Effective treatment of metastatic cancers usually requires the use of toxic chemotherapy. In most cases, multiple drugs are used, as resistance to single agents occurs almost universally. For this reason, elucidation of mechanisms that confer simultaneous resistance to different drugs with different targets and chemical structures - multidrug resistance - has been a major goal of cancer biologists during the past 35 years. Here, we review the most common of these mechanisms, one that relies on drug efflux from cancer cells mediated by ATP-binding cassette (ABC) transporters. We describe various approaches to combating multidrug-resistant cancer, including the development of drugs that engage, evade or exploit efflux by ABC transporters.

Targeting multidrug resistance in cancer

Publisher Summary This chapter reviews the sequence of cellular and other changes during cancer development in selected sites in experimental animals and in humans. It highlights the similarities and differences among the carcinogenic processes and discusses the evident generalities and working hypotheses derived from the analyses. It also discusses some perspective concerning the possible relationship of carcinogenesis to other types of chronic pathological processes such as some forms of adaptation and evolution. Major emphasis is given to three sites—namely, skin, liver, and breast. Several other sites or types of neoplasms are also discussed in the chapter, including urinary bladder, brain, kidney, uterine cervix, and foreign-body sarcoma. It focuses on the development of cancer with chemicals in experimental animals and in humans. To date, the major evidence for a beneficial role for new cell populations occurring during the preneoplastic phase of carcinogenesis concerns the liver. However, it seems appropriate to explore other systems from this point of view. In other organs or tissues, appropriate physiological or environmental factors should be sought as possible influences on early carcinogen-induced new cell populations. These influences might well constitute naturally occurring “promoting” environments in at least some carcinogenic process.

The sequential analysis of cancer development.

The stages of initiation and promotion in hepatocarcinogenesis.

Predicting drug sensitivity and resistance: profiling ABC transporter genes in cancer cells

Three new monoclonal antibodies (MAbs) (MOv16, MOv18 and MOv19) were raised against human ovarian carcinoma. To obtain more specific reagents than those produced so far, we adopted the following experimental approach which consisted of: the selection of a poorly differentiated ovarian carcinoma which was unreactive with all the MAb previously selected in our laboratory; and the application of a particular immunization protocol. The reactivity of the selected MAbs was studied by solid-phase RIA on live and fixed cells from tumor cell lines and by immunofluorescence on frozen sections from surgical specimens. The MAb MOv16 reacted with 60% of ovarian carcinomas as well as with a high percentage of other carcinomas and with some normal tissues. In contrast, MOv18 and MOv19 appeared to have restricted specificities for ovarian carcinomas and cystadenomas. Reactivity on other carcinomas was only observed in a few cases and no reactivity was found on non-epithelial tumors or normal tissues. Immunoprecipitation experiments indicated that MOv16 recognizes a 48-50-kDA protein, whereas MOv18 and MOv19 both identify a 38-40 kDA glycoprotein band. Cross-competition experiments, together with a double-determinant immunoradiometric assay which uses MOv18 as catcher and MOv19 as tracer, suggested that they recognize different epitopes carried by the same molecule. The affinity constants of MOv18 and MOv19 were estimated to be in the range of 10(8)-10(9) M-1. Taken together, the properties of these antibodies, their restricted ovarian tumor specificities and relative high affinity constants, suggest that they could represent promising tools for in vivo applications.

Characterization of human ovarian carcinoma‐associated antigens defined by novel monoclonal antibodies with tumor‐restricted specificity

The activity of γ-glutamyltransferase, as measured quantitatively and by histochemical staining, was studied in different cell populations during the induction of liver cancer with 2-acetylaminofluorene (2-AAF) or diethylnitrosamine and compared with findings in fetal and in intact and regenerating adult liver. The enzyme activity is 20-fold higher in 12-week nodules than in control livers and 30-fold higher in 20-week nodules than in controls. A similar 30-fold increase in activity relative to control is present in hepatomas, induced by either 2-AAF or diethylnitrosamine, and in fetal hepatocytes. The enzyme shows increases in activity in foci of very early putative preneoplastic hepatocytes induced by a single dose of diethylnitrosamine and selected by low doses of 2-AAF plus partial hepatectomy. By 7 days, the foci show a 4-fold increase in enzyme activity, and by 3 weeks they are 40-fold higher than in the control liver. Histochemically, the foci are strongly positive for γ-glutamyltransferase, especially in the bile canaliculi. By 21 days, the ductular (oval) cells induced by 2-AAF have disappeared. When stained for the enzyme activity, the foci stand out clearly against the negative background of the liver, allowing easy quantitation. It appears that γ-glutamyltransferase is a useful marker for preneoplastic hepatocytes.

