Discovery of potent, selective, bioavailable phosphodiesterase 2 (PDE2) inhibitors active in an osteoarthritis pain model, part I: transformation of selective pyrazolodiazepinone phosphodiesterase 4 (PDE4) inhibitors into selective PDE2 inhibitors.

We identified potent, selective PDE2 inhibitors by optimizing residual PDE2 activity in a series of PDE4 inhibitors, while simultaneously minimizing PDE4 activity. These newly designed PDE2 inhibitors bind to the PDE2 enzyme in a cGMP-like mode in contrast to the cAMP-like binding mode found in PDE4. Structure activity relationship studies coupled with an inhibitor bound crystal structure in the active site of the catalytic domain of PDE2 identified structural features required to minimize PDE4 inhibition while simultaneously maximizing PDE2 inhibition.

Discovery of potent selective bioavailable phosphodiesterase 2 (PDE2) inhibitors active in an osteoarthritis pain model. Part II: optimization studies and demonstration of in vivo efficacy.

Selective phosphodiesterase 2 (PDE2) inhibitors are shown to have efficacy in a rat model of osteoarthritis (OA) pain. We identified potent, selective PDE2 inhibitors by optimizing residual PDE2 activity in a series of phosphodiesterase 4 (PDE4) inhibitors, while minimizing PDE4 inhibitory activity. These newly designed PDE2 inhibitors bind to the PDE2 enzyme in a cGMP-like binding mode orthogonal to the cAMP-like binding mode found in PDE4. Extensive structure activity relationship studies ultimately led to identification of pyrazolodiazepinone, 22, which was >1000-fold selective for PDE2 over recombinant, full length PDEs 1B, 3A, 3B, 4A, 4B, 4C, 7A, 7B, 8A, 8B, 9, 10 and 11. Compound 22 also retained excellent PDE2 selectivity (241-fold to 419-fold) over the remaining recombinant, full length PDEs, 1A, 4D, 5, and 6. Compound 22 exhibited good pharmacokinetic properties and excellent oral bioavailability (F=78%, rat). In an in vivo rat model of OA pain, compound 22 had significant analgesic activity 1 and 3h after a single, 10 mg/kg, subcutaneous dose.

Phase I study of aziridinylbenzoquinone (AZQ, NSC 182986) in children with cancer.

Aziridinylbenzoquinone is a quinone compound capable of penetrating the central nervous system. It has demonstrated activity against both intracranial and i.p. murine tumors and human tumor xenographs. We have conducted a Phase I trial of aziridinylbenzoquinone in 60 children with advanced cancer who were refractory to conventional therapy. The drug was given by slow i.v. push on a daily schedule for 5 days every 3 to 4 weeks. The dose range explored included 6 dose levels, ranging from 6 to 12 mg/sq m daily for 5 days in patients with solid tumors and leukemia, and in patients with leukemia, 20, 25, and 30 mg/sq m daily for 5 days. Myelosuppression was the dose-limiting side effect. In patients with solid tumor the highest dose studied was 12 mg/sq m, and the median nadir white blood cell and platelet counts were 0.7 X 10(3) and 6.0 X 10(3)/microliter on Days 17 and 22, respectively. The median recovery day for white blood cells was 39. There may be some evidence of cumulative toxicity with prolonged thrombocytopenia. Other side effects were mild nausea, vomiting, and mucositis. Elevations in liver enzymes and bilirubin were transient and dose dependent, occurring 3 to 4 weeks after drug administration. Of the 34 children with solid tumors, 33 were evaluable for hematopoietic toxicity, 3 were early deaths, and 31 receiving a total of 55 courses were evaluable for therapeutic response. Partial responses lasting 3 weeks to 6 months were seen in the 4 patients with Hodgkin's disease, and in a child with a metastatic spinal cord ependymoma. Fifty-two courses were given to 9 patients with acute lymphocytic leukemia and 17 with acute nonlymphoblastic leukemia. Of the 15 patients with acute nonlymphoblastic leukemia treated at doses greater than or equal to 25 mg/sq m/day for 5 days there was one early death and there were 2 M1 (less than or equal to 5% blasts with normal cellularity), 3 M2A (6 to 15% blasts), and 2 M2B (16 to 39% blasts) bone marrow responses lasting 1 to 3.5 months. Aziridinylbenzoquinone demonstrated activity against acute nonlymphocytic leukemia with maximal tolerated doses of 30 mg/sq m daily for 5 days. Its effect in Hodgkin's disease is encouraging; however, further study will be required to determine its efficacy in central nervous system cancers. Recommended doses for Phase II studies, using daily schedule for 5 days in children with solid tumors, is 9 mg/sq m, and in children with leukemia, it is 25 mg/sq m.

