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High-dose acetaminophen (AAP) with delayed rescue using n-acetylcysteine (NAC), the FDA-approved antidote to AAP overdose, has demonstrated promising antitumor efficacy in early phase clinical trials. However, the mechanism of action (MOA) of AAP's anticancer effects remains elusive. Using clinically relevant AAP concentrations, we evaluated cancer stem cell (CSC) phenotype in vitro and in vivo in lung cancer and melanoma cells with diverse driver mutations. Associated mechanisms were also studied. Our results demonstrated that AAP inhibited 3D spheroid formation, self-renewal, and expression of CSC markers when human cancer cells were grown in serum-free CSC media. Similarly, anti-CSC activity was demonstrated in vivo in xenograft models - tumor formation following in vitro treatment and ex-vivo spheroid formation following in vivo treatment. Intriguingly, NAC, used to mitigate AAP's liver toxicity, did not rescue cells from AAP's anti-CSC effects, and AAP failed to reduce glutathione levels in tumor xenograft in contrast to mice liver tissue suggesting nonglutathione-related MOA. In fact, AAP mediates its anti-CSC effect via inhibition of STAT3. AAP directly binds to STAT3 with an affinity in the low micromolar range and a high degree of specificity for STAT3 relative to STAT1. These findings have high immediate translational significance concerning advancing AAP with NAC rescue to selectively rescue hepatotoxicity while inhibiting CSCs. The novel mechanism of selective STAT3 inhibition has implications for developing rational anticancer combinations and better patient selection (predictive biomarkers) for clinical studies and developing novel selective STAT3 inhibitors using AAP's molecular scaffold.

To map the cellular topography of the rare 3-O-sulfated structural motif of heparan sulfate (HS), we constructed quantum dot-based probes for antithrombin and FGF2, which reveal widely different distribution of the targeted HS motifs. The technology helps show that old and young aortic endothelia display widely different levels of the antithrombin-binding 3-O-sulfated HS motif.

Targeting of cancer stem cells (CSC) is expected to be a paradigm-shifting approach for the treatment of cancers. Cell surface proteoglycans bearing sulfated glycosaminoglycan (GAG) chains are known to play a critical role in the regulation of stem cell fate. Here, we show for the first time that G2.2, a sulfated nonsaccharide GAG mimetic (NSGM) of heparin hexasaccharide, selectively inhibits colonic CSCs in vivo. G2.2-reduced CSCs (CD133+/CXCR4+, Dual hi) induced HT-29 and HCT 116 colon xenografts’ growth in a dose-dependent fashion. G2.2 also significantly delayed the growth of colon xenograft further enriched in CSCs following oxaliplatin and 5-fluorouracil treatment compared with vehicle-treated xenograft controls. In fact, G2.2 robustly inhibited CSCs’ abundance (measured by levels of CSC markers, e.g., CD133, DCMLK1, LGR5, and LRIG1) and self-renewal (quaternary spheroids) in colon cancer xenografts. Intriguingly, G2.2 selectively induced apoptosis in the Dual hi CSCs in vivo eluding to its CSC targeting effects. More importantly, G2.2 displayed none to minimal toxicity as observed through morphologic and biochemical studies of vital organ functions, blood coagulation profile, and ex vivo analyses of normal intestinal (and bone marrow) progenitor cell growth. Through extensive in vitro, in vivo, and ex vivo mechanistic studies, we showed that G2.2′s inhibition of CSC self-renewal was mediated through activation of p38α, uncovering important signaling that can be targeted to deplete CSCs selectively while minimizing host toxicity. Hence, G2.2 represents a first-in-class (NSGM) anticancer agent to reduce colorectal CSCs.

Despite the development of promising direct oral anticoagulants, which are all orthosteric inhibitors, a sizable number of patients suffer from bleeding complications. We have hypothesized that allosterism based on the heparin-binding exosites presents a major opportunity to induce sub-maximal inhibition of coagulation proteases, thereby avoiding/reducing bleeding risk. We present the design of a group of sulfated benzofuran dimers that display heparin-binding site-dependent partial allosteric inhibition of thrombin against fibrinogen (ΔY = 55-75%), the first time that a small molecule (MW 800) has been found to thwart macromolecular cleavage by a monomeric protease in a controlled manner. The work leads to the promising concept that it should be possible to develop allosteric inhibitors that reduce clotting, but do not completely eliminate it, thereby avoiding major bleeding complications that beset anticoagulants today.

