Phase IIa study of fenretinide in superficial bladder cancer, using DNA flow cytometry as an intermediate end point

Design, synthesis and docking studies of novel 4-aminophenol-1,2,4-oxadiazole hybrids as apoptosis inducers against triple negative breast cancer cells targeting MAP kinase

In our study, a series of novel 4-aminophenol benzamide-1,2,4-oxadiazole hybrid analogues have been designed and synthesized by condensing 4-hydroxyphenyl arylamides (3a-c) and 5-chloromethyl-3-aryl-1,2,4-oxadiazoles (6a-d). The structure of the synthesised compounds was verified by various spectroscopic techniques (1H NMR, 13C NMR, IR and LC-MS). All the prepared compounds were subjected to in silico and in vitro antiproliferative study against TNBC cell lines MDA-MB-468 and MDA-MB-231. The investigations revealed that compound 7k significantly promoted apoptosis against MDA-MB-468 and MDA-MB-231 cells with IC50 values of 22.31 µM and 26.27 µM, respectively. Compound 7k interacted with crucial active sites of MAPK and exhibited the highest docking score of -7.06 kcal/mol. Docking was validated with molecular dynamic studies with simulation for 100 ns, depicting various stable interactions with MAPK. Consequently, 7k forms stable H-Bonds and π-π stacking with amino acid residues along with π-cation. Our investigations reveal that the in vitro antiproliferative study of 7k was in good correlation with the in silico studies. Hence, 7k serves as a potential novel lead for the inhibition of TNBCs by downregulating MAPK P38.Communicated by Ramaswamy H. Sarma.

[Prevention and Treatment of Cancer with Vitamin A and Its Derivatives: Cell Differentiation and Proliferation]

Normal differentiation and proliferation of cells are essential for maintaining homeostasis. Following the successful completion of whole genome sequencing, protein modification has been attracted increasing attention in order to understand the roles of protein diversification in protein function and to elucidate molecular targets in mechanisms of signal transduction. Vitamin A is an essential nutrient for health maintenance. It is present as β-carotene in green and yellow vegetables and retinyl ester in animal products and absorbed into the body from the intestines. After ingestion, it is converted to retinol and oxidized in target cells to retinal, which plays critical roles in vision. It is then further oxidized to retinoic acid (RA), which exhibits a number of effects prior to being metabolized by cytochrome P450 and excreted from the body. Since RA exhibits cell differentiation-inducing actions, it is used as a therapeutic agent for patients with acute promyelocytic leukemia. The current paper describes: (1) HL60 cell differentiation and cell differentiation induction therapy by RA; (2) roles played by RA and retinal and their mechanisms of action; (3) retinoylation, post-translational protein-modified by RA, a novel non-genomic RA mechanism of action without RA receptor; (4) new actions of β-carotene and retinol in vivo and (5) potent anticancer effects of p-dodecylaminophenol (p-DDAP), a novel vitamin A derivative created from the RA derivative fenretinide. We propose that nutritional management of vitamin A can be effective at preventing and treating diseases, and that p-DDAP is a promising anticancer drug.

Design and synthesis of 4-aminophenol-1,3,4-oxadiazole derivative potentiates apoptosis by targeting MAP kinase in triple negative breast cancer cells

Women below 40 years greatly suffer from triple negative breast cancers (TNBCs). Compared to other breast cancer cases, the poor prognosis and lower survival rate of TNBC patients make it an alarming task to save the human era from this dreadful disease. Therefore, identifying potential novel leads is urgently required to combat the TNBC. To discover a novel anticancer agent, we synthesized a series of novel 4-aminophenolbenzamide-1,3,4 oxadiazole hybrid analogues (7a-l). The structure of the compounds was confirmed by spectral methods (1H & 13C NMR, IR and MS). All the compounds were subjected to their in-silico and in-vitro antiproliferative studies against the TNBC cell lines MDA-MB-468 and MDA-MB-231. The investigations revealed that 7i has significantly promoted apoptosis against MDA-MB-468 and MDA-MB-231 cells with IC50 values of 16.89 and 19.43 µM, respectively. Molecular docking of 7i, with MAPK has exhibited the highest binding score of -7.10 kcal/mol by interacting with crucial amino acids present at the active sites. Molecular docking is further validated with molecular dynamic studies with simulation for 100 ns, depicting various stable interactions with MAPK. Compound 7i, forms stable H-bonds and π-π stacking with amino acid residues. Molecular dynamic simulation (MDS) reveals that hydrophobic and water bridges were very prominent for 7i to bind, with the amino acid residues in close proximity to the active site of p38 MAPK. The investigations show that the In-vitro antiproliferative study of 7i agreed with the in-silico studies. Collectively, our investigations depict 7i as a potent novel lead for the inhibition of TNBCs by targeting p38 MAPK.Communicated by Ramaswamy H. Sarma.

Vitamin A in health care: Suppression of growth and induction of differentiation in cancer cells by vitamin A and its derivatives and their mechanisms of action

Vitamin A is an important micro-essential nutrient, whose primary dietary source is retinyl esters. In addition, β-carotene (pro-vitamin A) is a precursor of vitamin A contained in green and yellow vegetables that is converted to retinol in the body after ingestion. Retinol is oxidized to produce visual retinal, which is further oxidized to retinoic acid (RA), which is used as a therapeutic agent for patients with promyelocytic leukemia. Thus, the effects of retinal and RA are well known. In this paper, we will introduce (1) vitamin A circulation in the body, (2) the actions and mechanisms of retinal and RA, (3) retinoylation: another RA mechanism not depending on RA receptors, (4) the relationship between cancer and actions of retinol or β-carotene, whose roles in vivo are still unknown, and (5) anti-cancer actions of vitamin A derivatives derived from fenretinide (4-HPR). We propose that vitamin A nutritional management is effective in the prevention of cancer.

Vitamin A and Retinoids in Bladder Cancer Chemoprevention and Treatment: A Narrative Review of Current Evidence, Challenges and Future Prospects

Bladder cancer (BC) is the tenth most common cancer worldwide with a high recurrence rate, morbidity and mortality. Therefore, chemoprevention and improved treatment of BC are of paramount importance. Epidemiological studies suggest that adequate vitamin A intake may be associated with reduced BC risk. In addition, retinoids, natural and synthetic derivatives of vitamin A, are intensively studied in cancer research due to their antioxidant properties and their ability to regulate cell growth, differentiation, and apoptosis. Findings from in vivo and in vitro models of BC show great potential for the use of retinoids in the chemoprevention and treatment of BC. However, translation to the clinical practice is limited. In this narrative review we discuss: (i) vitamin A and retinoid metabolism and retinoic acid signalling, (ii) the pathobiology of BC and the need for chemoprevention, (iii) the epidemiological evidence for the role of dietary vitamin A in BC, (iv) mechanistic insights obtained from in vivo and in vitro models, (v) clinical trials of retinoids and the limitations of retinoid use, (vi) novel systems of retinoid delivery, and (vii) components of retinoid signalling pathways as potential novel therapeutic targets.

