Myosteatosis evaluation using erector spinae and psoas muscles to predict adverse events during adjuvant chemotherapy for breast cancer.

BACKGROUND: Myosteatosis (intramuscular adiposity) is predictive of chemotherapy toxicity in women undergoing adjuvant chemotherapy for breast cancer (BC). We evaluated a novel, user-friendly and cost-effective technique utilizing a Picture Archiving and Communication Systems (PACS) tool that is readily available in the electronic medical record (EMR), using skeletal muscle density (SMD) to detect myosteatosis and then compared PACS results with those derived from widely used body composition software (SliceOMatic, QC, Canada). METHODS: Using retrospective data from a sample of women with early BC (Stage I-III) who had CT scan and received chemotherapy. Pearson correlation coefficients were used to compare SliceOMatic with PACS results. Associations of PACS results with chemotherapy-related adverse events were evaluated using multivariable (MV) log-binomial models adjusted for age, race, BMI, anthracycline-based therapy, and number of comorbidities. RESULTS: In 338 patients, mean age was 51, 32% were non-white, and 40% had obesity (BMI ≥ 30 kg/m2). Correlation of SMD using SliceOMatic whole muscle measurements with PACS psoas muscle was 0.76 (p < .0001) and with PACS erector spinae muscle 0.91 (p < .0001). Using PACS psoas muscle, myosteatosis was associated with any adverse event [RR 1.66, CI 1.22-2.26 (p < .0001)], dose reduction [RR 1.63, CI 1.01-2.65 (p = .05)], and early treatment discontinuation [RR 2.14, CI 1.10-4.14 (p = 0.03)]. Using PACS erector spinae muscle, myosteatosis was associated any adverse event [RR 1.59, CI 1.11-2.27 (p = 0.01)] and dose reduction [RR 1.91, CI 1.07-3.42 (p = .03)]. CONCLUSION AND RELEVANCE: Skeletal muscle density measures using PACS correlated strongly with SliceOMatic results and both are similarly predictive of chemotherapy-related adverse events.

The association of body composition parameters and adverse events in women receiving chemotherapy for early breast cancer.

BACKGROUND: Body composition metrics as predictors of adverse events are a growing area of interest in oncology research. One barrier to the use of these metrics in clinical practice is the lack of standardized cut points for identifying patients with at-risk body composition profiles. We examined the association of chemotherapy adverse events with several body composition measures, using alternative cut points from published studies. METHODS: This is a retrospective study of women diagnosed with early breast cancer (EBC). Axial computerized tomography (CT) images from lumbar L3 segments were analyzed for the following body composition measures: myosteatosis (low Skeletal Muscle Density/SMD), sarcopenia (low Skeletal Muscle Index/SMI), and high Visceral Adipose Tissue (VAT). Adverse events during chemotherapy were dose reduction, early treatment discontinuation, and hospitalization. Log-binomial modeling was used to evaluate associations between body composition measures at different cut points with adverse events, adjusting for age, race, Body Mass Index/BMI, and comorbidities. Relative risks were reported as the measure of association. RESULTS: In a sample of 338 women, mean age was 51, 14% were age 65 or older, 32% were non-white, 40% had obesity (/BMI ≥ 30 kg/m2), and mean number of comorbidities was 1.56. In multivariable analysis (MV), all three SMD cut points for myosteatosis had significant associations with total number of adverse events, as well as different cut points having significant associations with either dose reduction, early treatment discontinuation or hospitalization. SMI and VAT were not significant in the MV analysis; however, in some models, age and total comorbidities were significant for adverse events. CONCLUSIONS: Among CT-derived measures of body composition, myosteatosis determined at any of three SMD cut points was associated with total and individual adverse events during chemotherapy for early breast cancer.

Association of body composition with function in women with early breast cancer.

