<PAGE>
                                                                    Exhibit 10.6


               GREENWORKS MOLECULAR INSIGHT PHARMACEUTICALS LEASE

1.   DATE OF LEASE: June 19, 2003

2.   LANDLORD: RayJoe Limited Partnership, a Massachusetts limited partnership,
     which expression shall include its heirs, executors, administrators,
     successors and assigns.

2A.  LANDLORD'S ADDRESS: c/o Gravestar, Inc., One Broadway, Cambridge, MA 02142

3.   TENANT: MOLECULAR INSIGHT PHARMACEUTICALS, INC., which expression shall
     include its heirs, executors, administrators, successors and assigns.
     Please note that Tenant was formerly known as Biostream, Inc.

3A.  TENANT'S ADDRESS: Greenworks Building, 160 Second Street, Cambridge,
     Massachusetts 02142

4.   DEMISED PREMISES: Landlord hereby leases to Tenant and Tenant hereby leases
     from Landlord, upon and subject to the terms and provisions of this Lease,
     Office Space containing approximately 3,064 rentable square feet of floor
     area, and Laboratory Space containing approximately 1,481 rentable square
     feet of floor area all as more fully shown on EXHIBIT E, attached hereto,
     located in the Greenworks Building, 160 Second Street, Cambridge,
     Massachusetts ("Property"), together with the right to use in common with
     others entitled thereto, the hallways, stairways and elevator (if any)
     necessary for access to the Demised Premises, and lavatories nearest
     thereto, if there is no lavatory within the Demised Premises.

4A.  ACCEPTANCE OF DEMISED PREMISES: Tenant agrees that no representations or
     warranties respecting the condition of the Demised Premises and no promises
     to alter, repair or improve the Demised Premises have been made by
     Landlord, except as expressly provided for in this Lease. Tenant occupies
     office and laboratory space at the Greenworks Building under previous
     leases for office and laboratory spaces dated May 15, 1998, as amended,
     scheduled to terminate on June 30, 2003.

4B.  LABORATORY RELOCATION WORK: Landlord and Tenant agree to relocate Tenant's
     Third Floor laboratory space located in Unit #28 and Second Floor
     laboratory space located in Unit #20 to the New Laboratory Space on the
     Second Floor, Units #14, #15 and #20 pursuant to the Biostream Relocation
     Project Scope Summary, Design Build Specification, Electrical
     Specification, Equipment List, and Cavanaugh Tocci and Plumbing Permit
     Letters shown on EXHIBIT B, and Plans D.1.1, A.1.1 and A.6.1, dated May
     6, 2003 shown on EXHIBIT C, known in the aggregate as the Laboratory
     Relocation Work.

4C.  LABORATORY RELOCATION SCHEDULE: Landlord and Tenant agree to the proposed
     Laboratory Relocation Schedule provided by Marc Truant and Associates,
     dated May 2, 2003 as shown on EXHIBIT D. Landlord and Tenant agree that the
     attached Laboratory Relocation Schedule is provided as the most current and
     viable estimate for the Laboratory Relocation Work. Landlord and Tenant
     agree that neither Landlord, Gravestar, Inc., Marc Truant and Associates as
     Landlord's Contractor, nor Jennifer Pinck as Landlord's

                                                      GREENWORKS MOLECULAR LEASE

                                      -1-

<PAGE>

     Project Manager will assume any responsibility, financial or otherwise, for
     any delays in the Laboratory Relocation Schedule. Good faith efforts will
     be used to accommodate Tenant's needs in the event of unforeseen delays to
     the Laboratory Relocation Schedule. Biostream Inc, as Tenant is solely
     responsible for obtaining any and all permits and approvals for the
     operation of its laboratory(ies). Marc Truant and Associates, under
     contractual obligation with Landlord to provide pre-construction and
     construction services, is responsible for obtaining the local building
     permit required to execute the Laboratory Relocation Work and providing the
     local certificate of occupancy.

4D.  LABORATORY RELOCATION COST: Landlord and Tenant agree to share the cost of
     the Laboratory Relocation Work as shown on EXHIBIT A, as follows:

     1.   The GMP Contract between Landlord and Marc Truant and Associates
          estimates the cost of the Laboratory Relocation Work at $327,426. The
          GMP Contract Summary includes an itemized list of additional work to
          be performed for the benefit of Tenant in the amount of $19,800, which
          falls outside of the scope of the original agreed-upon relocation
          work.

