Teratogen metabolism: spontaneous decay products of thalidomide and thalidomide analogues are not bioactivated by liver microsomes

Thalidomide and lenalidomide for recurrent ovarian cancer: A systematic review of the literature

The present review aimed to assess the safety and efficacy of thalidomide and lenalidomide, two immunomodulatory drugs with anti-angiogenic properties, in women with recurrent ovarian, fallopian tube, and primary peritoneal cancer. A systematic review of the literature was conducted whereby Medline and the Cochrane Central Register of Controlled Trials were searched using terms associated with thalidomide, lenalidomide, and recurrent ovarian, fallopian tube and primary peritoneal cancer. Published English language case reports, trials and studies that described the safety and efficacy of thalidomide or lenalidomide alone, or in combination with other drugs were reviewed. A total of 16 clinical studies involving 394 patients treated with thalidomide (n=188), lenalidomide (n=77) and 129 controls were identified, including five case reports (n=6), three case series (n=45), two phase I trials (n=27), four phase II trials (n=109), and two randomized phase III trials (n=207). In a pooled analysis of thalidomide investigated as a single drug, the overall clinical benefit rate was 43% (43/99) with a mean time to progression of 5.6 months. The response rate (complete response + partial response) was 25%. In a phase III trial, the combination of thalidomide and topotecan significantly increased the overall response rate compared with topotecan alone [14/30 (47%) vs. 8/39 (21%)]. In another phase III trial involving women with asymptomatic biochemical recurrence, compared with tamoxifen, thalidomide was not more effective. Lenalidomide was investigated in three phase I trials and in one phase II trial with an overall clinical benefit rate of 52% (34/65), and a mean time to progression of 4.6 months. The response rate (complete response + partial response) was 6%. Systemic toxicity of both drugs was noted in >77% of patients with pneumonitis/pneumonia, fatigue, neuropathy and venous thromboembolism reported as the most common side effects. Thalidomide and lenalidomide are moderately active in recurrent ovarian cancer. Thalidomide possesses synergistic effects with topotecan. The toxicity of both drugs is considerable and there is a greater amount of data available for thalidomide compared to lenalidomide.

A pharmacogenetic study of docetaxel and thalidomide in patients with castration-resistant prostate cancer using the DMET genotyping platform

The anticancer agent docetaxel shows significant inter-individual variation in its pharmacokinetic and toxicity profile. Thalidomide is an active anticancer agent and also shows wide pharmacological variation. Past pharmacogenetic research has not explained this variation. Patients with prostate cancer enrolled in a randomized phase II trial using docetaxel and thalidomide versus docetaxel alone were genotyped using the Affymetrix DMET 1.0 platform, which tests for 1256 genetic variations in 170 drug disposition genes. Genetic polymorphisms were analyzed for associations with clinical response and toxicity. In all, 10 single-nucleotide polymorphisms (SNPs) in three genes were potentially associated with response to therapy: peroxisome proliferator-activated receptor-delta (PPAR-delta), sulfotransferase family, cytosolic, 1C, member 2 (SULT1C2) and carbohydrate (chondroitin 6) sulfotransferase 3 (CHST3). In addition, 11 SNPs in eight genes were associated with toxicities to treatment: spastic paraplegia 7 (pure and complicated autosomal recessive) (SPG7), CHST3, cytochrome P450, family 2, subfamily D, polypeptide 6 (CYP2D6), N-acetyltransferase 2 (arylamine N-acetyltransferase) (NAT2), ATP-binding cassette, sub-family C (CFTR/MRP), member 6 (ABCC6), ATPase, Cu++ transporting, alpha polypeptide (ATP7A), cytochrome P450, family 4, subfamily B, polypeptide 1 (CYP4B1) and solute carrier family 10 (sodium/bile acid cotransporter family), member 2 (SLC10A2). Genotyping results between drug metabolizing enzymes and transporters (DMET) and direct sequencing showed >96% of concordance. These findings highlight the role that non-CYP450 metabolizing enzymes and transporters may have in the pharmacology of docetaxel and thalidomide.

