SPRO Spero Therapeutics Inc

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Exhibit 99.1

Spero Therapeutics Announces SPR720 Phase 2a Interim Results and Provides a Business Update

Phase 2a proof-of-concept study of SPR720 for the treatment of Nontuberculous Mycobacterial Pulmonary Disease (NTM-PD) did not meet its primary endpoint, based on planned interim analysis of 16 patients

Phase 3 PIVOT-PO trial of tebipenem HBr remains on track for enrollment completion in 2H 2025

Cash runway extended into mid-2026 following a reduction in workforce and restructuring of operations; Unaudited Q3 2024 ending cash balance of $76.3M

CAMBRIDGE, Mass., October 29, 2024 — Spero Therapeutics, Inc. (Nasdaq: SPRO), a multi-asset clinical-stage biopharmaceutical company, focused on identifying and developing novel treatments for rare diseases and multi-drug resistant (MDR) bacterial infections, today announced that a planned interim analysis of the Phase 2a proof-of-concept study of SPR720 for the treatment of NTM-PD demonstrated that the program did not meet its primary endpoint. While the data showed antimicrobial activity associated with SPR720, the interim analysis did not show sufficient separation from placebo and highlighted potential dose limiting safety issues in subjects dosed at 1,000 mg orally once daily, including three cases of reversible grade 3 hepatotoxicity. In evaluating the totality of both the efficacy and safety data, the Company has elected to suspend its current development program for SPR720 and will evaluate other potential paths forward as the remaining data are collected and analyzed.

As a result of the suspension of the current SPR720 development program, Spero will undergo a restructuring and reduction in force of approximately 39%, which will extend cash runway and support operations into mid-2026, to further support the development of tebipenem HBr, SPR206, and potential strategic activities.

“Spero launched its proof-of-concept clinical study for SPR720 as a monotherapy to evaluate its potential efficacy and safety in treating NTM-PD. While a planned interim analysis provided evidence of antimicrobial activity, the trial unfortunately did not meet the primary endpoint,” said Sath Shukla, Spero’s President and Chief Executive Officer. “We are therefore suspending development of the SPR720 program and making adjustments to our organization accordingly. I want to offer my sincere thanks to all our Spero SPR720 colleagues, along with our investigators and patients, for their dedication in seeking new treatment options for this devastating disease. We remain committed to bringing forward new treatment options for patients in need, as we continue to advance our tebipenem HBr and SPR206 programs.”

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Restructuring to Prioritize Programs and Capital Allocation

Spero closed the third quarter ended September 30, 2024, with an unaudited cash estimate of $76.3 million. Following the reduction in force and restructuring, Spero estimates that its existing cash and cash equivalents, together with earned and non-contingent development milestone payments from GSK, as well as other non-dilutive funding commitments, will be sufficient to fund its operating expenses and capital expenditures into mid-2026. During this period, the Company remains focused on advancing tebipenem HBr in the ongoing global PIVOT-PO Phase 3 clinical trial and preparing for a Phase 2 clinical trial for SPR206 contingent on continued non-dilutive funding.

SPR720

SPR720 is an oral, chemically stable phosphate ester prodrug that is converted rapidly in vivo to SPR719, the active moiety. SPR719 targets the ATPase site of DNA gyrase B in mycobacteria, a mechanism that is distinct from that of other antibiotics in use for Non Tuberculous Mycobacterial-Pulmonary Disease (NTM-PD).

Recent updates:

 

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Phase 2a trial – enrollment concluded in July 2024, with 25 non-refractory patients enrolled in the proof-of-concept trial evaluating SPR720 in NTM-PD. A planned interim analysis based on 16 patients indicated the trial did not meet its primary endpoint of differentiation from placebo in the rate of change in log10 colony forming units per milliliter (CFU/mL). In addition, analysis of the full 25 patient safety data highlighted potential dose limiting safety issues in patients dosed at 1,000mg orally once daily, including three cases of reversible grade 3 hepatotoxicity. The Company plans to complete data analysis of all enrolled patients (n=25) and determine the next steps for the SPR720 program over the next several months. For more information on the trial, see ClinicalTrials.gov identifier NCT05496374.

