A Smo/Gli multitarget hedgehog pathway inhibitor impairs tumor growth

Pharmacological Hedgehog (Hh) pathway inhibition has emerged as a valuable anticancer strategy. A number of small molecules able to block the pathway at the upstream receptor Smoothened (Smo) or the downstream effector glioma-associated oncogene 1 (Gli1) has been designed and developed. In a recent study, we exploited the high versatility of the natural isoflavone scaffold for targeting the Hh signaling pathway at multiple levels showing that the simultaneous targeting of Smo and Gli1 provided synergistic Hh pathway inhibition stronger than single administration. This approach seems to effectively overcome the drug resistance, particularly at the level of Smo. Here, we combined the pharmacophores targeting Smo and Gli1 into a single and individual isoflavone, compound 22, which inhibits the Hh pathway at both upstream and downstream level. We demonstrate that this multitarget agent suppresses medulloblastoma growth in vitro and in vivo through antagonism of Smo and Gli1, which is a novel mechanism of action in Hh inhibition

SALL4 is a CRL3REN/KCTD11 substrate that drives Sonic Hedgehog-dependent medulloblastoma

The Sonic Hedgehog (SHH) pathway is crucial regulator of embryonic development and stemness. Its alteration leads to medulloblastoma (MB), the most common malignant pediatric brain tumor. The SHH-MB subgroup is the best genetically characterized, however the molecular mechanisms responsible for its pathogenesis are not fully understood and therapeutic benefits are still limited. Here, we show that the pro-oncogenic stemness regulator Spalt-like transcriptional factor 4 (SALL4) is re-expressed in mouse SHH-MB models, and its high levels correlate with worse overall survival in SHH-MB patients. Proteomic analysis revealed that SALL4 interacts with REN/KCTD11 (here REN), a substrate receptor subunit of the Cullin3-RING ubiquitin ligase complex (CRL3REN) and a tumor suppressor lost in ~30% of human SHH-MBs. We demonstrate that CRL3REN induces polyubiquitylation and degradation of wild type SALL4, but not of a SALL4 mutant lacking zinc finger cluster 1 domain (ΔZFC1). Interestingly, SALL4 binds GLI1 and cooperates with HDAC1 to potentiate GLI1 deacetylation and transcriptional activity. Notably, inhibition of SALL4 suppresses SHH-MB growth both in murine and patient-derived xenograft models. Our findings identify SALL4 as a CRL3REN substrate and a promising therapeutic target in SHH-dependent cancers

Synergistic inhibition of the Hedgehog pathway by newly designed Smo and Gli antagonists bearing the isoflavone scaffold

Hedgehog (Hh) signaling pathway inhibition has emerged in recent years as a druggable target for anticancer therapy. [1] We previously identified Glabrescione B (GlaB), an isoflavone naturally found in the seeds of Derris glabrescens (Leguminosae), as a novel small molecule that proved to interfere with Gli1/DNA interaction. [2] We provided the total synthesis of GlaB based on the deoxybenzoin route, allowing the structure activity relationship elucidation through the preparation of a small-size focused library of isoflavones. Target preference has been achieved by the introduction of specific bulky substitutions at meta position (targeting Gli1) or para position (targeting Smo) of the isoflavone’s ring B that is able to block the pathway respectively at the downstream effector Gli1 or the upstream receptor Smo. [3] Interestingly, the combined administration of two different isoflavones behaving as Smo and Gli1 antagonists in primary medulloblastoma cells has shown synergistic Hh inhibition at doses that are around 20-fold lower than single administration, thus leading the way to further and innovative combination therapy for the treatment of Hh-dipendent tumors. This approach seems to effectively overcome the drug resistance, particularly at the level of Smo. Thus, we combined the pharmacophores targeting Smo and Gli1 into a single and individual isoflavone, compound 22, which inhibits the Hh pathway at both upstream and downstream level and suppresses medulloblastoma growth in vitro and in vivo through antagonism of Smo and Gli1 providing a novel mechanism of action in Hh inhibition. Our study encourages the use of a multitargeting approach for the treatment of Hh-driven tumors and provides significant support in oncology research for the development of new clinically relevant Hh inhibitors. References: [1]. Ghirga F et al. (2018). Bioorganic Med. Chem. Lett. 28: 3131-3140. [2]. Infante P et al. (2015). The EMBO Journal 34: 200-217. [3]. Berardozzi S et al. (2018). Eur. J. Med. Chem. 156: 554-562. [4]. Lospinoso Severini et al. (2019). Cancers 11. 1518