<PAGE>

                                                                  Exhibit 10.5.3

                            THIRD AMENDMENT TO LEASE
                             (400 CORPORATE POINTE)

        THIS THIRD AMENDMENT TO LEASE ("THIRD AMENDMENT") is made and entered
into as of the 13th day of March, 1998, by and between ARDEN REALTY FINANCE
PARTNERSHIP, L.P., a California limited partnership ("LANDLORD") and INVESTMENT
TECHNOLOGY GROUP, INC., a Delaware corporation ("TENANT").

                                R E C I T A L S :

        A. 400 Corporate Pointe, Ltd., a California general partnership ("400
CORPORATE") and Integrated Analytics Corporation, a California corporation
("IAC") entered into that certain Standard Form Office Lease dated as of July
11, 1990 ("ORIGINAL LEASE"), whereby 400 Corporate leased to IAC and IAC leased
from 400 Corporate certain office space located in that certain building located
and addressed at 400 Corporate Pointe, Culver City, California 90230 (the
"BUILDING"). The Original Lease was subsequently amended by that certain First
Amendment to Lease dated June 1, 1995, by and between AEW/LBA Acquisition Co.
LLC, a California limited liability company ("AEW") as successor-in-interest to
400 Corporate, and Tenant, as successor-in-interest to IAC (the "FIRST
AMENDMENT") and by that certain Second Amendment to Lease dated December 5, 1996
by and between Arden Realty Limited Partnership, a Maryland limited partnership
("ARLP") as successor-in-interest to AEW and Tenant ("SECOND AMENDMENT").
Landlord is successor-in-interest to ARLP. The Original Lease, as amended by the
First Amendment and the Second Amendment, is referred to herein as the "LEASE".
Pursuant to the Lease, Tenant currently occupies 13,696 rentable square feet
located on the eighth (8th) floor of the Building and known as Suite 855 and
5,295 rentable square feet located on the seventh (7th) floor of the Building
and known as Suite 750 and 1,263 rentable square feet located on the seventh
(7th) floor of the Building known as Suite 725, for a total of 20,254 rentable
square feet (collectively, the "EXISTING PREMISES").

        B. By this Third Amendment, Landlord and Tenant desire to add certain
additional space on the sixth (6th) floor of the Building to the Existing
Premises, and to otherwise modify the Lease as provided herein.

        C. Unless otherwise defined herein, capitalized terms as used herein
shall have the same meaning as given thereto in the Original Lease.

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

                               A G R E E M E N T :

        1. EXPANSION OF EXISTING PREMISES. Effective as of the Additional Space
Effective Date (as defined below) and continuing until the expiration of the
Lease Term, the Existing Premises shall be modified to add the sixth (6th) floor
of the Building which the parties stipulate to contain 20,347 rentable (18,331
usable) square feet as outlined on the floor plan attached to this Third
Amendment as Exhibit "A" and incorporated herein by this reference ("ADDITIONAL
SPACE"). Accordingly, effective as of the Additional Space Effective Date,
Tenant shall lease an aggregate of 40,601 rentable square feet of space in the
Building consisting of the Existing Premises and the Additional Space, which
shall be referred to collectively as the "PREMISES." The term "ADDITIONAL SPACE
EFFECTIVE DATE" shall mean the first Monday following the date the Additional
Space is Ready for Occupancy (as defined in Section 5.1 of the Tenant Work
Letter attached to this Third Amendment as Exhibit "B"). The Additional Space
Effective Date is anticipated to be July 1, 1998. Tenant's lease of the
Additional Space shall expire co-terminously with Tenant's lease of the Existing
Premises on December 31, 2005, subject to extension as provided in Section 10
below. Following the Additional Space Effective Date, the term

<PAGE>

"Premises" as used in the Lease as amended by this Third Amendment shall refer
to the Existing Premises and the Additional Space. Promptly after the Additional
Space Effective Date, Landlord and Tenant shall execute a Confirmation of Lease
Term Dates in a form similar to Exhibit "C" attached hereto and made a part
hereof.

        2. BASE RENT FOR THE ADDITIONAL SPACE. Effective as of the Additional
Space Effective Date and continuing until the expiration of the Lease Term,
Tenant shall pay, in accordance with the provisions of this Section 2, Base Rent
for the Additional Space as follows:

<TABLE>
<CAPTION>
                                MONTHLY INSTALLMENT OF    MONTHLY BASIC RENT PER
               MONTH                  BASIC RENT           RENTABLE SQUARE FOOT
               -----                  ----------           --------------------
<S>                                   <C>                         <C>
                1-24                  $32,962.14                  $1.62

               25-48                  $37,031.54                  $1.82

       49-- December 31, 2005         $42,728.70                  $2.10
</TABLE>

        Concurrently with Tenant's execution of this Third Amendment, Tenant
shall pay to Landlord an amount equal to Basic Rent for the first full month of
Tenant's lease of the Additional Space.

        3. TENANT'S PERCENTAGE OF TOTAL RENTABLE AREA. Commencing as of the
Additional Space Effective Date, Tenant's Percentage of Total Rentable Area with
regard to the Additional Space only shall be 12.36%, and the Base Year (as
defined in Section 1.7 of the First Amendment) with regard to the Additional
Space only shall be calendar year 1998.

