Novel Organo-Substituted Cyclophosphazenes via Reaction of a Monohydro Cyclophosphazene and Acetyl Chloride.

A new olefin-substituted tetrachlorocyclotri-lambda(5)-phosphazene (NPCl(2))(2)NP(i)Pr{C[OC(O)Me]=CH(2)} (4) and an unique bicyclo-lambda(5)-triphosphazene [(NPCl(2))(2)NP(i)Pr](2)C(OH)Me (5) have been prepared from the reaction of MeC(O)Cl and (NPCl(2))(2)NP(i)PrH in the presence of Et(3)N. Exclusive formation of 4 could be achieved by using an excess of both Et(3)N and MeC(O)Cl. The phosphazene rings in 5 are bridged by one carbon atom. The presence of this C(OH)Me bridge induces an asymmetric environment which renders the isopropyl ligands no longer equivalent under NMR conditions. Crystals of 4 are monoclinic, space group P2(1)/n, with a = 13.158(1) Å, b = 9.555(1) Å, c = 14.859(1) Å, beta = 115.502(6) degrees, V = 1686.1(3) Å(3), and Z = 4. Crystals of 5 are monoclinic, space group P2(1)/c, with a = 13.255(2) Å, b = 12.050(2) Å, c = 16.280(2) Å, beta = 98.91(1) degrees, V = 2568.8(7) Å(3), and Z = 4.

Phase I and pharmacokinetic study of trans-N3P3Az2(NHMe)4.

trans-N3P3Az2(NHMe)4, an aziridinyl-substituted cyclophosphazene, was tested for its toxicity, pharmacokinetic behavior, and cytostatic activity in a phase I study in 30 patients. A total of 66 courses of a single iv bolus injection were given in five dose steps. Toxicity consisted of leukocytopenia and thrombocytopenia, dose limiting at 70 mg/m2, mild anemia, and some nausea. Leukocyte and platelet count nadirs fell between 2 and 3 weeks, with recovery at 6 weeks. A tendency for cumulative thrombocytopenia was noticed in three of 13 patients at risk. A three-phase plasma elimination model was applicable with t1/2 alpha of 9.9 minutes, t1/2 beta of 78.5 minutes, and t1/2 gamma of 435.5 minutes; renal drug excretion was substantial. Three partial remissions in 21 evaluable patients suggest some clinical activity for this drug.

Isomer-dependent cytostatic activity of bis(1-aziridinyl)cyclophosphazenes.

A number of recently synthesized mono- and bis(1-aziridinyl) derivatives of the inorganic ring systems (NPCl2)3 and (NPCl2)4 was tested for their cytostatic activity in vitro (L1210 and L5178Y cells) and in vivo (intraperitoneal leukemia L1210 in CDF1 mice). Generally, the nongeminal bis(1-aziridinyl) isomers (either trans or cis) appear to be potent tumor growth inhibitors in contrast to their geminally substituted and mono(1-aziridinyl)-substituted analogues. A relationship between the biological activity and the number of alkylating centers (i.e., P atoms carrying one or two aziridinyl groups) is proposed.

Different type of DNA damage caused by three aziridinyl substituted cyclophosphazenes in a human small cell lung carcinoma cell line.

Aziridinyl substituted cyclophosphazenes are a new group of inorganic chemical agents with in vitro and in vivo cytotoxic activity. We investigated the mode of action on DNA of three different compounds, 1,3,3,5,5-pentakis (1-aziridinyl)-1 lambda 6,2,4,6,3 lambda 5,5 lambda 5-thiatriazadiphosphorine -1-oxide (SOAz), trans-1,3-bis(1-aziridinyl)-1,3,5,5-tetrakis (methylamino)-2,4,6,1 lambda 5,3 lambda 5,5 lambda 5-triazatriphosphorine (AZP), and 1,trans-5-bis(1-azaridinyl)-gem-1,3,3'-cis-5,7,7'-hexakis (methylamino)-2,4,6,8,1 lambda 5,3 lambda 5,5 lambda 5,7 lambda 5 -tetraazatetraphosophocine (AZM), of this group in the Ehrlich ascites tumor cell line (EAT) and a human small cell carcinoma cell line. The DNA damage was evaluated by alkaline elution and ethidium bromide fluorescence assay. Each compound gave a different pattern of DNA damage. SOAz caused neither single strand breaks nor cross-links, AZP gave cross-links, and AZM gave single strand breaks and cross-links in both cell lines after drug incubation for 6 h. The range of concentrations leading to cytoxicity of AZP and AZM in the clonogenic assay coincided with the concentrations leading to DNA damage. Cell kill occurred with SOAz in the same range of concentrations, however, without detectable evidence of DNA damage. It was concluded that cyclophosphazenes are probably a heterogeneous group as far as their mode of action as cytostatic agents is concerned.

