Synthetic retinoid fenretinide in breast cancer chemoprevention

Fenretinide targets GATA1 to induce cytotoxicity in GATA1 positive Acute Erythroid and Acute Megakaryoblastic Leukemic cells

Patients with Acute Myeloid Leukemia (AML) subtypes, acute erythroleukemia and acute megakaryocytic leukemia (M6 and M7 AMLs, respectively) have a median survival of only a few months with no targeted effective treatment. Our gene expression analysis using the Cancer Cell Line Encyclopedia and CRISPR screen from DepMap showed that M6/M7 AMLs have high levels of the transcription factor GATA1 and depend on GATA1 for survival. While GATA1 was shown to support AML cell proliferation and resistance to chemotherapy, GATA1 has long been considered "undruggable". Here, we identify the small molecule N-(4-hydroxyphenyl)retinamide (4-HPR, Fenretinide) as a novel GATA1 targeting agent in M6 and M7 AML cells, with nM to low μM concentrations of 4-HPR causing loss of GATA1. In M6 AML OCIM1 cells, knock-down of GATA1 induced cytotoxicity similarly to low doses 4-HPR while overexpression of GATA1 significantly protected cells from 4-HPR-induced cytotoxicity. In M6 AML cells, 4-HPR synergized with the current standard-of-care (SOC), Azacytidine plus Venetoclax, overcoming cell resistance to the drugs. As single-agent, 4-HPR outperformed SOC. 4-HPR is a synthetic derivative of vitamin A, and numerous clinical trials have supported its safe profile in cancer patients; therefore, targeted use of 4-HPR against M6 and M7 AMLs may represent a novel therapeutic breakthrough.

Key Points

- Fenretinide (4-HPR) targets the transcription factor GATA1, which was previously thought to be "undruggable" and induces GATA1 loss.- M6 and M7 Acute Myeloid Leukemias (AML) have enriched expression of GATA1 and they can be considered GATA1 positive.- Loss of GATA1 contributes significantly to 4-HPR cytotoxicity in M6 OCIM1 cells.- 4-HPR treatment overcomes chemotherapeutic resistance in M6 Acute Myeloid Leukemia cells, synergizes with standard-of-care and outperforms standard-of-care as a single agent.

A nanoencapsulated oral formulation of fenretinide promotes local and metastatic breast cancer dormancy in HER2/neu transgenic mice

BACKGROUND

Prevention and treatment of metastatic breast cancer (BC) is an unmet clinical need. The retinoic acid derivative fenretinide (FeR) was previously evaluated in Phase I-III clinical trials but, despite its excellent tolerability and antitumor activity in preclinical models, showed limited therapeutic efficacy due to poor bioavailability. We recently generated a new micellar formulation of FeR, Bionanofenretinide (Bio-nFeR) showing enhanced bioavailability, low toxicity, and strong antitumor efficacy on human lung cancer, colorectal cancer, and melanoma xenografts. In the present study, we tested the effect of Bio-nFeR on a preclinical model of metastatic BC.

METHODS

We used BC cell lines for in vitro analyses of cell viability, cell cycle and migratory capacity. For in vivo studies, we used HER2/neu transgenic mice (neuT) as a model of spontaneously metastatic BC. Mice were treated orally with Bio-nFeR and at sacrifice primary and metastatic breast tumors were analyzed by histology and immunohistochemistry. Molecular pathways activated in primary tumors were analyzed by immunoblotting. Stem cell content was assessed by flow cytometry, immunoblotting and functional assays such as colony formation ex vivo and second transplantation assay in immunocompromised mice.

RESULTS

Bio-nFeR inhibited the proliferation and migration of neuT BC cells in vitro and showed significant efficacy against BC onset in neuT mice. Importantly, Bio-nFeR showed the highest effectiveness against metastatic progression, counteracting both metastasis initiation and expansion. The main mechanism of Bio-nFeR action consists of promoting tumor dormancy through a combined induction of antiproliferative signals and inhibition of the mTOR pathway.

CONCLUSION

The high effectiveness of Bio-nFeR in the neuT model of mammary carcinogenesis, coupled with its low toxicity, indicates this formulation as a potential candidate for the treatment of metastatic BC and for the adjuvant therapy of BC patients at high risk of developing metastasis.

