Abstract 5341: Bifunctional integrated molecules with combined retinoic acid receptor agonist/protein deacetylase inhibitory activities as therapeutic agents for breast cancer and neuroblastoma
Authors: Cotnoir-White David , Miller Angela , Zhao Bin , Weiss Isroel , Gleason James , Bettoun David , Mader Sylvie 
Published: August 2015

All-trans retinoic acid (ATRA), the oxidized form of Vitamin A, is a potent antiproliferative and differentiating agent that acts as an agonist of the retinoic acid receptors (RARs). Both 13-cis or all-trans retinoic acid are clinically used in differentiation or maintenance therapies for APL and neuroblastoma respectively. Their efficacy is however limited by resistance mechanisms. The use of small molecule inhibitors of HDACs (HDACi) for cancer treatment has been clinically validated for pan-HDAC inhibitors like SAHA (Vorinostat) or Romidepsin (Istodax) that are approved for the treatment of cutaneous T-cell lymphoma. The use of pan-HDAC inhibitors is restricted by dose-limiting toxicities at pharmacologically relevant doses, highlighting the need for alternative strategies such as use in combined therapies. Notably, synergistic activity was observed between retinoids and HDACs, which both induce cell differentiation, in a number of cancer models. Using molecular design we engineered a series of integrated hybrid small molecules that incorporates a deacetylase inhibitory activity and retinoic acid receptor (RAR) agonist. We show that these hybrid molecules inhibit the growth and survival of a wide range of cancer cell lines.

In breast cancer cell lines, hybrids were shown to induce the recruitment of co-activators to RARα to the same extent as retinoic acid (RA) and to induce the release of co-repressors from RARs. Regulation of RAR-dependent transcription was shown in breast cancer and neuroblastoma cell lines using RAR reporter assays. Compounds displayed EC50 in the 10-500 nM range and an efficacy comparable to 13 cis-RA. In addition, the ability of compounds to regulate the expression of RAR target genes was confirmed in cells of both breast and neuroblastoma origin. Biochemical enzymatic assays show that HR- hybrids differentially inhibit HDAC activities with a two-log selectivity toward HDAC6 and HDAC. This inhibitory profile translated in both increased cellular acetylation of target proteins and in the down-regulation of anti-apoptotic target genes.

Cytotoxicity toward breast or neuroblastoma cells correlated positively with targets’ activities. Strikingly, under conditions where 13 cis RA, SAHA or their combination had a modest or no effect on basal breast carcinoma cells viability, compounds with dual activity displayed a pronounced cytotoxic effect in the sub-uM range. Compounds were also active in the sub-micromolar range in N-Myc-amplified neuroblastoma lines IMR-32 or BE2C. In contrast compounds did not display significant cytotoxicity in non-tumorigenic primary cell lines under conditions where SAHA strongly inhibited the survival, proliferation or differentiation of these cells. Preliminary pharmacodynamic (PK) show that compounds were orally bioavailable and displayed favorable PK characteristics.

Citation Format: David Cotnoir-White, Angela Miller, Bin Zhao, Isroel Weiss, James Gleason, David Bettoun, Sylvie Mader. Bifunctional integrated molecules with combined retinoic acid receptor agonist/protein deacetylase inhibitory activities as therapeutic agents for breast cancer and neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5341. doi:10.1158/1538-7445.AM2015-5341