Tebipenem HBr

Tebipenem HBr is an investigational oral carbapenem antibiotic being developed for the treatment of cUTI including acute pyelonephritis (AP) to help patients avoid hospitalizations or reduce duration of in-patient therapy. Spero granted GSK an exclusive license to commercialize tebipenem HBr in all territories, except certain Asian territories. Spero received $66 million upfront from GSK when the license agreement was signed in 2022, $30 million when the Company reached the Special Protocol Assessment milestone in Q3 2023, and was entitled to receive $95 million in development milestones upon enrollment of the first patient in the PIVOT-PO Phase 3 trial, $47.5 million of which have been received thus far. Spero is further eligible to receive up to $400 million in development, sales, and commercial milestones payments, as well as low single-digit to low double-digit tiered royalties on net product sales.

 

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Enrollment on track in PIVOT-PO, the global Phase 3 clinical trial of tebipenem HBr in patients with cUTI. This randomized, double-blinded trial compares oral tebipenem HBr with intravenous imipenem cilastatin, in hospitalized adult patients with cUTI/AP. The primary endpoint is overall response (a combination of clinical cure and favorable microbiological response) at the Test-of-Cure (TOC) visit. Target enrollment for the trial is approximately 2,648 patients, with enrollment completion expected in the second half of 2025. For more information on PIVOT-PO, refer to ClinicalTrials.gov ID NCT06059846.

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SPR206

SPR206 is an investigational, intravenously administered next-generation polymyxin that has shown antibiotic activity against MDR Gram-negative pathogens, including carbapenem-resistant Enterobacterales, Acinetobacter baumannii and Pseudomonas aeruginosa in preclinical studies.

 

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The U.S. Food and Drug Administration (FDA) cleared the Company’s IND for a Phase 2 trial in participants with hospital-acquired or ventilator-associated bacterial pneumonia (HABP/VABP). The Company maintains its guidance to initiate the trial, contingent on availability of non-dilutive funding.

About Spero Therapeutics

Spero Therapeutics, headquartered in Cambridge, Massachusetts, is a multi-asset clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and MDR bacterial infections with high unmet need. For more information, visit www.sperotherapeutics.com

Forward Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including, without limitation, the timing, progress and results of the Company’s preclinical studies, clinical trials and research and development programs; management’s assessment of the results of such preclinical studies and clinical trials; and the expected cost-savings from the Company’s reduction in workforce and restructuring of its operations, the Company’s anticipated expenses and its anticipated cash runway . In some cases, forward-looking statements may be identified by terms such as “may,” “will,” “should,” “expect,” “plan,” “aim,” “anticipate,” “could,” “intent,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue,” the negative of these terms or other similar expressions. Any forward-looking statements in this press release are based on management’s current expectations and beliefs and are subject to a number of important risks, uncertainties and other factors that may cause actual results to differ materially from those indicated by such forward looking statements, including whether tebipenem HBr, SPR720 and SPR206 will advance through the clinical trial process on a timely basis, or at all, taking into account the effects of possible regulatory delays, slower than anticipated patient enrollment, manufacturing challenges, clinical trial design and clinical outcomes; whether the results of such trials will warrant submission for approval from the FDA or equivalent foreign regulatory agencies; whether the FDA will ultimately approve tebipenem HBr and, if so, the timing of any such approval; whether the FDA will require any additional clinical data or place labeling restrictions on the use of tebipenem HBr that would delay approval and/or reduce the commercial prospects of tebipenem HBr; whether a successful commercial launch can be achieved and market acceptance of tebipenem HBr can be established; whether results obtained in preclinical studies and clinical trials will be indicative of results obtained in future clinical trials; Spero’s reliance on third parties to manufacture, develop, and commercialize its product candidates, if approved; Spero’s need for additional funding; the ability to commercialize Spero’s product candidates, if approved; Spero’s ability to

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retain key personnel; Spero’s leadership transitions; whether Spero’s cash resources will be sufficient to fund its continuing operations for the periods and/or trials anticipated; and other factors discussed in the “Risk Factors” set forth in filings that Spero periodically makes with the SEC. The forward-looking statements included in this press release represent Spero’s views only as of the date hereof and should not be relied upon as representing its views as of any subsequent date. Except as required by law, Spero explicitly disclaims any obligation to update any forward-looking statements.

