FDA Removes Partial Clinical Hold on Salarius Pharmaceuticals’ Phase 1/2 Clinical Trial with Seclidemstat in Patients with Ewing Sarcoma

Decision Follows Review of Comprehensive Safety Data Package Submitted by the Company

Salarius Plans to Meet with FDA to Discuss Future Development and Potential Registration Pathways

HOUSTON, May 09, 2023 (GLOBE NEWSWIRE) — Salarius Pharmaceuticals, Inc. (NASDAQ: SLRX), a clinical-stage biopharmaceutical company using protein inhibition and protein degradation to develop cancer therapies for patients in need of new treatment options, announces that the U.S. Food and Drug Administration (FDA) has removed its partial clinical hold on Salarius’ Phase 1/2 Ewing sarcoma clinical trial evaluating seclidemstat, Salarius’ novel oral, reversible, targeted LSD1 inhibitor.

The FDA previously granted seclidemstat Fast Track Designation, Orphan Drug Designation and Rare Pediatric Disease Designation for Ewing sarcoma.

“We are confident in seclidemstat’s ability to improve the lives of patients with Ewing sarcoma and are delighted the FDA has removed the partial clinical hold,” said David Arthur, president and chief executive officer of Salarius. “I want to commend the team at Salarius for their tireless work to provide the necessary safety and clinical information to assure the FDA of seclidemstat’s compelling risk-benefit profile. Ewing sarcoma is a devasting bone and soft tissue cancer with limited treatment options that afflicts children, adolescents and young adults. We look forward to working with our clinical trial investigators to resume enrollment with the goal of advancing the development of seclidemstat as a potential treatment option.

“The FDA’s decision to remove the clinical hold puts us back on track to engage in dialogue with the FDA on various topics relating to further clinical development of seclidemstat and possible registration pathways. As we gain clarity in those discussions, we intend to provide updates to our investors,” Mr. Arthur added.

Previously Reported Seclidemstat Clinical Data

In December 2022 Salarius reported interim clinical results from its Phase 1/2 trial showing that treatment with seclidemstat in combination with topotecan and cyclophosphamide had 60% confirmed disease control and 7.4 months median time to tumor progression for Ewing sarcoma first-relapse patients. The results also suggest that first- and second-relapse Ewing sarcoma patients treated with seclidemstat in combination with topotecan and cyclophosphamide who achieve disease control may have an increased time to tumor progression (TTP) compared with treatment of topotecan and cyclophosphamide alone, per published data from the Phase 3 rEECur (International Randomized Controlled Trial of Chemotherapy for the Treatment of Recurrent and Primary Refractory Ewing Sarcoma) study. At ASCO 2022 the Euro Ewing Consortium presented rEECur Phase 3 study results in relapsed/refractory Ewing sarcoma patients that showed median event-free survival of 3.5 months in the topotecan/cyclophosphamide arm (n=73) compared with 5.7 months in the high-dose ifosfamide arm (n=73). The rEECur data includes approximately 80% primary refractor or first-relapse. Ewing sarcoma patients after relapse have 5-year overall survival of about 13% and 10-year overall survival of about 9%.¹ Single-agent activity has not been observed in the FET-rearranged sarcoma cohort of the trial.

In December 2022 investigators in the Department of Leukemia at the University of Texas MD Anderson Cancer Center (MD Anderson) presented clinical data on seclidemstat in patients with MDS or CMML at the 64^th American Society of Hematology Annual Meeting showing no serious adverse events were reported, and that all adverse events observed in the study were manageable. Of the eight evaluable patients, four (50%) had an objective response including one complete response patient who planned to receive potentially curative allogeneic stem cell transplantation, two marrow complete responses plus hematological improvement and one marrow complete response. The Phase 1 dose-escalation portion of this trial is designed to evaluate up to six dose levels of seclidemstat. The maximum tolerated dose, which will inform the Phase 2 portion of the trial, had not yet been reached.

About the Phase 1/2 Ewing Sarcoma Clinical Trial

The Phase 1/2 trial is now in its dose-expansion stage with one arm planned to enroll up to 30 patients with Ewing sarcoma, a rare and deadly pediatric bone cancer, that will investigate seclidemstat in combination with topotecan and cyclophosphamide, a commonly used second- and third-line chemotherapy regimen. Salarius believes data released during ASCO 2021 demonstrated synergy in an Ewing sarcoma cell line when seclidemstat was used in combination with these agents. Salarius also believes this treatment combination and its use as a second- and third-line therapy has the potential to expand the addressable patient population for seclidemstat and improve outcomes by allowing physicians to introduce seclidemstat earlier in the Ewing sarcoma continuum of care. As previously reported, single-agent activity has not been observed in the FET-rearranged sarcoma cohort of the trial, and at the time of the partial clinical hold Salarius was no longer enrolling patients in this cohort. Salarius has closed the FET-rearranged sarcoma patient cohort in the sarcoma clinical trial.

Salarius supports patient referrals to its sarcoma trial sites and provides travel assistance for clinical trial patients and families who are evaluating and participating in the sarcoma trial. Clinical trial sites include Seattle Cancer Care Alliance (SCCA), Seattle, WA, which is comprised of the Fred Hutchinson Cancer Research Center, Seattle Children’s Hospital and University of Washington Medical Center; Oregon Health & Sciences University in Portland, OR; Johns Hopkins All Children’s Hospital in St. Petersburg, FL; Children’s Hospital of Los Angeles in Los Angeles, CA; Moffitt Cancer Center in Tampa, FL; Dana-Farber Cancer Institute in Boston, MA; MD Anderson Cancer Center in Houston, TX; Nationwide Children’s Hospital in Columbus, OH; Memorial Sloan Kettering Cancer Center in New York, NY; Virginia Cancer Specialists in Fairfax, VA; Cleveland Clinic, Cleveland, OH; Washington University in St. Louis, MO and Fox Chase Cancer Center in Philadelphia, PA.