BACKGROUND: Advances in breast cancer research are making treatment options increasingly effective and reducing mortality. Body composition is an example of a prognostic tool that can help personalize breast cancer treatments and further increase their effectiveness. In this study, we examine the association of several body composition measures with comorbidities, physical function, and quality of life. METHODS: This study is a cross-sectional analysis of 99 women with early breast cancer scheduled for chemotherapy. Univariate regression models were used to identify significant associations of body composition metrics with patient demographics, clinical characteristics, measures of physical function, and patient-reported outcomes (PRO)s. Multivariable modeling was used to evaluate associations adjusted for age. RESULTS: Median age was 58 (range 24-83), 27% were non-white, and, 47% were obese (≥ 30 kg/m2). Increasing age was associated with lower Skeletal Muscle Density (SMD) (p = 0.0001), lower Skeletal Muscle Gauge (SMG) (p = 0.0005), and higher Visceral Adipose Tissue (VAT) (p < 0.0001). In patients with a prolonged Timed Up and Go tests (> 14 s), mean VAT was 57.87 higher (p = 0.004), SMD 5.70 lower (p = 0.04), and SMG 325.4 lower (p = 0.02). For each point of higher performance on the Short Physical Performance Battery (SPPB), VAT decreased 12.24 (p = 0.002) and SMD rose 1.22 (p = 0.02). In multivariable analysis adjusting for age, the association of TUG > 14 with higher VAT remained significant (p = 0.02). CONCLUSIONS: Suboptimal body composition prior to treatment is associated poor physical function and may be an indicator of clinical importance.

Muscle composition and outcomes in patients with breast cancer: meta-analysis and systematic review.

PURPOSE: Breast cancer is the most common cancer and leading cause of cancer death in women. Body composition parameters, especially those related to muscle, have become a growing focus of cancer research. In this review, we summarize the literature on breast cancer and muscle parameters as well as combine their outcomes for overall survival (OS), time to tumor progression (TTP), and chemotherapy toxicity in a meta-analysis. METHODS: A systematic search of the literature for randomized controlled trials and observational studies was conducted on MEDLINE, Cochrane CENTRAL, and EMBASE through May 1, 2019. Two reviewers independently searched and selected. Meta-analysis was conducted using a random-effects model. The risk of bias was evaluated using the Newcastle-Ottawa quality assessment for cohorts and GRADE summary of findings tool from Cochrane. RESULTS: A total of 754 articles were screened from which 6 articles and one abstract were selected. Using skeletal muscle index (SMI), patients classified as sarcopenic had a 68% greater mortality risk compared to non-sarcopenic patients (HR 1.68 95% CI 1.09-2.59, 5 studies) (p = .02) (i2 = 70%). Low muscle density was not predictive of OS (HR 1.44 95% CI 0.77-2.68, 2 studies) (p = .25) (i2 = 87%). Patients with sarcopenia (56%) had more grade 3-5 toxicity compared to non-sarcopenic (25%) (RR 2.17 95% CI 1.4-3.34, 3 studies) (p = .0005) (i2 = 0%). TTP was nearly 71 days longer in advanced/metastatic patients classified as non-sarcopenic compared to patients with sarcopenia (MD - 70.75 95% CI - 122.32 to - 19.18) (p = .007) (i2 = 0%). CONCLUSION: Our synthesis of the literature shows that patients with sarcopenia have more severe chemotherapy toxicity as well as shorter OS and TTP, and that low muscle density is prognostic of OS for women with metastatic breast cancer. Our findings suggest that in clinical practice, body composition assessment is valuable as a prognostic parameter in breast cancer.

Association between subclinical thyroid dysfunction and change in bone mineral density in prospective cohorts.

BACKGROUND: Subclinical hyperthyroidism (SHyper) has been associated with increased risk of hip and other fractures, but the linking mechanisms remain unclear. OBJECTIVE: To investigate the association between subclinical thyroid dysfunction and bone loss. METHODS: Individual participant data analysis was performed after a systematic literature search in MEDLINE/EMBASE (1946-2016). Two reviewers independently screened and selected prospective cohorts providing baseline thyroid status and serial bone mineral density (BMD) measurements. We classified thyroid status as euthyroidism (thyroid-stimulating hormone [TSH] 0.45-4.49 mIU/L), SHyper (TSH < 0.45 mIU/L) and subclinical hypothyroidism (SHypo, TSH ≥ 4.50-19.99 mIU/L) both with normal free thyroxine levels. Our primary outcome was annualized percentage BMD change (%ΔBMD) from serial dual X-ray absorptiometry scans of the femoral neck, total hip and lumbar spine, obtained from multivariable regression in a random-effects two-step approach. RESULTS: Amongst 5458 individuals (median age 72 years, 49.1% women) from six prospective cohorts, 451 (8.3%) had SHypo and 284 (5.2%) had SHyper. During 36 569 person-years of follow-up, those with SHyper had a greater annual bone loss at the femoral neck versus euthyroidism: %ΔBMD = -0.18 (95% CI: -0.34, -0.02; I2 = 0%), with a nonstatistically significant pattern at the total hip: %ΔBMD = -0.14 (95% CI: -0.38, 0.10; I2 = 53%), but not at the lumbar spine: %ΔBMD = 0.03 (95% CI: -0.30, 0.36; I2 = 25%); especially participants with TSH < 0.10 mIU/L showed an increased bone loss in the femoral neck (%Δ BMD = -0.59; [95% CI: -0.99, -0.19]) and total hip region (%ΔBMD = -0.46 [95% CI: -1.05, -0.13]). In contrast, SHypo was not associated with bone loss at any site. CONCLUSION: Amongst adults, SHyper was associated with increased femoral neck bone loss, potentially contributing to the increased fracture risk.