Anticancer efficacy of p-dodecylaminophenol against high-risk and refractory neuroblastoma cells in vitro and in vivo

Neuroblastoma is an aggressive and drug-resistant refractory cancer. The human high-risk neuroblastoma cell line, SK-N-AS (non-amplified N-myc) is derived from stromal cells and it is resistant to treatment with retinoic acid (1, RA), which is a chemotherapeutic agent used to induce neuronal cellular differentiation of neuroblastomas. We have developed p-dodecylaminophenol (3, p-DDAP), based on N-(4-hydroxyphenyl)retinamide (2, 4-HPR), a synthetic amide of 1, since 1 and 2 are associated with the side-effect of nyctalopia. In order to evaluate the effects of 3 on high-risk neuroblastomas, we employed SK-N-AS cells as well asa second high-risk human neuroblastoma cell line, IMR-32, which is derived from neuronal cells (amplified N-myc, drug sensitive). Compound 3 suppressed cell growth of SK-N-AS and IMR-32 cells more effectively than 1, 2, p-decylaminophenol (4, p-DAP), N-(4-hydroxyphenyl)dodecananamide (5, 4-HPDD) or N-(4-hydroxyphenyl)decananamide (6, 4-HPD). In SK-N-AS cells, 3 induced G₀/G₁ arrest and apoptosis to a greater extent than 1 and 2. In IMR-32 cells, 3 induced apoptosis to a similar extent as 1 and 2, potentially by inhibiting N-myc expression. In addition, i.p. administration of 3 suppressed tumor growth in SK-N-AS-implanted mice in vivo. Since 3 showed no effects on blood retinol concentrations, in contrast to reductions following the administration of 2, it exhibited excellent anticancer efficacy against high-risk neuroblastoma SK-N-AS and IMR-32 expressing distinct levels of N-myc. Compound 3 may have potential for clinical use in the treatment of refractory neuroblastoma with reduced side effects.

Synthesis of short retinoidal amides related to fenretinide: antioxidant activities and differentiation-inducing ability

PURPOSE

By a scaffold shortening strategy, a small series of retinoidal amides fenretinide (4-HPR) analogs have been synthesized from α, β-ionones and tested for their antiproliferative and differentiating activities, and antioxidant effect.

METHODS

The antiproliferative activity and triggering of apoptosis of our short retinoids were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and 4'-6-diamidino-2-phenylindole staining and microscope evaluation after 3- or 6-day exposure, while their differentiating activity was established by the analysis of the expression of the CD11b marker of differentiation in treated HL60 target cells and by the superoxide production assayed colorimetrically by the nitro blue tetrazolium-reducing activity assay. Finally, the antioxidant activity was determined by the 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) diammonium salt radical cation decolourisation assay utilizing the antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) as reference (Trolox equivalent antioxidant capacity, or TEAC). Docking analysis was performed to study the binding features to the Retinoic Acid Receptor alpha (RARα).

RESULTS

While no pharmacologically relevant antiproliferative activity was evidenced, some of our short retinoids showed a differentiating and antioxidant activity similar to that of 4-HPR. In particular, compound 2b6 displayed a scavenging activity two times more efficient than 4-HPR itself. Finally, the docking analysis showed that these short retinoids, like 4-HPR, bind to the RARα protein with good fitness scores.

CONCLUSION

Our data could pave the way for the design of new potent and less toxic antioxidant and differentiating compounds related to 4-HPR.

Prognostic Significance of VEGF after Twenty-Year Follow-up in a Randomized Trial of Fenretinide in Non-Muscle-Invasive Bladder Cancer

Non-muscle-invasive bladder cancer (NMIBC) may progress to muscle-invasive disease, but no effective preventive treatments are available. In addition, no reliable prognostic biomarkers have been identified. We assessed the long-term effect of the oral retinoid fenretinide and the prognostic value of circulating VEGF levels. We updated through the Tumor Registry the vital status of 99 patients with resected Ta/T1 bladder tumors who were recruited in a randomized trial of 2 years of fenretinide or no treatment in 1993-1994. Serum VEGF levels measured at baseline and 12 months were available in a subgroup of 62 patients. After a median of 20.5 years, 54 subjects died, 35 of any cancer and 14 of bladder cancer. Neither overall survival (OS), nor cancer survival (CS) or bladder cancer survival (BCS) was affected by fenretinide (log-rank P ≥ 0.2). DNA aneuploidy in bladder washing was associated with shorter OS (P = 0.02), CS (P = 0.05), and BCS (P = 0.09). Subjects with baseline VEGF levels in the top quintile (≥350 pg/mL) had a significantly shorter OS (P = 0.01), CS (P = 0.02), and BCS (P = 0.008). The trend across quintiles of VEGF was significant for BCS (P = 0.007). Multivariate analyses showed that, in addition to smoking status, VEGF level in the top quintile was an independent prognostic factor for OS (HR = 2.7; 95% CI, 1.1-6.5), CS (HR = 3.3; 95% CI, 1.1-9.4) and BCS (HR = 8.9; 95% CI,1.3-61). Fenretinide did not affect the long-term outcome of patients with NMIBC. High serum VEGF level was a significant predictor of overall and cancer death and may help to identify high-risk subjects who may benefit from a preventive therapy. Cancer Prev Res; 9(6); 437-44. ©2016 AACR.