Inhibition of 13-cis retinoic acid-induced gene expression of homeobox B7 by thalidomide

Thalidomide and 13-cis retinoic acid (RA) show anticancer effects as sole agents or in combination with other drugs. However, induction of homeobox (HOX) gene expression by 13-cis RA may contribute to tumor progression thereby potentially limiting its efficacy. The purpose was to test if thalidomide can inhibit 13-cis RA-induced HOXB7 expression and whether thalidomide may enhance the antiproliferative effect of 13-cis RA in U343MG glioblastoma cells. Quantitative real-time PCR showed significant inhibition of 13-cis RA-induced HOXB7 expression by thalidomide with IC(50) approximately 0.1-0.2 microg/ml when given simultaneously with 13-cis RA but not when administered 18 h later (p < 0.0001). 13-cis RA alone inhibited proliferation and colony formation in a concentration-dependent manner whereas growth inhibition by thalidomide alone at 5-100 microg/ml was constant at 80-90% of controls. At 10% serum concentration, growth inhibition by a combination of the 2 drugs was additive but at 1% serum, growth inhibition was synergistic. It is concluded that thalidomide inhibits the RA-induced HOXB7 expression in glioblastoma cells and that 13-cis RA/thalidomide combinations can in principle enhance cytotoxicity. The improved cell kill induced by thalidomide is attributed to downregulation of growth stimulatory factors induced by 13-cis RA. Implications for the modus operandi of thalidomide in embryogenesis are noted.

Current status of thalidomide and its role in the treatment of metastatic prostate cancer

Following the discovery of its anti-angiogenic properties and despite its tragic history, thalidomide has re-surfaced in the field of oncology. Concurrent with its evaluation in various clinical trials for cancer, thalidomide's mechanism of action is sought and new analogues with improved efficacy and pharmacological profile are emerging. This review is a critical evaluation of thalidomide metabolism, molecular targets, anti-angiogenic activity and clinical efficacy with an emphasis on metastatic prostate cancer.

5'-OH-thalidomide, a metabolite of thalidomide, inhibits angiogenesis

Despite its known teratogenic effects, thalidomide has been used to treat a variety of diseases ranging from alleviation of autoimmune disorders to prevention of metastasis of cancers. The exact method of action of thalidomide and its derivatives is still under investigation. Thalidomide undergoes very little metabolism by the cytochrome P 450 system in vitro, but at least two hydroxylated metabolites have been found in humans. The two metabolites are 5-hydroxythalidomide, formed by hydroxylation of the phthalimide ring, possibly via arene oxides, and 5'-hydroxythalidomide, formed by hydroxylation of the glutarimide ring, leading to diastereomeric products. These two metabolites, along with another minor metabolite of thalidomide, were tested in a rat aortic ring assay, a human saphenous vein model, and a tube formation assay to assess the metabolite's ability to inhibit angiogenesis. Of the metabolites tested, only 5'-OH-thalidomide showed biologic activity in the rat aortic ring assay, and none of the metabolites showed activity in the human model. The studies with thalidomide and thalidomide metabolites underline the difficulty and complexity of trying to isolate and evaluate a single biologically active agent. These studies, however, do suggest that at least one metabolite, 5'-OH-thalidomide, has moderate antiangiogenic activity at high concentrations. Unfortunately, because of the lack of observed activity of 5'-OH-thalidomide in the human saphenous vein assay, it remains unclear whether there is species specificity for the activity of this metabolite.

Evaluation of the developmental toxicity of thalidomide using frog embryo teratogenesis assay-xenopus (FETAX): biotransformation and detoxification

The developmental toxicity of thalidomide was evaluated using FETAX (Frog Embryo Teratogenesis Assay - Xenopus). Young X. Laevis embryos were exposed to this compound in each of two concentration-response experiments with and without differently induced exogenous metabolic activation systems (MASs) and/or inhibited MASs. Young male Sprague-Dawley rats were treated with either isoniazid or Aroclor 1254 to induce cytochrome P-450. Several of the rats were subsequently treated with diethyl maleate (DM) to deplete glutathione reserves. Specific aliquots of rat liver microsomes were treated with 3-amino-1,2,4-triazole (ATZ) or alpha-napthoflavone (alpha-N) to selectively inhibit P-450 activity. Bioactivation was indicated by increased developmental toxicity observed in MAS tests. Results obtained indicated that thalidomide was predominantly activated by P-450 isozyne CYP2E1, although weak cross-specificity between CYP1A1/A2 may have existed. Detoxification pathways for thalidomide were investigated by treatment of the MAS with cyclohexene oxide (CHO) and DM to inhibit the epoxide hydrolase and glutathione conjugation pathways, respectively. Results indicated that epoxide hydrolase was primarily responsible for the detoxification of bioactivated thalidomide. Teratogenesis Carcinog. Mutagen. 20:35-47, 2000.