     2.   Landlord agrees to pay 66.7% (2/3) of the final cost of the Laboratory
          Relocation Work minus the additional work to be performed for the
          benefit of Tenant (($327,426 - $19,800) x 0.667). Thus, Landlord's
          contribution is estimated at $205,186.54.

     3.   Tenant agrees to pay 33.3% (1/3) of the final cost of the original
          agreed-upon relocation work plus the additional work to be performed
          for the benefit of Tenant (($307,626 x 0.333) + $19,800). Thus,
          Tenant's contribution is estimated at $122,239.46.

     4.   Landlord and Tenant agree to share any net cost savings that may
          accrue from the GMP Contract estimate proportionately. Thus, Landlord
          will receive 66.7% and Tenant will receive 33.3% of any resulting net
          cost savings.

5.   LEASE TERM: Five (5) Lease Years.

5A.  COMMENCEMENT DATE: July 1, 2003, subject to the following exception:
     Pursuant to the New Laboratory Space on the Second Floor, if the Laboratory
     Relocation Work is completed prior to July 1, 2003 and Tenant is in
     physical possession of the New Laboratory Space on the Second Floor, all
     provisions of this Lease will apply to said New Laboratory Space on the
     Second Floor, except for the payment of rent, tax and operating expenses
     charges, which shall be governed by the provisions of the previous
     laboratory Lease (dated May 15, 1998, as amended), until June 30, 2003.

5B.  TERMINATION DATE: June 30, 2008

6.   PERMITTED USE: Tenant shall use the portions of the Demised Premises listed
     under Exhibit E, as Office Space solely and exclusively for the purpose of
     general offices and Laboratory Space solely and exclusively for the purpose
     of laboratory uses in conformance with the provisions of this Lease and in
     compliance with all applicable laws and regulations, including
     environmental laws, regulations, ordinances, orders and standards.

                                                      GREENWORKS MOLECULAR LEASE

                                      -2-

<PAGE>

7. RENT:

<TABLE>
<CAPTION>
                             Dates:          Yearly Rent:   Monthly Rent:      Rent psf.
                             ------          ------------   -------------      ---------
<S>                   <C>                    <C>            <C>                <C>
Office Space:         7/1/03 to 6/30/08       $79,668.00      $6,639.00         $26.00
Laboratory Space:     7/1/03 to 6/30/08       $44,430.00      $3,702.50         $30.00
</TABLE>

     Tenant agrees to pay rent to Landlord in monthly installments, in advance,
     on the first day of each and every month during the Lease Term.

7A.  PARKING CHARGE: Tenant agrees to pay $500.00 per month for the use of Five
     (5) assigned parking space(s) within the Property. Landlord, at its sole
     discretion, reserves the right to increase its parking charges in the
     future to adjust to market conditions. Said increase becomes effective upon
     30-day advance written notice to Tenant.

8.   SECURITY DEPOSIT: A Security Deposit in the amount of $5,248.75 is
     currently held by Landlord under the previous Lease, as security for the
     punctual performance of each and every obligation under the Lease. The
     Security Deposit will be refunded to Tenant within sixty (60) days after
     the end of the Lease Term without interest, subject to the Tenant's
     satisfactory compliance with the terms of the Lease.

9.   TAX CHARGE: Tenant shall pay to Landlord as additional rent hereunder,
     21.5% of real estate taxes charged to the land and buildings of which the
     Demised Premises are a part of, for each Lease Year. Tenant's Tax charge of
     14.5% in relation to the Office Space will be computed in excess of real
     estate taxes assessed for fiscal year 2003. Tenant's Tax Charge of 7% in
     relation to the Laboratory Space will be computed by multiplying the real
     estate taxes by 7%, without any initial tax base. Tenant shall make
     estimated monthly payments based upon reasonable projections made by
     Landlord, adjusted as needed. When the actual annual Tax liability is
     known, Landlord will promptly issue a written statement and refund any
     overpayment to Tenant or request Tenant to pay any underpayment balance.
     Tenant will pay any underpayment within 30 days after receipt of Landlord's
     statement.

