Spero Therapeutics (NASDAQ: SPRO) turns 2025 profit as tebipenem advances

Rhea-AI Filing Summary

Spero Therapeutics reported a strong turnaround for 2025, moving from a net loss in 2024 to net income. Total revenues rose to $66.8M for the year ended December 31, 2025, up from $48.0M, driven mainly by collaboration revenue, including from its tebipenem HBr partnership with GSK.

Full-year research and development expense fell to $38.5M from $96.8M, while general and administrative costs declined modestly to $21.2M. Net income attributable to common shareholders was $8.6M for 2025 versus a $68.6M loss in 2024, and fourth quarter diluted EPS reached $0.53.

Cash, cash equivalents and marketable securities were $40.3M as of December 31, 2025, and Spero estimates this will fund operations into 2028. Operationally, the company completed the global phase 3 trial of tebipenem HBr in cUTI, resubmitted its NDA, and highlighted an FDA PDUFA decision date of June 18, 2026.

Positive

• Spero returned to profitability in 2025, generating net income attributable to common shareholders of $8.6M versus a $68.6M loss in 2024, driven by higher collaboration revenue and significantly lower research and development expenses.
• Runway extended with lower burn, as cash, cash equivalents and marketable securities of $40.3M at December 31, 2025 are estimated by Spero to fund operations into 2028, while tebipenem HBr has a defined FDA PDUFA date of June 18, 2026.

Negative

• None.

Insights

Biopharma equity analyst

Spero shifts to profitability on collaboration revenue while derisking tebipenem HBr.

Spero Therapeutics delivered a notable financial inflection in 2025. Total revenues climbed to $66.8M, largely from collaboration payments, and operating expenses dropped sharply, especially R&D, which fell to $38.5M from $96.8M. This combination produced $8.6M in net income after a prior-year loss.

Strategically, the company completed a global phase 3 trial for tebipenem HBr in cUTI, resubmitted its NDA, and now targets an FDA PDUFA decision on June 18, 2026. Tebipenem HBr is partnered with GSK under an exclusive license, so execution and future milestones depend heavily on GSK’s development and commercialization decisions.

Spero ended 2025 with $40.3M in cash, cash equivalents and marketable securities and currently estimates this will fund operations into 2028, reducing near-term financing pressure. Future updates around the PDUFA decision and any milestone receipts under the GSK license will be key determinants of the sustainability of this profitability and the pace of pipeline expansion.

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): March 26, 2026

SPERO THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

Delaware		001-38266		46-4590683
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)

675 Massachusetts Avenue, 14th Floor Cambridge, Massachusetts		02139
(Address of principal executive offices)		(Zip Code)

Registrant’s telephone number, including area code (857) 242-1600

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.001 par value		SPRO		The Nasdaq Global Select Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On March 26, 2026, Spero Therapeutics, Inc. (the “Company”) issued a press release announcing its results for the fourth quarter and full year ended December 31, 2025. A copy of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

The information contained in this Item 2.02 and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation language in such filing.

Item 9.01 Financial Statements and Exhibits

(d) Exhibits

Exhibit No.		Description
99.1		Press release issued by Spero Therapeutics, Inc. on March 26, 2026
104		Cover Page Interactive Data File (embedded within the Inline XBRL document and incorporated as Exhibit 101)

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: March 26, 2026				SPERO THERAPEUTICS, INC.
				By:		/s/ Esther Rajavelu
						Esther Rajavelu
						Chief Executive Officer, Chief Financial Officer and Chief Business Office

Exhibit 99.1

Spero Therapeutics Announces Fourth Quarter and Full Year 2025 Operating Results and Provides a Business Update

• Spero announced the resubmission of tebipenem HBr New Drug Application (NDA) to the FDA for complicated urinary tract infections (cUTI), including pyelonephritis in December 2025

• In February, Spero’s licensing partner, GSK announced the FDA had set the PDUFA date as June 18, 2026

• Spero estimates cash and cash equivalents as of December 31, 2025 are sufficient to fund current operations into 2028

CAMBRIDGE, Mass., March 26, 2026 — Spero Therapeutics, Inc. (Nasdaq: SPRO), a clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and diseases with high unmet need, today announced financial results for the fourth quarter and full year ended December 31, 2025, and provided a business update.

“2025 was marked by important progress across the tebipenem HBr program in cUTI, including completion of the global Phase 3 trial and resubmission of the NDA,” said Esther Rajavelu, President and CEO of Spero. “With our licensing partner GSK’s global leadership in anti-infectives, tebipenem HBr, if approved, has the potential to address an important need and meaningfully improve treatment options for patients with cUTI. We look forward to the FDA’s decision in late June as we continue to execute our business strategy to deliver innovative therapies.”

Spero remains focused on completing its obligations under its License Agreement with GSK while advancing other corporate activities, including exploring opportunities to expand its portfolio of clinical-stage product candidates.

