Fifteen-year results of a randomized phase III trial of fenretinide to prevent second breast cancer

Qualitative age interactions in breast cancer studies: a mini-review

A qualitative age interaction is defined as the reversal of relative risks or rates according to age at onset, and is often evident in studies that examine the etiology, prognosis and treatment of breast cancer. For example, incidence rates (or risks) are higher for aggressive when compared with indolent breast cancers prior to age 40-50 years, after which rates are higher for indolent tumors. Nulliparity and obesity decrease breast cancer risk in younger women, but increase risk in older women. Curves depicting the annual hazard of breast cancer death are shaped differently for the early- and late-onset tumors. Clinical trials for mammography screening, fenretinide chemoprevention and neo-adjuvant chemotherapy show opposite effects in younger and older women. Finally, high-risk/early onset breast cancers are more common among African-American women than Caucasian women, and this may partly account for the racial survival disparities. Taken together, these examples imply that aging may modify breast cancer risk, prognosis and treatment. These qualitative age interactions (or effect modifications) are important because they suggest that high-risk/early-onset and low-risk/late-onset breast cancers are different diseases, derived from different carcinogenic pathways. When age interactions are suspected, breast cancer studies should be stratified by early versus late age of onset or analyzed age specifically.

Retinoid pathway and cancer therapeutics

The retinoids are a class of compounds that are structurally related to vitamin A. Retinoic acid, which is the active metabolite of retinol, regulates a wide range of biological processes including development, differentiation, proliferation, and apoptosis. Retinoids exert their effects through a variety of binding proteins including cellular retinol-binding protein (CRBP), retinol-binding proteins (RBP), cellular retinoic acid-binding protein (CRABP), and nuclear receptors i.e. retinoic acid receptor (RAR) and retinoid x receptor (RXR). Because of the pleiotropic effects of retinoids, understanding the function of these binding proteins and nuclear receptors assists us in developing compounds that have specific effects. This review summarizes our current understanding of how retinoids are processed and act with an emphasis on the application of retinoids in cancer treatment and prevention.

4-oxo-N-(4-hydroxyphenyl)retinamide: two independent ways to kill cancer cells

Background

The retinoid 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR) is a polar metabolite of fenretinide (4-HPR) very effective in killing cancer cells of different histotypes, able to inhibit 4-HPR-resistant cell growth and to act synergistically in combination with the parent drug. Unlike 4-HPR and other retinoids, 4-oxo-4-HPR inhibits tubulin polymerization, leading to multipolar spindle formation and mitotic arrest. Here we investigated whether 4-oxo-4-HPR, like 4-HPR, triggered cell death also via reactive oxygen species (ROS) generation and whether its antimicrotubule activity was related to a ROS-dependent mechanism in ovarian (A2780), breast (T47D), cervical (HeLa) and neuroblastoma (SK-N-BE) cancer cell lines.

Methodology/Principal Findings

We provided evidence that 4-oxo-4-HPR, besides acting as an antimicrotubule agent, induced apoptosis through a signaling cascade starting from ROS generation and involving endoplasmic reticulum (ER) stress response, Jun N-terminal Kinase (JNK) activation, and upregulation of the proapoptotic PLAcental Bone morphogenetic protein (PLAB). Through time-course analysis and inhibition of the ROS-related signaling pathway (upstream by vitamin C and downstream by PLAB silencing), we demonstrated that the antimitotic activity of 4-oxo-4-HPR was independent from the oxidative stress induced by the retinoid. In fact, ROS generation occurred earlier than mitotic arrest (within 30 minutes and 2 hours, respectively) and abrogation of the ROS-related signaling pathway did not prevent the 4-oxo-4-HPR-induced mitotic arrest.

Conclusions/Significance

These data indicate that 4-oxo-4-HPR anticancer activity is due to at least two independent mechanisms and provide an explanation of the ability of 4-oxo-4-HPR to be more potent than the parent drug and to be effective also in 4-HPR-resistant cell lines. In addition, the double mechanism of action could allow 4-oxo-4-HPR to efficiently target tumour and to eventually counteract the development of drug resistance.

Anti-tumor effects of retinoids combined with trastuzumab or tamoxifen in breast cancer cells: induction of apoptosis by retinoid/trastuzumab combinations

INTRODUCTION

HER2 and estrogen receptor (ER) are important in breast cancer and are therapeutic targets of trastuzumab (Herceptin) and tamoxifen, respectively. Retinoids inhibit breast cancer growth, and modulate signaling by HER2 and ER. We hypothesized that treatment with retinoids and simultaneous targeting of HER2 and/or ER may have enhanced anti-tumor effects.

METHODS

The effects of retinoids combined with trastuzumab or tamoxifen were examined in two human breast cancer cell lines in culture, BT474 and SKBR3. Assays of proliferation, apoptosis, differentiation, cell cycle distribution, and receptor signaling were performed.

RESULTS

In HER2-overexpressing/ER-positive BT474 cells, combining all-trans retinoic acid (atRA) with tamoxifen or trastuzumab synergistically inhibited cell growth, and altered cell differentiation and cell cycle. Only atRA/trastuzumab-containing combinations induced apoptosis. BT474 and HER2-overexpressing/ER-negative SKBR3 cells were treated with a panel of retinoids (atRA, 9-cis-retinoic acid, 13-cis-retinoic acid, or N-(4-hydroxyphenyl) retinamide (fenretinide) (4-HPR)) combined with trastuzumab. In BT474 cells, none of the single agents except 4-HPR induced apoptosis, but again combinations of each retinoid with trastuzumab did induce apoptosis. In contrast, the single retinoid agents did cause apoptosis in SKBR3 cells; this was only modestly enhanced by addition of trastuzumab. The retinoid drug combinations altered signaling by HER2 and ER. Retinoids were inactive in trastuzumab-resistant BT474 cells.

CONCLUSIONS

Combining retinoids with trastuzumab maximally inhibits cell growth and induces apoptosis in trastuzumab-sensitive cells. Treatment with such combinations may have benefit for breast cancer patients.

Brg-1 mediates the constitutive and fenretinide-induced expression of SPARC in mammary carcinoma cells via its interaction with transcription factor Sp1

Background

Secreted protein, acidic and rich in cysteine (SPARC) is a matricellular protein that mediates cell-matrix interactions. It has been shown, depending on the type of cancer, to possess either pro- or anti-tumorigenic properties. The transcriptional regulation of the SPARC gene expression has not been fully elucidated and the effects of anti-cancer drugs on this process have not been explored.