Targeting Retinol-Binding Protein 4 (RBP4) in the Management of Cardiometabolic Diseases

The ancient use of herbs for the treatment of various human diseases have been documented, with several scientific literatures supporting the use of medicinal plants. There is however a major concern about the phyto-constituents in the plants that performs the healing function and the mechanism by which it works for different ailments are still a research prospect. Cardiometabolic disease (CMD) is no doubt becoming more frequent globally and this is due to poor approach in therapy, contrary effects linked with intensive control, inept strategies with old drugs, inadequate control of some risk factors and lack of knowledge of the pathophysiological mechanisms that lead to this malaise. Retinol-binding protein 4 (RBP4) are predominantly secreted in the liver and adipose tissues and several researches have observed that elevation in serum levels of RBP4 often observed in obese experimental animals and human subjects causes CMD (obesity, insulin resistance, hyperlipidemia, etc.). RBP4 has gained special attention in the last 20 years in the field of metabolism research. This review aims to show research interaction of some medicinal plants targeting RBP4 in treating CMD and to encourage researchers, who are interested in CMD drug design, to focus on medicinal plants that inhibit the secretion of serum RBP4 in the adipose tissue for therapeutic approach to CMD. It also aims to identify the major bioactive compounds of plants that serves as a better and cheaper drug candidate for CMD and also study the signaling pathway which the plant material uses to regulate the metabolic consequences.

Advancements on the Multifaceted Roles of Sphingolipids in Hematological Malignancies

Dysregulation of sphingolipid metabolism plays a complex role in hematological malignancies, beginning with the first historical link between sphingolipids and apoptosis discovered in HL-60 leukemic cells. Numerous manuscripts have reviewed the field including the early discoveries that jumpstarted the studies. Many studies discussed here support a role for sphingolipids, such as ceramide, in combinatorial therapeutic regimens to enhance anti-leukemic effects and reduce resistance to standard therapies. Additionally, inhibitors of specific nodes of the sphingolipid pathway, such as sphingosine kinase inhibitors, significantly reduce leukemic cell survival in various types of leukemias. Acid ceramidase inhibitors have also shown promising results in acute myeloid leukemia. As the field moves rapidly, here we aim to expand the body of literature discussed in previously published reviews by focusing on advances reported in the latter part of the last decade.

Retinol binding protein 4 antagonists and protein synthesis inhibitors: Potential for therapeutic development

Retinol-binding protein 4 (RBP4) is a serum protein that transports Vitamin A. RBP4 is correlated with numerous diseases and metabolic syndromes, including insulin resistance in type 2 diabetes, cardiovascular diseases, obesity, and macular degeneration. Recently, RBP4 antagonists and protein synthesis inhibitors are under development to regulate the effect of RBP4. Several RBP4 antagonists, especially BPN-14136, have demonstrated promising safety profiles and potential therapeutic benefits in animal studies. Two RBP4 antagonists, specifically tinlarebant (Belite Bio) and STG-001 (Stargazer) are currently undergoing clinical trials. Some antidiabetic drugs and nutraceuticals have been reported to reduce RBP4 expression, but more clinical data is needed to evaluate their therapeutical benefits. As regulating RBP4 levels or its activities would benefit a wide range of patients, further research is highly recommended to develop clinically useful RBP4 antagonists or protein synthesis inhibitors.

Sustained, local delivery of the PARP inhibitor talazoparib prevents the development of mammary gland hyperplasia in Brca1-deficient mice

Mutations in BRCA genes are the leading cause of hereditary breast cancer. Current options to prevent cancer in these high-risk patients, such as anti-estrogen drugs and radical mastectomy, are limited by lack of efficacy, undesirable toxicities, or physical and emotional challenges. We have previously shown that PARP inhibitors can significantly delay tumor development in BRCA1-deficient mice. Here, we fabricated the PARP inhibitor talazoparib (TLZ) into spacer implants (InCeT-TLZ) for localized and sustained delivery. We hypothesized that this novel formulation will provide an effective chemopreventive strategy with minimal toxicity. TLZ was released gradually over 30 days as implants degraded. InCeT-TLZ significantly decreased proliferation and increased DNA damage in the mammary glands of BRCA1-deficient mice. Notably, the number of mice that developed hyperplasia in the mammary glands was significantly lower with InCeT-TLZ treatment compared to the control group. Meanwhile, InCeT-TLZ was also better tolerated than oral TLZ, without loss of body weight or anemia. This study provides proof of concept for a novel and safe chemopreventive strategy using localized delivery of a PARP inhibitor for high-risk individuals. Future studies will directly evaluate the effects of InCeT-TLZ for preventing tumor development.