Program Update

Tebipenem HBr

Tebipenem HBr is an investigational oral carbapenem antibiotic being developed for the treatment of cUTI, including pyelonephritis, to provide an effective oral therapeutic alternative to IV carbapenems. Spero granted GSK an exclusive license to commercialize tebipenem HBr in all territories, except certain Asian territories where Meiji holds development and commercialization rights.

• In December 2025, GSK resubmitted the tebipenem HBr NDA to the FDA. In February 2026, GSK announced that the FDA set the Prescription Drug User Fee Act (“PDUFA”) date as June 18, 2026. The NDA is supported by results from the successful Phase 3 PIVOT-PO trial that evaluated tebipenem HBr. The trial, which was stopped early for efficacy in May 2025, demonstrated non-inferiority of tebipenem HBr compared to intravenous imipenem-cilastatin in hospitalized patients with cUTI, including pyelonephritis, based on the overall response (composite of clinical cure plus microbiological eradication of the bacteria causing the infection) at the test of cure visit. Detailed results were presented in a late -breaking oral abstract session at IDWeek 2025.

• The safety and tolerability profile of tebipenem HBr in PIVOT-PO was consistent with results reported in other studies with tebipenem and in line with that of the carbapenem antibiotic class. The most frequently reported adverse events were diarrhea and headache; these events were all mild or moderate and non-serious.

• For more information on the PIVOT-PO trial, please refer to ClinicalTrials.gov ID NCT06059846.

Fourth Quarter and Full Year 2025 Financial Results

• Spero reported net income of $31.5 million for the fourth quarter of 2025 compared to a net loss of $(20.9) million for the fourth quarter of 2024, or a diluted net gain and net income per share of common stock of $0.53 and a diluted net loss and net loss per share of common stock of $(0.38), respectively. Net income for the year ended December 31, 2025, was $8.6 million compared to a net loss for the year ended December 31, 2024, of $(68.6) million, or a diluted net gain per share of common stock of $0.15 and a diluted net loss per share of common stock of $(1.27), respectively.

• Total revenue for the fourth quarter of 2025 was $41.3 million, compared to total revenue of $15.0 million for the fourth quarter of 2024. The revenue increase for the fourth quarter of 2025 was primarily due to an increase in collaboration revenue from our agreements with GSK and Pfizer. Total revenue for the year ended December 31, 2025, was $66.8 million, compared to $48.0 million for the year ended December 31, 2024. The revenue increase for the year was primarily due to the aforementioned collaboration revenue related to our agreements with GSK and Pfizer.

• Research and development expenses for the fourth quarter of 2025 were $5.6 million, compared to $28.8 million of research and development expenses for the same period in 2024. Research and development expenses for the year ended December 31, 2025, were $38.5 million, compared to $96.8 million for the year ended December 31, 2024. The decrease in research and development expenses year-over-year was primarily due to decreased clinical trial activity related to the PIVOT-PO trial.

• General and administrative expenses for the fourth quarter of 2025 were $4.3 million, compared to $7.1 million of general and administrative expenses for the same period in 2024. This decrease was primarily due to decreased legal and personnel related costs. General and administrative expenses for the year ended December 31, 2025, were $21.2 million, compared to $23.7 million for the year ended December 31, 2024, with lower expenses in 2025 compared to 2024 primarily due to decreases in legal, consulting and personnel related costs.

• As of December 31, 2025, Spero had cash and cash equivalents of $40.3 million. Spero estimates that its cash and cash equivalents as of December 31, 2025 will be sufficient to fund current operations into 2028.

• In Q1 2026, Spero received a $25 milestone payment from GSK, triggered by the tebipenem HBr NDA resubmission.

For further details on Spero’s financials, refer to Spero’s Annual Report on Form 10-K, filed with the U.S. Securities and Exchange Commission (SEC) today.

Government Agency Research Support

The views expressed in this press release are those of the authors and may not reflect the official policy or position of the Department of the Army, Department of Defense, or the U.S. Government.

Tebipenem HBr Research Support

Select tebipenem HBr studies have been funded in part with federal funds from the Department of Health and Human Services; Administration for Strategic Preparedness and Response; and Biomedical Advanced Research and Development Authority, under contract number HHSO100201800015C.

About Spero Therapeutics

Spero Therapeutics, headquartered in Cambridge, Massachusetts, is a clinical-stage biopharmaceutical company focused on identifying and developing novel treatments for rare diseases and diseases 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, statements regarding the anticipated PDUFA date set by the FDA as June 18, 2026; Spero’s exploration of opportunities to expand its portfolio of clinical stage product candidates; the potential of tebipenem HBr to be the first oral carbapenem antibiotic for US patients with cUTI, including pyelonephritis, and to set a new standard of care; the potential receipt of milestone payments under Spero’s license and collaboration agreements; Spero’s estimation that its cash and cash equivalents as of December 31, 2025 will be sufficient to fund operations into 2028; and the potential benefits of any of Spero’s current or future product candidates in treating patients. 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 the FDA will ultimately approve tebipenem HBr and, if so, the timing of any such approval, taking into account the effects of possible regulatory delays; 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; Spero’s reliance on third parties to manufacture, develop, and commercialize its product candidates, if approved; Spero’s reliance on GSK pursuant to the exclusive GSK License Agreement advance development of tebipenem HBr and GSK’s right thereunder to determine, in its sole discretion, whether to further develop and commercialize tebipenem HBr; Spero’s need for additional funding; Spero’s ability to retain key personnel; whether Spero’s cash resources will be sufficient to fund its continuing operations for the periods 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

Spero Therapeutics, Inc.

