Notes: Abstract  The catalytic cycle of topoisomerase II is the target of some of the most successful antitumor agents used today, e.g., etoposide (VP-16), in the treatment of testicular cancer and small-cell lung cancer. The cell kill mediated by topoisomerase II poisons can be antagonized by distinct drug types. Thus, we have demonstrated etoposide antagonism with the type-II anthracycline aclarubicin, the antimalarial drug chloroquine, and the cardioprotective agent ICRF-187. In other setups, combinations of agonist and antagonists have led to high-dose regimens for counteracting drug resistance. Thus, the exploitation of folinic acid rescue for methotrexate toxicity and the use of mesna to protect against cyclophosphamide toxicity have enabled the use of high-dose methotrexate and cyclophosphamide protocols. Using a similar approach, we have studied possible ways to apply antagonists to topoisomerase II poisons. NDF1-hybrid female mice were treated with the various drugs and drug combinations. Lethality (LD10 and LD50 values) was computed by use of the maximum-likelihood method, and the antitumor effect of the drugs was compared in mice inoculated i.p. with either L1210 cells or Ehrlich ascites tumor cells. In addition, the compounds were tested on L1210 cells inoculated intracranially. The toxicity of the various drugs was evaluated by weight and leukocyte counts. ICRF-187 rescues healthy mice from lethal doses of topoisomerase II poisons. In mice the ICRF-187 LD10 was 500 mg/kg. Within a wide nontoxic dose range (50–250 mg/kg) of ICRF-187 we found protection against m-AMSA and etoposide lethality. Thus, the LD10 of etoposide increased from 34 mg/kg for the single agent to 122 mg/kg for its combination with ICRF-187, corresponding to a 3.6-fold etoposide dose escalation. In contrast, ICRF-187 did not protect against lethal doses of the non-topoisomerase II-directed drug paclitaxel. We further investigated the antitumor effect of equitoxic schedules in mice inoculated i.p. with L1210 or Ehrlich ascites tumor cells. The L1210-bearing mice appeared to obtain a larger increase in life span from the etoposide and ICRF-187 combination as compared with etoposide alone, whereas this was not the case in mice inoculated with Ehrlich ascites tumor cells. As the hydrophilic ICRF-187 is not expected to cross the blood-brain barrier, in contrast to the lipophilic etoposide, we investigated the effect of the drug combination in mice inoculated intracranially with L1210 cells. We obtained a significant increase in life span in mice treated with ICRF-187 + etoposide as compared with mice treated with an equitoxic dose of etoposide alone. Thus, there appear to be potential routes by which one can benefit from this antagonism. ICRF-187 is a powerful nontoxic protector against the lethality of the topoisomerase II-directed drugs etoposide and m-AMSA in vivo. A brain tumor model demonstrates the superiority of high-dose etoposide treatment with ICRF-187 protection as compared with etoposide treatment alone. This implies that tumors in the brain can be reached by cytotoxic drug doses and that normal tissues can be protected due to differences in drug transport across the blood-brain barrier. ICRF-187 is therefore a promising lead compound for the development of schedules using high-dose topoisomerase II poisons in the treatment of brain tumors and metastases.

Notes: Abstract Tubular compliance is the response of tubular diameter to changes in intratubular pressure [7]. Proximal tubular compliance was determined directly by measurements of tubular diameter and pressure and indirectly using a mathematical model of tubular fluid flow based on measurements of the hydraulic pressure gradients along the tubule under free flow conditions and during an induced pressure reduction at the end of the proximal tubule. The two independent methods yielded similar values for compliance. Proximal tubular complicance was found to depend upon the intratubular pressure: tubular compliance was significantly higher (P〈0.001) when the intratubular pressure was reduced below normal (1.0 μm cm H2O−1) than when the pressure was increased above the control value (0.4 μm cm H2O−1) Almost identical compliance values were measured in sodium pentobarbital and inactin anaesthetized rats (P〉0.8). Intratubular pressure changes resulted in inverse changes in the diameters of the adjacent capillaries, suggesting that the peritubular capillaries are distensible structures.