Fumonisin B1 Inhibits Endoplasmic Reticulum Stress Associated-apoptosis After FoscanPDT Combined with C6-Pyridinium Ceramide or Fenretinide

BACKGROUND/AIM

Combining an anticancer agent fenretinide (HPR) or C6-pyridinium ceramide (LCL29) with Foscan-mediated photodynamic therapy (FoscanPDT) is expected to augment anticancer benefits of each substance. We showed that treatment with FoscanPDT+HPR enhanced accumulation of C16-dihydroceramide, and that fumonisin B1 (FB), an inhibitor of ceramide synthase, counteracted caspase-3 activation and colony-forming ability of head and neck squamous cell carcinoma (HNSCC) cells. Because cancer cells appear to be more susceptible to increased levels of the endoplasmic reticulum (ER) stress than normal cells, herein we tested the hypothesis that FoscanPDT combined with HPR or LCL29 induces FB-sensitive ER stress-associated apoptosis that affects cell survival.

MATERIALS AND METHODS

Using an HNSCC cell line, we determined: cell survival by clonogenic assay, caspase-3 activity by spectrofluorometry, the expression of the ER markers BiP and CHOP by quantitative real-time polymerase chain reaction and western immunoblotting, and sphingolipid levels by mass spectrometry.

RESULTS

Similar to HPR+FoscanPDT, LCL29+FoscanPDT induced enhanced loss of clonogenicity and caspase-3 activation, that were both inhibited by FB. Our additional pharmacological evidence showed that the enhanced loss of clonogenicity after the combined treatments was singlet oxygen-, ER stress- and apoptosis-dependent. The combined treatments induced enhanced, FB-sensitive, up-regulation of BiP and CHOP, as well as enhanced accumulation of sphingolipids.

CONCLUSION

Our data suggest that enhanced clonogenic cell killing after the combined treatments is dependent on oxidative- and ER-stress, apoptosis, and FB-sensitive sphingolipid production, and should help develop more effective mechanism-based therapeutic strategies.

Fenretinide (4-HPR) Targets Caspase-9, ERK 1/2 and the Wnt3a/β-Catenin Pathway in Medulloblastoma Cells and Medulloblastoma Cell Spheroids

Medulloblastoma (MB), a neuroectodermal tumor arising in the cerebellum, represents the most frequent childhood brain malignancy. Current treatments for MB combine radiation and chemotherapy and are often associated with relevant side effects; novel therapeutic strategies are urgently needed. N-(4-Hydroxyphenyl) retinamide (4-HPR, fenretinide), a synthetic analogue of all-trans retinoic acid, has emerged as a promising and well-tolerated cancer chemopreventive and chemotherapeutic agent for various neoplasms, from breast cancer to neuroblastoma. Here we investigated the effects of 4-HPR on MB cell lines and identified the mechanism of action for a potential use in therapy of MB. Flow cytometry analysis was performed to evaluate 4-HPR induction of apoptosis and oxygen reactive species (ROS) production, as well as cell cycle effects. Functional analysis to determine 4-HPR ability to interfere with MB cell migration and invasion were performed. Western Blot analysis were used to investigate the crucial molecules involved in selected signaling pathways associated with apoptosis (caspase-9 and PARP-1), cell survival (ERK 1/2) and tumor progression (Wnt3a and β-catenin). We show that 4-HPR induces caspase 9-dependent cell death in DAOY and ONS-76 cells, associated with increased ROS generation, suggesting that free radical intermediates might be directly involved. We observed 4-HPR induction of cell cycle arrest in G1/S phase, inactivated β-catenin, and inhibition of MB cell migration and invasion. We also evaluated the ability of 4-HPR to target MB cancer-stem/cancer-initiating cells, using an MB spheroids model, followed by flow cytometry and quantitative real-time PCR. 4-HPR treatment reduced DAOY and ONS-76 spheroid formation, in term of number and size. Decreased expression of the surface markers CD133⁺ and ABCG2⁺ as well as Oct-4 and Sox-2 gene expression were observed on BTICs treated with 4-HPR further reducing BITIC invasive activities. Finally, we analyzed 4-HPR ability to inhibit MB tumor cell growth in vivo in nude mice. Taken together, our data suggest that 4-HPR targets both parental and MB tumor stem/initiating cell-like populations. Since 4-HPR exerts low toxicity, it could represent a valid compound in the treatment of human MB.