        4. IMPROVEMENTS TO ADDITIONAL SPACE. Landlord shall construct the tenant
improvements to the Additional Space pursuant to the terms and conditions of the
Tenant Work Letter attached hereto as Exhibit "B," and the initial construction
of such tenant improvements shall be governed by the Tenant Work Letter rather
than by the provisions of Article 14 of the Original Lease. Except as
specifically set forth in the Tenant Work Letter, Tenant hereby acknowledges
that Landlord shall not be obligated to provide or pay for any improvement work
or services related to the improvement of the Additional Space. Tenant also
acknowledges that, except as provided in Section 1 of the Tenant Work Letter,
Landlord has made no representation or warranty regarding the condition of the
Additional Space.

        5. PARKING. Landlord and Tenant hereby acknowledge and agree that
pursuant to Section 1(w) of the Original Lease, Tenant is entitled to lease
parking spaces at a ratio of four (4) parking spaces per one thousand (1000)
rentable square feet contained within the Premises from time to time. Therefore,
in addition to the parking spaces currently rented by Tenant pursuant to Section
1.10 of the First Amendment and Section 5 of the Second Amendment, commencing as
of the Additional Space Effective Date, Tenant shall be entitled to the use and
rental of an allocation of up to eighty-one (81) additional parking spaces (some
of which may, at Tenant's election, be reserved spaces, subject to the
percentage limitation set forth in Paragraph 56 of the Original Lease)
(collectively, the "ADDITIONAL SPACES") located in the Building's on-site
parking facilities. Tenant shall pay to Landlord for such Additional Spaces the
prevailing rate applicable to such parking in the Building's on-site parking
facility; provided, however, that the rate charged by Landlord for such parking
during each calendar year after calendar year 1998 shall not increase by more
than five percent (5%) over the maximum rate chargeable in the immediately
preceding calendar year (whether or not such maximum rate was actually charged).
The maximum rate during calendar year 1998 shall be Fifty-five Dollars ($55.00)
per unreserved space per month and Seventy-five Dollars ($75.00) per reserved
space per month, plus applicable parking taxes (if any).

        6. STAIRWELL ACCESS. Section 12 of the Second Amendment is hereby
amended to provide that, commencing upon the Additional Space Effective Date,
Landlord agrees to allow Tenant access to the stairwells between the sixth
(6th), seventh (7th) and eighth (8th) floors of the Building during normal
business hours. In connection therewith, Tenant hereby acknowledges that Tenant
shall be required to install and maintain a time clock and associated locking
device at each of the two (2) stairwell doors on the sixth (6th) floor, at each
of the two


                                      -2-
<PAGE>

(2) stairwell doors on the seventh (7th) floor, and at each of the two (2)
stairwell doors on the eighth (8th) floor of the Building. Such time clocks and
associated locking devices shall be installed by the Building-designated
locksmith as a component of the Tenant Improvements to be constructed by
Landlord pursuant to the Tenant Work Letter.

        7. BROKERS. Each party represents and warrants to the other that no
broker, agent or finder negotiated or was instrumental in negotiating or
consummating this Third Amendment other than CB Commercial Real Estate Group,
Inc., who shall be compensated by Landlord pursuant to a separate agreement.
Each party further agrees to defend, indemnify and hold harmless the other party
from and against any claim for commission or finder's fee by any entity who
claims or alleges that they were retained or engaged by the first party or at
the request of such party.

        8. OPTION TO CANCEL. The parties hereby acknowledge and agree that
Tenant's Cancellation Option specified in Section 1.11 of the First Amendment
and as amended pursuant to Section 9 of the Second Amendment, shall continue to
apply with respect to the Existing Premises (as defined in Recital A of this
Third Amendment), but shall not apply to the Additional Space (as defined in
Section 1 of this Third Amendment).

        9. RIGHTS OF FIRST AND SECOND OFFER. Section 14 of Rider No. 1 to the
Original Lease and Section 1.21 of the First Amendment (as amended by Section 10
of the Second Amendment) shall be null and void and of no force or effect. In
lieu thereof, Landlord hereby grants to Tenant a right of first offer with
respect to all space in the Building not leased by Tenant pursuant to the Lease
(as amended by this Third Amendment) ("FIRST OFFER SPACE"). Notwithstanding the
foregoing (i) such first offer right of Tenant shall commence only following the
expiration or earlier termination of (A) any existing lease pertaining to the
First Offer Space, and (B) as to any First Offer Space which is vacant as of the
date of this Third Amendment, the first lease pertaining to any portion of such
First Offer Space entered into by Landlord after the date of this Lease
(collectively, the "SUPERIOR LEASES"), including any renewal or extension of
such existing or future lease, whether or not such renewal or extension is
pursuant to an express written provision in such lease, and regardless of
whether any such renewal or extension is consummated pursuant to a lease
amendment or a new lease, and (ii) such first offer right shall be subordinate
and secondary to all rights of expansion, first refusal, first offer or similar
rights (A) granted as of the date of this Third Amendment to any other tenant of
the Building, and (B) granted after the date of this Third Amendment (with
respect to any floor in the Building other than the seventh (7th) and eighth
(8th) floors) to any other tenant of the Building who is not a tenant as of the
date of this Third Amendment and who, at the time such tenant enters into its
lease, leases more rentable square feet in the Building than Tenant (the rights
described in items (i) and (ii), above to be known collectively as "SUPERIOR
RIGHTS"). Tenant's right of first offer shall be on the terms and conditions set
forth in this Section 9.

