Identification and characterization of a hepatoma cell-specific enhancer in the mouse multidrug resistance mdr1b promoter

Immunotherapy of hepatocellular carcinoma: Unique challenges and clinical opportunities

Current therapies for advanced hepatocellular carcinoma (HCC) are marginally effective and exacerbate underlying liver disease. The ability of immunotherapy to elicit nontoxic, systemic, long-lived anti-tumor activity makes it particularly well-suited for use in the setting of HCC. While therapeutic benefit has been achieved in early clinical trials, the efficacy of immune-based therapies is limited by several unique properties of HCC, most notably the inherently tolerogenic character of the liver in both healthy and diseased (chronically-infected or tumor-bearing) states. Therapeutic regimens that both counteract these immunosuppressive mechanisms and amplify tumor-specific immunity are expected to profoundly improve clinical outcomes for HCC patients.

Immunotherapy of hepatocellular carcinoma: Unique challenges and clinical opportunities

Current therapies for advanced hepatocellular carcinoma (HCC) are marginally effective and exacerbate underlying liver disease. The ability of immunotherapy to elicit nontoxic, systemic, long-lived anti-tumor activity makes it particularly well-suited for use in the setting of HCC. While therapeutic benefit has been achieved in early clinical trials, the efficacy of immune-based therapies is limited by several unique properties of HCC, most notably the inherently tolerogenic character of the liver in both healthy and diseased (chronically-infected or tumor-bearing) states. Therapeutic regimens that both counteract these immunosuppressive mechanisms and amplify tumor-specific immunity are expected to profoundly improve clinical outcomes for HCC patients.

Multiple courses of immunotherapy with different immune cell types for patients with hepatocellular carcinoma after microwave ablation

The aim of the present study was to investigate the therapeutic efficacy of immunotherapy after microwave ablation (MWA), which was used to improve liver function, reduce the recurrence rate and enhance survival period in patients with hepatocellular carcinoma (HCC). Between February 2009 and December 2010, 14 patients received immunotherapy after MWA (immunotherapy group) and 15 patients received MWA alone with no post-ablated adjuvant therapy (control group). Immune and liver parameters, recurrence rate and survival time were recorded. The absolute lymphocyte count in the immunotherapy group exceeded that in the control group after 3 courses of immunotherapy (P<0.05). No significant differences were detected in the lymphocyte subset distribution in the control and immunotherapy patients prior to ablation (P>0.05); however, certain cytotoxic subsets (CD3⁺/CD8⁺, CD8⁺CD28⁺ and CD3⁺CD16⁺CD56⁺ T cells) were over-represented and negative regulatory or helper subsets (CD4⁺CD8⁺, CD4⁺, CD4⁺CD25⁺) were under-represented in the immunotherapy group between 1 and 12 months after immunotherapy (P<0.05). After 2 courses of immunotherapy the proliferation rate of myeloid dendritic cells and T lymphocytes, including CD3⁺/CD8⁺ lymphocytes, significantly increased (P<0.05 and P<0.01, respectively). In addition, the level of albumin in the immunotherapy group exceeded that in the control group after 3 courses of immunotherapy (P<0.05). However, the rate of disease-free survival and overall survival within 16 months of MWA did not differ significantly between the two groups (P>0.05). In conclusion, the results of the present study indicate that immunotherapy improves the immune status and liver function of patients with HCC.

Alpha fetoprotein DNA prime and adenovirus boost immunization of two hepatocellular cancer patients

Background

Alpha fetoprotein (AFP) is an oncofetal antigen over-expressed by many hepatocellular cancers (HCC). We previously demonstrated that HLA-A2-restricted epitopes derived from AFP are immunogenic in vitro and in vivo despite high circulating levels of this oncofetal antigen. In order to test a more broadly applicable, HLA-unrestricted, inexpensive, cell-free vaccine platform capable of activating tumor antigen-specific CD8⁺ and CD4⁺ T cells, we tested full length AFP in a plasmid DNA construct in combination with an AFP-expressing replication-deficient adenovirus (AdV) in a prime-boost vaccine strategy.

