Peptide-Drug Conjugate TS-104 Clears FDA IND With $62.5M Series A

A peptide-based cancer therapy has cleared its first regulatory gate. TwoStep Therapeutics announced on September 9, 2026 that the U.S. Food and Drug Administration cleared its Investigational New Drug application for TS-104, a peptide-drug conjugate for solid tumors, and that it closed an oversubscribed $62.5 million Series A to fund the first-in-human trial. Patient enrollment is expected to begin later this year.

What an IND Clearance Actually Allows

An Investigational New Drug application is the filing a company submits before it may test an unapproved therapy in people, and it is the step that separates a laboratory program from a clinical one. The FDA describes the IND process and its requirements on its public site. Clearance does not establish that a drug works; it permits a sponsor to begin controlled testing under agency oversight.

TwoStep said clearance allows it to start a Phase 1 trial of TS-104 in oncology. The FDA does not publish IND clearances, so company announcements are the ordinary disclosure path for this stage of development.

“This financing, together with FDA clearance of the IND, marks an important inflection point for TwoStep and positions us to advance TS-104, our lead peptide-drug conjugate, through Phase 1 clinical development in oncology,” said Caitlyn Miller, PhD, co-founder and chief executive officer of TwoStep Therapeutics.

Five Targets Instead of One

Most tumor-targeted medicines depend on a single cell-surface target that is expressed strongly and uniformly. Solid tumors rarely cooperate. Target expression varies across tumor types, between patients, and even among cells inside the same tumor, which restricts who can be treated and allows target-low cells to escape therapy.

TwoStep’s answer is a polyspecific integrin-binding peptide, or PIP, used as the targeting component. PIP is a small synthetic peptide that engages five tumor-associated integrins found across a broad range of solid tumors. The company’s lead program, TS-104, pairs PIP with MMAE, a cytotoxic payload already used in approved antibody-drug conjugates.

By binding several targets rather than relying on high expression of one, PIP is designed to deliver its payload across more heterogeneous tumors. The company says the scaffold’s small size, rapid internalization, and adaptable conjugation chemistry let it pair the same targeting peptide with different payloads — an architecture it is also applying to a radioligand program.

That is a different design philosophy from the research peptides most readers of this site encounter. Peptides such as LL-37 are studied as signaling or antimicrobial molecules in their native form; TS-104 is an engineered conjugate in which a targeting peptide is used as a delivery vehicle for a separate cytotoxic drug.

Who Funded It

The $62.5 million Series A was led by Insight Partners and Medical Excellence Capital, with M Ventures — the corporate venture arm of Merck KGaA — and Pfizer Ventures joining as co-lead investors. Existing investors NFX and 2048 Ventures participated, as did Stanford University, where the foundational science was developed. The round brings TwoStep’s total capital raised to $71.2 million.

The company launched in 2024 as a Stanford spinout. It was co-founded by Miller in collaboration with three Stanford faculty: Jennifer Cochran, Nobel laureate Carolyn Bertozzi, and Ronald Levy.

“By engaging multiple tumor-associated integrins through a small and rapidly internalizing targeting agent, TwoStep’s approach has the potential to broaden the reach of targeted therapies across tumor types and patient populations,” said Matias Porras Paniagua, PhD, a vice president at Insight Partners.

Why This Matters Beyond One Company

Capital and regulatory clearance are flowing toward peptides with defined mechanisms, reviewed protocols, and objective endpoints. The same week, the peptide synthesis market was the subject of a separate $7 billion forecast, and oncology researchers have been publicly skeptical of consumer-facing peptide claims that lack human data.

The contrast is sharpest in consumer markets. The FDA has issued warning letters to multiple peptide vendors selling compounded and grey-market products outside the drug-approval pathway. TS-104 sits at the opposite end of that spectrum: an investigational drug that cannot be sold, marketed, or distributed to patients before the agency reviews trial data.

What Phase 1 Will and Will Not Show

Phase 1 trials are designed mainly to establish whether an experimental therapy is tolerable and how it behaves in the body, in a small number of participants. They are not built to prove that a treatment extends survival or shrinks tumors, and oncology programs routinely advance a lead candidate only to fail later, better-controlled trials.

TwoStep has not disclosed a start date beyond enrollment beginning later this year, and no clinical data from the trial has been released. The first meaningful readouts on the multi-specific targeting approach will follow once the study is under way.

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