by Michael Schultz and John Flavin

Antibody-drug conjugates are among the most active areas of oncology drug development, with 15 FDA-approved therapies and hundreds of clinical trials underway. Despite their promise, first-generation ADCs are limited by a narrow therapeutic index: dose-limiting toxicity often emerges before full efficacy is achieved. These limitations are multifaceted. Unstable linkers can release toxic payloads prematurely, causing off-target damage, while single-payload designs leave tumors vulnerable to resistance. What the field needs is a platform that improves linker stability while enabling delivery of multiple mechanistically distinct payloads, leveraging payload synergy to widen the therapeutic window.

Portal Innovations backed Crossbridge Bio at the earliest stage to address this problem. In April 2026, that bet was validated when Eli Lilly acquired the company, adding Crossbridge’s differentiated dual-payload ADC platform to its expanding oncology pipeline. This is the story of how it came together.

The Ecosystem Connection

Portal’s relationship with Crossbridge Bio grew out of a deliberate strategy: building deep networks in life sciences hubs where world-class science is underserved by venture capital. Our Houston presence, anchored by lab space in the Helix Park Collaborative Building, gave us early access to the talent and technology flowing through the Texas Medical Center. We had previously co-invested with TMC Innovation (TMCi) in March Biosciences, a clinical-stage CAR-T company spun out of Baylor College of Medicine, and the experience sharpened our eye for what a strong Houston deal looks like.

It was in that context that we met Michael Torres, a biotech entrepreneur who had co-founded ReCode Therapeutics and helped built it into a clinical-stage company. Speaking on the Lab Rats to Unicorns podcast, Torres reflected on his unlikely path: growing up in a small town in East Texas, living in section eight housing and on food stamps before earning an NIH scholarship and a PhD in cancer biology from UT Southwestern. He described his time at ReCode as formative: “I had the ability to watch management interact with some of the largest VCs in the world and see what they got right and what they didn’t — and those were lessons for me.”

Torres wanted to stay in Texas to build his next company: “I’m a third-generation Texan. I think there’s a lot of opportunity here. Texans are very proud of being Texans.” He joined TMCi’s entrepreneur-in-residence program, through which Portal got to know him early. He had spotted a compelling opening at UTHealth Houston, where two world-class research programs had converged on a novel linker chemistry for ADCs.

A Better Linker, a Better Drug

Crossbridge was founded on research from Kyoji Tsuchikama and Zhiqiang An’s labs at UTHealth Houston. Their complementary expertise in ADC linker chemistry and antibody therapeutics led to the development of a tripeptide cleavable linker called EGCit. The work, published in Nature Communications and Molecular Cancer Therapeutics, addressed two persistent problems with conventional ADC linkers. First, EGCit resists cleavage by neutrophil proteases, which can release cytotoxic payloads prematurely in the bloodstream and are a common cause of liver toxicity. Second, its branched architecture enables the attachment of two distinct drug payloads via orthogonal click chemistry, each at a precisely controlled drug-antibody ratio.

This dual-payload capability is the key differentiator. By delivering two mechanistically distinct agents to the same tumor cell, Crossbridge’s ADCs can broaden the therapeutic window through synergistic activity, mitigating toxicity constraints and overcoming resistance pathways that limit single-payload approaches. Critically, the ability to control the drug-antibody ratio independently for each payload ensures that both agents are delivered within their respective therapeutic ranges. Without that control, the more potent payload would dominate, and a true synergistic effect could not be achieved. Preclinical data confirmed genuine synergy between the two payloads, not merely an additive effect.

On the Lab Rats to Unicorns podcast, Michael Torres was direct about what sets the platform apart: “a two-in-one solution.” The pitch had already landed with potential acquirers. Torres noted that major pharma players had told him directly: “Once you have your safety data in non-human primates, then we know that this concept really has legs and we’re going to be all over it.”

Portal’s Role: More Than Capital

Portal invested at the pre-seed stage, providing some of the earliest institutional capital to license the intellectual property from UTHealth and stand up the company. But our contribution went beyond the check.

Portal’s therapeutics expertise helped attract co-investors. ADC development carries significant technical risk, and at the outset it was unclear what Crossbridge’s lead asset would be. The team needed to explore multiple targets and payload combinations to identify a viable candidate, an iterative process we had supported before, from target selection through IND-enabling studies.

Just as importantly, Portal provided the physical infrastructure to accelerate Crossbridge’s early work. Our lab space in the Helix Park Collaborative Building, located near Zhiqiang An’s UTHealth lab, enabled close collaboration between the company and its academic founders. The facility included specialized equipment, such as LC-MS instrumentation, that would otherwise have required significant time and capital to access. This proximity accelerated the timeline from company formation to data generation.

Milestones and Momentum

Crossbridge moved quickly after formation. The company nominated its lead clinical candidate, CBB-120, a TROP2-targeting ADC carrying a synergistic ATR inhibitor and topoisomerase I inhibitor payload combination. It expanded its pipeline to include other target-payload combinations.

The leadership team was built with equal urgency. Dan Pereira, with 25 years in oncology drug development and experience advancing multiple ADCs including the FDA-approved Padcev, joined as Chief Scientific Officer. Abhishake Chhibber, with prior roles at AstraZeneca and BioNTech, became Chief Operating Officer. Morris Rosenberg, formerly of Seagen and Immunomedics, joined as Acting Chief Technology Officer, rounding out a team with deep expertise across development, manufacturing, and strategy.

The seed round closed in late 2024, led by TMC Venture Fund and CE-Ventures, with participation from Portal. In November 2025, Crossbridge was awarded a $15 million CPRIT grant to fund IND-enabling activities for CBB-120, and the company won “Best Drug Developer” at the 2025 World ADC Awards, where its presentation became the most attended non-plenary session in the conference’s history.

The Road to Lilly

By early 2026, Crossbridge had generated strong non-human primate toxicology data demonstrating the linker stability that the platform had promised. The NHP results confirmed what the rodent data had suggested: Crossbridge’s EGCit linker maintained stability in circulation and released its payloads selectively in target tissues, a profile that differentiated it from other ADC linkers in development.

The NHP data proved to be a catalyst. Multiple top-tier venture firms engaged around a potential Series A, and several pharma strategics who had been tracking Crossbridge since its earliest days moved to deepen the relationship.

Among the interested parties was Eli Lilly, which had been actively expanding its ADC capabilities through prior acquisitions. As discussions progressed, conversations shifted from investment to acquisition, and Lilly made an offer to acquire the company outright. The board recognized the strategic fit with Lilly’s development infrastructure and the strength of the terms, and supported the transaction.

For Portal, the outcome validated a core thesis: backing exceptional founders with differentiated science in areas of strong strategic demand can generate outsized returns, particularly in emerging life sciences hubs. In under three years, Michael Torres and his team progressed from a university license to acquisition by the world’s largest pharmaceutical company. Portal’s relationships, expertise, and infrastructure, alongside the broader Houston life sciences community, were instrumental in that journey.

While M&A may mark the end of the story for investors, for cancer patients the story is just beginning. Under Eli Lilly’s stewardship, CBB-120 is positioned to advance rapidly through clinical development and potentially inaugurate a new class of dual-payload ADCs enabled by the EGCit linker, bringing new therapeutic options to patients and their families.