Results

In the present study, we demonstrated that chromatin remodeling factor Brg-1 is recruited to the proximal SPARC promoter region (-130/-56) through an interaction with transcription factor Sp1. We identified Brg-1 as a critical regulator for the constitutive expression levels of SPARC mRNA and protein in mammary carcinoma cell lines and for SPARC secretion into culture media. Furthermore, we found that Brg-1 cooperates with Sp1 to enhance SPARC promoter activity. Interestingly, fenretinide [N-4(hydroxyphenyl) retinamide, 4-HPR], a synthetic retinoid with anti-cancer properties, was found to up-regulate the transcription, expression and secretion of SPARC via induction of the Brg-1 in a dose-dependent manner. Finally, our results demonstrated that fenretinide-induced expression of SPARC contributes significantly to a decreased invasion of mammary carcinoma cells.

Conclusions

Overall, our results reveal a novel cooperative role of Brg-1 and Sp1 in mediating the constitutive and fenretinide-induced expression of SPARC, and provide new insights for the understanding of the anti-cancer effects of fenretinide.

Relationship among pharmacokinetics and pharmacodynamics of fenretinide and plasma retinol reduction in neuroblastoma patients

PURPOSE

Fenretinide (4-HPR), a synthetic retinoid currently used in clinic for cancer therapy and prevention, markedly lowers plasma retinol levels, an effect associated with nyctalopia. Our aim was to investigate the relationship between 4-HPR pharmacokinetics, plasma retinol reduction and incidence of nyctalopia.

PATIENTS AND METHODS

Children with neuroblastoma, participating in a phase I trial, were treated with oral 4-HPR, once a day for 28-day courses followed by a 7-day drug interruption, with escalating dose levels from 100 to 4,000 mg/m(2) per day. Blood samples were collected at baseline and up to 48 h after the 1st (50 patients) and 28th (41 patients) administration, and the plasma concentrations of 4-HPR and retinol were measured by HPLC.

RESULTS

After the first administration, nadir retinol concentrations were reached at 16-20 h post-dosing; the extent of retinol reduction was related to 4-HPR dose and plasma concentrations as well as to pretreatment retinol concentrations. After repeated treatments, nadir retinol concentrations (10-20% of baseline values) were maintained during the 24 h dosing interval and were similar at all doses; the extent of retinol reduction was significantly (r = 0.97, P < 0.0001) related to pretreatment retinol concentrations. After a single dose, the relationship between 4-HPR pharmacokinetics and pharmacodynamics indicated a counterclockwise hysteresis suggesting the presence of an effect compartment. At steady state, the hysteresis collapsed suggesting that the 4-HPR concentrations in plasma and in the effect compartments were in equilibrium. Nyctalopia was not related to the administered dose, but was significantly associated (P = 0.05) with lower nadir retinol concentrations (0.11 +/- 0.012 vs. 0.17 +/- 0.015 microM).

CONCLUSIONS

During 4-HPR chronic treatment, plasma retinol reduction is not proportional to the dose. Plasma retinol levels of 0.11 microM could be considered as a safety biomarker in children with neuroblastoma. Finally, since initial retinol levels strongly predict the extent of retinol reduction, retinol decrease could be used to monitor 4-HPR compliance.

Antimitotic effect of the retinoid 4-oxo-fenretinide through inhibition of tubulin polymerization: a novel mechanism of retinoid growth-inhibitory activity

The retinoid 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR), a metabolite of fenretinide (4-HPR) present in plasma of 4-HPR-treated patients, is very effective in inducing growth inhibition and apoptosis in several cancer cell lines. 4-Oxo-4-HPR and 4-HPR have different mechanisms of action because 4-oxo-4-HPR, unlike 4-HPR, causes marked cell accumulation in G2-M phase. Here, we investigated the molecular events involving 4-oxo-4-HPR-induced cell cycle perturbation in ovarian (A2780 and IGROV-1) and breast (T47D, estrogen receptor+ and BT-20, estrogen receptor-) cancer cells. 4-Oxo-4-HPR induced a delay of mitosis (with mitotic index increasing 5- to 6-fold in all cell lines) without progression beyond the anaphase, as shown by cyclin B1 expression. 4-Oxo-4-HPR induced multipolar spindle formation and phosphorylation of BUBR1, resulting in activation of the spindle checkpoint. Multipolar spindles were not due to impairment of pole-focusing process, loss of centrosome integrity, or modulation of the expression levels of molecules associated with spindle aberrations (Kif 1C, Kif 2A, Eg5, Tara, tankyrase-1, centractin, and TOGp). We show here that 4-oxo-4-HPR targets microtubules because, in treated cells, it interfered with the reassembly of cold-depolymerized spindle microtubules and decreased the polymerized tubulin fraction. In cell-free assays, 4-oxo-4-HPR inhibited tubulin polymerization (50% inhibition of microtubule assembly at 5.9 micromol/L), suggesting a direct molecular interaction with tubulin. In conclusion, by showing that 4-oxo-4-HPR causes mitotic arrest through antimicrotubule activities, we delineate a new molecular mechanism for a retinoid.

A phase II study of fenretinide in patients with hormone refractory prostate cancer: a trial of the Cancer Therapeutics Research Group

PURPOSE

Fenretinide is a synthetic retinoid with activity in prostate cancer and other cell lines. The aim of this study was to assess the efficacy and tolerability of fenretinide in chemotherapy-naïve men with hormone refractory prostate cancer.

METHODS

Eligibility criteria included hormone refractory prostate cancer with a rising PSA at least 6 weeks after peripheral anti-androgen withdrawal, ECOG performance status (PS) 0-1, and no prior chemotherapy. Fenretinide was administered orally at 900 mg m(-2) twice daily for 7 of every 21 days. PSA was measured before each cycle. The primary endpoint was a > or =50% reduction in PSA maintained for at least 3 weeks; secondary endpoints included duration of PSA response, time to treatment failure (TTF: treatment stopped for progression or toxicity) and adverse events (AE).