N-(4-hydroxyphenyl)retinamide promotes apoptosis of resting and proliferating B-cell chronic lymphocytic leukemia cells and potentiates fludarabine and ABT-737 cytotoxicity

The in vitro effects of the synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR, fenretinide) on primary B-cell chronic lymphocytic leukemia (CLL) cells from previously untreated CLL patients were investigated. 4HPR promoted the intrinsic apoptotic pathway by reactive oxygen species (ROS) generation and was accompanied by drop of Mcl-1 protein expression. The latter was not attributable to transcriptional downregulation but to protein degradation mediated by jun N-terminal kinase activation, and likely by NF-kB downregulation and Noxa upregulation. CLL cells stimulated in vitro with CD40L did not increase 4HPR chemoresistance if activation was accompanied by proliferation. Intra-patient analysis confirmed that the proliferating pool of CLL cells was more sensitive to the cytotoxic action of 4HPR than the activated but resting CLL subpopulation. The different 4HPR susceptibility of the two subpopulations was associated with higher Noxa expression in proliferating CLLs. Combination experiments revealed that 4HPR strongly potentiated ABT-737 cytotoxicity, especially in proliferating CLL cells that displayed amplified chemoresistance to ABT-737 alone. Synergic cytotoxicity was also demonstrated in combination with fludarabine, in both resting and stimulated CLL samples. This study entitles 4HPR to be assayed as a chemotherapeutic adjuvant for the treatment of CLL.

Oral fenretinide in biochemically recurrent prostate cancer: a California cancer consortium phase II trial

BACKGROUND

Fenretinide is a synthetic retinoid that is cytotoxic to a variety of cancers. We conducted a phase II trial of oral fenretinide in patients with biochemically recurrent prostate cancer.

PATIENTS AND METHODS

Eligible patients had histologically confirmed prostate cancer and a confirmed rising prostate-specific antigen (PSA) >or= 2 ng/mL following either radical prostatectomy and/or pelvic radiation therapy, without clinical or radiographic evidence of metastasis. The primary endpoint was PSA response, which was defined as a confirmed decrease by >or=50%, and >or=5 ng/mL, from the pretreatment value. Treatment comprised oral fenretinide 900 mg/m2 twice daily for 1 week, every 3 weeks, for 1 year.

RESULTS

After a median follow-up of 17.7 months, out of 23 patients, 7 (30%) patients had PSA stable disease (SD), 11 (48%) patients had PSA progression within 3 months, 4 patients had minimal increases over 3 months that did not qualify as SD or progression (17%), and one patient (4%) was not evaluable. Median time to PSA progression was 4.6 months (95% CI, 3.2-8.2 months). Observed grade 3 toxicities included fatigue, pain, hypermagnesemia, a rise in lipase, and nyctalopia.

CONCLUSION

Although well-tolerated, oral fenretinide did not meet prespecified PSA criteria for response in biochemically recurrent prostate cancer; however, 30% of patients had SD, which suggests modest single-agent clinical activity. The role of different formulations of fenretinide, which might allow for higher serum concentrations of the drug, is currently under investigation.

The origins of bladder cancer

Bladder cancer, arising from the transitional cells of the mucosal urothelium, may present as a noninvasive, papillary tumor protruding from the mucosal surface, or as a solid, nonpapillary tumor that invades the bladder wall and has a high propensity for metastasis. The nonpapillary tumors originate from in situ dysplasia. The most common environmental risk for bladder cancer is active smoking; occupational exposure to arsenic or other carcinogens is also a risk factor. A possible familial component to bladder cancer has been described. Conventional models of carcinogenesis suppose the existence of successive mutation events within a specific cell clone, enabling its eventual escape from regulation of cell division and maintenance of genomic integrity. Important new information has emerged from whole-organ mapping of the mucosal genome in bladders resected for invasive cancer (Majewski et al, Lab Invest; published online 5 May 2008). Mapping of genetic hits across the entire mucosa demonstrates genetic alterations in six chromosomal regions, not only in mucosal regions of evident dysplasia, but also in morphologically normal mucosa. These clonally expanded regions cover vast expanses of the bladder surface, as a 'first wave' of pre-neoplasia. Target genes in these regions are termed 'forerunner genes' (FR genes), based on the concept that these genes enable the initial clonal expansion of in situ urothelial neoplasia. Extensive further analysis of human populations with urothelial cancer implicates genetic polymorphisms in one of these genes, P2RY5, as being present in a familial cluster of cancers of multiple organs, and as imparting risk for development of bladder cancer in active smokers. P2RY5 is a gene encoded within intron 17 of RB1, a prototypic tumor suppressor gene whose expression is lost at a later stage of bladder carcinogenesis. Alterations of the FR gene status provide a novel opportunity to screen individuals at risk for the earliest stage of bladder pre-neoplasia and represent attractive targets for therapeutic and chemopreventive interventions. These findings support the hypothesis that bladder carcinogenesis is initiated by clonal expansion of genetically altered but histologically normal cells that cover broad expanses of the mucosa. Effort must now be given to identifying the biological function of these novel FR genes.

Phase III prevention trial of fenretinide in patients with resected non-muscle-invasive bladder cancer

PURPOSE

The study aims to evaluate the efficacy and toxicity of fenretinide in preventing tumor recurrence in patients with transitional cell carcinoma (TCC) of the bladder.

EXPERIMENTAL DESIGN

We conducted a multicenter phase III, randomized, placebo-controlled trial of fenretinide (200 mg/day orally for 12 months) in patients with non-muscle-invasive bladder TCC (stages Ta, Tis, or T1) after transurethral resection with or without adjuvant intravesical Bacillus Calmette-Guerin (BCG). Patients received cystoscopic evaluation and bladder cytology every 3 months during the 1-year on study drug and a final evaluation at 15 months. The primary endpoint was time to recurrence.

RESULTS

A total of 149 patients were enrolled; 137 were evaluable for recurrence. The risk of recurrence was considered to be "low" in 72% (no prior BCG) and intermediate or high in 32% (prior BCG) of the evaluable patients. Of the lower-risk group, 68% had solitary tumors and 32% had multifocal, low-grade papillary (Ta, grade 1 or grade 2) tumors. The 1-year recurrence rates by Kaplan-Meier estimate were 32.3% (placebo) versus 31.5% (fenretinide; P = 0.88 log-rank test). Fenretinide was well tolerated and had no unexpected toxic effects; only elevated serum triglyceride levels were significantly more frequent on fenretinide (versus placebo). The Data Safety and Monitoring Board recommended study closure at 149 patients (before reaching the accrual goal of 160 patients) because an interim review of the data showed a low likelihood of detecting a difference between the two arms, even if the original accrual goal was met.

CONCLUSIONS

Although well tolerated, fenretinide did not reduce the time-to-recurrence in patients with Ta, T1, or Tis TCC of the bladder.

