The cytochrome P450 CYP1B1 is consistently overexpressed in tumour cells as compared to their normal counterparts, but its precise role in drug resistance is yet to be defined. It has been reported that transfection of CYP1B1 results in increased resistance to docetaxel in V79 cells (McFadyen et al, 2001). In this study, we analysed changes in expression of CYP1B1 mRNA associated with pulse selection of MCF-7 cells with docetaxel. Docetaxel-selected MCF-7 cells (MCF-7 Txt), which showed increased resistance to this drug as compared to parental MCF-7 cells, showed a noteworthy increase in CYP1B1 mRNA expression, paralleled by increased ethoxyresorufin-O-deethylase (EROD) activity levels. This effect was not observed in cisplatin-or adriamycin-selected MCF-7 cells, or in docetaxel-selected colon, lung or pancreatic carcinoma cells. Short-term treatment with docetaxel induced CYP1B1 mRNA expression in MDA 453 and BT-20 breast carcinoma cells, but not in MCF-7 cells. Transfection of MCF-7 Txt cells with CYP1B1 siRNA did not significantly affect docetaxel-induced toxicity, but it decreased cell survival in the absence of drug. Preincubation of docetaxel with recombinant CYP1B1 did not affect drug toxicity in A549 cells. These results suggest that CYP1B1 does not directly inactivate docetaxel, but rather might promote cell survival in MCF-7 Txt cells, providing an explanation for its association with drug resistance. British Journal of Cancer (2008) Breast cancer affects a significant number of women worldwide and is a leading cause of cancer deaths (Chintamani et al, 2004). Current therapies for breast cancer include locoregional (surgical) treatment, anti-hormone therapy, radiotherapy and chemotherapy (O'Driscoll and Clynes, 2006). Chemotherapeutic treatment of breast cancer, although of great importance in the management of the disease, has limited benefits for many patients due to intrinsic or acquired resistance to the effects of anticancer drugs. Moreover, chemoresistance is often associated with a more aggressive phenotype with an increased tendency to invade and metastasise (Campbell et al, 2001).Cytochromes P450 are a family of enzymes implicated in the biotransformation of both xenobiotics and endogenous compounds. Their primary functions are the synthesis of steroids and bile acids and the detoxification of many foreign substances, such as drugs and environmental agents.CYP1B1 is the only member of the CYP1B subfamily; it catalyses the hydroxylation of 17-b-oestradiol at the C4 position (Jefcoate et al, 2000) and is involved in testosterone biotransformation as well (Shimada et al, 1999). It is also known to metabolise xenobiotics such as ethoxyresorufin, theophylline and caffeine (Shimada et al, 1997). CYP1B1 is constitutively expressed at the mRNA level in mammal steroidogenic tissues, such as rat granulosa cells (Dasmahapatra et al, 2002) and its expression can be induced in these and other tissues by peptide hormones, cAMP and ligands of the aryl hydrocarbon receptor (AhR). Crosstalk has been described...

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Studies of cancer invasion/metastasis and drug resistance have in the past generally proceeded along the separate pathways of research. Recently, however, interest has been focused on the possible relationship between drug resistance and cancer invasion and metastasis. A relationship between these two phenotypes has been demonstrated by two types of observation: firstly, some tumor cells selected for resistance to drugs are more invasive/metastatic relative to non-resistant parental cells; secondly, in some cases, secondary (more metastatic) tumors are more resistant to chemotherapeutic drugs than their primary counterparts. In other instances reported in the literature, no correlation is seen between drug exposure/resistance and cancer invasion/metastasis. The possibility that treatment with some chemotherapeutic drugs may be able to promote cancer invasion and metastasis needs further investigation because of its potential clinical relevance. A better understanding of any relationship between drug resistance and cancer invasion could lead to more effective cancer treatment.