Investor Relations Contact:

Shai Biran, PhD

Spero Therapeutics

IR@Sperotherapeutics.com

Media Inquiries:

media@sperotherapeutics.com

Corporate Presentation October 2024 Exhibit 99.2

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Forward-looking Statement This presentation contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995 regarding, among other things, the future development and commercialization of SPR720 and SPR206; the potential number of patients who could be treated by SPR 720 and tebipenem HBr and market demand for SPR720 and tebipenem HBr  generally; the potential regulatory path forward for tebipenem HBr, the potential approval of tebipenem HBr by the U.S. Food and Drug Administration (FDA) and the timing thereof; the potential commercialization of tebipenem HBr and its future value, the potential receipt of milestone payments and royalties on future sales of tebipenem HBr under the GlaxoSmithKline Intellectual Property (No. 3) Limited (GSK) license agreement; the effectiveness of tebipenem HBr and its potential impact on healthcare resource utilizations; the anticipated shift in treating patients from intravenous to oral administration; the initiation, timing, progress and results of the Company’s preclinical studies and clinical trials and its research and development programs, including management’s assessment of such results; the timing of the availability of data from the Company’s clinical trials; the timing of the Company’s filings with regulatory agencies; product candidate benefits; competitive position; business strategies; potential growth opportunities; potential market size; projected costs and the availability of additional non-dilutive funding from governmental agencies beyond any initially funded awards. In some cases, forward-looking statements can be identified by terms such as “may,” “will,” “should,” “expect,” “plan,” “aim,” “anticipate,” “could,” “intent,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions. All statements other than statements of historical facts contained in this presentation are forward-looking statements. The Company may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various factors, including whether the FDA will ultimately approve tebipenem HBr and, if so, the timing of any such approval; whether the FDA will require any additional clinical data or place labeling restrictions on the use of tebipenem HBr that would add costs for the Company, delay approval and/or reduce the commercial prospects of tebipenem HBr; the Company’s need for additional funding; the lengthy, expensive, and uncertain process of clinical drug development; the Company’s reliance on third parties to manufacture, develop, and commercialize its product candidates, if approved; the ability to develop and commercialize the Company’s product candidates, if approved; the Company’s ability to retain key personnel; whether results obtained in preclinical studies and clinical trials will be indicative of results obtained in future clinical trials and whether preliminary data from the Company’s clinical trials will be predictive of final results from such trials; the Company’s dependence on raising capital and whether the Company’s product candidates will advance through the preclinical development and clinical trial process on a timely basis, or at all, taking into account such factors as the effects of possible regulatory delays, slower than anticipated patient enrollment, manufacturing challenges, clinical trial design, clinical data requirements and clinical outcomes; whether the results of such clinical trials will warrant submission for approval from the FDA or equivalent foreign regulatory agencies; decisions made by the FDA and equivalent foreign regulatory agencies with respect to the development and commercialization of the Company’s product candidates; the commercial potential of the Company’s product candidates; the Company’s ability to obtain adequate third-party reimbursement for its product candidates; whether the Company will satisfy all of the pre-conditions to receipt of the milestone payments under its various license and collaboration agreements; the Company’s ability to implement its strategic plans; the Company’s ability to obtain, maintain and enforce intellectual property and other proprietary rights for its product candidates; the risks and uncertainties related to market conditions; whether the Company’s cash resources will be sufficient to fund its continuing operations for the periods and/or trials anticipated; and other factors discussed in the “Risk Factors” section of the Company’s periodic reports filed with the U.S. Securities and Exchange Commission (SEC), and risks described in other filings the Company may make with the SEC in the future. The forward-looking statements included in this presentation represent the Company’s views as of the date of this presentation. The Company anticipates that subsequent events and developments will cause its views to change. However, while the Company may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing the Company’s views as of any date subsequent to the date of this presentation.

