<PAGE>   1



                                                                    EXHIBIT 10.2

                                OPTION AGREEMENT



                  THIS OPTION AGREEMENT (this "Agreement") is made and entered
into as of April 1, 2001 by and between BOULDER HEADQUARTERS LLC, a California
limited liability company, having an address in care of Great Point Investors
LLC, 98 North Washington Street, 5th floor, Boston, MA 02114 ("Landlord") and
ARRAY BIOPHARMA INC., a Delaware corporation, having an address of 1885 33rd
Street, Boulder, Colorado 80301 ("Subtenant").

                                    RECITALS

                  WHEREAS, Landlord, as landlord, and Amgen Inc., as tenant,
("Amgen") entered into that certain Lease dated as of May 13, 1999 (as amended,
the "Lease"), pursuant to which Landlord leased to Amgen the property located at
3200 Walnut Street, Boulder, Colorado, as more fully described in the Lease (the
"Premises"), which is being amended by a First Amendment to Lease between
Landlord and Amgen dated as of the date hereof (the "First Amendment"). The term
of the Lease is scheduled to expire on March 31, 2008;

                  WHEREAS, Amgen and Subtenant entered into that certain Lease
dated as of July 15, 1998 (as amended, the "Approved Sublease") with respect to
the Premises, which has been amended by a First Amendment to Lease dated as of
April 1, 1999 and a Second Amendment to Lease dated as of the date hereof. The
term of the Approved Sublease is scheduled to expire concurrently with the
Lease;

                  WHEREAS, pursuant to the terms of the Lease and the Approved
Sublease, at any time after the fifth anniversary of the First Amendment, if
certain conditions are met, Subtenant may succeed to Amgen's interest as tenant
under the Lease;

                  WHEREAS, Subtenant has also requested the right to lease the
Premises from Landlord at the end of the scheduled term of the Lease, and
Landlord has agreed to provide Subtenant with an option to do so if certain
conditions are met; and

                  WHEREAS, Landlord and Subtenant desire to document their
agreement with respect the foregoing.

                  NOW, THEREFORE, in consideration of the mutual covenants
herein contained, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

All terms used herein and not defined herein shall have the meanings set forth
in the Lease.



<PAGE>   2



         1. Options to Lease the Premises.

         (a) Provided that as of the time of the giving of the notice described
below and the Commencement Date of the Term (as defined below), all of the
Conditions (as defined below) are satisfied, then Subtenant or its successor or
assign who has been approved by Landlord in accordance with the Lease and the
Approved Sublease ("Assignee") will have the right to lease the Premises from
Landlord by entering into a written lease agreement (the "New Lease") on the
same terms and conditions as those contained in the Lease and in the same form
as the Lease (except as otherwise expressly provided herein), commencing on the
day following the scheduled expiration of the term of the Lease (the
"Commencement Date of the Term"). The initial term of the New Lease shall be for
eight years. By giving notice, provided that as of the time of giving the notice
and the commencement date of the Extension Term (as defined below), all of the
Conditions are satisfied, Assignee shall have the option to extend the term of
the New Lease for two terms of five years each (the "Extension Terms"),
commencing the day following the scheduled expiration of the term of the New
Lease, or the first Extension Term (as applicable). Assignee will give Landlord
notice of its election to enter into the New Lease at least 18 months prior to
the scheduled expiration date of the term of the Lease, and will give Landlord
notice of its election to extend the term of the New Lease for the first or
second Extension Term (as applicable) at least 12 months prior to the scheduled
expiration date of the New Lease or the first Extension Term (as applicable)
(the "Notice Period") and at such time will provide Landlord with evidence of
the satisfaction of each of the Conditions. If Assignee does not give the notice
during the Notice Period, Assignee's right to enter into the New Lease, the
first Extension Term or the second Extension Term (as applicable) will terminate
after a notice stating that the notice has not been received by Landlord (the
"Expiration Notice") is given by Landlord to Assignee and Assignee fails to
provide notice within two weeks of receipt of the Expiration Notice. Time is of
the essence as to the giving of the notice.

