Ranking the Binding Energies of p53 Mutant Activators and Their ADMET Properties.

The guardian of the genome, p53, is the most mutated protein found in all cancer cells. Restoration of wild-type activity to mutant p53 offers promise to eradicate cancer cells using novel pharmacological agents. Several molecules have already been found to activate mutant p53. While the exact mechanism of action of these compounds has not been fully understood, a transiently open pocket has been identified in some mutants. In our study, we docked twelve known activators to p53 into the open pocket to further understand their mechanism of action and rank the best binders. In addition, we predicted the absorption, distribution, metabolism, excretion and toxicity properties of these compounds to assess their pharmaceutical usefulness. Our studies showed that alkylating ligands do not all bind at the same position, probably due to their varying sizes. In addition, we found that non-alkylating ligands are capable of binding at the same pocket and directly interacting with Cys124. The comparison of the different ligands demonstrates that stictic acid has a great potential as a p53 activator in terms of less adverse effects although it has poorer pharmacokinetic properties.

Phase I clinical and pharmacologic study of weekly cisplatin and irinotecan combined with amifostine for refractory solid tumors.

PURPOSE: This Phase I study was designed primarily to determine the maximum tolerated dose (MTD) and dose-limiting toxicities (DLTs) of irinotecan and cisplatin with and without amifostine in children with refractory solid tumors. PATIENTS AND METHODS: Cisplatin, at a fixed dose of 30 mg/m(2), and escalating doses of irinotecan (starting dose, 40 mg/m(2)) were administered weekly for four consecutive weeks, every 6 weeks. After the MTD of irinotecan plus cisplatin was determined, additional cohorts of patients were enrolled with amifostine (825 mg/m(2)) support. Leukocyte DNA-platinum adducts and pharmacokinetics of cisplatin and WR-1065 (amifostine-active metabolite) were also determined. RESULTS: Twenty-four patients received 43 courses of therapy. The MTD for irinotecan administered in combination with cisplatin (30 mg/m(2)) was 50 mg/m(2). The DLTs of this combination were neutropenia and thrombocytopenia. With the addition of amifostine, at an irinotecan dose of 65 mg/m(2) and cisplatin dose of 30 mg/m(2), the DLT was hypocalcemia. Although no objective responses were observed, six patients received at least three courses of therapy. The amounts of platinum adducts (mean +/- SD) were 10 +/- 20 molecules/10(6) nucleotides. The maximum plasma concentrations (C(max)) for free cisplatin and WR-1065 were 4.5 +/- 1.6 micro M and approximately 89 +/- 10 micro M, respectively. The half-life (t(1/2)) for free plasma cisplatin was 25.4 +/- 5.4 min. The initial t(1/2) for plasma WR-1065 was approximately 7 min and terminal t(1/2) approximately 24 min. CONCLUSION: The combination of cisplatin and irinotecan administered weekly for 4 weeks in children with refractory cancer is well tolerated. Amifostine offers some myeloprotection, likely permitting >/=30% dose escalation for irinotecan, when administered in a combination regimen with cisplatin. However, effective antiemetics and calcium supplementation are necessary with the use of amifostine. Further escalation of irinotecan dosing, using these precautions for amifostine administration, may be possible.

Enhancement of bone marrow radioprotection and reduction of WR-2721 toxicity by Ocimum sanctum.

The radioprotective effect of the leaf extract of Ocimum sanctum (OE) in combination with WR-2721 (WR) was investigated on mouse bone marrow. Adult Swiss mice were injected intraperitoneally (i.p.) with OE (10 mg/kg on 5 consecutive days), or 100-400 mg/kg WR (single dose) or combination of the two or double-distilled water (DDW) and whole-body exposed to 4.5 Gy gamma-irradiation (RT). Metaphase plates were prepared from femur bone marrow on days 1, 2, 7 and 14 post-treatment and chromosomal aberrations were scored. The maximum number of aberrant cells was observed at 24 h after irradiation in all the groups. However, pretreatment with OE or WR individually resulted in a significant decrease in aberrant cells as well as different types of aberrations. The combination of the two further enhanced this effect; resulting in a 2-fold increase in the protection factor (PF = 6.68) compared to 400 mg/kg WR alone. The percent aberrant cells decreased linear-quadratically with WR dose when given individually, while in the OE + WR pretreatment animals the values showed a linear dose response. Combination of OE with WR doses above 200 mg/kg completely eliminated rings, polyploidy and pulverization of chromosomes. Percent aberrant cells decreased with time in all groups, though the values remained higher than normal even on day 14 in the RT alone as well as those treated with single agent + RT. WR doses above 200 mg/kg before RT resulted in significantly higher frequency of aberrant cells compared to RT and OE + RT groups on day 14, suggesting delayed WR toxicity; but combination of OE with WR brought down these values to normal level, indicating that OE combination, in addition to enhancing WR protection, may also act as a detoxifier. The protective effect of OE and WR is also reflected in the enhancement of bone marrow CFU survival. Both OE and WR possessed significant free radical scavenging activity in vitro. The combination of the two further enhanced this effect, suggesting that the enhanced free radical scavenging activity by combining the two protectors results in the higher bone marrow cell protection. The significant elevation in chromosome protection obtained by combining OE with WR, with reduction in the latter's toxicity at higher doses, suggests that the combination may have promise for radioprotection in humans.

