New 'Molecular Glue' Drug Shows Striking Efficacy in Untreatable Melanoma

CAMBRIDGE, Mass. – April 17, 2026 – In a significant development for oncology, early clinical trial data has revealed a promising new weapon against a range of notoriously difficult-to-treat cancers. Nested Therapeutics, a clinical-stage biotechnology company, today announced encouraging initial results for its drug candidate, NST-628, showcasing potent anti-tumor activity in patients who had exhausted standard treatment options. The findings, presented at the prestigious American Association for Cancer Research (AACR) Annual Meeting 2026, have ignited hope, particularly for a large subgroup of melanoma patients with no currently approved targeted therapies.

The Phase 1 study data demonstrated that NST-628, a novel type of drug known as a “molecular glue,” achieved a 38% response rate and an 85% disease control rate in patients with advanced NRAS and BRAF Class II/III melanoma. This patient group, representing approximately one-third of all cutaneous melanoma cases, or about 8,000 new diagnoses annually in the U.S., has historically faced grim prognoses after failing immunotherapy. The new drug appears to offer a durable and well-tolerated alternative, marking a potential paradigm shift in a field with a critical unmet need.

Addressing a Critical Gap in Melanoma Treatment

For years, the treatment landscape for advanced melanoma has been divided. Patients with a specific mutation known as BRAF V600 (Class I) have benefited from a suite of targeted BRAF and MEK inhibitors. However, patients with other mutations, such as NRAS or the less common BRAF Class II and III alterations, have been left behind, lacking effective targeted options once immune checkpoint inhibitors fail.

Nested Therapeutics' data suggests NST-628 could fill this void. The ongoing trial has administered the drug to 69 patients with various advanced solid tumors driven by the RAS/MAPK signaling pathway. In the cohort of 13 heavily pretreated melanoma patients with NRAS or BRAF Class II/III mutations who received the recommended dose, the results were striking. Beyond the 38% response rate, the disease was controlled (meaning tumors either shrank or stopped growing) in 85% of these patients. With a median follow-up of 6.4 months, the responses appear durable, as the median duration of response has not yet been reached.

"These initial data support our hypothesis that targeting RAF/MEK signaling with a single-agent, fully brain-penetrant pan-RAF/MEK molecular glue can deliver meaningful clinical benefit," said Darrin Miles, Chief Executive Officer of Nested Therapeutics. "We are particularly encouraged by the durable responses in NRAS and BRAF Class II/III melanoma – large patient populations with historically poorer outcomes and for whom there are no approved targeted therapy options."

A Novel Mechanism with Brain-Penetrating Power

What sets NST-628 apart is its innovative mechanism. It is not a traditional inhibitor but a “molecular glue.” Instead of simply blocking a single protein's active site, it works by stabilizing the interaction between two key proteins in the cancer-driving pathway, RAF and MEK, locking them together in an inactive state. This unique approach is designed to prevent a common resistance mechanism known as pathway reactivation, where cancer cells find a way to bypass traditional inhibitors, leading to more durable suppression of tumor growth.

Furthermore, NST-628 was engineered to be “brain-penetrant,” a crucial feature that allows it to cross the protective blood-brain barrier. This barrier prevents most drugs from reaching the central nervous system, making brain metastases and primary brain tumors exceptionally difficult to treat. The trial provided compelling early evidence of this capability. One patient with a high-grade astrocytoma, a type of brain cancer, who had previously failed multiple lines of targeted therapy, experienced a remarkable 70% shrinkage of their tumor while on NST-628 monotherapy.

This brain-penetrating ability, combined with its novel mechanism, positions the drug as a potential foundational therapy for a wide array of RAS/MAPK-driven cancers, not just those on the skin.

Broad Potential Beyond Melanoma

The encouraging results were not limited to melanoma. The study showed NST-628 has broad activity across multiple tumor types and genetic profiles. Confirmed responses were observed in patients with KRAS-mutant ovarian and cervical cancers, as well as in colorectal and thymic cancers with specific RAS/RAF pathway mutations.

One particularly notable case involved a patient with KRAS G12V-mutant cervical cancer, who has had an ongoing partial response to the treatment for over a year. Cancers driven by KRAS mutations have long been considered “undruggable,” and seeing such activity from a single agent is a significant signal of the drug's broad potential.

"The clinical evidence of activity in malignancies with BRAF class III mutations, an emerging resistance mechanism to RAS inhibitors, and of brain penetrance consistent with preclinical findings is particularly noteworthy," stated Philip Komarnitsky, MD, PhD, Chief Medical Officer of Nested Therapeutics. He highlighted that these findings support the drug's continued development as both a standalone therapy and in combination with other cancer treatments.

A Favorable Profile Paves the Way Forward

For any new cancer drug, efficacy must be balanced with safety. Aggressive treatments that cause severe side effects can be difficult for sick patients to tolerate. On this front, NST-628 also delivered positive news. The vast majority of treatment-related adverse events were mild to moderate (Grade 1-2), with the most common being manageable skin, gastrointestinal, and ocular issues. Severe side effects were infrequent.

Crucially, at the recommended dose, the treatment was well-tolerated enough that patients maintained 82% of their intended dose intensity, and only 9% of patients had to discontinue treatment due to side effects. This favorable safety profile is essential for a therapy that may need to be taken for an extended period to control advanced cancer.

Backed by $125 million in financing from prominent investors including Goldman Sachs Asset Management and Versant Ventures, Nested Therapeutics is well-positioned to advance its lead candidate. The company plans to continue enrolling patients in the Phase 1 expansion cohorts and will explore NST-628 in other MAPK-driven diseases and in combination with other targeted inhibitors. The journey through clinical trials is long, but for thousands of patients, the data presented today represents a tangible new source of hope.