AMT-116: An Investigational Antibody-Drug Conjugate Targeting CD44v9 for Advanced Solid Tumors

Preliminary Note on Scope: The majority of available information identifies AMT-116 as an antibody-drug conjugate (ADC) for oncological applications. A single source [1] describes an "Autologous Mesenchymal Therapy 116" for musculoskeletal conditions. This report will focus exclusively on the ADC AMT-116, as this aligns with the predominant information and the typical context for such a drug identifier in pharmaceutical development.

I. Introduction to AMT-116

A. Overview and Drug Classification

AMT-116 is an investigational antibody-drug conjugate (ADC) currently under clinical development.[2] ADCs represent a sophisticated class of targeted cancer therapies engineered to selectively deliver a potent cytotoxic agent directly to tumor cells. This targeted approach aims to maximize therapeutic efficacy at the tumor site while minimizing exposure of healthy tissues to the cytotoxic payload, thereby potentially reducing systemic side effects commonly associated with traditional chemotherapy. AMT-116 is being evaluated for the treatment of various neoplasms, with a particular focus on advanced solid tumors.[3] The development of AMT-116 as an ADC is consistent with a significant trend in oncology towards precision medicine, which seeks to improve the therapeutic index of anticancer agents.

The compound is identified by several synonyms in scientific literature and databases, including ADC AMT-116, anti-CD44v9 ADC AMT-116, AMT 116, and AMT116.[2] The consistent use of these synonyms across various platforms facilitates accurate tracking of its development progress.

B. Chemical and Physical Properties

AMT-116 is a complex macromolecule composed of three principal components: a monoclonal antibody, a cytotoxic payload, and a chemical linker that connects them. The antibody component is a humanized immunoglobulin G1 (IgG1) monoclonal antibody specifically designed to recognize and bind to its target on cancer cells.[2] Humanization of the antibody is a critical step to reduce its potential immunogenicity in patients, allowing for repeated administrations with a lower risk of adverse immune reactions. The IgG1 isotype is a common choice for ADC backbones due to its favorable pharmacokinetic properties and its inherent ability to mediate antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), although the primary mechanism of action for most ADCs, including AMT-116, is the delivery of the cytotoxic payload.

The cytotoxic payload conjugated to the antibody is KL610023, which is characterized as a belotecan derivative.[2] Belotecan is a camptothecin analogue, placing KL610023 in the class of topoisomerase I inhibitors. The average drug-to-antibody ratio (DAR) for AMT-116 is reported to be 7-8.[5] This relatively high DAR suggests a substantial capacity for drug delivery per antibody molecule. While a higher DAR can enhance potency, it may also present challenges related to manufacturing consistency, pharmacokinetic stability, and potential for increased off-target toxicity if the ADC is not precisely targeted or if the payload is prematurely released. The optimization of DAR is a critical aspect of ADC design, balancing efficacy with safety.

It is important to note that some database entries [3] provide a molecular formula (C11​H22​N4​O4​) and CAS registry number (159858-33-0). These identifiers are characteristic of a small molecule and are inconsistent with the macromolecular structure of a complete ADC. Therefore, these details likely refer to a smaller component of the ADC or represent a database discrepancy and are not representative of the entire AMT-116 conjugate.

Table 1: Summary of AMT-116 Key Characteristics

Feature	Description	Source(s)
Drug Name	AMT-116	User Query
Synonyms	ADC AMT-116, anti-CD44v9 ADC AMT-116, AMT 116, AMT116	2
Drug Class	Antibody-Drug Conjugate (ADC)	2
Developer	Multitude Therapeutics, Inc.	3
Target Antigen	CD44 variant 9 (CD44v9)	2
Antibody Type	Humanized Immunoglobulin G1 (IgG1) monoclonal antibody	2
Payload Type	KL610023 (Belotecan derivative; Topoisomerase I inhibitor)	2
Linker Type	Hydrolysable linker	2
Average DAR	7-8	5

II. Developer Profile: Multitude Therapeutics, Inc.

A. Company Overview and Strategic Focus

AMT-116 is under development by Multitude Therapeutics, Inc..[3] Multitude Therapeutics is an American corporation headquartered in California, USA, and operates as a subsidiary of Abmart (Shanghai) Co., Ltd..[9] The company also maintains operations in China, identified as Multitude Therapeutics, Inc. (China) [3], and a clinical trial (NCT05725291) lists Multitude Therapeutics (Australia) Pty Ltd as a sponsor.[10] This international footprint facilitates global clinical development strategies and potentially broader market access upon successful drug approval.

