Introduction: The Therapeutic Challenge of RNA Splicing in Myeloid Malignancies
For clinicians treating relapsed or refractory (R/R) acute myeloid leukemia (AML) and higher-risk myelodysplastic syndrome (MDS), the therapeutic landscape remains one of the most challenging in hematology. Despite the advent of targeted therapies such as FLT3 and IDH inhibitors, a significant proportion of patients either fail to respond or eventually succumb to resistant disease. Recent genomic characterization has highlighted that mutations in splicing factors—such as SF3B1, SRSF2, U2AF1, and ZRSR2—are among the most frequent molecular alterations in myeloid malignancies, particularly in MDS and secondary AML. These mutations lead to aberrant mRNA splicing, driving oncogenesis and therapeutic resistance. Rogocekib (CTX-712) emerges as a first-in-class, orally available small-molecule inhibitor of CDC2-like kinase (CLK), offering a novel strategy to exploit these vulnerabilities by modulating the RNA splicing process.
Highlight
First-in-Class Mechanism
Rogocekib is a potent and selective inhibitor of CLK, a key regulator of the spliceosome, representing a novel therapeutic class for hematologic malignancies.
Encouraging Clinical Activity
In a Phase 1 setting, rogocekib achieved a 25% complete remission (CR) rate in patients with relapsed or refractory AML and a 50% CR rate in higher-risk MDS.
Target Engagement Confirmed
Pharmacodynamic analyses demonstrated a dose-dependent increase in exon skipping within peripheral blood cells, validating the drug’s mechanism of action in humans.
Manageable Safety Profile
The study identified a tolerable safety profile at the 70 mg and 105 mg dose levels, with dose-limiting toxicities being manageable and predictable.
Mechanism of Action: Inhibiting CDC2-like Kinase (CLK)
CDC2-like kinases (CLKs) play a pivotal role in the regulation of the spliceosome. They phosphorylate serine/arginine-rich (SR) proteins, which are essential for the selection of splice sites during pre-mRNA processing. By inhibiting CLK, rogocekib disrupts the phosphorylation cycle of these SR proteins, leading to widespread changes in alternative splicing. Preclinical data suggested that cancer cells, particularly those with existing splicing factor mutations or high transcriptional stress, are exquisitely sensitive to the pharmacological inhibition of CLK. Rogocekib’s ability to induce exon skipping and subsequent transcript degradation or protein isoform switching provides a unique mechanism to target the ‘splicing addiction’ of malignant cells.
Study Design and Methodology
This Phase 1 study was a first-in-human, open-label, dose-escalation trial conducted in Japan (jRCT2080224127). The primary objectives were to evaluate the safety, tolerability, and pharmacokinetics (PK) of rogocekib in patients with R/R hematologic malignancies, specifically focusing on AML and higher-risk MDS. Utilizing a traditional 3+3 dose-escalation design, the study was informed by previous safety data obtained from solid tumor cohorts.
Patients were administered rogocekib in capsule form twice weekly. The cohorts evaluated dose levels of 70 mg and 105 mg. The inclusion criteria targeted patients who had exhausted standard therapeutic options, representing a heavily pretreated population with poor prognostic outlooks. Key secondary endpoints included preliminary efficacy, assessed by international working group criteria, and pharmacodynamic (PD) markers of spliceosome modulation.
Key Findings: Efficacy and Clinical Response
The preliminary efficacy results from this Phase 1 trial are particularly noteworthy given the refractory nature of the patient population.
Acute Myeloid Leukemia (AML) Cohort
Among the 12 evaluable patients with AML, rogocekib demonstrated substantial clinical activity:
– Complete Remission (CR): 3 patients (25.0%)
– Complete Remission with Incomplete Hematologic Recovery (CRi): 1 patient (8.3%)
– Overall, 33.3% of the AML cohort experienced a significant clinical response.
Myelodysplastic Syndrome (MDS) Cohort
In the MDS group (n = 2), the response was equally encouraging:
– Complete Remission (CR): 1 patient (50.0%)
These findings suggest that rogocekib can induce deep molecular and hematologic responses even after multiple lines of prior therapy, including hypomethylating agents and venetoclax-based regimens.
Safety and Tolerability Profile
Safety is a paramount concern for splicing inhibitors, given the fundamental role of splicing in normal cellular homeostasis. In this study, rogocekib demonstrated a manageable safety profile.
At the 105 mg twice-weekly dose, one dose-limiting toxicity (DLT) was recorded: a case of grade 4 pneumonia. However, most adverse events were consistent with the underlying disease state and the known effects of intensive hematologic therapies. The twice-weekly dosing schedule appeared to provide a sufficient therapeutic window to allow for splicing modulation in malignant cells while minimizing systemic toxicity to healthy tissues.
Pharmacokinetics and Pharmacodynamics
Pharmacokinetic (PK) analysis revealed that rogocekib follows a dose-proportional increase in exposure. The mean maximum plasma concentration (Cmax) and the area under the curve (AUC0-24) were significantly higher in the 105 mg cohort compared to the 70 mg cohort.
Critically, the pharmacodynamic (PD) analysis confirmed target engagement. Researchers measured the relative magnitude of exon skipping in peripheral blood cells—a direct consequence of CLK inhibition. The results showed that exon skipping increased in a manner correlated with rogocekib exposure. This clear PK/PD relationship provides a robust rationale for dose selection in subsequent Phase 2 studies.
Expert Commentary: The Future of Splicing Inhibition
The success of rogocekib in achieving complete remissions in R/R AML and MDS highlights the maturing field of spliceosome-targeted oncology. While early attempts at inhibiting the spliceosome (e.g., targeting SF3B1 directly) were often limited by narrow therapeutic windows and significant gastrointestinal toxicity, targeting the regulatory kinases like CLK appears to offer a more nuanced and tolerable approach.
A limitation of the current study is the small sample size, typical of Phase 1 trials. Future analyses will need to determine if specific mutations—such as those in SRSF2 or U2AF1—predict a superior response to rogocekib. Furthermore, the observation of pneumonia as a DLT necessitates careful monitoring of pulmonary function and infectious complications in larger cohorts.
Conclusion
Rogocekib (CTX-712) represents a promising first-in-class therapeutic option for patients with relapsed or refractory AML and MDS. By successfully targeting the CLK-regulated splicing pathway, rogocekib has demonstrated the ability to induce complete remissions with a manageable safety profile. The ongoing Phase 1/2 study in the United States (NCT05732103) will be instrumental in refining the dose and further validating the efficacy of this novel agent. For the clinical community, rogocekib offers a potential new pillar in the precision medicine toolkit for myeloid malignancies.
Funding and Clinical Registry Information
This research was supported by the Japan Registry of Clinical Trials (jRCT2080224127). The ongoing global clinical evaluation is registered at ClinicalTrials.gov under the identifier NCT05732103.
References
1. Yokoyama H, Fukuhara N, Ando K, et al. Phase 1 study of rogocekib in patients with relapsed or refractory hematologic malignancies. Blood Adv. 2026 Jan 13;10(1):262-272. doi: 10.1182/bloodadvances.2025017601. PMID: 41056522.
2. Graubert TA, et al. Somatic mutations in the RNA splicing machinery in myelodysplastic syndromes. Nature. 2011;478(7367):103-107.
3. Seiler M, et al. Somatic Mutations in Subsets of Gastrointestinal Cancers Alter Mutually Exclusive Splicing and Generate Pro-tumorigenic Isoforms. Cell Rep. 2018;23(5):1461-1476.