Positive Topline Data Shows Fostamatinib Meets Primary Endpoint of Safety in Phase 2 Clinical Trial in Hospitalized Patients with COVID-19 Broad and consistent improvement in clinical outcomes including serious adverse e

Topline Data Shows Fostamatinib Meets Primary Endpoint of Safety in Phase 2 Clinical Trial in Hospitalized Patients with COVID-19

and consistent improvement in clinical outcomes including serious adverse events, mortality, ordinal scale assessment and number of days

plans to share these results with health authorities, including the US FDA

call and webcast today at 8:00 am ET/5:00 am PT

SOUTH SAN FRANCISCO,

Calif., April 13, 2021 /PRNewswire/ -- Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL), today announced positive topline results

from a multi-center, Phase 2 clinical trial to evaluate the safety of fostamatinib, its oral spleen tyrosine kinase (SYK) inhibitor,

for the treatment of hospitalized patients with COVID-19.

The trial, being conducted in collaboration

with the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health (NIH), and Inova Health System,

met its primary endpoint of safety. Fostamatinib reduced the incidence of Serious Adverse Events (SAEs) by half. By day 29, there were

three SAEs in the fostamatinib plus standard of care (SOC) group of thirty patients compared to six SAEs in the placebo plus SOC group

of twenty-nine patients (p=0.23). Of these, there was a reduction for the disease related SAE of hypoxia in the fostamatinib group compared

to placebo (1 vs 3, respectively; p=0.29).

"Despite the growing arsenal of

vaccines gaining emergency use authorization, COVID-19 continues to spread and patients remain in need of effective therapies. We are

extremely pleased with the outcome of this trial, which provides early indications of the potential positive impact of fostamatinib for

patients with COVID-19," said Raul Rodriguez, president and CEO of Rigel. "These results are an important addition to the

extensive accumulation of data evaluating fostamatinib in COVID-19, which also include the ongoing Phase 2 study with Imperial College

London and our own Phase 3 clinical trial being conducted in the U.S. and Latin America."

"Fostamatinib was shown to be

well tolerated in hospitalized patients with COVID-19 on oxygen. Taken altogether, the results of this trial suggest fostamatinib may

be a useful addition to improve the outcome of severe and critically ill COVID-19 patients who are at the highest risk of death despite

treatment with the best conventional therapies under the current standard of care (including remdesivir and steroids)," said Wolfgang

Dummer, M.D., Ph.D., Rigel's Chief Medical Officer. "Consistent with the observed clinical outcomes, we are encouraged to

see that in patients receiving fostamatinib there was a more rapid decline in a number of inflammatory biomarkers, that have previously

been shown to be associated with the course of COVID-19 disease, compared to those receiving placebo."

Key findings from the Phase 2 clinical

data readout include:

Investigators will conduct full and

detailed analyses in the coming weeks.

Based on these data, Rigel plans to

discuss the potential for emergency use authorization (EUA) with the U.S. Food and Drug Administration (FDA) of fostamatinib as a treatment

for hospitalized patients with COVID-19. Fostamatinib, marketed in the U.S. as TAVALISSE (fostamatinib disodium hexahydrate) tablets,

is approved in the U.S., Europe, and Canada as a treatment for adult chronic immune thrombocytopenia (ITP).

Phase 2 Clinical Trial Design

This is a double-blind, placebo-controlled

Phase 2 clinical trial sponsored by the NHLBI, part of the NIH, in collaboration with Inova Health System. Fifty-nine hospitalized patients

with COVID-19 who were a 5 to 7 on the 8-point ordinal scale (requiring supplemental oxygen via nasal canula or non-invasive ventilation,

requiring mechanical ventilation or extracorporeal membrane oxygenation) were randomly assigned to one of two cohorts: fostamatinib plus

SOC or matched placebo plus SOC (1:1). Treatment was administered orally twice daily for 14 days, with a follow-up period through day

60. Notably, all patients received dexamethasone as well as remdesivir.

For more information on Rigel's comprehensive

clinical program in COVID-19, go to: https://www.rigel.com/pipeline/proprietary-programs/covid-19

Conference Call and Webcast with

Slides Today at 8:00 am Eastern Time

Rigel will hold a live conference call

and webcast today to discuss the Phase 2 trial results at 8:00 am Eastern Time (5:00 am Pacific Time).

