© 2020 Salarius Pharmaceuticals, Inc. 1Q 2020 Company Overview Free Writing Prospectus dated January 29, 2020 Filed Pursuant to Rule 433 of the Securities Act of 1933, as amended Registration Statement No. 333-235879

This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Any statement in this presentation that is not a historical fact is a forward-looking statement. Forward-looking statements are subject to risks and uncertainties that could cause actual results to differ materially and reported results should not be considered as an indication of future performance. Examples of such statements include, but are not limited to: statements relating to the overall ability of epigenetic regulator drugs to correct gene changes in disease, including how modulation of LSD1 may increase responsiveness to checkpoint inhibition; the commercial or market opportunity and expansion for Salarius and each therapeutic option, including the availability and value of a pediatric priority review voucher for in-clinic treatments and potential for accelerated approval; the adequacy of Salarius’ capital to support its future operations and its ability to successfully initiate and complete clinical trials and regulatory submissions; Seclidemstat’s impact in Ewing sarcoma and as a potential new and less-toxic treatment; expected dose escalation and dose expansion; expected cohort readouts; expected therapeutic options for SP-2577 and related effects and projected efficacy, including SP-2577’s ability to inhibit LSD1; the potential for SP-2577 to differentiate itself from competing LSD1-inhibitors; timing of development and future milestones, including for each of SP-2577’s indications; the nature, strategy, focus and vision of Salarius; and the development, expected timeline and commercial potential of any product candidates of Salarius or its competitors. Salarius may not actually achieve the plans, carry out the intentions or meet the expectations, objectives or projections disclosed in the forward-looking statements and you should not place undue reliance on these forward-looking statements. Such statements are based on management’s current expectations and involve risks and uncertainties. Actual results and performance could differ materially from those projected in the forward-looking statements as a result of many factors, including, without limitation: risks and uncertainties associated with the availability of sufficient resources of Salarius to meet its business objectives and operational requirements; the ability to project future cash utilization and reserves needed for contingent future liabilities and business operations; the fact that the results of earlier studies and trials may not be predictive of future clinical trial results; the sufficiency of Salarius’ intellectual property protections; risks related to the drug development and the regulatory approval process; and the impact of competitive products and technological changes. 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. You should review additional disclosures we make in our filings with the Securities and Exchange Commission (“SEC”), including our Current Reports on Form 8-K, Quarterly Reports on Form 10-Q, and Annual Reports on Form 10-K. You may access these documents for no charge at http://www.sec.gov. Safe Harbor Statement

Investing in our securities includes a high degree of risk. You should consider carefully the specific factors discussed below, together with all of the other information contained in our SEC filings, including our Registration Statement on Form S-1 (File No. 333-235879). If any of the following risks actually occurs, our business, financial condition, results of operations and future prospects would likely be materially and adversely affected. This could cause the market price of our securities to decline and could cause you to lose all or part of your investment. Risks include but are not limited to: The approach Salarius is taking to discover and develop novel oncology therapeutics using epigenetic enzymes to moderate transcription factors and thereby control abnormal protein expression is unproven and may never lead to marketable products. Salarius’ therapeutic product candidates are based on a relatively novel technology, which makes it difficult to predict the timing and cost of development and of subsequently obtaining regulatory approval, if at all. Salarius’ product candidates may cause undesirable side effects or have other properties that could delay or prevent their regulatory approval, limit the commercial viability of an approved label, or result in significant negative consequences following marketing approval, if any. Some of Salarius’ product candidates may produce results in pre-clinical or clinical settings for indications other than those for which Salarius contemplates conducting development and seeking FDA approval, and Salarius cannot give any assurance that it will generate data for any of its product candidates sufficient to receive regulatory approval in its planned indications, which will be required before they can be commercialized. Salarius may find it difficult to enroll patients in its clinical trials given the limited number of patients who have the diseases for which its product candidates are being studied. Difficulty in enrolling patients is a common hurdle faced by early stage biotechnology companies and could, and often does, delay or prevent clinical trials of product candidates. Salarius has never generated any revenue from product sales and may never generate revenue or be profitable. Raising additional capital may cause dilution to Salarius’ stockholders, restrict its operations, or require Salarius to relinquish rights. Salarius may seek breakthrough therapy designation by the FDA for one or more of its product candidates, but it might not receive such designation. A potential breakthrough therapy designation by the FDA for Salarius’ product candidates may not lead to a faster development or regulatory review or approval process, and it does not increase the likelihood that Salarius’ product candidates will receive marketing approval. Reliance on government funding for Salarius’ programs may add uncertainty to its research and commercialization efforts with respect to those programs that are tied to such funding and may impose requirements that limit its ability to take specified actions, increase the costs of commercialization and production of product candidates developed under those programs, and subject Salarius to potential financial penalties, which could materially and adversely affect its business, financial condition, and results of operations. Risk Factors