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Indications with high unmet need in addressable patient populations  Orphan drug and/or QIDP designations Strong global intellectual property  Late-stage development pipeline  Diversified clinical stage portfolio Developing Therapies for Rare and Multi-drug Resistant Infectious Diseases QIDP: qualified infectious disease product Cash runway into mid-2026 enables delivery of key milestones Commercial partnerships could provide significant upside Strong financial foundation

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Asset Indication Preclinical Phase 1 Phase 2 Phase 3 Anticipated Milestone Partnered Assets Tebipenem HBr cUTI Complete Enrollment (2H 2025) SPR206 HABP/VABP Initiate Phase 21 Wholly Owned SPR720 First-line NTM-PD Program suspended2 Maturing Pipeline with Differentiated Clinical Assets Non-dilutive Funding Alliances Worldwide Rights (ex. Asia) Spero Retains Rights in United States China OUS, ex. China NTM-PD: non-tuberculous mycobacterial pulmonary disease; cUTI: complicated urinary tract infection; HABP: hospital-acquired bacterial pneumonia; VABP: ventilator-associated bacterial pneumonia 1.Contingent on non-dilutive funding. 2. The company has elected to suspend its current development program for SPR720.

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Tebipenem HBr Oral Carbapenem

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cUTI Patients Often Cycle through Multiple Therapies  Lack of effective oral treatment options has resulted in increased – Outpatient visits Emergency department visits Unwarranted outpatient IV use Unnecessary hospitalizations Hospital days Home health and long-term care stays post-hospitalization IV: intravenous; tebipenem HBr: tebipenem pivoxil hydrobromide (formerly SPR994); UTI: urinary tract infection 1. GSK Epidemiology data - fy-2023-epidemiology-report.xlsx (live.com) Annual cUTI treatment episodes estimated to be 3.4M1 Tebipenem, in development to offer an oral alternative to cUTI patients All translating to patient suffering and high financial burden

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Tebipenem HBr: Potential to Reduce Treatment Burden for cUTI Patients Potential first-to-market oral carbapenem Phase 3 enrolling Global commercial partnership Potential treatment of complicated UTI in outpatient setting vs current hospitalized setting Expand prescriber base beyond infectious disease specialists Robust IP through 2038 QIDP designation PIVOT-PO trial protocol approved under FDA Special Protocol Assessment (SPA) Enrollment began with first patient dosed in Q4 2023 Global trial with centers in the North and South America, Europe, Africa, and Asia Out-licensed global commercial rights (except Japan and certain other Asian countries) to GSK Robust financial terms including developmental, regulatory, and commercial milestones, as well as tiered sales royalties IP: intellectual property; tebipenem HBr: tebipenem pivoxil hydrobromide (formerly SPR994); QIDP: qualified infectious disease product; SPA: Special Protocol Assessment (by FDA); UTI: urinary tract infection

