Initial Report of a Randomized Trial Comparing Conventional vs. Novel Treatment Planning Technique to Ameliorate Immunosuppression from Lung SBRT

PURPOSE/OBJECTIVE(S)

SBRT is highly effective against early-stage non-small cell lung cancer. Radiation Therapy (RT) is known to modulate the immune system and contribute to the generation of anti-tumor T cells and stimulate T cell infiltration into tumors. However, this anti-tumor activity is offset by radiation-induced immunosuppression (RIIS) which results in lower tumor control and survival. Lymphocytes are highly radiosensitive and RIIS means destroying existing as well as newly created cytotoxic and helper T lymphocytes. We hypothesized that optimizing RT treatment planning by considering circulating blood and lymphatics as a critical Organ at Risk (OAR) may mitigate RIIS.

MATERIALS/METHODS

We conducted an IRB approved NCI funded clinical trial for 50 early-stage lung cancer patients treated with SBRT alone, from 2020 to 2023, to investigate the ability to reduce RIIS by reducing dose to circulating blood and lymphatics with the aid of a predictive algorithm. All SBRT plans adhered to treatment parameters from RTOG 0813 (central) or RTOG 0915 (peripheral). Patients were randomized to two arms: experimental optimization for RIIS (to reduce dose to blood and lymphatic rich organs) versus standard SBRT planning (without optimization for RIIS). Peripheral blood samples were collected at baseline, end of Tx, 4 weeks and 6 months post Tx. Patients with baseline absolute lymphocyte counts (ALC) less than 0.5x109 cells/L were ineligible for the trial. Data acquired for all blood cell types as well as lymphocyte sub populations CD3+, CD4+, CD8+, CD19+, CD56+. Two sample t-test was used to determine the statistical significance between the cohorts at the time points.

RESULTS

The standard arm had an ALC reduction of 28% at one week post Tx and a nadir at 4 weeks with a 34% reduction. Absolute percentage reductions in ALC from baseline in the optimized arm compared to the standard arm are: end of treatment point (13%, p = 0.03), 4 weeks (12%, p = 0.08), 6 months (15%, p = 0.1), and all three time points together 13% (p = 0.001). ALC recovery appears to be faster in the optimized arm. Radiation induced suppression of all blood cell types are also reduced in the optimized arm with respect to standard arm (relative percentages): ALC (34%), WBC (47%), RBC (46%), platelets (40%), monocytes (100%), and neutrophils (62%) at 4-week mark. Average percentage reductions on integral doses, and V5 (volume receiving a 5 Gy dose) of optimized compared to standard plans are: aorta: 26%, 41% heart: 8%, 33%, vena cava: 32%, 52%, T spine: 51%, 81%, lymph nodes: 35%, 57%, total lung- ITV: 1.6%, 1%, body: 10%, 14%.

CONCLUSION

For the first time, we have shown that it is possible to reduce RIIS in a statistically significant manner, compared to standard of care, via optimized RT planning using a predictive model. This has implications in increasing the efficacy of immunotherapy by preserving the existing tumor reactive T cells in the immune system to enhance anti-tumor activity, and in reducing hospitalizations and improving survival.

Veliparib (Vel) in combination with chemoradiotherapy (CRT) of carboplatin/paclitaxel (C/P) plus radiation in patients (pts) with stage III non-small cell lung cancer (NSCLC) (M14-360/AFT-07)