Enhanced apoptotic cancer cell killing after Foscan photodynamic therapy combined with fenretinide via de novo sphingolipid biosynthesis pathway

We and others have shown that stresses, including photodynamic therapy (PDT), can disrupt the de novo sphingolipid biosynthesis pathway, leading to changes in the levels of sphingolipids, and subsequently, modulation of cell death. The de novo sphingolipid biosynthesis pathway includes a ceramide synthase-dependent reaction, giving rise to dihydroceramide, which is then converted in a desaturase-dependent reaction to ceramide. In this study we tested the hypothesis that combining Foscan-mediated PDT with desaturase inhibitor fenretinide (HPR) enhances cancer cell killing. We discovered that by subjecting SCC19 cells, a human head and neck squamous cell carcinoma cell line, to PDT+HPR resulted in enhanced accumulation of C16-dihydroceramide, not ceramide. Concomitantly, mitochondrial depolarization was enhanced by the combined treatment. Enhanced activation of caspase-3 after PDT+HPR was inhibited by FB. Enhanced clonogenic cell death after the combination was sensitive to FB, as well as Bcl2- and caspase inhibitors. Treatment of mouse SCCVII squamous cell carcinoma tumors with PDT+HPR resulted in improved long-term tumor cures. Overall, our data showed that combining PDT with HPR enhanced apoptotic cancer cell killing and antitumor efficacy of PDT. The data suggest the involvement of the de novo sphingolipid biosynthesis pathway in enhanced apoptotic cell killing after PDT+HPR, and identify the combination as a novel more effective anticancer treatment than either treatment alone.

Sphingosine kinase 1 as a potential therapeutic target in epithelial ovarian cancer

Sphingosine kinase 1 (SK1) is over-expressed in multiple types of human cancer. SK1 has growth-promoting effects and has been proposed as a potential therapeutic target. We investigated the therapeutic effects of SK1 inhibition in epithelial ovarian carcinoma (EOC). SK1 siRNA or inhibitors were tested in EOC cell lines, including A2780, SKOV3ip1, A2780-CP20, SKOV3-TR, ES2 and RMG2. Cells were treated with SK inhibitor or FTY720, and cell proliferation, apoptosis, angiogenesis and invasion were examined by MTT, FACS, ELISA and wound-healing assays, respectively. In vivo experiments were performed to test the effects of FTY720 on tumor growth in orthotopic mouse xenografts of EOC cell lines A2780 or SKOV3ip1 and a patient-derived xenograft (PDX) model of clear cell ovarian carcinoma (CCC). Blocking SK1 with siRNA or inhibitors significantly reduced proliferation, angiogenesis and invasion, and increased apoptosis in chemosensitive (A2780 and SKOV3ip1) and chemoresistant (A2780-CP20, SKOV3-TR, ES2 and RMG2) EOC cells. SK1 inhibitors also decreased the intracellular enzymatic activity of SK1. Furthermore, FTY720 treatment significantly decreased the in vivo tumor weight in xenograft models of established cell lines (A2780 and SKOV3ip1) and a PDX model for CCC compared to control (p < 0.05). These results support therapeutic targeting of SK1 as a potential new strategy for EOC.