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Phase 3 Clinical Trial PIVOT-PO: Pivotal Design Entered FDA Special Protocol Assessment Agreement (SPA): The FDA has indicated that positive and persuasive results from PIVOT-PO, along with previously completed studies, could be sufficient to support approval of tebipenem HBr as a treatment for cUTI, including pyelonephritis, for a limited use indication AP: acute pyelonephritis; cUTI: complicated urinary tract infection; NI: non-inferiority; TBP-PI-HBr/tebipenem HBr: tebipenem pivoxil hydrobromide (formerly SPR994) Study Tebipenem HBr (NCT06059846): Phase 3 Clinical Trial in cUTI A Phase 3, Randomized, Double-blind, Double-dummy, Multi-center Study to Assess the Efficacy and Safety of Orally Administered Tebipenem Pivoxil Hydrobromide (TBP-PI-HBr), Compared to Intravenously Administered Imipenem-cilastatin in Patients with Complicated Urinary Tract Infection (cUTI) or Acute Pyelonephritis (AP) Patients with a diagnosis of cUTI (incl. AP) Approximately 2648 patients (Stratified by age, baseline diagnosis, etc.)  7-10 Days of Dosing  Treatment Population Endpoints Primary Endpoint:  Overall response at TOC in micro-ITT population Primary Analysis: Assessment of non-inferiority (NI) in micro-ITT population, based on a 10% NI margin Treatment Arms patients randomized 1:1 (blinded) R TBP-PI-HBR (600 mg) orally and “dummy” infusion IV, every 6 hours, days 1-10 (n=1324) Imipenem-cilastatin (500 mg) IV and matched “dummy” tablets, orally every 6 hours, days 1-10, (n=1324)

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Exclusive License Agreement with GSK for Tebipenem HBr and Equity Investment Global Collaboration (ex-Asia) Financial Terms Spero is responsible for execution and costs of the Tebipenem HBr Phase 3 in the United States GSK received exclusive license to: Develop Tebipenem in territories outside of United States (not including Japan and certain other Asian countries where rights are held by Meiji Seika); and Obtain regulatory approval and commercialize tebipenem HBr in all territories, except Meiji Seika Territories Received $66 Million upfront and $9 Million in common stock investment Received $30 Million upon SPA agreement with the FDA Upon FPFD, Spero qualified to receive $95 Million in development milestones payable in equal installments over two years Spero is eligible to receive up to $400 Million in additional potential regulatory, commercial and sales milestone payments, as well as royalties $25 Million to be paid upon GSK’s submission of tebipenem HBr’s New Drug Application (NDA) Up to $150 million in potential commercial milestones based on first commercial sales (US/EU) Up to $225 million in sales related milestone payments  Spero to receive tiered low-single digit to low-double digit (if sales exceed $1 billion) tiered royalties on net product sales FPFD: first patient first dose. SPA: Special Protocol Assessment

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SPR206 Direct Acting IV Potentiator

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SPR206: Ongoing Clinical Development Lends Potential to Address Significant Unmet Need Innovative, investigational IV direct-acting polymyxin antibiotic Destabilization of phospholipids and lipopolysaccharides (LPS) present Increased permeability, cell membrane disruption, bacterial cell death Received FDA Fast Track designation Next Steps: Phase 2 HABP/VABP Proof of Concept Study4 SPR206 has potential to fulfill unmet need for a well tolerated, efficacious therapeutic against carbapenem-resistant pathogens Current standard of care involves drug combinations that are often associated with nephrotoxicity HABP: hospital-acquired bacterial pneumonia; MAD: multiple ascending dose; SAD: single ascending dose; VABP: ventilator-associated bacterial pneumonia. 1. Bruss J, et al. Antimicrob Agents Chemother 2021;65:e0073921; 2.Rodvold KA, et al. Antimicrob Agents Chemother 2023;67:e0042623. 3. Bruss JB, et al. Antimicrob Agents Chemother 2023;67:e0050523; 4. Contingent on non-dilutive funding availability. SAD/MAD Phase 1 Trial1 No evidence of nephrotoxicity at predicted therapeutic dose levels Bronchoalveolar Lavage Phase 1 Trial2 Well-tolerated and achieved lung exposures consistent with predicted therapeutic levels Preclinical Studies Support increased efficacy beyond traditional antibiotics and potential for single agent activity Renal Impairment Phase 1 Trial3 Supportive of renal dosing in subsequent trials for patients impacted by differences in renal function 

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SPR720 Oral Antibiotic for Non-Tuberculosis Mycobacterium Pulmonary Disease (NTM-PD) The company is suspending its current development for SPR720