This presentation highlights basic information about us and the offering. Because it is a summary that has been prepared solely for informational purposes, it does not contain all of the information that you should consider before investing in our company. Except as otherwise indicated, this presentation speaks only as of the date hereof. This presentation does not constitute an offer to sell, nor a solicitation of an offer to buy, any securities by any person in any jurisdiction in which it is unlawful for such person to make such an offering or solicitation. Neither the SEC nor any other regulatory body has approved or disapproved of our securities or passed upon the accuracy or adequacy of this presentation. Any representation to the contrary is a criminal offense. This presentation includes industry and market data that we obtained from industry publications and journals, third-party studies and surveys, internal company studies and surveys, and other publicly available information. Industry publications and surveys generally state that the information contained therein has been obtained from sources believed to be reliable. Although we believe the industry and market data to be reliable as of the date of this presentation, this information could prove to be inaccurate. Industry and market data could be wrong because of the method by which sources obtained their data and because information cannot always be verified with complete certainty due to the limits on the availability and reliability of raw data, the voluntary nature of the data gathering process and other limitations and uncertainties. In addition, we do not know all of the assumptions that were used in preparing the forecasts from the sources relied upon or cited herein. We have filed a Registration Statement on Form S-1 with the SEC, including a preliminary prospectus dated January 28, 2020 (the “Preliminary Prospectus”), with respect to the offering of our securities to which this communication relates. Before you invest, you should read the Preliminary Prospectus (including the risk factors described therein) and, when available, the final prospectus relating to the offering, and the other documents filed with the SEC and incorporated by reference into the Preliminary Prospectus, for more complete information about us and the offering. You may obtain these documents, including the Preliminary Prospectus, for free by visiting EDGAR on the SEC website at http://www.sec.gov. Alternatively, we or any underwriter participating in the offering will arrange to send you the prospectus if you request it by contacting Ladenburg Thalmann & Co. Inc., Attn: Syndicate Department, 277 Park Avenue, 26th Floor, New York, NY 10172 or by email at prospectus@ladenburg.com. Free Writing Prospectus

Salarius is a Cancer Focused Biotechnology Company Developing Treatments for Patients Who Need Them The Most Drugs that regulate gene expression (“epigenetics”) have shown clinical efficacy plus immuno-oncology potential Non-Dilutive funding supports low monthly burn rate Up to $18.7M from Cancer Prevention Research Institute of Texas (CPRIT) Financial support from the National Pediatric Cancer Foundation Seclidemstat is a novel, oral, reversible LSD1 inhibitor that regulates gene expression and is currently in Phase 1/2 Ewing sarcoma and Phase 1/2 solid tumor clinical trials Seclidemstat FDA designations for Ewing sarcoma: (1) Rare Pediatric Disease Designation, (2) Orphan Drug Designation, and (3) Fast Track Approval Market expansion with immunotherapy (checkpoint inhibitor combos) and targeted cancers with LSD1 sensitive mutations $

Upcoming Development Milestones * * * * * Value inflection points

Seasoned Leadership Team Board of Directors Mark Rosenblum Chief Financial Officer David J. Arthur Chief Executive Officer Scott Jordan Chief Business Officer Margaret Dugan, MD Senior Medical Advisor Bruce McCreedy, PhD Acting Chief Scientific Officer Daniela Y Santiesteban, PhD Director of Research and BD John Walling, PhD VP Chemistry, Manufacturing & Control David Arthur, MBA Salarius Pharmaceuticals Jonathan Northrup, MBA Stingray Therapeutics Eli Lilly Tess Burleson, CPA Translational Genomics Research Institute Paul Lammers, MD MSc Triumvira Immunologics Merck Serono Bruce McCreedy, PhD Precision BioSciences Triangle Pharmaceuticals William McVicar, PhD Flex Pharma Sepracor Novartis Arnold Hanish, CPA Omeros Corporation Eli Lilly riangle Pharmaceuticals