A rapid, sensitive and selective liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry method for determination of fenretinide (4-HPR) in plasma

A simple and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method using an atmospheric pressure chemical ionization source (APCI) for the quantification of fenretinide (4-HPR) in mouse plasma was developed and validated. After a simple protein precipitation of plasma sample by acetonitrile, 4-HPR was analyzed by LC-APCI-MS/MS. High-performance liquid chromatography (HPLC) separation was conducted on a Hypurity C18 column (50mmx2.1mm, 5microm) with a flow rate 0.60mL/min using a gradient mobile phase comprised of 0.05% formic acid in water (A) and methanol (B), and a run time of 4.5min. The elimination of a tedious sample preparation process and a shorter run time substantially reduced total analysis time. The method was linear over the range 0.5-100ng/mL, with r>0.998. The intra- and inter-assay precisions were 1.4-9.2% and 5.1-8.2%, respectively, and the intra- and inter-assay accuracies were 93.9-98.6% and 92.7-95.3%, respectively. The absolute recoveries were 90.3% (1.5ng/mL), 97.0% (7.5ng/mL) and 92.1% (75.0ng/mL) for 4-HPR, and 99.1% for the internal standard (150ng/mL). The analytical method had excellent sensitivity using a small sample volume (30microL) with the lower limit of quantification (LLOQ) 0.5ng/mL. This method is robust and has been successfully employed in a pharmacokinetic study of 4-HPR in a mouse xenograft model of neuroblastoma.

p-Dodecylaminophenol derived from the synthetic retinoid, fenretinide: antitumor efficacy in vitro and in vivo against human prostate cancer and mechanism of action

Fenretinide, N-(4-hydroxyphenyl)retinamide (4-HPR) is an aminophenol-containing synthetic retinoid derivative of all-trans-retinoic acid, which is a potent chemopreventive and antiproliferative agent against various cancers. Clinical studies of 4-HPR have shown side effects consisting of night blindness and ocular toxicity. To maintain potent anticancer activity without side effects, p-dodecylaminophenol (p-DDAP) was designed based on structure-activity relationships of 4-HPR. In our study, we investigate whether p-DDAP shows anticancer activity against human prostate cancer cell line PC-3 when compared with 4-HPR. p-DDAP inhibited PC-3 cell growth progressively from low to high concentration in a dose-dependent manner. p-DDAP was the most potent antiproliferative agent in vitro among 6 p-alkylaminophenols and 3 4-hydroxyphenyl analogs examined including 4-HPR. Cells treated with p-DDAP were shown to undergo apoptosis, based on condensation nuclei, cytofluorimetric analysis, propidium iodide staining and the expression of bcl-2 and caspase 3. p-DDAP arrested the S phase of the cell cycle, while 4-HPR arrested the G(0)/G(1) phase. In addition, both the i.v. and i.p. administration of p-DDAP suppressed tumor growth in PC-3-implanted mice in vivo. p-DDAP showed no effects on blood retinol concentrations, in contrast to reductions after 4-HPR administration. These results indicate that p-DDAP exhibits excellent anticancer efficacy against hormonal independent prostate cancer in vitro and in vivo, and it may have great potential for clinical use in the treatment of prostate cancer with reduced side effects.

Prognostic Effect of DNA Aneuploidy from Bladder Washings in Superficial Bladder Cancer

BACKGROUND

Superficial (papillary) bladder cancer is associated with progression and death from muscle-invasive bladder cancer, but no reliable predictors of the outcomes have been identified.

METHODS

We analyzed the long-term prognostic effect of DNA flow cytometry in bladder washings from 93 subjects with previously resected T(a) and T(1) bladder tumors who participated in a chemoprevention trial of the synthetic retinoid fenretinide. Kaplan-Meier analysis and Cox regression were used to determine the prognostic effect of DNA aneuploidy on cancer progression and mortality in conjunction with conventional clinical factors after a median of 11.5 years (interquartile range, 9.5-11.7 years).

RESULTS

Overall, 58 of 93 (62%) specimens were DNA aneuploid at baseline. Progression-free survival was significantly shorter in subjects with stage T(1) [hazard ratio (HR), 31.6; 95% confidence interval (95% CI), 2.6-386.1; P < 0.001] and in subjects with baseline DNA aneuploid washing (HR, 10.5; 95% CI, 1.1-126.1; P = 0.03). The risk of death was also greater for stage T(1) tumors (HR, 2.6; 95% CI, 1.04-6.7; P = 0.04). DNA aneuploidy was a significant prognostic factor also for overall survival (HR, 2.8; 95% CI, 1.0-9.0; P = 0.05). Fenretinide treatment had no significant effect on cancer progression and death.

CONCLUSIONS

DNA aneuploidy in washings from endoscopically normal bladder is a significant predictor of progression and death in addition to tumor stage. This biomarker may help to identify and monitor a high-risk group who may benefit from a chemoprevention intervention.

Anti-proliferative activity of fenretinide in human hepatoma cells in vitro and in vivo

N-(4-hydroxyphenyl)-retinamide (fenretinide) is a synthetic derivative of all-trans-retinoic acid and induces apoptosis in several cancer cell lines. We determined the anti-cancer activity of fenretinide using human hepatoma cell lines, Bel-7402, HepG2 and Smmc-7721. An in-vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that fenretinide exhibited growth inhibition in these cell lines, with IC50 values ranging from 13.1 to 15.5 micromol/l. In Bel-7402 cells, apoptosis with 15 micromol/l fenretinide for 0 and 48 h was 3 and 48%, respectively. In-vivo studies using the Bel-7402 xenografted athymic mouse model showed tumor inhibition rates ranging from 37.2 to 57.2%, with fenretinide administration once per 3 days at the rate of 25-100 mg/kg. Western blot analysis further showed down-regulation of procaspase-3, X-linked inhibitor of apoptosis protein and poly(ADP-ribose) polymerase cleavage in Bel-7402 cells treated with 15 mumol/l fenretinide for 48 h. Overexpression of p53 was observed in a time-dependent manner, along with a decrease in the Bcl-2/Bax ratio. Depolarized mitochondrial membranes were found in fenretinide-induced apoptotic cells, in a time-dependent manner. We conclude that fenretinide effectively inhibits the proliferation of Bel-7402, both in vitro and in vivo. Both procaspase-3 and p53-mediated apoptotic pathways are involved in its potent anti-cancer activity.

