ALBERT

Description: This study compares the pharmacokinetic and the antithrombotic properties of two pentasaccharides with high affinity to antithrombin III with those of a conventional low molecular weight heparin, CY216, in the rabbit. On a weight basis, SR 90107A/ORG 31540 (natural pentasaccharide [NPS]) and SR 80027A/ORG 31550 (sulfated pentasaccharide [SPS]) were, respectively, 4.7 and 26 times more potent antifactor Xa inhibitory agents than CY216. They were devoid of antithrombin activity, whereas the antifactor Xa/antithrombin ratio of CY216 was 3.8. After bolus intravenous administration, the clearance (mL/kg/h) of CY216 decreased from 91 +/- 27 for the dose of 12.5 U/kg to 49 +/- 14 for the dose of 50 U/kg and then remained constant up to the highest dose tested (500 U/kg). The clearance of NPS was unrelated to the dose and comparable to that of CY216 over 50 U/kg, whereas that of SPS was 10 times lower. Consistent results were observed after continuous intravenous infusions for 9 hours and subcutaneous administration. The duration of the antithrombotic effect was compared after a single subcutaneous injection of 250 U/kg of either compound in the stasis-Wessler model using human serum as thrombogenic stimulus. Two hours after the injection, the three compounds provided a thrombus prevention of greater than 95% and mean plasma activities of 0.8, 0.9, and 1.9 U/mL for CY216, NPS, and SPS, respectively. Twelve hours after injection, the antithrombotic effects of CY216 and NPS had totally vanished, whereas that of SPS was 68%. At that time, the plasma anti-Xa activities were less than 0.06 U/mL for CY216 and NPS, but 1.1 U/mL for SPS. For the latter compound, significant antithrombotic effects and detectable anti-Xa activities were still recorded 48 hours after the injection. The antithrombotic potency of the three compounds was also compared as their ability to inhibit the growth of a standardized venous thrombosis during 4 hours. The lowest total doses providing the maximum inhibitory effect were 3,125, 1,428, and 62 micrograms/kg for CY216, NPS, and SPS, respectively. These doses generated mean steady state antifactor Xa activities of 1.06, 1.5, and 1.2 anti-Xa U/mL, respectively. These observations indicate that the amplification mechanisms triggered by thrombin bound to fibrin and leading to the generation of new thrombin are essential to ensure venous thrombosis growth and that these mechanisms may be efficiently inhibited by pure antifactor Xa targeting agents.

Description: This study compares the pharmacokinetic and the antithrombotic properties of two pentasaccharides with high affinity to antithrombin III with those of a conventional low molecular weight heparin, CY216, in the rabbit. On a weight basis, SR 90107A/ORG 31540 (natural pentasaccharide [NPS]) and SR 80027A/ORG 31550 (sulfated pentasaccharide [SPS]) were, respectively, 4.7 and 26 times more potent antifactor Xa inhibitory agents than CY216. They were devoid of antithrombin activity, whereas the antifactor Xa/antithrombin ratio of CY216 was 3.8. After bolus intravenous administration, the clearance (mL/kg/h) of CY216 decreased from 91 +/- 27 for the dose of 12.5 U/kg to 49 +/- 14 for the dose of 50 U/kg and then remained constant up to the highest dose tested (500 U/kg). The clearance of NPS was unrelated to the dose and comparable to that of CY216 over 50 U/kg, whereas that of SPS was 10 times lower. Consistent results were observed after continuous intravenous infusions for 9 hours and subcutaneous administration. The duration of the antithrombotic effect was compared after a single subcutaneous injection of 250 U/kg of either compound in the stasis-Wessler model using human serum as thrombogenic stimulus. Two hours after the injection, the three compounds provided a thrombus prevention of greater than 95% and mean plasma activities of 0.8, 0.9, and 1.9 U/mL for CY216, NPS, and SPS, respectively. Twelve hours after injection, the antithrombotic effects of CY216 and NPS had totally vanished, whereas that of SPS was 68%. At that time, the plasma anti-Xa activities were less than 0.06 U/mL for CY216 and NPS, but 1.1 U/mL for SPS. For the latter compound, significant antithrombotic effects and detectable anti-Xa activities were still recorded 48 hours after the injection. The antithrombotic potency of the three compounds was also compared as their ability to inhibit the growth of a standardized venous thrombosis during 4 hours. The lowest total doses providing the maximum inhibitory effect were 3,125, 1,428, and 62 micrograms/kg for CY216, NPS, and SPS, respectively. These doses generated mean steady state antifactor Xa activities of 1.06, 1.5, and 1.2 anti-Xa U/mL, respectively. These observations indicate that the amplification mechanisms triggered by thrombin bound to fibrin and leading to the generation of new thrombin are essential to ensure venous thrombosis growth and that these mechanisms may be efficiently inhibited by pure antifactor Xa targeting agents.

