IKAROS and CK2 regulate expression of BCL-XL and chemosensitivity in high-risk B-cell acute lymphoblastic leukemia.

High-risk B-cell acute lymphoblastic leukemia (B-ALL) is an aggressive disease, often characterized by resistance to chemotherapy. A frequent feature of high-risk B-ALL is loss of function of the IKAROS (encoded by the IKZF1 gene) tumor suppressor. Here, we report that IKAROS regulates expression of the BCL2L1 gene (encodes the BCL-XL protein) in human B-ALL. Gain-of-function and loss-of-function experiments demonstrate that IKAROS binds to the BCL2L1 promoter, recruits histone deacetylase HDAC1, and represses BCL2L1 expression via chromatin remodeling. In leukemia, IKAROS' function is impaired by oncogenic casein kinase II (CK2), which is overexpressed in B-ALL. Phosphorylation by CK2 reduces IKAROS binding and recruitment of HDAC1 to the BCL2L1 promoter. This results in a loss of IKAROS-mediated repression of BCL2L1 and increased expression of BCL-XL. Increased expression of BCL-XL and/or CK2, as well as reduced IKAROS expression, are associated with resistance to doxorubicin treatment. Molecular and pharmacological inhibition of CK2 with a specific inhibitor CX-4945, increases binding of IKAROS to the BCL2L1 promoter and enhances IKAROS-mediated repression of BCL2L1 in B-ALL. Treatment with CX-4945 increases sensitivity to doxorubicin in B-ALL, and reverses resistance to doxorubicin in multidrug-resistant B-ALL. Combination treatment with CX-4945 and doxorubicin show synergistic therapeutic effects in vitro and in preclinical models of high-risk B-ALL. Results reveal a novel signaling network that regulates chemoresistance in leukemia. These data lay the groundwork for clinical testing of a rationally designed, targeted therapy that combines the CK2 inhibitor, CX-4945, with doxorubicin for the treatment of hematopoietic malignancies.

Targeting Protein Translation in Melanoma by Inhibiting EEF-2 Kinase Regulates Cholesterol Metabolism though SREBP2 to Inhibit Tumour Development.

Decreasing the levels of certain proteins has been shown to be important for controlling cancer but it is currently unknown whether proteins could potentially be targeted by the inhibiting of protein synthesis. Under this circumstance, targeting protein translation could preferentially affect certain pathways, which could then be of therapeutic advantage when treating cancer. In this report, eukaryotic elongation factor-2 kinase (EEF2K), which is involved in protein translation, was shown to regulate cholesterol metabolism. Targeting EEF2K inhibited key parts of the cholesterol pathway in cancer cells, which could be rescued by the addition of exogenous cholesterol, suggesting that it is a potentially important pathway modulated by targeting this process. Specifically, targeting EEF2K significantly suppressed tumour cell growth by blocking mRNA translation of the cholesterol biosynthesis transcription factor, sterol regulatory element-binding protein (SREBP) 2, and the proteins it regulates. The process could be rescued by the addition of LDL cholesterol taken into the cells via non-receptor-mediated-uptake, which negated the need for SREBP2 protein. Thus, the levels of SREBP2 needed for cholesterol metabolism in cancer cells are therapeutically vulnerable by targeting protein translation. This is the first report to suggest that targeting EEF2K can be used to modulate cholesterol metabolism to treat cancer.

Moving Synergistically Acting Drug Combinations to the Clinic by Comparing Sequential versus Simultaneous Drug Administrations.

