The Cancer Drug That Waited for a Click

The great inconvenience of a cancer drug is that it must travel through a body to find the part of the body it is meant to harm. Along the way it meets everything else. Shasqi, a San Francisco biotechnology company, was founded on a question that sounds like a courier's problem: could the destination and the dangerous parcel arrive separately?

Its answer is CAPAC, short for Click Activated Protodrugs Against Cancer. One component finds or sits in a tumor. A second component, a chemically muted drug, travels through the bloodstream. When the two meet, a fast bioorthogonal reaction either releases an active drug or fixes a payload at the target. In the company's first human program, the reaction released doxorubicin, an old and useful chemotherapy drug whose toxicity limits how much doctors can give.

A surgeon thinks about the address

Founder José M. Mejía Oneto left an orthopedic surgery residency in 2014. Shasqi's account of the decision is unusually concrete: operating on one piece of a patient made the imprecision of systemic medicine hard to ignore. His organic chemistry training suggested a possible answer. A meeting with Carolyn Bertozzi, later a co-recipient of the 2022 Nobel Prize in Chemistry for bioorthogonal chemistry, helped propel the idea into Y Combinator. He founded Shasqi in 2015.

The name is a small clue to the obsession. It comes from the chasquis, runners who carried messages and goods across the Inca empire. The Shasqi version has two couriers: a target finder and a drug. The cleverness lies in making their handoff a chemical event, rather than hoping a single attached package stays intact until it gets there.

The first experiment had two verdicts

SQ3370, Shasqi's first candidate, paired SQL70, a biopolymer injected into a tumor, with SQP33, an intravenous doxorubicin protodrug. It reached patients in 2020. The phase 1/2a study eventually enrolled 53 people across dose escalation and a soft-tissue sarcoma expansion. This was a genuine technical first: published investigators described it as the first reported use of in vivo click chemistry in humans.

The dose finding result was arresting. Patients received as much as 15 times a conventional doxorubicin-equivalent dose per cycle without reported dose-limiting toxicities in phase 1; the team selected 12 times as the phase 2 dose. It would be easy to end the story there. It would also misread the study. A tolerable dose is a means to a therapeutic result, not the result itself.

In the 14-patient sarcoma expansion, two people had unconfirmed partial responses; ten had disease control. The prespecified criterion for continuing the study, however, was an objective response rate better than standard doxorubicin. The study was terminated when that bar was not met. The paper's conclusion is a model of clinical precision: the chemistry worked, clinical activity appeared, and the response rate was comparable to the old drug it sought to improve.

A chemical first is still obliged to answer a medical question.What SQ3370 made plain

What the $60 million bought

Shasqi announced a $10 million Series A in 2019 to finish manufacturing and enter human testing. A $50 million Series B followed in 2021, backed by a private investor group including Juan Jaen and Bill Rieflin. Those are disclosed financing rounds, not a published cost for SQ3370. The company has also reported National Cancer Institute grant support. There is no approved Shasqi medicine and no public product price.

The 2021 financing announcement already pointed beyond the first program. SQL70 had to be injected into an accessible tumor, a logistical and biological limit. Shasqi proposed antibody-directed targeting so the first component could seek cancers without a needle placed into a lesion. This change began before the sarcoma readout; it should not be turned into a tidy story of a company changing its mind overnight.

That broader platform is where the business now sits. Shasqi develops proprietary experimental drugs, publishes preclinical and clinical work, and collaborates with larger biopharmaceutical companies. Its announced research alliance with Johnson & Johnson Enterprise Innovation began in 2023 and expanded later that year. The intended customers, ultimately, would be oncologists and patients if a candidate wins approval. Today, partners and trial investigators are the people working with the technology; patients cannot buy it as a treatment.

The next address is an antigen

The company's newer work substitutes tumor-binding molecules for the injected biopolymer. One lead direction uses a binder for CEACAM5, an antigen found on some cancer cells, with SQP22, a clickable, attenuated form of the potent payload MMAE. Shasqi has also tested HER2-guided and other pairings in preclinical models. In a 2025 AACR abstract, the CEACAM5 combination showed tumor growth inhibition in animal models relative to controls. A 2026 abstract described continuing preclinical work. These are reasons to run the next experiments, not evidence of benefit in people.

This separates Shasqi from the standard antibody-drug conjugate, which physically attaches drug and antibody before dosing. A conventional conjugate's payload follows its binder through the body and can be released during normal clearance. CAPAC sends binder and payload separately, allowing their amounts and timing to be adjusted independently. That design may widen the therapeutic window. It also demands an exacting choreography: a target that binds well, a payload that stays muted in circulation, a reaction fast enough at the tumor, and sufficient drug exposure to change outcomes.

• Copy the logicSeparate the target-finding job from the dangerous payload when the combined package creates off-target exposure.
• Copy the disciplineSet a clinical go/no-go rule before the results arrive, then report both technical success and the missed therapeutic goal.
• Mind the boundaryAn injected-tumor design requires an accessible lesion. An antigen-guided design depends on reliable target expression and still needs human efficacy data.

The attraction of Shasqi's platform is easy to understand. Cancer treatment has long tried to deliver more of the useful part of a drug and less of the costly part. Shasqi has shown an ingenious delivery mechanism can work in a human body. Its first clinical test also showed why ingenuity is an opening argument, not a verdict. The next trial will need to show that a better address produces a better outcome.