         (b) The "Conditions" shall mean all of the following:

                  (i)      Assignee shall actually occupy at least 50% of the
                           Premises initially demised under the Approved
                           Sublease and any space added to the Premises pursuant
                           to the terms thereof;

                  (ii)     Assignee shall have a tangible net worth (i.e. total
                           stockholders' equity shown on the most recent balance
                           sheet) of not less than $30 million;

                  (iii)    (a) on the date that is 12 months prior to the
                           Commencement Date of the Term, Assignee shall post a
                           security deposit for the term of the New Lease (in
                           the form of an irrevocable letter of credit, issued
                           by a financial institution and in form acceptable to
                           Landlord, or in cash) in an amount equal to 6 months'
                           Rent; (b) within ten business days after the
                           Commencement Date of the Term, Amgen shall transfer
                           the unused portion of Assignee's security deposit
                           under the Approved Sublease to Landlord in accordance
                           with the terms of the Approved Sublease, and (c)
                           within ten business days after the Commencement Date
                           of the Term, Assignee will post the remaining amount
                           necessary so that Landlord has a security deposit
                           equal to 12 months' Rent under the New Lease; and

                  (iv)     Assignee shall not be in default under the Approved
                           Sublease or the Lease.

         (c) The initial Monthly Rent for the first year of the New Lease shall
be $30.75 per square foot per annum and will escalate by 3% per year on a
cumulative basis, the initial Monthly Rent for the first year of the first
Extension Term shall be $38.95 per square foot per annum and will escalate by 3%
per year on a cumulative basis, and the initial Monthly Rent for the first year
of the second Extension Term shall be $45.15 per square foot per annum and will
escalate by 3% per year on a cumulative basis.

         Alternatively, if at the time of the giving of Notice and the
Commencement Date of the Term, all Conditions are met and Assignee has a
tangible net worth (i.e. total stockholders' equity shown on the most




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recent balance sheet) of not less than $400 million and a reported profitability
for the two prior years of not less than $25 million annually; then the initial
Monthly Rent for the first year of the New Lease shall be $28.29 per square foot
per annum and will escalate by 3% per year on a cumulative basis, (B) initial
Monthly Rent for the first year of the first Extension Term shall be $35.83 per
square foot per annum and will escalate by 3% per year on a cumulative basis,
and (C) initial Monthly Rent for the first year of the second Extension Term
shall be $41.54 per square foot per annum and will escalate by 3% per year on a
cumulative basis.

         (d) Except as expressly set forth in this Agreement, Assignee's
occupancy of the Premises during the term of the New Lease and each Extension
Term thereof will be on the same terms and conditions as set forth in the Lease.
The Premises will be tendered on the commencement date of the New Lease and each
Extension Term in "as-is" condition. Landlord will have no obligation to
refurbish or otherwise improve the Premises for the term of the New Lease or any
Extension Term.

         (e) If Assignee exercises its option to enter into the New Lease,
Landlord will prepare, and both parties will execute the New Lease.

         2. Brokerage. Landlord and Subtenant each represent and warrant that it
has not dealt with, and will not deal with, any real estate agent or broker in
connection with this Agreement and will indemnify and hold the other party
harmless from and against any claims, liabilities, losses or expenses incurred
by the other in connection with any claims for a commission by any broker or
agent which may arise in connection with this Agreement by virtue of a breach of
the foregoing representation.

         3. Landlord's Liability and Indemnity. The obligations of this
Agreement run with the land, and this Agreement will be binding upon and inure
to the benefit of the parties hereto and their respective successors and
assigns. No owner of the Premises will be liable under this Agreement except for
liability accruing during its ownership of the Premises.

         4. Interpretation. The captions of the Sections of this Agreement are
not a part of the terms or provisions of this Agreement. Whenever required by
the context of this Agreement, the singular includes the plural and the plural
includes the singular. The masculine, feminine and neuter genders each include
the other. This Agreement does not, and nothing contained herein will, create a
partnership or other joint venture between Landlord and Subtenant. A
determination by a court of competent jurisdiction that any provision of this
Agreement or any part thereof is illegal or unenforceable will not invalidate
the remainder of such provision, which will remain in full force and effect.

         5. Incorporation of Prior Agreements; Modifications. This Agreement,
the Subordination, Nondisturbance and Attornment Agreement dated May 13, 1999,
and a consent to the Approved Sublease are the only agreements between the
parties pertaining to the lease of the Premises. All amendments to this
Agreement must be in writing and signed by all parties. Any other attempted
amendment will be void.

         6. Notices. All notices, requests and other communications required or
permitted under this Agreement will be in writing and personally delivered or
sent by a national overnight delivery service which maintains delivery records.
Notices will be delivered to the addresses set forth in the first paragraph of
this Agreement. All notices will be effective upon delivery (or refusal to
accept delivery). Either party may change its notice address upon written notice
to the other party.

