Phase II trial of 13-cis-retinoic acid in metastatic breast cancer

Retinoic Acids in the Treatment of Most Lethal Solid Cancers

Although the use of oral administration of pharmacological all-trans retinoic acid (ATRA) concentration in acute promyelocytic leukaemia (APL) patients was approved for over 20 years and used as standard therapy still to date, the same use in solid cancers is still controversial. In the present review the literature about the top five lethal solid cancers (lung, stomach, liver, breast, and colon cancer), as defined by The Global Cancer Observatory of World Health Organization, and retinoic acids (ATRA, 9-cis retinoic acid, and 13-cis retinoic acid, RA) was compared. The action of retinoic acids in inhibiting the cell proliferation was found in several cell pathways and compartments: from membrane and cytoplasmic signaling, to metabolic enzymes, to gene expression. However, in parallel in the most aggressive phenotypes several escape routes have evolved conferring retinoic acids-resistance. The comparison between different solid cancer types pointed out that for some cancer types several information are still lacking. Moreover, even though some pathways and escape routes are the same between the cancer types, sometimes they can differently respond to retinoic acid therapy, so that generalization cannot be made. Further studies on molecular pathways are needed to perform combinatorial trials that allow overcoming retinoic acids resistance.

Phase I trial of belinostat in combination with 13-cis-retinoic acid in advanced solid tumor malignancies: a California Cancer Consortium NCI/CTEP sponsored trial

PURPOSE

The reported maximum tolerated dose (MTD) of single-agent belinostat is 1000 mg/m² given days 1-5, every 21 days. Pre-clinical evidence suggests histone deacetylase inhibitors enhance retinoic acid signaling in a variety of solid tumors. We conducted a phase I study of belinostat combined with 50-100 mg/m²/day 13-cis-retinoic acid (13-cRA) in patients with advanced solid tumors.

METHODS

Belinostat was administered days 1-5 and 13-cRA days 1-14, every 21 days. Dose-limiting toxicity (DLT) was defined as cycle 1 hematologic toxicity grade ≥ 3 not resolving to grade ≤ 1 within 1 week or non-hematologic toxicity grade ≥ 3 (except controlled nausea and vomiting and transient liver function abnormalities) attributable to belinostat.

RESULTS

Among 51 patients, two DLTs were observed: grade 3 hypersensitivity with dizziness and hypoxia at 1700 mg/m²/day belinostat with 100 mg/m²/day 13-cRA, and grade 3 allergic reaction at 2000 mg/m²/day belinostat with 100 mg/m²/day 13-cRA. The MTD was not reached. Pharmacokinetics of belinostat may be non-linear at high doses. Ten patients had stable disease, including one with neuroendocrine pancreatic cancer for 56 cycles, one with breast cancer for 12 cycles, and one with lung cancer for 8 cycles. Partial responses included a patient with keratinizing squamous cell carcinoma of the tonsils, and a patient with lung cancer.

CONCLUSIONS

The combination of belinostat 2000 mg/m² days 1-5 and 13-cRA 100 mg/m² days 1-14, every 21 days, was well-tolerated and an MTD was not reached despite doubling the established single-agent MTD of belinostat.

Aldehyde dehydrogenases and cancer stem cells

Aldehyde dehydrogenases (ALDHs), as essential regulators of aldehyde metabolism in the human body, protect organisms from damage induced by active aldehydes. Given their roles in different cancer types, ALDHs have been evaluated as potential prognostic markers of cancer. ALDHs exhibit high activity in cancer stem cells (CSCs) and may serve as markers of CSCs. Moreover, studies indicated that ALDHs and their regulated retinoic acid, reactive oxygen species and reactive aldehydes metabolism were strongly related with various properties of CSCs. Besides, recent research evidences have demonstrated the transcriptional and post-translational regulation of ALDH expression and activation in CSCs. Thus, this review focuses on the function and regulation of ALDHs in CSCs, particularly ALDH1A1 and ALDH1A3.