Potent anticancer activities of novel aminophenol analogues against various cancer cell lines

Novel aminophenol analogues were synthesized based on the structure of fenretinide (N-(4-hydroxyphenyl)retinamide, 5), which is a potent anticancer agent. Our findings showed that the anticancer activities of 5 were due to the side chain attached to the aminophenol moiety. A p-octylaminophenol (p-OAP) provided the most potent anticancer activity among p-alkylaminophenols examined. In this study, we investigated anticancer activities against various cancer cell lines by the new aminophenols, p-dodecylaminophenol (1), p-decylaminophenol (2), N-(4-hydroxyphenyl)dodecananamide (3), and N-(4-hydroxyphenyl)decananamide (4), which exhibits a side chain as long as 5. Cell growth of breast cancer (MCF-7, MCF-7/Adr(R)), prostate cancer (DU-145), and leukemia (HL60) cells was suppressed by 1 and 2 in a fashion dependent on the length of the alkyl chain attached to the aminophenol. In contrast, 3 and 4 were extremely weak. Compound 5 was less potent than 1. Cell growth of liver cancer (HepG2) was not markedly affected by these compounds. In addition, apoptosis of HL60 cells was induced by 1 and 2 in a chain length-dependent manner, but not by 3 and 4. Incorporation of compounds into HL60 cells was in the order 1>2=3>4. These results indicated that anticancer activities for 1 and 2 are correlated with their incorporation into cancer cells and their capability to induce apoptosis, but not for 3 and 4. Compound 1, a potent anticancer agent with potency strikingly greater than 5, may potentially be useful in clinic.

All-trans retinoic acid down-regulates human albumin gene expression through the induction of C/EBPbeta-LIP

ATRA (all-trans retinoic acid), which is a major bioactive metabolite of vitamin A and a potent regulator of development and differentiation, mediates down-regulation of the human albumin gene. However, the mechanism of ATRA-mediated down-regulation is not well understood. In the present study, deletion analysis and luciferase assays demonstrate that ATRA causes a marked decrease in the activity of the albumin promoter, the region between nt -367 and -167 from the transcription start site, where C/EBP (CCAAT/enhancer-binding protein)-binding sites are tightly packed, is indispensable for ATRA-mediated down-regulation. ChIP (chromatin immunoprecipitation) assays revealed that in vivo binding of C/EBPalpha to the region markedly decreases upon incubation with ATRA, whereas ATRA treatment marginally increases the recruitment of C/EBPbeta. We found that ATRA has the ability to differentially and directly induce expression of a truncated isoform of C/EBPbeta, which is an LIP (liver-enriched transcriptional inhibitory protein) that lacks a transactivation domain, and to increase the binding activity of C/EBPbeta-LIP to its response element. Overexpression of C/EBPbeta-LIP negatively regulates the endogenous expression of albumin, as well as the activity of the albumin promoter induced by C/EBP transactivators such as C/EBPalpha and full-length C/EBPbeta. In conclusion, we propose a novel model for down-regulation of the albumin gene, in which ATRA triggers an increase in the translation of C/EBPbeta-LIP that antagonizes C/EBP transactivators by interacting with their binding sites in the albumin promoter.

Antioxidant and anticancer activities of novel p-alkylaminophenols and p-acylaminophenols (aminophenol analogues)

Novel compounds were designed based on fenretinide, N-(4-hydroxyphenyl)retinamide (2), which is a synthetic amide of all-trans-retinoic acid (1) that is a potent antioxidant and anticancer agent. Our recent findings indicated that antioxidant and anticancer activities were due to p-methylaminophenol moiety (8) in 2, and that p-octylaminophenol (7), which has an elongated alkyl chain, was more potent than 8. This finding lets us to investigate whether compounds containing alkyl or acyl chains linked to an aminophenol residue as long as 2 and 1, would show activities greater than 2. For this purpose, we prepared p-dodecanoylaminophenol (3), p-decanoylaminophenol (4), p-dodecylaminophenol (5), and p-decylaminophenol (6). The p-alkylaminophenols, 5 and 6, exhibited superoxide scavenging activities, but not p-acylaminophenols, 3 and 4. Elongation of the alkyl chain length reduced superoxide trapping capability (8>7>6>5). In contrast, lipid peroxidation in rat liver microsomes was reduced by 5 and 6 in dose-dependent manner. Compounds 3 and 4 were poor lipid peroxidation inhibitors, being approximately 400- to 1300-fold lower than 5 and 6. In addition, all compounds inhibited cell growth of human leukemia cell lines, HL60 and HL60R, in dose-dependent manners (5>6>3=4). The HL60R cell line is resistant against 1. Growth of both cell lines was suppressed by 5 and 6 in a fashion dependent on the length of the aminophenol alkyl chain, but not by 3 and 4. These results indicate that 5, a potent anticancer agent greater than 2, may potentially have clinical utility, and that its anticancer activity is correlated with inhibitory potency against lipid peroxidation, but not with superoxide scavenging activity.

Chemoprevention of bladder cancer

Chemoprevention of cancer can be accomplished using primary, secondary, or tertiary strategies. Tertiary chemoprevention has been the predominant approach for bladder cancer and addresses the need for preventing the occurrence of second primary cancers in patients who have previously been treated for cancer. Because non-muscle-invasive bladder cancer is associated with a high risk of recurrence, tertiary chemoprevention has been studied in this population. Although considerable preclinical data has demonstrated the feasibility of this approach, application to the clinical setting has met with limited success. This review discusses chemoprevention of bladder cancer and focuses on the drugs used in chemoprevention investigations and clinical study design.

Anticancer and superoxide scavenging activities of p-alkylaminophenols having various length alkyl chains

A series of p-alkylaminophenols including 3, p-butylaminophenol; 4, p-hexylaminophenol; 5, p-octylaminophenol; and 6, N-(p-methoxybenzyl)aminophenol were synthesized based on the structure of fenretinide, N-(4-hydroxyphenyl)retinamide (1). This latter agent is a synthetic amide of all-trans-retinoic acid (RA), which is a cancer chemopreventive and antiproliferative agent. It was found that elongation of the alkyl chain length in these compounds increased antioxidative activity and inhibition of lipid peroxidation. These findings led us to investigate whether antiproliferative activity against cancer cells was effected by the length of alkyl chains linked to the aminophenol residue. All p-alkylaminophenols inhibited growth of HL60 and HL60R cells in a dose-dependent manners. The HL60R line is a resistant clone against RA. Growth of various cancer cell lines (HL60, HL60R, MCF-7, MCF-7/Adr(R), HepG2, and DU-145) was suppressed by p-alkylaminophenols in a fashion dependent on the aminophenol alkyl chain length (5>4>3>p-methylaminophenol (2)), with 5 being the most potent inhibitor of cell growth against HL60R, MCF-7/Adr(R), and DU-145 cells among p-alkylaminophenols tested, including 1. In particular, with the exception of compound 2, antiproliferative activity against DU-145 cells by these p-alkylaminophenols was greater than by 1. In HL60 cells, growth inhibition was associated with apoptosis. On the other hand, elongation of the alkyl chain length reduced superoxide trapping capability (2>3>4>5) in contrast to the effects on inhibition of lipid peroxidation. These results indicate that anticancer activity of p-alkylaminophenols correlated with the inhibitory activity of lipid peroxidation, but not with the superoxide scavenging activity.

