The synthetic retinoid ST1926 as a novel therapeutic agent in rhabdomyosarcoma

Novel ST1926 Nanoparticle Drug Formulation Enhances Drug Therapeutic Efficiency in Colorectal Cancer Xenografted Mice

Cancer is a major public health problem that ranks as the second leading cause of death. Anti-cancer drug development presents with various hurdles faced throughout the process. Nanoparticle (NP) formulations have emerged as a promising strategy for enhancing drug delivery efficiency, improving stability, and reducing drug toxicity. Previous studies have shown that the adamantyl retinoid ST1926 displays potent anti-tumor activities in several types of tumors, particularly in colorectal cancer (CRC). However, phase I clinical trials in cancer patients using ST1926 are halted due to its low bioavailability. In this manuscript, we developed ST1926-NPs using flash nanoprecipitation with polystyrene-b-poly (ethyleneoxide) as an amphiphilic stabilizer and cholesterol as a co-stabilizer. Dynamic light scattering revealed that the resulting ST1926-NPs Contin diameter was 97 nm, with a polydispersity index of 0.206. Using cell viability, cell cycle analysis, and cell death assays, we showed that ST1926-NP exhibited potent anti-tumor activities in human CRC HCT116 cells. In a CRC xenograft model, mice treated with ST1926-NP exhibited significantly lowered tumor volumes compared to controls at low drug concentrations and enhanced the delivery of ST1926 to the tumors. These findings highlight the potential of ST1926-NPs in attenuating CRC tumor growth, facilitating its further development in clinical settings.

Synthetic lethality between ATR and POLA1 reveals a potential new target for individualized cancer therapy

The ATR-CHK1 pathway plays a fundamental role in the DNA damage response and is therefore an attractive target in cancer therapy. The antitumorous effect of ATR inhibitors is at least partly caused by synthetic lethality between ATR and various DNA repair genes. In previous studies, we have identified members of the B-family DNA polymerases as potential lethal partner for ATR, i.e. POLD1 and PRIM1. In this study, we validated and characterized the synthetic lethality between ATR and POLA1. First, we applied a model of ATR-deficient DLD-1 human colorectal cancer cells to confirm synthetic lethality by using chemical POLA1 inhibition. Analyzing cell cycle and apoptotic markers via FACS and Western blotting, we were able to show that apoptosis and S phase arrest contributed to the increased sensitivity of ATR-deficient cancer cells towards POLA1 inhibitors. Importantly, siRNA-mediated POLA1 depletion in ATR-deficient cells caused similar effects in regard to impaired cell viability and cumulation of apoptotic markers, thus excluding toxic effects of chemical POLA1 inhibition. Conversely, we demonstrated that siRNA-mediated POLA1 depletion sensitized several cancer cell lines towards chemical inhibition of ATR and its main effector kinase CHK1. In conclusion, the synthetic lethality between ATR/CHK1 and POLA1 might represent a novel and promising approach for individualized cancer therapy: First, alterations of POLA1 could serve as a screening parameter for increased sensitivity towards ATR and CHK1 inhibitors. Second, alterations in the ATR-CHK1 pathway might predict in increased sensitivity towards POLA1 inhibitors.

The Antitumor Effect of the DNA Polymerase Alpha Inhibitor ST1926 in Glioblastoma: A Proteomics Approach

Glioblastoma Multiforme (GBM) is the most aggressive form of malignant brain tumor. The median survival rate does not exceed two years, indicating an imminent need to develop novel therapies. The atypical adamantyl retinoid ST1926 induces apoptosis and growth inhibition in different cancer types. We have shown that ST1926 is an inhibitor of the catalytic subunit of DNA polymerase alpha (POLA1), which is involved in initiating DNA synthesis in eukaryotic cells. POLA1 levels are elevated in GBM versus normal brain tissues. Therefore, we studied the antitumor effects of ST1926 in several human GBM cell lines. We further explored the global protein expression profiles in GBM cell lines using liquid chromatography coupled with tandem mass spectrometry to identify new targets of ST1926. Low sub-micromolar concentrations of ST1926 potently decreased cell viability, induced cell damage and apoptosis, and reduced POLA1 protein levels in GBM cells. The proteomics profiles revealed 197 proteins significantly differentially altered upon ST1926 treatment of GBM cells involved in various cellular processes. We explored the differential gene and protein expression of significantly altered proteins in GBM compared to normal brain tissues.