               (i) PROCEDURE FOR OFFER. Landlord shall notify Tenant (the "FIRST
OFFER NOTICE") from time to time when Landlord determines that Landlord shall
commence the marketing of any First Offer Space because such space shall become
available for lease to third parties, where no holder of a Superior Right
desires to lease such space. The First Offer Notice shall describe the space so
offered to Tenant and shall set forth Landlord's proposed economic terms and
conditions applicable to Tenant's lease of such space (collectively, the
"ECONOMIC TERMS"). Notwithstanding the foregoing, Landlord's obligation to
deliver the First Offer Notice shall not apply during (A) the last nine (9)
months of the initial Lease Term or the First Option Term unless Tenant has
exercised the upcoming Option to Renew pursuant to Section 10 of this Third
Amendment, and (B) the last nine (9) months of the second (2nd) Option Term.

               (ii) PROCEDURE FOR ACCEPTANCE. On or before the date which is
five (5) business days after Tenant's receipt of the First Offer Notice (the
"ELECTION DATE"), Tenant shall deliver written notice to Landlord ("TENANT'S
ELECTION NOTICE") pursuant to which Tenant shall elect either to (A) lease the
entire First Offer Space described in the First Offer Notice upon the Economic
Terms set forth in the First Offer Notice and the same non-Economic Terms as set
forth in the Lease (as then amended), (B) refuse to lease such First Offer Space
identified in the First Offer Notice, specifying that such refusal is not based
upon the Economic Terms set forth by Landlord in the First Offer Notice, but
upon Tenant's lack of need for such First Offer Space,


                                      -3-
<PAGE>

in which event Landlord may lease such First Offer Space to any entity on any
terms Landlord desires (the "SUBSEQUENT LEASE") and Tenant's right of first
offer with respect to the First Offer Space specified in Landlord's First Offer
Notice shall thereupon terminate and be of no further force or effect until such
space once again becomes available after expiration of the Subsequent Lease
including any renewal or extension of such Subsequent Lease, whether or not such
renewal or extension is pursuant to an express written provision in such
Subsequent Lease, and regardless of whether any such renewal or extension is
consummated pursuant to a lease amendment or a new lease, or (C) refuse to lease
the First Offer Space, specifying that such refusal is based upon the Economic
Terms set forth in the First Offer Notice, in which event Tenant shall also
specify in Tenant's Election Notice revised Economic Terms upon which Tenant
would be willing to lease such First Offer Space from Landlord. If Tenant does
not so respond in writing to Landlord's First Offer Notice by the Election Date,
Tenant shall be deemed to have elected the option described in clause (ii)(B)
above. If Tenant timely delivers to Landlord Tenant's Election Notice pursuant
to clause (ii)(C) above, Landlord may elect either to: (a) lease such First
Offer Space to Tenant upon the revised Economic Terms specified by Tenant in
Tenant's Election Notice, and the same non-Economic Terms as set forth in the
Lease (as then amended); or (b) lease the First Offer Space to any person or
entity upon any terms Landlord desires; provided, however, if the Economic Terms
of Landlord's proposed lease to said third party are not less favorable to the
third party than those Economic Terms proposed by Tenant in Tenant's Election
Notice, before entering into such third party lease, Landlord shall notify
Tenant of such no less favorable Economic Terms and Tenant shall have the right
to lease the First Offer Space upon such no less favorable Economic Terms by
delivering written notice thereof to Landlord within three (3) business days
after Tenant's receipt of Landlord's notice. If Tenant does not elect to lease
such space from Landlord within said three (3) business-day period, Tenant shall
be deemed to have elected the option described in clause (ii)(B) above. In
determining whether the Economic Terms of Landlord's proposed lease to a third
party are no less favorable to the third party than those Economic Terms
proposed by Tenant in Tenant's Election Notice, all concessions shall be blended
into an effective rental rate over the term of the proposed lease to said third
party and such effective rental rate shall be compared with the effective rental
rate of the Economic Terms proposed by Tenant in Tenant's Election Notice.

               (iii) LEASE OF FIRST OFFER SPACE. If Tenant timely exercises
Tenant's right to lease the First Offer Space as set forth herein, Landlord and
Tenant shall execute an amendment adding such First Offer Space to the Premises
upon the same non-economic terms and conditions as applicable to the Premises,
and the economic terms and conditions as provided in this Section 9. Tenant
shall commence payment of rent for the First Offer Space and the Lease Term of
the First Offer Space shall commence upon the date of delivery of such space to
Tenant (except as otherwise specified in the Economic Terms). The Lease Term for
the First Offer Space shall expire co-terminously with Tenant's lease of the
Premises.

               (iv) NO DEFAULTS. The rights contained in this Section 9 shall be
personal to the Tenant named in this Third Amendment ("ORIGINAL TENANT") and any
successor to Tenant by merger, consolidation or otherwise ("SUCCESSOR"), and may
only be exercised by the Original Tenant or such Successor (and not any other
assignee, sublessee or other transferee of the Original Tenant) if Tenant or
such Successor occupies the entire Premises as of the date of the First Offer
Notice. Tenant shall not have the right to lease First Office Space as provided
in this Section 9 if, as of the date of the First Offer Notice, or, at
Landlord's option, as of the scheduled date of delivery of such First Offer
Space to Tenant, Tenant is in default under the Lease (as amended) beyond any
applicable cure period.