RESULTS

Twenty seven pts were recruited from 7 centres over 27 months. Median age was 74 (range 49-86), median baseline PSA was 129 (range 19-1,000), and 70% had a PS of 0. The median number of cycles received was 2 (range 0-11) and 20 pts completed at least 1 cycle. One pt (4%) achieved a 50% reduction in PSA lasting 39 days and 15 pts (56%) had not progressed within 6 weeks of starting fenretinide. The median TTF was 54 days (IQR 19-73): 22 (81%) failed with tumour progression, 3 (11%) failed with toxicity and 2 (7%) never commenced the drug. Grade 3 rash occurred in 1 patient, all other AE were grade 1 or 2. The most common AE were nausea (40%), hot flushes (36%), constipation (32%) and nyctalopia (32%).

CONCLUSION

High-dose fenretinide had limited anti-tumour activity in patients with advanced hormone refractory prostate cancer: further evaluation in this setting is not warranted.

Converting redox signaling to apoptotic activities by stress-responsive regulators HSF1 and NRF2 in fenretinide treated cancer cells

BACKGROUND

Pharmacological intervention of redox balance in cancer cells often results in oxidative stress-mediated apoptosis, attracting much attention for the development of a new generation of targeted therapy in cancer. However, little is known about mechanisms underlying the conversion from oxidative signaling to downstream activities leading cells to death.

METHODOLOGY/PRINCIPAL FINDINGS

We here report a systematic detection of transcriptome changes in response to oxidative signals generated in leukemia cells upon fenretinide treatment, implicating the occurrence of numerous stress-responsive events during the fenretinide induced apoptosis, such as redox response, endoplasmic reticulum stress/unfolded protein response, translational repression and proteasome activation. Moreover, the configuration of these relevant events is primarily orchestrated by stress responsive transcription factors, as typically highlighted by NF-E2-related factor-2 (NRF2) and heat shock factor 1 (HSF1). Several lines of evidence suggest that the coordinated regulation of these transcription factors and thus their downstream genes are involved in converting oxidative signaling into downstream stress-responsive events regulating pro-apoptotic and apoptotic activities at the temporal and spatial levels, typifying oxidative stress-mediated programmed death rather than survival in cancer cells.

CONCLUSIONS/SIGNIFICANCE

This study provides a roadmap for understanding oxidative stress-mediated apoptosis in cancer cells, which may be further developed into more sophisticated therapeutic protocols, as implicated by synergistic induction of cell apoptosis using proteasome inhibitors with fenretinide.

Breast cancer chemoprevention - a vision not yet realized

Despite recent advances in the surgical and medical treatment of breast cancer, the number of patients dying from the disease is still high. In addition to improvements of early diagnosis and treatment, the overall mortality of breast cancer could be reduced by means of preventive intervention in both women with particularly normal and with high risk. Preventing the potentially deadly disease is presumably more effective than treatment, for life quality issues as well as for the economic perspective. Chemoprevention though is still a research field with results from large prevention trials being discussed controversially. For women with a defined increased risk for breast cancer, tamoxifen may be a choice for chemoprevention, balancing carefully benefits against risks. With promising results in adjuvant settings, aromatase inhibitors may deliver better prevention treatment options in the future, nevertheless, more research is needed to reliably predict risk on an individual basis in the future.

Randomized double-blind 2 x 2 trial of low-dose tamoxifen and fenretinide for breast cancer prevention in high-risk premenopausal women

PURPOSE

Tamoxifen and fenretinide are active in reducing premenopausal breast cancer risk and work synergistically in preclinical models. The authors assessed their combination in a two-by-two biomarker trial.

PATIENTS AND METHODS

A total of 235 premenopausal women with pT1mic/pT1a breast cancer (n = 21), or intraepithelial neoplasia (IEN, n = 160), or 5-year Gail risk > or = 1.3% (n = 54) were randomly allocated to either tamoxifen 5 mg/d, fenretinide 200 mg/d, their combination, or placebo. We report data for plasma insulin-like growth factor I (IGF-I), mammographic density, uterine effects, and breast neoplastic events after 5.5 years.

RESULTS

During the 2-year intervention, tamoxifen significantly lowered IGF-I and mammographic density by 12% and 20%, respectively, fenretinide by 4% and 10% (not significantly), their combination by 20% and 22%, with no evidence for a synergistic interaction. Tamoxifen increased endometrial thickness principally in women becoming postmenopausal, whereas fenretinide decreased endometrial thickness significantly. The annual rate of breast neoplasms (n = 48) was 3.5% +/- 1.0%, 2.1% +/- 0.8%, 4.7% +/- 1.3%, and 5.2% +/- 1.3% in the tamoxifen, fenretinide, combination, and placebo arms, respectively, with hazard ratios (HRs) of 0.70 (95% CI, 0.32 to 1.52), 0.38 (95% CI, 0.15 to 0.90), and 0.96 (95% CI, 0.46 to 1.99) relative to placebo (tamoxifen x fenretinide adverse interaction P = .03). There was no clear association with tumor receptor type. Baseline IGF-I and mammographic density did not predict breast neoplastic events, nor did change in mammographic density.

CONCLUSION

Despite favorable effects on plasma IGF-I levels and mammographic density, the combination of low-dose tamoxifen plus fenretinide did not reduce breast neoplastic events compared to placebo, whereas both single agents, particularly fenretinide, showed numerical reduction in annual odds of breast neoplasms. Further follow-up is indicated.

N-Myc down regulation induced differentiation, early cell cycle exit, and apoptosis in human malignant neuroblastoma cells having wild type or mutant p53

Neuroblastomas, which mostly occur in children, are aggressive metastatic tumors of the sympathetic nervous system. The failure of the previous therapeutic regimens to target multiple components of N-Myc pathway resulted in poor prognosis. The present study investigated the efficacy of the combination of N-(4-hydroxyphenyl) retinamide (4-HPR, 0.5 microM) and genistein (GST, 25 microM) to control the growth of human neuroblastoma cells (SH-SY5Y and SK-N-BE2) harboring divergent molecular attributes. Combination of 4-HPR and GST down regulated N-Myc, Notch-1, and Id2 to induce neuronal differentiation. Transition to neuronal phenotype was accompanied by increase in expression of e-cadherin. Induction of neuronal differentiation was associated with decreased expression of hTERT, PCNA, survivin, and fibronectin. This is the first report that combination of 4-HPR and GST mediated reactivation of multiple tumor suppressors (p53, p21, Rb, and PTEN) for early cell cycle exit (due to G1/S phase arrest) in neuroblastoma cells. Reactivation of tumor suppressor(s) repressed N-Myc driven growth factor mediated angiogenic and invasive pathways (VEGF, b-FGF, MMP-2, and MMP-9) in neuroblastoma. Repression of angiogenic factors led to the blockade of components of mitogenic pathways [phospho-Akt (Thr 308), p65 NF-kappaB, and p42/44 Erk 1/2]. Taken together, the combination of 4-HPR and GST effectively blocked survival, mitogenic, and angiogenic pathways and activated proteases for apoptosis in neuroblastoma cells. These results suggested that combination of 4-HPR and GST could be effective for controlling the growth of heterogeneous human neuroblastoma cell populations.