Indication Preclinical Phase 1 Phase 2 Status Ewing Sarcoma Phase 1/Phase 2 enrolling up to 50 patients Safety and efficacy data in 2020 Advanced Solid Tumors Phase 1/Phase 2 enrolling up to 50 patients Safety and efficacy data in 2020 Immunotherapy Identifying checkpoint combinations for clinical trials Development Pipeline 1. Expanded Phase 2 in Ewing sarcoma could potentially be a registration study with improvements in response or duration of response compared to the existing standard of care and FDA’s agreement 2. Open to all non-Ewing sarcoma solid tumor patients except for primary CNS tumors, enriching patients with sensitive mutations and prostate cancer that can be monitored with prostate stimulated antigen (PSA) Seclidemstat Dose Escalation and Expansion Dose Escalation and Expansion In vitro and In vivo studies ongoing Identifying opportunities in hematological cancers and select tumor mutations 1 2

Seclidemstat Overview

Modulation of Gene Expression (Epigenetics) Plays an Important Role in Regulating Healthy Cells and also Disease Progression DNA transcription translation RNA RNA Correct Gene Expression = Healthy Balance of Proteins = Healthy Cells Incorrect Gene Expression = Imbalance of Proteins = Cancer Progression transcription translation

Cancers driven by incorrect modulation of gene expression can be treated with drugs – like Seclidemstat, an LSD1 inhibitor- that corrects abnormal epigenetic enzyme activity and restores correct gene expression Tumor suppressors correctly expressed Targeting Epigenetic Enzymes to Treat Cancer Addresses Dysregulation and Incorrect Gene Expression Cell cycle, differentiation proteins* correctly expressed + Epigenetic drugs e.g., Seclidemstat *oncoproteins

Epigenetic Research is Gaining Momentum and Epigenetic Focused Biotechs are Increasing in Valuation Novel epigenetic drugs with clinical proof of concept support billion-dollar valuations Other clinical companies include: GSK, Zenith Epigenetics, Resverlogix, 4SC, Viracta, Syndax EZH2 inhibitor (tazemetostat) Approved in epithelioid sarcoma – monotherapy NDA submitted for follicular lymphoma – monotherapy Market Cap: ~$2.1B1 BET inhibitor (CPI-0610) Positive Phase 2 data in combination with existing standard of care in myelofibrosis Market Cap: ~$1.4B1 PubMed (NASDAQ: EPZM) (NASDAQ: CNST) 1 As of 01/28/2020

LSD1 - A Validated Target For Cancer Therapy Lysine Specific Demethylase 1 (LSD1) is an epigenetic target for solid tumors and hematological cancers Affects gene expression through enzymatic activity and scaffolding properties (protein-protein interactions) 1Majello,B. Cancers 2019. LSD1 in Healthy Cells and Cancer Cells1 Healthy Cells LSD1 is necessary for stem cell maintenance and cell development processes (e.g., blood cells) Cancer Cells LSD1 is over expressed LSD1 acts incorrectly to silence or activate genes leading to disease progression Validated target: LSD1 CRISPR deletion often kills cancerous cells Seclidemstat (SP-2577) reversible LSD1 inhibitor Reverses incorrect gene expression, killing or preventing the growth of cancer cells Inhibits both the enzymatic and scaffolding activity Oral tablet Strong patent estate – Composition of matter expires 2032 Companies developing LSD1 inhibitors in clinic (Phase 1 or 2):

More Comprehensive Inhibition of LSD1 Positively Impacts Therapeutic Activity Enzymatic activity – Demethylation Impact: Moderately alter gene expression Partial scaffolding* inhibition of LSD1 – protein interaction Impact: alter gene expression in cancers (AML, SCLC) driven by SNAG domain proteins (e.g. GFI1B) Broader scaffolding inhibition of LSD1 – protein interaction Impact: Potential efficacy in broader range of cancer types, destabilize LSD1 and complexes Favorable Toxicology Profile Differential activity and competitors Reduces LSD1 expression and competitors OFF SNAG domain Degree of LSD1 inhibition *scaffolding properties – protein to protein interactions