[The radioprotective efficacy and pharmacological properties of S,beta-amidinoethylthiophosphate]. / Radiozashchitnaia éffektivnost' i nekotorye farmakologicheskie svoistva S,beta-amidinoétiltio fosfata.

S,beta-Amidinoethyl thiophosphate, a radioprotective agent that was synthesized and studied, was shown to have certain advantages over cystamine: it was effective when used in a lesser amount; it was less toxic, had higher therapeutic effect, and, in contrast to castamine, it did not inhibit physical efficiency of animals. S,beta-Amidinoethyl thiophosphate and gammaphos were very similar in properties.

Radioprotection by metals: selenium.

The need exists for compounds that will protect individuals from high-dose acute radiation exposure in space and the agents that might be less protective but less toxic and longer acting. Metals and metal derivatives provide a small degree of radioprotection (dose reduction factor < or = 1.2 for animal survival after whole-body irradiation). Emphasis is placed here on the radioprotective potential of selenium (Se). Both the inorganic salt, sodium selenite, and the organic Se compound, selenomethionine, enhance the survival of irradiated mice (60Co, 0.2 Gy/min) when injected IP either before (-24 hr and -1 hr) or shortly after (+15 min) radiation exposure. When administered at equitoxic doses (one-fourth LD10; selenomethionine = 4.0 mg/kg Se, sodium selenite = 0.8 mg/kg Se), both drugs enhanced the 30-day survival of mice irradiated at 9 Gy. Survival after 10-Gy exposure was significantly increased only after selenomethionine treatment. An advantage of selenomethionine is lower lethal and behavioral toxicity (locomotor activity depression) compared to sodium selenite, when they are administered at equivalent doses of Se. Sodium selenite administered in combination with WR-2721, S-2-(3-aminopropylamino)ethylphosphorothioic acid, enhances the radioprotective effect and reduces the lethal toxicity, but not the behavioral toxicity, of WR-2721. Other studies on radioprotection and protection against chemical carcinogens by different forms of Se are reviewed. As additional animal data and results from human chemoprevention trials become available, consideration also can be given to prolonged administration of Se compounds for protection against long-term radiation effects in space.

Selenium pretreatment enhances the radioprotective effect and reduces the lethal toxicity of WR-2721.

Although WR-2721, S-2-(3-aminopropylamino)ethylphosphorothioic acid, is an effective radioprotector, its use is limited by its toxicity. Combining WR-2721 with other agents might decrease its toxicity and/or increase its effectiveness. The effect of selenium (Se) pretreatment on the acute toxicity and radioprotective effect of WR-2721 was studied in male CD2F1 mice. Injection of 1.6 mg/kg Se 24 hr before WR-2721 (800-1200 mg/kg, IP) decreased the lethality of WR-2721 significantly. Lower doses of Se were also effective, but simultaneous administration was not effective. Se injection alone (1.6 mg/kg) 24 hr before cobalt-60 irradiation increased the survival (dose reduction factor, DRF = 1.1) significantly. A synergistic effect on post-irradiation survival was observed when Se was injected 24 hr before WR-2721 (200-600 mg/kg IP 1/2 before irradiation). For example, after exposure to 22 Gy (1 Gy/min), 30-day survival was 100% when mice were treated with both Se and 600 mg/kg WR-2721, and was 13% with WR-2721 alone. The DRF after 400 mg/kg WR-2721 was 2.6 with Se compared to 2.2 without Se pretreatment. Alkaline phosphatase activity in bone marrow cells and serum was significantly depressed after treatment with 1.6 mg/kg Se, suggesting that a retardation of conversion of WR-2721 to its active free sulfhydryl form through the action of alkaline phosphatase might be partly responsible for the effects of Se. Other possible mechanisms related to the antioxidant properties of Se are under investigation.

Protection of cultured mammalian cells by S-2-(3-aminopropylamino)ethylphosphorothioic acid(WR-2721).

The ability of WR-2721 to protect cultured mammalian cells against radiation-induced killing was nearly the same as that of cysteamine when WR-2721 was activated by mouse liver extract. Without the liver extract, protection by WR-2721 required long incubations with the cells prior to irradiation. The protective activity increased in proportion to the cell concentration. The dose reduction factor at a concentration of 4 mM WR-2721 was 1.11 and 1.41 for 1.5 X 10(5) cells/ml and 15 X 10(5) cells/ml of cultured cells, respectively. A non-protein bound sulfhydryl group was detected in cell suspensions after incubation with WR-2721, but it was not a dephosphorylated product of WR-2721.