Jacob J. Clement

Tumor Reoxygenation and Postirradiation Vascular Changes

Postirradiation reoxygenation kinetics of the Walker 256 carcinoma were examined and related to radiation-induced changes in tumor vascular functions. Changes in the hypoxic cell component of irradiated Walker tumors may occur by two mechanisms. Reoxygenation of previously hypoxic cells may be due to an increased rate of blood flow in some parts of the tumor. Hypoxic tumor cells may also be eliminated by cell death due to prolonged or severe hypoxia in other parts of the tumor as a result of substantial damage to the tumor vasculature as seen in radiation-induced changes in vascular volume and blood vessel permeability. Reoxygenation of experimental tumors following single, massive doses of radiation may be different from that occurring in human tumors during the course of multifraction radiotherapy.

Changes in functional vascularity and cell number following x-irradiation of a murine carcinoma

Abstract Post-irradiation changes in vascular function and cell number in the transplantable SCL carcinoma of AJ mice were examined Vascular volume/g tumor, as measured by 15 Cr-labeled red blood cell dilution, increased within 1 day after 1000 or 2000 rad and then decreased. The number of living cells/g tumor, estimated from single-cell preparations, declined to a minimum at day three post-irradiation with 1000 or 2000 rad. Calculation of vascularity on a per living cell basis indicated that the vascular volume increased to 197% and 286% of controls 3 days after irradiation with 1000 and 2000 rad, respectively. These data indicate that post-irradiation reoxygenation of hypoxic tumor cells may be caused by a decrease in oxygen consuming cells which is greater in magnitude than the corresponding decrease in functional vascularity.

Efficacy of clarithromycin for treatment of experimental Lyme disease in vivo.

Clarithromycin provided effective therapy against arthritis induced by Borrelia burgdorferi infection in the hamster. In vitro, clarithromycin was at least 1 log more potent than tetracycline against two isolates of B. burgdorferi from human sources, as measured by MICs and 50% inhibitory concentrations. Clarithromycin was effective in preventing the onset of B. burgdorferi-induced arthritis, as determined by several parameters of paw swelling. When administered after the onset of arthritis, clarithromycin therapy reduced the degree of swelling and decreased recovery time. These results suggest that clarithromycin has potential as an effective therapy for Lyme disease.

Cytotoxic and Radiosensitizing Effects of 5-Thio-d-Glucose on Hypoxic Cells

The effect of 5-thio-D-glucose on the viability and radiosensitivity of P815-X2 mouse mastocytoma cells was studied in vitro. By itself, this compound is specifically cytotoxic toward hypoxic cells; moreover, it sensitizes hypoxic cells to irradiation while it protects aerobic cells from radiation damage. These features, together with its low toxicity, suggest that 5- thio-D-glucose may be useful adjuvant to radiotherapy

Antitumor activity and biochemical effects of topsentin

Abstract Topsentin, a bis(indolyl)imidazole marine natural product, inhibited the proliferation of cultured human and murine tumor cells at micromolar concentrations (ic50 values ranged from 4 to 40 μM) and was active against in vivo P388 leukemia (% T C = 137, 150 mg/kg , QD1-5) and B16 melanoma (% T C = 144, 37.5 mg/kg , QD1-9) tumors. Effects of 30 μM topsentin (1-hr exposures) on incorporation of radiolabeled precursors by P388 cells indicated inhibition of DNA synthesis (91%) and to a lesser extent RNA synthesis (57%), whereas synthesis of protein was unaffected (0%). Fluorescence spectral changes and competitive binding experiments with ethidium bromide indicated that topsentin interacted with DNA. No evidence for intercalation was observed in DNA unwinding studies, but competitive binding experiments with Hoechst 33342 and CC-1065 indicated that topsentin bound to DNA in the minor groove.

Clarithromycin therapy of experimental Treponema pallidum infections in hamsters.

Clarithromycin was shown to be effective therapy for Treponema pallidum infections in hamsters. Clarithromycin therapy was effective when initiated either 1 or 8 days after infection. The delay in initiation of therapy allowed an active infection to develop. The treponemal burden in lymph tissue of treated hamsters was eradicated, as determined by dark-field microscopy and by inoculation of lymph material into susceptible hamsters. Treatments with clarithromycin and the 14-hydroxy metabolite of clarithromycin were equally effective. Therapy with clarithromycin and penicillin was not antagonistic and did not appear to be synergistic when the two drugs were given concurrently. Pharmacokinetic evaluation of clarithromycin in hamsters showed that the doses which produced effective therapy yielded concentrations in serum similar to those routinely achieved in human sera. These findings demonstrate that clarithromycin is effective in treating active or incubating syphilis in the hamster model and could be useful in treating humans.