Drug combinations acting synergistically to kill cancer cells have become increasingly important in melanoma as an approach to manage the recurrent resistant disease. Protein kinase B (AKT) is a major target in this disease but its inhibitors are not effective clinically, which is a major concern. Targeting AKT in combination with WEE1 (mitotic inhibitor kinase) seems to have potential to make AKT-based therapeutics effective clinically. Since agents targeting AKT and WEE1 have been tested individually in the clinic, the quickest way to move the drug combination to patients would be to combine these agents sequentially, enabling the use of existing phase I clinical trial toxicity data. Therefore, a rapid preclinical approach is needed to evaluate whether simultaneous or sequential drug treatment has maximal therapeutic efficacy, which is based on a mechanistic rationale. To develop this approach, melanoma cell lines were treated with AKT inhibitor AZD5363 [4-amino-N-[(1S)-1-(4-chlorophenyl)-3-hydroxypropyl]-1-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperidine-4-carboxamide] and WEE1 inhibitor AZD1775 [2-allyl-1-(6-(2-hydroxypropan-2-yl)pyridin-2-yl)-6-((4-(4-methylpiperazin-1-yl)phenyl)amino)-1H-pyrazolo[3,4-d]pyrimidin-3(2H)-one] using simultaneous and sequential dosing schedules. Simultaneous treatment synergistically reduced melanoma cell survival and tumor growth. In contrast, sequential treatment was antagonistic and had a minimal tumor inhibitory effect compared with individual agents. Mechanistically, simultaneous targeting of AKT and WEE1 enhanced deregulation of the cell cycle and DNA damage repair pathways by modulating transcription factors p53 and forkhead box M1, which was not observed with sequential treatment. Thus, this study identifies a rapid approach to assess the drug combinations with a mechanistic basis for selection, which suggests that combining AKT and WEE1 inhibitors is needed for maximal efficacy.

Biochemical and pharmacological characterization of Trimersurus malabaricus snake venom.

Trimeresurus malabaricus is a venomous pit viper species endemic to southwestern part of India. In earlier reports, we have shown that envenomation by T. malabaricus venom leading to strong local tissue damage but the mechanism of action is not clearly revealed. Local tissue damage affected by T. malabaricus venom is of great importance since the poison has serious systemic effects including death in the case of multiple attacks. The present study details the major manifestations of T. malabaricus venom and the induction of local tissue damage, which suggests that most toxins are present in the form of hydrolytic enzymes. Hydrolytic activity of the enzymes was measured and the data indicated that protease and phospholipase A2 activity was high which is responsible for local tissue damage. Furthermore, the role of hydrolytic enzymes in the induction of pathological events such as hemorrhage, edema, myotoxicity, and blood coagulation examination were assessed through animal models.

Swiprosin-1: Its Expression and Diverse Biological Functions.

Swiprosin-1/EFhd2 is a Ca2+ binding adapter protein involved in the various cellular functions. Swiprosin-1 is significantly upregulated in a number of pathological conditions of inflammation, neurodegeneration, and cancer. Swiprosin-1 associated with actin and its expression level amplifies the production of proinflammatory mediators and modulates the activation of transcription factor during immune cells activation. This review aims at providing an overview of the expression and function of swiprosin-1/EFhd2 in various pathophysiological conditions. We also discussed the key role of swiprosin-1 in immune cell activation, cell migration, apoptosis, humoral immunity, cancer invasion and metastasis, neuronal transport, and major signaling cascades. J. Cell. Biochem. 119: 150-156, 2018. © 2017 Wiley Periodicals, Inc.

Nanoliposomal delivery of cytosolic phospholipase A2 inhibitor arachidonyl trimethyl ketone for melanoma treatment.

Drug resistance and toxicity are major limitations of cancer treatment and frequently occurs during melanoma therapy. Nanotechnology can decrease drug resistance by improving drug delivery, with limited toxicity. This study details the development of nanoparticles containing arachidonyl trifluoromethyl ketone (ATK), a cytosolic phospholipase A2 inhibitor, which can inhibit multiple key pathways responsible for the development of recurrent resistant disease. Free ATK is toxic, limiting its efficacy as a therapeutic agent. Hence, a novel nanoliposomal delivery system called NanoATK was developed, which loads 61.7% of the compound and was stable at 4oC for 12 weeks. The formulation decreased toxicity-enabling administration of higher doses, which was more effective at inhibiting melanoma cell growth compared to free-ATK. Mechanistically, NanoATK decreased cellular proliferation and triggered apoptosis to inhibit melanoma xenograft tumor growth without affecting animal weight. Functionally, it inhibited the cPLA2, AKT, and STAT3 pathways. Our results suggest the successful preclinical development of a unique nanoliposomal formulation containing ATK for the treatment of melanoma.