8510

Background: CRT is standard treatment (Tx) for pts with unresectable stage III NSCLC. Vel, a potent oral PARP1/2 inhibitor, interferes with repair of chemotherapy- or radiation-induced DNA damage. In a phase 2 study, Vel showed favorable efficacy vs placebo when added to C/P in stage IV NSCLC. The reported phase 1 trial assessed the safety and efficacy of Vel + C/P-based CRT in Tx of stage III NSCLC (NCT02412371). Methods: Eligible pts (≥18 yr, unresectable stage III NSCLC, no prior NSCLC therapy) received Vel + CRT of weekly C area under the curve (AUC) 2 + P 45 mg/m2 weekly + 60 Gy (2 Gy/day) RT over 6–9 weeks (wk). Vel was dose escalated from 60 mg twice daily (BID) to 240 mg BID followed by Vel 120 mg BID added to consolidation therapy (CON) once every 3 wk of C AUC 6 + P 200 mg/m2 for 2 cycles (cohort 1–5). Cohort 6 received Vel 240 mg BID + CRT followed by Vel 240 mg BID + CON. Samples for pharmacokinetic (PK) analysis were collected on wk 4 day –3. The primary endpoint was to establish the recommended phase 2 dose (RP2D) of Vel + CRT/Vel + CON. Results: As of Sep 2018, 48 pts enrolled into cohorts 1–6 at Vel 60 mg/120 mg (n = 7), 80 mg/120 mg (n = 9), 120 mg/120 mg (n = 7), 200 mg/120 mg (n = 8), 240 mg/120 mg (n = 12), and 240 mg/240 mg (n = 5) added to CRT/CON; median age 65 yr (range, 48–81). Vel PK was dose proportional; 39 (81.3%) pts completed therapy. Grade ≥3 Tx-emergent adverse events (AEs) were reported in 37 (77.1%) pts; anemia and febrile neutropenia (10.4% each) were the most common. Serious AEs were observed in 19 (39.6%) pts. Dose-limiting toxicities occurred at 200 mg/120 mg (n = 1; influenza and pneumonia), 240 mg/120 mg (n = 1; insomnia), and 240 mg/240 mg (n = 2; febrile neutropenia, neutropenia, thrombocytopenia, esophagitis, suprapubic pain, sepsis); Vel 240 mg BID + CRT/Vel 120 mg + CON was chosen as the maximum tolerated dose/RP2D. Of 41 pts evaluable for tumor assessment, 26 (63.4%) had a confirmed response. Interim median progression-free survival was 24.1 mo (range, 8.9 – not reached); updated results will be reported. Conclusions: Vel 240 + CRT/Vel 120 mg BID + CON was well tolerated with promising antitumor activity in stage III NSCLC and was determined as RP2D. Clinical trial information: NCT02412371.

Equivalence of cell survival data for radiation dose and thermal dose in ablative treatments: analysis applied to essential tremor thalamotomy by focused ultrasound and gamma knife

Thermal dose and absorbed radiation dose have historically been difficult to compare because different biological mechanisms are at work. Thermal dose denatures proteins and the radiation dose causes DNA damage in order to achieve ablation. The purpose of this paper is to use the proportion of cell survival as a potential common unit by which to measure the biological effect of each procedure. Survival curves for both thermal and radiation doses have been extracted from previously published data for three different cell types. Fits of these curves were used to convert both thermal and radiation dose into the same quantified biological effect: fraction of surviving cells. They have also been used to generate and compare survival profiles from the only indication for which clinical data are available for both focused ultrasound (FUS) thermal ablation and radiation ablation: essential tremor thalamotomy. All cell types could be fitted with coefficients of determination greater than 0.992. As an illustration, survival profiles of clinical thalamotomies performed by radiosurgery and FUS are plotted on a same graph for the same metric: fraction of surviving cells. FUS and Gamma Knife have the potential to be used in combination to deliver a more effective treatment (for example, FUS may be used to debulk the main tumour mass, and radiation to treat the surrounding tumour bed). In this case, a model which compares thermal and radiation treatments is valuable in order to adjust the dose between the two.

Tolerability of veliparib (V) in combination with carboplatin (C)/paclitaxel (P): Based chemoradiotherapy (CRT) in subjects with stage III non-small cell lung cancer (NSCLC)

