- Data Describes Nimotuzumab's Unique Binding Properties Resulting In
    Superior Side-Effect Profile Compared To Other EGFR-Targeting Drugs -

    MISSISSAUGA, ON, July 21 /CNW/ - YM BioSciences Inc. (AMEX:   YMI, TSX: YM,
AIM: YMBA), an oncology company that identifies, develops and commercializes
differentiated products for patients worldwide, today announced that the
results from research examining the binding dynamics of nimotuzumab, a
humanized monoclonal antibody that targets the epidermal growth factor
receptor (EGFR), compared to two other EGFR-targeting drugs cetuximab and
panitumumab, will be presented today in a poster at the AACR Centennial
Conference on Translational Cancer Medicine 2008, held in Monterey, California
from July 20 - 23, 2008. The data describe the unique binding properties of
nimotuzumab to EGFR that allows the antibody drug to be effective against
cancers without causing the severe side effects of other EGFR-targeting drugs.
    "This research describes the distinct molecular properties of nimotuzumab
responsible for its more favorable side-effect profile which differentiates
our drug from all of the other currently marketed anti-EGFR antibodies. The
ongoing 59-patient Phase II study in colorectal cancer of nimotuzumab with
irinotecan confirms the low level of interaction between nimotuzumab and
normal tissue with less than a quarter of the patients exhibiting skin
toxicity and in all of whom it was both mild and transitory," said
David Allan, Chairman and CEO. "These data further support the value
proposition for our lead drug - nimotuzumab has the potential to become
best-in-class in the enormous market for EGFR-targeting therapies."
    The EGF receptor is expressed on numerous non-cancerous cells, including
skin cells, GI mucosa, and renal cells, while over-expressed on many types of
cancer cells. The presentation describes the mechanism through which
nimotuzumab discriminates between normal cells and cancer cells, binding
preferentially to cancer cells over-expressing EGFR, whereas the currently
approved anti-EGFR antibodies, cetuximab and panitumumab, bind to all tissues
expressing EGFR. Unlike the other two drugs, the attachment of nimotuzumab to
EGFR required bivalent binding (i.e. with both antibody arms), which occurs
more readily when EGFR density is elevated. In contrast, when EGFR density is
low, such as in healthy tissue, cetuximab and panitumumab continued to
interact strongly with EGFR through monovalent binding, while nimotuzumab
monovalent binding was transient thus sparing healthy tissues and avoiding the
associated severe toxicities. The selective targeting of tumors with high EGFR
density by nimotuzumab is similar to observations with Herceptin(R), where the
antibody is only active against Her2-overexpressing malignancies.
    EGFR tyrosine-kinase activity is increased in human cancer cells in
response to radiation. Inhibition of EGFR signaling exerts an additive, to
supra-additive, effect on radiation in tumor cells in-vitro. This
radio-sensitizing effect has been achieved in-vivo using monoclonal antibodies
against EGFR. Radiation treatment may further enhance the ability of
nimotuzumab to bind to cancer cells with initially low EGFR expression.
    "Data presented at this meeting combined with compelling survival data
from a phase I Non-Small Cell Lung Cancer (NSCLC) trial of nimotuzumab plus
radiation recently presented at ASCO 2008 provide a strong rationale for YM to
aggressively pursue the development of nimotuzumab in NSCLC and other
indications where EGFR expression is high or in indications where regimens
that stimulate EGFR expression are used, such as radiation or chemoradiation,"
added Dr. Paul Keane, Director, Medical Affairs of YM BioSciences.
    The research poster, entitled "Bivalent Binding Properties of Epidermal
Growth Factor Receptor (EGFR) Targeted Monoclonal Antibodies: Factors
Contributing to Differences in Observed Clinical Profiles", will be presented
by the author, Ilia Tikhomirov of YM BioSciences, and will be available on YM
BioSciences' website, www.ymbiosciences.com.

    About nimotuzumab

    Nimotuzumab is a humanized monoclonal antibody that targets the epidermal
growth factor receptor. In clinical trials and commercial sales of nimotuzumab
involving approximately 3,000 patients worldwide nimotuzumab has been observed
to have a significantly improved side-effect profile compared to other
EGFR-targeting drugs while demonstrating substantial clinical benefit in Phase
II trials and being approved for marketing in eight countries. No case of
Grade 3-4 rash has been reported for nimotuzumab and reports of any of the
other side effects that are typical of EGFR-targeting molecules have been
    YM's licensees for nimotuzumab, that include Daiichi Sankyo in Japan,
Oncoscience AG in Europe, Innogene Kalbiotech in Singapore/Indonesia and
Kuhnil in Korea, have a well-established, focused and advanced development
program underway for this highly differentiated EGFR-targeting molecule.
    Nimotuzumab is currently being evaluated in two Phase III trials as a
first-line treatment for pediatric pontine glioma and adult glioma, a Phase
II/III trial as a treatment for pancreatic cancer and a phase II study in
colorectal cancer. Two additional late stage trials in NSCLC and esophageal
cancer are also planned for initiation during 2008 by YM and other members of
the consortium. In addition the drug has been approved for marketing in eight
countries and is under review for marketing approval by EMEA.

    About YM BioSciences

    YM BioSciences Inc. is an oncology company that identifies, develops and
commercializes differentiated products for patients worldwide. In addition to
nimotuzumab, the Company is developing AeroLEF(TM), a proprietary,
inhaled-delivery composition of free and liposome-encapsulated fentanyl in
development for the treatment of moderate to severe pain, including cancer

    This press release may contain forward-looking statements, which reflect
the Company's current expectation regarding future events. These
forward-looking statements involve risks and uncertainties that may cause
actual results, events or developments to be materially different from any
future results, events or developments expressed or implied by such
forward-looking statements. Such factors include, but are not limited to,
changing market conditions, the successful and timely completion of clinical
studies, the establishment of corporate alliances, the impact of competitive
products and pricing, new product development, uncertainties related to the
regulatory approval process and other risks detailed from time to time in the
Company's ongoing quarterly and annual reporting. Certain of the assumptions
made in preparing forward-looking statements include but are not limited to
the following: that nimotuzumab will continue to demonstrate a competitive
safety profile in ongoing and future clinical trials; that AeroLEF- will
continue to generate positive efficacy and safety data in future clinical
trials; and that YM and its various partners will complete their respective
clinical trials within the timelines communicated in this release. We
undertake no obligation to publicly update or revise any forward-looking
statements, whether as a result of new information, future events or

    %SEDAR: 00004652E

For further information:

For further information: Enquiries: James Smith, the Equicom Group Inc.,
Tel. (416) 815-0700 x 229, Email: jsmith@equicomgroup.com; Thomas Fechtner,
the Trout Group LLC, Tel. (646) 378-2931, Email: tfechtner@troutgroup.com;
Nominated Adviser, Canaccord Adams Limited, Ryan Gaffney, Tel. +44 (0)20 7050

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