10.  OPERATING EXPENSES CHARGE: Tenant shall pay to Landlord as additional rent
     hereunder, 21.5% of all costs and expenses incurred by Landlord for each
     Lease Year in connection with the operation and maintenance of the land and
     buildings of which the Demised Premises are a part of. Tenant's Operating
     Expenses Charge of 14.5% in relation to the Office Space will be computed
     in excess of actual operating expenses for the calendar year 2003. Tenant's
     Operating Expenses Charge of 7% in relation to the Laboratory Space will be
     computed by multiplying the actual operating expenses by 7%, without any
     initial operating expenses base. Tenant shall make estimated monthly
     payments based upon reasonable projections made by Landlord, adjusted as
     needed. Within 90 days after the end of each calendar year during the Lease
     Term, Landlord will issue a written statement of actual annual operating
     expenses and refund any overpayment to Tenant or request Tenant to pay any
     underpayment balance. Tenant will pay any underpayment within 30 days after
     receipt of Landlord's statement.

11.  LATE PAYMENTS: Any installment of Rent, additional rent and any other
     required payment not paid by Tenant within ten (10) days after the due
     date, shall bear a late charge until paid, equal to the lesser of 1.5% of
     the amount due for each month or the highest rate permitted by law.

                                                      GREENWORKS MOLECULAR LEASE

                                       -3-

<PAGE>

12.  TENANT'S WORK: Upon the prior written consent of Landlord, Tenant shall, at
     its own expense, complete any work in and to the Demised Premises, in a
     good and workmanlike manner with materials of the highest quality, without
     interference to other work or businesses within the Greenworks Building,
     and in compliance with the terms of this Lease and all applicable laws,
     codes, ordinances and regulations. Landlord reserves the right, upon
     twenty-four (24) hours written notice to Tenant, to order Tenant to cease
     any and all Tenant's Work, if such work appears to cause disharmony, does
     not comply with union work rules applicable at the Property or interferes
     with the orderly operation of the other Tenants within the Property.
     Tenant's Work shall be performed only in accordance with applicable rules
     and regulations contained in the Greenworks Policy Manual and complete
     plans and specifications submitted to and approved in advance by Landlord.

13.  TENANT COVENANTS & OBLIGATIONS: Tenant agrees to conform to the following
     provisions during the Lease Term:

     (a) Tenant will conform and abide to the rules and regulations contained in
     the Greenworks Policy Manual, attached as EXHIBIT F. Landlord may, from
     time to time, amend the Greenworks Policy Manual, effective upon advance
     written notice to Tenant.

     (b) Tenant will not make any alterations, improvements and/or additions to
     the Demised Premises without the advance written consent of Landlord, not
     to be unreasonably withheld. Any consent request will include such plans,
     specifications and details as Landlord may reasonably request.

     (c) Tenant agrees to maintain the Demised Premises in a clean, safe and
     sanitary condition in accordance with all applicable federal, state and
     local laws, codes, ordinances and regulations. Tenant shall not permit or
     commit any waste.

     (d) Tenant agrees to reimburse Landlord for the cost of replacement light
     bulbs and ballasts for fluorescent light fixtures within the Demised
     Premises.

     (e) Tenant agrees to obtain prior written consent from Landlord before the
     installation of any signage visible from the outside of the Demised
     Premises.

     (f) Tenant agrees not to perform or conduct any act or practice which may
     injure the Demised Premises or the property, or which is unlawful,
     improper, noisy, offensive or in any manner contrary to all applicable
     federal, state and local laws, codes, ordinances and regulations.

     (g) Tenant agrees not to do any spray painting within the Demised Premises.

     (h) Tenant agrees not to allow any mechanics' liens or other similar liens
     to be placed upon the Property, as a result of any work related to Tenant
     or its Demised Premises. Tenant will immediately cause any such liens to be
     released of record, at its sole expense.

     (i) Tenant agrees to periodically shampoo and/or wax any carpeting and/or
     tiled flooring within the Demised Premises, as needed to maintain them in a
     clean and good operating condition.

14.  LANDLORD'S RIGHT TO CHANGE THE PROPERTY: Landlord reserves the right (but
     not any obligation), from time to time, to alter, replace, construct, raze
     or otherwise modify any buildings, structures, improvements, systems,
     equipment, signs, or any other features within the Property, provided it
     does not permanently interfere with Tenant's right to use the Demised
     Premises.

