A Phase II Study of PX-866 in Patients With Recurrent or Metastatic Castration-resistant Prostate Cancer: Canadian Cancer Trials Group Study IND205

BACKGROUND

In PTEN-loss models, the phosphatidylinositol 3-kinase (PI3K)/AKT and androgen receptor signaling pathways cross-regulate by reciprocal feedback whereby inhibition of one activates the other, creating a rationale for co-targeting. We studied the irreversible, pan-isoform inhibitor of Class I PI-3K PX-866 singly (part A) and with abiraterone acetate (AA) in patients on AA with rising prostate-specific antigen (PSA) (part B).

PATIENTS AND METHODS

The primary endpoint was lack of progression at 12 weeks. Exploratory endpoints included changes in circulating tumor cells (CTC), pharmacodynamic studies on platelets (part A), and archival tumor exploration of PTEN as predictor of response (part B).

RESULTS

A total of 43 and 25 patients accrued to parts A and B, respectively. In part A, 14 (33%) patients were progression-free at 12 weeks, with 2 partial objective responses and 1 confirmed PSA response. Favorable CTC conversion (< 5 CTC/7.5 mL) occurred in 6 (24%) of 25 evaluable patients. In part B, 11 of 25 patients had measurable disease. Six (24%) patients were progression-free at 12 weeks. No objective or PSA responses were observed. For all 68 patients, the most common toxicities were diarrhea (53 patients), nausea (36), anorexia (24), fatigue (22), and vomiting (20). Among 17 patients for whom PTEN testing was possible, 3 had PTEN homozygous deletion and 14 had no change. No correlation between PTEN status and response was seen.

CONCLUSIONS

PX-866 had modest single agent activity. Adding AA to PX-866 showed no evidence of resistance reversal. Strategies to combine PI3K inhibition with androgen receptor-targeted therapies could consider initiation earlier, combination with other agents, and/or recruiting a selected population.

Colorectal cancer lung metastasis treatment with polymer-drug nanoparticles

Colorectal cancer (CRC) is the second leading cause of cancer deaths in the United States; the predominant cause for mortality is metastasis to distant organs (e.g., lung). A major problem limiting the success of chemotherapy in metastatic CRC is the inability to target tumor tissues selectively and avoid severe side effects to normal tissues and organs. Here, we demonstrate polymeric nanoparticles (PNPs) entrapping chemotherapeutic agents provide a new therapeutic option for treating CRC that has metastasized to the lung. PNPs assembled from FDA approved biocompatible block copolymer accumulated predominantly in lung tissue. PNPs showed negligible accumulation in liver, spleen and kidneys, which was confirmed by fluorescent nanoparticle imaging and analysis of PI3K inhibition in the organs. PNPs entrapping PI3K inhibitors (i.e., wortmannin and PX866) suppressed CRC lung metastasis growth, and SN-38-loaded PNPs completely eliminated CRC lung metastasis. Our results demonstrate that polymer-drug nanoparticles offer a new approach to reduce toxicity of cancer therapy and has the potential to improve outcomes for patients with lung metastasis.

A Randomized, Phase II Trial of Cetuximab With or Without PX-866, an Irreversible Oral Phosphatidylinositol 3-Kinase Inhibitor, in Patients With Metastatic Colorectal Carcinoma

BACKGROUND

The phosphotidylinositol-3 kinase (PI3K)/serine-threonine kinase/mammalian target of rapamycin signaling pathway is frequently altered in colorectal cancer (CRC). PX-866 is an oral, irreversible, pan-isoform inhibitor of PI3K. This randomized phase II study evaluated cetuximab with or without PX-866 in patients with metastatic, anti-epidermal growth factor receptor-naive, KRAS codon 12 and 13 wild-type CRC.

PATIENTS AND METHODS

Patients with metastatic CRC who had received both oxaliplatin and irinotecan were randomized (1:1) to cetuximab (400 mg/m² loading then 250 mg/m² weekly) with or without PX-866 (8 mg orally daily; arms A and B, respectively). The primary endpoint was progression-free survival (PFS). Secondary endpoints included objective response rate, overall survival (OS), toxicity, and correlation of relevant biomarkers with efficacy outcomes.

RESULTS

A total of 85 patients were enrolled. The median PFS was 59 days versus 104 days for arms A (cetuximab + PX-866) and B (cetuximab alone), respectively (P = .77). OS between the 2 arms (266 vs. 333 days for arm A vs. B) were similar (P = .83). Overall toxicity, including treatment-related toxicity, was higher in arm A compared with arm B, especially in terms of all-grade nausea (66% vs. 37%), vomiting (50% vs. 29%), diarrhea (64% vs. 18%), and rash (66% vs. 37%). Grade 3 diarrhea occurred in 19% of patients in Arm A and 0% in Arm B. PIK3CA mutations and PTEN loss by immunohistochemistry were infrequently seen.