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First-line treatment options include 6-12 months (or more) on a combination of antibiotics, including a macrolide NTM-PD is a Chronic Debilitating Disease with Significant Patient Burden NTM: non-tuberculous mycobacteria; NTM-PD: NTM pulmonary disease; *SPR720 is being developed for MAC NTM-PD. 1. Marras TK, et al. Respir Med 2018; 145:80-88. 2. Kim RD, et al. Am J Respir Crit Care Med 2008; 178:1066-74; mortality rate represents midpoint of published range. Fatigue 83% Cough 78% Sputum (phlegm) 67% Short of breath 65% Night sweats 54% Fever 44% Hemoptysis 29% Weight loss 3.7 ± 5.2 kg 5 High-Resolution CT Scans (HRCT) Confirms NTM-PD diagnosis and severity 4 Worsening of lung damage Select pre-existing indications include: Bronchiectasis COPD Cystic fibrosis M. avium complex (80-85%)* Additional species, including M. abscessus Patient with existing structural lung damage and/or immunocompromised status 1 Exposure to NTM species 2 Presentation of signs and symptoms of NTM-PD 3 Drug-resistance &/or exacerbations eventually leads to 5-yr all-cause mortality rate of ~35%1,2 6

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High Unmet Need in First-Line Patients With Long Treatment Duration, and Lack of Efficacy and Tolerability from Current Treatment Options Rare Disease with High Unmet Need ~245,000 diagnosed patients in developed markets1 ~35% Five-year all-cause mortality rate2  Chronic condition requiring long-term treatment No Approved First-Line Treatment Off-label use of Azithromycin Ethambutol Rifampin Inhaled amikacin in Phase 3 trial No other oral agent in clinical development  Current SOC Treatments Have Severe Limitations Poor outcomes driven by emergence of resistance Safety & tolerability  concerns & high rate of treatment drop-offs ~50% of treated patients experience infection recurrence3 Inhaled amikacin approved for refractory (2L) patients; 1.Winthrop KL, et al. Ann Am Thorac Soc 2020; 17:178-85 and Spero internal analysis. 2.Kim RD, et al. Am J Respir Crit Care Med 2008; 178:1066-74; mortality rate represents midpoint of published range 3. Hamed KA and Tillotson G. Expert Rev Respir Med 2023;17:973-88. 

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SPR720 is An Oral Small Molecule Gyrase B Inhibitor  M.: Mycobacterium; MAC: Mycobacterium avium complex; NTM: non-tuberculous mycobacteria; SOC: standard of care; QIDP: qualified infectious disease product 1. Brown-Elliott BA, et al. Antimicrob Agents Chemother. 2018; 62:e01503-18. 2. Aragaw WW, et al. Microbiol Spectr 2022;10:e0132121. 3. Pillar CM, et al. IDWeek poster presentation, available online. in vitro potency against multiple NTM pathogens, such as MAC (including macrolide-resistant MAC) and M. abscessus1 Novel mechanism of action for NTM-PD not exploited by current antibiotics May be administered with or without food No evidence of cross resistance against marketed antibiotics1 Low propensity for development of resistance as monotherapy and in combination with SOC antibiotics2,3  Data support epithelial lining fluid and lung macrophage penetration4 Composition of matter patent into 2032 Granted Orphan Drug, QIDP and Fast Track designations Phosphate ester prodrug Active moiety Oral absorption SPR720 SPR719

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SPR720's Novel Mechanism of Action Not Exploited by Existing Antibiotics for NTM-PD SPR720/719 targets DNA gyrase (GyrB subunit), a critical enzyme for DNA replication and RNA transcription1 1 Azithromycin (AZM) disrupts ribosomal activity; AZM blocks passage of growing peptide & RNA through ribosome 2 Ethambutol (EMB) disrupts Arabinogalactan formation, a critical cell wall component 3 Arabinosyl transferase Arabinose ethambutol Arabinogalactan DNA replication and transcription mRNA Ribosomes Translation Ribosome Peptide AZM 1 2 3 SPR720/719 mRNA transcription DNA replication DNA gyrase Cell wall production and integrity Arabinogalactan Critical component of mycobacterial cell walls 1. Winthrop KL, et al. Expert Rev Anti Infect Ther 2023; 21:1177-87.