Multitude Therapeutics specializes in the discovery and development of innovative antibody-drug conjugates for cancer treatment.[9] The company's strategic approach is centered on leveraging proprietary technology platforms. These include the Human Membrane Proteome MabArrayTM (HMP-MabArrayTM) for target identification and antibody discovery, and a distinct ADC platform designated T1000 for the construction of the conjugates.[11] The integration of these platforms, from initial target discovery to the final ADC assembly, affords the company significant control over the development pipeline and the capacity to rapidly generate and optimize novel ADC candidates. The company's pipeline encompasses both first-in-class and best-in-class ADCs targeting various solid and hematological tumors.[11] Besides AMT-116, other publicly mentioned pipeline candidates include AMT-151, AMT-253, AMT-562, and AMT-676, indicating a productive discovery engine.[9]

B. Leadership and Partnerships

The leadership team at Multitude Therapeutics includes experienced professionals in the biotechnology and pharmaceutical sectors. Key figures are Xun Meng, Ph.D., serving as Chief Executive Officer; Shu-Hui Liu, Ph.D., as Chief Scientific Officer; Yanfang Tang as Chief Operating Officer; and Xiaona Jing, Ph.D., as Senior Vice President of Global Product Development & Partnering.[2] Dr. Meng has a documented history of successfully launching biotechnology companies and developing antibody discovery platforms, such as MabArray.[12] Dr. Liu brings expertise in advancing discovery programs into clinical evaluation.[12] Such experienced leadership is vital for navigating the multifaceted challenges inherent in bringing novel therapeutic modalities like ADCs from concept to market.

Multitude Therapeutics has also engaged in strategic partnerships, which can serve to validate its technology and provide avenues for co-development or financial support. A notable example is the licensing agreement with Adcendo, a Danish biotechnology company, for an anti-Tissue Factor (TF) ADC, ADCE-T02, which was originally licensed from Multitude.[9] This particular deal, reported to be potentially worth up to $1 billion in biobucks (milestone payments and royalties), underscores the perceived value of Multitude's ADC assets and underlying technology by external parties.[9]

III. Mechanism of Action

The therapeutic activity of AMT-116 is predicated on a multi-step process involving specific targeting of cancer cells, internalization of the ADC, and intracellular release of a potent cytotoxic payload.

A. The Target: CD44 Variant 9 (CD44v9)

The monoclonal antibody component of AMT-116 is designed to specifically target CD44 variant 9 (CD44v9), a tumor-associated antigen (TAA).[2] CD44v9 is a particular splicing isoform of CD44, a transmembrane glycoprotein that functions as a cell surface adhesion receptor involved in cell-cell and cell-matrix interactions.[2]

CD44v9 exhibits aberrant overexpression across a wide spectrum of human malignancies. These include, but are not limited to, cancers of the head and neck, lung, esophagus, pancreas, colorectum, breast, bladder, liver, cervix, and stomach.[2] The expression of CD44v9 is not only elevated in these cancers but is also functionally implicated in key aspects of tumor biology, including tumorigenicity, the maintenance of cancer stem cell (CSC) populations, tumor invasiveness, metastatic dissemination, and the development of resistance to conventional chemotherapy and radiotherapy.[2] Consequently, CD44v9 expression has been correlated with poor prognosis in patients with various cancers.[14]

A specific molecular mechanism contributing to its role in cancer progression involves the interaction of CD44v9 with the glutamate-cystine transporter xCT (SLC7A11). This interaction stabilizes xCT at the cell surface, enhancing the uptake of cystine and subsequently promoting the synthesis of reduced glutathione (GSH). Increased intracellular GSH levels bolster the cancer cells' antioxidant capacity, thereby contributing to their resistance against reactive oxygen species (ROS)-induced stress, which is often a mechanism of action for cytotoxic therapies.[15]

The selection of CD44v9 as a target for an ADC like AMT-116 is of considerable strategic interest. Its preferential overexpression on cancer cells, particularly on CSCs which are often responsible for tumor recurrence and treatment failure, and its direct involvement in pathways conferring treatment resistance make it a compelling molecular address for targeted drug delivery.[2] An ideal ADC target is highly expressed on tumor cells with limited or no expression on critical normal tissues, which contributes to a favorable therapeutic window.