Interplay between estrogen and retinoid signaling in breast cancer--current and future perspectives

All-trans-retinoic acid (RA) is a promising agent for breast cancer treatment, but it induces several adverse effects and the few clinical trials performed up to now in breast cancer patients have provided disappointing results. The combination of RA and antiestrogenic compounds, such as tamoxifen, synergistically decreases the proliferation of breast cancer cells and an interplay between retinoid and estrogen signaling has begun to be unraveled, turning these combinations into an appealing strategy for breast cancer treatment. This review focus on the current knowledge regarding the interplay between retinoid and estrogen signaling in breast cancer and the combinations of RA with antiestrogens, aiming their future utilization in cancer therapy.

Molecular pathways: current role and future directions of the retinoic acid pathway in cancer prevention and treatment

Retinoids and their naturally metabolized and synthetic products (e.g., all-trans retinoic acid, 13-cis retinoic acid, bexarotene) induce differentiation in various cell types. Retinoids exert their actions mainly through binding to the nuclear retinoic acid receptors (α, β, γ), which are transcriptional and homeostatic regulators with functions that are often compromised early in neoplastic transformation. The retinoids have been investigated extensively for their use in cancer prevention and treatment. Success has been achieved with their use in the treatment of subtypes of leukemia harboring chromosomal translocations. Promising results have been observed in the breast cancer prevention setting, where fenretinide prevention trials have provided a strong rationale for further investigation in young women at high risk for breast cancer. Ongoing phase III randomized trials investigating retinoids in combination with chemotherapy in non-small cell lung cancer aim to definitively characterize the role of retinoids in this tumor type. The limited treatment success observed to date in the prevention and treatment of solid tumors may relate to the frequent epigenetic silencing of RARβ. Robust evaluation of RARβ and downstream genes may permit optimized use of retinoids in the solid tumor arena.

Epigenetics as a therapeutic target in breast cancer

Epigenetics refers to alterations in gene expression due to modifications in histone acetylation and DNA methylation at the promoter regions of genes. Unlike genetic mutations, epigenetic alterations are not due to modifications in the gene primary nucleotide sequence. The importance of epigenetics in the initiation and progression of breast cancer has led many investigators to incorporate this novel and exciting field in breast cancer drug development. Several drugs that target epigenetic alterations, including inhibitors of histone deacetylase (HDAC) and DNA methyltransferase (DNMT), are currently approved for treatment of hematological malignancies and are available for clinical investigation in solid tumors. In this manuscript, we review the critical role of epigenetics in breast cancer including the potential for epigenetic alterations to serve as biomarkers determining breast cancer prognosis and response to therapy. We highlight initial promising results to date with use of epigenetic modifiers in patients with breast cancer and the ongoing challenges involved in the successful establishment of these agents for the treatment of breast cancer.

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.

Hypercalcemia and osteoblastic lesions induced by 13-Cis-retinoic acid mimicking relapsed neuroblastoma

A 6-year-old male diagnosed with extensive neuroblastoma was treated with chemotherapy, surgery, autotransplantation, and radiotherapy. He was then enrolled on a study to assess the monoclonal antibody Ch14.18 (anti-GD2) with 13 cis-retinoic acid. 13-cis-retinoic acid therapy caused severe bone pain and hypercalcemia. Bone scans showed multiple osteoblastic lesions suggesting recurrent disease however MIBG scans were negative. Serum markers of bone turnover were increased and the patient required pamidronate therapy to treat persistent hypercalcemia. Retinoic acid toxicity needs to be considered in the differential of painful osteoblastic lesions and/or hypercalcemia. MIBG scans can assist in differentiating from recurrent disease.