Induction of apoptosis in primary meningioma cultures by fenretinide

Fenretinide, a synthetic retinoid that induces apoptosis in tumor cells in vitro, is being evaluated in clinical trials as a chemotherapeutic agent against several malignancies. Due to its ease of administration, long-term tolerability, and low incidence of long-term side effects, we explored its potential as a therapeutic agent against meningiomas by examining its efficacy in vitro against such cells in primary culture. Cells, cultured from freshly resected benign, atypical, or malignant meningiomas, were exposed to fenretinide (10 mumol/L). Treatment effects were assessed using flow cytometry, Western blot analysis, semiquantitative reverse transcription-PCR for retinoid receptor expression, and changes in insulin-like growth factor-I (IGF-I)-induced proliferation. Fenretinide induced apoptosis in the three grades of meningioma primary cells tested, as shown by the appearance of a sub-G(1) fraction in flow cytometric analysis and by the detection of poly-adenosyl ribonucleotidyl phosphorylase cleavage indicating caspase activation. Fenretinide treatment also increased levels of the death receptor DR5 and caused mitochondrial membrane depolarization. The levels of the retinoid receptors, retinoic acid receptor alpha and retinoid X receptor gamma, were up-regulated in response to fenretinide, suggestive of ligand-induced receptor up-regulation. IGF-I-induced proliferation in the meningioma cells was abolished by fenretinide. We conclude that fenretinide induces apoptosis in all three histologic subtypes of meningioma and exerts diverse cellular effects, including DR5 up-regulation, modulation of retinoid receptor levels, and inhibition of IGF-I-induced proliferation. These results provide preliminary evidence that fenretinide has activity against meningiomas and suggest that further studies are warranted to explore its potential as a therapeutic agent against meningiomas.

Phase II study of fenretinide (NSC 374551) in adults with recurrent malignant gliomas: A North American Brain Tumor Consortium study

PURPOSE

Fenretinide induces apoptosis in malignant gliomas in vitro. This two-stage phase II trial was conducted to determine the efficacy of fenretinide in adults with recurrent malignant gliomas.

PATIENTS AND METHODS

Twenty-two patients with anaplastic gliomas (AG) and 23 patients with glioblastoma (GBM) whose tumors had recurred after radiotherapy and no more than two chemotherapy regimens were enrolled. Fenretinide was given orally on days 1 to 7 and 22 to 28 in 6-week cycles in doses of 600 or 900 mg/m(2) bid.

RESULTS

Six of 21 (29%) patients in the AG arm and two of 23 (9%) patients in the GBM arm had stable disease at 6 months. One patient with AG treated at 900 mg/m(2) bid dosage had a partial radiologic response. Median progression-free survival (PFS) was 6 weeks for the AG arm and 6 weeks for the GBM arm. PFS at 6 months was 10% for the AG arm and 0% for the GBM arm. Grade 1 or 2 fatigue, dryness of skin, anemia, and hypoalbuminemia were the most frequent toxicities reported. The trial was closed after the first stage because of the inadequate activity at the fenretinide doses used. The first-administration mean plasma C(max) for fenretinide was 832 +/- 360 ng/mL at the 600 mg/m(2) bid dosage and 1,213 +/- 261 ng/mL at the 900 mg/m(2) bid dosage.

CONCLUSION

Fenretinide was inactive against recurrent malignant gliomas at the dosage used in this trial. However, additional studies using higher doses of the agent are warranted based on the tolerability of the agent and the potential for activity of a higher fenretinide dosage, as suggested in this trial.

Reduced Lecithin

PURPOSE

Retinoids, which include vitamin A (retinol; ROL) and its derivatives, have been investigated in the treatment of bladder cancer. We have shown that expression of the enzyme lecithin:ROL acyltransferase (LRAT), which converts ROL to retinyl esters, is reduced in several human cancers. Here we evaluated expression of LRAT protein and mRNA in normal and malignant bladder tissue specimens from human patients. We also examined the effect of retinoids on LRAT expression in bladder cancer cell lines.

EXPERIMENTAL DESIGN

We evaluated 49 bladder cancer specimens for LRAT protein expression using immunohistochemistry with affinity-purified antibodies to human LRAT. LRAT mRNA expression was assessed using reverse transcription-PCR in bladder specimens from an additional 16 patients. We examined the effect of retinoic acid and ROL on LRAT mRNA expression in five human bladder cancer cell lines.

RESULTS

LRAT protein was detected throughout the nonneoplastic bladder epithelium in all of the specimens. In bladder tumors, LRAT protein expression was reduced compared with the nonneoplastic epithelium or was completely absent in 7 of 32 (21.9%) superficial tumors versus 16 of 17 (94.1%) invasive tumors (P < 0.001). All of the non-neoplastic bladder specimens tested (11 of 11) showed LRAT mRNA expression, compared with 5 of 8 (62%) superficial tumors and 0 of 5 (0%) invasive tumors (P = 0.001). Three of five human bladder cancer cell lines expressed LRAT mRNA independent of retinoid exposure, whereas in two cell lines LRAT mRNA expression was induced by retinoid treatment.

CONCLUSIONS

We report a significant reduction in LRAT expression in bladder cancer. Moreover, we demonstrate an inverse correlation of LRAT mRNA and protein expression with increasing tumor stage. These data suggest that loss of LRAT expression is associated with invasive bladder cancer.

Chemoprevention of superficial bladder cancer

Patients who have bladder cancer with superficial disease are at high risk for recurrence but low risk for progression to muscle invasive disease and are regularly monitored with cystoscopy to detect recurrent tumors. This clinical setting (high recurrence rate, excellent surveillance, and low risk of progression in stage) provides an ideal setting for secondary chemoprevention. Vitamins, difluoromethylornithine, and cyclooxygenase inhibitors have demonstrated activity in preclinical models of bladder cancer. Limited clinical data suggests that vitamins and their analogs may be useful for decreasing the rate of tumor recurrence in patients with superficial bladder cancer. Ongoing clinical trials are exploring the roles of fenretinide, difluoromethylornithine, and celecoxib in the treatment of patients with a history of superficial bladder cancer.