B. Antibody Component: Humanized Anti-CD44v9 IgG1

AMT-116 incorporates a humanized immunoglobulin G1 (IgG1) monoclonal antibody that is directed against CD44v9.[2] The process of humanization involves grafting the complementarity-determining regions (CDRs) from a parent murine antibody (which provides the binding specificity) onto a human antibody framework. This genetic engineering step is crucial for minimizing the immunogenicity of the therapeutic antibody when administered to humans, thereby reducing the risk of anti-drug antibody (ADA) formation, which can otherwise lead to allergic reactions, altered pharmacokinetics, and loss of efficacy upon repeated dosing. The IgG1 isotype is frequently selected for ADC development due to its relatively long serum half-life, which allows for sustained drug exposure, and its inherent ability to engage Fc-gamma receptors (FcγRs) and C1q, potentially mediating immune effector functions such as ADCC and CDC. While the primary tumor-killing mechanism of AMT-116 is intended to be the delivered payload, any contribution from these effector functions could be additive.

C. Linker Technology: Hydrolysable Linker

The humanized anti-CD44v9 IgG1 antibody is conjugated to the cytotoxic payload KL610023 via a hydrolysable linker.[2] The linker is a critical component of an ADC, as its properties dictate the stability of the conjugate in systemic circulation and the efficiency of payload release at the target site. Hydrolysable linkers are designed to maintain stability in the bloodstream (neutral pH) to prevent premature release of the toxic payload, which could lead to systemic toxicity. Upon internalization of the ADC into the target cancer cell, these linkers are cleaved, often in response to the distinct biochemical environment within cellular compartments like endosomes or lysosomes (e.g., lower pH or presence of specific enzymes). The term "hydrolysable" is general; the specific chemical nature of the linker (e.g., hydrazone, ester, or certain peptide sequences) determines its precise cleavage mechanism and release kinetics. The available information does not specify the exact chemical composition of the hydrolysable linker used in AMT-116. Efficient and selective payload release within the tumor cell is paramount for maximizing the therapeutic index of the ADC.

D. Payload: KL610023 (Belotecan Derivative, Topoisomerase I Inhibitor)

The cytotoxic warhead of AMT-116 is KL610023.[2] This compound is identified as a derivative of belotecan and functions as a topoisomerase I inhibitor (TOP1i).[2] The payload KL610023 is attributed to Sichuan Kelun-Biotech.[5] DNA topoisomerase I is a nuclear enzyme essential for managing DNA topology during critical cellular processes such as replication, transcription, and repair. It functions by creating transient single-strand breaks in DNA, allowing the DNA to unwind or untangle, and then resealing the break. TOP1i drugs, like camptothecin and its analogues (e.g., irinotecan, topotecan, belotecan), trap the cleavable complex formed between topoisomerase I and DNA. This stabilization of the enzyme-DNA complex prevents DNA re-ligation, leading to the accumulation of single-strand breaks. During the S-phase of the cell cycle, when DNA replication occurs, these single-strand breaks are converted into lethal double-strand breaks by the advancing replication fork, ultimately triggering cell cycle arrest and apoptosis.

It is noteworthy that some database entries [3] also list "Tubulin" as a target and "Tubulin inhibitors" as a mechanism for AMT-116. However, the characterization of KL610023 as a topoisomerase I inhibitor is more consistently and specifically reported across multiple detailed descriptions of AMT-116's composition and mechanism.[2] Therefore, this report prioritizes the topoisomerase I inhibitor mechanism for KL610023.

Topoisomerase I inhibitors are a well-established class of anticancer agents with broad activity against various tumor types. Their incorporation into ADCs is a growing strategy, exemplified by several approved and investigational ADCs. The designation "belotecan derivative" suggests that KL610023 may possess modifications to belotecan's structure aimed at optimizing properties such as potency, solubility, or suitability for conjugation to the linker. The high drug-to-antibody ratio (DAR) of 7-8 for AMT-116 [5], combined with a potent TOP1i payload, suggests a design intended for robust cell-killing efficacy upon successful delivery to the target cell.

E. Cellular Uptake and Payload Release

The mechanism of action of AMT-116 follows the canonical pathway for internalizing ADCs:

1. Administration and Targeting: Following intravenous administration, the AMT-116 conjugate circulates in the bloodstream. The monoclonal antibody moiety specifically seeks out and binds to CD44v9 antigens expressed on the surface of tumor cells.[2]
2. Internalization: Upon binding to CD44v9, the ADC-antigen complex is internalized by the tumor cell, typically through receptor-mediated endocytosis.[2]
3. Intracellular Trafficking and Payload Release: Once inside the cell, the ADC is trafficked through endosomal and lysosomal compartments. Within these organelles, the hydrolysable linker is cleaved, likely due to the acidic pH or the presence of specific lysosomal enzymes, releasing the active payload KL610023 into the cytoplasm.[2]
4. Cytotoxic Action: The released KL610023, a topoisomerase I inhibitor, then translocates to the nucleus where it interacts with DNA topoisomerase I. By inhibiting this enzyme, KL610023 disrupts DNA replication and transcription, leading to DNA damage, cell cycle arrest, and ultimately, apoptotic cell death of the CD44v9-expressing cancer cell.[2]

The efficacy of AMT-116 is dependent on the efficiency of each of these steps, from specific binding and internalization to linker cleavage and payload activity. The selective expression of CD44v9 on tumor cells is fundamental to achieving targeted delivery and minimizing toxicity to normal cells.