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SPR720 Provides a Better Resistance Profile When Used with SOC Agents MIC90: minimum inhibitory concentration at which 90% of isolates were inhibited; NTM: non-tuberculous mycobacteria; SPR719 is the active moiety of the prodrug SPR720 and is used for in vitro testing. Brown-Elliott BA, et al. Antimicrob Agents Chemother 2018; 62:e01503-18. SPR720, Investigator Brochure Edition 5; 07Apr2022, on file with Spero Low MIC90 values for SPR719 suggest consistent activity against most clinically important NTM species Low variability in MIC90 values across species support thesis that SPR719 has a novel mechanism with minimal pre-existing drug resistance MAC organism (n) Agent MIC 90% (µg/mL) M. avium (12) SPR719 2 Amikacin 64 Clarithromycin 8 Linezolid 64 Moxifloxacin 8 M. intracellulare (19) SPR719 2 Amikacin >64 Clarithromycin >64 Linezolid 64 Moxifloxacin 8 MAC-X (10) SPR719 1 Amikacin 32 Clarithromycin 4 Linezolid 64 Moxifloxacin >8 SPR719 Inhibits Growth of MAC Isolates at Lower Concentrations (MICs) than SOC Agents in vitro

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SPR719 had a low propensity for resistance development and showed no instances of antagonism when combined with SOC agents Selective agent Organism Putative mutant ID MIC (µg/mL) Clarithromycin SPR719 Clarithromycin at 4 x MIC M. avium ATCC 700898 Parent 1 1 Mutant 8* >256 1 Mutant 31 >256 1 Mutant 41 >256 1 MAC MMX-9461 Parent >256 2 Mutant 32 >256 2       Rifampin SPR719 Rifampin at 4 x MIC M. avium ATCC 700898 Parent 64 1 Mutant 35 >128 0.5 Mutant 36 >128 0.5 Mutant 37 >128 0.5 MAC MMX-9461 Parent 128 2 Mutant 40 >128 2 Resistance to CLR or RIF did not affect SPR719 MICs Mutant MAC strains, resistant to Clarithromycin or Rifampin, show no added resistance to SPR719, reaffirming the lack of overlap in the resistance mechanisms. Pillar CM, IDWeek poster presentation, October 18, 2024

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In Vivo Murine Data Demonstrate Increased Potency When Combined with SOC SPR720 as monotherapy and in combination with SOC agents SPR720 active as monotherapy with evidence of dose response Demonstrates improved efficacy when used in combination with SOC agents BID: twice daily; CFU: colony forming units; CLR: clarithromycin; EMB: ethambutol; SOC: standard of care; QD: once daily Cotroneo N, et al. J Antimicrob Chemother 2024; doi: 10.1093/jac/dkae046. Online ahead of print.

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SAD: single ascending dose. N=6 per group Talley AK, et al. Antimicrob Agents Chemother 2021; 65:e0120821. SPR720 Plasma Concentration Increases with Dose Escalation; No Clinically Significant Food Effect Observed Phase 1 SAD/MAD study Mean plasma concentration-time curves following single ascending dosing (SAD) of SPR720 

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SPR719 Penetrates Well into Epithelial Lining Fluid (ELF) and Alveolar Macrophages (AM)  Ratios: ELF to plasma AUC0-24 ELF to plasma Cmax AM to plasma AUC0-24 AM to plasma Cmax Total Plasma 1.14 1.26 2.44 3.02 Unbound Plasmaa 19.87 21.88 42.50 52.53 a Corrected for 94.25% protein-bound fraction and 5.75% unbound fraction1 Phase 1 healthy volunteer study to evaluate the intrapulmonary PK following oral administration of SPR720 1000mg QD for 7 days, including 30 subjects, demonstrated that SPR719 had significant lung uptake and enhanced concentrations in the ELF and AM Reference Rodvold, KA, Antimicrobial Agents and Chemotherapy, https://doi.org/10.1128/aac.01103-24. 1.Spero Data on File