N-(4-hydroxyphenyl)retinamide increases ceramide and is cytotoxic to acute lymphoblastic leukemia cell lines, but not to non-malignant lymphocytes

The retinoid, N-(4-hydroxyphenyl)retinamide (4-HPR), mediates p53-independent cytotoxicity and can increase reactive oxygen species and ceramide in solid tumor cell lines. We determined changes in ceramide and cytotoxicity upon treatment with 4-HPR (3-12 microM) in six human acute lymphoblastic leukemia (ALL) cell lines: T cell (MOLT-3, MOLT-4, CEM), pre-B-cell (NALM-6, SMS-SB), and null cell (NALL-1). Exposure to 4-HPR (12 microM) for 96 h caused 4.7 (MOLT-3), 3.5 (MOLT-4), 3.9 (CEM), 2.9 (NALM-6), 4.7 (SMS-SB), AND 4.5 (NALL-1) logs of cell kill. The average 4-HPR concentration that killed 99% of cells (LC(99)) for all six lines was 4.8 microM (range: 1.5-8.9 microM). Treatment with 4-HPR (9 microM) for 24 h resulted in an 8.9 +/- 1.0-fold (range: 4.9-15.7-fold) increase of ceramide. Ceramide increase was time- and dose-dependent and abrogated by inhibitors of de novo ceramide synthesis. Concurrent inhibition of ceramide glycosylation/acylation by d,l-threo-(1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol) (PPMP) further increased ceramide levels, and synergistically increased 4-HPR cytotoxicity in four of six ALL cell lines. 4-HPR was minimally cytotoxic to peripheral blood mononuclear cells and a lymphoblastoid cell line, and increased ceramide <2-fold. Thus, 4-HPR was cytotoxic and increased ceramide in ALL cell lines, but not in non-malignant lymphoid cell types.

Apoptosis of squamous cells at different stages of carcinogenesis following 4-HPR treatment

Squamous cell carcinoma (SCC) is the end product of a multistep process characterized by a progression from normal epithelial cells through metaplastic or dysplastic intraepithelial changes that evolve into invasive cancer. Since retinamides have shown promising in vivo anti-tumoral activity, we studied effects and effector mechanisms of the synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) on squamous cells at progressing stages of tumorigenesis. To this end, an in vitro model of squamous carcinogenesis consisting of normal human keratinocytes, human papilloma virus (HPV)-immortalized keratinocytes (UP) and tumorigenic HPV-immortalized/v-Ha-ras transfected keratinocytes (UPR) was used. 4-HPR treatment affected cell growth at doses higher than 1.5 microM. Flow cytometric measurements of DNA content and annexin V revealed that cell growth decrease was mainly due to apoptosis at 4-HPR concentrations of or below 15 microM, and necrosis at higher concentrations. The effects were similar in the three cell types of the in vitro model, as well as in three SCC cell lines, suggesting that sensitivity to 4-HPR is independent of the degree of squamous cell tumorigenesis in the in vitro model. We further investigated whether mitochondrial damage was involved in the course of 4-HPR-induced apoptosis. Treatment of squamous cells with the antioxidant L-ascorbic acid inhibited apoptosis, indicating that 4-HPR increases production of free radicals. Measures of mitochondrial membrane potentials showed that 4-HPR induced membrane permeability transition (MPT), and that MPT-inhibitors were able to reduce apoptosis. This indicates that MPT is involved in apoptosis signalling by 4-HPR. Finally, we studied the role of caspases. We found that caspases 8, 9 and 3 participate in 4-HPR-mediated apoptosis of squamous cells, and that MPT is an upstream event that regulates caspase activity. Caspase 8 was activated independently of the Fas-Fas ligand pathway.

Retinoids in the prevention of bladder cancer

Superficial bladder cancer has an unpredictable natural history but in many patients it has a tendency for multiple recurrences over many years. Chemoprevention approaches are ideally tested in this type of tumor and may delay or prevent recurrences of superficial bladder cancer or prevent progression to invasive disease. Vitamin A and its derivatives, the retinoids, have been studied in detail in this disease. This article reviews the data on this subject and includes in vitro and in vivo preclinical studies as well as the clinical studies performed in the secondary prevention of this disease.

Fenretinide and cancer prevention

A characteristic feature of fenretinide is the ability to inhibit cell growth through the induction of apoptosis with mechanisms that may be both receptor-dependent and receptor-independent. Chemopreventive efficacy of fenretinide has been investigated in clinical trials targeted at different organs. Results of a phase III secondary prevention trial suggest a benefit in preventing second breast malignancies in premenopausal women with early breast cancer. A potential benefit of fenretinide with ovarian cancer and a reduction of new occurrences of leukoplakia have also been observed in clinical trials with this agent. However, no effects on DNA content of urothelial cells from bladder washings and on recurrence rate were noted in a study of patients with superficial bladder tumors. Future trials using surrogate biomarkers may aid in rapid evaluation of the chemopreventive activity of fenretinide with various targeted organs.

Assessment of DNA flow cytometry as a surrogate end point biomarker in a bladder cancer chemoprevention trial

Although conventional cytology represents the most widely performed cytometric analysis of bladder cancer cells, DNA flow cytometry has, over the past decade, been increasingly used to evaluate cell proliferation and DNA ploidy in cells from bladder washings. We have investigated whether DNA flow cytometry and conventional cytology of epithelial cells obtained from bladder washings provide reliable surrogate endpoint biomarkers in clinical chemoprevention trials. We used cytometric and clinical data from a chemoprevention trial of the synthetic retinoid Fenretinide on 99 patients with superficial bladder cancer. A total of 642 bladder washing specimens obtained from the patients at 4 month intervals was analyzed. Intra-individual agreement and correlation of flow cytometric DNA ploidy (diploid vs. aneuploid), DNA Index, Hyper-Diploid-Fraction (proportion of cells with DNA content higher than 2C), and conventional cytologic examination, as assessed by kappa statistics and Spearman's correlation test, were poor from baseline through 24 months. Moreover, no correlation was found between DNA ploidy and cytology at each time point. The same results were obtained when the analyses were stratified by treatment group. In addition, the association between the results of bladder washing (by either DNA flow cytometry or cytology) and concomitant tumor recurrence was significant only for abnormal cytology, while neither biomarker was predictive of tumor recurrence at the subsequent visit. During the time of this study only four patients progressed to muscle-invasive bladder cancer, indicating the "low-risk" features of the patient population. We conclude that DNA flow cytometry and conventional cytology on epithelial cells obtained from bladder washings do not appear to provide suitable surrogate endpoint biomarkers during the early stages of bladder carcinogenesis.