About the Phase 1/2 Investigator-initiated Hematological or Blood Cancer Clinical Trial

The objective of this investigator-initiated Phase 1/2 dose-escalation trial at MD Anderson is to evaluate the safety, tolerability, maximum tolerated dose and overall response of seclidemstat in combination with azacytidine in adult patients with higher-risk MDS or CMML who previously failed or relapsed after hypomethylating agent therapy. As of October 2022, nine patients were enrolled with a median follow-up time of 3.9 months. Typically, overall survival is four to six months for patients after failing therapy with hypomethylating agents. Following the partial clinical hold on Phase 1/2 Ewing Sarcoma Clinical Trial, FDA also placed this investigator-initiated trial on partial clinical hold. Salarius is supporting MD Anderson in its efforts to have its partial clinical hold lifted.

2023 BIO International Convention and European Hematology Association 2023 Congress

Salarius also announces that it will be participating in the 2023 BIO International Convention being held in Boston from June 5^th through 8^th, 2023 and the European Hematology Association 2023 Congress being held in Frankfurt, Germany from June 8^th through 11^th, 2023. Management plans to hold business development meetings with representatives of biotechnology and pharmaceutical companies to expand awareness of both seclidemstat and its lead targeted protein degrader, SP-3164. As previously announced, Salarius is planning to submit an Investigational New Drug Application (IND) for SP-3164 in the second quarter of 2023 and begin a Phase 1 clinical trial shortly thereafter.

About Salarius Pharmaceuticals
Salarius Pharmaceuticals, Inc. is a clinical-stage biopharmaceutical company developing therapies for patients with cancer in need of new treatment options. Salarius’ product portfolio includes seclidemstat, Salarius’ lead candidate, which is being studied as a potential treatment for pediatric cancers, sarcomas and other cancers with limited treatment options, and SP-3164, an oral small molecule protein degrader. Seclidemstat is currently in a Phase 1/2 clinical trial for relapsed/refractory Ewing sarcoma. Seclidemstat has received fast track, orphan drug and rare pediatric disease designations for Ewing sarcoma from the U.S. Food and Drug Administration. Salarius is also exploring seclidemstat’s potential in several cancers with high unmet medical need, with an investigator-initiated Phase 1/2 clinical trial in hematologic cancers at MD Anderson Cancer Center. Salarius has received financial support from the National Pediatric Cancer Foundation to advance the Ewing program and was a recipient of a Product Development Award from the Cancer Prevention and Research Institute of Texas (CPRIT). SP-3164 is currently in IND-enabling studies and is anticipated to enter the clinic in the second half of 2023. For more information, please visit salariuspharma.com or follow Salarius on Twitter and LinkedIn.

Forward-Looking Statements
This press release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. All statements, other than statements of historical facts, included in this press release are forward-looking statements. These forward-looking statements may be identified by terms such as “will,” “believe,” “developing,” “expect,” “may,” “progress,” “potential,” “plan,” “could,” “look forward,” “encouraging,” “might,” “should,” and similar terms or expressions or the negative thereof. Examples of such statements include, but are not limited to, statements relating to the following: the impact that the addition of new clinical sites will have on the development of Salarius’ product candidates; the timing of Salarius’ IND submissions to the FDA and subsequent timing for initiating clinical trials; interim data related to Salarius’ clinical trials, including the timing of when such data is available and made public; Salarius’ growth strategy; the value of seclidemstat as a treatment for Ewing sarcoma, Ewing-related sarcomas, and other cancers and its ability to improve the life of patients; expanding the scope of Salarius’ research and focus to high unmet need patient populations; milestones of Salarius’ current and future clinical trials, including the timing of data readouts. Salarius may not actually achieve the plans, carry out the intentions or meet the expectations or objectives disclosed in the forward-looking statements. You should not place undue reliance on these forward-looking statements. These statements are subject to risks and uncertainties which could cause actual results and performance to differ materially from those discussed in the forward-looking statements. These risks and uncertainties include, but are not limited to, the following: the sufficiency of Salarius’ capital resources; the ability of, and need for, Salarius to raise additional capital to meet Salarius’ business operational needs and to achieve its business objectives and strategy; future clinical trial results and the impact of such results on Salarius; that the results of studies and clinical trials may not be predictive of future clinical trial results; risks related to the drug development and the regulatory approval process; the competitive landscape and other industry-related risks; and other risks described in Salarius’ filings with the Securities and Exchange Commission, including its Annual Report on Form 10-K for the fiscal year ended December 31, 2022, as revised or supplemented by its Quarterly Reports on Form 10-Q and other documents filed with the SEC. The forward-looking statements contained in this press release speak only as of the date of this press release and are based on management’s assumptions and estimates as of such date. Salarius disclaims any intent or obligation to update these forward-looking statements to reflect events or circumstances that exist after the date on which they were made.

CONTACT:

LHA Investor Relations
Kim Sutton Golodetz
kgolodetz@lhai.com
212-838-3777

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¹ Risk of recurrence and survival after relapse in patients with Ewing sarcoma, Pediatric Blood & Cancer, Volume 57, Issue 4. First published October 2011.