Antitumor activity of novel POLA1-HDAC11 dual inhibitors

Hybrid molecules targeting simultaneously DNA polymerase α (POLA1) and histone deacetylases (HDACs) were designed and synthesized to exploit a potential synergy of action. Among a library of screened molecules, MIR002 and GEM144 showed antiproliferative activity at nanomolar concentrations on a panel of human solid and haematological cancer cell lines. In vitro functional assays confirmed that these molecules inhibited POLA1 primer extension activity, as well as HDAC11. Molecular docking studies also supported these findings. Mechanistically, MIR002 and GEM144 induced acetylation of p53, activation of p21, G1/S cell cycle arrest, and apoptosis. Oral administration of these inhibitors confirmed their antitumor activity in in vivo models. In human non-small cancer cell (H460) xenografted in nude mice MIR002 at 50 mg/kg, Bid (qd × 5 × 3w) inhibited tumor growth (TGI = 61%). More interestingly, in POLA1 inhibitor resistant cells (H460-R9A), the in vivo combination of MIR002 with cisplatin showed an additive antitumor effect with complete disappearance of tumor masses in two animals at the end of the treatment. Moreover, in two human orthotopic malignant pleural mesothelioma xenografts (MM473 and MM487), oral treatments with MIR002 and GEM144 confirmed their significant antitumor activity (TGI = 72-77%). Consistently with recent results that have shown an inverse correlation between POLA1 expression and type I interferon levels, MIR002 significantly upregulated interferon-α in immunocompetent mice.

Phase I study of tamibarotene monotherapy in pediatric and young adult patients with recurrent/refractory solid tumors

PURPOSE

Tamibarotene is a synthetic retinoid that inhibits proliferation and induces differentiation of malignant cells by binding to the retinoic acid receptor α/β. Previous in vitro studies have shown that some pediatric solid tumors with retinoic acid receptors differentiate in response to retinoic acid. We conducted a phase I dose-escalation study to determine the recommended dose of tamibarotene for further study in pediatric and young adult patients with recurrent/refractory solid tumors.

METHODS

Pediatric and young adult patients with recurrent/refractory solid tumors were administered tamibarotene at 4, 6, 8, 10, and 12 mg/m²/day for 14 or 21 days of a 28 day cycle. Safety, efficacy, and pharmacokinetics of tamibarotene were evaluated.

RESULTS

Twenty-two patients (median age 8 years) were enrolled in this study. No dose-limiting toxicity (DLT) was encountered, and tamibarotene was generally well tolerated. Two patients experienced severe adverse events (AEs), leading to discontinuation of the treatment. One grade 4 venous thrombosis and one grade 2 erythema multiforme were observed, which promptly resolved after tamibarotene discontinuance. The grade 4 venous thrombosis was a severe AE but not DLT because it occurred after the evaluation period. Pharmacokinetic analyses showed a dose-dependent increase in the maximum drug concentration (C_max) and area under the concentration-time curve (AUC). None of the patients achieved a complete response or partial response. Seven patients had stable disease lasting longer than 18 weeks.

CONCLUSIONS

The recommended dose for phase II study of tamibarotene in pediatric and young adult patients with refractory solid tumors is 12 mg/m²/day for 21 days in a 28 day cycle.

Physiological Tolerance to ssDNA Enables Strand Uncoupling during DNA Replication

It has been long assumed that normally leading strand synthesis must proceed coordinated with the lagging strand to prevent strand uncoupling and the pathological accumulation of single-stranded DNA (ssDNA) in the cell, a dogma recently challenged by in vitro studies in prokaryotes. Here, we report that human DNA polymerases can function independently at each strand in vivo and that the resulting strand uncoupling is supported physiologically by a cellular tolerance to ssDNA. Active forks rapidly accumulate ssDNA at the lagging strand when POLA1 is inhibited without triggering a stress response, despite ssDNA formation being considered a hallmark of replication stress. Acute POLA1 inhibition causes a lethal RPA exhaustion, but cells can duplicate their DNA with limited POLA1 activity and exacerbated strand uncoupling as long as RPA molecules suffice to protect the elevated ssDNA. Although robust, this uncoupled mode of DNA replication is also an in-built weakness that can be targeted for cancer treatment.