SPEED TO MARKET Seclidemstat in Ewing Sarcoma

Ewing Sarcoma - Unmet Need Represents a Meaningful Product Opportunity 500 patients diagnosed each year1 Median age of diagnosis ~15 years 75% localized 25% with metastasis About 40% of patients are refractory or relapse2 70-90% 5-year mortality rate2 No standardized 2nd line treatment Diagnosis Standard of Care Salarius’ Vision An effective, non-toxic, oral treatment option: Accelerated US approval Rapid market uptake $200M+ Global Sales3 (est) Possible Priority Review Voucher of $80M - $150M Fast Track Designation Rare Pediatric Drug Designation 2 Van Mater, et al. Oncotargets (2019) 1 Pishas, K. et al. (2016) Orphan Drug Designation Surgery and Amputations Chemo Radiation 3 Represents longer term vision and does not represent estimate of future performance, financial or otherwise. There is no assurance that we will achieve our longer term vision.

Ewing sarcoma is driven by an easily diagnosed chromosomal translocation, i.e., EWS-FLI Sankar et al. Clinical cancer research 20.17 (2014) Oncogenes (Tumor growth) Co-Activator LSD1 Tumor Suppressors NuRD LSD1 Incorrect transcription factor leads to gene dysregulation Targeting The Root Cause Of Ewing Sarcoma Via LSD1 Inhibition Ewing’s cells (A673) Tumor Growth Tumor Suppressive Vehicle Control sh-RNA Seclidemstat analog EWS-FLI sh-RNA Genes correctly turned on/off Seclidemstat corrects gene expression Red = turned ON Blue = turned OFF Potent anti-tumor activity in SKNMC (Ewing sarcoma cells) in vivo studies Tumor volume Tumor volume RES 004 Salarius RES 006 Salarius *p<0.0003 * Seclidemstat targets this interaction

Ewing Sarcoma Phase 1/2: Safety and Efficacy Data in 2020 Open-label dose escalation / dose expansion trial design Dose escalation (ongoing) Dose escalation in cohort 6 Maximum Tolerated Dose (MTD) expected in 1H2020 Dose expansion (after MTD is established) ~20 patients at MTD Safety and early efficacy data in 2H2020 Primary objective: Safety, PK Secondary objectives: Anti-tumor assessment Exploratory: Hemoglobin F, cfDNA, CTCs Plasma PK is dose proportional Targeting ASCO 2020 for trial update

MARKET EXPANSION Seclidemstat in Advanced Solid Tumors Select Tumor Mutations Immunotherapy

LSD1 Overexpression Increases With Disease Progression And Correlates With Poor Patient Prognosis – Seclidemstat Reduces LSD1 Activity Low LSD1 High Survival High LSD1 Low Survival Nagasawa, S. et al (2015) Low LSD1 High Survival High LSD1 Low Survival Kashyap, V., et al. (2013). Castration Resistant Prostate Cancer Triple Negative Breast Cancer (TNBC) Percent Survival 1 Sehrawat, A. et. al., 2018 Increased LSD1 expression correlates with solid tumor progression High LSD1 expression in ~30% of primary prostate tumors, but >90% of advanced castration resistant prostate cancer1 LSD1 expression associated with shorter survival in Triple Negative Breast cancer Ongoing Phase 1 Advanced Solid Tumor Study sites: Honor Health, Phoenix AZ and Sarcoma Oncology Center, Santa Monica CA

Increasing Probability Of Success Via Identification Of Sensitizing Mutations Genetic screens (e.g., Foundation Medicine) can help identify patients with an increased chance of response to seclidemstat Patients with an increased chance of response to seclidemstat

Exploring Additional Opportunities: LSD1 Inhibition Turns Cold Tumors Hot And Increases Efficacy Of Checkpoint Inhibitors Sensitizing cancers resistant to checkpoint inhibitors (CI) increases patients available for treatment ~$15B CI market1 with ~70% patients2 resistant to CI treatment (cold tumors) LSD1 inhibition turns cold tumors hot by increasing CD8+ effector T cells within the tumor Expands CI market into patients currently resistant to CI treatment Cold tumor Minimal or no response to checkpoint inhibition LSD1 inhibition Hot tumor Increased response to checkpoint inhibition Many CD8+ effector T cells Few CD8+ effector T cells 1. GlobalData 2. Seliger, B. Front in Immun (2019)