Modulating cancer cell survival by targeting intracellular cholesterol transport.

BACKGROUND: Demand for cholesterol is high in certain cancers making them potentially sensitive to therapeutic strategies targeting cellular cholesterol homoeostasis. A potential approach involves disruption of intracellular cholesterol transport, which occurs in Niemann-Pick disease as a result of acid sphingomyelinase (ASM) deficiency. Hence, a class of lysosomotropic compounds that were identified as functional ASM inhibitors (FIASMAs) might exhibit chemotherapeutic activity by disrupting cancer cell cholesterol homoeostasis. METHODS: Here, the chemotherapeutic utility of ASM inhibition was investigated. The effect of FIASMAs on intracellular cholesterol levels, cholesterol homoeostasis, cellular endocytosis and signalling cascades were investigated. The in vivo efficacy of ASM inhibition was demonstrated using melanoma xenografts and a nanoparticle formulation was developed to overcome dose-limiting CNS-associated side effects of certain FIASMAs. RESULTS: Functional ASM inhibitors inhibited intracellular cholesterol transport leading to disruption of autophagic flux, cellular endocytosis and receptor tyrosine kinase signalling. Consequently, major oncogenic signalling cascades on which cancer cells were reliant for survival were inhibited. Two tested ASM inhibitors, perphenazine and fluphenazine that are also clinically used as antipsychotics, were effective in inhibiting xenografted tumour growth. Nanoliposomal encapsulation of the perphenazine enhanced its chemotherapeutic efficacy while decreasing CNS-associated side effects. CONCLUSIONS: This study suggests that disruption of intracellular cholesterol transport by targeting ASM could be utilised as a potential chemotherapeutic approach for treating cancer.

Targeting casein kinase II restores Ikaros tumor suppressor activity and demonstrates therapeutic efficacy in high-risk leukemia.

Ikaros (IKZF1) is a tumor suppressor that binds DNA and regulates expression of its target genes. The mechanism of Ikaros activity as a tumor suppressor and the regulation of Ikaros function in leukemia are unknown. Here, we demonstrate that Ikaros controls cellular proliferation by repressing expression of genes that promote cell cycle progression and the phosphatidylinositol-3 kinase (PI3K) pathway. We show that Ikaros function is impaired by the pro-oncogenic casein kinase II (CK2), and that CK2 is overexpressed in leukemia. CK2 inhibition restores Ikaros function as transcriptional repressor of cell cycle and PI3K pathway genes, resulting in an antileukemia effect. In high-risk leukemia where one IKZF1 allele has been deleted, CK2 inhibition restores the transcriptional repressor function of the remaining wild-type IKZF1 allele. CK2 inhibition demonstrated a potent therapeutic effect in a panel of patient-derived primary high-risk B-cell acute lymphoblastic leukemia xenografts as indicated by prolonged survival and a reduction of leukemia burden. We demonstrate the efficacy of a novel therapeutic approach for high-risk leukemia: restoration of Ikaros tumor suppressor activity via inhibition of CK2. These results provide a rationale for the use of CK2 inhibitors in clinical trials for high-risk leukemia, including cases with deletion of one IKZF1 allele.

A non-cytotoxic N-dehydroabietylamine derivative with potent antimalarial activity.