Natural and synthetic retinoids in preclinical colorectal cancer models

Colorectal cancer (CRC) remains a leading cause of cancer-related morbidity and mortality worldwide. Although targeted therapy in combination with chemotherapy in CRC prolongs the overall survival of patients with metastatic disease, acquired resistance and relapse hinder their clinical benefits. Moreover, patients with some specific genetic profile are unlikely to benefit from targeted therapy, suggesting the need for safe and effective treatment strategies. Retinoids, comprising of natural and synthetic analogs, are a class of chemical compounds that regulate cellular proliferation, differentiation, and cell death. Retinoids have been used in the clinic for several leukemias and solid tumors, either as single agents or in combination therapy. Furthermore, retinoids have shown potent chemotherapeutic and chemopreventive properties in different cancer models, including CRC. In this review, we summarize the major preclinical findings in CRC in which natural and synthetic retinoids showed promising antitumor activities and stress on the proposed mechanisms of action. Understanding of the retinoids' antitumor mechanisms would provide insights to support and warrant their development in the management of CRC.

Novel adamantyl retinoid-related molecules with POLA1 inhibitory activity

Atypical retinoids (AR) or retinoid-related molecules (RRMs) represent a promising class of antitumor compounds. Among AR, E-3-(3'-adamantan-1-yl-4'-hydroxybiphenyl-4-yl)acrylic acid (adarotene), has been extensively investigated. In the present work we report the results of our efforts to develop new adarotene-related atypical retinoids endowed also with POLA1 inhibitory activity. The effects of the synthesized compounds on cell growth were determined on a panel of human and hematological cancer cell lines. The most promising compounds showed antitumor activity against several tumor histotypes and increased cytotoxic activity against an adarotene-resistant cell line, compared to the parent molecule. The antitumor activity of a selected compound was evaluated on HT-29 human colon carcinoma and human mesothelioma (MM487) xenografts. Particularly significant was the in vivo activity of the compound as a single agent compared to adarotene and cisplatin, against pleural mesothelioma MM487. No reduction of mice body weight was observed, thus suggesting a higher tolerability with respect to the parent compound adarotene.

DNA polymerases in the risk and prognosis of colorectal and pancreatic cancers

Human cancers arise from the alteration of genes involved in important pathways that mainly affect cell growth and proliferation. DNA replication and DNA damages recognition and repair are among these pathways and DNA polymerases that take part in these processes are frequently involved in cancer onset and progression. For example, damaging alterations within the proofreading domain of replicative polymerases, often reported in patients affected by colorectal cancer (CRC), are considered risk factors and drivers of carcinogenesis as they can lead to the accumulation of several mutations throughout the genome. Thus, replicative polymerases can be involved in cancer when losses of their physiological functions occur. On the contrary, reparative polymerases are often involved in cancer precisely because of their physiological role. In fact, their ability to repair and bypass DNA damages, which confers genome stability, can also counteract the effect of most anticancer drugs. In addition, the altered expression can characterise some type of cancers, which exacerbates this aspect. For example, all of the DNA polymerases involved a damage bypass mechanism, known as translesion synthesis, with the only exception of polymerase theta, are downregulated in CRC. Conversely, in pancreatic ductal adenocarcinoma (PDAC), most of these polymerase result upregulated. This suggests that different types of cancer can rely on different reparative polymerases to acquire drug resistance. Here we will examine all of the aspects that link DNA polymerases with CRC and PDAC.

ST1926 inhibits glioma progression through regulating mitochondrial complex II

The antitumor activity of atypical adamantyl retinoid ST1926 has been frequently reported in cancer studies; nevertheless, its effect on glioma has not been fully understood. Mitochondria are critical in regulating tumorigenesis and are defined as a promising target for anti-tumor therapy. In the present study, we found that ST1926 might be a mitochondria-targeting anti-glioma drug. ST1926 showed significantly inhibitory role in the viability of glioma cells mainly through inducing apoptosis and autophagy. The results showed that ST1926 alleviated mitochondria-regulated bioenergetics in glioma cells via reducing ATP production and promoting reactive oxygen species production. Importantly, ST1926 significantly impaired complex II (CII) function, which was associated with the inhibition of succinate dehydrogenase (SDH) activity. In addition, the effects of ST1926 on the induction of apoptosis and ROS were further promoted by the treatment of CII inhibitors, including TTFA and 3-NPA. Furthermore, the in vivo experiments confirmed the role of ST1926 in suppressing xenograft tumor growth with few toxicity. Therefore, ST1926 might be an effective anti-glioma drug through targeting CII.