CONCLUSION

The addition of PX-866 to cetuximab did not improve PFS, objective response rate, or OS in patients with metastatic CRC. The combination arm had greater toxicity and may have been harmful in this study.

A randomized, phase 2 trial of docetaxel with or without PX-866, an irreversible oral phosphatidylinositol 3-kinase inhibitor, in patients with relapsed or metastatic head and neck squamous cell cancer

INTRODUCTION

The phosphotidylinositol-3 kinase (PI3K)/serine-threonine kinase (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is frequently altered in head and neck squamous cell cancer (HNSCC). PX-866 is an oral, irreversible, pan-isoform inhibitor of PI3K. Preclinical models revealed synergy with docetaxel and a phase 1 trial demonstrated tolerability of this combination. This randomized phase 2 study evaluated PX-866 combined with docetaxel in patients with advanced, refractory HNSCC.

METHODS

Patients with locally advanced, recurrent or metastatic HNSCC who had received at least one and no more than two prior systemic treatment regimens were randomized (1:1) to a combination of docetaxel (75mg/m(2) IV every 21days) with or without PX-866 (8mg PO daily; Arms A and B, respectively). The primary endpoint was progression free survival (PFS). Secondary endpoints included objective response rate (RR), overall survival (OS), toxicity, and correlation of biomarker analyses with efficacy outcomes.

RESULTS

85 patients were enrolled. There was a non-significant improvement in response rate in the combination arm (14% vs. 5%; P=0.13). Median PFS was 92days in Arm A and 82days in Arm B (P=0.42). There was no difference in OS between the two arms (263 vs. 195days; P=0.62). Grade 3 or higher adverse events were infrequent, but more common in the combination arm with respect to diarrhea (17% vs. 2%), nausea (7% vs. 0%), and febrile neutropenia (21% vs. 5%); grade 3 or higher anemia was more frequent in arm B (7% vs. 27%). PIK3CA mutations or PTEN loss were infrequently observed.

CONCLUSION

The addition of PX-866 to docetaxel did not improve PFS, RR, or OS in patients with advanced, refractory HNSCC without molecular pre-selection.

A randomized, phase II trial of cetuximab with or without PX-866, an irreversible oral phosphatidylinositol 3-kinase inhibitor, in patients with relapsed or metastatic head and neck squamous cell cancer

BACKGROUND

The phosphotidylinositol-3 kinase (PI3K)/serine-threonine kinase/mammalian target of rapamycin signaling pathway is frequently altered in head and neck squamous cell cancer (HNSCC). PX-866 is an oral, irreversible, pan-isoform inhibitor of PI3K. A phase I trial demonstrated tolerability of this combination. This randomized phase II study evaluated PX-866 combined with cetuximab in patients with advanced, refractory HNSCC.

METHODS

Patients with recurrent or metastatic HNSCC who had received at least one and no more than two prior systemic treatment regimens were randomized (1 : 1) to cetuximab with or without PX-866 (8 mg p.o. daily; arms A and B, respectively). The primary end point was progression-free survival (PFS). Secondary end points included objective response rate (ORR), overall survival (OS), toxicity, and correlation of key biomarkers with efficacy outcomes.

RESULTS

Eighty-three patients were enrolled. There was a similar response rate between arms (10% versus 7%). Of patients for whom tissue was assessable, 57% were human papillomavirus (HPV) positive. Median PFS was 80 days in both arms and there was no difference in OS between the two arms (211 versus 256 days). Overall toxicity was higher in arm A compared with arm B, especially in terms of nausea (53% versus 23%), vomiting (45% versus 15%), fatigue (43% versus 23%), diarrhea (40% versus 21%), and hypokalemia (25% versus 10%). Grade 3 or higher adverse events were infrequent, but more common in the combination arm although without a specific pattern. PIK3CA mutations were observed in 17% of the cases assessed, and PTEN loss was infrequently observed.

CONCLUSION

The addition of PX-866 to cetuximab did not improve PFS, RR, or OS in patients with advanced, refractory HNSCC enrolled without molecular preselection. In this contemporary cohort, HPV-positive patients comprised the majority, and neither HPV-positive nor HPV-negative patients derived clinical benefit for the addition of cetuximab plus PX-866.