Increase of ceramide and induction of mixed apoptosis/necrosis by N-(4-hydroxyphenyl)- retinamide in neuroblastoma cell lines

BACKGROUND

The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR or fenretinide) is toxic to myeloid leukemia and cervical carcinoma cell lines, probably in part due to its ability to increase levels of reactive oxygen species (ROS). We have studied the effects of 4-HPR on neuroblastoma cell lines. Since neuroblastomas commonly relapse in bone marrow, a hypoxic tissue compartment, and many chemotherapeutic agents are antagonized by hypoxia, our purpose was to study in these cell lines several factors influencing 4-HPR-induced cytotoxicity, including induced levels of ROS, effects of physiologic hypoxia and antioxidants, levels of ceramide, and the mechanism of cell death.

METHODS

ROS generation was measured by carboxydichlorofluorescein diacetate fluoresence. Ceramide was quantified by radiolabeling and thin-layer chromatography. Immunoblotting was used to assess p53 protein levels. Apoptosis (programmed cell death) and necrosis were analyzed by nuclear morphology and internucleosomal DNA fragmentation patterns. Cytotoxicity was measured by a fluorescence-based assay employing digital imaging microscopy in the presence or absence of the pancaspase enzyme inhibitor BOC-d-fmk. Statistical tests were two-sided.

RESULTS/CONCLUSIONS

In addition to increasing ROS, 4-HPR (2.5-10 microM) statistically significantly increased the level of intracellular ceramide (up to approximately 10-fold; P<.001) in a dose-dependent manner in two neuroblastoma cell lines, one of which is highly resistant to alkylating agents and to etoposide. Cell death induced by 4-HPR was reduced but not abrogated by hypoxia in the presence or absence of an antioxidant, N-acetyl-L-cysteine. Expression of p53 protein was not affected by 4-HPR. Furthermore, the pan-caspase enzyme inhibitor BOC-d-fmk prevented apoptosis, but not necrosis, and only partially decreased cytotoxicity induced by 4-HPR, indicating that 4-HPR induced both apoptosis and necrosis in neuroblastoma cells.

IMPLICATIONS

4-HPR may form the basis for a novel, p53-independent chemotherapy that operates through increased intracellular levels of ceramide and that retains cytotoxicity under reduced oxygen conditions.

Effect of fenretinide on bone mineral density and metabolism in women with early breast cancer

Prolonged administration of natural or synthetic retinoids has been associated with significant skeletal abnormalities, including osteoporosis. We studied the effects of the synthetic retinoid fenretinide (N-4-hydroxyphenylretinamide, or 4-HPR) administered for a mean of 40 months on bone mineral density and metabolism in 66 consecutive women with early breast cancer belonging to a secondary prevention trial. The mean (+/-SD) bone mineral density at the distal and ultradistal forearm were, respectively, 0.61+/-0.08 and 0.30+/-0.05 g/cm2 in 33 treated women and 0.62+/-0.07 and 0.29+/-0.07 g/cm2 in 33 control women (p = ns for both). Also, no significant difference was observed in markers of bone formation such as bone alkaline phosphatase and osteocalcin, nor in urinary bone resorption markers such as calcium, hydroxyproline, and type I bone collagen cross-linked N-telopeptide (NTx). However, a border-line higher excretion of urinary calcium and NTx was found in the 4-HPR group after adjustment for menopausal status. We conclude that prolonged administration of 4-HPR is not associated with significant alterations of bone mineral density of the forearm. However, a trend towards an increase in bone resorption markers suggests the need for further assessment at different skeletal sites.

Induction of differentiation in human promyelocytic leukemia cell line HL60 by a new type of polyenes, falconensone A and its derivatives

Falconensones A and B are new type of yellow pigment isolated from the mycelial extract of ascomycetous fungi, Emericella falconensis or Emericella fruticulosa, whose structures are similar to retinoic acid (RA). To date, biological activities of falconensones have not been reported. Herein, we reported that falconensone A inhibited growth of HL60 human leukemia cells, when used either singly or in combination with RA. Falconensone A alone did not induce differentiation of HL60 cells. However, falconesone A enhanced the differentiation of HL60 cells induced by 10 nM RA, and its effect was synergistic. On the other hand, falconensone B, the 4'-nor-methyl derivative of falconensone A, showed much lower activity than falconensone A on the inhibition of cell growth. In addition, synthetic derivatives of falconensone A, falconensone A p-bromophenylhydrazone and falconensone A dioxime, were more potent on the inhibition of cell growth and the induction of differentiation than natural falconensones A and B. These compounds induced differentiation of HL60 cells into monocyte/macrophage-like cells, different from granulocyte-like cells induced by RA. These results suggest that falconensone A may be a new type of antiproliferative agent, and that the methyl residue at the 4' position of the cyclopentenone ring of falconensone A may be necessary for biological activity. In addition, falconensone A enhanced RA-induced differentiation of HL60 cells, while its derivatives alone showed growth inhibition and induction of differentiation of HL60 cells. Based on these results, falconensone A and its derivatives may have clinical utility in the treatment of leukemia.

Effect of dietary vitamin A or N-acetylcysteine on ethylnitrosourea-induced rat gliomas

It is our hypothesis that low grade gliomas are the glial counterparts of other precancerous lesions such as colon polyps and, therefore, suitable targets for chemoprevention. Steps in the molecular progression of gliomas have been described, indicating that an accumulation of abnormalities is required for progression to a high grade and interruption of this progression might be possible. An animal model of chemical glial carcinogenesis was used to test this hypothesis. Pregnant rats were injected intravenously with ENU (ethylnitrosourea) on the 18th day of gestation to induce gliomas in the offspring, which were randomized to receive control diet, diet supplemented with vitamin A palmitate, or diet supplemented with N-acetylcysteine. Animals exposed to ENU and receiving a control diet developed brain tumors and had a shortened life expectancy compared with rats unexposed to ENU. The animals treated with NAC showed no statistically significant delay in the time to tumor and no change in the histologic grade of the tumors when compared with animals receiving control diet, but the time to death from any cause of NAC treated animals differed significantly from untreated animals. Animals receiving high dose VA had statistically significantly prolonged time to tumor, survived significantly longer than untreated animals, but had no reduction in the total number of tumors or change in the histologic grade of their tumors. The theoretical basis of these results is likely due to the putative mechanism of action of these agents. These data indicate that glioma chemoprevention is possible and deserves further exploration.