Induction of Myogenic Differentiation Improves Chemosensitivity of Chemoresistant Cells in Soft-Tissue Sarcoma Cell Lines

Rhabdomyosarcoma (RMS) and rhabdoid tumors (RT) are rare soft-tissue malignancies with the highest incidence in infants, children, and adolescents. Advanced, recurrent, and/or metastatic RMS and RT exhibit poor response to treatment. One of the main mechanisms behind resistance to treatment is believed to be intratumoral heterogeneity. In this study, we investigated the myogenic determination factor 1 (MYOD1) and Noggin (NOG) markers in an embryonal RMS (ERMS) cell line and an RT cell line and the differential response of the MYOD1 and NOG expressing subpopulations to chemotherapy. Importantly, we found that these markers together identify a subpopulation of cells (MYOD1+ NOG+ cells) with primary resistance to Vincristine and Doxorubicin, two commonly used chemotherapies for ERMS and RT. The chemoresistant MYOD1+ NOG+ cells express markers of undifferentiated cells such as myogenin and ID1. Combination of Vincristine with TPA/GSK126, a drug combination shown to induce differentiation of RMS cell lines, is able to partially overcome MYOD1/NOG cells chemoresistance.

CDK1 and CCNB1 as potential diagnostic markers of rhabdomyosarcoma: validation following bioinformatics analysis

Background

Rhabdomyosarcoma (RMS), a common soft-tissue malignancy in pediatrics, presents high invasiveness and mortality. However, besides known changes in the PAX3/7-FOXO1 fusion gene in alveolar RMS, the molecular mechanisms of the disease remain incompletely understood. The purpose of the study is to recognize potential biomarkers related with RMS and analyse their molecular mechanism, diagnosis and prognostic significance.

Methods

The Gene Expression Omnibus was used to search the RMS and normal striated muscle data sets. Differentially expressed genes (DEGs) were filtered using R software. The DAVID has become accustomed to performing functional annotations and pathway analysis on DEGs.

The protein interaction was constructed and further processed by the STRING tool and Cytoscape software. Kaplan–Meier was used to estimate the effect of hub genes on the ending of sarcoma sufferers, and the expression of these genes in RMS was proved by real-time polymerase chain reaction (RT-PCR). Finally, the expression of CDK1 and CCNB1 in RMS was validated by immunohistochemistry (IHC).

Results

A total of 1932 DEGs were obtained, amongst which 1505 were up-regulated and 427were down-regulated. Up-regulated genes were largely enriched in the cell cycle, ECM-receptor interaction, PI3K/Akt and p53 pathways, whilst down-regulated genes were primarily enriched in the muscle contraction process. CDK1, CCNB1, CDC20, CCNB2, AURKB, MAD2L1, HIST2H2BE, CENPE, KIF2C and PCNA were identified as hub genes by Cytoscape analyses. Survival analysis showed that, except for HIST2H2BE, the other hub genes were highly expressed and related to poor prognosis in sarcoma. RT-PCR validation showed that CDK1, CCNB1, CDC20, CENPE and HIST2H2BE were significantly differential expression in RMS compared to the normal control. IHC revealed that the expression of CDK1 (28/32, 87.5%) and CCNB1 (26/32, 81.25%) were notably higher in RMS than normal controls (1/9, 11.1%; 0/9, 0%). Moreover, the CCNB1 was associated with the age and location of the patient’s onset.

Conclusions

These results show that these hub genes, especially CDK1 and CCNB1, may be potential diagnostic biomarkers for RMS and provide a new perspective for the pathogenesis of RMS.