8546

Background: CRT is a standard for patients with Stage III NSCLC. V is a potent, orally bioavailable PARP1/2 inhibitor that can delay DNA repair following chemotherapy or radiation induced damage. A Phase 2 study indicated favorable efficacy of V vs placebo when added to C/P in advanced NSCLC (Ramalingam et al. Clin Cancer Res. 2016). Based on these results, a Phase 1/2 trial was initiated to study the safety and efficacy of V/C/P-based CRT in the treatment of Stage III NSCLC. Methods: Subjects without prior NSCLC therapy suitable for definitive CRT received V plus C AUC 2 + P 45 mg/m2 weekly + 60 Gy over 6-9 weeks. V was escalated from 60 mg BID to a maximum planned dose based on prior studies of 240 mg BID via 3+3 design with allowed over-enrollment followed by consolidation therapy of V 120 mg BID + C AUC 6 + P 200 mg/m2 for up to two 21-day cycles. Results: Thirty-one subjects (median age 64; 10 male) have been enrolled to date into dosing cohorts at 60 mg (7), 80 mg (9), 120 mg (7) and 200 mg (8). PK of V was dose proportional. CRT or V required dose reduction for 0 or 1 subject, respectively. Four (13%) subjects discontinued study during CRT. No DLTs have been observed and an MTD has not yet been identified. The most common any grade AEs were fatigue (16), esophagitis (15), nausea (13), neutropenia (12), thrombocytopenia (12), constipation (10) and decreased appetite (10). 21 SAEs were observed including 8 with reasonable attribution to V but outside the DLT window including G3/4 febrile neutropenia (2), G3 dehydration (1), G3 vomiting (1), G3 radiation esophagitis (1), G3 esophageal stricture (1), G3 intractable N/V (1) and G5 sepsis during consolidation (1). Of 21 subjects evaluable for tumor assessment, best response was CR (1), PR (11), SD (6), and PD (3). Conclusions: V/C/P-based CRT followed by V/C/P consolidation therapy is a tractable regimen for the treatment of Stage III NSCLC. A randomized placebo-controlled Phase 2 extension of this study is planned. Clinical trial information: NCT02412371.

Magnetic resonance guided focused ultrasound surgery for palliation of painful bone metastasis: Results of a multicenter phase III trial

9500

Background: Pain due to bone metastases is a common cause of cancer-related morbidity. Magnetic resonance guided focused ultrasound surgery (MRgFUS) is a non-invasive approach to thermal tissue ablation. This multi-center phase III trial assessed efficacy of MRgFUS compared with sham treatment to alleviate pain due to bone metastases. Methods: Subjects with a painful bone metastasis amenable to MRgFUS treatment for whom radiation therapy was ineffective or contraindicated were randomized 3:1 to MRgFUS or sham treatment in a single blind design. Un-blinding of sham subjects who did not experience significant pain relief within 2 weeks was permitted with crossover allowed to salvage MRgFUS treatment. Pain response and impact on quality of life (QOL) were assessed using the numerical rating scale (NRS) and Brief Pain Inventory-Quality of Life (BPI-QOL). Safety was also assessed. Results: 142 randomized subjects were included in an intent-to-treat analysis. 67% (95%CI: 57.5-76.0%) of 107 subjects in the MRgFUS arm experienced clinically significant pain relief, equating with an anchor descriptor of “much improved” or better at 3 months compared to 20% of 35 sham arm subjects (p<0.0001). Median baseline and 3 month NRS scores were 7.0 and 2.0 for the MRgFUS arm vs. 7.0 and 6.0 for the sham arm. A clinically significant improvement at 3 months in BPI-QOL score for MRgFUS but not sham treatment was noted [average change: 2.4 vs. 0.2 respectively, (p<0.0001)]. MRgFUS treatment was well tolerated. Conclusions: MRgFUS, as demonstrated by this phase III trial, results in excellent rates of pain relief and improvement in QOL for patients with oncologic related bone pain who are not candidates for radiation therapy. Given these excellent results coupled with a favorable side effect profile, MRgFUS should be considered a primary choice for this patient population. Clinical trial information: NCT00656305.

Androgen receptor degradation by the E3 ligase CHIP modulates mitotic arrest in prostate cancer cells

The androgen receptor (AR) has a vital role in the onset and progression of prostate cancer by promoting G1-S progression, possibly by functioning as a licensing factor for DNA replication. We here report that low dose 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, induces mitotic arrest in prostate cancer cells involving activation of the E3 ligase CHIP (C-terminus of Hsp70-interacting protein) and degradation of the AR. Depletion of the AR by small interfering RNA (siRNA) eliminates 2-ME-induced arrest and introducing AR into PC3-M cells confers 2-ME-induced mitotic arrest. Knockdown of CHIP or MDM2 (mouse homolog of double minute 2 protein) individually or in combination reduced AR degradation and abrogated M phase arrest induced by 2-ME. Our data link AR degradation via ubiquitination to mitotic arrest. Targeting the AR by activating E3 ligases such as CHIP represents a novel strategy for the treatment of prostate cancer.