IV. Therapeutic Rationale and Target Indications

A. Intended Use: Advanced Solid Tumors and Neoplasms

AMT-116 is being developed primarily for the treatment of neoplasms, with active clinical investigations focusing on patients with "Advanced Malignant Solid Neoplasm" and "Solid tumor" indications.[3] This broad initial scope is characteristic of early-phase oncology drug development, where the primary goals are to establish safety, determine appropriate dosing, and identify preliminary signals of anti-tumor activity across a diverse range of cancer types. The rationale for this broad approach is supported by the reported widespread expression of the target antigen, CD44v9, across numerous solid tumor histologies.[2] As clinical data mature, the development focus typically narrows to those tumor types that demonstrate the most significant and consistent responses, or those with the highest unmet medical need and strong biological rationale for the drug's mechanism. The designation "advanced" generally implies that patients have metastatic or locally advanced disease that is not amenable to curative-intent local therapies, and often have received prior lines of systemic treatment.

B. Specific Tumor Types Under Investigation (Preferred Tumor Types in Early Trials)

Clinical trial protocols for AMT-116, such as NCT05725291 and NCT06782334, specify a list of preferred tumor types for patient enrollment. These include head and neck cancer, non-small cell lung cancer (NSCLC), esophageal cancer, pancreatic cancer, large cell lung cancer, colorectal cancer, cervical cancer, breast cancer, bladder cancer, gastric cancer, biliary tract cancer, skin squamous cell carcinoma, liver cancer (hepatocellular carcinoma), and basal cell carcinoma.[4] This selection of tumor types aligns closely with published literature and abstracts indicating high expression levels of CD44v9 in these malignancies.[2]

Preliminary clinical data from the NCT05725291 study have reported early signs of anti-tumor activity in a patient with anal squamous cell carcinoma (achieving an unconfirmed partial response) and a patient with hepatocellular carcinoma (achieving stable disease with tumor shrinkage).[5] While these are early observations in a small number of patients, such signals are crucial for guiding future cohort expansions or the design of dedicated studies in these specific tumor types if the findings are substantiated with further data.

C. Therapeutic Context and Unmet Medical Need

AMT-116 is being investigated in a patient population with a significant unmet medical need. Eligibility criteria for the ongoing clinical trials typically stipulate that patients must have unresectable advanced solid tumors, have experienced disease progression following at least one prior line of systemic therapy, and either have no further standard therapeutic options available or are intolerant to existing standard therapies.[4] This describes a heavily pre-treated population where prognosis is often poor and treatment options are limited.

The biological role of CD44v9 further underscores the unmet need that AMT-116 aims to address. CD44v9's association with tumorigenicity, cancer stem cell properties, and, critically, resistance to conventional cancer treatments (chemotherapy and radiotherapy) makes it a particularly relevant target.[2] If AMT-116 can effectively target and eliminate CD44v9-expressing cancer cells, especially those that have developed resistance to other therapies, it could offer a valuable new therapeutic avenue for these difficult-to-treat cancers. The selection criteria for clinical trials, such as an Eastern Cooperative Oncology Group (ECOG) performance status of 0-1, adequate organ function, and an anticipated survival duration of at least three months, aim to enroll patients who are sufficiently fit to receive an investigational therapy but are battling advanced, treatment-refractory disease.[4]

V. Non-Clinical and Pre-Clinical Findings

The available documentation predominantly focuses on the clinical development program and the proposed mechanism of action of AMT-116. Detailed pre-clinical efficacy data, comprehensive toxicology studies in animal models, or extensive pharmacokinetic/pharmacodynamic (PK/PD) characterizations from non-clinical experiments are not extensively detailed in the provided sources. However, the progression of AMT-116 into Phase 1 human clinical trials inherently implies the existence of a substantial body of pre-clinical data that would have been reviewed by regulatory authorities (such as ethics committees and national health agencies) prior to trial approval. This pre-clinical package typically includes in vitro studies demonstrating target binding, cellular uptake, and cytotoxicity in cancer cell lines, as well as in vivo studies in animal tumor models to assess anti-tumor activity and establish a preliminary safety profile.