Hydroxylated metabolites of thalidomide: formation in-vitro and in-vivo in man

There is renewed interest in the clinical use of thalidomide, because of its unique immunomodulating action. Because data on the metabolism of thalidomide in man are very sparse, the aim of this study was to develop HPLC assays for the 5-hydroxy, 5,6-dihydroxy, 4,5-dihydroxy and 5'-hydroxy metabolites of thalidomide and to investigate their possible formation in man-in-vitro in liver homogenates and in-vivo in healthy volunteers. Reversed-phase HPLC assays with UV detection were developed for quantification of the metabolites in the low ng mL(-1) range in plasma and incubate samples. The stability of the metabolites was investigated and degradation was avoided by rapid chilling and acidification of the samples. After incubation of thalidomide with fraction S9 from human liver, formation of the 5-hydroxy and 5'-hydroxy metabolites could be demonstrated. The 5'-hydroxy metabolite was found, in low concentrations, in plasma samples from eight healthy male volunteers who had received thalidomide orally. The other three metabolites could not be found by HPLC with detection limits of 1-2 ng mL(-1). Thus the formation of two hydroxylated metabolites of thalidomide in the liver in man was demonstrated, but only one of these could be detected in the circulation.

Stimulation of gap junctional intercellular communication by thalidomide and thalidomide analogs in human skin fibroblasts

It has been speculated that gap junctional intercellular communication (GJIC), an intercellular signalling pathway, is involved in embryogenesis by coupling compartments of the same developmental potential. We found that thalidomide induces GJIC in human fibroblasts after activation by liver microsomes in concentrations as low as 10(-7) M. Treatment of cells with the thalidomide analog EM-12 increased GJIC without prior activation. No alteration of GJIC was detected with phthalimide and glutamate, the components of thalidomide. However, 2-phthalimido glutaric acid (PGA), a hydrolysis product of thalidomide, stimulated GJIC without activation at concentrations between 10(-10) M and 10(-5) M. We suggest modification of GJIC as a biochemical mechanism responsible for pharmacological and toxicological properties of thalidomide and related compounds.

The thalidomide analog, EM 12, enhances 1,2-dimethylhydrazine-induction of rat colon adenocarcinomas

Young male Sprague-Dawley rats in 3 groups were fed a basal diet supplemented with 0.10 wt. % each of thalidomide and its imide-analog of much higher teratogenicity, EM 12. Following an induction period of 17 days on the diets, all animals were injected subcutaneously with 1,2-dimethylhydrazine at 20 mg/kg for a total of 20 weekly doses and killed on week 18 after the 20th injection. The total number of colon adenocarcinomas and their occurrence in the proximal and distal portions for the thalidomide-treated rats were similar to those of the respective controls. However, the EM 12-fed group elicited statistically significant increases both in the total and ascending colon-based adenocarcinomas as compared with the control findings, in keeping with its greater teratogenicity and embryotoxicity. The numbers of small intestinal adenocarcinomas were equally higher in the imide-fed groups in contrast to the control frequency.

Teratologic studies on the Himalayan rabbit: new aspects of thalidomide-induced teratogenesis

The aim of our study was to determine the period of maximum sensitivity for the induction of characteristic malformations with thalidomide (TH) in Himalayan rabbits. TH was administered orally in different doses (50, 100, 150 and 200 mg/kg) four times at 24-h intervals starting at 192 h of gestation. The malformations affected various organs: renal defects (dysplasia) and limb anomalies (dysmelia)--which had never occurred spontaneously in this strain--appeared as dose-dependent effects of the drug. By administering single doses of TH (200 and 300 mg/kg body wt) between hours 192 and 264 of gestation, we discovered the different periods of maximum sensitivity for induction of renal dysplasia (clearly prior to the 220th h of gestation) and dysmelia (between hours 230 and 240 of gestation). The types of limb malformations that we observed in the rabbit were identical to those produced in man following the intake of TH. Three doses of TH (300 mg/kg each) given between hours 222 and 228 of gestation produced characteristic limb malformations in 9 of 11 litters treated. These results make it possible to conduct in vivo experiments on a readily available laboratory animal with minor drug exposure of the gravid dam and under avoidance of toxic side effects.