Abstract P3-05-05: Preclinical evaluation of novel HDAC6 selective inhibitors N008 with potent in vitroandin vivoprofiles in non-solid tumor and solid tumors
Authors: Shen Xiaokun , Li Zeng 
Published: March 2022

HDAC inhibitors are an emerging class of anticancer agents with the approved indications of multiple myeloma, cutaneous and/or peripheral T cell lymphoma. However, non-selective pan-HDAC inhibitors are often reported associated with heart, hematologic and gastrointestinal toxicities. Among HDAC subtypes, inhibiting HDAC6 selectively may not only enhance potency, but may also reduce the toxicity related to off-target effects of pan-HDACis. In previous studies, pioneer HDAC6 selective inhibitors have been demonstrated with the potential to treat both non-solid tumor and solid tumors along or in combination with chemotherapy, proteasome inhibitors or checkpoint inhibitors. Here, we report the design, in vitro and in vivo evaluation of a class of novel HDAC6 selective inhibitors, series N008, with potent antitumor profiles in non-solid tumor such as multiple myeloma, and solid tumors such as breast cancer. Results:1. HDAC enzymes activity, selectivity and cell assaysAccording to the HDAC Caliper assay, N008 series compounds were identified as HDAC6 selective inhibitors bearing 5-20X selectivity over HDAC3, 20-100X selectivity over HDAC1 and HDAC8, with the HDAC6 potency upto &lt;5 nM. The compounds exhibited a priority selectivity than clinical candidates ACY-1215 and ACY-241.Lead compounds inhibited non-solid tumor such as MM.1S, REC-1, and SK-MEL-5 with the IC50 up to 1 micromole, which were equal or better compared with positive control ACY-241 (2-5 micromole). For Breast cancer cell line MCF-7 and MDA-MB-231, exemplified molecules performed higher cytotoxicity (1-5 micromole) over ACY-241 (5-15 micromole). 2. Drug-like profilesExemplified compounds were tested to demonstrate no cytochrome P450 inhibition (IC50 &gt; 25 µm), no hERG inhibition (@ 40 μM). Moreover, these novel molecules showed better metabolic stability in mouse, rat and human liver microsome (MF%&gt;80%) compared with ACY-241 (MF%: 50-70%). Exemplified molecules were identified not P-gp substrates with high permeability in MDRI-MDCKII and potential BBB penetrability. Taken all results together, this series compounds contribute a predominant drug-like advantages than current clinical candidates.3. Xenograft studyIn MM.1s CDX models, lead compounds N008209 and N008219 were more potent than ACY-241 at 30mg/kg in tumor proliferation as monotherapy. N008209 and N008219 in combination with Bortezomib (0.5 mg/kg) significate inhibit tumor growth compared with monotherapy and ACY-241+Bortezomib (p&lt;0.05). N008 monotherapy and in combination with PTX in MCF-7 CDX, and in combination with PD-1 inhibitor in B16F10 CDX models are under investigating. Moreover, the two compounds possessed very promising safety profiles in both monotherapy and combination therapy. Among all groups, no animal was dead and no body weight was declined over 5% in 24-days treatment. Conclusions:Compounds of series N008 exhibited a priority potency than the clinical candidate ACY-241 on HDAC6 inhibition and selectivity with promising drug-like profiles. In CDX models, lead compounds possessed better in vivo efficacy than ACY-241 in both monotherapy and combination therapy with bortezomib, as well as very promising safety profiles. These data reveal optimistic expectation for the clinical development of novel HDAC6 selective inhibitors on anti-cancer indications, especially on both non-solid and solid tumors such as multiple myeloma and breast cancer. Lead compound is expected to enter clinical study in 2022.

Citation Format: Xiaokun Shen, Zeng Li. Preclinical evaluation of novel HDAC6 selective inhibitors N008 with potent in vitroandin vivoprofiles in non-solid tumor and solid tumors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-05-05.