Methods

HCC patients who had an AFP⁺ tumor and previous treatment for HCC were screened and two patients received vaccination with three plasmid DNA injections followed by a single AdV injection, all delivered intramuscularly (i.m.).

Results

The vaccine was well tolerated and safe. Both patients showed immunologic evidence of immunization. The first patient had a weak AFP-specific T cell response, a strong AdV-specific cellular response and recurred with an AFP-expressing HCC at nine months. The second patient developed a strong AFP-specific CD8⁺ and CD4⁺ cellular response and an AdV neutralizing antibody response, and recurred at 18 months without an increase in serum AFP.

Conclusions

The AFP DNA prime-AdV boost vaccine was safe and immunogenic. Circulating anti-AdV neutralizing antibodies at baseline did not prohibit the development of AFP-specific cellular immunity. The patient who developed CD8⁺ and CD4⁺ AFP-specific T cell immunity had more favorable progression-free survival. The observations with these two patients support development of this vaccine strategy in a larger clinical trial.

Trial registration

ClinicalTrials.gov: NCT00093548

mRNA levels of related Abcb genes change opposite to each other upon histone deacetylase inhibition in drug-resistant rat hepatoma cells

The multidrug-resistant phenotype of tumor cells is acquired via an increased capability of drug efflux by ABC transporters and causes serious problems in cancer treatment. With the aim to uncover whether changes induced by epigenetic mechanisms in the expression level of drug transporter genes correlates with changes in the drug resistance phenotypes of resistant cells, we studied the expression of drug transporters in rat hepatoma cell lines. We found that of the three major rat ABC transporter genes Abcb1a, Abcb1b and Abcc1 the activity of only Abcb1b increased significantly in colchicine-selected, drug-resistant cells. Increased transporter expression in drug-resistant cells results primarily from transcriptional activation. A change in histone modification at the regulatory regions of the chromosomally adjacent Abcb1a and Abcb1b genes differentially affects the levels of corresponding mRNAs. Transcriptional up- and down-regulation accompany an increase in acetylation levels of histone H3 lysine 9 at the promoter regions of Abcb1b and Abcb1a, respectively. Drug efflux activity, however, does not follow tightly the transcriptional activity of drug transporter genes in hepatoma cells. Our results point out the need for careful analysis of cause-and-effect relationships between changes in histone modification, drug transporter expression and drug resistance phenotypes.

Absence or pharmacological blocking of placental P-glycoprotein profoundly increases fetal drug exposure

It was recently shown that naturally occurring Mdr1a mutant fetuses of the CF-1 outbred mouse stock have no placental Mdr1a P-glycoprotein (P-gp) and that this absence is associated with increased sensitivity to avermectin, a teratogenic pesticide. To further define the role of placental drug-transporting P-gp in toxicological protection of the fetus, we used mice with a targeted disruption of the Mdr1a and Mdr1b genes. Mdr1a(+/-)/1b(+/-) females were mated with Mdr1a(+/-)/1b(+/-) males to obtain fetuses of 3 genotypes (Mdr1a(+/+)/1b(+/+), Mdr1a(+/-)/1b(+/-), and Mdr 1a(-/-)/1b(-/-)) in a single mother. Intravenous administration of the P-gp substrate drugs [(3)H]digoxin, [(14)C]saquinavir, or paclitaxel to pregnant dams revealed that 2.4-, 7-, or 16-fold more drug, respectively, entered the Mdr1a(-/-)/1b(-/-) fetuses than entered wild-type fetuses. Furthermore, placental P-gp activity could be completely inhibited by oral administration of the P-gp blockers PSC833 or GG918 to heterozygous mothers. Our findings imply that the placental drug-transporting P-gp is of great importance in limiting the fetal penetration of various potentially harmful or therapeutic compounds and demonstrate that this P-gp function can be abolished by pharmacological means. The latter principle could be applied clinically to improve pharmacotherapy of the unborn child.