        10. OPTIONS TO RENEW. Section 1.12(a) of the First Amendment (as
previously amended pursuant to Section 11 of the Second Amendment) is hereby
amended in its entirety to read as follows:

                      "(a) Landlord hereby grants to Tenant two (2) separate
               options to renew (the "OPTIONS TO RENEW") the Lease for (i) the
               entire sixth (6th) floor of the Building and/or any other full
               floors added to the Premises pursuant to Section 9 above (subject
               to the next sentence below), and/or (ii) a minimum of 5,000
               rentable square feet of the remaining portion of the Premises on
               the seventh


                                      -4-
<PAGE>

               (7th), eighth (8th) and/or any other multi-Tenant floors of the
               Building on which a portion of the Premises is then located
               (subject to Landlord's prior reasonable approval of such 5,000
               rentable square foot portion(s), which approval right shall be
               limited to the issue of whether the remaining space on such
               floors of the Building is in a configuration which is leasable to
               a third party) for terms (the "OPTION TERMS") of five (5) years
               each. Notwithstanding the foregoing, if at the time Tenant
               exercises its Option to Renew Tenant occupies three (3) or more
               full floors in the Building, Tenant may not exercise its Option
               to Renew as to any full floor unless Tenant also exercises its
               Option to Renew for either all of the full floors (if any) then
               leased by Tenant above such full floor or all of the full floors
               (if any) then leased by Tenant below such full floor. The first
               (1st) Option Term would extend the Term scheduled to expire on
               December 31, 2005 and the second (2nd) Option Term would extend
               the first Option Term. In no event shall Tenant be entitled to
               exercise an Option to Renew for any portion of the Premises for
               the second (2nd) Option Term unless Tenant timely and properly
               exercises the corresponding Option to Renew for the first Option
               Term. The Annual Basic Rent payable during the Option Terms shall
               be equal to 95% of the Fair Market Rental Rate (defined in
               Section 1.12(b) of the First Amendment) for the applicable
               portion of the Premises as of the date of such exercise for the
               first (1st) Option Term and 100% of the Fair Market Rental Rate
               for the applicable portion of the Premises as of the date of such
               exercise for the second (2nd) Option Term; however, (1) in no
               event shall the Annual Basic Rent for the first (1st) Option Term
               be below $2.10 per rentable square foot per month (after taking
               into consideration the concessions described in the definition of
               Fair Market Rental Rate), and (2) in no event shall the Annual
               Basic Rent for the second (2nd) Option Term be below that
               applicable during the last year of the first (1st) Option Term
               (after taking into consideration the concessions described in the
               definition of Fair Market Rental Rate). All other terms and
               conditions of the Lease, as then amended, shall continue to apply
               during the Option Terms. Each Option to Renew shall be exercised,
               if at all, by written notice from Tenant to Landlord delivered
               not later than nine (9) months prior to the expiration of the
               then-existing Lease Term."

        11. SIGNING AUTHORITY. Concurrently with Tenant's execution of this
Third Amendment, Tenant shall provide to Landlord a copy of a resolution of the
Board of Directors of Tenant authorizing the execution of this Third Amendment
on behalf of such corporation, which copy of resolution shall be duly certified
by the secretary or an assistance secretary of the corporation to be a true copy
of the resolution duly adopted by the Board of Directors of said corporation and
shall be in the form of Exhibit "D" attached hereto and made a part hereof, or
in some other form reasonably acceptable to Landlord.

        12. NO FURTHER MODIFICATION. Except as set forth in this Third
Amendment, all of the terms and provisions of the Lease shall apply to the
Additional Space and shall remain unmodified and in full force and effect. From
and after the date of this Third Amendment, all references in the Lease to the
"Premises" shall refer to the Existing Premises and the Additional Space.


                                      -5-
<PAGE>

        IN WITNESS WHEREOF, this Third Amendment has been executed as of the day
and year first above written.

                                          "Landlord":

                                          ARDEN REALTY FINANCE PARTNERSHIP,
                                          L.P., a California limited partnership

                                          By:    ARDEN REALTY FINANCE, INC.,
                                                 a California corporation
                                                 Its sole general partner

                                                 By:
                                                        ----------------------
                                                        VICTOR J. COLEMAN
                                                        Its: President and COO

                                                 By:
                                                        ----------------------
                                                        Its:
                                                            ------------------

                                          "Tenant":

                                          INVESTMENT TECHNOLOGY GROUP, INC., a
                                          Delaware corporation

                                          By:
                                                 ------------------------
                                                 Its:
                                                     --------------------

                                          By:
                                                 ------------------------
                                                 Its:
                                                     --------------------


                                      -6-
<PAGE>

                                   EXHIBIT "A"

                         FLOOR PLAN OF ADDITIONAL SPACE
<PAGE>

                                   EXHIBIT "B"

                               TENANT WORK LETTER

        This Tenant Work Letter shall set forth the terms and conditions
relating to the construction of the Additional Space. This Tenant Work Letter is
essentially organized chronologically and addresses the issues of the
construction of the Additional Space, in sequence, as such issues will arise
during the actual construction of the Additional Space. The Additional Space may
be referred to herein as the "IMPROVED SPACE." All references in this Tenant
Work Letter to Articles or Sections of "this Third Amendment" shall mean the
relevant portions of the Third Amendment to Lease to which this Tenant Work
Letter is attached as Exhibit B, and all references in this Tenant Work Letter
to Sections of "this Tenant Work Letter" shall mean the relevant portions of
Sections 1 through 5 of this Tenant Work Letter.