LSD1 Inhibition Sensitizes Triple Negative Breast Cancer to Checkpoint Blockade in vivo LSD1 inhibition (Seclidemstat analog) drives increased immune cell infiltration, and sensitizes resistant tumors to checkpoint inhibition “Cold” tumors turn “Hot” and then respond to checkpoint inhibition Increased response by ~65% Qin, Ye, et al. Oncogene (2018). Vehicle Isotype (IgG) PD-1 mAb Seclidemstat analog + PD-1 mAb Days post-tumor inoculation Tumor volume (mm3) Syngeneic Breast Tumor Model (EMT-6) Seclidemstat analog *p < 0.05, **p < 0.01, and ***p < 0.001

Combination of Possibilities Presents Significant Market Opportunity for Seclidemstat Orphan Drug Status Rare Pediatric Disease Designation (Priority Review Voucher) Fast Track Designation Potential for accelerated approval, priority review Possible Pediatric Priority Review Voucher (est) $80M-$150M $200M+ Global Sales per year (est)1 Status: Phase 1/2 clinical trial Market Potential in Solid Tumors 2,3,4,5,6 $1B+ EXPANDING INTO LARGER MARKETS ADVANCED SOLID TUMORS Status: Phase 1 clinical trial SPEED TO MARKET Ongoing work to identify SELECT TUMOR MUTATIONS that may increase patient response to LSD1 inhibition (e.g. SWI/SNF) Sensitizing resistant cancers to checkpoint Inhibitors Status: Preclinical Market Potential7 $1B+ Citations in Appendix A Ewing Sarcoma 500 patients diagnosed/year POTENTIAL TO ENTER INTO IMMUNOTHERAPY About 25% of solid tumors (e.g., breast, ovarian, prostate, lung) have mutations in that may sensitize to seclidemstat6

COMPETITIVE LANDSCAPE Seclidemstat’s differentiation

Company Drug Name Binding Mechanism Binding Mechanism Indications and Phase SP-2577 (Seclidemstat) Reversible Reversible Ewing sarcoma (Ph1/2), Advanced Solid Tumors (Ph1/2) INCB59872 Irreversible Irreversible Advanced malignancies (AML, SCLC) (Ph1/2), Ewing sarcoma (Ph1b) ORY-1001 (RG6016) Irreversible Irreversible AML (Ph2b), SCLC (Ph2a) CC-90011 Reversible Reversible Non-Hodgkin’s lymphoma and AST (Ph1), SCLC (Ph1) IMG-7289 Irreversible Irreversible AML and myelodysplastic syndrome (Ph1/2a completed), myelofibrosis (Ph2b) BEA-17 Reversible Glioblastoma RASP-201 Reversible AML HM9XXX series Reversible AML and SCLC LSD1 Competitive Landscape Highlights Seclidemstat’s Differentiation 2Not an exhaustive list of companies in preclinical stage In clinic1 Preclinic2 1Clinicaltrials.gov Seclidemstat’s differentiated binding mechanism and binding location shows potential increased therapeutic activity and safety* Preclinical research is shifting to develop reversible LSD1 inhibitors *Being studied in our ongoing Phase 1 trials

Financial Position & Capitalization

Financial Position & Capitalization Capitalization as of January 2, 2020 Common Shares Outstanding 4,511,174 Warrants (weighted average exercise price $16.03) 185,639 Options (weighted average exercise price $36.11) 156,233 RSUs 8,361 Fully Diluted Shares 4,861,407 Cash & Cash Equivalents: $3.7M as of Dec 31, 2019

Salarius Investment Opportunity: An Early- Clinical Stage Focused Biotech With Several Value-driving Inflection Points Occurring In 2020 Lead compound is in the growing epigenetic therapy space Extensive non-dilutive funding supports low quarterly burn rate Recipient of FDA designations that facilitates rapid product development Readouts from two ongoing clinical trials is expected to include safety, pharmacokinetic, and early efficacy data (value inflection points) Up to $18.7M from CPRIT Financial support from NPCF Orphan Drug Designation Rare Pediatric Disease Designation Fast Track Designation Salarius has worked to establish itself for a newsworthy 2020: Attractive price for investors interested in this growing therapeutic area

© 2020 Salarius Pharmaceuticals, Inc. Thank you!