American society of clinical oncology clinical practice guideline update on the use of pharmacologic interventions including tamoxifen, raloxifene, and aromatase inhibition for breast cancer risk reduction

PURPOSE To update the 2002 American Society of Clinical Oncology guideline on pharmacologic interventions for breast cancer (BC) risk reduction. METHODS A literature search identified relevant randomized trials published since 2002. Primary outcome of interest was BC incidence (invasive and noninvasive). Secondary outcomes included BC mortality, adverse events, and net health benefits. An expert panel reviewed the literature and developed updated consensus guidelines. Results Seventeen articles met inclusion criteria. In premenopausal women, tamoxifen for 5 years reduces the risk of BC for at least 10 years, particularly estrogen receptor (ER) -positive invasive tumors. Women < or = 50 years of age experience fewer serious side effects. Vascular and vasomotor events do not persist post-treatment across all ages. In postmenopausal women, raloxifene and tamoxifen reduce the risk of ER-positive invasive BC with equal efficacy. Raloxifene is associated with a lower risk of thromboembolic disease, benign uterine conditions, and cataracts than tamoxifen in postmenopausal women. No evidence exists establishing whether a reduction in BC risk from either agent translates into reduced BC mortality. Recommendations In women at increased risk for BC, tamoxifen (20 mg/d for 5 years) may be offered to reduce the risk of invasive ER-positive BC, with benefits for at least 10 years. In postmenopausal women, raloxifene (60 mg/d for 5 years) may also be considered. Use of aromatase inhibitors, fenretinide, or other selective estrogen receptor modulators to lower BC risk is not recommended outside of a clinical trial. Discussion of risks and benefits of preventive agents by health providers is critical to patient decision making.

PLAB induction in fenretinide-induced apoptosis of ovarian cancer cells occurs via a ROS-dependent mechanism involving ER stress and JNK activation

Fenretinide [N-(4-hydroxyphenyl)-retinamide (4HPR)] is a synthetic retinoid with antitumor activity that induces apoptosis in various types of cancer cell. We showed previously that 4HPR upregulates the proapoptotic gene placental bone morphogenetic protein (PLAB), which is a mediator of 4HPR-induced apoptosis in ovarian cancer cells. Here, we investigated the signaling cascade involving PLAB that mediates the apoptotic effect. In 4HPR-sensitive ovarian cancer cells, 4HPR-induced reactive oxygen species (ROS) are involved in PLAB upregulation and apoptosis, both events abrogated by the antioxidants vitamin C and butylated hydroxyanisole. We analyzed the expression and activation of endoplasmic reticulum (ER) stress-associated molecules and show that 4HPR-induced ER stress is a consequence of ROS generation. Salubrinal, an ER stress inhibitor, abrogated 4HPR-induced PLAB upregulation and protected the cells from apoptosis. Downstream of ROS generation and ER stress, 4HPR activated c-Jun N-terminal kinase (JNK), which was inhibited by vitamin C and salubrinal. The JNK inhibitor SP600125 reduced 4HPR-induced PLAB upregulation, by decreasing PLAB mRNA half-life, and protected the cells from apoptosis. These data indicate that 4HPR-induced PLAB upregulation occurs downstream of a signaling cascade involving ROS generation, ER stress induction and JNK activation and that these steps are mediators of 4HPR-induced apoptosis.

N-(4-Hydroxyphenyl) retinamide potentiated paclitaxel for cell cycle arrest and apoptosis in glioblastoma C6 and RG2 cells

Glioblastoma grows aggressively due to its ability to maintain abnormally high potentials for cell proliferation. The present study examines the synergistic actions of N-(4-hydroxyphenyl) retinamide (4-HPR) and paclitaxel (PTX) to control the growth of rat glioblastoma C6 and RG2 cell lines. 4-HPR induced astrocytic differentiation that was accompanied by increased expression of the tight junction protein e-cadherin and sustained down regulation of Id2 (member of inhibitor of differentiation family), catalytic subunit of rat telomerase reverse transcriptase (rTERT), and proliferating cell nuclear antigen (PCNA). Flow cytometric analysis showed that the microtubule stabilizer PTX caused cell cycle deregulation due to G2/M arrest. This in turn could alter the fate of kinetochore-spindle tube dynamics thereby halting cell cycle progression. An interesting observation was the induction of G1/S arrest by a combination of 4-HPR and PTX, altering the G2/M arrest induced by PTX alone. This was further ratified by the upregulation of tumor suppressor protein retinoblastoma, which repressed the expression of the key signaling moieties to induce G1/S arrest. Collectively, the combination of 4-HPR and PTX diminished the survival factors (e.g., rTERT, PCNA, and Bcl-2) to make glioblastoma cells highly prone to apoptosis with activation of cysteine proteases (e.g., calpain, cathepsins, caspase-8, caspase-3). Hence, the combination of 4-HPR and PTX can be considered as an effective therapeutic strategy for controlling the growth of heterogeneous glioblastoma cell populations.

Retinoids and breast cancer prevention

Preclinical models suggest that retinoids inhibit mammary carcinogenesis. Induction of apoptosis is a unique feature of fenretinide, the most studied retinoid in clinical trials of breast cancer chemoprevention due to its selective accumulation in breast tissue and its favorable toxicological profile. In a phase III breast cancer prevention trial, fenretinide showed a very strong trend of reduction of incidence of second breast malignancies in premenopausal women, which was confirmed by the 15-year follow-up. Interestingly, ovarian cancer incidence appeared reduced during treatment in the same trial. This warrants further research on fenretinide mechanisms of action and potential efficacy and provides the rationale for a phase III primary prevention trial in young women at high risk for breast cancer.

