Structural revision of the Mcl-1 inhibitor MIM1: synthesis and biological studies on ovarian cancer cells with evaluation of designed analogues

In the area of cancer research, the development of new and potent inhibitors of anti-apoptotic proteins is a very active and promising topic. The small molecule MIM1 has been reported earlier as one of the first selective inhibitors of the anti-apoptotic protein Mcl-1. In the present paper, we first revised the structure of this molecule based on extensive physicochemical analyses. Then we designed and synthesized a focused library of analogues for the corrected structure of MIM1. Next, these molecules were subjected to a panel of in cellulo biological studies, allowing the identification of dual Bcl-x_L/Mcl-1 inhibitors, as well as selective Mcl-1 inhibitors. These results have been complemented by fluorescence polarization assays with the Mcl-1 protein. Preliminary structure-activity relationships were discussed and extensive molecular modelling studies allowed us to propose a rationale for the biological activity of this series of new inhibitors, in particular for the selectivity of inhibition of Mcl-1 versus Bcl-x_L.

Pyridoclax-loaded nanoemulsion for enhanced anticancer effect on ovarian cancer

BACKGROUND

Pyridoclax is an original lead, recently identified as very promising in treatment of chemoresistant ovarian cancers. To correct the unfavorable intrinsic physico-chemical properties of this BCS II drug, a formulation strategy was implied in the drug discovery step. Pyridoclax-loaded nanoemulsions (NEs) were developed to permit its preclinical evaluation.

RESULTS

The resulting nanoemulsions displayed a mean size of about 100 nm and a high encapsulation efficiency (>95%) at a drug loading of 2 wt%, enabling a 1,000-fold increase of the Pyridoclax apparent solubility. NEs have enabled a sustained release of the drug as assayed by a dialysis bag method. In addition, anti-tumor effects of the Pyridoclax-loaded nanoemulsions (PNEs) showed a 2.5-fold higher activity on chemoresistant ovarian cancer cells than free Pyridoclax. This effect was confirmed by a drastic increase of caspase 3/7 activation from 10 µM PNEs, as newly objectified by real time apoptose imaging. The Pyridoclax bioavailability was kept unchanged after encapsulation in nanoemulsions as determined in a mice model after oral administration.

CONCLUSION

Thus, NEs should permit valuable Pyridoclax oral administration, and valorization of this promising anticancer drug by maintaining its original anticancer activity, and by reducing the Pyridoclax therapeutic concentration.

Structure-guided design of pyridoclax derivatives based on Noxa / Mcl-1 interaction mode

Protein-protein interactions are attractive targets because they control numerous cellular processes. In oncology, apoptosis regulating Bcl-2 family proteins are of particular interest. Apoptotic cell death is controlled via PPIs between the anti-apoptotic proteins hydrophobic groove and the pro-apoptotic proteins BH3 domain. In ovarian carcinoma, it has been previously demonstrated that Bcl-x_L and Mcl-1 cooperate to protect tumor cells against apoptosis. Moreover, Mcl-1 is a key regulator of cancer cell survival and is a known resistance factor to Bcl-2/Bcl-x_L pharmacological inhibitors making it an attractive therapeutic target. Here, using a structure-guided design from the oligopyridine lead Pyridoclax based on Noxa/Mcl-1 interaction we identified a new derivative, active at lower concentration as compared to Pyridoclax. This new derivative selectively binds to the Mcl-1 hydrophobic groove and releases Bak and Bim from Mcl-1 to induce cell death and sensitize cancer cells to Bcl-2/Bcl-x_L targeting strategies.

Atelocollagen-mediated in vivo siRNA transfection in ovarian carcinoma is influenced by tumor site, siRNA target and administration route

Ovarian cancer is the leading cause of death from gynecological malignancies worldwide, and innate or acquired chemoresistance of ovarian cancer cells is the major cause of therapeutic failure. It has been demonstrated that the concomitant inhibition of Bcl-xL and Mcl-1 anti-apoptotic activities is able to trigger apoptosis in chemoresistant ovarian cancer cells. In this context, siRNA-mediated Bcl‑xL and Mcl-1 inhibition constitutes an appealing strategy by which to eliminate chemoresistant cancer cells. However, the safest and most efficient way to vectorize siRNAs in vivo is still under debate. In the present study, using in vivo bioluminescence imaging, we evaluated the interest of atelocollagen to vectorize siRNAs by intraperitoneal (i.p.) or intravenous (i.v.) administration in 2 xenografted ovarian cancer models (peritoneal carcinomatosis and subcutaneous tumors in nude mice). Whereas i.p. administration of atelocollagen-vectorized siRNA in the peritoneal carcinomatosis model did not induce any gene downregulation, a 70% transient downregulation of luciferase expression was achieved after i.v. injection of atelocollagen-vectorized siRNA in the subcutaneous (s.c.) model. However, the use of siRNA targeting Bcl-xL or Mcl-1 did not induce target-specific downregulation in vivo in nude mice. Our results therefore show that atelocollagen complex formulation, the administration route, tumor site and the identity of the siRNA target influence the efficiency of atelocollagen‑mediated siRNA delivery.