Acceptability of chemoprevention trials in high-risk subjects

The development and current widespread acceptance of clinical trials is one of the major conceptual advances in research medicine introduced during the second half of the 20th century. Despite general agreement on the scientific merits of randomization, many patients and physicians are however reluctant to participate in randomized, controlled trials. If we focus on chemoprevention in healthy subjects, it is even more essential to evaluate the ethics, logistics, patient's and doctor's acceptability, acute and late toxic effect, patient accrual and compliance of treatment. Furthermore, the decision-making process about participating in a cancer chemoprevention trial is often poorly understood. Adherence to a cancer prevention trial requires in fact a strong sense of awareness and an ability to carefully assess risks and benefits. We review the main aspects in the chemo-preventive approach to patients at high risk for breast and ovarian cancer, focusing on different pharmacological risk reduction strategies, ongoing phase III chemoprevention studies in carriers of BRCA1/2 germline mutation, the psychological and clinical factors implicated in decision making about a trial, and the possible impact of the trial design on the overall acceptability and adherence.

The science behind vitamins and natural compounds for breast cancer prevention. Getting the most prevention out of it

This review highlights the role of vitamins and natural compounds in breast cancer prevention, with a particular focus on Vitamin D. In the last decades, both encouraging and discouraging results about the association between antioxidant supplementation and cancer have been reported to public and scientific community. Their safe and favorable toxicity profile makes them suitable to be investigated in a preventive setting. However, a recent large meta-analysis showed that treatment with beta carotene, vitamin A, and vitamin E may increase mortality, whereas the potential roles of vitamin C and selenium on mortality need further study. Likewise, folate levels were not associated with reduced breast cancer risk in a recent meta-analysis. Several studies have shown that a high proportion of women at-risk for breast cancer or affected by the disease have deficient vitamin D levels, i.e., 250 H-D <20 ng/ml or 50 nmol/L. While the association between Vitamin D levels and breast cancer risk/prognosis is still controversial, the U-shaped relationship between 250 H-D levels observed in different studies suggests the need to avoid both deficient and too high levels. Further trials using an optimal dose range are needed to assess the preventive and therapeutic effect of vitamin D. Finally, Fenretinide, a pro-apoptotic and pro-oxidant vitamin A derivative, has shown promise in several trials and its preventive potential is being assessed in young women at very high risk for breast cancer.

In vitro activities of novel 4-HPR derivatives on a panel of rhabdoid and other tumor cell lines

BACKGROUND

Rhabdoid tumors (RTs) are aggressive pediatric malignancies with poor prognosis. N-(4-hydroxy phenyl) retinamide (4-HPR or fenretinide) is a potential chemotherapeutic for RTs with activity correlated to its ability to down-modulate Cyclin D1. Previously, we synthesized novel halogen-substituted and peptidomimetic-derivatives of 4-HPR that retained activity in MON RT cells. Here we analyzed the effect of 4-HPR in inhibiting the growth of several RT, glioma, and breast cancer cell lines and tested their effect on cell cycle, apoptosis and Cyclin D1 expression.

METHODS

Effect of compounds on RT cell cycle profiles, and cell death were assessed by MTS cell survival assays and FACS analysis. The effects of treatment on Cyclin D1 expression were determined by immunoblotting. The efficacy of these compounds on glioma and breast cancer cell lines was also determined using MTS assays.

RESULTS

Low micromolar concentrations of 4-HPR derivatives inhibited cell survival of all RT cells tested. The 4-HPR derivatives altered RT cell cycle profiles and induced high levels of cell death that was correlated with their potency. ATRA exhibited high IC50 values in all cell lines tested and did not cause cell death. In MON RT cells, the iodo-substituted compounds were more active than 4-HPR in inducing cell cycle arrest and apoptosis. Additionally, the activity of the compounds correlated with their ability to down-modulate Cyclin D1: while active compounds reduced Cyclin D1 levels, inactive ATRA did not. In glioma and breast cancer cell lines, 4-HPR and 4-HPR derivatives showed variable efficacy.

CONCLUSIONS

Here we demonstrate, for the first time, that the inhibitory activities of novel halogen-substituted and peptidomimetic derivatives of 4-HPR are correlated to their ability to induce cell death and down-modulate Cyclin D1. These 4-HPR derivatives showed varied potencies in breast cancer and glioma cell lines. These data indicate that further studies are warranted on these derivatives of 4-HPR due to their low IC50s in RT cells. These derivatives are of general interest, as conjugation of halogen radioisotopes such as 18F, 124I, or 131I to 4-HPR will allow us to combine chemotherapy and radiotherapy with a single drug, and to perform PET/SPECT imaging studies in the future.