Background information in ASCO abstracts [6] alludes to the pre-clinical rationale supporting the development of AMT-116. Furthermore, one source mentions the development of an anti-drug antibody (ADA)-tolerant pharmacokinetic (PK) assay in monkey plasma for an exatecan-based ADC.[9] Exatecan is a topoisomerase I inhibitor, similar to the payload class of AMT-116 (belotecan derivative). The development of such specialized assays is important for accurately characterizing the behavior of ADCs in vivo, particularly in the presence of ADAs which can complicate PK interpretation. While this specific assay may not be directly for AMT-116, it reflects the type of supportive non-clinical work undertaken for ADCs with similar payloads, potentially within the same developer's portfolio. Such assays are crucial for understanding drug exposure and its relationship to efficacy and toxicity during pre-clinical and clinical development.

VI. Clinical Development Program

A. Overview of Clinical Phases and Regulatory Milestones

AMT-116 is currently advancing through Phase 1/2 of clinical development.[3] This stage typically involves initial safety assessments in humans (Phase 1) followed by preliminary efficacy evaluations in targeted patient populations (Phase 2). The dual Phase 1/2 trial design is a common strategy in oncology to expedite the drug development process by allowing a seamless transition from dose-finding to efficacy assessment within a single protocol, often in specific expansion cohorts.

Key regulatory milestones achieved for AMT-116 include:

• Investigational New Drug (IND) approval for the treatment of Solid tumors in China, granted on January 18, 2024. This approval was obtained through Multitude Therapeutics, Inc. (China).[3]
• Designation of having reached Phase 2 development for Advanced Malignant Solid Neoplasm in China on May 7, 2024, under Multitude Therapeutics, Inc..[3] This likely corresponds to the initiation of the Phase 2 component of the combined Phase 1/2 study (NCT06782334) in that region.

These regulatory achievements, particularly the IND approval in China, signify that AMT-116 has met the initial safety and pre-clinical efficacy thresholds mandated by regulatory authorities for proceeding with human trials.

B. Key Clinical Trials

Two principal clinical trials are currently underway to evaluate AMT-116:

Table 2: Overview of Key Clinical Trials for AMT-116

Trial ID	Phase	Title/Purpose	Sponsor	Key Objectives	Status	Regions
NCT05725291	Phase 1	First-in-Human, Phase 1 Study of AMT-116 in Patients With Advanced Solid Tumors	Multitude, Inc. 3; multitude therapeutics (australia) pty ltd 10	Determine MTD/RP2D; assess safety, tolerability, preliminary anti-tumor activity, PK, immunogenicity	Recruiting	Australia
NCT06782334	Phase 1/2	Phase 1/2 Study of AMT-116 in Patients with Advanced Solid Tumors (AMT-116-02)	Multitude Therapeutics, Inc.	Evaluate safety and efficacy of AMT-116 monotherapy; Part I: Dose escalation, Part II: Dose expansion at RP2D	Recruiting	China

1. Phase 1 First-in-Human Study (NCT05725291)

• Study Design, Objectives, and Endpoints: This ongoing, first-in-human, non-randomized, open-label, multicenter study is designed to evaluate AMT-116 in patients with advanced solid tumors.5 Participants receive escalating intravenous doses of AMT-116 every two weeks (Q2W), commencing at 1.5 mg/kg. Dose escalation is guided by a Bayesian Logistic Regression Model (BLRM) incorporating the Escalation with Overdose Control (EWOC) principle, an adaptive design aimed at optimizing dose selection while controlling for toxicity.5 The primary objectives are to determine the Maximum Tolerated Dose (MTD) and the Recommended Phase 2 Dose (RP2D) of AMT-116, and to comprehensively assess its safety and tolerability profile.3 Secondary objectives include evaluating the preliminary anti-tumor activity, pharmacokinetic (PK) profile, and immunogenicity of AMT-116.3 Exploratory objectives involve the assessment of biomarkers potentially related to AMT-116 response, with a particular focus on CD44v9 expression levels.8 The trial, which began on July 25, 2023 3, is actively recruiting participants.3 The primary study sites are located in Australia 5, with recruitment indicated in New South Wales (NSW), Queensland (QLD), South Australia (SA), and Victoria (VIC).18
• Patient Population and Key Eligibility Criteria: Eligible participants are adults (≥18 years) with a histologically confirmed, unresectable advanced solid tumor.5 Notably, for this initial phase, patients are enrolled unselected for CD44v9 target expression to first establish broad safety.5 Patients must have experienced disease progression after at least one prior systemic therapy and have no further standard therapy options available, or be intolerant to such therapies.10 Other key inclusion criteria include the presence of at least one measurable lesion according to RECIST version 1.1 criteria, an ECOG performance status of 0 or 1, and adequate organ function.10 Significant exclusion criteria include prior treatment with an ADC that utilizes a topoisomerase I inhibitor payload, active or untreated central nervous system (CNS) metastases, certain active skin disorders or ocular conditions requiring systemic therapy, and persistent toxicities (Grade >1) from previous anti-neoplastic treatments.10
• Preliminary Clinical Data (ASCO 2024 Abstract/Presentation - Data as of February 1, 2024): Preliminary findings from this study were presented, based on data available up to February 1, 2024.3
• Enrollment and Dosing: Eight patients had been treated in Australia across three dose cohorts: four patients at 1.5 mg/kg, three patients at 3 mg/kg, and one patient at 5 mg/kg.
• Safety and Tolerability: Patients in the 1.5 mg/kg and 3 mg/kg cohorts completed the 28-day dose-limiting toxicity (DLT) evaluation period. No DLTs were observed in these cohorts. Consequently, the MTD had not yet been reached. Treatment-related adverse events (TRAEs) were reported in 5 of the 8 treated patients. The most common TRAEs (occurring in ≥2 patients) were fatigue (n=3) and nausea (n=3). Only one Grade 3 TRAE, leukopenia, was reported in a single patient. Importantly, no Grade 4 or Grade 5 TRAEs were observed, and there were no treatment-related serious adverse events (SAEs). One source specifically highlighted that no DLT events were observed with AMT-116 at the 3 mg/kg dose level.[3] Dose escalation was ongoing, with subject enrollment in the 5 mg/kg cohort underway at the time of the report.