Description: In this study, we evaluated the individual in vitro sensitivity of fresh acute myeloid leukemia (AML) cells to VP-16, and attempted to correlate VP-16 cytotoxicity with AML cell growth characteristics and drug-induced DNA single-strand breaks (SSB). Primary (PE1) colony inhibition assays allowed us to characterize two distinct groups of AML: group I (patients 1 through 6), which displayed sensitivity to VP- 16 similar to that of normal CFU-GM (IC90 of 20.52 +/- 2.44 micrograms/mL v 20.48 +/- 2.23 micrograms/mL after 1 hour drug exposure, respectively); and group II (patients 7 through 11), which was more sensitive to VP-16 (IC90 of 7.26 +/- 2.93 micrograms/mL, P = .004). Subsequently, groups I and II were termed normosensitive and hypersensitive, respectively. This objective VP-16 sensitivity classification, as determined by PE1, remained unaltered when assessed by secondary (PE2) colony inhibition assay (evaluating the self-renewal fraction of AML progenitors), or by cytofluorometric viability assay (evaluating the ultimately differentiated blast cell population). These findings would suggest that individual sensitivity to VP-16 of a particular cell population is maintained throughout CFU-AML differentiation. Finally, we report that sensitivity of AML cells to VP- 16 did not correlate either with cell growth characteristics or with SSB generation. Indeed, AML cell sensitivity to VP-16 appeared more closely related to DNA repair kinetics after drug removal, ie, hypersensitivity being essentially characterized by a prolonged retention of SSB during the posttreatment period. Interestingly, the established HL-60 cell line, which presented greater sensitivity to VP- 16 cytotoxicity than KG1, HEL, and K562, was also found to exhibit delayed DNA SSB repair kinetics, as compared with the other AML cell lines. These results suggest that hypersensitivity to VP-16 of some AML cells may be related to a deficient DNA-repair mechanism.

Description: In this study, we evaluated the individual in vitro sensitivity of fresh acute myeloid leukemia (AML) cells to VP-16, and attempted to correlate VP-16 cytotoxicity with AML cell growth characteristics and drug-induced DNA single-strand breaks (SSB). Primary (PE1) colony inhibition assays allowed us to characterize two distinct groups of AML: group I (patients 1 through 6), which displayed sensitivity to VP- 16 similar to that of normal CFU-GM (IC90 of 20.52 +/- 2.44 micrograms/mL v 20.48 +/- 2.23 micrograms/mL after 1 hour drug exposure, respectively); and group II (patients 7 through 11), which was more sensitive to VP-16 (IC90 of 7.26 +/- 2.93 micrograms/mL, P = .004). Subsequently, groups I and II were termed normosensitive and hypersensitive, respectively. This objective VP-16 sensitivity classification, as determined by PE1, remained unaltered when assessed by secondary (PE2) colony inhibition assay (evaluating the self-renewal fraction of AML progenitors), or by cytofluorometric viability assay (evaluating the ultimately differentiated blast cell population). These findings would suggest that individual sensitivity to VP-16 of a particular cell population is maintained throughout CFU-AML differentiation. Finally, we report that sensitivity of AML cells to VP- 16 did not correlate either with cell growth characteristics or with SSB generation. Indeed, AML cell sensitivity to VP-16 appeared more closely related to DNA repair kinetics after drug removal, ie, hypersensitivity being essentially characterized by a prolonged retention of SSB during the posttreatment period. Interestingly, the established HL-60 cell line, which presented greater sensitivity to VP- 16 cytotoxicity than KG1, HEL, and K562, was also found to exhibit delayed DNA SSB repair kinetics, as compared with the other AML cell lines. These results suggest that hypersensitivity to VP-16 of some AML cells may be related to a deficient DNA-repair mechanism.