Oxidative stress and therapeutic opportunities: focus on the Ewing's sarcoma family of tumors

Reactive oxygen species (ROS) are highly reactive by-products of energy production that can have detrimental as well as beneficial effects. Unchecked, high levels of ROS result in an imbalance of cellular redox state and oxidative stress. High levels of ROS have been detected in most cancers, where they promote tumor development and progression. Many anticancer agents work by further increasing cellular levels of ROS, to overcome the antioxidant detoxification capacity of the cancer cell and induce cell death. However, adaptation of the level of cellular antioxidants can lead to drug resistance. The challenge for the design of effective cancer therapeutics exploiting oxidative stress is to tip the cellular redox balance to induce ROS-dependent cell death but without increasing the antioxidant activity of the cancer cell or inducing toxicity in normal cells.

Identification of dihydroceramide desaturase as a direct in vitro target for fenretinide

The dihydroceramide desaturase (DES) enzyme is responsible for inserting the 4,5-trans-double bond to the sphingolipid backbone of dihydroceramide. We previously demonstrated that fenretinide (4-HPR) inhibited DES activity in SMS-KCNR neuroblastoma cells. In this study, we investigated whether 4-HPR acted directly on the enzyme in vitro. N-C8:0-d-erythro-dihydroceramide (C(8)-dhCer) was used as a substrate to study the conversion of dihydroceramide into ceramide in vitro using rat liver microsomes, and the formation of tritiated water after the addition of the tritiated substrate was detected and used to measure DES activity. NADH served as a cofactor. The apparent K(m) for C(8)-dhCer and NADH were 1.92 ± 0.36 μm and 43.4 ± 6.47 μm, respectively; and the V(max) was 3.16 ± 0.24 and 4.11 ± 0.18 nmol/min/g protein. Next, the effects of 4-HPR and its metabolites on DES activity were investigated. 4-HPR was found to inhibit DES in a dose-dependent manner. At 20 min, the inhibition was competitive; however, longer incubation times demonstrated the inhibition to be irreversible. Among the major metabolites of 4-HPR, 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR) showed the highest inhibitory effect with substrate concentration of 0.5 μm, with an IC(50) of 1.68 μm as compared with an IC(50) of 2.32 μm for 4-HPR. N-(4-Methoxyphenyl)retinamide (4-MPR) and 4-Oxo-N-(4-methoxyphenyl)retinamide (4-oxo-4-MPR) had minimal effects on DES activity. A known competitive inhibitor of DES, C(8)-cyclopropenylceramide was used as a positive control. These studies define for the first time a direct in vitro target for 4-HPR and suggest that inhibitors of DES may be used as therapeutic interventions to regulate ceramide desaturation and consequent function.

Sphingosine kinase mediates resistance to the synthetic retinoid N-(4-hydroxyphenyl)retinamide in human ovarian cancer cells

A2780 human ovarian carcinoma cells respond to treatment with the synthetic retinoid N-(4-hydroxyphenyl)retinamide (HPR) with the production of dihydroceramide and with a concomitant reduction of cell proliferation and induction of apoptosis. The derived HPR-resistant clonal cell line, A2780/HPR, is less responsive to HPR in terms of dihydroceramide generation. In this report, we show that the production of sphingosine 1-phosphate (S1P) is significantly higher in A2780/HPR versus A2780 cells due to an increased sphingosine kinase (SK) activity and SK-1 mRNA and protein levels. Treatment of A2780 and A2780/HPR cells with a potent and highly selective pharmacological SK inhibitor effectively reduced S1P production and resulted in a marked reduction of cell proliferation. Moreover, A2780/HPR cells treated with a SK inhibitor were sensitized to the cytotoxic effect of HPR, due to an increased dihydroceramide production. On the other hand, the ectopic expression of SK-1 in A2780 cells was sufficient to induce HPR resistance in these cells. Challenge of A2780 and A2780/HPR cells with agonists and antagonists of S1P receptors had no effects on their sensitivity to the drug, suggesting that the role of SK in HPR resistance in these cells is not mediated by the S1P receptors. These data clearly demonstrate a role for SK in determining resistance to HPR in ovarian carcinoma cells, due to its effect in the regulation of intracellular ceramide/S1P ratio, which is critical in the control of cell death and proliferation.

