Induction of breast cancer resistance protein by the camptothecin derivative DX-8951f is associated with minor reduction of antitumour activity

DX-8951f (exatecan mesylate), a new water-soluble derivative of camptothecin, is currently being evaluated in phase II clinical trials. Resistance may be acquired when treating cancer patients with DX-8951f. Therefore, we selected a subline of the human ovarian cancer cell line A2780 for resistance against DX-8951f to investigate possible mechanisms of resistance. This DX-8951f-resistant subline, designated 2780DX8 (resistance factor=9.3), displayed a typical cross-resistance pattern including compounds, such as topotecan (resistance factor =34), SN-38 (resistance factor =47), mitoxantrone (resistance factor =59) and doxorubicin (resistance factor =2.9), which have previously been associated with the expression of breast cancer resistance protein. 2780DX8 cells did not show changes in the topoisomerase I gene, in topoisomerase I protein levels or catalytic activity. Overexpression of breast cancer resistance protein could be detected, both at the mRNA and protein level, while staining for Pgp, MRP1, or LRP was negative. GF120918, an inhibitor of breast cancer resistance protein, was able to reverse the DX-8951f-induced resistance in 2780DX8 cells. In vivo experiments in well-established 2780DX8 human tumour xenografts demonstrated that the growth inhibition induced by CPT-11 was more affected by breast cancer resistance protein expression than that of DX-8951f. These data indicate for the first time that DX-8951f is able to induce breast cancer resistance protein as a mechanism of resistance. Breast cancer resistance protein, however, results in only minor reduction of antitumour activity of DX-8951f which is an advantage over topotecan and CPT-11/SN-38

Acute effects of hydrocortisone on plasma nitrate/nitrite activity and forearm vasodilator responsiveness in normal human subjects

1. The aim of the present study was to examine the acute effects of cortisol infusion on plasma nitrate/nitrite (NO) activity and forearm vascular responsiveness to acetylcholine. 2. We performed two randomized, placebo-controlled, cross-over studies. Study A examined the effects of intravenous hydrocortisone (200 mg over a 3 h period) on blood pressure (BP) and plasma NO activity in six healthy male volunteers. Study B examined the effects of intra-arterial hydrocortisone on cholinergic vasodilator responsiveness in six healthy male volunteers. Vasodilator responsiveness was measured by bilateral strain gauge plethysmography. 3. In study A, there was no significant change in BP during the hydrocortisone infusion. Comparing values obtained following 180 min infusion of hydrocortisone and control, there were significant increases in plasma cortisol (3441 ± 342 vs 209 ± 29 nmol/L, respectively; P < 0.001) and glucose (5.7 ± 0.2 vs 4.6 ± 0.2 mmol/L, respectively; P < 0.05) and a reduction in plasma renin concentration (PRC) (8.1 ± 1.2 vs 11.0 ± 1.8 pg/mL, respectively; P < 0.05) following hydrocortisone infusion. However, there were no significant changes in either plasma NO or in the endogenous NO synthase inhibitors asymmetrical and symmetrical dimethylarginine. 4. In study B, there was no significant change in BP or in cholinergic vasodilator responsiveness during the hydrocortisone infusion. 6. Short-term cortisol infusions do not alter biochemical or physiological markers of NO activity. If cortisol-induced hypertension is mediated by suppression of NO activity in humans, it seems likely that these changes take more than 3 h to become detectable

Altered serine/arginine-rich protein phosphorylation and exonic enhancer-dependent splicing in Mammalian cells lacking topoisomerase I

DNA topoisomerase I (Topo I) specifically phosphorylates arginine-serine-rich (SR proteins) splicing factors and is potentially involved in pre-mRNA-splicing regulation. Using a Topo I-deficient murine B lymphoma-derived subclone (P388-45/C) selected for its resistance to high dosage of the antitumor drug camptothecin, we show that Topo I depletion results in the hypophosphorylation of SR proteins and impairs exonic splicing enhancer (ESE)-dependent but not constitutive splicing. The Affymetrix GeneChip system analysis revealed that several alternatively spliced genes, characterized by small exons and large introns, are down-regulated in Topo I-deficient cells. Given that ectopic expression of green fluorescent protein-Topo I fusion in Topo I-deficient cells restores both wild-type phosphorylation of SR proteins and ESE-dependent splicing, we conclude that Topo I-mediated phosphorylation plays a specific role in ESE-regulated splicing

High sensitivity M-protein detection in a case of light-chain cardiac amyloidosis without evidence of plasma cell dyscrasia

https://www.ncbi.nlm.nih.gov/pubmed/3057510

Altered serine/arginine-rich protein phosphorylation and exonic enhancer-dependent splicing in Mammalian cells lacking topoisomerase I

DNA topoisomerase I (Topo I) specifically phosphorylates arginine-serine-rich (SR proteins) splicing factors and is potentially involved in pre-mRNA-splicing regulation. Using a Topo I-deficient murine B lymphoma-derived subclone (P388-45/C) selected for its resistance to high dosage of the antitumor drug camptothecin, we show that Topo I depletion results in the hypophosphorylation of SR proteins and impairs exonic splicing enhancer (ESE)-dependent but not constitutive splicing. The Affymetrix GeneChip system analysis revealed that several alternatively spliced genes, characterized by small exons and large introns, are down-regulated in Topo I-deficient cells. Given that ectopic expression of green fluorescent protein-Topo I fusion in Topo I-deficient cells restores both wild-type phosphorylation of SR proteins and ESE-dependent splicing, we conclude that Topo I-mediated phosphorylation plays a specific role in ESE-regulated splicing