FOXA1 in breast cancer

Breast cancer is a heterogeneous disease and classification is important for clinical management. At least five subtypes can be identified based on unique gene expression patterns; this subtype classification is distinct from the histopathological classification. The transcription factor network(s) required for the specific gene expression signature in each of these subtypes is currently being elucidated. The transcription factor network composed of the oestrogen (estrogen) receptor alpha (ERalpha), FOXA1 and GATA3 may control the gene expression pattern in luminal subtype A breast cancers. Breast cancers that are dependent on this network correspond to well-differentiated and hormone-therapy-responsive tumours with good prognosis. In this review, we discuss the interplay between these transcription factors with a particular emphasis on FOXA1 structure and function, and its ability to control ERalpha function. Additionally, we discuss modulators of FOXA1 function, ERalpha-FOXA1-GATA3 downstream targets, and potential therapeutic agents that may increase differentiation through FOXA1.

Longitudinal biological exposure to carotenoids is associated with breast cancer-free survival in the Women's Healthy Eating and Living Study

In some cohort studies, a high-vegetable diet has been associated with greater likelihood of recurrence-free survival in women diagnosed with breast cancer. Carotenoids are obtained primarily from vegetables and fruit and they exhibit biological activities that may specifically reduce the progression of mammary carcinogenesis. The present analysis examines the relationship between plasma carotenoids at enrollment and 1, 2 or 3, 4, and 6 years and breast cancer-free survival in the Women's Healthy Eating and Living Study participants (N = 3,043), who had been diagnosed with early-stage breast cancer. The primary end point was time to a second breast cancer event (a recurrence or new primary breast cancer). An average carotenoid concentration over time was estimated for each participant as the average area under the plasma carotenoid curve formed by the plasma carotenoid concentrations at scheduled clinic visits. Multiple regression Cox proportional hazards analysis with adjustment for prognostic and other factors was used to examine the association between carotenoids and breast cancer-free survival. A total of 508 (16.7%) breast cancer events occurred over a median 7.12 years follow-up. Compared with the lowest tertile, the hazard ratio for the medium/high plasma carotenoid tertiles was 0.67 (95% confidence interval, 0.54-0.83) after adjustment. The interaction between the study group and tertile of average carotenoid concentration over time was not significant (P = 0.23). Higher biological exposure to carotenoids, when assessed over the time frame of the study, was associated with greater likelihood of breast cancer-free survival regardless of study group assignment.

Prevention of ER-negative breast cancer

The successful demonstration that the selective estrogen receptor modulators (SERMs) tamoxifen and raloxifene reduce the risk of breast cancer has stimulated great interest in using drugs to prevent breast cancer in high-risk women. In addition, recent results from breast cancer treatment trials suggest that aromatase inhibitors may be even more effective at preventing breast cancer than are SERMs. However, while SERMs and aromatase inhibitors do prevent the development of many estrogen-receptor (ER)-positive breast cancers, these drugs do not prevent the development of ER-negative breast cancer. Thus, there is an urgent need to identify agents that can prevent ER-negative breast cancer. We have studied the cancer preventative activity of several classes of drugs for their ability to prevent ER-negative breast cancer in preclinical models. Results from these studies demonstrate that rexinoids (analogs of retinoids that bind and activate RXR receptors), tyrosine kinase inhibitors (such as EGFR inhibitors and dual kinase inhibitors that block EGFR and HER2/neu signaling), and cyclo-oxygenase 2 (COX-2) inhibitors all prevent ER-negative breast cancer in transgenic mice that develop ER-negative breast cancer. Other promising agents now under investigation include vitamin D and vitamin D analogs, drugs that activate PPAR-gamma nuclear receptors, and statins. Many of these agents are now being tested in early phase cancer prevention clinical trials to determine whether they will show activity in breast tissue and whether they are safe for use in high-risk women without breast cancer. The current status of these studies will be reviewed. It is anticipated that in the future, drugs that effectively prevent ER-negative breast cancer will be used in combination with hormonal agents such SERMs or aromatase inhibitors to prevent all forms of breast cancer.

Effect of fenretinide and low-dose tamoxifen on insulin sensitivity in premenopausal women at high risk for breast cancer

The prevalence of metabolic syndrome is increasing along with breast cancer incidence worldwide. Because fenretinide improves insulin action and glucose tolerance in insulin-resistant obese mice and because tamoxifen has shown to regulate several markers involved in metabolic syndrome, we sought to investigate the effect of fenretinide or tamoxifen at low dose on features linked to insulin resistance in premenopausal women at risk for breast cancer. We randomized 235 women to low-dose tamoxifen (5 mg/daily), fenretinide (200 mg/daily), or their combination or placebo for 2 years. We used the homeostasis model assessment (HOMA; fasting insulin x glucose/22.5) to estimate insulin sensitivity. Women were considered to improve insulin sensitivity when they shifted from a HOMA >/=2.8 to <2.8. There was no effect of fenretinide or tamoxifen on HOMA overall, but overweight women (body mass index, >or=25 kg/m(2)) had a 7-fold greater probability to normalize HOMA after 2 years of fenretinide treatment [odds ratio (OR), 7.0; 95% confidence interval (95% CI), 1.2-40.5], with 25% of women improving their insulin sensitivity, whereas tamoxifen decreased insulin sensitivity by almost 7 times compared with subjects not taking tamoxifen (OR, 0.15; 95% CI, 0.03-0.88). In this group only, 5% improved their insulin sensitivity. Interestingly, women with intraepithelial or microinvasive neoplasia had higher HOMA (3.0) than unaffected subjects (2.8; P = 0.07). Fenretinide can positively balance the metabolic profile in overweight premenopausal women and this may favorably affect breast cancer risk. Furthermore, features of the metabolic syndrome should be taken into consideration before proposing tamoxifen for breast cancer prevention. The clinical implications of these results require further investigations.

Involvement of Rac in fenretinide-induced apoptosis

The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) has shown potential as a chemopreventive and therapeutic agent. The ability of 4HPR to enhance production of reactive oxygen species (ROS) leading to apoptosis has been suggested as a possible mechanism underlying these effects. We explored the possibility that ROS induction by 4HPR involves the small GTPase Ras-related C3 botulinum toxin substrate (Rac), a regulatory subunit of the NADPH oxidase complex. Rac was activated in human head and neck squamous cell carcinoma (HNSCC) cells as early as 5 minutes following 4HPR exposure. Moreover, inhibition of Rac activity or silencing of its expression by RNA interference decreased ROS generation in human head and neck, lung, and cervical cancer cells and murine melanoma cells. In HNSCC UMSCC-22B cells, this decrease correlated with reduction in apoptosis induction by 4HPR. Expression of a constitutive active mutant Rac increased basal and 4HPR-induced ROS generation and poly(ADP-ribose) polymerase cleavage. In addition, the metastatic DM14 cells exhibited higher Rac activation following 4HPR treatment compared with the primary Tu167-C2 cells. Furthermore, the metastatic cancer cells tested exhibited higher ROS generation and growth inhibition due to 4HPR exposure compared with their primary cancer cell counterparts. These findings show a preferential susceptibility of metastatic cells to the proapoptotic retinoid 4HPR through Rac activation and support the use of ROS-inducing agents such as 4HPR against metastatic cancer cells.