                                                      GREENWORKS MOLECULAR LEASE

                                      -4-
<PAGE>

15.  LANDLORD'S ACCESS: Landlord and its designees, shall have the right (but
     not any obligation) at all times, upon reasonable advance notice to Tenant,
     to enter upon the Demised Premises for the purpose of inspecting or
     performing routine maintenance or repairs, or for any other reasonable
     purpose, as determined by Landlord. No advance notice will be required in
     the event of emergencies.

16.  LANDLORD'S MAINTENANCE & REPAIR OBLIGATIONS: Landlord agrees to keep in the
     same good order, condition and repair, as at present, less reasonable wear
     and tear, the roof, and the exterior face and structural portions of the
     Demised Premises. Landlord's obligations do not apply to damage caused by
     fire, other insured casualty or condemnation. Landlord shall not be
     responsible to repair or restore any damage caused by any act, omission or
     negligence of Tenant, its employees, agents, licensees, invitees or
     contractors, and Tenant shall bear the entire cost of such damage.

16A. CLEANING: Landlord agrees to empty customary office-type waste baskets on
     each business day, vacuum at least once per week and clean windows twice
     per year.

17.  TENANT'S INSURANCE: Tenant agrees to pay for and maintain in full force
     during the Lease Term, a policy of comprehensive general liability
     insurance for personal injury and property damage on an occurrence basis,
     under which the Landlord or others as may be set out in written notice by
     landlord to Tenant, from time to time, are named as additional insureds.
     Each policy will be written by a company(ies) licensed to do business in
     Massachusetts and rated A-VIII or higher by A.M. Best's Rating Agency and
     will be non-cancelable without at least thirty (30) days' prior written
     notice to Landlord. The minimum limits of liability of such insurance shall
     be not less than $1,000,000, combined single limit for personal injury and
     death, and for property damage arising out of any one incident or disaster.
     Tenant shall provide Landlord with evidence of full coverage prior to
     Tenant's occupancy. Tenant will provide Landlord with a renewed Certificate
     of Insurance, thirty (30) days prior to the expiration of the current
     policy.

17A. TENANT'S PROPERTY INSURANCE: Tenant shall keep its fixtures, equipment,
     furniture and other personal property insured against loss or damage by
     fire with the usual extended coverage endorsements. Tenant assumes all risk
     of damage or loss to its own property arising from any cause, including
     theft.

17B. INCREASE IN INSURANCE RATES: Tenant agrees that it will not use, do or
     permit anything to be done in or upon the Demised Premises, which makes
     voidable or increases the rate of insurance on the property or any part
     thereof, and agrees to pay for any increase which may arise from such use
     or action.

17C. INDEMNIFICATION: Tenant agrees to indemnify and save harmless Landlord from
     and against all claims, actions or damages of whatever nature arising from
     any act, omission or negligence of the Tenant or Tenant's contractors,
     licensees, invitees, agents, servants or employees, on or about the Demised
     Premises or Property, during the Lease Term. Landlord agrees to indemnify
     and save harmless Tenant from and against all claims, actions or damages of
     whatever nature arising from any act, omission or negligence of the
     Landlord or Landlord's contractors, licensees, invitees, agents, servants
     or employees, on or about the Demised Premises, during the Lease Term.

                                                      GREENWORKS MOLECULAR LEASE

                                      -5-
<PAGE>

18.  UTILITIES: Landlord will provide and maintain all utilities serving the
     Demised Premises. Landlord reserves the right to place and maintain within
     the Demised Premises utility lines, pipes, fixtures, conduits and the like
     to serve the Demised Premises and other premises. Landlord shall not be
     liable to Tenant in damages or otherwise for any interruption, curtailment
     or suspension of any utility services. Tenant agrees to install, maintain
     and pay for all expenses associated with telephone and internet services.

19.  ASSIGNMENT AND SUBLETTING: Tenant may not assign this Lease or sublet the
     Demised Premises without Landlord's prior written approval, not to be
     unreasonably withheld. Notwithstanding any consent, Tenant shall remain
     liable to Landlord for the payment of all rents and for the full
     performance of the terms of this Lease.