         7. Choice of Law. The laws of the state in which the Premises is
located govern this Agreement. The parties hereto waive trial by jury in any
action, proceeding or counterclaim brought by any party(ies) against any other
party(ies) on any matter arising out of or in any way connected with this
Agreement or the relationship of the parties hereunder.

         8. Execution. This Agreement may be executed in counterparts and, when
all counterpart documents are executed, the counterparts will constitute a
single binding instrument. Landlord's delivery of this Agreement to Subtenant is
not be deemed to be an offer to contract and will not be binding upon either
party until executed and delivered by both parties.



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         9. Legal Costs. In any enforcement proceeding brought by either party
with respect to this Agreement, the non-prevailing party will pay to the
prevailing party in such proceeding all costs, including reasonable attorneys'
fees and court costs, incurred by such other party with respect to said
proceeding and any appeals therefrom.

         10. Recording. The parties agree that a Memorandum of this Agreement in
the form attached hereto as Exhibit A may be recorded.


                         [SIGNATURES ON FOLLOWING PAGE]
















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         IN WITNESS WHEREOF, the parties have executed this Agreement as of the
day and year first above written.


LANDLORD:

BOULDER HEADQUARTERS LLC

By: MSC/Bancroft Portfolio LLC, Manager

    By: MSC Boulder LLC, Primary Member

        By: /s/ John H. Baxter
            ----------------------
            Name:  John H. Baxter
            Title:  Vice President



SUBTENANT:

ARRAY BIOPHARMA INC.

By: /s/ Michael Carruthers
    ------------------------------
    Name:  Michael Carruthers
    Title: Chief Financial Officer




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<PAGE>   6


                                    EXHIBIT A



                         MEMORANDUM OF OPTION AGREEMENT

                  This Memorandum of Option Agreement dated as of April 1, 2001
is by and between Boulder Headquarters LLC, a California limited liability
company ("Boulder Headquarters") and Array BioPharma, Inc., a Delaware
corporation ("Array").

                  Boulder Headquarters and Array are parties to an Option
Agreement dated as of April 1, 2001 (the "Agreement"), pursuant to which
Agreement Boulder Headquarters has granted Array an option, subject to certain
conditions, to lease certain premises on the following principal terms:

         1. Name and Address of Boulder Headquarters: Boulder Headquarters, LLC,
c/o Great Point Investors LLC, 98 North Washington Street, 5th Floor, Boston, MA
02114.

         2. Name and Address of Array: Array BioPharma, Inc., 1885 33rd Street,
Boulder, CO 80301.

         3. Description of Premises: Lot 1, Synergen Subdivision Filing No. 3,
County of Boulder, State of Colorado, the Plat of which was recorded November 7,
1996 on Film 2168 as Reception No. 1656392 in Plan File P-32, No. 25. Also known
as Amgen Buildings AC 1-4 (3200 Walnut Street, Boulder, Colorado).

         4. Term of Lease/Extension Options: Leased for a term to commence on
April 1, 2008, and terminate on March 31, 2016. Array has the option to renew
the lease for two (2) additional terms of five (5) years each.

                         [SIGNATURES ON FOLLOWING PAGE]



<PAGE>   7



         IN WITNESS WHEREOF, the parties have executed this Memorandum of Option
Agreement on the date first stated above.

BOULDER HEADQUARTERS LLC

By: MSC/Bancroft Portfolio LLC, Manager

    By: MSC Boulder LLC, Primary Member

        By: /s/ John H. Baxter
            ---------------------------
\           Name:  John H. Baxter
            Title: Vice President


ARRAY BIOPHARMA INC.

By: /s/ Michael Carruthers
    -----------------------------
Name: Michael Carruthers
      ---------------------------
Title: Chief Financial Officer
       --------------------------

STATE OF                         )
         ------------------------
                                 ) ss
COUNTY OF                        )
         ------------------------

                  The foregoing instrument was acknowledged before me this ____
day of _______________, 2001 by John H. Baxter, Vice President of MSC Boulder
LLC, as Primary Member of MSC/Bancroft Portfolio LLC, Manager of Boulder
Headquarters LLC.

                  Witness my hand and official seal

                  My commission expires:
                                        --------------------------------


                                            --------------------------------
                                            Notary Public


STATE OF                         )
         ------------------------
                                 ) ss
COUNTY OF                        )
         ------------------------

                  The foregoing instrument was acknowledged before me this ___
day of ____________, 2001 by ________________, ____________________ of Array
BioPharma, Inc.

                  Witness my hand and official seal

                  My commission expires:
                                        --------------------------------


                                            --------------------------------
                                            Notary Public