Toxicity of aziridinylbenzoquinone for aerobic and hypoxic cells of a transplanted mouse mammary tumor and interaction of the drug with radiation and adriamycin.

Aziridinylbenzoquinone (AZQ), an experimental drug with good tissue penetration, was tested against aerobic and hypoxic cells of the 16/C transplantable mouse mammary tumor. The drug was given alone or with local tumor radiation to kill most of the aerobic cells. The end point of response was growth delay. AZQ gave additive effects with tumor irradiation and was equally effective against aerobic and hypoxic cells. AZQ was also given in combination with Adriamycin, since the latter drug is known to have poor penetration in solid tissue. Combined treatment led to greater antitumor effects than were obtained with maximally tolerated doses of either drug alone. Isobologram analysis of the interaction between the drugs suggested a superadditive effect, and the addition of Adriamycin had little effect on myelosuppression induced by AZQ. The combination of AZQ and Adriamycin is worthy of further study.

Phase I evaluation and pharmacokinetics of aziridinylbenzoquinone using a weekly intravenous schedule.

Quinone derivatives have shown intensive antitumor activity in a broad variety of neoplasias. Aziridinylbenzoquinone is designed to have adequate lipid solubility to attain useful drug concentrations in the central nervous system. A Phase I study of aziridinylbenzoquinone was conducted in 32 patients with advanced solid cancers. The drug was given as a slow i.v. injection on Days 1, 8, 15, and 22 of a 42-day cycle with a 2-week rest. Five dose levels ranging from 5 to 20 mg/sq m were studied, with 3 to 10 patients treated at each level; a total of 156 doses were administered. The major toxicity was myelosuppression with the median nadir in platelet and white blood cells occurring at Days 15 to 27 of the cycle, and first appearing at doses greater than 10 mg/sq m. Anemia was first seen at the 10-mg/sq m dose level, occurring between Days 22 and 40. Nonmyelosuppressive toxic effects included nausea and vomiting, anorexia, diarrhea, stomatitis, slight alopecia, and transient fever. The highest tolerated dose was 20 mg/sq m, the recommended dose for Phase II studies. Plasma and urine pharmacokinetics were studied in 17 patients by a high-pressure liquid chromatography method. Plasma decay curves could be fitted to a two-compartment open-system model with an overall average alpha and beta half-life values of 10.5 +/- 6.28 min and 16.90 +/- 8.63 (S.D.) hr. Aziridinylbenzoquinone levels were determined in urine samples of 12 patients, but less than 0.1% of the dose was excreted in the 0- to 4-hr sample of two patients, and none was detected in the urine of 10 patients.

Phase I trial and pharmacokinetics of aziridinylbenzoquinone (NSC 182986) in humans.

2,5-Diaziridinyl-3,6-(carboethoxyamino)-1,4-benzoquinone (AZQ) is a rationally designed antitumor agent which possesses sufficient lipid solubility to allow central nervous system penetration as well as adequate aqueous solubility for drug formulation and administration. We have conducted a Phase I trial of AZQ in 40 previously treated patients with advanced cancer. The drug was given as a 15-min i.v. infusion on Days 1 and 8 of a 28-day cycle. Seven dose levels ranging from 1 to 25 mg/sq m were studied with 3 to 11 patients treated at each level. Sixty-nine evaluable cycles of AZQ were administered. The major toxicity was myelosuppression, with the nadir in white blood cells and/or platelet count occurring at Days 15 to 20 of the cycle and first appearing at doses greater than 10 mg/sq m. The highest tolerated dose was 20 mg/sq m, and this dose is recommended for Phase II trials. Other toxicities were mild nausea, slight alopecia, and anemia. Plasma pharmacokinetics was studied in 11 patients by a high-performance liquid chromatography assay. Plasma decay curves could be fitted to a two-compartment open model of drug disappearance with a dose-independent terminal half-life of 33.3 +/- 4.5 (S.D.) min. Cerebrospinal fluid AZQ levels were determined in three patients and revealed readily detectable levels of AZQ.

Treatment of patients with recurrent primary brain tumors with AZQ.

We have evaluated the efficacy of intravenous 2,5-diaziridinyl-3,6-biscarboethoxyamino-1,4-benzoquinone (diaziquone or AZQ, NSC-182986) in the treatment of recurrent primary anaplastic brain tumors. Three of 16 evaluable patients (18.8%) showed clinical and radiographic improvement that permitted discontinuation of corticosteroids, 4 patients (25%) showed either clinical or radiographic improvement and were considered partial responders, and 9 patients (56.2%) showed no effects after two courses of AZQ. The treatment was well tolerated, and hematologic toxicity was mild. Pharmacokinetic studies indicated rapid decay of the parent compound from plasma using two different infusion schedules. These results compare favorably with those obtained using the nitrosoureas or procarbazine as single agents.