Malaria caused by the Plasmodium parasites continues to be an enormous global health problem owing to wide spread drug resistance of parasites to many of the available antimalarial drugs. Therefore, development of new classes of antimalarial agents is essential to effectively treat malaria. In this study, the efficacy of naturally occurring diterpenoids, dehydroabietylamine and abietic acid, and their synthetic derivatives was assessed for antimalarial activity. Dehydroabietylamine and its N-trifluoroacetyl, N-tribromoacetyl, N-benzoyl, and N-benzyl derivatives showed excellent activity against P. falciparum parasites with IC50 values of 0.36 to 2.6 µM. Interestingly, N-dehydroabietylbenzamide showed potent antimalarial activity (IC50 0.36), and negligible cytotoxicity (IC50 >100 µM) to mammalian cells; thus, this compound can be an important antimalarial drug. In contrast, abietic acid was only marginally effective, exhibiting an IC50 value of ~82 µM. Several carboxylic group-derivatives of abietic acid were moderately active with IC50 values of ~8.2 to ~13.3 µM. These results suggest that a detailed understanding of the structure-activity relationship of abietane diterpenoids might provide strategies to exploit this class of compounds for malaria treatment.

Identification of aurora kinase B and Wee1-like protein kinase as downstream targets of (V600E)B-RAF in melanoma.

BRAF is the most mutated gene in melanoma, with approximately 50% of patients containing V600E mutant protein. (V600E)B-RAF can be targeted using pharmacological agents, but resistance develops in patients by activating other proteins in the signaling pathway. Identifying downstream members in this signaling cascade is important to design strategies to avoid the development of resistance. Unfortunately, downstream proteins remain to be identified and therapeutic potential requires validation. A kinase screen was undertaken to identify downstream targets in the (V600E)B-RAF signaling cascade. Involvement of aurora kinase B (AURKB) and Wee1-like protein kinase (WEE1) as downstream proteins in the (V600E)B-RAF pathway was validated in xenografted tumors, and mechanisms of action were characterized in size- and time-matched tumors. Levels of only AURKB and WEE1 decreased in melanoma cells, when (V600E)B-RAF, mitogen-activated protein kinase 1/2, or extracellular signal-regulated kinase 1/2 protein levels were reduced using siRNA compared with other identified kinases. AURKB and WEE1 were expressed in tumors of patients with melanoma at higher levels than observed in normal human melanocytes. Targeting these proteins reduced tumor development by approximately 70%, similar to that observed when inhibiting (V600E)B-RAF. Furthermore, protein or activity levels of AURKB and WEE1 decreased in melanoma cells when pharmacological agents targeting upstream (V600E)B-RAF or mitogen-activated protein kinase were used to inhibit the (V600E)B-RAF pathway. Thus, AURKB and WEE1 are targets and biomarkers of therapeutic efficacy, lying downstream of (V600E)B-RAF in melanomas.

Activating Sphingosine-1-phospahte signaling in endothelial cells increases myosin light chain phosphorylation to decrease endothelial permeability thereby inhibiting cancer metastasis.

Targeting the metastatic process to prevent disease dissemination in cancer remains challenging. One step in the metastatic cascade involves cancer cells transiting through the vascular endothelium after inflammation has increased the permeability of this cellular layer. Reducing inflammation-mediated gaps in the vascular endothelium could potentially be used to retard metastasis. This study describes the development of a novel ASR396-containing nanoparticle designed to activate the Sphingosine-1-Phosphate Receptor 1 (S1PR1) in order to tighten the junctions between the endothelial cells lining the vascular endothelium thereby inhibiting metastasis. ASR396 was derived from the S1PR1 agonist SEW2871 through chemical modification enabling the new compound to be loaded into a nanoliposome. ASR396 retained S1PR1 binding activity and the nanoliposomal formulation (nanoASR396) made it systemically bioavailable upon intravenous injection. Studies conducted in microvessels demonstrated that nanoASR396 significantly attenuated inflammatory mediator-induced permeability increase through the S1PR1 activation. Similarly, nanoASR396 inhibited gap formation mediated by inflammatory agents on an endothelial cell monolayer by decreasing levels of phosphorylated myosin light chain protein thereby inhibiting cellular contractility. In animal models, nanoASR396 inhibited lung metastasis by up to 80%, indicating its potential for retarding melanoma metastasis. Thus, a novel bioavailable nanoparticle-based S1PR1 agonist has been developed to negate the effects of inflammatory mediators on the vascular endothelium in order to reduce the metastatic dissemination of cancer cells.