Bone marrow toxicity of cyclophosphazenes is related to their structure and the treatment schedule.

For three aziridinyl-substituted inorganic heterocycles belonging to the cyclophosphazene group, the tendency for cumulative bone marrow toxicity was studied in mice. In a one-day regimen, one of these drugs, gem-N3P3Az4Pyr2 (Az = aziridinyl, Pyr = pyrrolidinyl) (AZX), led to an increased death rate after a repeated injection, the number of bone marrow stem cells (CFUgm) being decreased 5 weeks after the second injection of this drug. In a four-day regimen two drugs, (NPAz2)2 NSOAz (Soaz) and AZX, led to an increased death rate after the second treatment course. In surviving animals leucocyte and thrombocyte counts were significantly lower in the second than in the first course. CFUgm counts were decreased for both drugs. For the third drug, trans-N3P3(Az)2(NHMe)4 (AZP), no evidence of cumulative bone marrow toxicity was demonstrated. It is suggested that whereas cytostatic activity of these compounds seems to be comparable, their tendency to cause cumulative marrow toxicity may vary.

Phase I evaluation of SOAz (1,3,3,5,5 pentakis(aziridino)-1 lambda 6, 2,4,6,3 lambda 5, 5 lambda 5 thiatriaza-diphosphorine-1-oxide) in a weekly schedule.

Eleven patients with advanced cancer were treated with SOAz, the first aziridino substituted inorganic heterocyclic compound to undergo phase I clinical trials. The agent was administered as a rapid i.v. infusion once a week in a dose of 50, 75 or 100 mg/m2. Severe myelotoxicity, which was prolonged and delayed in onset, precluded continuing treatment for more than three courses in 9 of 11 patients. In two patients thrombocytopenia showed no signs of recovery 9 and 11 weeks after the last infusion. Two minor responses were noted and there was one therapy-related death. Because of severe myelotoxicity, which is cumulative and may be irreversible, this treatment schedule seems unsuitable for phase II studies.

Determination of the antitumor agent SOAz (1,3,3,5,5 pentakis(aziridino)-1 lambda 6,2,4,6,3 lambda 5, 5 lambda 5 thia-triazadiphosphorine-1-oxide) by a gas chromatographic assay suitable for pharmacokinetic studies in man.

A sensitive method, based on capillary gas chromatography using a thermionic detector, has been developed for the new antitumor agent pentakis(aziridino)-thiatriazadiphosphorine-oxide, (NPAz2)2NSOAz ('SOAz'), in order to obtain pharmacokinetic data from patients receiving this drug IV in clinical trials. A structural analog of SOAz, (NPAz2)2NSOPh ('SOPh'), was used as an internal standard. The detection limit of SOAz with this method was 0.01 mg/l for serum and 0.04 mg/l for urine. The coefficient of variation (n = 10) was 6,0% at 1.5 mg/l in serum and 1.6% at 75.0 mg/l in urine. Analytical recoveries averaged 89.9% from serum and 86.7% from urine. In two patients treated with subtoxic doses of SOAz (55 mg/m2), serum levels were found ranging from 3.0 to 0.16 mg/l at 10 min and 12 h, respectively, after administration. This assay seems to be useful for determining SOAz in samples from patients receiving subtoxic doses of SOAz.

Clinical pharmacokinetics of (NPAz2)2NSOAz: 'SOAz'.