Potentiation of melphalan activity in the KHT sarcoma by the radiosensitizer RSU 1069.

The radiation sensitizer misonidazole (MISO) has been shown to potentiate the cytotoxic action of a variety of anti-cancer agents. Even larger enhancement ratios than those observed with MISO have been found with certain other nitroimidazoles. One agent reported to be particularly effective in combination with the chemotherapeutic agent melphalan is the sensitizer RSU 1069. The present studies therefore were designed to evaluate the effect of combining these two agents in the treatment of intramuscularly growing KHT sarcomas. Tumor response was assessed using an in vivo to in vitro clonogenic cell survival assay. When given at times ranging from 60 min before to 30 min after melphalan exposure, RSU 1069 was found to increase the tumoricidal activity of the chemotherapeutic agent. Complete dose response curves combining RSU 1069 and a range of melphalan doses then were determined. For comparison the effects of combining MISO or benznidazole (BENZO) with melphalan also were evaluated. All sensitizers were administered i.p. either 30 min before (BENZO) or simultaneously with (MISO, RSU 1069) the chemotherapeutic agent. Survival of clonogenic tumor cells assessed 22 to 24 hr after treatment was used to assay tumor response. When combined with melphalan, doses of RSU 1069 (0.38 mmol/kg), BENZO (0.3 mmol/kg) and MISO (5.0 mmol/kg) were found to yield dose modifying factors of 1.6, 1.5, and 1.4, respectively. These results indicate that potentiation of melphalan activity occurs at RSU 1069 doses which are approximately 10-fold lower than those of MISO, making this sensitizer as effective a potentiator of melphalan as so far tested in the KHT sarcoma.

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.

Synthesis and properties of bis(2,2-dimethylaziridinyl)phosphinic amides: a series of new antineoplastic agents.

In continuation of efforts to improve the antitumor selectivity of the 2,2-dimethylaziridine class of alkylating agents, a series of N-substituted bis(2,2-dimethyl-1-aziridinyl)phosphinic amides has been synthesized and evaluated. All of these compounds (3-15) were tested in vivo against leukemia P-388 in mice, where most of them caused significant increase of survival time at nontoxic dose levels. Some of the most active compounds were also tested against leukemia L1210, B16 melanoma, and colon 26 carcinoma; in the latter tests, the parent unsubstituted amide 3 appeared to show the highest antitumor activity. Since the dose-limiting toxicity of the clinically tested prototypes of this class of anticancer agents AB-132 (1) and AB-163 (2) had been found to be CNS toxicity attributable mainly to the inhibition of cholinesterase, the compounds were tested in vitro against the cholinesterases from horse serum, electric eel, and bovine erythrocytes, as well as in vivo for the inhibition of the cholinesterase present in the whole blood of mice. In all of these assays, the various members of the present series showed a wide range of anticholinesterase activities, ranging from almost zero (for 3) to even higher potency than that of the prototype 2. A similarly wide range of stability was observed toward hydrolytic ring opening of the 2,2-dimethylaziridine moieties. Several of the compounds, particularly 3, deserve further study.

In the search for new anticancer drugs XI. Anticancer activity of nitroxyl labeled phosphoric N,N;N',N';N",N"-tris[1,2-ethanediyl]triamide(TEPA) and phosphorothioic N,N;N',N';N",N"-tris[1,2-ethanediyl]triamide(thio-TEPA) derivatives.

In order to further evaluate the effect of the nitroxyl moiety on the anticancer activity of nitroxyl labeled analogues of phosphoric N,N;N',N';N",N"-tris[1,2-ethanediyl]triamide (TEPA) and phosphorothioic N,N;N',N';N",N"-tris[1,2-ethanediyl]triamide (thio-TEPA), the activity of these compounds was compared in vivo, using murine lymphoid leukemia L1210, with the reduced forms of the drugs, i.e. the hydroxylamines and amine congeners. At optimum dose, all compounds were active. However, the nitroxyl containing compounds were more active than the corresponding reduced forms. An admixture of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl had no effect on the activity of thio-TEPA. Consequently, the nitroxyl moiety must be an integral part of the anticancer drug's structure in order to influence that drug's performance.

Phase I study of ethylbis(2,2-dimethyl-1-aziridinyl) phosphinate (AB-163).

Ethylbis(2,2-dimethyl-1-aziridinyl)phosphinate (AB-163) was used to treat 27 patients in a phase I trial. The limiting toxicity on a weekly schedule of IV administration involved nausea and vomiting associated with a variety of cholinergic side effects, including possible seizures. A starting dose of 300--400 mg/M2/week is suggested for a Phase II trial. One partial response in a patient with squamous-cell carcinoma of the cervix metastatic to the lungs was seen.

Combined therapeutic effects of an immunomodulator, PSK, and chemotherapy with carboquone on rat bladder carcinoma.