20.  FIRE, CASUALTY AND EMINENT DOMAIN: Landlord may elect to terminate this
     Lease if the Demised Premises or the Property are substantially damaged by
     fire, other casualty or taken by condemnation or the right to eminent
     domain. Landlord's obligation to repair and restore in the event of partial
     damage by fire or other casualty is limited by the actual net amount of
     insurance proceeds. Tenant may elect to terminate this Lease if Landlord
     fails to give written notice within thirty (30) days after the event, of
     its intention to restore the Demised Premises or Landlord fails to restore
     the Demised Premises to a condition reasonably suited for its intended use
     within ninety (90) days after said event. Landlord will provide Tenant with
     a just and proportionate abatement of rent during the time the Demised
     Premises remain substantially unsuitable for their intended use. Landlord
     reserves and Tenant assigns to Landlord all rights which Tenant may have
     for damages or injury to the Demised Premises for any condemnations or
     takings by eminent domain.

21.  SURRENDER OF PREMISES: Upon the expiration or sooner termination of this
     Lease, Tenant shall remove all Tenant's equipment, furniture and other
     personal property and surrender the Demised Premises in good and tenantable
     order and repair and in good operating condition, except for ordinary wear
     and tear. If Tenant fails to surrender the premises as required, Landlord
     may retain or dispose of Tenant's property or restore the premises, all at
     Tenant's expense. Any fixtures or other improvements installed by Landlord
     or Tenant remain Landlord's property and should not be removed by Tenant
     without Landlord's prior written consent.

21A. HOLDOVER BY TENANT: If Tenant remains in possession, after the expiration
     or sooner termination of this Lease without an executed renewal, this Lease
     becomes a month to month tenancy, at a monthly rental equal to two hundred
     (200%) percent of the rent payable during the last month of the Lease Term,
     subject to all other charges and terms contained in this Lease.

22.  ENVIRONMENTAL MATTERS: Tenant agrees not to use, store, generate,
     manufacture, process or dispose of (or suffer or permit the use, storage,
     generating, manufacturing, processing or disposal of) oil, grease,
     chemical, hazardous, toxic or dangerous materials, substances or waste at
     or around the Demised Premises, Property or within any pipes, conduits,
     drains, mains or ducts or into any septic, sewer, drainage or other
     systems, except for materials used in Tenant's Laboratory Space solely and
     exclusively for the purpose of

                                                      GREENWORKS MOLECULAR LEASE

                                      -6-
<PAGE>

     laboratory uses in conformance with the provisions of this Lease and
     stored, used and disposed in strict compliance with all applicable laws and
     regulations, including environmental laws, regulations, ordinances, orders
     and standards. Tenant shall at all times comply with all applicable
     federal, state and local environmental laws, ordinances, orders or
     regulations now or hereafter affecting or applicable to the Demised
     Premises or Property. Tenant agrees to indemnify, defend, save and hold
     harmless Landlord from all claims, actions, liens, demands, costs,
     expenses, fines and judgments resulting from any spills or contamination of
     any kind caused by the acts or omissions of Tenant or its agents,
     employees, licensees, servants or contractors or any other violation of
     applicable environmental laws or this Provision of this Lease. Tenant
     agrees to pay all costs associated with the evaluation and remediation of
     any environmental matter and enforcement of this Environmental Provision
     including any reasonable engineering, consulting or legal fees and
     expenses. Landlord reserves the right to request Tenant to provide data,
     specifications and professional opinions in connection with any
     environmental concern related to Tenant or the Demised Premises.

23.  SUBORDINATION: Tenant's rights under this Lease shall be subject and
     subordinate to any mortgages or deeds of trust or other instruments in the
     nature of a mortgage or lien on the Property and Tenant, upon request,
     shall promptly execute and deliver any written instrument necessary to show
     the subordination of this Lease.

24.  EVENTS OF DEFAULT: In the event that: (a) Tenant shall default in the
     payment of rent or any other payments and such default shall continue for
     ten (10) days; or (b) Tenant shall default in the performance of any
     covenant or obligation under the terms of this Lease and such default shall
     not be corrected within fifteen (15) days after written notice thereof; or
     (c) Tenant shall be declared bankrupt or insolvent according to law, or, if
     any assignment shall be made of Tenant's property for the benefit of
     creditors, then:

     Landlord shall have the right at any time thereafter, while such default
     continues, to re-enter the Demised Premises and take complete possession,
     to declare the term of this Lease ended, and remove the Tenant's effects,
     without prejudice to any other remedies that might be otherwise used for
     unpaid rents or other defaults. Tenant shall indemnify Landlord against
     loss of rent and other payments that the Landlord may incur by reason of
     such termination during the remainder of the Lease Term.