Table 3: Summary of Key Safety Findings from NCT05725291 (as of Feb 1, 2024)

Dose Level (mg/kg)	No. of Patients	DLTs Observed	MTD Reached	Common TRAEs (any grade)	Grade ≥3 TRAEs	Treatment-Related SAEs
1.5	4	0	No	Fatigue, Nausea	None reported	None
3.0	3	0	No	Fatigue, Nausea	Leukopenia (G3, n=1)	None
5.0	1 (ongoing)	Pending	No	Data pending	Data pending	Data pending

*Source: Based on data from [5, 7, 8, 17]*

*   **Pharmacokinetics (PK) and Pharmacodynamics (PD):** While PK and PD assessments are secondary and exploratory objectives of the study [3, 8, 16, 18], specific data from human subjects were not detailed in the preliminary abstracts beyond the general objectives. *   **Preliminary Anti-Tumor Activity:** Seven of the eight patients had completed at least one post-treatment tumor assessment. At the 3 mg/kg dose level, promising early signals of anti-tumor activity were observed:    *   One patient with anal squamous cell carcinoma achieved an unconfirmed Partial Response (PR), with a reported tumor shrinkage of 31%.    *   One patient with hepatocellular carcinoma achieved Stable Disease (SD), with a tumor shrinkage of 23% from baseline.

**Table 4: Summary of Preliminary Efficacy Data from NCT05725291 (as of Feb 1, 2024)**

Dose Level (mg/kg)	Tumor Type	No. of Evaluable Patients at Dose Level (Overall)	Best Overall Response	Tumor Shrinkage (%)
3.0	Anal Squamous Cell Carcinoma	1 (of 7 total evaluable)	Unconfirmed PR	31%
3.0	Hepatocellular Carcinoma	1 (of 7 total evaluable)	SD	23%

*Source: Based on data from [5, 7, 8]*

The preliminary results from NCT05725291 are generally encouraging. AMT-116 appears to be well-tolerated at the initial dose levels tested, with no DLTs reported up to 3 mg/kg and a manageable TRAE profile consisting primarily of low-grade fatigue and nausea. The absence of Grade 4/5 TRAEs or treatment-related SAEs at these doses is a positive safety indicator. The observation of early anti-tumor activity, including an unconfirmed PR and an SD with notable tumor shrinkage in heavily pre-treated patients, provides an initial positive signal of clinical potential. The "unselected for target expression" strategy in this first-in-human trial, combined with exploratory biomarker analysis (specifically CD44v9 expression) [8], is a standard approach. This allows for initial safety establishment across a broader population, followed by identification of potential predictive biomarkers that could guide patient selection in subsequent trial phases. The use of a sophisticated adaptive trial design like BLRM with EWOC for dose escalation facilitates efficient and safe determination of the MTD. The ongoing dose escalation to 5 mg/kg will be critical for further defining the safety profile and potentially observing enhanced efficacy.