Retinoid toxicity

The long-term effects of N-ethylretinamide (NER) on the haematology of the rat, and the dose-related effects of retinoids on lymphoid organs of the mouse and rat were investigated. Retinoid-induced long-bone changes were used to develop a method for quantifying skeletal effects. This technique was used to investigate the activity of five retinamides in inducing long-bone changes in the rat. The ability of non-steroidal anti-inflammatory compounds (NSAICs) to prevent retinoid-induced skeletal effects was examined, and preliminary investigations made into the mechanisms of retinoid-induced long-bone remodelling. NER-fed rats had reduced red blood cell counts and fibrinogen values. Retinoids caused dose-related proliferation of the spleen and lymph nodes in the mouse and to a lesser extent in the rat. They induced dose-related reductions in femoral diaphysis and medullary cavity diameters in both rats and mice. Aspirin prevented NER-induced changes of rat long bones, but subsequent studies indicated this effect may be closely dependent on the dose level of both the retinoid and NSAIC administered. Retinoids induce rapid long-bone remodelling in the rat which tends to revert on feeding a control diet, but remodelling processes are different in the young growing rat and the mature animal.

Activity of MDI-301, a novel synthetic retinoid, in xenografts

The efficacy of MDI-301, a non-toxic novel synthetic retinoid, was found to be equivalent to the natural 9-cis-retinoic acid (RA) in vitro against estrogen-dependent MCF7 and T47D breast cancer cell lines which express RA receptor (RAR) alpha. Both retinoids also showed similar efficacy against established PC-3 prostate carcinoma xenografts. MCF7 tumor xenografts showed a reduction in tumor growth of 48% without systemic side-effects upon treatment with MDI-301 compared with MCF7 controls. Tumor xenografts derived from MDA-MB-231, an estrogen-independent breast cancer cell line that expresses low levels of RARalpha, were unresponsive. This study demonstrates that MDI-301 is as efficacious as 9-cis-RA against cancer cells with RARalpha, with no signs of toxicity in vivo, making it a potential candidate for cancer therapy.

Altered localization of retinoid X receptor alpha coincides with loss of retinoid responsiveness in human breast cancer MDA-MB-231 cells

To understand the mechanism of retinoid resistance, we studied the subcellular localization and function of retinoid receptors in human breast cancer cell lines. Retinoid X receptor alpha (RXR alpha) localized throughout the nucleoplasm in retinoid-sensitive normal human mammary epithelial cells and in retinoid-responsive breast cancer cell line (MCF-7), whereas it was found in the splicing factor compartment (SFC) of the retinoid-resistant MDA-MB-231 breast cancer cell line and in human breast carcinoma tissue. In MDA-MB-231 cells, RXR alpha was not associated with active transcription site in the presence of ligand. Similarly, ligand-dependent RXR homo- or heterodimer-mediated transactivation on RXR response element or RARE showed minimal response to ligand in MDA-MB-231 cells. Infecting MDA-MB-231 cells with adenoviral RXR alpha induced nucleoplasmic overexpression of RXR alpha and resulted in apoptosis upon treatment with an RXR ligand. This suggests that nucleoplasmic RXR alpha restores retinoid sensitivity. Epitope-tagged RXR alpha and a C-terminus deletion mutant failed to localize to the SFC. Moreover, RXR alpha localization to the SFC was inhibited with RXR alpha C-terminus peptide. This peptide also induced ligand-dependent transactivation on RXRE. Therefore, the RXR alpha C terminus may play a role in the intranuclear localization of RXR alpha. Our results provide evidence that altered localization of RXR alpha to the SFC may be an important factor for the loss of retinoid responsiveness in MDA-MB-231 breast cancer cells.

In situ production of estrogens in human breast carcinoma

Recent studies have demonstrated that biologically active estrogens are locally produced from circulating inactive steroids in the estrogen-dependent breast carcinoma. The in situ production of estrogens in the breast carcinoma is considered to play an important role in the proliferation of breast cancer cells, especially in the postmenopausal women. Therefore, the total blockade of this pathway may inhibit estrogenic actions in breast cancer tissues and lead to an improvement in the prognosis in these patients. In this review, we describe the recent studies concerning the expression of enzymes related to intratumoral estrogen production, including aromatase, 17beta-hydroxysteroid dehydrogenase, steroid sulfatase, and estrogen sulfotransferase in human breast carcinoma tissues, and discuss the biological significance of local production of estrogens in human breast cancer.