N-(4-hydroxyphenyl)all-trans-retinamide (4-HPR) high dose effect on DMBA-induced hamster oral cancer: a histomorphometric evaluation

N-(4-hydroxyphenyl)all-trans-retinamide (4-HPR) has shown cancer chemoprevention activity in many experimental and clinical situations. The purpose of this research is to evaluate the in vivo efficacy of 4-HPR in preventing 7,12-dimethylbenz(alpha)antracene (DMBA)-induced oral carcinogenesis and to study histomorphometric changes. 76 Syrian hamsters were separated into four groups: group 1, untreated controls (16 animals); group 2, 4-HPR controls (16 animals); group 3, DMBA-treated animals (28); group 4, animals treated with DMBA and 4-HPR (16). Hamsters were painted with a 0.5% solution of DMBA three times a week in their left buccal pouch. A diet of 2 mmol of 4-HPR/kg was administered. At week 9, 50% of the animals were killed; the remainder were killed at week 12. Pathology and histomorphometric tests were performed on epithelium, dysplasia and carcinomas. At week 9, 5 carcinomas were found in group 3, and 13 in group 4. Cancers in group 4 were more numerous, endophytic and infiltrating than those in group 3 animals. At week 12, 16 carcinomas were detected in group 3 animals, but group 4 developed more carcinomas per animal than group 3. Using these experimental concentrations, 4-HPR cannot express its best chemopreventive effect.

Role of Sox-9, ER81 and VE-cadherin in retinoic acid-mediated trans-differentiation of breast cancer cells

Many aspects of development, tumor growth and metastasis depend upon the provision of an adequate vasculature. This can be a result of regulated angiogenesis, recruitment of circulating endothelial progenitors and/or vascular trans-differentiation. The present study demonstrates that treatment of SKBR-3 breast cancer cells with retinoic acid (RA), an important regulator of embryogenesis, cancer and other diseases, stimulates the formation of networks in Matrigel. RA-treatment of SKBR-3 cells co-cultured with human umbilical vein endothelial cells resulted in the formation of mixed structures. RA induces expression of many endothelial genes including vascular endothelial (VE) cadherin. VE-cadherin was also induced by RA in a number of other breast cancer cells. We show that RA-induced VE-cadherin is responsible for the RA-induced morphological changes. RA rapidly induced the expression of Sox-9 and ER81, which in turn form a complex on the VE-cadherin promoter and are required to mediate the transcriptional regulation of VE-cadherin by RA. These data indicate that RA may promote the expression of endothelial genes resulting in endothelial-like differentiation, or provide a mechanism whereby circulating endothelial progenitor cells could be incorporated into a growing organ or tumor.

Chemoprevention of breast cancer

Breast cancer remains the second leading cause of malignancy-related death in women in the USA, regardless of advances in novel therapeutic agents. High priority should be given to research aimed at the study of pharmacological and natural compounds that could potentially prevent the development of breast cancer in susceptible patients. Tamoxifen has been shown to reduce the incidence of estrogen receptor-positive invasive breast cancer in women with a high risk of developing this condition by nearly 50%, and studies in osteoporosis have revealed a similar protective effect of raloxifene in postmenopausal women. The aromatase inhibitors are superior to tamoxifen in reducing the recurrence of breast cancer in postmenopausal women; large clinical trials are currently evaluating the chemopreventive effect of these agents. The list of agents with the potential for chemoprevention in breast cancer is extensive and continues to expand. There is an immense need to develop drugs that will decrease the incidence of estrogen receptor-negative breast cancer in women at high risk of developing the disease. Herein, we review the most important chemopreventive agents in breast cancer and clinical trials that have evaluated their efficacy.

Biodiversity of sphingoid bases ("sphingosines") and related amino alcohols

"Sphingosin" was first described by J. L. W. Thudichum in 1884 and structurally characterized as 2S,3R,4E-2-aminooctadec-4-ene-1,3-diol in 1947 by Herb Carter, who also proposed the designation of "lipides derived from sphingosine as sphingolipides." This category of amino alcohols is now known to encompass hundreds of compounds that are referred to as sphingoid bases and sphingoid base-like compounds, which vary in chain length, number, position, and stereochemistry of double bonds, hydroxyl groups, and other functionalities. Some have especially intriguing features, such as the tail-to-tail combination of two sphingoid bases in the alpha,omega-sphingoids produced by sponges. Most of these compounds participate in cell structure and regulation, and some (such as the fumonisins) disrupt normal sphingolipid metabolism and cause plant and animal disease. Many of the naturally occurring and synthetic sphingoid bases are cytotoxic for cancer cells and pathogenic microorganisms or have other potentially useful bioactivities; hence, they offer promise as pharmaceutical leads. This thematic review gives an overview of the biodiversity of the backbones of sphingolipids and the broader field of naturally occurring and synthetic sphingoid base-like compounds.

N-(4-Hydroxyphenyl)retinamide induced differentiation with repression of telomerase and cell cycle to increase interferon-gamma sensitivity for apoptosis in human glioblastoma cells

Glioblastoma is the most malignant and prevalent brain tumor in humans. It is composed of heterogenic abnormal astroglial cells that avoid differentiation, maintain proliferation, and hardly commit apoptosis. N-(4-Hydroxyphenyl)retinamide (4-HPR) induced astrocytic differentiation and increased sensitivity to interferon-gamma (IFN-gamma) for apoptosis in human glioblastoma A172, LN18, and SNB19 cells. Combination of 4-HPR and IFN-gamma significantly inhibited human telomerase reverse transcriptase (hTERT), cyclin dependent kinase 2 (CDK2), and survivin to up-regulate caspase-8, caspase-9, and caspase-3 for increasing apoptosis in all glioblastoma cell lines. Hence, combination of 4-HPR and IFN-gamma should be considered for controlling growth of different human glioblastoma cells.

