Abstract 1018: Structural features of novel dimeric quinacrines that have single-agent antitumor activity determine the mechanism of action: destabilization of mTORC1/lysosomal interaction versus DNA damage
Authors: Rebecca Vito W. , Nicastri Michael , McGlaughlin Noel , McAfee Quentin , Zhang Gao , Alicea Gretchen M. , Piao Shengfu , Fennelly Colin , Murugan Sengottuvelan , Wei Zhi , Mills Gordon B. , Lu Yiling , Herlyn Meenhard , Winkler Jeffrey D. , Amaravadi Ravi K. 
Published: July 2016

The safety and preliminary activity of hydroxychloroquine in phase I cancer clinical trials have established the feasibility and rationale for targeting the lysosome in cancer. We previously reported a more potent lysosomal inhibitor Lys05, which is a dimeric chloroquine (CQ) linked with a triamine linker. Here we report that high throughput screening of &gt;100 Lys05 derivatives (72-hour viability assay) revealed extending linker length between the CQ motifs markedly enhanced anti-proliferative potency (IC50 &lt;500 nM v. 5 μM Lys05). Longer linker dimeric CQs produced significantly greater autophagy inhibition (2-5 fold improved v. Lys05; mCherry-eGFP-LC3 reporter) and apoptosis (2-8 fold improved v. Lys05) in human pancreatic cancer, melanoma and in KRAS mutant P53-/- mouse pancreatic cells. We then substituted the CQ heterocycle of Lys05 with other antimalarial heterocycles including those found in mefloquine, primaquine and quinacrine. Dimeric quinacrines (DQ’s) were exquisitely cytotoxic to cancer cell lines (IC50 9 - 90nM; ≥40 fold improvement v. quinacrine). These agents were renamed DQ221-661, where the first and second digit of each compound indicates the number of carbons flanking the central nitrogen and the third digit reflects whether the central nitrogen in the dimeric molecule is methylated (1) or not (0). Inherent fluorescence of the DQs uncovered a striking pattern of subcellular localization dependent on central nitrogen methylation. All of the methylated DQs localized to the lysosome and inhibited autophagic flux (bafilomycin clamp assay), while all of the unmethylated DQ's localized to the nucleus, produced pH2AX-positive DNA damage, and induced autophagy. Methylated DQs produced lysosomal membrane permeabilization (LMP; galectin-3 puncta), and equal cytotoxicity in ATG5 WT and ATG5-null MEFs, indicating their cytotoxicity is not dependent on functional upstream canonical autophagy. Reverse phase protein array analysis of dimeric CQs Lys05, Lys75 and DQ661 revealed a signature associated with inactivation of mTORC1 (decreased phosphorylation of S6K, 4E-BP1, PRAS40). DQ661 disrupted mTOR/LAMP2 co-localization and induced greater levels of apoptosis compared to BRAF/MEK inhibition in BRAF-MT melanoma cells, gemcitabine in pancreatic cancer cells, or early stage autophagy inhibitors Spautin-1 and SBI-0206965. Unlike quinacrine, which had no effect, or DQ660, which produced a modest but significant growth impairment, DQ661 produced significant tumor regression in a melanoma xenograft model, establishing the therapeutic potential of this compound in cancer. Our data identifies a new class of lysosomal inhibitors, the centrally methylated dimeric quinacrines, devoid of DNA damaging properties, that are capable of concurrently inhibiting autophagy-lysosome function and mTORC1 through LMP.

Citation Format: Vito W. Rebecca, Michael Nicastri, Noel McGlaughlin, Quentin McAfee, Gao Zhang, Gretchen M. Alicea, Shengfu Piao, Colin Fennelly, Sengottuvelan Murugan, Zhi Wei, Gordon B. Mills, Yiling Lu, Meenhard Herlyn, Jeffrey D. Winkler, Ravi K. Amaravadi. Structural features of novel dimeric quinacrines that have single-agent antitumor activity determine the mechanism of action: destabilization of mTORC1/lysosomal interaction versus DNA damage. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1018.