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                                                                  EXHIBIT 10.10

                                                                 EXECUTION COPY

THIS CONVERTIBLE PROMISSORY NOTE AND THE SHARES OF COMMON STOCK ISSUABLE UPON
CONVERSION HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, AND MAY NOT UNDER ANY CIRCUMSTANCES BE SOLD, TRANSFERRED OR OTHERWISE
DISPOSED OF WITHOUT AN EFFECTIVE REGISTRATION STATEMENT FOR SUCH SECURITIES
UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND ANY APPLICABLE STATE
SECURITIES LAWS, OR AN OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT
REGISTRATION IS NOT REQUIRED UNDER SUCH ACT OR APPLICABLE STATE SECURITIES LAWS.

THE TRANSFER OF THE SECURITIES REPRESENTED BY THIS CERTIFICATE IS ALSO SUBJECT
TO THE RESTRICTIONS CONTAINED IN THAT CERTAIN SECURITIES PURCHASE AGREEMENT,
DATED OCTOBER 20, 1999, BY AND BETWEEN PHOTOGEN TECHNOLOGIES, INC. AND ELAN
INTERNATIONAL SERVICES, LTD.


                           PHOTOGEN TECHNOLOGIES, INC.
                           CONVERTIBLE PROMISSORY NOTE


U.S. $4,806,000                                             OCTOBER 20, 1999
                                                            NEW YORK, NEW YORK

                  The undersigned, PHOTOGEN TECHNOLOGIES, INC., a Nevada
corporation with offices at 7327 Oak Ridge Highway, Suite B, Knoxville,
Tennessee 37931 (the "COMPANY"), unconditionally promises to pay to ELAN
INTERNATIONAL SERVICES, LTD., a Bermuda exempted limited liability company
("EIS"), or its permitted assigns, transferees and successors as provided herein
(collectively, the "HOLDER"), on October 20, 2005 (the "MATURITY DATE"), at such
place as may be designated by the Holder to the Company, the principal amount
outstanding hereunder (not to exceed U.S.$4,806,000), together with interest
thereon accrued at a rate PER ANNUM equal to 8.0%, from and after the date of
the initial disbursement of funds hereunder (the "ORIGINAL ISSUE DATE"),
compounded on a semi-annual basis, the initial such compounding to commence on
the date that is 180 days from and after the Original Issue Date and thereafter
on each 180 day anniversary (each such date, a "COMPOUNDING DATE").

         SECTION 1.  SECURITIES PURCHASE AGREEMENT AND FUNDING AGREEMENT.

                  This Note is issued pursuant to a Securities Purchase
Agreement dated as of the date hereof, by and between the Company and EIS (as
amended at any time, the "SECURITIES PURCHASE AGREEMENT"), and is intended to be
afforded the benefits thereof, including the representations and warranties set
forth therein. The Company shall use the proceeds of the issuance and sale of
this Note solely in accordance with the provisions set forth therein and as

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required therein and in a certain Funding Agreement, dated as of the date hereof
(as amended at any time, the "FUNDING AGREEMENT"), by and among Elan Pharma
International Limited, an Irish private limited company and the parent
corporation of EIS, EIS and the Company, and as described in Section 6 below.
Capitalized terms used but not otherwise defined herein shall, unless otherwise
indicated, have the meanings given such terms in the Securities Purchase
Agreement.

         SECTION 2.  DISBURSEMENTS.

         (a)      From and after the date hereof and until October 20, 2002,
disbursements shall be made by the Holder to the Company hereunder in minimum
increments of U.S.$500,000 (except in the event that an amount less than
U.S.$500,000 shall be remaining and available for funding hereunder, in which
case such lesser amount may be funded hereunder); provided, that the Company
shall deliver notice of a request therefor to the Holder in the form attached
hereto as EXHIBIT A (the "DISBURSEMENT NOTICE"), together with an Officer's
Certificate confirming that as of such date no Event of Default exists
hereunder; the Holder shall, subject to the terms and conditions hereof, fund
such amount within 10 business days of the receipt of the Disbursement Notice,
subject to the receipt by the Holder of any required approvals under the Mergers
and Takeovers (Control) Acts 1978-1996. A "business day" is any day that
commercial banks are open for the transaction of business in the City of New
York.

         (b)      Subject to the remainder of this Section 2, if the Holder and
the Company agree to extend the Research and Development Term (as defined in the
JDOA), then disbursements shall be made by the Holder to the Company hereunder
until the end of the Research and Development Term.

         (c)      Disbursements shall be made hereunder only if EIS agrees to
provide the corresponding Subsequent Funding under Section 1.2 of the Funding
Agreement.