A multicenter phase 1 study of PX-866 and cetuximab in patients with metastatic colorectal carcinoma or recurrent/metastatic squamous cell carcinoma of the head and neck

BACKGROUND

This phase I, dose-finding study determined the safety, maximum tolerated dose (MTD)/recommended phase 2 dose (RP2D), and antitumor activity of PX-866, a phosphatidylinositol 3-kinase inhibitor, combined with cetuximab in patients with incurable colorectal cancer or squamous cell carcinoma of the head and neck.

METHODS

PX-866 was administered at escalating doses (6-8 mg daily) combined with cetuximab given at a 400 mg/m(2) loading dose followed by 250 mg/m(2) weekly. A "3 + 3" study design was used. Prior therapy with anti-EGFR therapies, including cetuximab, was allowed.

RESULTS

Eleven patients were enrolled. The most frequent treatment-emergent adverse event was diarrhea (90.1%), followed by hypomagnesemia (72.2%), vomiting (72.2%), fatigue (54.5%), nausea (54.5%), rash (45.5%) and peripheral edema (40%). No dose limiting toxicities were observed. The RP2D was 8 mg, the same as the single-agent PX-866 MTD. Best responses in 9 evaluable patients were: 4 partial responses (44.4%), 4 stable disease (44.4%), and 1 disease progression (11.1%). The median progression free survival was 106 days (range: 1-271).

CONCLUSION

Treatment with PX-866 and cetuximab was tolerated with signs of anti-tumor activity. Further development of this combination is warranted.

Potentiation of the antitumor effect of tamoxifen by combination with the antiprogestin onapristone

The present study was undertaken to investigate the antitumor effect of a combination of the antiestrogen tamoxifen (TAM) and either the antiprogestin onapristone (ON) or the progestogen megestrol acetate (MEG) in experimental mammary tumor models. Rats bearing DMBA- or NMU-induced mammary tumors were treated with ON or MEG either alone or in combination with TAM for four weeks. In the DMBA-tumor model, treatment with ON or TAM alone caused tumor remissions, whereas the combination of ON and TAM was almost as effective as ovariectomy (100% remission) and led to a remission of 86-100%. The combination of TAM and ON was distinctly more effective than that of TAM and MEG. A similar potentiation of the antitumor effect of TAM and ON was observed in the NMU-tumor model. In DMBA-tumors, the concentration of progesterone receptors was found to increase after treatment for three days with TAM and ON. In hosts bearing DMBA-tumors, treatment with the combination of TAM and ON caused a reduction in ovarian and uterine weights. In the same animals, the basal level of progesterone was decreased in spite of a slight increase in the LH level. These findings suggest that the high antitumor effect of the combination of TAM and ON compared to the corresponding monotherapies can be related not only to the interaction of antihormones and receptors, but also to the up-regulation of PR and to a decrease in progesterone production. These data clearly suggest the sense of a combination of TAM with an antiprogestin in breast cancer treatment.

Endometrial contraception: modulation of molecular determinants of uterine receptivity

Modulation of endometrial receptivity is a promising approach for fertility regulation since it allows a contraceptive to act specifically at the endometrium. This was corroborated by our previous observations that treatment with low doses of a pure progesterone antagonist (PA, antiprogestin), onapristone (ZK 98299), in bonnet monkeys inhibited fertility by selectively retarding endometrial development, without affecting the hypophyseal-hypothalamic function. In the present study, further investigations, undertaken to analyze the molecular repertoire of a nonreceptive primate endometrium, determined expression of: steroid hormone receptors, i.e. progesterone receptor (PR) and estrogen receptor (ER); cytokines, i.e. leukemia inhibitory factor (LIF): transforming growth factor beta (TGFbeta) and its receptor (TGFbetaR); and cell adhesion molecules, i.e. integrins (alpha(v)beta(3), alpha(1)beta(1)). These studies were conducted during the different phases of the normal menstrual cycle and following treatment with different doses of onapristone (2.5 mg, 5 mg, or 10 mg every third day for one cycle) in bonnet monkeys. The molecules were analysed collectively to explore the possibility of a correlation between expression of these markers and endometrial receptivity and to investigate whether there exists a regulatory link between expression of these molecules under in vivo conditions. Three types of expression patterns of endometrial factors were observed during the peri-implantation period following onapristone treatment: 1) LIF, alpha(v)beta(3), and alpha(1)beta(1) showed significant (P < 0.02) down regulation in glandular epithelium of endometria in animals treated with all three doses of onapristone as compared to the control group. This was indicative of their critical role in the progesterone-driven cascade leading to implantation. 2) PR, TGFbeta, and TGFbetaR remained unaffected in the endometria from 2.5 mg treated animals and showed down regulation in animals treated with 5 and 10 mg onapristone as compared to the control group, thereby suggesting that the expression of these markers may not truely reflect endometrial receptivity per se. However, their facilitatory role in preparing the endometrium for implantation can not be ruled out since continued perturbation in the expression of these molecules may affect endometrial growth, remodelling, and differentiation, which in turn may render the endometrium nonreceptive; 3) ER remained unaltered in endometria of animals rendered infertile with 2.5, 5, and 10 mg onapristone. This observation indirectly suggests that onapristone-induced endometrial changes are mediated via some specific mechanisms. The present study clearly demonstrates that endometrial non-receptivity induced at low doses of onapristone is associated with changes in the expression pattern of specific molecular markers. However, no direct correlation was observed between in vivo expression of TGFbeta, LIF, and integrins, thereby lending support to the concept that there exists redundancy or multiple pathways which regulate implantation events.