2. Phase 1/2 Study (NCT06782334)

• Study Design, Objectives, and Endpoints: This trial, also identified as AMT-116-02 4, is a Phase 1/2 study evaluating AMT-116 monotherapy in patients with advanced solid tumors.3 The study is sponsored by Multitude Therapeutics, Inc. 3 and its primary purpose is to evaluate the safety and efficacy of AMT-116.3 The study is structured in two parts: Part I is a dose-escalation phase, planning to evaluate five dose levels of AMT-116. Part II is a dose-expansion phase, where patients will be enrolled at the RP2D determined from the data generated in Part I.3 The trial design is non-randomized, open-label, with sequential assignment of patients to cohorts.4 The estimated total enrollment is 144 participants across the two parts of the study.4 This trial commenced on May 7, 2024, and is currently recruiting participants.3 The study is being conducted in China, with several clinical sites actively enrolling or preparing to enroll patients. These include Dongguan People's Hospital (Dongguan, Guangdong), Hunan Cancer Hospital (Changsha, Hunan), The Second Affiliated Hospital and Yuying Childrens Hospital of Wenzhou Medical University (Wenzhou, Zhejiang), Guangxi Medical University Cancer Hospital (Nanning, Guangxi), and Zhejiang Cancer Hospital (Hangzhou, Zhejiang).4
• Patient Population and Key Eligibility Criteria: The eligibility criteria for NCT06782334 are largely similar to those for NCT05725291. Patients must be adults (≥18 years) with histologically confirmed, unresectable advanced solid tumors who have received at least one prior systemic therapy and have documented disease progression, with no further standard therapy available or being intolerable to it.4 Other requirements include at least one measurable lesion per RECIST 1.1, ECOG performance status of 0-1, an anticipated survival of no less than three months, and adequate organ function. Stringent contraception methods are required for patients of childbearing potential.4 A notable inclusion criterion for this study is the availability of a tumor tissue sample (either an archival specimen or fresh biopsy material) at screening 4, which strongly supports planned correlative biomarker research. Key exclusion criteria mirror those of the first-in-human study, including prior therapy with a topoisomerase I inhibitor-based ADC, active CNS metastases, certain active skin or ocular conditions, significant cardiac disease, a history of interstitial lung disease (ILD)/pneumonitis, thromboembolic or cerebrovascular events within the preceding six months, and concurrent use of strong inhibitors or inducers of the cytochrome P450 3A4 (CYP3A4) enzyme.4 The initiation of this Phase 1/2 study in China, particularly its dose expansion phase (Part II), will be instrumental in gathering more robust efficacy data. These expansion cohorts will likely focus on specific tumor types, potentially guided by CD44v9 expression levels or promising signals observed in NCT05725291 and Part I of NCT06782334. The mandatory provision of tumor tissue samples [4] is a clear indication of the intent to conduct comprehensive correlative biomarker studies to identify predictors of response. Conducting this trial in China aligns with the IND approval and the "Phase 2 reached" status reported for AMT-116 in that country [3], suggesting a strategic focus on this geographical region, which could be influenced by factors such as patient recruitment rates, the local regulatory environment, or market positioning strategies. The planned enrollment of 144 patients suggests that the study is adequately powered for initial efficacy assessments in selected patient populations during the dose expansion phase.

C. Overall Clinical Development Strategy

Multitude Therapeutics appears to be employing a parallel and geographically diversified clinical development strategy for AMT-116. The first-in-human study (NCT05725291), primarily conducted in Australia, serves to establish the initial safety profile, MTD, and early pharmacodynamic and efficacy signals. Concurrently, a larger Phase 1/2 study (NCT06782334) is underway in China, designed for both dose escalation and subsequent dose expansion. This approach may accelerate overall development timelines and provide data relevant to different regulatory authorities. The focus on heavily pre-treated patients with advanced solid tumors addresses a clear and significant unmet medical need. A consistent element across these trials is the emphasis on biomarker analysis, particularly the evaluation of CD44v9 expression, which will be vital for identifying patient populations most likely to derive benefit from AMT-116 and for refining patient selection strategies in future, potentially registrational, trials. This aligns with modern precision oncology principles.

VII. Regulatory Status and Future Perspectives

A. Current Regulatory Standing

As of the latest available information, the regulatory progress for AMT-116 is most prominent in China and Australia (the latter primarily as a location for clinical trial conduct). Key regulatory milestones include:

• Investigational New Drug (IND) approval for Solid tumor indications in China, granted on January 18, 2024.[3] This was a prerequisite for initiating clinical trials in that country.
• A designation indicating that AMT-116 reached Phase 2 development status for Advanced Malignant Solid Neoplasm in China on May 7, 2024.[3] This milestone likely coincides with the formal initiation of the Phase 1/2 trial NCT06782334, which includes a Phase 2 dose expansion component.