Efficacy of AZT therapy in reducing p24 antigen burden in a modified SCID mouse model of HIV infection

A modified severe combined immunodeficient (SCID) mouse model of HIV infection which utilized multiple reconstitutions with human lymphocytes and a large inoculum of HIV was investigated. This mouse model yielded splenic HIV p24 antigen concentrations detectable by standard clinical means. The concentration of p24 exceeded 600 pg/g of spleen through 4 weeks postinfection. A 1-week course of AZT therapy initiated after infection produced a dose responsive reduction in p24 antigen burden. Up to a 95% reduction in p24 antigen burden was observed following AZT therapy at 50 mg/kg/day, while AZT therapy at 5 and 0.5 mg/kg/day produced 52 and 18% reductions. In vitro and pharmacokinetic evaluations correlated potency and tissue concentrations of AZT with treatment efficacy. Active HIV replication in the SCID mice was suggested by both the recovery of viable virus from SCID spleens, and by the efficacy of a brief course of AZT therapy. This SCID mouse model of HIV infection was more quantitative than previous mouse models that utilize PCR-based techniques for detection of HIV. The high HIV burden in this SCID mouse model allowed reductions in p24 concentration to be monitored in response to AZT therapy. A dose response to AZT therapy was demonstrated, even when the first dose was administered after infection. This result suggests greater sensitivity than in previous models in which pretreatment with AZT was required to produce a protective response. This SCID mouse model may be useful for determining efficacy of experimental HIV therapeutics prior to clinical use. An effective animal model could result in a reduction in cost and more rapid development of effective HIV therapeutics.

Skin radioprotection by 5-thio-D-glucose

The radioprotective effect of 5-thio-D-glucose on mouse skin was studied. Intraperitoneal injection of A/J mice with 1.5 g/kg of 5-thio-D-glucose 2 hr prior to X irradiation of the foot reduced early foot skin damage through Day 40 postirradiation by a dose modification factor of 1.3 +/- 0.1. Similarly, late foot deformity during Days 60-90 postirradiation was reduced by a factor of 1.2 +/- 0.1. The radioprotective effect of 5-thio-D-glucose was also compared with that of WR-2721, an aminothiol radioprotector, in CDF1 mice. An intraperitoneal injection of 1.5 g/kg of 5-thio-D-glucose reduced early radiation-induced skin damage by a dose modification factor of 1.2 +/- 0.1 as compared to that of 1.5 +/- 0.2 by 0.65 g/kg of WR-2721 in this strain of mice. 5-Thio-D-glucose is also known to specifically kill and radiosensitize hypoxic tumor cells. Consequently, this drug may be a useful radiotherapy adjuvant, reducing normal tissue damage and enhancing tumor control by minimizing hypoxic protection.

Tumor Cell Respiration Following Irradiation

Oxygen consumption rates for mouse mastocytoma cells examined from 3 to 4 hours after x-irradiation with 250-2000 rads were consistently higher than controls. Cyclic fluctuations in oxygen consumption per cell were dose-dependent; peaks in consumption were generally greater in magnitude and occurred later in time with increasing dose. The cyclic response in consumption is probably due to cell synchronization effects, while the overall higher respiration rates of irradiated cells may reflect increased metabolic activity in response to radiation damage. Oxygen consumption rates for the total cell population were cyclic after 250 and 500 rads, but declined steadily after 1000 or 2000 rads; oxygen consumption rates tended to be lower than controls, especially 12-24 hours postirradiation. Differences between cellular and population oxygen consumption rates reflect changes in cell number after irradiation. It is suggested that postirradiation reoxygenation kinetics in solid tumors may result from changes in tumor oxygen demand.

Intracisternal A and bar-shaped particles in murine neuroblastoma C 1300.

Transplantable murine neuroblastoma C 1300 was studied ultrastructurally a t varying time intervals ranging from 2 hours to 40 days before and after X-irradiation. Following X-irradiation, 2000 and 4000 rads in a single dose, the uniformly small tumor cells became progressively enlarged, multinucleated and degenerated, starting a t one to two days. At five to seven days, the uni- and multinucleated giant cells predominated over the small tumor cells, while the giant cells progressively disappeared thereafter and the small tumor cells predominated over the giant cells a t 10 to 14 days. The giant cells contained abundant subcellular organelles and the X-irradiated tumor cells apparently continued to produce the organelles until they degenerated. Two types of cytoplasmic particles, intracisternal A and bar-shaped, were observed in the tumor cells. The intracisternal A particles occurred in almost all non-irradiated tumor cells though their number varied considerably from cell to cell, while they were observed less frequently in the radiation-induced giant cells probably due to a dilution effect rather than an actual numerical decrease. The bar-shaped particles, hitherto undescribed in the neuroblastoma, were 23 nm in diameter, variable in length and occasionally tubular. They occurred only in degenerating cells regardless of X-irradiation but were encountered more frequently in irradiated tumors than in non-irradiated ones. It is suggested that they may represent an unknown degenerative product of cytoplasm and/or nucleus rather than virus particles, despite their morphological resemblance to certain virus particles.