         (d)      The Holder shall not be required to disburse more than a
maximum principal amount hereunder, excluding accruals of interest, of
U.S.$4,806,000.

         SECTION 3.  PAYMENTS AND COVENANTS.

     (a) Unless earlier converted in accordance with the terms of Section 4
below, or prepaid in accordance with the terms hereof, the entire outstanding
principal amount of this Note, together with any accrued and unpaid interest
thereon, shall be due and payable on the Maturity Date.

     (b) Accrued interest hereon shall not be paid in cash, but shall be
capitalized and added to the principal amount outstanding hereunder on each
Compounding Date.

         SECTION 4.  CONVERSION.

         (a)     CONVERSION RIGHT.

                  (i) From and after the Original Issue Date and until this Note
is repaid in full, the Holder shall have the right from time to time, in its
sole discretion, to convert all or any portion of the outstanding principal
amount and accrued and unpaid interest then-outstanding hereunder,

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(the "CONVERSION RIGHT"), into such number of shares of Common Stock that
shall be obtained by dividing the sum of the outstanding principal amount and
all accrued and unpaid interest by $18.15, subject to adjustment as provided
below in this Section (the "CONVERSION PRICE").

                  (ii) The Holder shall be entitled to exercise a Conversion
Right upon at least five days' prior written notice to the Company, such notice
to be in the form attached hereto as EXHIBIT B. Within 10 days of the conversion
date specified in such notice, the Company shall issue stock certificates to EIS
representing the aggregate number of shares of Common Stock due to EIS as a
result of such conversion.

         (b) RECLASSIFICATION, ETC. In case of (i) any reclassification,
reorganization, change or conversion of securities of the class issuable upon
conversion of the outstanding principal amount and accrued and unpaid interest
then-outstanding hereunder (other than a change in par value, or from par value
to no par value), or (ii) any consolidation of the Company with or into another
entity (other than a merger or consolidation with another entity in which the
Company is the surviving entity and that does not result in any reclassification
or change of the class of securities issuable upon the conversion of the
outstanding principal amount and accrued and unpaid interest then-outstanding
hereunder), or (iii) any sale of all or substantially all the assets of the
Company (excluding the transactions contemplated by the Transaction Documents),
then the Company, or such successor or purchasing entity, as the case may be,
shall duly execute and deliver to the Holder a new Note or a supplement hereto
(in form and substance reasonably satisfactory to the Holder of this Note), so
that the Holder shall have the right to receive, in lieu of the shares of Common
Stock otherwise issuable upon the conversion of such outstanding principal
amount and accrued and unpaid interest then-outstanding hereunder, the kind and
amount of shares of stock and other securities, money and property receivable
upon such reclassification, reorganization, change, merger, consolidation or
conversion by a holder of the number of shares of Common Stock then issuable
under this Note. Such new Note shall provide for adjustments that shall be as
nearly equivalent as may be practicable to the adjustments provided for in this
Section 4. The provisions of this Section 4(b) shall similarly attach to
successive reclassifications, reorganizations, changes, mergers, consolidations,
transfers or conversions.

         (a) NO IMPAIRMENT. The Company will not, by amendment of its
Articles of Incorporation or bylaws or through any reorganization,
recapitalization, transfer of assets, consolidation, merger, dissolution,
issue or sale of securities or any other voluntary action, avoid or seek to
avoid the observance or performance of any of the terms to be observed or
performed hereunder by the Company, but will at all times in good faith
assist in the carrying out of all the provisions of this Section 4 and in the
taking of all such action as may be necessary or appropriate in order to
protect the rights of EIS against impairment. This provision shall not
restrict the Company from otherwise amending and/or restating its Articles of
Incorporation in accordance with Nevada General Corporation Act.

         (b) NOTICE OF ADJUSTMENTS. Whenever the consideration issuable upon a
conversion hereunder shall be changed pursuant to this Section 4, the Company
shall prepare a certificate setting forth, in reasonable detail, the event
requiring the change and the kind and amount of shares of stock and other
securities, money and property subsequently issuable upon a conversion hereof.
Such certificate shall be signed by its chief financial officer and shall be
delivered to

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EIS.

         (c) FRACTIONAL SHARES; ROUNDING. No fractional shares of Common Stock
will be issued in connection with any exercise hereunder, but in lieu of such
fractional shares the Company shall make a cash payment therefor based on the
applicable Conversion Price. All calculations under this Section 4 shall be made
to the nearest cent or to the nearest one-hundredth of a share, as the case may
be.

         SECTION 5.  EXCHANGE RIGHT.