Dual targeting of MTOR as a novel therapeutic approach for high-risk B-cell acute lymphoblastic leukemia.

Children of Hispanic/Latino ancestry have increased incidence of high-risk B-cell acute lymphoblastic leukemia (HR B-ALL) with poor prognosis. This leukemia is characterized by a single-copy deletion of the IKZF1 (IKAROS) tumor suppressor and increased activation of the PI3K/AKT/mTOR pathway. This identifies mTOR as an attractive therapeutic target in HR B-ALL. Here, we report that IKAROS represses MTOR transcription and IKAROS' ability to repress MTOR in leukemia is impaired by oncogenic CK2 kinase. Treatment with the CK2 inhibitor, CX-4945, enhances IKAROS activity as a repressor of MTOR, resulting in reduced expression of MTOR in HR B-ALL. Thus, we designed a novel therapeutic approach that implements dual targeting of mTOR: direct inhibition of the mTOR protein (with rapamycin), in combination with IKAROS-mediated transcriptional repression of the MTOR gene (using the CK2 inhibitor, CX-4945). Combination treatment with rapamycin and CX-4945 shows synergistic therapeutic effects in vitro and in patient-derived xenografts from Hispanic/Latino children with HR B-ALL. These data suggest that such therapy has the potential to reduce the health disparity in HR B-ALL among Hispanic/Latino children. The dual targeting of oncogene transcription, combined with inhibition of the corresponding oncoprotein provides a paradigm for a novel precision medicine approach for treating hematological malignancies.

Salubrinal in Combination With 4E1RCat Synergistically Impairs Melanoma Development by Disrupting the Protein Synthetic Machinery.

Increased protein synthesis is a key process in melanoma, which is regulated by the ALDH18A1 gene encoding pyrroline-5-carboxylate synthase (P5CS). P5CS is involved in proline biosynthesis and targeting ALDH18A1 has previously been shown to inhibit melanoma development by decreasing intracellular proline levels to increase the phosphorylation of eIF2α mediated by GCN2, which then impairs mRNA translation. Since there are no current inhibitors of P5CS, decreased eIF2α phosphorylation in melanoma was targeted using salubrinal (a specific inhibitor of eIF2α phosphatase enzymes). While salubrinal alone was ineffective, the combined use of salubrinal and 4E1RCat (a dual inhibitor of eIF4E:4E-BP1 and eIF4E:eIF4G interaction to prevent assembly of the eIF4F complex and inhibit cap-dependent translation) was found to be effective at decreasing protein synthesis, protein translation, and cell cycle progression to synergistically decrease melanoma cell viability and inhibited xenograft melanoma tumor development. The combination of these agents synergistically decreased melanoma cell viability while having minimal effect on normal cells. This is the first report demonstrating that it is possible to inhibit melanoma viability by targeting eIF2α signaling using salubrinal and 4E1RCat to disrupt assembly of the eIF4F complex.

The role of exosomes in metastasis and progression of melanoma.

The mechanisms of melanoma metastasis have been the subject of extensive research for decades. Improved diagnostic and therapeutic strategies are of increasing importance for the treatment of melanoma due to its high burden of mortality in the advanced stages of the disease. Intercellular communication is a critical event for the progression of cancer. Collective evidence suggests that exosomes, small extracellular membrane vesicles released by the cells, are important facilitators of intercellular communication between the cells and the surrounding environment. Although the emerging field of exosomes is rapidly gaining traction in the scientific community, there is limited knowledge regarding the role of exosomes in melanoma. This review discusses the multifaceted role of melanoma-derived exosomes in promoting the process of metastasis by modulating the invasive and angiogenic capacity of malignant cells. The future implications of exosome research and the therapeutic potential of exosomes are also discussed.