Thyroid diseases and bone health.

Thyroid hormones are essential for skeletal development and are important regulators of bone maintenance in adults. Childhood hypothyroidism causes delayed skeletal development, retarded linear growth and impaired bone mineral accrual. Epiphyseal dysgenesis is evidenced by classic features of stippled epiphyses on X-ray. In severe cases, post-natal growth arrest results in a complex skeletal dysplasia. Thyroid hormone replacement stimulates catch-up growth and bone maturation, but recovery may be incomplete dependent on the duration and severity of hypothyroidism prior to treatment. A severe phenotype characteristic of hypothyroidism occurs in children with resistance to thyroid hormone due to mutations affecting THRA encoding thyroid hormone receptor α (TRα). Discovery of this rare condition recapitulated animal studies demonstrating that TRα mediates thyroid hormone action in the skeleton. In adults, thyrotoxicosis is well known to cause severe osteoporosis and fracture, but cases are rare because of prompt diagnosis and treatment. Recent data, however, indicate that subclinical hyperthyroidism is associated with low bone mineral density (BMD) and an increased risk of fracture. Population studies have also shown that variation in thyroid status within the reference range in post-menopausal women is associated with altered BMD and fracture risk. Thus, thyroid status at the upper end of the euthyroid reference range is associated with low BMD and increased risk of osteoporotic fragility fracture. Overall, extensive data demonstrate that euthyroid status is required for normal post-natal growth and bone mineral accrual, and is fundamental for maintenance of adult bone structure and strength.

Weight gain during adjuvant endocrine treatment for early-stage breast cancer: What is the evidence?

Most breast cancer (BC) tumors are early stage and hormone receptor positive, where treatment generally includes adjuvant endocrine treatment (ET). Oncology providers and women about to start ET want to know about side effects, including potential weight gain. The aim of this study was a literature review to identify the independent effect of ET on post-diagnosis weight gain. Weight gain is of concern with regard to potential associations with BC recurrence, mortality, and quality of life in survivorship. We conducted a targeted review of the literature. Thirty-eight studies met our inclusion criteria. Patient-reported weight gain ranged widely from 18 to 52 % of patients in Year 1 and from 7 to 55 % in Year 5. Some studies reported categories of weight change: lost weight (9-17 %), stable weight (47-64 %), and gained weight (27-36 %). Most studies comparing ET with placebo or tamoxifen with AI reported no significant difference between the two groups. Wide-ranging and inconsistent results point to the need for further research to clarify annual weight change (loss, gain, stability) from BC diagnosis through 5 years of ET and beyond. There is also a need to explore weight change by type of ET and to explore risk factors for weight gain in women on ET, including tumor type, sociodemographic characteristics, and health behaviors. More specific information is needed to identify high-risk BC patients who could be targeted for weight management interventions.

Quantitative X-ray microradiography for high-throughput phenotyping of osteoarthritis in mice.

OBJECTIVE: To investigate and validate digital X-ray microradiography as a novel, high-throughput and cost-effective screening approach to identify abnormal joint phenotypes in mice. METHOD: Digital X-ray microradiography was used to quantify the subchondral bone mineral content (BMC) in the medial tibial plateau. Accuracy and reproducibility of the method were determined in 22 samples from C57BL/6(B6Brd;B6Dnk;B6N-Tyr(c-Brd)) wild-type mice. The method was then validated in wild-type mice that had undergone surgical destabilisation of medial meniscus (DMM) and in a genetically modified mouse strain with an established increase in trabecular bone mass. RESULTS: The measurement of subchondral BMC by digital X-ray microradiography had a coefficient of variation of 3.6%. Digital X-ray microradiography was able to demonstrate significantly increased subchondral BMC in the medial tibial plateau of male mice 4 and 8 weeks after DMM surgery and in female mice 8 weeks after surgery. Furthermore, digital X-ray microradiography also detected the increase in subchondral BMC in a genetically modified mouse strain with high trabecular bone mass. CONCLUSION: Quantitation of subchondral BMC by digital X-ray microradiography is a rapid, sensitive and cost-effective method to identify abnormal joint phenotypes in mice of both genders at several ages.