         In the event that EIS shall exercise the EIS Exchange Right, EIS shall,
at its option, (i) cause to be paid to the Company, within 30 days of such
exercise, an amount equal to 30.1% of the aggregate amount of the Development
Funding (as such term is defined in the Funding Agreement) to date provided by
each of the parties to Newco, in accordance with the terms of the Funding
Agreement, but not including any interest thereon, from and after the date
hereof and until the date of such exercise, or (ii) offset against the amount
payable under this Note an amount equal to 30.1% of the total amount of
Development Funding provided by each of the parties to Newco, in accordance with
the terms of the Funding Agreement, from and after the date hereof and until the
date of the exercise of the Exchange Right, against the principal amount
outstanding hereunder, if any, or (iii) effect a combination of (i) and (ii)
above if applicable.

         SECTION 6.  USE OF PROCEEDS.

                  The Company shall use the proceeds of this Note solely for
developmental funding of Newco; provided, that the Board of Directors of Newco
has determined that such developmental funding is necessary (which approval
shall in all events include the consent of all directors designated by the
Company and at least one director designated by EIS) and that the parties
thereto are in continuing agreement as to the Business Plan. Accordingly, total
disbursements hereunder shall not exceed the amount of Development Funding
funded by the Company to Newco pursuant to the Funding Agreement.

         SECTION 7.  EVENTS OF DEFAULT.

                  The occurrence of any of the following events shall constitute
an event of default (an "EVENT OF DEFAULT"):

         (a)       a default in the payment of the principal amount of this
Note, when and as the same shall become due and payable;

         (b)     a default in the payment of any accrued and unpaid interest on
this Note, when and as the same shall become due and payable;

         (c)      a material breach by the Company of its obligations under any
of the Transaction Documents, which breach remains uncured 60 days after written
notice thereof by EIS;

         (d)      a distress, execution, sequestration or other process is
levied or enforced upon the Company or sued out against a material part of its
property which is not discharged or challenged within 60 days;

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         (e)      the Company is unable to pay its debts in the normal course
of business;

         (f)      the Company ceases wholly or substantially to carry on its
business, otherwise than for the purpose of a reconstruction or amalgamation,
without the prior written consent of the EIS Director (such consent not to be
unreasonably withheld);

         (g)      the appointment of a liquidator, receiver, administrator,
examiner, trustee or similar officer of the Company or over all or substantially
all of its assets under the law; or

         (h)      any other termination of the JDOA.

         SECTION 8.  REMEDIES IN THE EVENT OF DEFAULT.

         (a) In the case of any Event of Default by the Company, the Holder, may
in its sole discretion, demand that the aggregate amount of funds advanced to
the Company under this Note and outstanding hereunder and accrued and unpaid
interest thereon shall, in addition to all other rights and remedies of the
Holder hereunder and under applicable law, be and become immediately due and
payable upon written notice delivered by the Holder to the Company.
Notwithstanding the preceding sentence, the rights of the Holder as set forth in
Section 4 hereunder shall survive any such acceleration and payment. If the
Holder shall accelerate and be paid and thereafter elect to exercise the
Conversion Right, within 15 days thereafter the Holder shall pay to the Company
in cash the Conversion Price then applicable to the shares of Common Stock so
issuable to the Holder under such Conversion Right.

         (b) The Company hereby waives demand and presentment for payment,
notice of nonpayment, protest and notice of protest, diligence, filing suit, and
all other notice and promises to pay the Holder its costs of collection of all
amounts due hereunder, including reasonable attorneys' fees.

         (c) In the case of any Event of Default under this Note by the Company
this Note shall continue to bear interest after such default at the interest
rate otherwise in effect hereunder plus 3% PER ANNUM (but in any event not in
excess of the maximum rate of interest permitted by applicable law).

         SECTION 9.  MISCELLANEOUS.

         (a) EIS may assign this Note to its affiliates and subsidiaries, as
well as any special purpose financing or similar vehicle established by EIS or
its affiliates. This Note and all of the provisions hereof shall be binding upon
and inure to the benefit of the parties hereto and their respective successors
and permitted assigns; provided, however, that EIS and the Company shall remain
liable for their respective obligations hereunder after any such assignment.