The retinoic acid receptor antagonist, BMS453, inhibits normal breast cell growth by inducing active TGFbeta and causing cell cycle arrest

We have previously shown that a retinoic acid receptor (RAR) antagonist BMS453, which does not activate RAR-dependent gene transcription in breast cells, inhibits normal breast cell growth. In this study we have investigated the mechanisms by which this retinoid receptor antagonist inhibits cell growth. Both all trans retinoic acid (atRA) and BMS453 inhibited the proliferation of normal breast cell growth without significantly inducing apoptosis. Both retinoids caused a G1 block in the cell cycle with an increase in the proportion of cells in G0/G1 and a decrease in the proportion of cells in S phase. We then investigated the effects of the retinoids on molecules that regulate the G1 to S transition. These studies demonstrated that both atRA and BMS453 induce Rb hypophosphorylation and decrease CDK2 kinase activity. We then studied the effect of the retinoids on the expression of CDK inhibitors. atRA and BMS453 increased total p21 protein levels and CDK2-bound p21 protein, but did not change CDK4-bound p21. These results suggest that atRA and BMS453 increase p21, decrease CDK2 kinase activity, which in turn leads to hypophosphorylation of Rb and G1 arrest. Because transforming growth factor beta (TGFbeta) has been proposed as a mediator of retinoid-induced growth inhibition, we next investigated whether TGFbeta mediates the anti-proliferative effect of atRA and BMS453 in normal breast cells. These studies showed that atRA and BMS453 increased total TGFbeta activity by 3-5-fold. However, BMS453 increased active TGFbeta activity by 33-fold while atRA increased active TGFbeta activity by only threefold. These results suggest that BMS453 treatment induces conversion of latent TGFbeta to active TGFbeta. To investigate whether this increase in active TGFbeta mediates the anti-proliferative effects of these retinoids, a TGFbeta-blocking antibody was used in an attempt to prevent retinoid-induced growth inhibition. Results from these experiments showed that the anti-TGFbeta antibody prevented the inhibition of cell proliferation induced by BMS453, but did not prevent the inhibition of cell proliferation induced by atRA. These results demonstrate that BMS453 inhibits breast cell growth predominantly through the induction of active TGFbeta, while atRA inhibits growth through other mechanisms. These results suggest that retinoid analogs that increase active TGFbeta may be promising agents for the prevention of breast cancer.

Retinoid therapy of childhood cancer

In vitro studies that showed RA could cause growth arrest and differentiation of myelogenous leukemia and neuroblastoma led to clinical trials of retinoids in APL and neuroblastoma that increased survival for both of those diseases. In the case of APL, ATRA has been the drug of choice, and preclinical and clinical data support direct combinations of ATRA with cytotoxic chemotherapy. For neuroblastoma, a phase I study defined a dose of 13-cis-RA, which was tolerable in patients after myeloablative therapy, and a phase III trial that showed postconsolidation therapy with 13-cis-RA improved EFS for patients with high-risk neuroblastoma. Preclinical studies in neuroblastoma indicate that ATRA or 13-cis-RA can antagonize cytotoxic chemotherapy and radiation, so use of 13-cis-RA in neuroblastoma is limited to maintenance after completion of cytotoxic chemotherapy and radiation. A limitation on the antitumor benefit of ATRA in APL is the marked decrease in drug levels that occurs during therapy as a result of induction of drug metabolism, resulting in a shorter drug half-life and decreased plasma levels. Although early studies sought to overcome the pharmacologic limitations of ATRA therapy in APL, the demonstration that ATO is active against APL in RA-refractory patients has led to a focus on studies employing ATO. Use of 13-cis-RA in neuroblastoma has avoided the decreased plasma levels seen with ATRA. It is likely that recurrent disease seen during or after 13-cis-RA therapy in neuroblastoma is due to tumor cell resistance to retinoid-mediated differentiation induction. Studies in neuroblastoma cell lines resistant to 13-cis-RA and ATRA have shown that they can be sensitive, and in some cases collaterally hypersensitive, to the cytotoxic retinoid fenretinide. Fenretinide induces tumor cell cytotoxicity rather than differentiation, acts independently from RA receptors, and in initial phase I trials has been well tolerated. Clinical trials of fenretinide, alone and in combination with ceramide modulators, are in development.