The synthetic retinoid ST1926 attenuates prostate cancer growth and potentially targets prostate cancer stem-like cells

Retinoids are vitamin A derivatives that regulate crucial biological processes such as cellular proliferation, apoptosis, and differentiation. The use of natural retinoids in cancer therapy is limited due to their toxicity and the acquired resistance by cancer cells. Therefore, synthetic retinoids were developed, such as the atypical adamantyl retinoid ST1926 that provides enhanced bioavailability and reduced toxicity. We have assessed the in vitro and in vivo antitumor properties and mechanism of action of ST1926 in targeting cancer stem-like cells population of human prostate cancer (PCa) cell lines, DU145 and PC3, and mouse PCa cell lines, PLum-AD and PLum-AI. We demonstrated that ST1926 substantially reduced proliferation of PCa cells and induced cell cycle arrest, p53-independent apoptosis, and early DNA damage. It also decreased migration and invasion of PCa cells and significantly reduced prostate spheres formation ability in vitro denoting sufficient eradication of the self-renewal ability of the highly androgen-resistant cancer stem cells. Importantly, ST1926 potently inhibited PCa tumor growth and progression in vivo. Our results highlight the potential of ST1926 in PCa therapy and warrant its clinical development.

Role of FoxO Proteins in Cellular Response to Antitumor Agents

FoxO proteins (FoxOs) are transcription factors with a common DNA binding domain that confers selectivity for DNA interaction. In human cells, four proteins (FoxO1, FoxO3, FoxO4 and FoxO6), with redundant activity, exhibit mainly a positive effect on genes involved in cell cycle, apoptosis regulation and drug resistance. Thus, FoxOs can affect cell response to antitumor agent treatment. Their transcriptional activity depends on post-translational modifications, including phosphorylation, acetylation, and mono/poly-ubiquitination. Additionally, alterations in microRNA network impact on FoxO transcripts and in turn on FoxO levels. Reduced expression of FoxO1 has been associated with resistance to conventional agents (e.g., cisplatin) and with reduced efficacy of drug combinations in ovarian carcinoma cells. FoxO3 has been shown as a mediator of cisplatin toxicity in colorectal cancer. A requirement for FoxO3-induced apoptosis has been reported in cells exposed to targeted agents (e.g., gefitinib). Recently, the possibility to interfere with FoxO1 localization has been proposed as a valuable approach to improve cell sensitivity to cisplatin, because nuclear retention of FoxO1 may favor the induction of pro-apoptotic genes. This review focuses on the role of FoxOs in drug treatment response in tumor cells and discusses the impact of the expression of these transcription factors on drug resistance/sensitivity.

The histone deacetylase inhibitor Suberoylanilide Hydroxamic Acid (SAHA) as a therapeutic agent in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is an aggressive childhood sarcoma with two distinct subtypes, embryonal (ERMS) and alveolar (ARMS) histologies. More effective treatment is needed to improve outcomes, beyond conventional cytotoxic chemotherapy. The pan-histone deacetylase inhibitor, Suberoylanilide Hydroxamic Acid (SAHA), has shown promising efficacy in limited preclinical studies. We used a panel of human ERMS and ARMS cell lines and xenografts to evaluate the effects of SAHA as a therapeutic agent in both RMS subtypes. SAHA decreased cell viability by inhibiting S-phase progression in all cell lines tested, and induced apoptosis in all but one cell line. Molecularly, SAHA-treated cells showed activation of a DNA damage response, induction of the cell cycle inhibitors p21^Cip1 and p27^Kip1 and downregulation of Cyclin D1. In a subset of RMS cell lines, SAHA promoted features of cellular senescence and myogenic differentiation. Interestingly, SAHA treatment profoundly decreased protein levels of the driver fusion oncoprotein PAX3-FOXO1 in ARMS cells at a post-translational level. In vivo, SAHA-treated xenografts showed increased histone acetylation and induction of a DNA damage response, along with variable upregulation of p21^Cip1 and p27^Kip1. However, while the ARMS Rh41 xenograft tumor growth was significantly inhibited, there was no significant inhibition of the ERMS tumor xenograft RD. Thus, our work shows that, while SAHA is effective against ERMS and ARMS tumor cells in vitro, it has divergent in vivo effects . Together with the observed effects on the PAX3-FOXO1 fusion protein, these data suggest SAHA as a possible therapeutic agent for clinical testing in patients with fusion protein-positive RMS.