There is no information in the provided sources regarding specific designations from the U.S. Food and Drug Administration (FDA) (e.g., Fast Track, Orphan Drug Designation, Breakthrough Therapy Designation) or the European Medicines Agency (EMA) for AMT-116.[2] While one document discusses the FDA's Advanced Manufacturing Technologies (AMT) designation program in general terms [19], it is not in specific relation to AMT-116. Other documents mention such designations for different therapeutic agents.[20] The absence of information on FDA or EMA designations at this stage does not preclude future applications for such statuses as more clinical data become available. Future regulatory submissions to these major agencies will be contingent upon the outcomes of the ongoing Phase 1/2 studies.

B. Future Perspectives

AMT-116 represents a rationally designed ADC targeting CD44v9, a tumor-associated antigen with significant clinical relevance due to its widespread expression on various cancers and its established role in tumor progression, cancer stem cell biology, and treatment resistance. The construct, featuring a humanized IgG1 antibody, a hydrolysable linker for controlled payload release, and a potent topoisomerase I inhibitor payload (KL610023) at a relatively high drug-to-antibody ratio of 7-8, provides a strong mechanistic basis for its potential anti-tumor activity.

Preliminary Phase 1 data from the NCT05725291 study are encouraging, suggesting that AMT-116 is well-tolerated at the initial dose levels evaluated (up to 3 mg/kg Q2W), with no DLTs observed and a manageable adverse event profile. Crucially, early signs of anti-tumor activity have been noted in heavily pre-treated patients with advanced solid tumors. The MTD has not yet been reached, and dose escalation continues, which will further clarify the safety profile and optimal dosing.

The ongoing Phase 1/2 trial (NCT06782334) will be pivotal in further defining the safety, tolerability, RP2D, and, importantly, the efficacy of AMT-116. The dose expansion cohorts in this study will allow for a more focused assessment of activity in specific tumor types, likely guided by emerging efficacy signals and correlative biomarker analyses, particularly CD44v9 expression levels.

Key next steps in the clinical development of AMT-116 will include:

• The definitive determination of the MTD and RP2D from the dose escalation portions of both ongoing trials.
• A thorough evaluation of anti-tumor efficacy in specific tumor types within the dose expansion cohorts of NCT06782334, with a strong emphasis on correlating clinical outcomes with CD44v9 expression and other potential biomarkers.
• Comprehensive characterization of the pharmacokinetic and pharmacodynamic profiles of AMT-116, as well as its immunogenicity potential in a larger patient population.
• While current trials are focused on AMT-116 monotherapy, future development could explore its potential in combination with other anticancer agents, depending on its single-agent activity and safety profile.

The development trajectory of AMT-116 is at a critical stage. Successful completion of the current Phase 1/2 studies, demonstrating a clear and clinically meaningful benefit in well-defined patient populations with an acceptable safety profile, will be essential for its progression to later-phase pivotal trials and eventual consideration for regulatory approval. The high DAR and potent topoisomerase I inhibitor payload offer the potential for significant efficacy; however, this will necessitate careful ongoing assessment and management of the therapeutic window to ensure that benefits outweigh risks. The validation of CD44v9 as a predictive biomarker will be a key area of investigation, potentially enabling a more personalized treatment approach. Given the competitive landscape of ADC development and the increasing number of ADCs utilizing topoisomerase I inhibitor payloads, AMT-116 will need to demonstrate distinct advantages or address specific unmet medical needs to carve out its place in the oncology treatment paradigm.

VIII. Conclusion

AMT-116 is an investigational antibody-drug conjugate engineered to target CD44v9, an antigen frequently overexpressed on various solid tumors and implicated in cancer progression and therapeutic resistance. Its design, incorporating a humanized IgG1 antibody, a hydrolysable linker, and the topoisomerase I inhibitor payload KL610023 at a high drug-to-antibody ratio, reflects a rational approach to targeted cancer therapy.

Currently in Phase 1/2 clinical development, AMT-116 has demonstrated preliminary signals of tolerability and anti-tumor activity in early human trials involving patients with heavily pre-treated advanced solid tumors. Ongoing studies, particularly NCT05725291 in Australia and NCT06782334 in China, are focused on determining the optimal dose, further characterizing the safety profile, and evaluating efficacy in broader patient cohorts, with a significant emphasis on biomarker analysis to identify populations most likely to benefit.

The continued investigation of AMT-116 holds promise for addressing unmet medical needs in oncology. Future data from the ongoing clinical trials will be critical in defining its therapeutic potential and guiding its path toward potential regulatory approval and clinical use. The successful establishment of a favorable risk-benefit profile, particularly in biomarker-defined patient populations, will be paramount for its advancement in the evolving landscape of cancer therapeutics.

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