Doxorubicin-and paclitaxel-selected variants of an in vitro invasive clonal population of the human breast cancer cell line, MDA-MB-435S, were established by pulse selection, and exhibited a novel 'superinvasive' phenotype. This phenotype is characterised by an ability to relocate to another surface following invasion through matrigel and membrane pores, by decreased adhesion to extracellular matrix proteins and by increased motility. This may represent an in vitro model of a step in the metastatic process occurring subsequent to invasion. The paclitaxel-resistant variants, MDA-MB-435S-F/Taxol-10p and MDA-MB-435S-F/Taxol-10p4p were resistant to paclitaxel, vincristine and docetaxel, but not to doxorubicin, carboplatin, etoposide or 5-fluorouracil. The doxorubicin-selected variants MDA-MB-435S-F/Adr-10p and MDA-MB-435S-F/Adr-10p10p, in contrast, exhibited only small increases in resistance to doxorubicin, although they were slightly resistant to VP-16 and docetaxel, and exhibited increased sensitivity to paclitaxel, carboplatin and 5-fluorouracil. Invasion and metastasis are intimately involved in the pathology of cancer, but the biological and molecular natures of these phenomena remain incompletely understood. A possible association exists between multiple drug resistance and invasive potential in carcinoma cells (Liang et al, 2001(Liang et al, , 2002.The majority of previous studies focus on the direct effect of drug exposure on the invasive potential (invasion in the presence of the drug), as opposed to the long-term effects of drug treatment on the invasive phenotype of cell, coupled with emerging drug resistance. While a few reports indicate that paclitaxel exposure increases motility and invasion (Welch et al, 1989;Silbergeld et al, 1995), others indicate an inhibitory effect on invasion (Westerlund et al, 1997;Sgadari et al, 2000). Silbergeld et al (1995) reported that increasing the paclitaxel concentration caused increased locomotion in glioblastoma cell lines. Welch et al (1989) showed that pretreatment of cell lines, with low and high invasive potentials, with vincristine, colcemid, or colchicine (but not paclitaxel), at noncytotoxic levels, resulted in inhibition of invasion. Westerlund et al (1997) showed that OVCAR-3 cell attachment, migration and in vitro invasion were significantly decreased after paclitaxel treatment. Sgadari et al (2000) found that paclitaxel promoted regression of Kaposi's sarcoma (KS) lesions in vivo and that it blocked the growth, migration, and invasion of KS cells in vitro. Doxorubicin appears to have an inhibitory effect on invasion (Repesh et al, 1993;Hikawa et al, 2000).Previous studies in this laboratory showed that selection of RPMI 2650, a noninvasive cell line, with the chemotherapeutic agents paclitaxel and melphalan, resulted in multiple drugresistant phenotypes and in the case of melphalan but not paclitaxel, a highly invasive phenotype (Liang et al, 2001). To further investigate the effects of chemotherapeutic drug selection, in particular doxorubicin and paclit...

The human lung carcinoma cell line DLKP was exposed to sequential pulses of 10 commonly used chemotherapeutic drugs (VP-16, vincristine, taxotere, mitoxantrone, 5-fluorouracil, methotrexate, CCNU, BCNU, cisplatin and chlorambucil); resulting cell lines exhibited resistance to the selecting agents (ranging approx. 1.5-to 36-fold) and, in some cases, cross-resistance to methotrexate (approx. 1.4-to 22-fold), vincristine (1.6-to 262-fold), doxorubicin (Adriamycin, approx. 1.1-to 33-fold) and taxotere (approx. 1.1-to 36-fold). Several of the variants displayed collateral sensitivity to cisplatin. A marked increase in in vitro invasiveness and motility was observed with variants pulsed with mitoxantrone, 5-fluorouracil, methotrexate, BCNU, cisplatin and chlorambucil. There was no significant change in invasiveness of cells pulsed with VP-16, vincristine, taxotere or CCNU. All of the pulseselected variants showed elevated levels of MDR-1/P-gp protein by Western blot analysis, although mdr-1 mRNA levels were not increased (except for DLKP-taxotere). In DLKPtaxotere, MRP1 protein levels were also greatly elevated, but mrp1 mRNA levels remained unchanged. BCRP was upregulated in DLKP-mitoxantrone at both the mRNA and protein levels. Gelatin zymography, Western blot and RT-PCR showed that DLKP and its variants secreted MMPs 2, 9 and 13. MMP inhibition assays suggested that MMP-2 plays a more important role than MMPs 9 and 13 in cell invasion of these DLKP drug-resistant variants in vitro. Reducing intracellular drug levels, often associated with overexpression of P-gp, 3 members of the MRP family 4 and the BCRP/ MXR protein, 5 is an important and frequent mechanism of MDR.Invasion through basement membrane is believed to be a critical step in metastasis. There are 4 main classes of proteases involved in proteolytic degradation of the ECM: serine-, cysteine-and aspartyl-proteases as well as MMPs. 6 The MMPs are a family of more than 20 members produced by tumour cells, connective tissue cells and inflammatory cells. MMPs are secreted as latent proenzymes and activated by proteolytic removal of an aminoterminal domain. 7 A large body of evidence shows that MMPs play a crucial role in cancer invasion and metastasis. Based on sequence homology and substrate specificity, MMP-2 and MMP-9 are classified as type IV collagenases that degrade the major component (type IV collagen) of basement membrane; 8 MMP-13, also called "collagenase-3", belongs to a group known as interstitial collagenases, which degrade collagen types I, II, III, VII, VIII and X. 9 The possibility of a relationship between drug resistance and invasion/metastasis phenotypes has been raised by 2 types of observation: 10 firstly, some tumour cells selected for resistance to drugs are invasive/metastatic relative to nonresistant parental cells; secondly, in some cases, secondary (more metastatic) tumours are more resistant to chemotherapeutic drugs than their primary counterparts. In support of this, Osmak et al. 11 reported a study of drug-resistant cervical and ...