                                    SECTION 1

                         DELIVERY OF THE IMPROVED SPACE

        Except as provided in this Section 1 below, the cost of any improvements
to the Additional Space shall be charged to the Tenant Improvement Allowance and
the Additional Space will be delivered for renovation in its presently existing
"as is" condition. However, Landlord shall, at Landlord's sole cost and expense,
perform the following work in the Additional Space prior to the Additional Space
Effective Date: (i) ensure that the Building systems, including the HVAC and
electrical systems are in good working order and condition, and (ii) perform any
work in the elevator lobby, corridors and restrooms on the sixth (6th) floor of
the Building required to bring such areas into compliance with all code
requirements in existence as of the Additional Space Effective Date. In
addition, if, as a result of applicable code requirements, Tenant is required to
make any life safety improvements on the sixth (6th) floor of the Building and
if, as a result of such life safety improvements installed by Tenant, any
modifications to the "backbone" base Building life safety system is required,
Landlord agrees to perform such modifications at Landlord's sole cost and
expense. Tenant shall be entitled to add supplemental HVAC units to the Improved
Space, subject to Landlord's review and reasonable approval of plans and
specifications for such installation and Tenant's compliance with the terms and
provisions of Article 14 of the Original Lease in connection with such
installation and Tenant's payment, pursuant to Section 18 of the Original Lease,
for any extraordinary usage of utilities resulting from such supplemental HVAC
units. If Tenant does so install any supplemental HVAC units, Tenant shall
maintain, at Tenant's sole cost and expense, a repair and maintenance contract
with a contractor reasonably approved by Landlord throughout the Lease Term in
order to provide repair and maintenance services for such equipment.

                                    SECTION 2

                               TENANT IMPROVEMENTS

        2.1 TENANT IMPROVEMENT ALLOWANCE. Tenant shall be entitled to a one-time
tenant improvement allowance (the "TENANT IMPROVEMENT ALLOWANCE") in the amount
of $458,275.00 (i.e., $25.00 per usable square foot of the Additional Space) for
the costs relating to the design and construction of Tenant's improvements which
are permanently affixed to the Additional Space (the "TENANT IMPROVEMENTS");
provided, however, that up to an amount equal to Two Dollars ($2.00) per usable
square foot of the Additional Space of the Tenant Improvement Allowance may be
used by Tenant, at Tenant's discretion, for Tenant Improvements to space leased
by Tenant in the Building other than the Additional Space. In addition to the
Tenant Improvement Allowance, Landlord shall make available to Tenant an
allowance of up to ten cents ($0.10) per usable square foot of the Additional
Space for costs relating to the preparation of a preliminary space plan for the
Additional Space. In no event shall Landlord be obligated to make disbursements
pursuant to this Tenant Work Letter in a total amount which exceeds the Tenant
Improvement Allowance.
<PAGE>

        2.2    DISBURSEMENT OF THE TENANT IMPROVEMENT ALLOWANCE.

               2.2.1 TENANT IMPROVEMENT ALLOWANCE ITEMS. Except as otherwise set
forth in this Tenant Work Letter, the Tenant Improvement Allowance shall be
disbursed by Landlord only for the following items and costs (collectively the
"TENANT IMPROVEMENT ALLOWANCE Items"):

                      2.2.1.1 Payment of the fees of the "Architect" and the
"Engineers," as those terms are defined in Section 3.1 of this Tenant Work
Letter and of other engineers and consultants which Tenant may reasonably
require for the design and construction of the Tenant Improvements (including,
without limitation, lighting, acoustic and ergonomic consultants), and payment
of the out-of-pocket costs (if any) incurred by Landlord and Landlord's
consultants in connection with documents and materials supplied by Landlord (if
any) and/or the review of the "Construction Drawings," as that term is defined
in Section 3.1 of this Tenant Work Letter;

                      2.2.1.2 The payment of plan check, permit and license fees
relating to construction of the Tenant Improvements;

                      2.2.1.3 The cost of construction of the Tenant
Improvements, including, without limitation, testing and inspection costs,
after-hours freight elevator usage, trash removal costs, and contractors' fees
and general conditions (provided, however, the Contractor and any subcontractors
shall not be charged for parking);

                      2.2.1.4 The cost of any changes to the Construction
Drawings or Tenant Improvements required by applicable code; and

                      2.2.1.5 Sales and use taxes and Title 24 fees.

               2.2.2 DISBURSEMENT OF TENANT IMPROVEMENT ALLOWANCE. Landlord
shall make payment of the Tenant Improvement Allowance for the Tenant
Improvement Allowance Items pursuant to Landlord's standard draw cycle
throughout the course of construction of the Tenant Improvements. If the total
amount of the Tenant Improvement Allowance Items exceeds the amount of the
Tenant Improvement Allowance, Tenant shall pay such excess on a pro-rata basis
throughout the course of construction of the Tenant Improvements as such costs
are incurred. Such payment shall be deemed to constitute additional rent
pursuant to the Lease (as amended) and shall be made within ten (10) days after
Tenant's receipt of invoice therefore from Landlord. Landlord shall only be
obligated to make disbursements from the Tenant Improvement Allowance to the
extent costs are incurred for Tenant Improvement Allowance Items. All Tenant
Improvement Allowance Items for which the Tenant Improvement Allowance has been
made available shall be deemed Landlord's property. Tenant shall not be entitled
to any portion of the Tenant Improvement Allowance not used by Tenant on or
before the date which is six (6) months after the Additional Space Effective
Date.

        2.3 SPECIFICATIONS. Landlord has established specifications (the
"Specifications") for the Building standard components to be used in the
construction of the Tenant Improvements in the Improved Space (collectively, the
"STANDARD IMPROVEMENT Package"). The quality of Tenant Improvements shall be
equal to or of greater quality than the quality of the Specifications, provided
that the Tenant Improvements shall comply with certain Specifications as
designated by Landlord. Landlord may make changes to the Specifications for the
Standard Improvement Package from time to time. However, Landlord's approval of
the Final Working Drawings (as defined in Section 3.3 of this Tenant Work
Letter) shall be conclusive as to the compliance of the Final Working Drawings
with the Specifications (to the extent Specifications are expressly delineated
in the Final Working Drawings) and Tenant shall not be obligated thereafter to
modify the Approved Working Drawings or the Tenant Improvements by reason of any
changes in the Specifications or any other failure of such drawings to comply
with the Specifications (to the extent items to which the Specifications apply
are expressly delineated in the Approved Working Drawings).


