Stem cells from bone marrow, skeletal muscle and possibly other tissues can be identified by the 'side-population' (SP) phenotype. Although it has been assumed that expression of ABC transporters is responsible for this phenotype, the specific molecules involved have not been defined. Here we show that expression of the Bcrp1 (also known as Abcg2 murine/ABCG2 human) gene is a conserved feature of stem cells from a wide variety of sources. Bcrp1 mRNA was expressed at high levels in primitive murine hematopoietic stem cells, and was sharply downregulated with differentiation. Enforced expression of the ABCG2 cDNA directly conferred the SP phenotype to bone-marrow cells and caused a reduction in maturing progeny both in vitro and in transplantation-based assays. These results show that expression of the Bcrp1/ABCG2 gene is an important determinant of the SP phenotype, and that it might serve as a marker for stem cells from various sources.

The ABC transporter Bcrp1/ABCG2 is expressed in a wide variety of stem cells and is a molecular determinant of the side-population phenotype

The ABCG2 transporter is an efficient Hoechst 33342 efflux pump and is preferentially expressed by immature human hematopoietic progenitors

Cytostatic antibiotics of the anthracycline class are the best known of the chemotherapeutic agents that cause cardiotoxicity. Alkylating agents such as cyclophosphamide, ifosfamide, cisplatin, carmustine, busulfan, chlormethine and mitomycin have also been associated with cardiotoxicity. Other agents that may induce a cardiac event include paclitaxel, etoposide, teniposide, the vinca alkaloids, fluorouracil, cytarabine, amsacrine, cladribine, asparaginase, tretinoin and pentostatin. Cardiotoxicity is rare with some agents, but may occur in >20% of patients treated with doxorubicin, daunorubicin or fluorouracil. Cardiac events may include mild blood pressure changes, thrombosis, electrocardiographic changes, arrhythmias, myocarditis, pericarditis, myocardial infarction, cardiomyopathy, cardiac failure (left ventricular failure) and congestive heart failure. These may occur during or shortly after treatment, within days or weeks after treatment, or may not be apparent until months, and sometimes years, after completion of chemotherapy. A number of risk factors may predispose a patient to cardiotoxicity. These are: cumulative dose (anthracyclines, mitomycin); total dose administered during a day or a course (cyclophosphamide, ifosfamide, carmustine, fluorouracil, cytarabine); rate of administration (anthracyclines, fluorouracil); schedule of administration (anthracyclines); mediastinal radiation; age; female gender; concurrent administration of cardiotoxic agents; prior anthracycline chemotherapy; history of or pre-existing cardiovascular disorders; and electrolyte imbalances such as hypokalaemia and hypomagnesaemia. The potential for cardiotoxicity should be recognised before therapy is initiated. Patients should be screened for risk factors, and an attempt to modify them should be made. Monitoring for cardiac events and their treatment will usually depend on the signs and symptoms anticipated and exhibited. Patients may be asymptomatic, with the only manifestation being electrocardiographic changes. Continuous cardiac monitoring, baseline and regular electrocardiographic and echocardiographic studies, radionuclide angiography and measurement of serum electrolytes and cardiac enzymes may be considered in patients with risk factors or those with a history of cardiotoxicity. Treatment of most cardiac events induced by chemotherapy is symptomatic. Agents that can be used prophylactically are few, although dexrazoxane, a cardioprotective agent specific for anthracycline chemotherapy, has been approved by the US Food and Drug Administration. Cardiotoxicity can be prevented by screening and modifying risk factors, aggressively monitoring for signs and symptoms as chemotherapy is administered, and continuing follow-up after completion of a course or the entire treatment. Prompt measures such as discontinuation or modification of chemotherapy or use of appropriate drug therapy should be initiated on the basis of changes in monitoring parameters before the patient exhibits signs and symptoms of cardiotoxicity.

Cardiotoxicity of chemotherapeutic agents: incidence, treatment and prevention.