A new class of synthetic retinoid antibiotics effective against bacterial persisters

A challenge in the treatment of Staphylococcus aureus infections is the high prevalence of methicillin-resistant S. aureus (MRSA) strains and the formation of non-growing, dormant 'persister' subpopulations that exhibit high levels of tolerance to antibiotics and have a role in chronic or recurrent infections. As conventional antibiotics are not effective in the treatment of infections caused by such bacteria, novel antibacterial therapeutics are urgently required. Here we used a Caenorhabditis elegans-MRSA infection screen to identify two synthetic retinoids, CD437 and CD1530, which kill both growing and persister MRSA cells by disrupting lipid bilayers. CD437 and CD1530 exhibit high killing rates, synergism with gentamicin, and a low probability of resistance selection. All-atom molecular dynamics simulations demonstrated that the ability of retinoids to penetrate and embed in lipid bilayers correlates with their bactericidal ability. An analogue of CD437 was found to retain anti-persister activity and show an improved cytotoxicity profile. Both CD437 and this analogue, alone or in combination with gentamicin, exhibit considerable efficacy in a mouse model of chronic MRSA infection. With further development and optimization, synthetic retinoids have the potential to become a new class of antimicrobials for the treatment of Gram-positive bacterial infections that are currently difficult to cure.

Accelerated inflammation and oxidative stress induced by LPS in acute lung injury: Ιnhibition by ST1926

Bioavailable and less toxic synthetic retinoids, such as the atypical adamantyl retinoid ST1926, have been well developed and investigated in clinical trials for many diseases. The aim of our study was to explore the role of ST1926 in lipopolysaccharide (LPS)-induced acute lung injury (ALI) and to reveal the possible molecular mechanism. Mice were treated with LPS to induce acute lung injury followed by ST1926 administration. After LPS induction, mice administered with ST1926 showed lower inflammation infiltration in bronchoalveolar lavage (BAL) fluid, and pro-inflammatory cytokines, including interleukin-1β (IL-1β), IL-18, IL-6 and tumor necrosis factor-α (TNF-α) in serum and lung tissue samples obtained from mice. In addition, western blot assays suggested that ST1926 suppressed nuclear factor-κB (NF-κB), inhibitor-κB kinase-α (IκBα) and IκB kinase (IKKα), as well as Toll-like receptor 4 (TLR4) induced by LPS. In addition, reactive oxygen species (ROS) stimulated by LPS was also suppressed for ST1926 through inhibiting p38 and extracellular receptor kinase (ERK) signaling pathway. Taken together, the data here indicated that ST1926 may be of potential value in treating acute lung injury through inflammation and ROS suppression via inactivating TLR4/NF-κB and p38/ERK1/2 signaling pathways.

Evolving Strategies for Therapeutically Targeting Cancer Stem Cells

Cancer is a multifactor and multistep process that is affected intrinsically by the genetic and epigenetic makeup of tumor cells and extrinsically by the host microenvironment and immune system. A key component of cancer involves a unique subpopulation of highly malignant cancerous cells referred to as cancer stem cells (CSCs). CSCs are positioned at the apex of the tumor hierarchy with an ability to both self-renew and also generate non-CSC/differentiated progeny, which contribute to the majority of the tumor mass. CSCs undergo functional changes and show plasticity that is stimulated by specific microenvironmental cues and interactions in the tumor niche, which contribute to the complexity and heterogeneity of the CSC population. The prognostic value of CSCs in the clinic is evident since there are many examples in which CSCs serve as markers for poor patient prognosis. CSCs are innately resistant to many standard therapies and they display anoikis resistance, immune evasion, tumor dormancy, and field cancerization, which may result in metastasis and relapse. Many academic laboratories and biotechnology companies are currently focusing on strategies that target CSCs. Combination therapies, epigenetic modifiers, stemness inhibitors, CSC surface marker-based therapies, and immunotherapy-based CSC-targeting drugs are currently undergoing clinical trials. Potential new targets/strategies in CSC-targeted therapy include MDA-9/Syntenin (SDCBP), Patched (PTCH), epigenetic targets, noncoding RNAs, and differentiation induction. Defining ways of targeting and destroying CSCs holds potential to impact significantly on cancer therapy, including prevention of metastasis and cancer recurrence.