     In the event that Tenant shall default in the performance of any covenant
     or obligation under the terms of this Lease, excluding non-payment of rent
     or other charges, and such default shall not be corrected within fifteen
     (15) days after written notice thereof, Landlord may (but is not obligated
     to do so) remedy such default at the expense of Tenant, to be paid as
     additional rent.

     Failure by Landlord to complain of any action or non-action on the part of
     Tenant, no matter how long or frequent the same may continue, shall never
     be deemed to be a waiver by Landlord of any rights hereunder.

25.  NO BROKERAGE: Landlord and Tenant warrant and represent that they have had
     no contact or dealings with any broker or any person or entity intending to
     claim a commission, in connection with this Lease or the Demised Premises.

                                                      GREENWORKS MOLECULAR LEASE

                                      -7-
<PAGE>

26.  LIMITATION OF LIABILITY: Landlord shall not be liable to Tenant for any
     failure to perform its obligations under the terms of this Lease due to any
     cause beyond Landlord's reasonable control or caused by an act or neglect
     of Tenant or its servants, agents, employees or licensees. Landlord shall
     never be liable to Tenant for any indirect or consequential damages. No
     trustee, beneficiary, agent, employee, officer or partner of Landlord, nor
     any person, firm or entity having an interest in Landlord, shall ever be
     personally liable for any performance of Landlord's obligations under this
     Lease or any related judgments. Landlord's obligations are limited to the
     provisions of this Lease, during its ownership interest in the Property and
     are not binding upon any other assets held by Landlord.

27.  NOTICES: Any notice required under the terms of this Lease shall be in
     writing and shall be hand-delivered or sent to Landlord at Landlord's
     Address and to Tenant at Tenant's Address. Notice shall be sent by
     registered or certified mail, return receipt requested, postage prepaid or
     by a recognized national courier that maintains records of delivery, such
     as Federal Express. Notice shall be deemed given when received, refused or
     tendered for delivery, provided it is correctly addressed.

28.  AUTHORIZATION: The person signing this Lease on behalf of Tenant by virtue
     of his or her signature hereon personally represents and warrants to
     Landlord that Tenant has taken all necessary actions to authorize his or
     her signature hereon on behalf of such Tenant and that upon the signing and
     delivery hereof to the Landlord by him or her, this Lease will be binding
     upon Tenant.

     WITNESS the execution hereof, under seal, in any number of counterpart
     copies, each which shall be deemed to be an original for all purposes as of
     the day and year first above written.

   LANDLORD:                                 TENANT:

   RAYJOE LIMITED PARTNERSHIP                MOLECULAR INSIGHT
   By: KDO Real Estate Holdings, Inc.        PHARMACEUTICALS, INC.

   By: /s/ Deborah A. Ciolfi                 By: /s/ John E. McCray
       ------------------------                  ------------------------
   Deborah A. Ciolfi                         Name: John E. McCray
   Treasurer, duly authorized.               Title: COO, duly authorized

                                             ATTEST By:

                                             /s/ Wendy Graham Coco
                                             ------------------------------
                                             Name: Wendy Graham Coco
                                             Title: Dir. Business Development &
                                                    Operations

                                                      GREENWORKS MOLECULAR LEASE

                                      -8-
<PAGE>

     FIRST AMENDMENT TO MOLECULAR INSIGHT PHARMACEUTICALS, INC., GREENWORKS
     OFFICE LEASE

     For good and valuable consideration, the receipt and sufficiency of which
is hereby acknowledged, RayJoe Limited Partnership ("Landlord") and Molecular
InSight Pharmaceuticals, Inc., ("Tenant"), confirm the following facts and their
agreement as follows:

     1. RECITALS. Landlord and Tenant are parties to a Lease Agreement dated
June 19, 2003 ("Lease"). By mutual agreement, the parties hereby agree to lease
two (2) additional office spaces until the expiration date of the Lease on June
30, 2008. The spaces are shown under attached EXHIBIT A.

The purpose of this writing is to set forth the entire agreement of the parties
with respect thereto.

     2. AMENDMENT. The Lease is hereby amended as follows:

     A. ADDITIONAL SPACE #1: Tenant shall lease Unit # 18, the Pioneer Financial
     office space, as is, containing approximately 198 rsf, for a term of five
     (5) years, commencing on September 1, 2003 until June 30, 2008 ("Additional
     Space #1"). Tenant agrees that Landlord has made no representations or
     warranties respecting the condition of the Additional Space #1.