Onapristone suppresses prolactin production in explant cultures of leiomyoma

OBJECTIVE

To assess the action of onapristone, a type I antiprogestin, on prolactin (PRL) production by explant cultures of leiomyoma and myometrium.

DESIGN

Explant cultures of myometrium and leiomyomas from 3 premenopausal women undergoing hysterectomy in the proliferative phase of the menstrual cycle.

MAIN OUTCOME MEASURES

PRL secretion measured by radioimmunoassay.

RESULTS

PRL secretion was decreased in leiomyomas by onapristone. There was no effect in the myometrium. There was no additional effect with the addition of the type II antiprogestin mifepristone (RU 486).

CONCLUSION

PRL production is suppressed in leiomyomas but not in myometrium after treatment with onapristone in vitro. This suppression may serve as a marker for the clinical effectiveness of agents used in the treatment of leiomyomas.

Synergistic role of nitric oxide and progesterone during the establishment of pregnancy in the rat

Successful pregnancy is strictly dependent on the trophoblast-decidual interaction and on an adequate blood supply to the implantation sites. Nitric oxide (NO) has been shown to play an important role during advanced gestation, although its role during early pregnancy is unclear. The aim of the present study in rats was to evaluate whether NO plays a role during the preimplantation [days 1-4 post coitum (p.c.)] and peri-implantation (days 6-8 p.c.) phases of pregnancy. The rats were treated with the non-specific nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME), and the iNOS inhibitor aminoguanidine in the presence and absence of low-dose antiprogestin, onapristone, and evaluated on days 9 p.c. and 19 p.c., respectively. Before implantation, the treatments alone (L-NAME, aminoguanidine, onapristone) had little effect on pregnancy outcome. Conversely, aminoguanidine plus onapristone treatment completely prevented pregnancy, whereas L-NAME plus onapristone reduced the pregnancy rate to approximately 50%. In addition, both treatments drastically reduced decidualization. Oviductal flushing experiments revealed arrest of embryo development at around the 8-cell stage after aminoguanidine plus onapristone treatment on days 1-4 p.c. Similarly, treatment during the peri-implantation period with L-NAME, aminoguanidine, and onapristone each had only marginal effects on pregnancy. However, a combination of L-NAME and onapristone, and aminoguanidine plus onapristone prevented pregnancy in 71% and 42% of dams, respectively, as determined on day 19 p.c. These treatments also markedly inhibited the decidualization process. This study demonstrates synergistic effects of NOS inhibitors and an antiprogestin in preventing pregnancy. NOS, particularly the cytokine- and progesterone-inducible iNOS, may represent a new target for novel therapeutic agents capable of promoting or inhibiting pregnancy.

Contrasting effects of diethylenetriamine-nitric oxide, a spontaneously releasing nitric oxide donor, on pregnant rat uterine contractility in vitro versus in vivo

OBJECTIVE

The aim of the study was to investigate the in vitro (on tension) and in vivo (on intrauterine pressure) effects of a spontaneously releasing nitric oxide adduct, diethylenetriamine-nitric oxide, on rat uterine contractility.

STUDY DESIGN

Contractile responses to the nitric oxide donor diethylenetriamine-nitric oxide on isometric tension of rat uterine strips (in vitro) and on intrauterine pressure (in vivo) in anesthetized and conscious animals were quantified at late gestation and during preterm and term labor. Preterm labor was induced with the administration of a single injection of the antiprogestin onapristone (10 mg). All control animals were injected with diethylenetriamine, the parent compound, without nitric oxide.