Topotecan- or mitoxantrone-selected cell lines (T8 and MX3, respectively), derived from the human IGROV1 ovarian cancer cell line, were resistant to the topoisomerase I inhibitors topotecan, SN-38 (the active metabolite of irinotecan), and 9-aminocamptothecin, as well as to the topoisomerase II drug mitoxantrone. In both resistant cell lines, decreased accumulation of topotecan and mitoxantrone was observed, caused by enhanced energy-dependent efflux of the drugs involved. In both cell lines, we found that the breast cancer resistance protein/mitoxantrone resistance/placenta-specific ATP binding cassette (BCRP/MXR/ABCP) gene was overexpressed. Furthermore, BCRP/MXR/ABCP expression levels in various partially revertant T8 cells correlated with the levels of resistance to topotecan, SN-38, and mitoxantrone, strongly suggesting BCRP/MXR/ABCP to be the transporter responsible for the enhanced efflux. Pharmacodynamic analysis demonstrated that BCRP/MXR/ABCP is a very efficient transporter of topotecan; in vitro, 70% of the intracellular topotecan pool was transported out of the T8 or MX3 cells within 30 s. In conclusion, we report for the first time that BCRP/MXR/ABCP can also be up-regulated upon exposure of tumor cells to the clinically important drug topotecan, and that BCRP-mediated efflux of topotecan is very efficient. This highly efficient efflux of topotecan by BCRP/MXR/ABCP may have clinical relevance for patients being treated with topotecan.

https://cancerres.aacrjournals.org/content/canres/59/18/4559.full.pdf

Overexpression of the BCRP/MXR/ABCP Gene in a Topotecan-selected Ovarian Tumor Cell Line

Recombinant human tumor necrosis factor (TNF), purified to greater than 99% homogeneity, increases surface expression of class I major histocompatibility complex (MHC) antigens to a maximum of 9-fold on cultured human endothelial cells (HEC) and human dermal fibroblasts (HDF). The increase is concentration dependent (peak 20-100 units/ml) and time dependent (nearly maximal by 4 days); expression remains elevated in the continued presence of TNF and requires greater than 7 days to return to basal levels upon TNF withdrawal. The increase in surface expression appears to result from increases in steady-state mRNA levels for the class I antigens, although the increase in mRNA is proportionately greater than for surface expression. No surface expression of or mRNA for class II MHC antigens is detectable in either control or TNF-treated HEC or HDF. These effects are similar to those produced by leukocyte or fibroblast (type I) interferons (IFNs). The protein synthesis inhibitor cycloheximide (CHX), when added coincidentally with type I IFNs, leads to superinduction of mRNA for class I MHC antigens and, unexpectedly, leads to the appearance of mRNA for class II MHC antigens. CHX has no effect by itself upon mRNA levels for class I or class II MHC antigens, nor does it modulate the increases in mRNA produced by immune (type II) IFN. Most interesting, CHX blocks the increase in mRNA for class I MHC antigens induced by TNF. Thus TNF appears to act on MHC gene expression through a newly synthesized protein intermediate. Our results provide direct evidence that TNF can modulate gene expression in normal (untransformed) cell types and contribute to under- standing the complex nature of MHC gene regulation. Finally, they suggest that TNF may act in vivo as an immunoregulatory molecule.

Recombinant human tumor necrosis factor increases mRNA levels and surface expression of HLA-A,B antigens in vascular endothelial cells and dermal fibroblasts in vitro (monokines/lymphokines/major histocompatibility complex/interferons/HLA-DR antigen)

Erratum: A multidrug resistance transporter from human MCF-7 breast cancer cells (Proceedings of the National Academy of Sciences of the USA (December 22, 1998) 95 (15665-15670))

A multidrug resistance transporter from human MCF-7 breast cancer cells (erratum in PNAS USA 1999; 96(5): 2569)

