Decreased hepatic drug metabolising enzyme activity in rats with nitrosamine-induced tumours

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

Drug metabolism by tumours: its nature, relevance and therapeutic implications

Drug-metabolising enzymes (DMEs) are present in tumours and are capable of biotransforming a variety of antineoplastics. Tumoural drug metabolism is both a potential mechanism of resistance and a means of achieving optimal therapy. This review addresses the classes of DMEs, their cytotoxic substrates and distribution in specific malignancies. The limitations of preclinical and clinical studies are highlighted. Their role in predicting therapeutic response, the activation of prodrugs and the potential for their modulation for gain is also addressed. The contribution of tumoural DMEs to cancer therapy can only be ascertained through large prospective studies and supported by new technologies. Only then can efforts be concentrated in the design of better prodrugs or combination therapy to optimise individual therapy.

Effect of Solanum trilobatum on hepatic drug metabolising enzymes during diethylnitrosamine-induced hepatocarcinogenesis promoted by Phenobarbital in rat

The present study was aimed to investigate the chemopreventive effects of Solanum trilobatum (ST) extract against diethylnitrosamine (DEN)-induced hepatocarcinogenesis promoted by Phenobarbital (PB) in Wistar rats. Hepatocarcinogenesis was initiated by a single intraperitoneal injection of DEN (200 mg/kg b.w.) and promoted with PB (0.05%) in basal diet. The experimental study extended for periods of 13 and 26 weeks. Alcoholic extract of ST was orally administered for the entire experimental period after initiation along with commencement of promotion. The chemopreventive effect of ST was assessed from the incidence of nodules, drug metabolizing phase I components such as contents of cytochrome P450, cytochrome b(5), activities of NADPH cytochrome c reductase, NADH - cytochrome b(5) reductase and phase II components such as levels of glutathione, activities of UDP-glucuronyl transferase, glutathione S-transferase and gamma-glutamyl transpeptidase in the liver. Lipid peroxidation at basal and prooxidants-induced (NADPH + ADP + Fe and Ascorbate + Fe) states was assessed in the microsomes. Animals administered with ST extract evidenced significant inhibition of tumor nodular incidence in DEN + PB + ST animals compared to DEN + PB animals, with favorable alterations in the hepatic drug-metabolizing phase I and phase II components. Administration of ST inhibited basal and pro-oxidant-induced lipid peroxidation. The present result suggests the probable mediation of chemoprevention by ST against DEN-induced carcinogenesis by the modulation of drug metabolizing components in the liver of treated animals.

Is nuclear factor kappa-B the missing link between inflammation, cancer and alteration in hepatic drug metabolism in patients with cancer?

In the last few years, several studies have provided a causal link between constitutive activation of nuclear factor kappa-B (NF-kappaB) and the initiation and development of cancer. More recently, it appears that a cancer-induced inflammatory response may be an important factor in the inter-individual variability of the response to and toxic effects of cancer chemotherapy, as well as in the alteration of drug metabolism enzyme expression in patients. The relationships between chronic inflammation (or infection), cancer and drug metabolism are many: chronic infections lead to inflammation, inflammation may lead to cancer, cancer usually leads to an inflammatory syndrome, and inflammation alters the expression of drug metabolising enzymes and thus of the efficiency of cancer chemotherapy. This review focuses on the functional consequences of NF-kappaB activation during oncogenesis and on the expression of the major cytochrome P450s (CYP) involved in anticancer therapies. Finally, the potential role of NF-kappaB as the missing link between inflammation, cancer and alteration in hepatic drug metabolism in patients with cancer is discussed.

Altered expression of cytochrome P450 and possible correlation with preneoplastic changes in early stage of rat hepatocarcinogenesis

AIM

Correlation of cytochrome P450 (CYPs) with preneoplastic changes in the early stage of hepatocarcinogenesis is still unclear. To detect the expression of carcinogen-metabolizing related microsomal P450 enzymes, namely the CYP1A1, CYP1A2, CYP2B1/2, CYP2E1, and CYP3A, we performed the medium-term bioassay of Ito's model in Sprague-Dawley rats.

METHODS

The amount and activity of CYP were assessed by biochemical and immunohistochemical methods in week 8. The correlation between CYP expression and microsomal oxidative stress was investigated by comparing the generation of microsomal lipid peroxidation in the presence or absence of specific CYP inhibitor.

RESULTS

In the DEN-2-AAF and 2-AAF alone groups, the expression of CYP1A1 and CYP2E1 were up-regulated and the expression of CYP2B1/2 and CYP1A2 were quite the contrary. Strong staining of CYP2E1 and CYP2B1/2 was found around the centrolobular vein and weak staining in the altered hepatic foci revealed by immunohistochemical procedure. There was no significant change in the activity of CYP3A among the 4 groups. Altered hepatic tissue bore more microsomal NADPH (nicotinamide adenine dinucleotide phosphate,reduced form)-dependent lipid peroxidation than normal tissue. And the difference among the 4 groups disappeared when CYP2E1 was inhibited. More microsomal lipid peroxidation was generated when incubated with CYP1A inhibitor a-naphthoflavone.