Condensed Consolidated Balance Sheet Data

(in thousands)

(Unaudited)

		December 31, 2025				December 31, 2024				Change
Cash, cash equivalents and marketable securities		$	40,265			$	52,889			$	(12,624	)
Other assets			28,654				57,654				(29,000	)
Total assets		$	68,919			$	110,543			$	(41,624	)
Total liabilities		$	9,898			$	64,420			$	(54,522	)
Total stockholder’s equity			59,021				46,123				12,898
Total liabilities and stockholders’ equity		$	68,919			$	110,543			$	(41,624	)

Spero Therapeutics, Inc.

Condensed Consolidated Statements of Operations

(in thousands, except share and per share data)

(unaudited)

		Three Months Ended December 31,								Year Ended December 31,
		2025				2024				2025				2024				$ Change
Revenues:
Grant revenue		$	1,639			$	5,688			$	7,183			$	20,581			$	(13,398	)
Collaboration revenue - related party			27,084				9,304				47,033				27,025				20,008
Collaboration revenue			12,574				52				12,586				371				12,215
Total revenues			41,297				15,044				66,802				47,977				18,825
Operating expenses:
Research and development			5,592				28,836				38,467				96,757				(58,290	)
General and administrative			4,300				7,056				21,176				23,704				(2,528	)
Impairment of long-term asset			—				—				587				—				587

Restructuring			—				877				258				877				(619	)
Total operating expenses			9,892				36,769				60,488				121,338				(60,850	)
Income (loss) from operations			31,405				(21,725	)			6,314				(73,361	)			79,675
Other income, net			376				1,127				2,519				4,795				(2,276	)
Net income (loss) before income taxes			31,781				(20,598	)			8,833				(68,566	)			77,399
Income tax expense			(261	)			(290	)			(261	)			—				(261	)
Net income (loss) attributable to common shareholders of Spero Therapeutics, Inc.		$	31,520			$	(20,888	)		$	8,572			$	(68,566	)		$	77,138
Net income (loss) per share attributable to common shareholders per share, basic		$	0.56			$	(0.38	)		$	0.15			$	(1.27	)
Net income (loss) per share attributable to common shareholders per share, diluted		$	0.53			$	(0.38	)		$	0.15			$	(1.27	)
Weighted average shares outstanding, basic:			56,020,363				54,538,547				56,020,363				54,037,917
Weighted average shares outstanding, diluted:			59,368,159				54,538,547				59,039,225				54,037,917

FAQ

How did Spero Therapeutics (SPRO) perform financially in 2025?

Spero Therapeutics reported net income of $8.6 million for 2025, compared with a $68.6 million loss in 2024. Total revenues rose to $66.8 million, while sharply reduced research and development spending helped drive the move to profitability.

What were Spero Therapeutics’ revenues and key expense trends in 2025?

Total revenues reached $66.8 million in 2025, up from $48.0 million, mainly from collaboration revenue. Research and development expense declined to $38.5 million from $96.8 million, and general and administrative costs fell to $21.2 million, improving the overall cost structure.

What is Spero Therapeutics’ cash position and funding runway after 2025?

As of December 31, 2025, Spero held $40.3 million in cash, cash equivalents and marketable securities. The company estimates this balance will be sufficient to fund operations into 2028, providing several years of operational runway under current planning assumptions.

What progress did Spero make with tebipenem HBr in 2025?

Spero completed the global Phase 3 trial of tebipenem HBr in complicated urinary tract infections and resubmitted its NDA. Tebipenem HBr is licensed to GSK for commercialization in most territories, advancing toward a key regulatory decision point.

When is the FDA PDUFA decision date for Spero’s tebipenem HBr?

The anticipated FDA PDUFA decision date for tebipenem HBr is June 18, 2026. This decision will determine whether the investigational oral carbapenem antibiotic can be approved for U.S. patients with complicated urinary tract infections, including pyelonephritis.

How did Spero Therapeutics’ fourth quarter 2025 results compare to 2024?

Fourth quarter 2025 total revenues were $41.3 million versus $15.0 million in 2024. Net income attributable to common shareholders was $31.5 million, compared with a $20.9 million net loss, reflecting higher collaboration revenue and lower operating expenses.

Filing Exhibits & Attachments

4 documents

Press Releases

• EX-99.1 EX-99.1 64.8 KB

Other Documents

• EX-101 XBRL TAXONOMY EXTENSION SCHEMA 2.8 KB
• EX-101 XBRL TAXONOMY EXTENSION LABEL LINKBASE 17.6 KB
• EX-101 XBRL TAXONOMY EXTENSION PRESENTATION LINKBASE 11.0 KB