Notes: Summary Large peritubular capillaries were infused consecutively (20 nl · min−1) in random sequence with isotonic saline and angiotensin II (20–80 ng · ml−1). The diameters of the infused capillaries were measured, without knowledge of the infusate used, from colour photographs of the infused area. Angiotensin II induced a significant (p〈0.001) decrease in capillary diameter (Δ=−1.2±0.2 (SE) μm and Δ=−2.1±0.2 (SE) μm with 20 ng · ml−1 and 80 ng · ml−1 angiotensin II infusates, respectively). This decrease was shown to be independent of external tubular compression: separate experiments in which the surrounding tubules were collapsed by injection of oil blocks yielded similar results. The possibility that the observed reduction in diameter was caused by an angiotensin II induced change in capillary permeability to the staining solution was excluded, since the angiotensin II effect was unchanged when fluorescent dextran (mol. wt. 150000) was substituted for lissamin green. These experiments indicate that peritubular capillaries contract actively when infused with angiotensin II.

Notes: Abstract Smooth-muscle specimens from the lower esophagus of nine patients operated on for esophageal achalasia were examined with routine hematoxylin-eosin staining. This procedure revealed only a few eosinophils in or between the external smooth-muscle layers. Using specific immunohistochemical methods for the detection of the eosinophil cationic protein (ECP), however, varying degrees of eosinophil infiltration and extracellular deposit of ECP were disclosed in the achalasia specimens. The ECP also reacted with the monoclonal antibody, EG2, indicating secretion of the cytotoxic ECP. Few or no eosinophils were seen in the muscularis externa in specimens from six control patients without esophageal disease. In two controls many eosinophils were observed in the muscularis externa. However, no extracellular ECP was detected and very few eosinophils reacted with the monoclonal antibody (EG2), suggesting that these eosinophils were not activated. Depletion or total absence of peptidergic innervation was seen in all achalasia specimens but not in controls. Since the eosinophil cationic protein (ECP), in its activated form, is cytotoxic, we propose a pathogenic role of the eosinophil infiltration in achalasia.

Notes: Summary In previous studies, we found that VP-16 (etoposide) induced cytotoxicity and protein-concealed strand break formation was prevented in a small cell lung cancer (SCLC) cell line, when the cells were incubated with aclarubicin prior to treatment with VP-16. In the present work, we studied the effect of adding aclarubicin to the cell suspension after VP-16. In a clonogenic assay, we found that the cytotoxicity induced by VP-16 in SCLC cells was inhibited when cells were postincubated with aclarubicin. The addition of aclarubicin at any time in relation to VP-16 was able to stop further cytotoxicity induced by the topoisomerase II (topo-II) targeting drug. Aclarubicin was also found to antagonize the cytotoxicity induced by VM-26 (teniposide), and m-AMSA. With the alkaline elution technique we found that postincubating the cells with aclarubicin inhibited VP-16-induced DNA strand break formation. In anin vitro system with purified topo-II and naked DNA we likewise found, that postincubation with aclarubicin prevented VP-16 induced cleavage. In the samein vitro system, also baseline cleavage induced by topo-II was inhibited when aclarubicin was present. Importantly, aclarubicin exerted the antagonism to topo-II targeting drugs both when administered prior to and after the topo-II targeting agents. Thus, our data suggest that sequential rather than simultaneous administration of aclarubicin and topo-II targeting agents may be superior with respect to net-cytotoxicity. In conclusion, our results support the notion that aclarubicin interferes with steps prior to the formation of the cleavable complex in the catalytic cycle of topo-II, and further that the antagonism of aclarubicin on the effect of topo-II targeting drugs may be due to a decrease in the initial noncovalent binding of topo-II to DNA.