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SPR720 Proof-of-Concept Phase 2a Trial Design Overview Study SPR720-202 (NCT05496374): Phase 2a study in NTM-PD – suspended following interim analysis Intense PK sub-study (open label) Treatment-naïve/ experienced (non-refractory) patients with NTM due to M. avium complex 25 patients enrolled 56 Days of Dosing  Treatment Population Endpoints Primary Endpoint:  1. The rate of change in log10 Colony Forming Units per milliliter (CFU/ml) Secondary Endpoints: The rate of change in time to positivity (TTP) Safety & tolerability 3. Plasma PK Treatment Groups patients randomized 1:1:1 (blinded) R   Placebo   SPR720 (500 mg) A study to evaluate the efficacy, safety, tolerability, and pharmacokinetics of SPR720, as compared with placebo for the treatment of patients with mycobacterium avium complex (MAC) pulmonary disease   SPR720 (1000 mg) SPR720 (1000 mg) SPR720 (500 mg BID) BID: twice daily; MAC: Mycobacterium avium complex; NTM-PD: non-tuberculous mycobacterial pulmonary disease; PK: pharmacokinetics. *interim analysis of the Phase 2a proof-of-concept study of SPR720 for the treatment of NTM-PD demonstrated that the program did not meet its primary endpoint. The interim analysis did not show sufficient separation from placebo and highlighted potential dose limiting safety issues in subjects dosed at 1,000mg orally once daily, including three cases of grade 3 hepatotoxicity.

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Overview of CFU and TTP Microbiological Endpoints Sputum CFU Analysis Diluted sputum inoculated on culture plate Visually count colonies TTP Analysis Diluted sputum inoculated in liquid medium Assay device incubates and detects growth Assay device automatically records time to positive growth signal # of colonies Time of sample collection Decreasing values indicate lowering of NTM burden Time to positive signal Time of sample collection Increasing values indicate lowering of NTM burden 3-4 wk incubation Danho, Rabi et al., CHEST, Volume 161, Issue 2, 370 - 372

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Esther Rajavelu Chief Financial Officer and Chief Business Officer Over two decades of life science sector experience, combining equities research, investment banking, strategy consulting, and M&A Prior CFO at Fulcrum Therapeutics. Senior equity research analyst at UBS, Oppenheimer and Deutsche Bank. Healthcare Investment Banker at Bank of America Merrill Lynch Sath Shukla President and Chief Executive Officer Prior CFO at Spero Therapeutics; Prior CFO at Ziopharm Oncology; VP and Global Head of Corporate Finance at Vertex  Over 20 years of financial leadership, executing within commercial and clinical companies Leadership Team Timothy Keutzer Chief Operating Officer Previously, Spero’s Chief Development Officer Prior VP Program and Portfolio Management, Cubist  Extensive antibiotic development experience from pre-clinical to approval Over 30 years in the pharmaceutical industry James Brady Chief Human Resource Officer Prior CHRO at uniQure Therapeutics; Vice President, Human Resources at Intarcia Therapeutics Close to 30 years of senior human resources experience with over 17 years in the life science space

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Thank You

v3.24.3

Document and Entity Information	Oct. 29, 2024
Cover [Abstract]
Security 12b Title	Common Stock, $0.001 par value per share
Amendment Flag	false
Entity Central Index Key	0001701108
Document Type	8-K
Document Period End Date	Oct. 29, 2024
Entity Registrant Name	SPERO THERAPEUTICS, INC.
Entity Incorporation State Country Code	DE
Entity File Number	001-38266
Entity Tax Identification Number	46-4590683
Entity Address, Address Line One	675 Massachusetts Avenue
Entity Address, Address Line Two	14th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	(857)
Local Phone Number	242-1600
Written Communications	false
Soliciting Material	false
Pre Commencement Tender Offer	false
Pre Commencement Issuer Tender Offer	false
Trading Symbol	SPRO
Security Exchange Name	NASDAQ
Entity Emerging Growth Company	false

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