Appendix A: Additional Sources Combination of Possibilities Presents Significant Market Opportunity for Seclidemstat 1 Represents longer term vision and does not represent estimate of future performance, financial or otherwise. There is no assurance that we will achieve our longer term vision. 2 Cancer of the Ovary – Cancer Stat Facts, The National Cancer Institute: Surveillance, Epidemiology and End Results Program https://seer.cancer.gov/statfacts/html/ovary.html. 3 GlobalData: Prostate Cancer: Global Drug Forecast and Market Analysis to 2028 4 GlobalData and Epidemiology Market Size Database, TNBC 5 GlobalData: Opportunity Analyzer: Ovarian Cancer - Opportunity Analysis and Forecast to 2025 6 Morel, D., et al. Ann of Oncology 2017 7 https://www.forbes.com/sites/greatspeculations/2019/03/12/how-much-can-mercks-share-price-grow-if-keytruda-gets-10-share-of-oncology-drug-market/#77edba677e18

Exploring Additional Opportunities: Personalized Medicine via Identification of Sensitizing Mutations SENSITIZING TUMOR MUTATIONS Certain mutations in chromatin modifying proteins (e.g. UTX, TET2, SWI/SNF) can show increased sensitivity to LSD1 inhibition Up to ~25% of solid tumors have mutations in chromatin modifying proteins1 Cancer cells with a mutation may become more dependent on LSD1 activity à more susceptible to LSD1 inhibition E.g. UTX mutation depicted below2 2.We et al, Sig Trans (2019) 1. Morel, D. Ann of Onc (2017) Non-functional UTX enzyme (mutation) incorrectly alters gene expression Treatment with Seclidemstat analog inhibits LSD1 and restores correct gene expression in UTX mutated cell lines

Cancers with Specific Mutations Show Greater Sensitization to Checkpoint Inhibitors Following Treatment with Seclidemstat Mutations in the SWI/SNF complex are present in more than 20% of cancers.1 They may include: SMARCA4, ARID1A, and SMARCB4 SWI/SNF complex mutations sensitize to LSD1 immunomodulatory effects, turning cold tumor organoids hot. Selecting more patients with SWI/SNF mutations would identify a target population with increased sensitivity to Seclidemstat and checkpoint inhibitor combination Seclidemstat Inactive Analog DMSO Soldi, R. et al. bioRxiv. 2020 COLD tumor: not responsive to checkpoint inhibitor HOT tumor: responsive to checkpoint inhibitor 1. Kadoch, C et al. Human Cancer 2015 Ovarian Cancer Cell Line

Seclidemstat increases sensitization to CTLA-4 antibody CT26 syngeneic colon cancer mouse model – unresponsive to CTLA-4 inhibition Seclidemstat significantly increased response to anti-CTLA-4 checkpoint inhibitor Potential for combining Seclidemstat with both PD-1 and/or CTLA-4 inhibitors SP-2577 (50 mg/kg; BID, IP) CTLA-4 (10 mg/kg; IP, twice a week) Sharma, S. et al., not published

LSD1 as a validated target LSD1 is an essential gene for survival of both developing embryonic cells and cancer cells, implicating LSD1 as a viable pharmacological target for cancer therapy. Jin, Y. et al. BBRC. 2019 LSD1 CRISPR-suppressor scanning in AML results in cell death LSD1 CRISPR knockout Small Cell Lung Cancer Cells demonstrate reduced cell viability If the protein target is essential for cell growth, cells harboring frameshift indels will drop out from the population due to knockout of the essential target protein. Vineyard, M. et al. Cell 2019 Majority of sgRNAs result in cell depletion

Seclidemstat Is A Selective and Differentiated LSD1 Inhibitor Cerep Safety Screen 87 indicates minimal off-target binding Romo‐Morales, Antonio, et al.  Pediatric Blood & Cancer: 2019 Selective Differentiated Minimal activity against other epigenetic enzymes; BRDs, methyltransferases, HDACs Salarius PHARM 013 Salarius PHARM 002, 003, 009 and 011 SP-2577 TCP MAO-A MAO-B SP-2577 LSD1 IC50 Salarius PHARM 003, 010