Participants can access the live conference

call by dialing (877) 407-3088 (domestic) or (201) 389-0927 (international). The conference call and accompanying slides will also be

webcast live and can be accessed from the Investor Relations section of the company's website at www.rigel.com. The webcast will be archived

and available for replay after the call via the Rigel website.

About COVID-19 & SYK

COVID-19 is the infectious disease caused

by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). SARS-CoV-2 primarily infects the upper and lower respiratory tract and

can lead to acute respiratory distress syndrome (ARDS). Additionally, some patients develop other organ dysfunction including myocardial

injury, acute kidney injury, shock resulting in endothelial dysfunction and subsequently micro and macrovascular thrombosis.1 Much

of the underlying pathology of SARS-CoV-2 is thought to be secondary to a hyperinflammatory immune response associated with increased

risk of thrombosis.2

SYK is involved in the intracellular

signaling pathways of many different immune cells. Therefore, SYK inhibition may improve outcomes in patients with COVID-19 via inhibition

of key Fc gamma receptor (Fc R) and c-type lectin receptor (CLR) mediated drivers of pathology, such as inflammatory cytokine release

by monocytes and macrophages, production of neutrophil extracellular traps (NETs) by neutrophils, and platelet aggregation.3,4,5

Furthermore, SYK inhibition in neutrophils and platelets may lead to decreased thromboinflammation, alleviating organ dysfunction

in critically ill patients with COVID-19.

About Rigel (www.rigel.com)

Rigel Pharmaceuticals, Inc., is

a biotechnology company dedicated to discovering, developing and providing novel small molecule drugs that significantly improve the

lives of patients with hematologic disorders, cancer and rare immune diseases. Rigel's pioneering research focuses on signaling pathways

that are critical to disease mechanisms. The company's first FDA approved product is TAVALISSE (fostamatinib disodium hexahydrate)

tablets, the only oral spleen tyrosine kinase (SYK) inhibitor, for the treatment of adult patients with chronic immune thrombocytopenia

who have had an insufficient response to a previous treatment. The product is also commercially available in Europe (TAVLESSE) and Canada

(TAVALISSE) for the treatment of chronic immune thrombocytopenia in adult patients.

Fostamatinib is currently being studied

in a Phase 3 trial for the treatment of warm autoimmune hemolytic anemia (wAIHA)6; an NIH/NHLBI-sponsored Phase 2 trial for

the treatment of hospitalized COVID-196 patients, in collaboration with Inova Health System; and a Phase 2 trial for the treatment

of COVID-19 being conducted by Imperial College London. Additionally, Rigel has launched a Phase 3 clinical trial of fostamatinib for

the treatment of hospitalized COVID-19 patients.

Rigel's other clinical programs include

its interleukin receptor-associated kinase (IRAK) inhibitor program, and a receptor-interacting serine/threonine-protein kinase (RIP1)

inhibitor program in clinical development with partner Eli Lilly and Company. In addition, Rigel has product candidates in development

with partners AstraZeneca, BerGenBio ASA, and Daiichi Sankyo.

Please see www.TAVALISSE.com

for full Prescribing Information.

Forward Looking Statements

This release contains forward-looking

statements relating to, among other things, the ability to improve the outcome of all COVID-19 patients

by the use of fostamatinib; the continuing need for effective therapies for COVID-19 patients; Rigel's plans for the further investigation

of fostamatinib in COVID-19 patients; as well as Rigel's plans to seek emergency use authorization for fostamatinib for the treatment

of COVID-19. Any statements contained in this press release that are not statements of historical fact may be deemed to be forward-looking

statements. Words such as "potential," "may," "expects" and similar expressions are intended to identify

these forward-looking statements. These forward-looking statements are based on Rigel's current expectations and inherently involve significant

risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward looking

statements as a result of these risks and uncertainties, which include, without limitation, risks that the FDA, EMA or other regulatory

authorities may make adverse decisions regarding fostamatinib; risks that clinical trials may not be predictive of real-world results

or of results in subsequent clinical trials; risks that fostamatinib may have unintended side effects, adverse reactions or incidents

of misuses; the availability of resources to develop Rigel's product candidates; market competition; as well as other risks detailed

from time to time in Rigel's reports filed with the Securities and Exchange Commission, including its Annual Report on Form 10-K

for the year ended December 31, 2020 and subsequent filings. Rigel does not undertake any obligation to update forward-looking statements