Glycosaminoglycan (GAG) sequences that selectively target heparin cofactor II (HCII), a key serpin present in human plasma, remain unknown. Using a computational strategy on a library of 46 656 heparan sulfate hexasaccharides we identified a rare sequence consisting of consecutive glucuronic acid 2‐O‐sulfate residues as selectively targeting HCII. This and four other unique hexasaccharides were chemically synthesized. The designed sequence was found to activate HCII ca. 250‐fold, while leaving aside antithrombin, a closely related serpin, essentially unactivated. This group of rare designed hexasaccharides will help understand HCII function. More importantly, our results show for the first time that rigorous use of computational techniques can lead to discovery of unique GAG sequences that can selectively target GAG‐binding protein(s), which may lead to chemical biology or drug discovery tools.

High mobility group box 1 (HMGB1) is an alarmin released from macrophages after infection or inflammation and is a biomarker of lung disease progression in patients with cystic fibrosis. We reported that 2-O, 3-O desulfated heparin (ODSH) inhibits the release of HMGB1 from murine macrophages triggered by neutrophil elastase both in vivo and in vitro. HMGB1 shuttles between the nucleus and the cytoplasm. When acetylated at lysine residues in the nuclear localization signal domains, HMGB1 is sequestered in the cytoplasm and is fated for secretion. In this study, we investigated the mechanism by which ODSH blocks HMGB1 secretion. We tested whether ODSH inhibits the activity of p300, a histone acetyltransferase that has been linked to HMGB1 acetylation and release. ODSH inhibited both neutrophil elastase and LPS-triggered HMGB1 release from the murine macrophage cell line RAW264.7 in a concentration-dependent manner. Fluorescein-labeled ODSH was taken up by RAW264.7 cells into the cytoplasm as well as the nucleus, suggesting an intracellular site of action of ODSH for blocking HMGB1 release. ODSH inhibited RAW264.7 cell nuclear extract, human macrophage nuclear extract, and recombinant p300 HAT activity in vitro, resulting in the failure to acetylate HMGB1. In silico molecular modeling predicted that of the numerous possible ODSH sequences, a small number preferentially recognizes a specific binding site on p300. Fluorescence binding studies showed that ODSH bound p300 tightly (dissociation constant ∼1 nM) in a highly cooperative manner. These results suggest that ODSH inhibited HMGB1 release, at least in part, by direct molecular inhibition of p300 HAT activity.

// Nirmita J. Patel 1, 3 , Chetna Sharon 1 , Somesh Baranwal 1, 2 , Rio S. Boothello 1, 2 , Umesh R. Desai 3 , Bhaumik B. Patel 1, 2 1 Hunter Holmes McGuire VA Medical Center, Richmond, VA 23249, USA 2 Division of Hematology, Oncology, and Palliative Care, Department of Internal Medicine and Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA 3 Department of Medicinal Chemistry and Institute for Structural Biology, Drug Discovery and Development, Virginia Commonwealth University, Richmond, VA 23219, USA Correspondence to: Bhaumik B. Patel, email: bhaumik.patel@vcuhealth.org Keywords: cancer stem cells, colorectal cancer, glycosaminoglycans, p38 mitogen activated protein kinase, heparan sulfate Received: June 17, 2016 Accepted: September 05, 2016 Published: September 30, 2016 ABSTRACT Heparan sulfate (HS) plays a role in the majority of essential hallmarks of cancer, yet its ability to modulate self-renewal, especially of cancer stem cells (CSCs), remains unknown. We have discovered that a non-anticoagulant HS hexasaccharide (HS06) sequence, but not other shorter or longer sequences, selectively inhibited CSC self-renewal and induced apoptosis in colorectal, pancreatic, and breast CSCs suggesting a very general phenomenon. HS06 inhibition of CSCs relied upon early and sustained activation of p38α/β mitogen activated protein kinase (MAPK) but not other MAPKs family members i.e. ERK and JNK. In contrast, polymeric HS induced exactly opposite changes in MAPK activation and failed to inhibit CSCs. In fact, TCF4 signaling, a critical regulator of CSC self-renewal, was inhibited by HS06 in a p38 activation dependent fashion. In conclusion, HS06 selectively inhibits CSCs self-renewal by causing isoform specific activation of p38MAPK to inhibit TCF4 signaling. These observations on chain length-induced specificity carry major mechanistic implications with regard to HS in cancer biology, while also presenting a novel paradigm for developing novel anti-CSC hexasaccharides that prevent cancer relapse. STATEMENT OF SIGNIFICANCE Heparan sulfate (HS) of specific length, i.e., hexasaccharide (HS06), but not longer or shorter sequences, selectively inhibit cancer stem cells (CSCs) through isoform specific activation of p38 mitogen-activated protein kinase. These findings will have major implication for developing chemical probes to decipher complex signaling events that govern cancer stem cells. Additionally, there are direct implications for designing glycosaminoglycan based cancer therapies to selectively target CSCs that escape killing by traditional chemotherapy threatening cancer relapse.