https://cancerres.aacrjournals.org/content/canres/38/3/823.full.pdf

Gamma-glutamyltransferase in putative premalignant liver cell populations during hepatocarcinogenesis.

Carcinoembryonic antigen (CEA) levels were determined in 742 postoperative patients with breast cancer. Within this group the percentage of elevated (greater than or equal to 4.0 ng/ml) assays increased with UICC clinical stage and was 14.8% (12/81), 23.7% (27/114), 73.1% (190/260) and 20.0% (49/245) for stages I, II, III, IV and X (unstagable due to insufficient data) patients. We have now followed the above 482 stages I, II, III and X patients in whom CEA was performed less than or equal to 3 months after initial surgery at a time when there was no evidence of residual disease, for an average interval of 255 days from date of diagnosis. At present 16.2% (17/105) of patients with elevated CEA values compared to only 4.8% (18/377) of patients with normal values have developed recurrent disease (p less than .0005). There is an association of elevation of CEA postoperatively with different clinical stages of breast cancer. Elevated CEA levels postoperatively are associated with an increased risk of development of recurrent disease in breast cancer patients.

Carcinoembryonic antigen in breast cancer

The diuretic Amiloride competitively inhibits the catalytic activity of the urokinase-type plasminogen activator on plasminogen in vitro. This effect was tested on a rat adenocarcinoma model and its invasive potential in the host lung. While the inhibitory effect on intact cell cultures of the tumour was slight, continuous exposure of tumour-injected animals to the drug completely prevented the formation of lung metastasis.

Antimetastatic effect of amiloride in an animal tumour model.

In 302 patients with tumors of the cervix, corpus uteri, and ovaries, assessment by clinical staging (tumors-nodules-metastasis system) (4) and histopathology has been related to the presence of serum heat-stable, placenta-like alkaline phosphatase (PLAP) activity.

Early stages of cervical tumors show the highest incidence of this isoenzyme. In advanced stages of this disease, a decrease in frequency was observed that might be interpreted as the result of gradual dedifferentiation of the tumor cells to a point where synthesis of PLAP became undetectable. The same observation was made in adenocarcinomas of the corpus uteri, i.e. , patients with advanced disease tended to have the lowest incidence of serum PLAP.

Only in cancers of the ovaries did we find a positive correlation between this enzyme marker and the extent of the disease. In more than one-third of the patients examined, PLAP levels were an index of the tumor burden.

Placenta-like alkaline phosphatase in gynecological cancers.

Combinations of carcinoembryonic antigen (CEA), gamma glutamyl transpeptidase (GGT), pregnancy-associated macroglobulin (PAM) and placenta-like alkaline phosphatase (PLAP) were studied in groups of patients with ovarian and cervical cancer. In ovarian cancer, only CEA and PLAP levels appeared to reflect tumor burden and were complementary in detecting active disease. In cervical cancer, CEA and GGT reflected tumor burden, while PLAP showed just the reverse--the highest degree of positivity being present in minimal disease. PLAP positivity was even more pronounced in patients with cervical dysplasia and carcinoma in situ while CEA and GGT were negative. The data indicate that the use of marker combinations can improve our capacity to detect minimal disease and provide information regarding tumor biology that may not be available by studying individual markers or by other means. It remains to be determined whether the use of tumor markers can influence existing therapy sufficiently to alter the outcome in cancers which are notoriously difficult to treat.

Kellen Ja

Papers

Gamma-glutamyltransferase in putative premalignant liver cell populations during hepatocarcinogenesis.

Carcinoembryonic antigen in breast cancer

Antimetastatic effect of amiloride in an animal tumour model.

Placenta-like alkaline phosphatase in gynecological cancers.

Carcinoembryonic antigen (CEA) and other tumor markers in ovarian and cervical cancer