RESULTS

The nitric oxide donor diethylenetriamine-nitric oxide relaxes rat uterine tissues when given in vitro during gestation (median effective dose 0.30 +/- 0.09 mmol/L) but fails to have an effect on uterine tissues from laboring term and preterm animals in the muscle bath. Intraperitoneal injection of the nitric oxide adduct in doses of 5 mg and 50 mg produced a significant and sustained decrease in intrauterine pressure in both delivering and nondelivering animals compared with intrauterine pressure values before administration. Analysis of intrauterine pressure levels at different time frames (before injection, immediately after injection, and after 30, 60, and 90 minutes) in anesthetized rats between days 19 and 21 of gestation shows that the dose of 5 mg diethylenetriamine-nitric oxide significantly (p < 0.05) decreased contractility starling at 30 minutes after administration. Similarly, during labor diethylenetriamine-nitric oxide (5 mg intraperitoneally) decreased contractility (p < 0.05) but only starting at 60 minutes after injection. However, with the dose of 50 mg diethylenetriamine-nitric oxide contractility was reduced 30 minutes (p < 0.05) after treatment during pregnancy (days 19 to 21). The same dose of diethylenetriamine-nitric oxide produced a greater relaxation immediately after intraperitoneal injection (p < 0.05) in the laboring group. Diethylenetriamine-nitric oxide (50 mg) also induced an earlier onset and greater relaxation in animals delivering preterm compared with nondelivering animals at the same stage of gestation. The intrauterine pressure maintained constant contractility levels throughout the 100-minute recording period in the control groups of anesthetized and conscious animals that were injected with diethylenetriamine at the equivalent doses. In the preterm laboring group the effects were similar in both anesthetized and conscious animals.

CONCLUSION

Although in vitro studies of uterine muscle show decreased inhibitory responses to nitric oxide donors during spontaneous term labor and preterm labor compared with tissues collected during late pregnancy (day 19), studies in vivo demonstrate that nitric oxide donors can decrease uterine contractility even more effectively during delivery. The results suggest that nitric oxide donors may act indirectly or that the fetal-placental unit increases the availability of nitric oxide in vivo. Therefore, despite what in vitro studies alone suggest, nitric oxide donor drugs may be very effective in suppressing either term or preterm labor.

Influence of estradiol and progesterone withdrawal on the secretion of and the temporal correlation between pulses of oxytocin and prostaglandin F2(alpha) in ewes

The primary objective was to examine the effects of estradiol and the progesterone receptor antagonist onapristone on the pulsatile secretion of prostaglandin F(2alpha) (PGF(2alpha)) and ovarian and pituitary oxytocin. A 2 x 2 factorial arrangement of estradiol and onapristone treatments was administered to groups of 5 ewes after destruction of ovarian follicles on Day 8 of the cycle. Estradiol treatments consisted of the administration of a silicone elastomer implant, either containing or not containing estradiol, on Day 8 plus 50 microg of estradiol or corn oil on Days 11 and 12. Onapristone (2 mg/kg) or its vehicle were administered on Day 13, immediately preceding the simultaneous collection of blood samples from the carotid artery, jugular vein, and vena cava at 7.5-min intervals for 7 h. Ewes were immediately killed for measurements of uterine oxytocin receptor concentrations and phosphatidylinositide turnover. More oxytocin pulses were detected in the jugular vein than in the carotid artery (p < 0.01), suggesting that the pituitary is a source of oxytocin. A similar number (p > 0.1) of PGF(2alpha) pulses were correlated with oxytocin pulses as were not. The linked PGF(2alpha) pulses were longer in duration (p = 0.01) with a tendency toward a higher amplitude (p = 0.08). The corresponding vena caval oxytocin pulses had a longer duration (p = 0.02) than those not linked to PGF(2alpha). Estradiol increased oxytocin receptor concentrations and the turnover of phosphatidylinositides (p = 0.02) without affecting PGF(2alpha) pulse characteristics. Onapristone increased (p = 0.03) PGF(2alpha) pulse amplitude. Although a lower than expected temporal correlation between oxytocin and PGF(2alpha) pulses was observed, the distinguishing characteristics of linked pulses may be indicative of their physiological significance.