The response of class I major histocompatibility complex antigen expression to in vitro administration of interferon and tumor necrosis factor α (TNF-α) was measured using class I major histocompatibility complex-deficient small cell lung cancer cell lines. Significant induction also was observed using γ interferon (IFN-γ) alone, whereas TNF-α alone yielded only modest induction. Classic small cell lung cancer cell lines NCI-H146 and NCI-H209 best demonstrated synergistic HLA and β2-microglobulin antigen induction with IFN-γ and TNF-α with the following dose schedule: 3–6 days of TNF-α (200 units/ml) followed by 48 h of IFN-γ (100 IU/ml). Induction was quantitated using an 125I-Protein A radioimmunoassay. Synergistic induction of the HLA and β2-microglobulin surface antigens on NCI-H146 was also possible with α interferon and TNF-α but required a higher concentration of the interferon, i.e., 3–6 days of TNF-α (200 units/ml) followed by 48 h of α interferon (1000 units/ml). Small cell lung cancer cell line NCI-H146 was further studied for expression of major histocompatibility complex messenger RNA using the optimal doses and sequence of addition of IFN-γ and TNF-α as indicated above. A significant induction with IFN-γ alone and synergistic induction with both IFN-γ and TNF-α was quantitated for both HLA-A2 and β2-microglobulin transcripts using Northern blot analysis. Incubation with relatively low subcytotoxic doses of IFN-γ and TNF-α also resulted in a marked synergistic decrease in c-myc message.

https://cancerres.aacrjournals.org/content/canres/49/22/6232.full.pdf

Potentiation of Interferon Induction of Class I Major Histocompatibility Complex Antigen Expression by Human Tumor Necrosis Factor in Small Cell Lung Cancer Cell Lines

The multidrug resistance phenotype of human breast carcinoma MCF-7/AdrVp cells is characterized by overexpression of a 95-kilodalton membrane glycoprotein (p95), accompanied by a marked reduction in intracellular anthracycline accumulation, without overexpression of P-glycoprotein or the multidrug resistance protein. We discovered that the mRNA of the H19 gene is overexpressed in MCF-7/AdrVp cells relative to parental MCF-7 cells or drug-sensitive MCF-7/AdrVp revertant cells. H19 is an imprinted gene with an important role in fetal differentiation, as well as a postulated function as a tumor suppressor gene. Another p95-overexpressing multidrug-resistant cell line, human lung carcinoma NCI-H1688, also displays high levels of H19 mRNA. In contrast, several multidrug-resistant cell lines that overexpress P-glycoprotein or the multidrug resistance protein do not have higher levels of H19 mRNA than their drug-sensitive counterparts. This is the first report of H19 gene overexpression accompanying any form of drug resistance. The association of H19 and p95 gene expression in drug resistance warrants further study.

https://cancerres.aacrjournals.org/content/canres/56/13/2904.full.pdf

H19 Gene Overexpression in Atypical Multidrug-resistant Cells Associated with Expression of a 95-Kilodalton Membrane Glycoprotein

Forty-five patients with advanced, measurable, or evaluable non-small bronchogenic carcinoma (NSCBC) were treated with doxorubicin and mitomycin C combination chemotherapy. The lirst 27 patients received doxorubicin 50 mg/m2) I.V. every 3 weeks and mitomycin C 10 mg/m2. I.V. every 3 weeks. Because o

Combination chemotherapy with doxorubicin and mitomycin C in non-small cell bronchogenic carcinoma: severe pulmonary toxicity from q 3 weekly mitomycin C

L. A. Doyle

Papers

Erratum: A multidrug resistance transporter from human MCF-7 breast cancer cells (Proceedings of the National Academy of Sciences of the USA (December 22, 1998) 95 (15665-15670))

A multidrug resistance transporter from human MCF-7 breast cancer cells (erratum in PNAS USA 1999; 96(5): 2569)

Potentiation of Interferon Induction of Class I Major Histocompatibility Complex Antigen Expression by Human Tumor Necrosis Factor in Small Cell Lung Cancer Cell Lines

H19 Gene Overexpression in Atypical Multidrug-resistant Cells Associated with Expression of a 95-Kilodalton Membrane Glycoprotein

Combination chemotherapy with doxorubicin and mitomycin C in non-small cell bronchogenic carcinoma: severe pulmonary toxicity from q 3 weekly mitomycin C