Overcoming multidrug-resistance in cancer: statins offer a logical candidate.

About seven million people die of cancer every year. This is largely due to development of drug resistance, particularly multidrug resistance, in the tumor cells. Multidrug resistance (MDR) arises due to over-expression of MDR proteins in the cancer cells, which cause efflux of anticancer drugs from the cells using ATP. MDR proteins are members of the family of ABC transporters that occur universally, and are structurally and functionally conserved during evolution. In Drosophila, the germ cell attractant peptide is secreted by an ABC transport protein, mdr49. Recently, the peptide has been shown to undergo conjugation with the lipid geranylgeranyl before secretion. If conjugation with the lipid is inhibited, mdr49 protein is unable to transport the peptide. Similarly, in the case of yeast mating factor pheromone, farnesylation is required to occur before the export of the pheromone by ste6 protein, an ABC transporter. In view of the homology of mdr49 and ste6 proteins with mammalian MDR proteins, we postulate that the drug transporters also require their ligands to be conjugated to a lipid. This view finds support from the studies with synthetic inhibitors of geranylgeranyl-/farnesyl-diphosphate synthetase or transferase: The inhibitors are reported to overcome multidrug resistance in cancer cell lines or xenografts in animals. Thus, the MDR transporters also appear to require their substrates to be conjugated with a lipid. Statins are the widely used inhibitors of HMG-CoA reductase. By depleting precursors of the mevalonate pathway, statins can prevent the formation of lipids like geranylgeranyl and farnesyl. Accordingly, they should also be able to overcome multidrug resistance in cancer. A few reports in the literature indicate that they appear to do so. Statins are in wide clinical use, and their pharmacology is well known. Besides, statins per se have mild beneficial effect on the outcome of the disease. We propose that statins should be seriously investigated for their ability to overcome multidrug resistance in cancer. This should be done after careful standardization of the protocol of simultaneous treatment with anticancer drugs and a statin.

Elevated levels and fragmented nature of cellular fibronectin in the plasma of gastrointestinal and head and neck cancer patients.

BACKGROUND: Tumor invasion occurs following enzymatic degradation of components of the extracellular matrix. The proteolysis-resistant domains of matrix components are likely to appear in the blood plasma during invasion, and could be used as markers of malignancy. Cellular fibronectin (cFN), a major ECM component, possesses 3 alternately spliced principal protease resistant domains; two of which, extra domain A (EDA) and III connecting segment (IIICS), were selected for this study of the nature of the plasma cFN molecules and its levels in normal subjects (n=51), and patients with gastrointestinal (G-I, n=145) or head and neck (H-N, n=127) cancers. METHODS: ELISA was used to measure the cFN levels in plasma and Western blotting to analyze its fragmented nature in plasma samples from normal individuals and patients with G-I or H-N cancers. RESULTS: cFN in blood plasma, as probed by anti-EDA and anti-IIICS antibodies on Western blots, is found to exist entirely in a fragmented form in normal subjects and G-I and H-N cancer patients. The cFN polypeptides in plasma have Mr of 160 and 100. The levels of plasma cFN, determined by ELISA using the 2 antibodies, are found to be increased in G-I and H-N cancers. In a significant number of stomach (43%), gall bladder (35%) and colon (17%) cancer cases an additional anti-EDA-reactive 30 kD peptide is seen in the plasma. CONCLUSIONS: The mean rise for all sites is statistically significant, and 65% of all patients show cFN levels >80th percentile of normal values. The characterization of the 30 kD peptide showed that it does not contain the IIICS domain and also lacks the central cell- and heparin-binding sites.

Increased sialylation and defucosylation of plasma proteins are early events in the acute phase response.

Within hours of turpentine injection to stimulate the acute phase (AP) response in rats, the N-acetylneuraminic acid content of plasma proteins increases and that of fucose decreases, each by about 60%. The two changes are inversely related (r = -0.97). The NeuAc/Gal ratio increases from the normal 0.75 to 1.0 on day 2 of the AP. Whereas 50% of the isolated oligosaccharides of normal plasma proteins are retarded on immobilized Ricinus communis agglutinin, those from day 2 AP plasma fail to do so. This indicates that NeuAc caps the normally Gal-terminated chains. alpha1-Acid glycoprotein (a positive AP protein), alpha1-macroglobulin (a non-AP protein), and alpha1-inhibitor3 (a negative AP protein) also show similar alterations in NeuAc/Gal ratio and decreases in Fuc. alpha2-Macroglobulin, which arises only during the AP, does not contain significant amounts of Fuc. Sambucus nigra agglutinin (alpha2,6-linked NeuAc-specific) binds a majority of plasma proteins, and binding is increased during the AP response. Maackia amurensis lectin (alpha2,3-linked NeuAc-specific) binds only three proteins in normal plasma and three additional proteins in AP plasma. The Fuc-specific Aleuria aurantia agglutinin and Lens culinaris agglutinin each detect five proteins in normal plasma. Their binding decreases during the AP response. These results show that: (1) sialylation and defucosylation of preexisting plasma proteins occur rapidly in the AP response; (2) sialylation caps the preexisting Gal-terminating oligosaccharides; and (3) the oligosaccharides of even the non-AP and negative AP proteins are modified. These changes are distinct from the elevation in the levels of protein-bound monosaccharides and the altered concanavalin A-binding profile the oligosaccharides of AP proteins acquire in diseases.

Cancer-related anemia in a rat model: alpha2-macroglobulin from Yoshida sarcoma shortens erythrocyte survival.

Implantation of Yoshida ascites sarcoma in rats was found to lead to a reduction in the hemoglobin content, the erythrocyte count and the packed cell volume of blood to 30% of normal in 4 d; however, there was no decrease in the mean cell hemoglobin, the mean cell volume and the mean corpuscular hemoglobin concentration, or suppression of erythropoiesis. The red cells from the circulation of tumor-bearing animals, tagged with (51)Cr and injected intravenously in normal rats, showed significantly faster clearance than normal. The erythrocytes contaminating the tumor ascites exhibited extremely short survival, suggesting that one or more secreted tumor product(s) may be responsible for the effect. Incubation of red cells from normal rats in the cell-free ascites fluid, or with an isoform of alpha2-macroglobulin purified from it, also led to reduction in the survival; but the ascites fluid depleted specifically of alpha2-macroglobulin was without any effect. The erythrocytes exhibiting reduced survival showed a proportionate decrease in their cellular deformability. The study identifies a tumor product that is directly responsible for the causation of anemia in the host, and the mechanism by which it does so.