Local delivery of tacrolimus using electrospun poly-ϵ-caprolactone nanofibres suppresses the T-cell response to peripheral nerve allografts.

Objective.Repair of nerve gap injuries can be achieved through nerve autografting, but this approach is restricted by limited tissue supply and donor site morbidity. The use of living nerve allografts would provide an abundant tissue source, improving outcomes following peripheral nerve injury. Currently this approach is not used due to the requirement for systemic immunosuppression, to prevent donor-derived cells within the transplanted nerve causing an immune response, which is associated with severe adverse effects. The aim of this study was to develop a method for delivering immunosuppression locally, then to test its effectiveness in reducing the immune response to transplanted tissue in a rat model of nerve allograft repair.Approach.A coaxial electrospinning approach was used to produce poly-ϵ-caprolactone fibre sheets loaded with the immunosuppressant tacrolimus. The material was characterised in terms of structure and tacrolimus release, then testedin vivothrough implantation in a rat sciatic nerve allograft model with immunologically mismatched host and donor tissue.Main results.Following successful drug encapsulation, the fibre sheets showed nanofibrous structure and controlled release of tacrolimus over several weeks. Materials containing tacrolimus (and blank material controls) were implanted around the nerve graft at the time of allograft or autograft repair. The fibre sheets were well tolerated by the animals and tacrolimus release resulted in a significant reduction in lymphocyte infiltration at 3 weeks post-transplantation.Significance.These findings demonstrate proof of concept for a novel nanofibrous biomaterial-based targeted drug delivery strategy for immunosuppression in peripheral nerve allografting.

Thyroid hormones and bone development.

Thyroid hormones are critical determinants of postnatal skeletal development. Thyroid hormone deficiency or excess in children results in severe abnormalities of linear growth and bone maturation. These clinical observations have been recapitulated in mutant mice and these models have facilitated studies of the mechanisms of thyroid hormone action in the developing skeleton. In this review, we consider in detail the direct and indirect effects of thyroid hormone on bone and the molecular mechanisms involved.

Myosteatosis and prognosis in cancer: Systematic review and meta-analysis.

BACKGROUND: The evidence that body composition parameters influence multiple cancer outcomes is rapidly expanding. Excess adiposity deposits in muscle tissue, termed myosteatosis, can be detected in CT scans through variations in the density of muscle tissues (Hounsfield Units). Patients with similar muscle mass but different amounts of intramuscular adipose infiltration have increased chemotherapy toxicity, time to tumor progression and other adverse outcomes among different cancer types. Our review examines the impact of myosteatosis on overall survival (OS) in patients with cancer. METHODS: A systematic search of the literature was conducted on PubMed/ MEDLINE, Cochrane CENTRAL, and EMBASE. Meta-analysis was conducted using a random-effects model. Risk of bias was evaluated using the Newcastle-Ottawa Quality assessment for cohort studies, funnel plot (publication bias), and GRADE summary of findings tool from Cochrane. RESULTS: A total of 4880 articles were screened from which 40 articles selected, including 21,222 patients. The overall mean proportion of patients with myosteatosis was 48 % (range 11-85 %). Using skeletal muscle density (SMD), patients classified as having myosteatosis had 75 % greater mortality risk compared to non-myosteatosis patients (HR 1.75 95 % CI 1.60-1.92, 40 studies) (p < .00001) (i2 = 62 %). Specifically, myosteatosis was prognostic for worse OS in patients with gynecological, renal, periampullary/pancreatic, hepatocellular, gastroesophageal, and colorectal carcinoma, and lymphomas. CONCLUSION: Our analysis of the literature shows that cancer patients with myosteatosis have shorter survival. Our findings suggest that in oncological practice, muscle density assessment is valuable as a prognostic parameter.

Controlled local release of PPARγ agonists from biomaterials to treat peripheral nerve injury.