                                     Page 2
<PAGE>

                                    SECTION 3

                              CONSTRUCTION DRAWINGS

        3.1 SELECTION OF ARCHITECT/CONSTRUCTION DRAWINGS. Tenant shall retain an
architect/space planner reasonably approved by Landlord (the "ARCHITECT") to
prepare the "Construction Drawings," as that term is defined in this Section
3.1. Tenant shall retain the engineering consultants designated by Landlord (the
"ENGINEERS") to prepare all plans and engineering working drawings relating to
the structural, mechanical, electrical, plumbing, HVAC and lifesafety work in
the Improved Space, which work is not part of the Landlord Work. Landlord shall
ensure that the charges of the Engineers are competitive (although not
necessarily the lowest available). The plans and drawings to be prepared by
Architect and the Engineers hereunder (consisting of the Final Space Plan and
the Final Working Drawings (as those terms are defined below)) shall be known
collectively as the "CONSTRUCTION DRAWINGS." All Construction Drawings shall
comply with the drawing format and specifications determined by Landlord, and
shall be subject to Landlord's approval, which Landlord shall not unreasonably
withhold or delay. Tenant and Architect shall verify, in the field, the
dimensions and conditions as shown on the relevant portions of the base building
plans, and Tenant and Architect shall be solely responsible for the same, and
Landlord shall have no responsibility in connection therewith. Landlord's review
of the Construction Drawings as set forth in this Section 3, shall be for its
sole purpose and shall not imply Landlord's review of the same, or obligate
Landlord to review the same, for quality, design, Code compliance or other like
matters. Accordingly, notwithstanding that any Construction Drawings are
reviewed by Landlord or its space planner, architect, engineers and consultants,
and notwithstanding any advice or assistance which may be rendered to Tenant by
Landlord or Landlord's space planner, architect, engineers, and consultants,
Landlord shall have no liability whatsoever in connection therewith and shall
not be responsible for any omissions or errors contained in the Construction
Drawings, and Tenant's waiver and indemnity set forth in Section 20 of the
Original Lease shall specifically apply to the Construction Drawings.

        3.2 FINAL SPACE PLAN. On or before March 9, 1998, Tenant shall supply
Landlord with two (2) copies signed by Tenant of its final space plan for the
Improved Space before any architectural working drawings or engineering drawings
have been commenced. The final space plan (the "FINAL SPACE PLAN") shall include
a layout and designation of all offices, rooms and other partitioning, their
intended use, and equipment to be contained therein. Landlord may request
clarification or more specific drawings for special use items not included in
the Final Space Plan. Landlord shall advise Tenant within five (5) business days
after Landlord's receipt of the Final Space Plan for the Improved Space if the
same is unsatisfactory or incomplete in any respect and Landlord's failure to
give Tenant written notice of any such objection within said five (5)
business-day period shall be deemed approval by Landlord of the Final Space
Plan. If Tenant is so advised, Tenant shall within three (3) business days
thereafter cause the Final Space Plan to be revised to correct any deficiencies
or other matters Landlord may reasonably require.

        3.3 FINAL WORKING DRAWINGS. After the Final Space Plan has been approved
by Landlord, Tenant shall supply the Engineers with a complete listing of
standard and non-standard equipment and specifications, including, without
limitation, B.T.U. calculations, electrical requirements and special electrical
receptacle requirements for the Improved Space, to enable the Engineers and the
Architect to complete the "Final Working Drawings" (as that term is defined
below) in the manner as set forth below. Within twenty-eight (28) days after
approval of the Final Space Plan by Landlord, Tenant shall promptly cause the
Architect and the Engineers to complete the architectural and engineering
drawings for the Improved Space, and Architect shall compile a fully coordinated
set of architectural, structural, mechanical, electrical and plumbing working
drawings in a form which is complete to allow subcontractors to bid on the work
and to obtain all applicable permits (collectively, the "FINAL WORKING
DRAWINGS") and shall submit the same to Landlord for Landlord's approval.
However, if Tenant reasonably determines that the Engineers are not reasonably
responsive to Tenant's requirements, Tenant may so notify Landlord in writing
and if Landlord does not cause such Engineers to be so responsive within one (1)
business day after receipt of Tenant's notice, then said twenty-eight (28) day
period shall be extended for each day after the expiration of said one (1)
business day cure period that completion of the Final Working Drawings are so
delayed as a result of the failure of the


                                     Page 3
<PAGE>

Engineers to be reasonably responsive. Tenant shall supply Landlord with two (2)
copies signed by Tenant of such Final Working Drawings. Landlord shall advise
Tenant within five (5) business days after Landlord's receipt of the Final
Working Drawings for the Improved Space if the same is unsatisfactory or
incomplete in any respect and Landlord's failure to give Tenant written notice
of any such objection within said five (5) business-day period shall be deemed
approval by Landlord of the Final Working Drawings. If Tenant is so advised,
Tenant shall within five (5) business days thereafter revise the Final Working
Drawings in accordance with such review and any disapproval of Landlord in
connection therewith.