Regulation and expression of multidrug resistance (MDR) transcripts in the intestinal epithelium

A paucity of information exists on the regulation of gene expression in the undifferentiated intestine. The intestinal epithelium is one of the few normal tissues expressing the multidrug resistance (MDR) genes that confer the multidrug resistant phenotype to a variety of tumours. Expression of mdr1a has been observed in the primitive rat intestinal epithelial cell line, IEC-18. It is hypothesized that characterization of MDR gene expression in IEC-18 cells will provide insight into gene regulation in undifferentiated intestinal cells. A series of hamster mdr1a promoter deletion constructs was studied in IEC-18 and a region with 12-13-fold enhancer activity was identified. This region was shown to function in an orientation- and promoter context-independent manner, specifically in IEC-18 cells. Unexpectedly, Northern probing revealed a greater expression of mdr1b than mdr1a in IEC-18 cells. A quantitative reverse transcription polymerase chain reaction assay was used to compare the relative expression of MDR genes in IEC cells, fetal intestine, and in the undifferentiated and differentiated components of adult intestinal epithelium. MDR transcript levels in IEC cells were found to resemble those of fetal intestine and small intestinal crypts, where a conversion from mixed mdr1a/mdr1b to predominantly mdr1a expression occurs as cells mature. This work describes two contributions to the field of gene regulation in the undifferentiated intestine--first, the initial characterization of a putative mdr1a enhancer region with specificity for primitive intestinal cells and secondly, the first report of mdr1b detection in the intestine and its expression in primitive cell types.

The multidrug resistance-associated protein (MRP) is over-expressed and functional in rat hepatoma cells

Expression of multidrug-resistance-associated protein (MRP), a drug efflux pump transporting a wide range of xenobiotics, including anti-cancer drugs and chemical carcinogens, and present at low levels in normal hepatocytes, was investigated in rat hepatoma cells. Northern-blot analysis allowed detection of high levels of MRP mRNA in rat diethylnitrosamine-induced hepatocarcinomas when compared with normal liver. Similarly, elevated expression of MRP transcripts were evidenced in 6 rat hepatoma cell lines of different origins, especially in HTC cells, that, in contrast, failed to express mRNA of the canalicular multispecific organic anion transporter (cMOAT), an efflux pump sharing numerous substrates with MRP. HTC cells were also found by Western blotting to display much higher amounts of MRP than those observed in normal hepatocytes. In contrast, the MRP gene copy number was similar both in hepatoma HTC cells and in hepatocytes, as assessed by Southern blotting. Analysis of MRP-related transport using 3 types of MRP substrates, namely, the fluorescent glutathione-bimane, the anionic dye calcein and the cationic anti-cancer drug vincristine, demonstrated that HTC cells displayed cellular efflux of these 3 compounds, an efflux strongly inhibited by MRP modulators such as indomethacin. These results indicate that MRP is over-expressed and functional in rat hepatoma cells and may therefore be included in the de-toxifying pathways that are altered during hepatocarcinogenesis and are thus thought to contribute to the known multidrug resistance of liver tumors.