Chemoprevention of NMU-induced rat mammary carcinoma with the combination of melatonin and 9-cis-retinoic acid

In experimental trials using the N-nitroso-N-methylurea (NMU)-induced rat mammary tumor model, a significant decrease in tumor incidence (to 5%) was observed in rats treated with melatonin and 9-cis-retinoic acid (9 cRA) compared to controls (55%). Although 9cRA alone decreased tumor incidence to 26%, this response did not reach statistical significance. Tumor incidence was significantly inhibited to 20% in the animals that received melatonin and 9cRA on alternating days. Latency to tumor onset was prolonged in animals receiving either of the combination treatments compared with controls, and tumor multiplicity was also significantly decreased.

Retinoid receptors in human breast carcinoma: possible modulators of in situ estrogen metabolism

Retinoid receptors (retinoic acid (RARs) and retinoid X (RXRs) receptors) were immunolocalized in 32 human invasive ductal breast carcinomas. These findings were correlated with clinicopathological parameters to study their biological significance in breast carcinoma. Retinoid receptor immunoreactivity, except for RXRgamma, was detected in the nuclei of carcinoma cells. Percentage of positive cases were RARalpha; 81%, RARbeta; 6%, RARgamma; 28%, RXRalpha; 81%, and RXRbeta; 59%. A significant correlation was detected between RARalpha labeling index (LI), and RXRalpha LI (r = 0.667, p < 0.001). Results from immunoblotting performed in three cases were consistent with those of immunohistochemistry. There was a significant correlation between RARalpha LI and 17beta-hydroxysteroid dehydrogenase (17beta-HSD) type 1 immunoreactivity (p < 0.05). A significant correlation was also detected between RARalpha (r= 0.413, p = 0.019) or RXRalpha (r = 0.429, p = 0.014) LI, and estrogen receptor (ER) LI. In T-47D breast cancer cells, which express RARalpha, RXRalpha and ER, 17beta-HSD reductive activity increased 1.76-fold (p < 0.001), five days following treatment with 10 nM retinoic acid. These data suggest that retinoid receptors modulate various effects of retinoids, including estrogen metabolism in human breast carcinomas.

Role of retinoid receptors in the prevention and treatment of breast cancer

Retinoids are vitamin A-related compounds that have been found to prevent cancer in animals and humans. In this review, we discuss the role of retinoids and their receptors in the treatment and prevention of breast cancer. The retinoid receptors are expressed in normal and malignant breast cells, and are critical for normal development. In breast cells, when bound by retinoid hormones, these proteins regulate proliferation, apoptosis, and differentiation. The mechanism by which retinoids inhibit breast cell growth has not been completely elucidated, however, retinoids have been shown to affect multiple signal transduction pathways, including IGF-, TGFbeta-, and AP-1-dependent pathways. Retinoids have also been shown to suppress the growth and prevent the development of breast cancer in animals. These agents suppress tumorigenesis in carcinogen-treated rats and in transgenic mice, and inhibit the growth of transplanted breast tumors. These promising preclinical results have provided the rationale to test retinoids in clinical trials for the treatment and prevention of breast cancer. Several retinoids, including all trans retinoic acid and 9-cis retinoic acid, have been shown to have modest activity in the treatment of breast cancer, and these agents are now in clinical trials in combination with cytotoxic agents and anti-estrogens. Another retinoid, 4-HPR, is currently being tested in a human cancer prevention trial. Preliminary results suggest that 4-HPR may suppress breast cancer development in premenopausal women. Future clinical trials will focus on testing new synthetic retinoids that have reduced toxicity and enhanced therapeutic and preventive efficacy.