Responses of bladder cancer in ACI rats to combination therapy with an immunomodulator, PSK, and an alkylating agent, carboquone, are reported. PSK is a protein-bound polysaccharide isolated from Basidiomycetes, and carboquone is the alkylating agent 2,5-bis(1-aziridinyl)-3-(2-hydroxy-1-methanoxyethyl)-6-methyl-p- benzoquinone carbonate, molecular weight 3,214. The immunomodulator, PSK, was shown to enhance the effectiveness of the chemotherapeutic agent, carboquone. The therapeutic effect of combination treatment was monitored by measuring growth rates of tumors transplanted SC and by measuring decreases in metastatic spread to lungs in tumor-bearing animals. Effects of PSK on host immunity were monitored by measuring serum levels of immunosuppressive substance.

A phase II trial of diaziquone in patients with head and neck cancer.

Diaziquone (AZQ) is a lipophilic alkylating agent which crosses the blood-brain barrier and has marked antitumor activity in a broad spectrum of murine tumor systems. Myelosuppression has been the dose-limiting toxicity in phase I trials. In this study 36 patients with head and neck cancer received diaziquone. Thirty-one of these patients (28 male, 3 female) were evaluable for efficacy. The initial starting dose was 7 mg/m2/day X 5 days i.v. repeated every 28 days. Because of the severe myelosuppression encountered in the first four patients, the starting dose was decreased by 20% to 5.5 mg/m2/day X 5 days repeated every 28 days. The majority of patients were considered to be good-risk patients as evidenced by performance status (80% 0-1 Zubrod) and prior therapy. Even with this dosage reduction, myelosuppression (especially thrombocytopenia) was again the dose-limiting toxicity with 25% of patients experiencing granulocyte and platelet nadirs below 1000/mm3 and 50,000/mm3 respectively. Thirty-five percent of patients required a subsequent dosage reduction of 20% prior to receiving a second course of therapy. There was one complete (CR), four partial (PR) and three minor (MR) responses. All but the CR were of relatively short duration (mean of 30 days). The patient with a CR has remained disease-free for nearly 3 years. In this group of patients the activity of diaziquone as a single agent at this dose and schedule (CR + PR + MR = 26%; CR + PR = 16%) is less than that of methotrexate, bleomycin, and cis-platinum but is encouraging. Further trials utilizing combinations are warranted.

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.

CB 1954 revisited. II. Toxicity and antitumour activity.

We have assessed the antitumour activity of the nitrophenylaziridine CB 1954 in vitro and in vivo. For EMT6 mouse mammary tumour multicellular spheroids under hypoxic conditions in vitro, a 6-h exposure to 40 micrograms/ml reduced the surviving fraction to as low as 10(-3) and the growth delay was 5.4 days. Oxic cells were twofold less sensitive. Phenyl AIC protected oxic and hypoxic cells equally. Under oxic conditions minimal cell killing was seen with HT29 cells, either in multicellular spheroids or in monolayer; a 6-h exposure to 40 micrograms/ml gave a spheroid growth delay of 1.5-1.7 days. No growth delay was seen with single maximum tolerated doses of CB 1954 against HT29 grown as a xenograft in immunosuppressed mice. Only minimal growth delays of 1-2 days were seen with similar doses against the EMT6 tumour and the RIF-1 and KHT sarcomas in mice. Little activity was seen with maximum tolerated doses given once a day for 5 days against EMT6 and RIF-1. No chemosensitization was measurable with CCNU, cyclophosphamide or melphalan in the KHT tumour.

Therapeutic effects of BM 12,531 (Prop. INN azimexon).

The antitumor effect of BM 12,531, 2-[2-cyanaziridinyl-(1)]-2[carbamoylaziridinyl-(1)]-propane (Prop. INN azimexon), on L1210 leukemia in mice is described. The immunostimulating compound BM 12,531 can also reduce the acute toxicity of X-irradiation in mice. The most effective doses in these experiments are 1 or 5 mg/kg twice a week, whereas 50 and 500 mg/kg twice a week decrease the therapeutic effect. The mortality of Candida-infected and irradiated mice is also reduced by oral administration of BM 12,531. BM 12,531 has synergistic effects with subtherapeutic doses of chloramphenicol in an experimental E. coli infection in mice.

Immunorestoration of anergic cancer patients by azimexon.

Azimexon, a new synthetic immunoadjuvant, can act on delayed-type hypersensitivity (DTH) reactions. Seven of 11 anergic cancer patients have been immunorestored by a relatively low dosage of azimexon. The effect on the lymphocyte responsiveness, and particularly of a new T-lymphocyte mitogen (TPA), are described. The possible mechanisms of the anergy of the cancer patients and of the mode of action of azimexon are discussed.