Seclidemstat’s Differentiated MOA Disrupts Additional LSD1 Scaffolding Functions SNAG domain Catalytic inhibitors disrupt SNAG domain binding SNAG domain containing Transcription Factors: GFI1(B), SNAIL1/2/3, SCRATCH1, ISMI-1, OCOL-1 Competitors have only demonstrated inhibition of LSD1 scaffolding function when associations occur in the catalytic site (via SNAG domain): In addition to inhibiting association with SNAG domain transcription factors, Seclidemstat and its analog show differential inhibition of LSD1 association with: ZNF-217 (Sehrawat, A. et al 2018) Androgen Receptor (Salarius RS-00257) CoREST (Fiskus, W. et al, 2014) Additional coregulators studies are ongoing Vineyard, M. et al. Cell 2019. Click for Differentiation Slide AR Saccà, C.D., et al. Can Met. 2019.

Augert, A. et al., Sci Signal. (2019) Irreversible LSD1 Inhibitors Show Minimal Activity Outside Of SCLC And Hematological Cancers Irreversible inhibitors works well in a subset of AML and SCLC (reason for clinical focus in these indications) Oryzon is currently conducting clinical trials in AML and SCLC1 Differential MOA grants Seclidemstat potency across various cancer cell lines Drug concentration (nM)

Seclidemstat And Its Analog Demonstrate Single Agent Activity Across A Range Of Solid Tumors Cao, Chunyu, et al.  International journal of cancer (2018) Seclidemstat analog showed ~50% single agent activity, and synergy with an HDAC inhibitor in MDAMB231 mouse model Triple Negative Breast Cancer (TNBC) Seclidemstat analog + HDAC Inh. Seclidemstat analog Tumor Volume (mm3) p<0.05 *, p<0.01 **, p<0.001 ***. Seclidemstat or its analog have shown tumor growth inhibition (TGI) across a range of preclinical solid tumor models: Animal model (cells)* TGI TNBC (MDAMB231) [see graph] 50% TNBC (EMT6) 40% Prostate (22rv1) 30% Prostate (PC3) 50% Clear cell sarcoma 90% Lung cancer 25% Uterine serous carcinoma 45% Clear cell bladder cancer 50% We are attempting to enrich for these types of patients in our ongoing AST trial * Select list of preclinical studies

Date Voucher Awarded Company Voucher Held or Sold Status 2014 BioMarin Sold July 2014 to Sanofi $67M Redeemed 2015 United Therapeutics Sold August 2015 to AbbVie $350M Redeemed 2015 Asklepion Pharmaceutics Transferred to Retrophon and Sold May 2015 to Sanofi $245M Redeemed 2015 Wellstat Therapeutics Transferred to AstraZeneca Unused 2015 Alexion Pharmaceuticals Held Redeemed 2015 Alexion Pharmaceuticals Held Unused 2016 Sarepta Therapeutics Sold February 2017 to Gilead for $125M Redeemed 2016 Ionis Pharmaceuticals Held Unused 2017 Marathon Pharmaceuticals Held Unused 2017 BioMarin Sold November 2017 for $125M Unused 2017 Novartis Held Redeemed 2017 Ultragenyx Pharmaceutical Sold December 2017 to Novartis $130M Redeemed 2017 Spark Therapeutics Sold April 2018 to Jazz $110M Unused 2018 Ultragenyx Sold July 2018 for $81M Unused 2018 GW Pharma Sold March 2019 to Biohaven for $105M Unused 2018 Leadiant Bioscience Inc. Held Unused 2018 Sobi and Novimmune Sold August 2019 to Astra Zeneca for $95M Unused 2019 Vertex Held Unused 2019 Alexion Held Unused 2019 Novartis Held Unused Seclidemstat Is Eligible To Receive A Pediatric Priority Review Voucher (PRV) Upon Ewing Approval, $80-150M Value https://www.raps.org/regulatory-focus/news-articles/2017/12/regulatory-explainer-everything-you-need-to-know-about-fdas-priority-review-vouchers Average PRV value: $144M Median PRV value: $118M