Inhibition of trans-retinoic acid-resistant human breast cancer cell growth by retinoid X receptor-selective retinoids

All-trans-retinoic acid (trans-RA) and other retinoids exert anticancer effects through two types of retinoid receptors, the RA receptors (RARs) and retinoid X receptors (RXRs). Previous studies demonstrated that the growth-inhibitory effects of trans-RA and related retinoids are impaired in certain estrogen-independent breast cancer cell lines due to their lower levels of RAR alpha and RARbeta. In this study, we evaluated several synthetic retinoids for their ability to induce growth inhibition and apoptosis in both trans-RA-sensitive and trans-RA-resistant breast cancer cell lines. Our results demonstrate that RXR-selective retinoids, particularly in combination with RAR-selective retinoids, could significantly induce RARbeta and inhibit the growth and induce the apoptosis of trans-RA-resistant, RAR alpha-deficient MDA-MB-231 cells but had low activity against trans-RA-sensitive ZR-75-1 cells that express high levels of RAR alpha. Using gel retardation and transient transfection assays, we found that the effects of RXR-selective retinoids on MDA-MB-231 cells were most likely mediated by RXR-nur77 heterodimers that bound to the RA response element in the RARbeta promoter and activated the RARbeta promoter in response to RXR-selective retinoids. In contrast, growth inhibition by RAR-selective retinoids in trans-RA-sensitive, RAR alpha-expressing cells most probably occurred through RXR-RAR alpha heterodimers that also bound to and activated the RARbeta promoter. In MDA-MB-231 clones stably expressing RAR alpha, both RARbeta induction and growth inhibition by RXR-selective retinoids were suppressed, while the effects of RAR-selective retinoids were enhanced. Together, our results demonstrate that activation of RXR can inhibit the growth of trans-RA-resistant MDA-MB-231 breast cancer cells and suggest that low cellular RAR alpha may regulate the signaling switch from RAR-mediated to RXR-mediated growth inhibition in breast cancer cells.

Retinoic acid receptor beta mediates the growth-inhibitory effect of retinoic acid by promoting apoptosis in human breast cancer cells

Retinoids are known to inhibit the growth of hormone-dependent but not that of hormone-independent breast cancer cells. We investigated the involvement of retinoic acid (RA) receptors (RARs) in the differential growth-inhibitory effects of retinoids and the underlying mechanism. Our data demonstrate that induction of RAR beta by RA correlates with the growth-inhibitory effect of retinoids. The hormone-independent cells acquired RA sensitivity when the RAR beta expression vector was introduced and expressed in the cells. In addition, RA sensitivity of hormone-dependent cells was inhibited by a RAR beta-selective antagonist and the expression of RAR beta antisense RNA. Introduction of RAR alpha also restored RA sensitivity in hormone-independent cells, but this restoration was accomplished by the induction of endogenous RAR beta expression. Furthermore, we show that induction of apoptosis contributes to the growth-inhibitory effect of RAR beta. Thus, RAR beta can mediate retinoid action in breast cancer cells by promoting apoptosis. Loss of RAR beta, therefore, may contribute to the tumorigenicity of human mammary epithelial cells.