The rexinoid, bexarotene, prevents the development of premalignant lesions in MMTV-erbB2 mice

Retinoids, vitamin A analogues that bind to retinoic acid receptor (RAR) or retinoid X receptor (RXR), play important roles in regulating cell proliferation, apoptosis, and differentiation. Recently, RXR-selective ligands, also referred to as rexinoids, have been investigated as potential chemopreventive agents for breast cancer. Our previous studies demonstrated that the rexinoid bexarotene significantly prevented ER-negative mammary tumourigenesis with less toxicity than naturally occurring retinoids in animal models. To determine whether bexarotene prevents cancer at the early stages during the multistage process of mammary carcinogenesis, we treated MMTV-erbB2 mice with bexarotene for 2 or 4 months. The development of preinvasive mammary lesions such as hyperplasias and carcinoma-in-situ was significantly inhibited. This inhibition was associated with reduced proliferation, but no induction of apoptosis. We also examined the regulation of a number of rexinoid-modulated genes including critical growth and cell cycle regulating genes using breast cell lines and mammary gland samples from mice treated with rexinoids. We showed that two of these genes (DHRS3 and DEC2) were modulated by bexarotene both in vitro and in vivo. Identification of these rexinoid-modulated genes will help us understand the mechanism by which rexinoid prevents cancer. Such rexinoid-regulated genes also represent potential biomarkers to assess the response of rexinoid treatment in clinical trials.

Pharmacokinetics of oral fenretinide in neuroblastoma patients: indications for optimal dose and dosing schedule also with respect to the active metabolite 4-oxo-fenretinide

PURPOSE

Pharmacokinetic data on fenretinide (4-HPR) are scant, thus limiting the rational use of the drug. We investigated the pharmacokinetics of 4-HPR and its active metabolite 4-oxo-fenretinide (4-oxo-4-HPR).

EXPERIMENTAL DESIGN

Pharmacokinetics were assessed in 18 children (3 for each dose) with neuroblastoma who received oral 4-HPR once daily for 28 days at the doses of 100, 300, 400, 600, 1,700 and 4,000 mg/m(2)/day. 4-HPR and 4-oxo-4-HPR were determined by HPLC in plasma collected up to 48 h after the first and 28th administration.

RESULTS

After single administration, 4-HPR mean C (max) ranged from 0.9 to 6.6 microM and these concentrations roughly doubled at steady state (range 1.6-14.5 microM). 4-HPR mean t (1/2) was 22 h. 4-HPR pharmacokinetics were linear in the dose range 100-1,700 mg/m(2); less than dose-proportional increase in exposure was found at 4,000 mg/m(2). At steady state, pharmacologically relevant plasma concentrations (range 0.7-10 microM and 0.4-5 microM for 4-HPR and 4-oxo-4-HPR, respectively) were maintained during the 24 h dosing interval in the dose range 300-4,000 mg/m(2).

CONCLUSIONS

4-HPR pharmacokinetics supports once-daily dosing. Steady state concentrations of 4-HPR and 4-oxo-4-HPR in children with neuroblastoma are in line with those found to have in vitro growth inhibitory effects in neuroblastoma cells.

Molecular pathways for cancer angioprevention

By analogy to the success of cardiovascular medicine in reducing mortality through preventive measures, cancer chemoprevention has the potential to significantly reduce incidence and mortality due to tumors. Angiogenesis is an event inhibited by most of the promising cancer chemoprevention compounds, a concept we termed "angioprevention." Here, we review the signaling pathways that are targeted by diverse angioprevention compounds in endothelial cells. We highlight diverse mechanisms of action, implying that combination angioprevention approaches could further improve efficacy and be transferred to clinical practice.

The unhydrolyzable fenretinide analogue 4-hydroxybenzylretinone induces the proapoptotic genes GADD153 (CHOP) and Bcl-2-binding component 3 (PUMA) and apoptosis that is caspase- dependent and independent of the retinoic acid receptor

The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) induces apoptosis in a variety of cell lines and has shown promise as an anticancer agent both in vitro and in vivo. The clinical dose of 4-HPR, however, is limited by residual-associated toxicities, indicating a need for a less toxic drug. In this study, we show that 4-hydroxybenzylretinone (4-HBR), the unhydrolyzable analogue of 4-HPR, is effective in producing apoptosis in a variety of 4-HPR-sensitive cell lines, including breast cancer, neuroblastoma, and leukemia cells. We also show through the use of a pan-caspase inhibitor that this 4-HBR-induced apoptosis is dependent, at least in part, on caspase activity. 4-HBR is shown to exhibit binding to the retinoic acid receptors (RAR) at concentrations necessary to induce cell death and induces expression of all-trans-retinoic acid-responsive genes that can be blocked by a RAR pan-antagonist. However, through the use of this RAR pan-antagonist, 4-HBR-induced apoptosis and cell death is shown to be independent of the RAR signaling pathway. To further characterize the mechanism of action of 4-HBR, expression of the endoplasmic reticulum stress-induced genes GADD153 and Bcl-2-binding component 3 was examined. These mRNAs are shown to be rapidly induced in 4-HBR-treated and 4-HPR-treated breast cancer cells, and this up-regulation is also shown to be independent of the RARs. These results suggest that a stress-mediated apoptotic cascade is involved in the mechanism of action of these retinoids.

Plasma Testosterone and Prognosis of Postmenopausal Breast Cancer Patients

Purpose

High endogenous testosterone is associated with increased breast cancer (BC) risk. We designed this study specifically to assess the long-term prognostic role of testosterone in a cohort of postmenopausal BC patients.

Patients and Methods

We considered 194 postmenopausal women, operated on for early BC (T1-2N0M0), who never received chemotherapy or hormonal therapy, and who participated in a fenretinide BC prevention trial as untreated controls. Blood samples were collected 3 months (median) after surgery; plasma samples, stored at −80°C, were radioimmunoassayed for testosterone. Median follow-up was 14 years. The main end point was any cancer event. Event-free survival was estimated by the Kaplan-Meier method. Hazard ratios (HRs) of events by testosterone level were estimated by the Cox model, adjusting for age, tumor size, and histology.

Results

Patients with high testosterone (≥ 0.40 ng/mL, median of distribution) had significantly lower event-free survival than those with low testosterone (log-rank P = .004). The adjusted HR of patients with high versus low testosterone was 2.05 (95% CI, 1.28 to 3.27). High testosterone was also associated with a significantly higher risk of BC events (relapse and second primary) with an adjusted HR of 1.77 (95% CI, 1.06 to 2.96). Eleven second primaries (non-BC) occurred in the high-testosterone group, four in the low-testosterone group.

