Why the Myristoyl Pocket Changes Everything in CML

The BCR-ABL oncoprotein drives chronic myeloid leukemia by constitutively activating a tyrosine kinase that forces uncontrolled proliferation of myeloid cells — and targeting it with small molecules has been one of oncology’s most instructive success stories. The first wave of BCR-ABL tyrosine kinase inhibitors (TKIs), including imatinib, binds the ATP-binding site of the kinase domain, locking the enzyme in its inactive conformation. This approach transformed CML from a disease with a poor prognosis into one manageable with daily oral therapy, as recognised by Nobel Prize-adjacent science and validated by decades of clinical data catalogued by institutions including NIH.

The limitation of ATP-site inhibitors is resistance. Point mutations in the BCR-ABL kinase domain — most notoriously the T315I “gatekeeper” mutation — sterically block drug binding, leaving patients without effective therapy. Second- and third-generation ATP-site TKIs (dasatinib, nilotinib, bosutinib, ponatinib) addressed many resistance mutations but not T315I uniformly, and their safety profiles carry cardiovascular and other liabilities.

STAMP inhibitors exploit this structural biology insight. By binding the myristoyl pocket rather than the ATP site, they inhibit BCR-ABL through a mechanistically orthogonal route. This means resistance mutations that disable ATP-site TKIs do not automatically confer resistance to STAMP inhibitors, and the two drug classes can in principle be combined for additive or synergistic inhibition — a combination strategy now being explored in clinical trials across the CML pipeline.

TERN-701: Mechanism, Chemistry, and Clinical Position

TERN-701 is an oral, once-daily BCR-ABL STAMP inhibitor belonging to the aminopyrimidine chemical class, developed by Terns Pharmaceuticals specifically to target the myristoyl pocket of BCR-ABL. Patent filings by Terns Pharmaceuticals covering compounds of Formula (I) — the aminopyrimidine scaffold underlying TERN-701 — describe utility in treating both chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL), the two primary BCR-ABL-driven malignancies.

The aminopyrimidine scaffold is a deliberate chemical choice. Aminopyrimidine-based compounds have established precedent in kinase drug discovery for combining potency with oral bioavailability, and Terns’ extensive patent portfolio — spanning more than 30 US and PCT applications filed between October 2022 and early 2025 — reflects the breadth of chemical space the company has explored around this core scaffold. The patent families include not only composition-of-matter claims for individual compounds but also method-of-treatment claims covering the use of BCR-ABL inhibitors in CML and Ph+ ALL, filed as recently as February 2025 (US20250049768A1 and WO2025035026A1).

TERN-701 is currently in Phase 2 clinical development for CML. Its STAMP mechanism — allosteric inhibition of BCR-ABL through the myristoyl pocket — is designed to retain activity against the T315I gatekeeper mutation that limits the utility of most ATP-site TKIs. This positions TERN-701 not only as a potential therapy for TKI-resistant patients but also as a candidate for combination regimens with existing ATP-site inhibitors, a strategy that could deepen molecular responses and potentially improve rates of treatment-free remission.

Merck’s $6.7B Bet: What the Acquisition Signals

Merck’s agreement to acquire Terns Pharmaceuticals for approximately $6.7 billion is one of the largest oncology deals of 2025, and its logic is straightforward: TERN-701 represents a potential best-in-class or first-in-class opportunity in a CML market that Novartis’s asciminib (Scemblix) has demonstrated is commercially substantial and scientifically expandable. Merck is paying a significant premium to enter the STAMP inhibitor class with a Phase 2 asset rather than building from scratch.

“Merck’s $6.7 billion acquisition of Terns Pharmaceuticals is a direct wager that the STAMP inhibitor mechanism — allosteric BCR-ABL inhibition via the myristoyl pocket — will define the next generation of CML treatment, and that TERN-701 can compete with or surpass asciminib.”

The deal reflects several converging pressures in the CML drug development landscape. First, the market for CML therapy is durable: patients typically remain on treatment for years or indefinitely, generating long-term revenue streams that justify large upfront acquisition costs. Second, the STAMP mechanism has been clinically validated by asciminib’s regulatory approval and commercial uptake, reducing the mechanistic risk that would otherwise attach to a novel allosteric approach. Third, TERN-701’s Phase 2 stage means Merck is acquiring a programme with meaningful human clinical data, compressing the timeline to potential regulatory submission compared to earlier-stage assets.

For the broader oncology deal-making environment, the acquisition underscores how differentiated mechanism — not just indication — is driving M&A premiums. TERN-701 is not a “me-too” CML drug; its STAMP mechanism, aminopyrimidine chemistry, and specific myristoyl pocket binding profile give it a distinct intellectual property position, as evidenced by Terns’ extensive patent estate. Merck is acquiring both the clinical asset and the IP fortress that protects it, as tracked across PatSnap’s innovation intelligence platform.