Retinoid receptors in human lung cancer and breast cancer

Retinoids, the natural and synthetic vitamin A derivatives, are known to inhibit the proliferation of lung cancer and breast cancer cells and the growth of carcinogen-induced bronchogenic squamous cell carcinoma and mammary tumors, and have been used as chemoprevention agents against both types of cancer. However, clinical trials of retinoids in patients with advanced lung cancer and breast cancer have not been successful. In studying how retinoid sensitivity is lost in cancer cells, we have found that lack of the retinoic acid receptor beta (RAR beta) gene expression and its abnormal regulation by retinoic acid (RA) are common features in human lung cancer and breast cancer cells. The absence and abnormal RA regulation of RAR beta correlates with the loss of anti-proliferation effect of RA in hormone-independent breast cancer cells, and is due to different abnormalities found in cancer cells. Furthermore, expression of RAR beta gene in hormone-independent breast cancer cells restores their RA sensitivity. These data demonstrate that RAR beta can mediate the growth inhibitory effect of RA and suggest that the lack of RAR beta may contribute to retinoid resistance in certain cancer cells.

Interferon-beta, retinoids, and tamoxifen in the treatment of metastatic breast cancer: a phase II study

Based on the additive or synergistic antiproliferative effect of interferon and tamoxifen on breast cancer cell lines and on preclinical and clinical data on retinoids alone and in combination with antiestrogen or interferon, we designed a pilot phase II study to test the toxicity of simultaneous administration of interferon-beta (IFN-beta), retinoids (R), and tamoxifen (TAM) and the efficacy of this combination as salvage therapy in a group of patients with metastatic breast cancer (MBC). A total of 49 stage IV breast cancer patients, 11 pretreated with hormones, 26 with chemotherapy, and 12 with both, received 30 mg TAM and two dose levels of IFN-beta and retinyl palmitate. Among 49 evaluable patients, 27 achieved a clinical response (55%; 95% CI 41-69%), 10 had stable disease (20%), and in 12 (25%) the disease progressed. Toxicity with both dose levels was moderate and mainly hepatic. Median response duration, not statistically different in estrogen receptor-positive and negative patients, was 31.4 months (range 4.9-67). Median overall survival was 19.2 months (range 2-69). We have shown that long-term administration of TAM, IFN-beta, and retinyl palmitate is feasible with moderate toxicity. We have also demonstrated that this regimen is active in pretreated MBC patients and that responses are not influenced by receptor status.

Hypercalcemia associated with all-trans-retinoic acid in the treatment of acute promyelocytic leukemia

Recent reports have described clinical benefits of all-trans-retinoic acid (ATRA) therapy for acute promyelocytic leukemia (APL). This paper describes severe hypercalcemia (serum calcium: 18.7 mg/dl) in association with ATRA treatment in a 14 year old girl with APL. Serum parathyroid hormone (PTH) concentrations were normal (0.21 ng/ml), which precludes the possibility of primary hyperparathyroidism or ectopic PTH secretion as a cause of the hypercalcemia. As for the factors which can accelerate mineral resorption, there were no apparent increases in the levels of PTH-related protein (PTH-rP), prostaglandins and vitamin D metabolites. In our in vitro experiment, ATRA did not stimulate the leukemic cells to produce PTH-rP. We speculate that ATRA, like PTH, may increase osteoclastic activity and induce hypercalcemia.

Combination therapy with cisplatin: modulation of activity and tumour sensitivity

Although cisplatin is applied with success in clinical oncology, this success is limited because some cancers are initially unresponsive to cisplatin or become so during treatment. In this review, some strategies to overcome this problem are discussed. Among these are combination with the differentiation inducing agent, retinoic acid, combination with radiotherapy, and the use of hyperthermia.