Influence of an antiprogestin (onapristone) on in vivo and in vitro fertilization

The effects of a progesterone antagonist (onapristone) on heat synchronization, luteinizing hormone (LH) surge, ovulation, oocyte maturation and fertilization of superovulated ewes were studied. Its effects on in vitro bovine oocyte maturation and fertilization were also studied. Estrus synchronization and superovulation treatments were applied to 39 adult ewes using an intravaginal sponge with fluorgestone acetate for 9 days with injections of prostaglandin F2 alpha and pregnant mare's serum gonadotrophin given 24 h before sponge withdrawal. The animals were randomly assigned to four different groups; T1 receiving only the synchrony treatment (n = 11); T2 ewes received two injections of onapristone (1 mg kg-1, i.v.) 12 h apart from 3 h after sponge withdrawal (n = 10); T3 ewes received two injections of progesterone 12 h apart from sponge withdrawal (n = 10); and, T4 ewes received both onapristone and progesterone as described (n = 8). Ewes were mated by a fertile male during estrus. Progesterone and LH were measured during the superovulation period in plasma samples taken every 4 h. Uterine flushings for ova recovery were performed at 5 days (n = 25), 48 h (n = 5) and 24 h (n = 5). Non-fertilized oocytes collected at 24 and 48 h were checked for meiosis resumption. The effects of two doses of onapristone (D1 and D2) on in vitro bovine oocyte maturation (control = 100, D1 = 100 and D2 = 100) and fertilization (control = 107, D1 = 40 and D2 = 75) were also studied. The percentage of animals showing heat signs was significantly lower in group T3 (50% vs. 100%). The onset of oestrus (27.6, 24.8, 68.8 and 25.5 h, respectively for T1, T2, T3 and T4) and an LH surge (32.3, 28.8, 76.5 and 30.5 h, respectively for T1, T2, T3 and T4) after sponge withdrawal were significantly delayed in group T3. There were no significant differences in the intervals between estrus and LH surge among groups (4.61 +/- 0.75 h). The response and ovulation rates until 40 h after sponge withdrawal (group T3 excluded) were similar among groups, but the fertilization rates were significantly lower in groups T2 and T4 when compared with T1 (2% and 3% vs. 41%, respectively; P < 0.001) due to sperm arrest in the cervix. Ova recovery rate decreased significantly from 24-48 h to 5 days and was not affected by treatments (76.9% vs. 37.1% respectively). Onapristone did not affect the resumption of meiosis. Fertilization of bovine oocytes in vitro decreased significantly only in group D2 when compared to control (48% vs. 62.6%, respectively). In conclusion, onapristone treatment during the preovulatory period did not interfere with normal synchronization of estrus, ovulation and oocyte maturation but severely compromised fertilization by arresting spermatozoa in the cervix.

Comparative effectiveness of three antiprogestins alone and in combination with anordiol in terminating pregnancy in the rat

The effectiveness of mifepristone, onapristone, and ORG 31806 alone or in combination with anordiol to terminate pregnancy in the rat was evaluated. ORG 31806 at a dose of 2 mg/kg/day, mifepristone at 4 mg/kg/day, and onapristone at 8 mg/kg/day, terminated pregnancy in all treated animals. Anordiol, an antiestrogen, at a dose of 5 mg/kg/day, terminated pregnancy in all treated animals. Anordiol acted synergistically with all three antiprogestins terminating pregnancy in the rat. The antiprogestins at doses that were either partially effective or non-effective became 100% effective when administered with a non-effective dose of anordiol. Thus, combination of ORG 31806 (1 mg/kg/day) plus anordiol (0.31 mg/kg/ day), mifepristone (1 mg/kg/day) plus anordiol (0.62 mg/ kg/day), and onapristone (2 mg/kg/day) plus anordiol (2.5 mg/kg/day) terminated pregnancy in all treated animals. These combinations of the antiprogestins and anordiol decreased significantly the serum progesterone levels but not serum 17 beta-estradiol levels. The present results indicate that the most potent combination was ORG 31806 plus anordiol.

Preterm birth in rats produced by the synergistic action of a nitric oxide inhibitor (NG-nitro-L-arginine methyl ester) and an antiprogestin (onapristone)

OBJECTIVE

The aim of this study was to determine whether inhibition of nitric oxide synthesis would affect the action of an antiprogesterone to provoke preterm labor.

STUDY DESIGN

Pregnant rats were continuously infused with NG-nitro-L-arginine methyl ester starting on day 16 of gestation. On day 17 of gestation groups of animals were injected subcutaneously with a single dose of either 3 or 30 mg/kg onapristone; animals were monitored for preterm labor and delivery for up to 48 hours.