OBJECTIVE: Poor clinical outcomes following peripheral nerve injury (PNI) are partly attributable to the limited rate of neuronal regeneration. Despite numerous potential drug candidates demonstrating positive effects on nerve regeneration rate in preclinical models, no drugs are routinely used to improve restoration of function in clinical practice. A key challenge associated with clinical adoption of drug treatments in nerve injured patients is the requirement for sustained administration of doses associated with undesirable systemic sideeffects. Local controlled-release drug delivery systems could potentially address this challenge, particularly through the use of biomaterials that can be implanted at the repair site during the microsurgical repair procedure. APPROACH: In order to test this concept, this study used various biomaterials to deliver ibuprofen sodium or sulindac sulfide locally in a controlled manner in a rat sciatic nerve injury model. Following characterisation of release parameters in vitro, ethylene vinyl acetate tubes or polylactic-co-glycolic acid wraps, loaded with ibuprofen sodium or sulindac sulfide, were placed around directly-repaired nerve transection or nerve crush injuries in rats. MAIN RESULTS: Ibuprofen sodium, but not sulindac sulfide caused an increase in neurites in distal nerve segments and improvements in functional recovery in comparison to controls with no drug treatment. SIGNIFICANCE: This study showed for the first time that local delivery of ibuprofen sodium using biomaterials improves neurite growth and functional recovery following PNI and provides the basis for future development of drug-loaded biomaterials suitable for clinical translation.

Benzofuran derivatives and the thyroid.

Amiodarone and dronedarone are two clinically important benzofuran derivatives. Amiodarone has been used widely for treating resistant tachyarrhythmias in the past three decades. However amiodarone and its main metabolically active metabolite desethylamiodarone can adversely affect many organs, including the thyroid gland. Amiodarone-induced thyroid disorders are common and often present as a management challenge for endocrinologists. The pathogenesis of amiodarone-induced thyroid dysfunction is complex but the inherent effects of the drug itself as well as its high iodine content appear to play a central role. The non-iodinated dronedarone also exhibits anti-arrhythmic properties but appears to be less toxic to the thyroid. This review describes the biochemistry of benzofuran derivatives, including their pharmacology and the physiology necessary for understanding the cellular mechanisms involved in their actions. The known effects of these compounds on thyroid action are described. Recommendations for management of amiodarone-induced hypothyroidism and thyrotoxicosis are suggested. Dronedarone appears to be an alternative but less-effective anti-arrhythmic agent and it does not have adverse effects on thyroid function. It may have a future role as an alternative agent in patients being considered for amiodarone therapy especially those at high risk of developing thyroid dysfunction but not in severe heart failure.

Cloning and characterization of two novel thyroid hormone receptor beta isoforms.

Thyroid hormone (T(3)) activates nuclear receptor transcription factors, encoded by the TRalpha (NR1A1) and TRbeta (NR1A2) genes, to regulate target gene expression. Several TR isoforms exist, and studies of null mice have identified some unique functions for individual TR variants, although considerable redundancy occurs, raising questions about the specificity of T(3) action. Thus, it is not known how diverse T(3) actions are regulated in target tissues that express multiple receptor variants. I have identified two novel TRbeta isoforms that are expressed widely and result from alternative mRNA splicing. TRbeta3 is a 44.6-kDa protein that contains an unique 23-amino-acid N terminus and acts as a functional receptor. TRDeltabeta3 is a 32.8-kDa protein that lacks a DNA binding domain but retains ligand binding activity and is a potent dominant-negative antagonist. The relative concentrations of beta3 and Deltabeta3 mRNAs vary between tissues and with changes in thyroid status, indicating that alternative splicing is tissue specific and T(3) regulated. These data provide novel insights into the mechanisms of T(3) action and define a new level of specificity that may regulate thyroid status in tissue.

Genetic analysis reveals different functions for the products of the thyroid hormone receptor alpha locus.

Thyroid hormone receptors are encoded by the TRalpha (NR1A1) and TRbeta (NR1A2) loci. These genes are transcribed into multiple variants whose functions are unclear. Analysis by gene inactivation in mice has provided new insights into the functional complexity of these products. Different strategies designed to modify the TRalpha locus have led to strikingly different phenotypes. In order to analyze the molecular basis for these alterations, we generated mice devoid of all known isoforms produced from the TRalpha locus (TRalpha(0/0)). These mice are viable and exhibit reduced linear growth, bone maturation delay, moderate hypothermia, and reduced thickness of the intestinal mucosa. Compounding TRalpha(0) and TRbeta(-) mutations produces viable TRalpha(0/0)beta(-/-) mice, which display a more severe linear growth reduction and a more profound hypothermia as well as impaired hearing. A striking phenotypic difference is observed between TRalpha(0/0) and the previously described TRalpha(-/-) mice, which retain truncated TRDeltaalpha isoforms arising from a newly described promoter in intron 7. The lethality and severe impairment of the intestinal maturation in TRalpha(-/-) mice are rescued in TRalpha(0/0) animals. We demonstrate that the TRDeltaalpha protein isoforms, which are natural products of the TRalpha locus, are the key determinants of these phenotypical differences. These data reveal the functional importance of the non-T3-binding variants encoded by the TRalpha locus in vertebrate postnatal development and homeostasis.