The acquisition also has implications for combination therapy development. TERN-701’s myristoyl pocket mechanism is mechanistically complementary to ATP-site TKIs, and Merck’s broader oncology portfolio provides potential combination partners. Regulatory agencies including the FDA have shown willingness to approve combination regimens in haematological malignancies when clinical benefit is demonstrated, creating a pathway for TERN-701 to be developed both as monotherapy and as part of a combination backbone.

The BCR-ABL Patent Race: Terns’ IP Fortress

Terns Pharmaceuticals has constructed one of the most extensive BCR-ABL inhibitor patent portfolios in the pharmaceutical industry, with more than 30 patent applications filed across US and PCT jurisdictions between October 2022 and February 2025. The patent families cover aminopyrimidine compounds of Formula (I) — the chemical scaffold underlying TERN-701 — through multiple composition-of-matter filings that collectively claim a broad chemical space around the myristoyl pocket-binding aminopyrimidine series.

The filing strategy is notable for its layered architecture. Early PCT applications filed in October 2022 (WO2022213061A1 through WO2022213066A1) established the foundational composition-of-matter claims for the aminopyrimidine series. These were followed by successive US national phase and continuation applications throughout 2023 and 2024, progressively refining the claimed chemical structures and expanding into distinct structural subsets. The most recent filings in early 2025 (US20250049768A1 and WO2025035026A1) shift from composition-of-matter to method-of-treatment claims, covering the use of BCR-ABL inhibitors specifically for treating CML and Ph+ ALL — a strategic move that extends IP protection beyond the compound itself to the therapeutic application.

This layered filing strategy — composition of matter followed by method of treatment — is a well-established pharmaceutical IP approach documented in patent strategy literature and reviewed by bodies including WIPO. It means that even after composition-of-matter patents expire, method-of-treatment patents can continue to provide exclusivity for specific therapeutic indications. For Merck, acquiring this portfolio means inheriting not just TERN-701 as a compound but a multi-layer IP structure designed to defend market position across the BCR-ABL inhibitor space for an extended period.

The CML Competitive Pipeline: STAMP Inhibitors Head-to-Head

The STAMP inhibitor class in CML is currently defined by two principal assets: asciminib (Scemblix), the approved Novartis drug that established the class, and TERN-701, the Terns/Merck challenger now in Phase 2. Understanding how they compare — and where TERN-701 may differentiate — is central to assessing the strategic rationale for Merck’s $6.7 billion acquisition.

Asciminib: The Class-Defining Benchmark

Asciminib was the first STAMP inhibitor to receive regulatory approval, establishing proof of concept for myristoyl pocket targeting in CML. Its approval covered patients with CML in chronic phase who had been previously treated with two or more TKIs, and separately for patients with the T315I mutation — precisely the patient population where ATP-site TKIs fail. Asciminib’s commercial success has validated the STAMP mechanism and created the market infrastructure — clinical familiarity, reimbursement pathways, patient identification — that any subsequent STAMP inhibitor will benefit from.

TERN-701: Differentiation Thesis

TERN-701’s differentiation thesis rests on several potential advantages over asciminib that Terns Pharmaceuticals has pursued through its aminopyrimidine chemical programme. The once-daily oral dosing schedule — consistent with Terns’ development goals as reflected in their patent and clinical filings — is designed to match or improve on asciminib’s dosing convenience. The aminopyrimidine scaffold was selected to optimise the pharmacokinetic and selectivity profile of myristoyl pocket binding, with Terns’ extensive patent portfolio reflecting the depth of medicinal chemistry optimisation that went into identifying TERN-701 as the lead candidate from the broader aminopyrimidine series.

The Broader CML Pipeline Context

Beyond the STAMP inhibitor class, the CML pipeline reflects the disease’s maturation as a treatable condition where the frontier of innovation has shifted from achieving response to achieving treatment-free remission (TFR) — the goal of allowing patients to discontinue therapy entirely while maintaining molecular remission. This goal drives interest in combination approaches pairing STAMP inhibitors with ATP-site TKIs, and potentially with emerging agents targeting BCR-ABL-independent survival pathways. The European Medicines Agency (EMA) and FDA have both signalled openness to combination endpoints in haematological malignancies, creating regulatory pathways for the combination strategies that TERN-701’s mechanism enables.

For IP strategists and R&D leaders tracking the CML space, the Merck-Terns deal sets a new benchmark for how the market values a differentiated BCR-ABL asset. The $6.7 billion price tag — for a Phase 2 compound in a disease with an existing approved drug in the same class — reflects the long-duration revenue profile of CML therapy, the depth of TERN-701’s IP protection, and Merck’s assessment that the STAMP mechanism has substantial remaining commercial runway. Monitoring the evolving patent landscape, clinical milestones, and competitive filings in this space is now a strategic priority for any organisation with exposure to oncology drug development, as detailed in PatSnap’s innovation intelligence resources.