RESULTS

Significant findings included the following results. (1) Combined treatment with NG-nitro-L-arginine methyl ester (50 mg per day) and low-dose onapristone (3 mg/kg) produced preterm labor, > 70% of the fetuses were delivered within 27 hours of treatment, whereas < 5% of the fetuses were delivered in the animals receiving either of these compounds alone. (2) NG-nitro-D-arginine methyl ester (50 mg per day) had no effect. (3) inhibition of nitric oxide by NG-nitro-L-arginine methyl ester also significantly increased the efficacy of high-dose onapristone (30 mg/kg) in preterm labor and delivery.

CONCLUSION

Treatment of pregnant rats with a combination of a nitric oxide inhibitor with onapristone significantly potentiated the ability of the antiprogesterone to induce preterm labor. The interaction of nitric oxide and progesterone may be required to maintain pregnancy.

The effects of post-ovulatory administration of onapristone on the developmnent of a secretory endometrium

The purpose of this study was to assess the ability of the anti-progestin onapristone administered in the immediate post-ovulatory period to disrupt endometrial differentiation as a potential method of fertility control. In all, 10 healthy female volunteers were given 400 mg onapristone 2 days after the mid-cycle luteinizing hormone (LH) surge in urine (LH+2). An endometrial biopsy was taken 4 or 6 days after the LH surge (i.e. LH+4 or LH+6) in a control cycle and on the corresponding day of the treatment cycle. Biopsies were assessed for histological dating and immunolocalization of oestrogen receptors, progesterone receptors and 15-hydroxyprostaglandin dehydrogenase (PGDH). On day LH+12, blood was taken for the measurement of insulin-like growth factor binding protein-1 (IGFBP-1) and placental protein 14 (PP14). Hormonal measurements in blood and urine were used to monitor the effects on the menstrual cycle. In addition, the concentration of cortisol in plasma was measured to determine if this dose of onapristone exerted significant anti-glucocorticoid activity. Treatment with onapristone retarded the development of secretory changes within the endometrium without affecting the length of the luteal phase. Intense nuclear immunostaining of oestrogen and progesterone receptors was evident in glands and stroma after treatment, suggesting that the progesterone-dependent down-regulation of steroid receptors was inhibited by the anti-progestin. Onapristone also affected the production of luteal phase endometrial proteins, as judged by the pronounced reduction in immunostaining of PGDH within the glands and the significant reduction in plasma concentrations of PP14. However, plasma concentrations of IGFBP-1 did not differ between cycles. Onapristone did not appear to exert significant anti-glucocorticoid activity because concentrations of cortisol were unaffected. These findings suggest that onapristone could potentially be used as a method of postovulatory fertility control.

Onapristone (ZK 98.299): a potential antiprogestin for endometrial contraception

OBJECTIVES

The effects of the antiprogestin onapristone (ZK 98.299) on fertility; menstrual cycle length; duration of menses; serum estradiol, progesterone, and cortisol concentrations; and endometrial morphologic features were studied in adult bonnet monkeys.

STUDY DESIGN

Five animals were treated subcutaneously with the vehicle and another nine with either 2.5 (n = 4) or 5 mg of onapristone per animal (n = 5). Treatment was initiated on day 5 of the first treatment cycle, and thereafter onapristone was administered every third day for four to seven consecutive cycles. The females were placed with adult males during the periovulatory period, which was assessed by frequent analysis of serum estradiol concentrations. In the final treatment cycle an endometrial biopsy was performed on day 8 after a midcycle estradiol peak in the ovulatory cycle, or around day 20 if the cycle was anovulatory. Blood samples for estradiol, progesterone, and cortisol measurement were collected every third day, except for the periovulatory period when sampling was more frequent.

RESULTS

Each of the five animals treated with the vehicle became pregnant: one in the first, three in the second, and one in the third mated cycle, whereas only one of nine treated with onapristone became pregnant. Four animals treated with 2.5 mg of onapristone for 17 cycles and another four treated with a 5 mg dose for 21 cycles did not conceive. In eight animals that did not conceive the first three treatment cycles of six were ovulatory, and in the remaining two animals two cycles of each were ovulatory. During treatment the mean menstrual cycle length was not altered significantly; however, in one it was shortened and in another two it was prolonged. Similarly, the mean duration of menses was not significantly affected, but in some cycles it was reduced. Moreover, there was only slight bleeding in some treatment cycles. Ovulation occurred in 30 of 45 treatment cycles, including the final treatment cycle during which the biopsy was taken, as indicated by serum estradiol and progesterone concentrations. In some of the ovulatory cycles prolonged treatment suppressed luteal activity; however, in the ovulatory cycles the duration of follicular and luteal phases was not significantly affected. In the anovulatory cycles there was a delayed increase in serum estradiol concentrations, suggesting a partial inhibition of folliculogenesis. In treated animals endometrial growth and development was retarded and rendered out of phase. In animals treated with the higher (5 mg) onapristone does the endometrial glands had partially regressed, the secretory activity was blocked, and stromal compaction was evident. The treatment had no significant effect on serum cortisol levels.