CONCLUSION

CYP altered their expression levels and these alterations can play important roles in the alteration of cell redox status of preneoplastic tissue in the early stage of hepatocarcinogenesis.

Phase I/II enzyme gene polymorphisms and esophageal cancer risk: A meta-analysis of the literature

AIM: Phase I/II enzymes metabolize environmental carcin-ogens and several functional polymorphisms have been reported in their encoding genes. Although their significance with regard to esophageal carcinogenicity has been examined epidemiologically, it remains controversial. The present systematic review of the literature was performed to clarify associations.

METHODS: Eligible studies were case-control or cohort studies published until September 2004 that were written in any language. From PubMed and a manual review of refe-rence lists in relevant review articles, we obtained 16 studies related to the CYP1A1 Ile-Val substitution in exon 7, CYP1A1 MspI polymorphisms, CYP2E1 RsaI polymorphisms, GSTM1 null type, GSTT1 null type and GSTP1 Ile104Val. All were of case-control design. Summary statistics were odds ratios (ORs) comparing heterozygous-, homozygous-non-wild type or these two in combination with the homozygous wild type, or the null type with the non-null type for GSTM1 and GSTT1. A random effect model was used to estimate the summary ORs. A meta-regression analysis was applied to explore sources of heterogeneity.

RESULTS: Individuals with the Ile-Val substitution in CYP1A1 exon 7 had increased esophageal cancer risk, with ORs (95%CI) compared with Ile/Ile of 1.37 (1.09-1.71), 2.52 (1.62-3.91) and 1.44 (1.17-1.78) for Ile-Val, Val/Val genotype and the combined group. No significant association was found between esophageal cancer risk and the other genetic parameters.

CONCLUSION: A significant association exists between the CYP1A1 Ile-Val polymorphism and risk of esophageal cancer. Polymorphisms that increase the internal exposure to activated carcinogens may increase the risk of esophageal cancer.

Tumoral drug metabolism: overview and its implications for cancer therapy

Drug-metabolizing enzymes (DME) in tumors are capable of biotransforming a variety of xenobiotics, including antineoplastics, resulting in either their activation or detoxification. Many studies have reported the presence of DME in tumors; however, heterogeneous detection methodology and patient cohorts have not generated consistent, firm data. Nevertheless, various gene therapy approaches and oral prodrugs have been devised, taking advantage of tumoral DME. With the need to target and individualize anticancer therapies, tumoral processes such as drug metabolism must be considered as both a potential mechanism of resistance to therapy and a potential means of achieving optimal therapy. This review discusses cytotoxic drug metabolism by tumors, through addressing the classes of the individual DME, their relevant substrates, and their distribution in specific malignancies. The limitations of preclinical models relative to the clinical setting and lack of data on the changes of DME with disease progression and host response will be discussed. The therapeutic implications of tumoral drug metabolism will be addressed-in particular, the role of DME in predicting therapeutic response, the activation of prodrugs, and the potential for modulation of their activity for gain are considered, with relevant clinical examples. The contribution of tumoral drug metabolism to cancer therapy can only be truly ascertained through large-scale prospective studies and supported by new technologies for tumor sampling and genetic analysis such as microarrays. Only then can efforts be concentrated in the design of better prodrugs or combination therapy to improve drug efficacy and individualize therapy.

Amelioration of immune cell number depletion and potentiation of depressed detoxification system of tumor-bearing mice by curcumin

BACKGROUND

The true therapeutic benefit of the use of natural products, especially acceptable dietary components such as curcumin, which can spare the normal cells and boost host immunity, has opened new horizons in cancer prevention and treatment.

METHODS

In our model system we used Ehrlich's ascites carcinoma cells grown in peritoneal carity of Swiss albino mice and curcumin was fed every alternative day.

RESULTS

Here, we report that curcumin administration to tumor-bearing mice decreased tumor cell number significantly in a dose-dependent manner. Furthermore, tumor-induced depletion of immune cell number of the host, as was evidenced from the decrease in bone marrow progenitor as well as thymic and splenic mononuclear cell numbers, was reintrated by curcumin. In fact, curcumin inhibited tumor-induced apoptosis of both thymocytes and splenocytes thereby restoring immune cell numbers to normal level in treated Ehrlich's ascites carcinoma-bearing mice. Moreover, curcumin was not toxic to the host; rather in tumor-bearing mice it inhibited hematopoietic toxicity, acted as a hepatoprotective agent and activated depressed anti-oxidant and detoxification systems.

CONCLUSION

The ability of curcumin to regress tumor as well as to protect the host from tumor-induced immunosuppression and toxicity strongly supports the candidacy of curcumin as a potential agent for the dietary therapy of cancer.