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         (b) All notices, demands and requests of any kind to be delivered to
any party in connection with this Agreement shall be in writing and shall be
deemed to have been duly given if personally delivered or if sent by
nationally-recognized overnight courier or by registered or certified mail,
return receipt requested and postage prepaid, or by facsimile transmission,
addressed as follows:


                                    (i) if to the Company:

                                    Photogen Technologies, Inc.
                                    7327 Oak Ridge Highway, Suite B
                                    Knoxville, Tennessee  37931
                                    Attention:  Chief Executive Officer
                                    Facsimile:  (423) 769-4013

                                    with a copy to:

                                    Grippo & Elden
                                    Suite 3600
                                    227 West Monroe Street
                                    Chicago, Illinois 60606
                                    Attn: Theodore Grippo, Esq.
                                    Facsimile: (312) 558-1195

                                    (ii) if to EIS, to:

                                    Elan International Services, Ltd.
                                    102 St. James Court
                                    Flatts, Smiths Parish
                                    Bermuda  FL04
                                    Attention: President
                                    Fax:  (441) 292-2224

                                    with a copy to:

                                    Brock Silverstein LLC
                                    800 Third Avenue
                                    New York, New York 10022
                                    Attention: David Robbins, Esq.
                                    Fax:  (212) 371-5500

Each party, by written notice given to the other in accordance with this Section
9(b) may change the address to which notices, other communication or documents
are to be sent to such party. All notices, other communications or documents
shall be deemed to have been duly given when received. Any such notice or
communication shall be deemed to have been effectively given, (a) in the case of
personal delivery, on the date of such delivery, (b) in the case of
nationally-recognized overnight courier, on the second business day after the
date when sent, (c)

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in the case of mailing, on the fifth business day following that day on which
the piece of mail containing such communication is posted, and (d) in the
case of facsimile transmission, on the date of transmission.

         (a) This Note may not be modified or amended, or any of the provisions
hereof waived, except by written agreement of the Company and EIS.

         (b) This Note shall be governed by and construed in accordance with the
laws of the State of New York, without giving effect to principles thereof
relating to conflicts of laws.

         (c) This Note may be executed in any number of counterparts, and each
such counterpart hereof shall be deemed to be an original instrument, but all
such counterparts together shall constitute one note. The Note may be signed and
delivered to the other party by a facsimile transmission; such transmission
shall be deemed a valid signature.

         (d) Each of the parties shall be responsible for its own costs and
expenses incurred in connection with the transactions contemplated hereby.


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                  IN WITNESS WHEREOF, the Company and EIS have executed this
Note on the date first above written.

                                      PHOTOGEN TECHNOLOGIES, INC.


                                      By:      /s/ John Smolik
                                           ------------------------------
                                           Name:   John Smolik
                                           Title:  President


                                      ELAN INTERNATIONAL SERVICES, LTD.


                                      By:      /s/ Kevin Insley
                                           ------------------------------
                                           Name: Kevin Insley
                                           Title: Kevin Insley



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                                    EXHIBIT A

                       NOTICE OF REQUEST FOR DISBURSEMENT


Date:

To:      Elan International Services, Ltd.

From:    Photogen Technologies, Inc.

Re:      Disbursement Request

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         Pursuant to the terms of the Convertible Promissory Note (the "Note")
issued by Photogen Technologies, Inc. (the "Company") to Elan International
Services, Ltd. ("EIS"), dated ______, 1999, the Company hereby notifies EIS of
its request for a disbursement thereunder in the amount of $_________. Please
provide funding in the requested amount to the Company in accordance with the
following wire instructions

                  [





                                                       ]




                                   Sincerely,

                                   PHOTOGEN TECHNOLOGIES, INC.


                                   By:
                                       ----------------------------------
                                         Name:
                                         Title:



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                                    EXHIBIT B

                NOTICE OF ELECTION TO EXERCISE A CONVERSION RIGHT


Date:

To:      Photogen Technologies, Inc.

From:    Elan International Services, Ltd.

Re:      Exercise of a Conversion Right

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-------------------------------------------------------------------------------

         Pursuant to the terms of the Convertible Promissory Note (the "Note")
issued by Photogen Technologies, Inc. (the "Company") to Elan International
Services, Ltd. ("EIS"), dated ___________, 1999, specifically Section 4 thereof,
EIS hereby notifies the Company of its intention to exercise a right of
conversion.

         Pursuant to Section 4 of the Note, EIS hereby elects to convert
[$__________]* in aggregate principal amount and all accrued and unpaid interest
thereon for shares of the Company's Common Stock, par value $.001 per share,
effective [__________, ____]

         We have instructed our attorneys to contact the Company to discuss the
timing and documentation of the conversion.


                                   Sincerely,

                                   ELAN INTERNATIONAL SERVICES, LTD.


                                   By:
                                       ----------------------------------
                                         Name:
                                         Title:





-----------------------
* Amount must represent one or more tranches drawn down by the Company under
the Note.