Targeting werner helicase with synthetic lethality in microsatellite instability cancers: Promising therapeutic approaches

Two recent companion papers published in Nature have reported two promising drug candidates, HRO761¹ and VVD-133214,² for microsatellite instability (MSI) cancers targeting the werner syndrome RecQ helicase (WRN), a synthetic lethal target in cancer cells with MSI. Currently, both candidates are undergoing clinical trials to evaluate their safety, tolerability, and preliminary antitumor activity in MSI patients.

Microsatellites, also known as short tandem repeats, are susceptible to slippage errors during replication, rendering them heavily reliant on the DNA mismatch repair (MMR) system. MMR deficiency results in widespread MSI by failing to correct replication errors, thus initiating cancer via aberrant tumor suppressor gene function. The prevalence of MSI ranges from 10% to 30% across multiple cancer types, such as colorectal, endometrial, ovarian, and gastric cancers.^1-3 In MSI tumors, deficiencies in MMR mechanisms heighten genomic instability, prompting the activation of alternative DNA repair pathways, including those implicating WRN. Inhibitors targeting WRN in MSI cancer cells, which already possess compromised DNA repair mechanisms, may induce synthetic lethality, thereby triggering DNA damage and subsequent cancer cell death. This targeted approach is ineffective against normal or microsatellite instability (MSS) cells, as their MMR mechanisms remain intact. Hence, WRN inhibitors emerge as a highly promising synthetic lethal agent, with the potential to selectively eradicate tumor cells while sparing normal cells (Figure 1A).

Novartis researchers reported HRO761,¹ a novel WRN helicase inhibitor (Figure 1B) which targets the ATPase of WRN as a noncovalent inhibitor. Cocrystal structures of HRO761 with WRN helicase revealed its binding to a nonconserved site at the D1–D2 interface, immobilizing WRN in an inactive conformation with an approximate 180° rotation relative to the adenosine triphosphate (ATP)-bound conformation (Figure 1C). Despite its 702 Da molecular weight, HRO761 displayed favorable physicochemical properties and pharmacokinetics (PK), with a clean off-target profile. In vitro cellular assays showed that HRO761 exhibits an IC₅₀ of 100 nM in ATPase assays at high ATP concentration, effectively impairing the viability of MSI cancer cells, while showing no effect in MSS cells. Furthermore, characterization of HRO761 treatment effects on MSI cells revealed time- and dose-dependent cell cycle arrest and DNA damage, regardless of p53 mutation status. In the SW48 cell-derived xenografts (CDX) model, oral administration of 15–60 mg/kg HRO761 resulted in significant tumor regression without observed toxicity. Additionally, combination therapy involving HRO761 with other antitumor drugs may enhance treatment efficacy and reduce side effects and resistance. In vivo studies show complete tumor regression with combination of HRO761 and irinotecan, without affecting body weight. Consequently, clinical trial NCT05838768 is presently underway to explore the synergistic effects of HRO761 when combined with either irinotecan or tislelizumab.

On the same day, Vividion Therapeutics researchers reported another WRN inhibitor, VVD-133214 (also known as RO7589831).² Unlike HRO761, VVD-133214 acts as an irreversible covalent inhibitor. Cocrystal analysis revealed that VVD-133214 can bind to the ATPase domain simultaneously with adenosine diphosphate (ADP), forming a covalent bond with the sulfur atom of C727 (Figure 1C). VVD-133214 demonstrates ADP cooperativity, wherein preincubation with ADP reduces its IC₅₀ to 0.1 μM, compared to 3 μM in the absence of ADP. In vitro studies showed that VVD-133214 exhibited sensitivity in nearly 80% of MSI-high (MSI-H) cell lines (11 out of 14), while MSS cell lines showed no responsiveness. Oral administration of VVD-133214 at ≥5 mg/kg once daily achieved nearly complete (approximately 95%) tumor target engagement. Remarkably, VVD-133214 exhibited efficacy in decreasing tumor burden in six out of seven distinct MSI-H colorectal cancer patient-derived xenograft (PDX) models, including those with p53 mutations.

Synthetic lethality is a significant advancement in cancer treatment, offering a novel strategy, particularly for addressing previously challenging mutations. Unlike traditional therapies that target rapidly dividing cells indiscriminately, synthetic lethality exploits genetic differences to selectively eliminate tumor cells with specific mutations while sparing normal cells. This approach minimizes side effects and damage to healthy tissues, providing more precise and effective treatment options for cancer patients.

In 2014, AstraZeneca's PARP inhibitor olaparib became the first FDA-approved synthetic lethality inhibitor for treating breast cancer susceptibilty gene mutated ovarian cancer, marking the beginning of synthetic lethality therapy for cancer. In 2019, a series of independent studies revealed a therapeutic potential synthetic lethality relationship between WRN and MSI tumors, sparking interest in targeted drug development against WRN, and attracted attention from global pharmaceutical giants such as Roche, Novartis, and GSK. Novartis possesses patents for several WRN inhibitors, notably HRO761. Additionally, Vividion, a Bayer subsidiary, collaborated with Roche to develop VVD-133214 in 2020, while GSK acquired IDEAYA's WRN project for developing candidate drugs targeting WRN. Figure 1B lists some active WRN inhibitors, among which the Vividion and GSK⁴ series are known as covalent inhibitors. Their diverse scaffolds suggest considerable potential for further exploration in developing WRN-targeting inhibitors.

However, identifying inhibitors targeting WRN has presented challenges due to the abundance of false positives, such as protein interference. Previously published compounds like NSC617145, NSC19630, and ML216 have undergone rigorous validation and have been proven not to be specific WRN inhibitors.⁵ Moreover, targeting the ATPase domain poses challenges due to the conservative nature of the domain, prompting exploration of allosteric inhibitors as a promising strategy for reducing drug toxicities. Both HRO761 and VVD-133214 bind to the allosteric site near C727, inducing conformational changes in WRN, thereby enhancing specificity in regulating the target protein's function. Furthermore, the selectivity of WRN inhibitors towards other members of the RECQ helicase family is crucial, as these enzymes play significant roles in cellular functions such as senescence and DNA repair. Off-target effects may lead to severe toxic side effects. HRO761 shows excellent selectivity, with an IC₅₀ of 0.1 μM for WRN and >100 μM for other RECQ helicases, indicating promising development prospects.

In summary, recent reports in Nature highlight the growing interest in WRN synthetic lethality in MSI tumor therapy. Both HRO761 and VVD-133214 exhibit specificity for MSI cancer cells, inducing cancer cell death while preserving healthy cells. Preclinical studies demonstrate their efficacy in reducing tumor burden and inducing regression in MSI cancer models. Currently, both compounds are undergoing Phase I clinical trials to evaluate their safety and tolerability. These discoveries highlight the significant potential of WRN inhibitors in the treatment of MSI cancers, and advancing precision medicine strategies in oncology.

Huanzhang Xie: Visualization (lead); writing—original draft (lead). Jing Zhang: Conceptualization (lead); writing—review and editing (equal). Both authors have read and approved the final manuscript.

The authors declare no conflict of interest.

The authors have nothing to report.