     B. FIXED RENT FOR ADDITIONAL SPACE #1: Provided Landlord has delivered the
     Additional Space #1, Tenant shall pay Fixed Rent ("Rent"), commencing on
     September 1, 2003, as follows:

<TABLE>
<CAPTION>
    Dates:                     Yearly Rent:                  Monthly Rent:
    ------                     ------------                  -------------
<S>                            <C>                           <C>
9/1/03 - 6/30/08               $ 5,148.00                      $ 429.00
</TABLE>

     C. ADDITIONAL SPACE #1 AVAILABILITY CONTINGENCY: In the event that,
     Additional Space #1 is not delivered to Tenant as of December 1, 2003, the
     portions of this Amendment relating to Additional Space #1 will become void
     and unenforceable, unless Landlord and Tenant mutually agree to extend the
     delivery date for said unavailable space.

     D. ADDITIONAL SPACE #2: Tenant shall lease Unit #16, currently occupied by
     Stella Tarnay, as is, containing approximately 170 rsf, for a term of five
     (5) years, commencing on October 1, 2003 until June 30, 2008 ("Additional
     Space #2"). Tenant agrees that Landlord has made no representations or
     warranties respecting the condition of the Additional Space #2.

     E. FIXED RENT FOR ADDITIONAL SPACE #2: Provided Landlord has delivered the
     Additional Space #2, Tenant shall pay Fixed Rent ("Rent"), commencing on
     October 1, 2003, as follows:

<TABLE>
<CAPTION>
    Dates:                      Yearly Rent:                 Monthly Rent:
    ------                      ------------                 -------------
<S>                             <C>                          <C>
10/1/03 - 6/30/08               $ 4,416.00                    $ 368.00
</TABLE>

                                               MOLECULAR INSIGHT FIRST AMENDMENT

                                      -1-
<PAGE>

     F. ADDITIONAL SPACE #2 AVAILABILITY CONTINGENCY: In the event that,
     Additional Space #2 is not delivered to Tenant as of December 1, 2003, the
     portions of this Amendment relating to Additional Space #2 will become void
     and unenforceable, unless Landlord and Tenant mutually agree to extend the
     delivery date for said unavailable space.

     G.   ADDITIONAL RENT ADJUSTMENT PERCENTAGES:

     1.   TAX CHARGE: Tenant shall pay 16 % of real estate taxes for the
          Property over the 2003 fiscal year tax base, as additional rent in
          relation to its office space.

     2.   OPERATING COST: Tenant shall pay 16 % of operating expenses for the
          Property over the 2003 calendar year base operating expenses, as
          additional rent in relation to its office space.

     H. BASEMENT STORAGE: Tenant shall pay a charge of $110.00 per month for its
     lease of a wire cage in the basement, containing approximately 110 square
     feet for storage purposes only, commencing on July 1, 2003 until June 30,
     2008. Landlord shall not be liable for any damage or losses incurred by
     Tenant due to theft, fire or any other cause. Tenant agrees to insure the
     personal property stored in said wire cage and assumes full responsibility
     for its security.

     3. GENERAL. The individual signing this writing on behalf of Tenant
personally represents and warrants to Landlord that all necessary corporate
action authorizing the same has been duly taken and that upon the execution and
delivery hereof, this writing shall be binding upon the Tenant and enforceable
in accordance with its terms. Landlord and Tenant confirm that, as except as
modified hereby, the Lease remains in full force and effect upon all the other
terms and provisions.

EXECUTED as a sealed instrument_____________________________, 2003.

LANDLORD:                               TENANT:
RAYJOE LIMITED PARTNERSHIP              MOLECULAR INSIGHT
By: KDO Real Estate Holdings, Inc.      PHARMACEUTICALS, INC.

By: _____________________________       By: /s/ John E. McCray
    Deborah A. Ciolfi                       ------------------
    Treasurer, duly authorized          Name: John E. McCray
                                        Title: COO, as duly authorized.

                                        ATTEST By:

                                        /s/ John W. Babich
                                        --------------------
                                        Name: JOHN W. BABICH
                                        Title: PRESIDENT & CSO

                                        MOLECULAR INSIGHT FIRST AMENDMENT

                                      -2-
<PAGE>

                                                                       EXHIBIT A

                                  [FLOOR PLAN]