Sphingolipidomics of A2780 human ovarian carcinoma cells treated with synthetic retinoids

The dihydroceramide, ceramide, sphingomyelin, lactosylceramide, and ganglioside species of A2780 human ovarian carcinoma cells treated with the synthetic retinoids N-(4-hydroxyphenyl)retinamide (fenretinide, 4-HPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR) in culture were characterized by ESI-MS. We characterized 32 species of ceramide and dihydroceramide, 15 of sphingomyelin, 12 of lactosylceramide, 9 of ganglioside GM2, and 6 of ganglioside GM3 differing for the long-chain base and fatty acid structures. Our results indicated that treatment with both 4-HPR and 4-oxo-4-HPR led to a marked increase in dihydroceramide species, while only 4-oxo-4-HPR led to a minor increase of ceramide species. Dihydroceramides generated in A2780 cells in response to 4-HPR or 4-oxo-4-HPR differed for their fatty acid content, suggesting that the two drugs differentially affect the early steps of sphingolipid synthesis. Dihydroceramides produced upon treatments with the drugs were further used for the synthesis of complex dihydrosphingolipids, whose levels dramatically increased in drug-treated cells.

Design, synthesis of novel peptidomimetic derivatives of 4-HPR for rhabdoid tumors

Rhabdoid tumors (RTs) are an extremely aggressive pediatric malignancy that results from loss of the INI1/hSNF5 tumor suppressor gene. Loss of INI1 results in aberrant expression of Cyclin D1, which supports rhabdoid tumorigenesis and survival. 4-HPR, a synthetic retinoid that down-modulates Cyclin D1, has shown promise in treating various tumors including RTs. In this study, we have generated a chemical library of peptidomimetic derivatives of 4-HPR in an attempt to create a more biologically active compound for use as a therapeutic agent against RTs and other tumors. We have synthesized novel peptidomimetic compound by substituting alkene backbone with a ring structure that retains the biological activity in cell culture models of rhabdoid tumors. We further identified derivative of peptidomimetic compound (11d, IC(50) approximately 3 microM) with approximately five times higher potency than 4-HPR (1, IC(50) approximately 15 microM) based on a survival assay against rhabdoid tumor cells. These studies indicate that peptidomimetic derivatives that retain the cytotoxic activity are promising novel chemotherapeutic agents against RTs and other tumors.

Design and synthesis of 4-HPR derivatives for rhabdoid tumors

Rhabdoid tumors (RTs) are aggressive pediatric malignancies with poor prognosis that arise due to loss of the hSNF5/INI1 tumor suppressor. Molecular studies indicate that cyclin D1, a downstream effector of INI1 is up regulated in RT, and is essential for this tumor formation. Previously we demonstrated that 4-HPR, a synthetic retinoid that targets Cyclin D1, is a potential chemotherapeutic agent for RT. To facilitate further chemical development of this retinoid, and to determine its active moiety, we synthesized small chemical libraries of 4-HPR and tested their cytotoxic effect on RT cells. We synthesized 4-HPR (1) and the derivatives (5a-5n) starting from retinoic acid. First, retinoic acid was converted to acid chloride derivatives, then in the presence of DMF, base, and aniline derivatives, we synthesized the corresponding 4-hydroxy phenyl amine derivatives (5a-5n). This procedure gave 70-90% yield. Then, the 4-HPR derivatives were tested for their ability to inhibit RT cells using an in vitro cell survival assay. We found that the 4-hydroxy group at para-position is essential for cytotoxic activity against RT cells. Furthermore, we identified a few derivatives of 4-HPR with higher cytotoxic potencies than 4-HPR. In addition, we demonstrate that either chloro, fluoro or iodo derivatives at meta-position of phenyl ring retain the cytotoxic activity. Interestingly, substitution of iodo-moiety at meta-position (5j) substantially increased the efficacy (IC(50) approximately 3muM, Fig. 1D). These results indicate that chemical modification of 4-HPR may result in derivatives with increased therapeutic potential for RTs and that halogen substituted 4-HPR that retain the activity can be synthesized for further therapeutic and diagnostic use.