Design, synthesis characterization and biological evaluation of novel multi-isoform ALDH inhibitors as potential anticancer agents.

The aldehyde dehydrogenases (ALDHs) are a family of detoxifying enzymes that are overexpressed in various cancers. Increased expression of ALDH is associated with poor prognosis, stemness, and drug resistance. Because of the critical role of ALDH in cancer stem cells, several ALDH inhibitors have been developed. Nonetheless, all these inhibitors either lack efficacy or are too toxic or have not been tested extensively. Thus, the continued development of ALDH inhibitors is warranted. In this study, we designed and synthesized potent multi-ALDH isoform inhibitors based on the isatin backbone. The early molecular docking studies and enzymatic tests revealed that 3(a-l) and 4(a-l) are the potent ALDH1A1, ALDHA2, and ALDH3A1 inhibitors. ALDH inhibitory IC50s of 3(a-l) and 4(a-l) were 230 nM to >10,000 nM for ALDH1A1, 939 nM to >10,000 nM for ALDH2 and 193 nM to >10,000 nM for ALDH3A1. The most potent compounds 3(h-l) had IC50s for killing melanoma cells ranged from 2.1 to 5.7 µM, while for colon cancer cells, it ranged from 2.5 to 5.8 µM and for multiple myeloma cells ranging from 0.3 to 4.7 µM. Toxicity studies of 3(h-l) revealed that 3h to be the least toxic multi-ALDH isoform inhibitor. Mechanistically, 3(h-l) caused increased ROS activity, lipid peroxidation, and toxic aldehyde accumulation, secondary to potent multi-ALDH isoform inhibition leading to increased apoptosis and G2/M cell cycle arrest. Together, the study details the design, synthesis, and evaluation of potent, multi-isoform ALDH inhibitors to treat cancers.

Development of a Novel Multi-Isoform ALDH Inhibitor Effective as an Antimelanoma Agent.

The aldehyde dehydrogenases (ALDH) are a major family of detoxifying enzymes that contribute to cancer progression and therapy resistance. ALDH overexpression is associated with a poor prognosis in many cancer types. The use of multi-ALDH isoform or isoform-specific ALDH inhibitors as anticancer agents is currently hindered by the lack of viable candidates. Most multi-ALDH isoform inhibitors lack bioavailability and are nonspecific or toxic, whereas most isoform-specific inhibitors are not effective as monotherapy due to the overlapping functions of ALDH family members. The present study details the development of a novel, potent, multi-isoform ALDH inhibitor, called KS100. The rationale for drug development was that inhibition of multiple ALDH isoforms might be more efficacious for cancer compared with isoform-specific inhibition. Enzymatic IC50s of KS100 were 207, 1,410, and 240 nmol/L toward ALDH1A1, 2, and 3A1, respectively. Toxicity of KS100 was mitigated by development of a nanoliposomal formulation, called NanoKS100. NanoKS100 had a loading efficiency of approximately 69% and was stable long-term. NanoKS100 was 5-fold more selective for killing melanoma cells compared with normal human fibroblasts. NanoKS100 administered intravenously at a submaximal dose (3-fold lower) was effective at inhibiting xenografted melanoma tumor growth by approximately 65% without organ-related toxicity. Mechanistically, inhibition by KS100 significantly reduced total cellular ALDH activity to increase reactive oxygen species generation, lipid peroxidation, and accumulation of toxic aldehydes leading to apoptosis and autophagy. Collectively, these data suggest the successful preclinical development of a nontoxic, bioavailable, nanoliposomal formulation containing a novel multi-ALDH isoform inhibitor effective in the treatment of cancer.

Aldehyde Dehydrogenase Inhibitors for Cancer Therapeutics.