Phase II study of tamoxifen and high-dose retinyl acetate in patients with advanced breast cancer

Retinoids have shown a tumor growth inhibition and a synergistic activity with hormonal manipulations in human breast cancer cell lines and rat mammary carcinoma. To investigate the potential usefulness of this synergistic activity in human breast cancer, 33 postmenopausal patients with advanced disease were treated with the combination of tamoxifen (10 mg p.o. three times a day) and retinyl acetate (300,000 IU p.o. daily). Out of 31 evaluable patients, 3 achieved complete response, 9 partial response (overall response rate: 38.5%, 95% confidence interval = 21%-56%) and 16 (52%) showed no change. The median duration of response was 11.5 months (range: 3-19+ months), while the 2-year overall survival rate for the entire group of patients was 63%. Toxicity was generally mild, hot flushes, nausea (and/or vomiting), headache and cutaneous itching being the most frequent side-effects. Only 1 patient discontinued treatment for severe toxicity. These preliminary results suggest that the combination of tamoxifen and high-dose retinyl acetate is a safe and effective regimen for breast cancer patients. However, the study design does not allow us to establish whether the very low rate of early disease progression we observed might be related to a possible synergistic effect between retinoids and antiestrogens or rather to the quite indolent disease of the patients who have been selected for entry into this trial.

Therapeutic effect of N-(4-hydroxyphenyl)retinamide on N-methyl-N-nitrosourea-induced rat mammary cancer

Virgin Sprague--Dawley rats received a single i.v. injection of 40 mg N-methyl-N-nitrosourea (MNU)/kg body wt. at 50 days of age. After the first palpable mammary tumor reached 10 mm in size, the animals were sequentially allocated to one of 4 groups: (I) placebo diet, (II) 10 micrograms tamoxifen s.c. 3 times per week, (III) 3 mmol N-(4-hydroxyphenyl)retinamide (4-HPR)/kg diet, or (IV) both (II) and (III). Weekly measurements of initial tumors and subsequent tumors were made throughout the study. 4-HPR administration resulted in a complete regression (non-palpable state) of the first mammary tumor in 6 animals (22%) and partial regression or nonprogression in 5 others (19%). Tamoxifen alone induced only partial response in 9 animals (33%). 4-HPR and tamoxifen resulted in 19% total and 26% partial response. The data suggests therapeutic value of 4-HPR in MNU-induced rat mammary carcinoma.

13-Cis-retinoic acid: pharmacology, toxicology, and clinical applications for the prevention and treatment of human cancer

Retinoids, particularly 13-cis-retinoic acid, have shown great promise against a number of benign, but serious dermatological conditions. In animal models, 13-cis-retinoic acid functions is a potent antipromoter whether a cancer has been initiated by chemical, physical, or viral agents. Additionally, substantial antiproliferative activity of this compound has been demonstrated in vitro in many culture systems. Clinical activity noted against several types of skin malignancies has led to several investigations to determine the anticancer activity of 13-cis-retinoic acid. Response of a variety of preneoplastic and neoplastic lesions of epithelial histology has been demonstrated. The toxicity of 13-cis-retinoic acid largely reflects its tissue distribution with skin and subcutaneous side-effects limiting dose escalation. The pharmacology and pharmacokinetics of 13-cis-retinoic acid has been explored in a number of patients and a long terminal half-life demonstrated. This review will discuss 13-cis-retinoic acid as a good model for a biological response modifier.

Effect of retinoic acid and 4-hydroxytamoxifen on human breast cancer cell lines

Using established breast cancer cell lines in a cell culture model we studied the growth effect of retinoic acid (RA) alone or in combination with the antiestrogen 4-hydroxytamoxifen (OHT). Cytoplasmic 3HRA binding sites were determined by sucrose density gradient centrifugation analysis. Of the three cell lines Hs578T, BT 20, and 734 B only the last showed a significant amount of specific RA binding (10(5) sites/cell). This cell line showed a dose dependent decrease in proliferation after a long-term incubation with RA whereas the 3H-thymidine uptake was highly significantly increased after incubation with 10(-6)M of RA for 20 hr. Growth inhibition was not further increased by the addition of OHT (10(-6) M), but the increase in thymidine incorporation due to RA was neutralized by OHT. Hs578T and BT 20 cells were not affected by any of the treatments. The different action of RA on proliferation and thymidine incorporation suggests a cell cycle specific mechanism.