        3.4 APPROVED WORKING DRAWINGS. The Final Working Drawings shall be
approved by Landlord (the "APPROVED WORKING DRAWINGS") prior to the commencement
of construction of the Improved Space by Landlord. After approval by Landlord of
the Final Working Drawings, Landlord shall submit the same to the appropriate
municipality for all applicable building permits. No changes, modifications or
alterations in the Approved Working Drawings may be made without the prior
written consent of Landlord, which consent may not be unreasonably withheld or
delayed. If Tenant proposes a change, modification or alteration to the Approved
Working Drawings, Landlord shall advise Tenant of the potential cost associated
with such change, modification or alteration and the potential Tenant Delay
which may result therefrom.

                                    SECTION 4

                     CONSTRUCTION OF THE TENANT IMPROVEMENTS

        4.1 SELECTION OF CONTRACTOR. The contractor which shall construct the
Tenant Improvements shall be a contractor selected pursuant to the following
procedure. The Final Working Drawings shall be submitted by Landlord to (i) two
(2) general contractors selected by Landlord and (ii) two (2) general
contractors selected by Tenant on or before the date the Final Working Drawings
are approved by Landlord and which contractors so selected by Tenant shall be
subject to Landlord's reasonable approval. Each such contractor shall submit a
sealed, fixed price contract bid (on such bid form as Landlord shall designate)
to construct the Tenant Improvements. Each contractor shall be notified in the
bid package of the time schedule for construction of the Tenant Improvements.
The subcontractors utilized by the Contractor shall be subject to Landlord's
reasonable approval and the bidding instructions shall provide that as to work
affecting the structure of the Building and/or the systems and equipment of the
Building, Landlord shall be entitled to designate the subcontractors. The bids
shall be submitted promptly to Landlord and a reconciliation shall be performed
by Landlord to adjust inconsistent or incorrect assumptions so that a like-kind
comparison can be made and a low bidder determined. Within ten (10) days after
the Final Working Drawings are approved by Landlord, Tenant shall select the
contractor who shall be the lowest bidder and who states that it will be able to
meet Landlord's reasonable construction schedule. The parties acknowledge that,
for purposes of the immediately preceding sentence, Landlord's reasonable
construction schedule shall not include any scheduled overtime. The contractor
selected may be referred to herein as the "CONTRACTOR". Landlord shall retain
the Contractor to construct the Tenant Improvements in accordance with the
Approved Working Drawings.

        4.2 WARRANTIES. Landlord shall require that the Contractor and all
subcontractors provide industry-standard warranties for defects in workmanship
and materials.

        4.3 MEETINGS. Commencing upon the execution of this Third Amendment,
Landlord and Tenant shall hold regular periodic meetings at a reasonable time
with the Architect and the Contractor regarding the progress of the preparation
of Construction Drawings and the construction of the Tenant Improvements, which
meetings shall be held at a location reasonably designated by Landlord.

                                    SECTION 5

                                  MISCELLANEOUS

        5.1 READY FOR OCCUPANCY. For purposes of this Third Amendment, the
Additional Space shall be deemed "READY FOR OCCUPANCY" upon the Substantial
Completion of the Tenant


                                     Page 4
<PAGE>

Improvements in the Additional Space. For purposes of this Third Amendment,
"SUBSTANTIAL COMPLETION" of the Tenant Improvements in the Additional Space
shall occur upon the completion of construction of the Tenant Improvements in
the Additional Space pursuant to the Approved Working Drawings, with the
exception of any punch list items and any tenant fixtures, work-stations,
built-in furniture, or equipment to be installed by Tenant.

        5.2 DELAY OF THE SUBSTANTIAL COMPLETION. If there shall be a delay or
there are delays in the Substantial Completion of the Tenant Improvements in the
Additional Space as a result of any of the following (collectively, "TENANT
DELAYS "):

               5.2.1 Tenant's failure to comply with any of the time periods set
forth in the Tenant Work Letter;

               5.2.2 Tenant's failure to timely approve any matter requiring
Tenant's approval;

               5.2.3 A breach by Tenant of the terms of this Tenant Work Letter
or the Lease;

               5.2.4 Changes in any of the Construction Drawings after
reasonable disapproval of the same by Landlord or because the same do not comply
with Code or other applicable laws (provided, however, that changes required to
the first Final Space Plan and/or the first set of Final Working Drawings
submitted to Landlord due to Landlord's disapproval thereof (but not any
subsequent disapproval) shall not constitute a Tenant Delay hereunder provided
that Tenant resubmits revised Construction Drawings within the time periods
specified in Sections 3.2 or 3.3 above (as applicable));

               5.2.5 Tenant's request for changes in the Approved Working
Drawings;

               5.2.6 Tenant's requirement for materials, components, finishes or
improvements which are not available in a commercially reasonable time given the
anticipated date of Substantial Completion of the Tenant Improvements in the
Additional Space, or which are different from, or not included in, the Standard
Improvement Package;

               5.2.7 Any other acts or omissions of Tenant, or its agents, or
employees; then, notwithstanding anything to the contrary set forth in the Third
Amendment or this Tenant Work Letter and regardless of the actual date of the
Substantial Completion of the Tenant Improvements in the Additional Space, the
date of Substantial Completion thereof shall be deemed to be the date that
Substantial Completion would have occurred if no Tenant Delay or Delays, as set
forth above, had occurred.

        5.3 TENANT'S REPRESENTATIVE. Tenant has designated Mark Wright as its
sole representative with respect to the matters set forth in this Tenant Work
Letter, who shall have full authority and responsibility to act on behalf of the
Tenant as required in this Tenant Work Letter.