Aldehyde dehydrogenases (ALDHs) are highly expressed in the chemotherapy- and radiotherapy-resistant cell subpopulations of many different cancer types. Accordingly, the development of ALDH inhibitors may be the most direct approach to target these cell populations. However, inhibiting multiple ALDH family members can be toxic and isoform-specific inhibition is often ineffective. This review discusses the role of ALDH in cancer and therapy resistance, and then overviews the various available ALDH inhibitors with a focus on the clinical potential and limitations of these agents as cancer therapeutics. Finally, challenges and future research directions to effectively target ALDH in the management of cancer therapy resistance are discussed.

Loss of miR-155 upregulates WEE1 in metastatic melanoma.

Significant advances have been made in the treatment of melanoma by targeting key cellular pathways, but additional targets are needed as many patients do not respond or relapse with resistant disease. MicroRNA-155 (MiR-155) has previously been shown to regulate melanoma cell growth and acts as a tumor suppressor. We tested a clinical population of melanoma tumors for miR-155 expression, and find that expression is low in most patients, although not predictive of outcome. We identified the protein kinase WEE1 as a novel target of miR-155. A mouse model of experimental metastasis finds that both increased expression of miR-155 and silencing of WEE1 lead to decreased metastases. Loss of miR-155 and increased expression of WEE1 may contribute to the metastatic phenotype in patients with melanoma.

PARI (PARPBP) suppresses replication stress-induced myeloid differentiation in leukemia cells.

Hyperproliferative cancer cells face increased replication stress, which can result in accumulation of DNA damage. As DNA damage can arrest proliferation, and, in the case of myeloid leukemia, induce differentiation of cancer cells, understanding the mechanisms that regulate the replication stress response is paramount. Here, we show that PARI, a replisome protein involved in regulating DNA repair and replication stress, suppresses differentiation of myeloid leukemia cells. We show that PARI is overexpressed in myeloid leukemia cells, and its knockdown reduces leukemia cell proliferation in vitro and in vivo in xenograft mouse models. PARI depletion enhances replication stress and DNA-damage accumulation, coupled with increased myeloid differentiation. Mechanistically, we show that PARI inhibits activation of the NF-κB pathway, which can initiate p21-mediated differentiation and proliferation arrest. Finally, we show that PARI expression negatively correlates with expression of differentiation markers in clinical myeloid leukemia samples, suggesting that targeting PARI may restore differentiation ability of leukemia cells and antagonize their proliferation.

Schweinfurthin natural products induce regression of murine melanoma and pair with anti-PD-1 therapy to facilitate durable tumor immunity.

Metastatic melanoma is a significant clinical problem with a 5-year survival rate of only 15-20%. Recent approval of new immunotherapies and targeted inhibitors have provided much needed options for these patients, in some cases promoting dramatic disease regressions. In particular, antibody-based therapies that block the PD-1/PD-L1 checkpoint inhibitory pathway have achieved an increased overall response rate in metastatic melanoma, yet durable response rates are reported only around 15%. To improve the overall and durable response rates for advanced-stage melanoma, combined targeted and immune-based therapies are under investigation. Here, we investigated how the natural products called schweinfurthins, which have selective anti-proliferative activity against many cancer types, impact anti-(α)PD-1-mediated immunotherapy of murine melanomas. Two different compounds efficiently reduced the growth of human and murine melanoma cells in vitro and induced plasma membrane surface localization of the ER-resident protein calreticulin in B16.F10 melanoma cells, an indicator of immunogenic cell death. In addition, both compounds improved αPD-1-mediated immunotherapy of established tumors in immunocompetent C57BL/6 mice either by delaying tumor progression or resulting in complete tumor regression. Improved immunotherapy was accomplished following only a 5-day course of schweinfurthin, which was associated with initial tumor regression even in the absence of αPD-1. Schweinfurthin-induced tumor regression required an intact immune system as tumors were unaffected in NOD scid gamma (NSG) mice. These results indicate that schweinfurthins improve αPD-1 therapy, leading to enhanced and durable anti-tumor immunity and support the translation of this novel approach to further improve response rates for metastatic melanoma.