Pharmacokinetic studies of 1,3,3,5,5 pentakis (aziridino)-1 lambda 6,2,4,6,3 lambda 5,5 lambda 5 thiatriazadiphosphorine-1-oxide ('SOAz'), a new antineoplastic agent containing an inorganic ring system and five aziridino groups, were performed in six patients who took part in a phase I clinical trial of the agent. The drug was administered as a rapid IV infusion. Serum decay curves could be fitted to an open two-compartment model of drug disappearance. After a short initial phase with a t 1/2 (+/- SD) of 7.8 +/- 4.2 min a terminal phase with a dose-independent half-life of 203 +/- 17 min occurred. The coefficient of apparent distribution was 0.71 +/- 0.13. The renal clearance was 75 +/- 11 ml/min and the total body clearance 162 +/- 23 ml/min. A percentage of 46.5 +/- 6.6 of the administered drug could be recovered unchanged in the urine within 24 h. It is concluded that in view of concentrations known to be effective in vitro, administration in large single doses may be advantageous. Dose adjustments should be made for patients with impaired renal function.

Phase I clinical trial of (NPAz2)2NSOAz: 'SOAz'.

(NPAz2)2NSOAz ('SOAz') is the first of a new class of cytotoxic agents containing an inorganic heterocyclic ring system to enter clinical trial. It was used to treat 31 patients with advanced cancer by IV infusion over 30 min on days 1, 2, 3, and 4 of a 21-day cycle, which was postponed if necessary to allow for hematological recovery. A total of 46 courses evaluable for toxicity was given and the tumor response was evaluable in 21 patients. Seven dose levels, ranging from 25 mg/m2 to 300 mg/m2, were studied, with three to six patients at each level. The only major toxicity was myelosuppression, especially thrombocytopenia, which was dose-limiting. Platelets decreased from the 14th day onward, with a nadir 4-5 weeks after administration. Leukopenia was less predictable and reached a nadir 3-5 weeks after administration. In most patients recovery was complete after 6-9 weeks. Myelosuppression was clearly cumulative in succeeding courses and proved irreversible in three patients. Anemia also occurred, but otherwise SOAz was remarkably well tolerated. There were no responses and no therapy-related deaths. The highest tolerated dose for patients who had received no or only minor chemotherapy prior to treatment with SOAz was 300 mg/m2, and that for heavily pretreated patients, 175 mg/m2. Because of cumulative myelotoxicity phase II studies with SOAz are not recommended.

Cytostatic activity of inorganic heterocycles in an in vitro screening system.

Six representatives of inorganic cyclic systems (NPAz2)2 NSOX(Az = aziridino, X = F, Az, Ph) and (NPAz2)2 NPAzR [R = Az, Morph (morpholino), Pyr (pyrrolidino)] show cytostatic activity in an in vitro screening system. The technique of the in vitro screening system used is described. L5178Y and Ehrlich ascites cells are grown as suspension cultures in concave-bottomed wells in microtiter test plates using serial dilutions of the drugs in the medium. The diameter of the cell sedimentation spots, which can be compared visually is taken to determine the lowest active dose. The results of this test correspond with the cytostatic activities observed in former in vivo experiments.

Mass spectrometry as a technique for testing the purity of drugs for biological use: the case of new antitumor cyclophosphazenes.

Mass spectrometry has been used for testing the chemical purity of some new antitumor cyclophosphazene compounds. the spectrum of N3P3Az6 (code name MYKO 63)--which exhibits noticeable activity on murine P 388, L 1210 and B 16 tumors--appeared to be remarkably simple, as most of the fragmentations arose from successive losses of the aziridino radicals. Traces of the pentaziridinomonochloro impurity formed by an incomplete substitution of N3P3Cl6 chlorine atoms under aziridinolysis could be detected in an impure and toxic sample by spectral subtraction. Quantification of this impurity was performed by selected ion monitoring in the direct inlet mode of sample introduction. The mass spectra of other derivatives of this class of compounds are slightly more complex, since the decomposition pathways showed more intense H-transfers associated with the loss of substituents.