        5.4 LANDLORD'S REPRESENTATIVE. Landlord has designated Herbert Porter
and Kimberly Harris as its sole representatives with respect to the matters set
forth in this Tenant Work Letter, each of whom, until further notice to Tenant,
shall have full authority and responsibility to act on behalf of the Landlord as
required in this Tenant Work Letter.

        5.5 TIME OF THE ESSENCE IN THIS TENANT WORK LETTER. Unless otherwise
indicated, all references herein to a "number of days" shall mean and refer to
calendar days. If any item requiring approval is timely disapproved by Landlord,
the procedure for preparation of the document and approval thereof shall be
repeated until the document is approved by Landlord.

        5.6 TENANT'S LEASE DEFAULT. Notwithstanding any provision to the
contrary contained in this Lease, if an event of default as described in Section
25(a) of the Original Lease or this Tenant Work Letter has occurred at any time
on or before the Substantial Completion of the Improved Space, then (i) in
addition to all other rights and remedies granted to Landlord pursuant to this
Lease, Landlord may cause Contractor to cease the construction of the Improved
Space (in which case, Tenant shall be responsible for any delay in the
substantial completion of the Improved Space caused by such work stoppage), and
(ii) all other obligations of Landlord under


                                     Page 5
<PAGE>

the terms of this Tenant Work Letter shall be forgiven until such time as such
default is cured pursuant to the terms of the Lease, as amended by this Third
Amendment (in which case, Tenant shall be responsible for any delay in the
substantial completion of the Improved Space caused by such inaction by
Landlord).


                                     Page 6
<PAGE>

                                   EXHIBIT "C"

                           NOTICE OF LEASE TERM DATES
                        AND TENANT'S PROPORTIONATE SHARE

TO:_____________________________________                  DATE:_________________
   _____________________________________
   _____________________________________

RE:     Third Amendment to Lease dated March __, 1998, between ARDEN REALTY
        FINANCE PARTNERSHIP, L.P., a California limited partnership
        ("LANDLORD"), and INVESTMENT TECHNOLOGY GROUP, INC., a Delaware
        corporation ("TENANT"), concerning the sixth (6th) floor ("ADDITIONAL
        SPACE") of the building located at 400 Corporate Pointe, Culver City,
        California.

Ladies and Gentlemen:

        In accordance with the Third Amendment, Landlord wishes to advise and/or
confirm the following:

               1. That the Additional Space has been accepted herewith by the
Tenant as being substantially complete in accordance with the Third Amendment
and that, to Tenant's knowledge, there is no deficiency in construction.

               2. That the Tenant has taken possession of the Additional Space
and acknowledges that under the provisions of the Third Amendment the Term of
Tenant's lease of such space shall commence as of ____________ for a term ending
on December 31, 2005 (subject to extension as provided in Section 10 of the
Third Amendment).

               3. That in accordance with the Third Amendment, Basic Rental for
the Additional Space commenced to accrue on ________________________.

               4. If the Additional Space Effective Date is other than the first
day of the month, the first billing will contain a prorata adjustment. Each
billing thereafter shall be for the full amount of the monthly installment as
provided for in the Third Amendment.

               5. Rent is due and payable in advance on the first day of each
and every month during the Term of said Lease. Your rent checks should be made
payable to ________________________ at
_____________________________________________.

               6. The exact number of rentable square feet within the Additional
Space is 20,347 rentable square feet.

               7. Tenant's Proportionate Share, as adjusted based upon the exact
number of rentable square feet within the Additional Space is 12.36%.

AGREED AND ACCEPTED:

TENANT:

___________________________,
a__________________________


By:  ______________________
     Its:__________________
<PAGE>

                                   EXHIBIT "D"

                                CERTIFIED COPY OF
                         BOARD OF DIRECTORS RESOLUTIONS
                                       OF
                        INVESTMENT TECHNOLOGY GROUP, INC.

        The undersigned, being the duly elected Corporate Secretary of
Investment Technology Group, Inc., a Delaware corporation ("CORPORATION"),
hereby certifies that the following is a true, full and correct copy of the
resolutions adopted by the Corporation by unanimous written consent in lieu of a
special meeting of its Board of Directors, and that said resolutions have not
been amended or revoked as of the date hereof.

        RESOLVED, that the Corporation, is hereby authorized to execute, deliver
and fully perform that certain document entitled Third Amendment to Lease
("AMENDMENT") by and between the Corporation and Arden Realty Finance
Partnership, L.P., a California limited partnership, for the lease of space at
400 Corporate Pointe, Culver City, California.

        RESOLVED FURTHER, that the Corporation is hereby authorized and directed
to make, execute and deliver any and all, consents, certificates, documents,
instruments, amendments, confirmations, guarantees, papers or writings as may be
required in connection with or in furtherance of the Amendment (collectively
with the Amendment, the "DOCUMENTS") or any transactions described therein, and
to do any and all other acts necessary or desirable to effectuate the foregoing
resolution.

        RESOLVED FURTHER, that the following officers acting together:
_______________ as _____________ and ____________ as _______________ are
authorized to execute and deliver the Documents on behalf of the Corporation,
together with any other documents and/or instruments evidencing or ancillary to
the Documents, and in such forms and on such terms as such officer(s) shall
approve, the execution thereof to be conclusive evidence of such approval and to
execute and deliver on behalf of the Corporation all other documents necessary
to effectuate said transaction in conformance with these resolutions.

Date: _____________, 1998
                                           _____________________________________
                                           ________________, Corporate Secretary