a good faith estimate of the cost to complete the Initial
              Alterations. Upon completion of the Initial Alterations, and prior
              to final disbursement of the Allowance, Tenant shall furnish
              Landlord with: (1) general contractor and architect's completion
              affidavits, (2) full and final waivers of lien, (3) receipted
              bills covering all labor and materials expended and used, (4)
              as-built plans of the Initial Alterations, and (5) the
              certification of Tenant and its architect that the Initial
              Alterations have been installed in a good and workmanlike manner
              in accordance with the approved plans, and in accordance with
              applicable laws, codes and ordinances. In no event shall Landlord
              be required to disburse the Allowance more than one time per
              month. If the Initial Alterations exceed the Allowance, Tenant
              shall be entitled to the Allowance in accordance with the terms
              hereof, but each individual disbursement of the Allowance shall be
              disbursed in the proportion that the Allowance bears to the total
              cost for the Initial Alterations, less the 10% retainage
              referenced above. Notwithstanding anything herein to the contrary,
              Landlord shall not be obligated to disburse any portion of the
              Allowance during the continuance of an uncured default under the
              Lease, and Landlord's obligation to disburse shall only resume
              when and if such default is cured.

       C.     In no event shall the Allowance be used for the purchase of
              equipment, furniture or other items of personal property of
              Tenant. If Tenant does not submit a request for payment of the
              entire Allowance to Landlord in accordance with the provisions
              contained in this Exhibit by January 31, 2007, any unused amount
              shall accrue to the sole benefit of Landlord, it being understood
              that Tenant shall not be entitled to any credit, abatement or
              other concession in connection therewith. Tenant shall be
              responsible for all applicable state sales or use taxes, if any,
              payable in connection with the Initial Alterations and/or
              Allowance.

       D.     Tenant agrees to accept the Premises in its "as-is" condition and
              configuration, it being agreed that Landlord shall not be required
              to perform any work or, except as provided above with respect to
              the Allowance, incur any costs in connection with the construction
              or demolition of any improvements in the Premises.

       E.     This Exhibit shall not be deemed applicable to any additional
              space added to the Premises at any time or from time to time,
              whether by any options under the Lease or otherwise, or to any
              portion of the Original Premises or any additions to the Premises
              in the event of a renewal or extension of the Extended Term of the
              Lease, whether by any options under the Lease or otherwise, unless
              expressly so provided in the Lease or any amendment or supplement
              to the Lease.

                                       14
<Page>

                                    EXHIBIT D

                     OUTLINE AND LOCATION OF OFFERING SPACES

       This Exhibit is attached to and made a part of the Amendment by and
between MA-RIVERVIEW/245 FIRST STREET, L.L.C., A DELAWARE LIMITED LIABILITY
COMPANY ("LANDLORD") and COMBINATORX, INCORPORATED, A DELAWARE CORPORATION
("TENANT") for space in the Buildings located at 245 First Street, Cambridge,
Massachusetts.

                           [Diagram of space omitted]

                                       15
<Page>

                                    EXHIBIT E

                        COPY OF ORIGINAL LETTER OF CREDIT

                                       16