cyclic-gmp and Fibrosarcoma

The effects of insulin on tumor oxygenation, perfusion, oxygen consumption,and radiation sensitivity were studied on two different mouse tumor models (TLT, a liver tumor, and FSAII, a fibrosarcoma). Anesthetized mice were infused with insulin i.v. at a rate of 16 milliUnits/kg/min for 25 min. Local tumor oxygenation measurements were carried out using two independent techniques: electron paramagnetic resonance oximetry and a fiber-optic device (OxyLite). Two complementary techniques were also used to assess the blood flow inside the tumor: a laser Doppler system (OxyFlo) and contrast-enhanced magnetic resonance imaging. The oxygen consumption rate of tumor cells after in vivo insulin infusion was measured using high frequency electron paramagnetic resonance oximetry. To know if insulin was able to enhance radiation-induced tumor regrowth delay, tumor-bearing mice were treated with 16 Gy of 250 kV radiation dose after insulin infusion. We provide evidence that insulin increases the local pressure of oxygen of tumors (from 0-3 mm Hg to 8-11 mm Hg) as well as the tumor response to irradiation (increasing regrowth delay by a factor of 2.11). We found that the insulin-induced increase of tumor pressure of oxygen: (a) is not caused by an increase in the tumor blood flow, which is even decreased after insulin infusion; (b) is because of a decrease in the tumor cell oxygen consumption (in vivo insulin consumed oxygen three times slower than control cells); and (c) is inhibited by a nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester, when injected i.p. at 15 micromol/kg(-1), 1 h before insulin infusion. We demonstrate by immunoblotting that the NO pathway involves a phosphorylation of endothelial NO synthase and showed a concomitant increase in the cyclic GMP tumor level. These findings provide unique insights into biological processes in tumors, new possible management for treating cancer patients, and raise major questions about the role of insulin secretion (fasting status and diabetes) in the clinical response of tumors to radiation therapy.

Topics: Animals; Cyclic GMP; Energy Metabolism; Fibrosarcoma; Insulin; Liver Neoplasms, Experimental; Mice; Mice, Inbred C3H; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Oxygen; Oxygen Consumption; Partial Pressure; Phosphorylation; Radiation-Sensitizing Agents

Cisplatin resistance, induced in murine fibrosarcoma cells (SSK) in vitro or in vivo by low-dose irradiation, can be overcome by activation of the cyclic GMP(cGMP)-dependent transduction pathway. This is mediated either by stimulating cGMP formation with sodium nitroprusside or by replacing cGMP with a selective activator of the cGMP-dependent protein kinase, 8-bromo-cGMP. The cyclic AMP-dependent transduction pathway is not involved in cisplatin resistance. Instead, activation of cAMP sensitises both parental and resistant SSK cells equally to the action of cisplatin. There is a 1.8 to 2.5-fold increase in drug toxicity, depending on the activating agent. Enhancement of cisplatin sensitivity is induced by specific inhibition of cAMP hydrolysis, increase in cAMP formation or by increasing the activation potential to cAMP-dependent protein kinase by specific cAMP analogues. Cells that have lost cisplatin resistance respond to cGMP- or cAMP-elevating agents in the same way as the parental SSK cells. The radiation sensitivity is unchanged in all cell lines, even after activation of cAMP or cGMP. These results suggest that specific DNA repair pathways are altered by radiation but affected only in cisplatin damage repair, which is regulated by cGMP. Although there is ample cooperativity and interaction between the cAMP- and the cGMP-dependent transduction pathways, specific substrate binding by cGMP appears to play an important role in radiation-induced cisplatin resistance.

Topics: Animals; Cell Survival; Cisplatin; Combined Modality Therapy; Cyclic AMP; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Drug Resistance; Fibrosarcoma; Isoproterenol; Mice; Phosphodiesterase Inhibitors; Signal Transduction; Tumor Cells, Cultured

The murine fibrosarcoma cell line HSDM1C1 synthesizes prostaglandin E2 in response to thrombin and bradykinin, two products of the coagulation pathway. These physiologic effectors interact with two independent cell-surface receptor systems whose properties we have characterized. HSDM1C1 cells possess a B2 bradykinin receptor, a type more sensitive to native bradykinin than to related peptides, including Met-Lys- and desArg9-bradykinin. A period of bradykinin desensitization follows the initial response. Recovery occurs within 1 hr by a process independent of serum factors. The thrombin-mediated pathway differs in several respects. The maximum amount of prostaglandin E2 synthesized is 40% lower. Prolonged desensitization of the thrombin response occurs after an initial exposure; recovery requires at least 3 hr and depends strictly on the presence of serum. Antithrombin III and hirudin, two proteins that specifically inactivate thrombin, act in serum-free medium to relieve thrombin desensitization. Thrombin's prolonged desensitization thus suggests a persistent ligand-receptor association. The expression of receptor-mediated prostaglandin synthesis governed by multiple physiologic effectors in the same cell may reflect environmental conditions, such as the relative proportions of each effector and the presence of exogenous factors that modulate the ligand-receptor interaction.

Topics: Animals; Antithrombin III; Bradykinin; Cell Line; Cyclic AMP; Cyclic GMP; Dinoprostone; Fibrosarcoma; Mice; Prostaglandins E; Receptors, Bradykinin; Receptors, Cell Surface; Receptors, Thrombin; Thrombin