pidnarulex (CX-5461)

Our study examined two "first-in-class" RNA Pol I inhibitors, CX-5461 and BMH-21, which differentially regulate NK cell-activating and inhibitory ligand expression in MM. This effect was modulated by Lenalidomide and Panobinostat. Moreover, RNA Pol I inhibition enhanced Daratumumab-mediated antibody-dependent cellular cytotoxicity (ADCC) of NK cells against MM, uncovering novel immuno-mediated antitumor mechanisms.

This is particularly important given that several clinical trials, including a Phase Ib study of CX-5461 in patients with solid tumours [ NCT04890613 ] and a National Cancer Institute sponsored Phase I trial [ NCT06606990 ] are currently enrolling patients. These ongoing and planned clinical efforts highlight both the therapeutic promise of CX-5461 and the importance of evaluating this agent within rigorous and clinically relevant frameworks.

To investigate the therapeutic potential of three G4 ligands-pidnarulex, APTO-253, and BRACO-19-a high-throughput drug combination screen was conducted in thirty-one multi-cell type tumor spheroids derived from patient tumors and established cancer cell lines. Brightfield imaging corroborated enhanced spheroid growth suppression from synergistic combinations. These findings underscore the context-dependent activity of G4 ligands and support the use of integrated functional and imaging-based approaches to characterize potential therapeutic combinations in physiologically relevant 3D cancer models.

In this study, we examine the response of HGSOC cells to standard of care cisplatin chemotherapy and to the RNA Polymerase I transcription inhibitor CX-5461/Pidnarulex, two drugs that elicit a potent DNA damage response and growth arrest. Mechanistically, we demonstrate that senescent HGSOC cells have altered expression of regulators of iron metabolism leading to intracellular iron overload that underpins this targetable vulnerability. Together, we highlight elevated levels of iron as a TIS biomarker in HGSOC and the potential of inducing ferroptosis to eradicate residual HGSOC cells following initial therapy.

While etoposide similarly induces G4-related DNA damage, it does not affect the ATRX-TOP2B interaction, highlighting CX-5461's unique mechanism. Our findings establish TOP2B as a critical player in G4 resolution, reveal CX-5461's dual function as a TOP2B poison and G4 stabilizer, and propose G4-associated replication stress as a potential therapeutic target in ATRX-deficient gliomas.

P1/2, N=50, Not yet recruiting, National Cancer Institute (NCI) | Initiation date: Sep 2025 --> Dec 2025

Reduction of rDNA transcription by CX-5461, an RNA polymerase I inhibitor, significantly inhibited NSCLC cell proliferation...DCAF13 knockout inhibited NSCLC cell proliferation, colony formation, and migration, indicating that DCAF13 is a poor prognosis indicator of NSCLC. In summary, we found that DCAF13 promotes NSCLC cell proliferation by coordinating with TAF1A to regulate rDNA transcription and maintain high ribosome biogenesis.

Combining a translation inhibitor with an rRNA synthesis inhibitor may synergize to prevent the synthesis of proteins that NPC cells depend on for growth and survival. Given that c-myc, Cyclin D1 and eIF5A are essential in cell cycle progression and cell proliferation, this finding puts forward a promising new synergistic treatment approach for NPC.

P1, N=52, Recruiting, Senhwa Biosciences, Inc. | Trial completion date: Jun 2025 --> Dec 2026 | Trial primary completion date: Dec 2024 --> Dec 2025

Here, using the well-established IMR-32 cell line along with a previously established panel of patient-derived neuroblastoma cell lines with varying MYCN status, we show that RNA polymerase I inhibition following exposure to CX-5461 and BMH-21 suppressed cell proliferation at nanomolar concentrations and induced ribosomal stress, leading to the activation of apoptosis and the p21 pathway...In conclusion, our study reinforces the therapeutic potential of ribosome biogenesis inhibition in neuroblastoma and expands the list of potential targets to include rRNA maturation factors. These findings highlight the relevance of targeting ribosome biogenesis as a novel approach for neuroblastoma treatment.

P1/2, N=50, Not yet recruiting, National Cancer Institute (NCI)

Notably, CX-5461, a first-in-class RNA PolI inhibitor currently in clinical trials, synergizes with GPX4 blockade to induce ferroptotic cell death both in vitro and in vivo. This therapeutic synergy extends beyond PM, suggesting broader relevance in ferroptosis-resistant cancers. Together, our findings reveal a novel mechanism of ferroptosis evasion and establish a promising combinatorial strategy to overcome therapy resistance in cancer.