Increased P-glycoprotein messenger RNA stability in rat liver tumors in vivo

P-glycoproteins (Pgp) are comprised of a small family of plasma membrane proteins whose abundance in cultured cells is often associated with the multidrug resistance phenotype. Overexpression of Pgp has been observed in many types of human cancers, but the molecular basis for this overexpression has not been established. We have used primary monolayer cultures of adult rat hepatocytes and a stepwise model of rat liver carcinogenesis to study the regulation of Pgp gene expression. We observed a marked overexpression of Pgp, specifically the class II Pgp, in both systems. In addition, we observed that a number of unrelated genes including alpha-tubulin, beta-actin, gamma-actin, cytokeratin 8, cytokeratin 18, and c-myc are overexpressed in cultured hepatocytes, and they are also overexpressed during liver carcinogenesis and in transplantable tumors. Nuclear run-on assays showed no increase in the transcriptional activity of Pgp genes in transplantable liver tumors compared to normal liver. Studies of in vivo mRNA stability, however, revealed that all three Pgp mRNAs were relatively stable in transplantable liver tumors (t(1/2) > 12 h), in contrast to what was found in normal liver (t(1/2) < 2 h). In addition, mRNA for several other genes, including alpha-tubulin, c-myc, and cyclin D1, all appear to be stabilized in the tumors. These findings suggest that the overexpression of Pgp genes in rat liver tumors may be the result of a mechanism involving stabilization of a diverse group of mRNAs.

Transcriptional regulation of MDR genes

The emergence of resistance in a tumor population is most often associated with a disregulation of gene expression, usually at the level of transcription. A major goal in the field of cancer chemotherapy is to define the mechanisms underlying transcriptional regulation of drug resistance genes in an effort to identify targets for therapeutic intervention. Recently, considerable progress has been made in identifying the molecular mechanisms involved in the transcriptional regulation of the P-glycoprotein (Pgp) gene. When overexpressed in tumor cells, Pgp confers resistance to a variety of chemotherapeutic agents; this resistance has been termed MDR (multidrug resistance). Moreover, Pgp is a normal component of a variety of highly differentiated cell types and, as such, is regulated by both internal and external environmental stimuli. In this review, we will discuss the current knowledge regarding the DNA elements and protein factors involved in both constitutive and inducible regulation of Pgp transcription in normal and tumor cells.

Wild-type p53-mediated induction of rat mdr1b expression by the anticancer drug daunorubicin

The expression of P-glycoproteins encoded by the mdr gene family is associated with the emergence of the multidrug resistance phenotype in animal cells. mdr expression can be induced by many extracellular stimulants including cytotoxic drugs and chemical carcinogens. However, little is known about the mechanisms involved. Here, we report that the expression of the rat mdr1b can be induced by anticancer drug daunorubicin. Further analysis identified a bona fide p53-binding site spanning from base pairs -199 to -180 (5'-GAACATGTAGAGACATGTCT-3') in the rat mdr1b promoter that is essential for basal and daunorubicin-inducible promoter activities. In addition, our results show that wild-type p53 can up-regulate not only the promoter function but also endogenous expression of the rat mdr1b. To the best of our knowledge, this is the first report showing that a specific p53-binding site is involved in the transcriptional regulation of mdr gene by wild-type p53. Since p53 is a sensor for a wide variety of genotoxic stresses, our finding has broad implications for understanding the mechanisms involved in the inducible expression of mdr gene by anticancer drugs, chemical carcinogens, UV light, and other DNA-damaging agents.

Biochemical, genetic, and metabolic adaptations of tumor cells that express the typical multidrug-resistance phenotype. Reversion by new therapies

Among the genetic and metabolic alterations that cancer cells undergo, several allow their survival under extreme environmental conditions. The resulting aberrant metabolism is compatible with tumor progression at the expenses of high energy needs, especially for maintaining high division rate. When treated with chemotherapeutic drugs many cancer cells take advantage of their ability to develop a resistance phenotype, as part of an adaptative mechanism. Two main actors of this multidrug phenotype (MDR) are represented by the P-glycoprotein and by the more recently discovered multidrug-resistance associated protein (MRP), two membrane proteins of the ABC superfamily of transporters that can extrude chemotherapeutic drugs under an ATP-dependent mechanism. We will briefly review the major metabolic aberrations that several cancers develop, followed by the molecular, genetic, structural, and functional aspects related mainly to P-glycoprotein, with a concern for the regulation of mdr gene expression. We will point out the role that membrane cholesterol may play in the MDR phenotype, relate this phenotype to bioenergetic considerations, and review the ways of modulating it by the use of new therapeutic approaches.