Conclusion

High plasma testosterone strongly predicts poorer prognosis in postmenopausal BC patients not administered adjuvant therapy. Testosterone levels should be determined as part of the prognostic work-up.

Novel cell death pathways induced by N-(4-hydroxyphenyl)retinamide: therapeutic implications

We previously reported that N-(4-hydroxyphenyl)retinamide (4HPR) inhibits retinoblastoma tumor growth in a murine model in vivo and kills Y79 retinoblastoma cells in vitro. In this work, we assayed different cell death-related parameters, including mitochondrial damage and caspase activation, in Y79 cells exposed to 4HPR. 4HPR induced cytochrome c release from mitochondria, caspase-3 activation, and oligonucleosomal DNA fragmentation. However, pharmacologic inactivation of caspases by the pan-caspase inhibitor BOC-D-fmk, or specific caspase-3 inhibition by Z-DEVD-fmk, was not sufficient to prevent cell death, as assessed by loss of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction, lactate dehydrogenase release, disruption of mitochondrial transmembrane potential (Deltapsi(m)), and ATP depletion. We found that 4HPR causes lysosomal membrane permeabilization and cytosolic relocation of cathepsin D. Pepstatin A partially rescued cell viability and reduced DNA fragmentation and cytosolic cytochrome c. The antioxidant N-acetylcysteine attenuated cathepsin D relocation into the cytosol, suggesting that lysosomal destabilization is dependent on elevation of reactive oxygen species and precedes mitochondrial dysfunction. Activation of AKT, which regulates energy level in the cell, by the retinal survival facto]r insulin-like growth factor I was impaired and insulin-like growth factor I was ineffective against ATP and Deltapsi(m) loss in the presence of 4HPR. Lysosomal destabilization, associated with mitochondrial dysfunction, was induced by 4HPR also in other cancer cell lines, including PC3 prostate adenocarcinoma and the vascular tumor Kaposi sarcoma KS-Imm cells. The novel finding of a lysosome-mediated cell death pathway activated by 4HPR could have implications at clinical level for the development of combination chemoprevention and therapy of cancer.

The tumour microenvironment as a target for chemoprevention

New data indicate that primary dysfunction in the tumour microenvironment, in addition to epithelial dysfunction, can be crucial for carcinogenesis. These recent findings make a compelling case for targeting the microenvironment for cancer chemoprevention. We review new insights into the pathophysiology of the microenvironment and new approaches to control it with chemopreventive agents. The microenvironment of a cancer is an integral part of its anatomy and physiology, and functionally, one cannot totally dissociate this microenvironment from what have traditionally been called 'cancer cells'. Finally, we make suggestions for more effective clinical implementation of this knowledge in preventive strategies.

Breast conservation: Current results and future perspectives at the European Institute of Oncology

In the recent 10 years breast cancer treatments' scenario is radically changed. Extraordinary new surgical approaches give more and more conservative solutions both for the breast and especially for the axilla avoiding dissection in more than 80% of early cases. Instrumental early diagnosis and clinical prediction are now able to identify very initial cases often in premalignant stage. Technology arrived in the operating theatre for the intraoperative radiotherapy treatments giving to the patients the better quality of life with the help also of the plastic surgeons. There are still near horizons to reach: modern neo-adjuvant and adjuvant treatments are going quickly from the laboratory to patient's bed.

Analysis of gene expression identifies PLAB as a mediator of the apoptotic activity of fenretinide in human ovarian cancer cells

Fenretinide (4-HPR) is a synthetic retinoid with antitumor activity, which induces apoptosis in cancer cell lines of different histotypes. To identify genes contributing to its apoptotic activity in ovarian cancer cells, we monitored, by cDNA arrays, gene expression changes after 4-HPR exposure in A2780, a human ovarian carcinoma cell line sensitive to the retinoid. Among the differentially expressed transcripts, PLAcental Bone morphogenetic protein (PLAB), a proapoptotic gene, was the most highly induced. In a panel of ovarian carcinoma cell lines with different 4-HPR sensitivities, PLAB upregulation was associated with cellular response to 4-HPR, its overexpression increased basal apoptosis and its silencing by small interfering RNA decreased the ability of 4-HPR to induce apoptosis. PLAB induction by 4-HPR was p53- and EGR-1 independent and was regulated, at least in part, by increased stability of PLAB mRNA. PLAB up-modulation by 4-HPR also occurred in vivo: in ascitic cells collected from patients with ovarian cancer before and after 4-HPR treatment, PLAB was upmodulated in 2/4 patients. Our results in certain ovarian cancer cell lines indicate a role for PLAB as a mediator of 4-HPR-induced apoptosis. The correlation of increased PLAB in vivo with antitumor activity remains to be established.

Transport of a novel anti-cancer agent, fenretinide across Caco-2 monolayers

Fenretinide is a synthetic retinoid with chemotherapeutic activity against various malignancies. Upon oral administration to animals, fenretinide was found to be incompletely absorbed and excreted primarily in feces. The purpose of this study was to determine the possible reasons for poor oral absorption of fenretinide using Caco-2 cell monolayers. To achieve this purpose, a solid dispersion of fenretinide with Povidone K25 was used. The apparent permeability coefficient (P(app)) of fenretinide across Caco-2 monolayers in the presence of bovine serum albumin (BSA) in the receiver was determined. Apical to basolateral (AP-BL) and basolateral to apical (BL-AP) flux studies were performed to determine the role of an efflux mechanism. In the presence of 4% BSA in the receiver, the P(app) was found to be (8.8 +/- 0.5) x 10(-8) cm/sec. The AP-BL flux increased linearly with an increase in fenretinide concentration (125-640 microM) in the presence of 4% BSA in the receiver. Efflux and paracellular pathways played an insignificant role in the permeability of fenretinide. A significant amount of drug, approximately 13-15% of the initial amount accumulated in the cell membrane. The amount of fenretinide in the donor decreased by 16% over a 3 h period. However, only 0.12% of the initial amount was found in the receiver. Also, the P(app) increased with an increase in plasma protein concentration in the receiver. On the basis of these results, the poor permeability of fenretinide can be attributed to its accumulation in the lipophilic cell membrane and poor partitioning into the receiver medium.