Thyroid Stimulating Hormone Suppression in the Long-term Follow-up of Differentiated Thyroid Cancer.

Differentiated thyroid cancer is the most common form of thyroid cancer and its prognosis is favourable in most cases. Suppression of thyroid stimulating hormone (TSH) by supra-physiological thyroid hormone replacement has been the mainstay of long-term management for over 60 years. However, evidence for a beneficial outcome of TSH suppression is conflicting and intervention must be balanced against adverse effects, particularly affecting the cardiovascular system and skeleton. Here we discuss the role of TSH suppression in the long-term management of differentiated thyroid cancer in the context of risk stratification for disease recurrence and the latest clinical guidelines.

Thyroid hormone regulates heparan sulfate proteoglycan expression in the growth plate.

Thyroid hormone is essential for normal skeletal development. Hypothyroidism is associated with growth arrest, failure of chondrocyte differentiation, and abnormal matrix synthesis. Thyroid hormone modulates the Indian hedgehog/PTHrP feedback loop and regulates fibroblast growth factor (FGF)/FGF receptor signaling. Because heparan sulfate (HS) proteoglycans (Prgs) (HSPGs) are absolutely required by these signaling pathways, we have investigated whether thyroid status affects HSPG expression within the growth plate. Tibial growth plate sections were obtained from 12-wk-old rats rendered euthyroid, thyrotoxic, or hypothyroid at 6 wk of age, 14-d-old congenitally hypothyroid Pax8-null mice, and TRalpha/TRbeta double-null mice lacking all thyroid hormone receptors. HS and chondroitin sulfate Prg expression was determined by immunohistochemistry using three monoclonal antibodies. There was increased HS staining in growth plates from hypothyroid animals predominantly within the extracellular matrix of reserve and proliferative zones. Cellular HS staining was also increased particularly in prehypertrophic chondrocytes. T3 regulation of HSPG core protein and HS synthetic and modification enzyme expression was studied in ATDC5 cells using semiquantitative RT-PCR. Thyroid hormone negatively regulated expression of the core protein Gpc6, the polymerase Ext1, and the modification enzyme Hs6st2. These studies demonstrate that the expression and distribution of growth plate Prgs are regulated by thyroid hormone, and the regulation of HSPG expression provides an important additional link between FGF and Indian hedgehog signaling and T3. These novel observations suggest that the cartilage matrix and especially HSPGs are critical mediators of the skeletal response to thyroid hormone.

Antiproliferative responses to two human colon cancer cell lines to vitamin D3 are differently modified by 9-cis-retinoic acid.

1 alpha,25-Dihydroxyvitamin D3 [1,25(OH)2D3] exerts antiproliferative actions in colorectal cancer, but their underlying molecular mechanisms have not been determined. 1,25(OH)2D3 regulates target gene transcription via a specific nuclear vitamin D receptor (VDR), which mediates hormone action preferentially as a heterodimer with 9-cis-retinoic acid receptors (RXRs). We investigated the actions of 1,25(OH)2D3 and 9-cis-retinoic acid (RA) in two human colon cancer cell lines, HT-29 and Caco-2. Both expressed mRNAs encoding VDR, RXR alpha, and RXR gamma, and VDR was regulated posttranscriptionally in Caco-2 cells. There was an antiproliferative response of both cell lines to 1,25(OH)2D3. 9-cis-RA exerted antiproliferative effects on Caco-2 cells but blocked 1,25(OH)2D3 actions in HT-29 cells. The 1,25(OH)2D3-responsive gene 25-hydroxyvitamin D3 24-hydroxylase was induced in both cell lines b 1,25(OH)2D3 but in only HT-29 cells by 9-cis-RA. 1,25(OH)2D3 and 9-cis-RA cotreatment enhanced 24-hydroxylase expression in HT-29 cells only. The 24-hydroxylase enzyme is known to result in catabolism of 1,25(OH)2D3 and attenuation of its actions. Increased 24-hydroxylase activity in HT-29 cells, but not in Caco-2 cells, in response to 9-cis-RA may account for some of the complex cell-specific responses demonstrated in these studies.