Introduction: Cancer cell dormancy and the cancer stem cell (CSC) phenotype are interlinked and play a crucial role in disease relapse. The pp38/pERK signaling ratio positively regulates cellular dormancy. We observed that heparin hexasaccharide (HS06) inhibited colon CSC self-renewal through isoform specific induction of pp38α/β, increasing the pp38/pERK ratio, and downregulation of C-terminal binding protein-2 (CtBP2) levels which is known to play a critical role in CSC growth. Hence, we hypothesized that HS06 inhibits CSCs self-renewal and prevents dormancy escape through regulation of CtBP2 in a manner dependent on p38 activation. Method: Spheroid culture of HT29 and HCT116 colon cancer cells was used for CSC self-renewal monitoring. Transient transfection with p38α, p14ARF, CtBP2 shRNA and/or expression vector with appropriate scrambled or vector controls was used to modulate cell signaling through this pathway. Standard western blotting, Q-PCR, flow cytometry, and immunoprecipitation were used to examine protein levels, their phosphorylation status and protein-protein interactions. Short term exposure of colon cancer cells (HT29) to chemotherapy (5-Fluorouracil (125μM) and oxaliplatin (5μM) (5-FUOX)) was used to study a transient dormancy-like state followed by growth escape. HT29 CSC (1x105 CD133+/CXCR4+ cells) induced xenografts were established s.c. in NCr nude mice were treated with HS06 (150mg/kg 3xwk., 3 weeks) and monitored for tumor growth, and xenografts were analyzed for CSC makers and p38-p14ARF-CtBP2 axis status. Results: HS06 inhibited CtBP2 levels but increased the expression of its negative regulator p14 ARF in vitro and in vivo in a manner dependent on p38 activation, as SB203580, a selective p38α/β inhibitor, as well as p38α shRNA, both near-completely reversed the effects of HS06 on p14ARF, CtBP2, and CSC self-renewal. This regulation of p14ARF and CtBP2 was post-transcriptional in nature. Moreover, reciprocal coimmunoprecipitation studies revealed a novel physical interaction between endogenous pp38 and p14ARF, which resulted in serine phosphorylation of p14ARF in a p38 activation-dependent manner that was critical for regulation of CtBP2 levels and CSC self-renewal. Using a chemotherapy induced cellular dormancy model, we observed that activation/upregulation of p38 and p14ARF prevented escape from dormancy in vitro, whereas increased CtBP2 had the opposite effect. Conclusion: We have discovered a novel p38-p14ARF-CtBP2 axis that plays a dual role in colon cancer CSC self-renewal and cellular dormancy. Agents targeting this pathway e.g., HS06 and CtBP2 inhibitors, represent novel therapeutic strategies to inhibit CSCs and prevent dormancy escape leading to reduced tumor relapse and/or cure. Citation Format: Rio S. Boothello, Nirmita J. Patel, Priyadarshan K. Damle, Chetna Sharon, Kranthi Kumar Chougoni, Umesh R. Desai, Steven R. Grossman, Bhaumik B. Patel. p38-p14ARF-CtBP2 axis as a novel regulator of CSC phenotype and tumor cell dormancy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3460.