<PAGE>
                                                                               .
                                                                               .
                                                                               .

<Table>
<Caption>

<S>                                          <C>                                            <C>
CONTACTS:
LORUS THERAPEUTICS INC.                      CANADIAN MEDIA CONTACT:                        US MEDIA CONTACT:

Corporate Communications                     Hugh Mansfield                                 Jennifer Taylor
Grace Tse                                    Mansfield Communications Inc.                  Mansfield Communications Inc.
Tel:  (416) 798-1200, ext.380                Tel:  (416) 599-0024                           Tel:  (212) 370-5045
Email:   ir@lorusthera.com                   Email:  hugh@mcipr.com                         E-mail:  jennifer@mcipr.com
</Table>



   LORUS THERAPEUTICS' SCIENTIFIC PUBLICATION EXPANDS THE POTENTIAL ANTICANCER
                          APPLICATIONS OF VIRULIZIN(R)
            - Studies published in peer reviewed scientific journal -

TSE:              LOR
OTC BB:           LORFF

TORONTO, CANADA, APRIL 23, 2003 - Lorus Therapeutics Inc. ('Lorus') has
published the results of experimental studies demonstrating the anti-tumor
activity of Virulizin as a monotherapy and in combination with standard
chemotherapy drugs. These studies, carried out in mouse models bearing human
tumors, are unique as they expand the potential application of Virulizin(R) to
include breast, ovarian and prostate cancers.

The findings of the study are published in an April issue of Anti-Cancer Drugs
(volume 14, issue 4, pages 289 to 294, 2003) in an article entitled,
"Preclinical efficacy of Virulizin(R) in human breast, ovarian and prostate
tumor models." These results complement previously published data that
demonstrated the effectiveness of Virulizin(R) as an anti-tumor agent in human
pancreatic cancer and melanoma mouse models in Cancer Chemotherapy and
Pharmacology (volume 51,issue 3, pages 247-255, 2003).

The published results will be included in the preclinical portion of regulatory
submissions needed to obtain marketing approval for Virulizin(R).


                                     (more)
<PAGE>

                                      - 2 -

"These recently published preclinical studies provide information for
determining further clinical development and expansion of the indications for
Virulizin(R), our lead anticancer immunotherapy drug. Reporting findings in peer
reviewed scientific journals further validate the results from our research
program, adds to our regulatory dossier and enhances our drug development
activities," said Dr. Jim Wright, chief executive officer, Lorus.

Virulizin (R) is currently in a Phase III clinical trial in North America for
the treatment of pancreatic cancer, and was awarded orphan drug status and
fast-track status from the United States Food and Drug Administration in
clinical studies for the treatment of pancreatic cancer. The drug is approved in
Mexico for the treatment of melanoma and is commercially available in Mexico
through Lorus' marketing partner.


About Lorus
Lorus is a biopharmaceutical company focused on the research and development of
cancer therapies. Lorus' goal is to capitalize on its research, pre-clinical,
clinical and regulatory expertise by developing new drug candidates that can be
used, either alone, or in combination, to successfully manage cancer. Through
its own discovery efforts and an active acquisition and in-licensing program,
Lorus is building a portfolio of promising anti-cancer drugs. Late-stage
clinical developments and marketing will be done in cooperation with strategic
pharmaceutical partners. Founded in 1986, Lorus Therapeutics Inc. is a public
company listed on the Toronto Stock Exchange under the symbol LOR, and on the
OTC BB exchange under the symbol LORFF.

Except for historical information, this press release contains forward-looking
statements, which reflect the Company's current expectation regarding future
events. These forward-looking statements involve risks and uncertainties, which
may cause actual results to differ materially from those statements. Those risks
and uncertainties 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 filings,
annual information form, annual reports and 20-F filings.

Lorus Therapeutics Inc.'s press releases are available through the Company's
Internet site: http://www.lorusthera.com.


                                     - 30 -