CONCLUSIONS

This study demonstrates that low-dose onapristone treatment throughout the menstrual cycle prevents pregnancy without disturbing the menstrual cycle and ovulation in the majority of cycles. However, anovulation and luteal insufficiency occurred in some animals during prolonged treatment. The contraceptive effect in the ovulatory cycles seems primarily related to the retardation of endometrial development resulting in the inhibition of endometrial receptivity. It appears likely that a dose or treatment regimen of onapristone that will inhibit endometrial receptivity and prevent implantation without affecting the menstrual cycle even on prolonged treatment could be identified.

Enhancement of the antitumor efficacy of the antiprogestin, onapristone, by combination with the antiestrogen, ICI 164384

So far, no combination of endocrine treatments has been routinely used in the therapy of breast Cancer. It was, therefore, our interest to determine whether the combination of the antiprogestin, onapristone (ON), and the pure antiestrogen, ICI 164384 (ICI) might provide a more effective therapy than either monotherapy in experimental mammary tumors containing both estrogen and progesterone receptors. In the MXT-mammary tumor of the mouse, ON (5 mg/kg) administered for 3 weeks exerted an ovariectomy-like antitumor effect (56% inhibition), whereas ICI (30 mg/kg) was weakly effective (28% inhibition). The combination of ON and ICI was, however, distinctly more effective than the monotherapies or ovariectomy, causing 78% inhibition. A similar potentiation of antitumor effect by the combination was manifested in the dimethylbenzanthracene-induced mammary tumor of the rat when ON (5 mg/kg) and ICI (30 mg/kg) were administered once daily for 4 weeks (s.c.). The remission rates of tumors found after treatment with ICI, ON, the combination and ovariectomy (complete and partial remission) were 15%, 46%, 71% and 100% respectively. In the animals bearing DMBA-induced tumors, treatment with ON alone significantly increased the serum levels of luteinizing hormone and prolactin, but caused only a slight increase in the peripheral levels of estradiol and progesterone. ON had no appreciable effect on the uterine and ovarian weights. ICI reduced the uterine weight and the serum progesterone level. In the combination with ON, ICI reversed the effect of ON on the progesterone level without influencing the luteinizing hormone and prolactin levels. These findings suggest that the augmentation of antitumor effectiveness by the combination of two antihormones can be ascribed not only to their effects at estrogen- and progesterone-receptor-binding sites, but also to the decrease in the peripheral level of progesterone. Thus, an appropriate combination of antiprogestin and pure antiestrogen may be useful in the management of breast cancer.

Human chorionic gonadotropin secretion from the early human placenta: in vitro regulation by progesterone and its antagonist

Local actions of placental neurohormones and sex steroids have been proposed to play a role in the regulation of human chorionic gonadotropin (hCG) release from the human placenta. Accordingly, we utilized an in vitro perifusion system and cultures of placental explants to investigate short- and long-term effects of progesterone and its respective antagonist on hCG secretion from the human first-trimester placenta. Tissue slices (100 mg) obtained from legal pregnancy terminations of 9-12 weeks of gestation were continuously perifused and the effluent collected in fractions of 2-20 min. After initial perifusion periods of 30-140 min, either progesterone, a progesterone antagonist (ZK 98-299), or both were added to the perifusion medium at final concentrations of 10(-4)-10(-9) mol/l. Administration was either continuous or intermittent in 10-min pulses. Furthermore, 50-mg pieces of placental explants were cultured in multiwell tissue culture plates for up to 5 days. During the perifusion studies, hCG (determined by enzyme immunoassay) was released in a pulsatile fashion. This hCG pulsatility was decreased in response to both progesterone and progesterone antagonist at all concentrations tested. In contrast, intermittent administration of either treatment increased the hCG secretion. Secretion of hCG was not affected when progesterone and its antagonist were co-administered at equimolar concentrations. These observations demonstrate the diverging effects of progesterone and its antagonist on hCG secretion from the human first-trimester placenta in vitro, depending on the experimental conditions. Thus, progesterone-modulated hCG secretion appears to be regulated in a complex manner, its fine tuning involving other, as yet uninvestigated intraplacental factors.