Disruption of spermatogenesis and Sertoli cell structure and function by the indenopyridine CDB-4022 in rats

The present studies were undertaken to determine the testicular cell type(s) affected by the antispermatogenic indenopyridine CDB-4022. At the oral threshold dose (2.5 mg/kg), CDB-4022 induced infertility in all males. CDB-4022 did not alter (P > 0.05) Leydig cell function as assessed by circulating testosterone, seminal vesicle, and ventral prostate weights or body weight gain compared to controls. Conversely, CDB-4022 reduced (P < 0.05) testicular weight, spermatid head counts, and percentage of seminiferous tubules undergoing spermatogenesis. In a second study, adult male rats received a maximally effective oral dose of CDB-4022 (12.5 mg/kg), dipentylphthalate (DPP; 2200 mg/kg; a Sertoli cell toxicant), or vehicle and were necropsied 3, 6, or 12 h after dosing to determine acute effects. Serum inhibin B levels were suppressed (P < 0.05) by 6 h after CDB-4022 or DPP treatment, but epididymal androgen-binding protein (ABP) levels were not altered (P > 0.05), compared to controls. CDB-4022 and DPP increased (P < 0.05) the percentage of tubules with apoptotic germ cells, particularly differentiating spermatogonia and spermatocytes, by 12 h after dosing. Microscopic examination of the testis indicated a greater degree of vacuolation in Sertoli cells and initial signs of apical germ cell sloughing/shedding by 3 or 12 h after CDB-4022 or DPP treatment, respectively. In a third study, prepubertal male rats were treated with vehicle, 12.5 mg/kg of CDB-4022, or 2200 mg/kg of DPP, and the efferent ducts of the right testis were ligated 23 h before necropsy. Seminiferous tubule fluid secretion (difference in weight of testes), serum inhibin B levels, and ABP levels in the unligated epididymis were reduced (P < 0.05) at 24 and 48 h after dosing in CDB-4022- and DPP-treated rats compared to controls. Collectively, these data suggest that CDB-4022 disrupts spermatogenesis by inducing apoptosis in early stage germ cells via a direct action on the Sertoli cell.

Histone H1 and H3 dephosphorylation are differentially regulated by radiation-induced signal transduction pathways

We recently demonstrated that linker histone H1, which is thought to have a fundamental role in higher-order chromatin structure, becomes transiently dephosphorylated after ionizing radiation (IR) in a mutated ataxia telangiectasia (ATM) dependent manner. To establish whether H1 dephosphorylation was a component of a damage-response pathway that included dephosphorylation of other histones, we asked whether H3 was dephosphorylated in response to IR in a manner similar to H1. H1 and H3 are maximally phosphorylated in metaphase and both are dephosphorylated after IR. However, the duration of IR-induced H3 dephosphorylation is significantly longer than that of IR-induced H1 dephosphorylation. Moreover, H1 dephosphorylation is ATM-dependent, whereas H3 dephosphorylation is ATM-independent. These observations suggest that the damage-sensing pathways regulating H3 and H1 dephosphorylation diverge upstream of ATM.

Circulating concentrations of the antiprogestins CDB-2914 and mifepristone in the female rhesus monkey following various routes of administration

The overall aim of these studies was to investigate the oral and i.m. bioavailability of CDB-2914 in intact female rhesus monkeys, and to compare the serum concentrations of CDB-2914 with that of mifepristone following oral administration. In the first study, a 50 mg bolus of CDB-2914 per monkey was administered intravenously, orally or intramuscularly. The area under the serum concentration-time curve for 72 h (AUC(0-72)) following i.v. injection was 18 320 +/- 2718 ng/ml*h, and that for oral administration was 10 464 +/- 3248 ng/ml*h. Thus, the oral bioavailability of CDB-2914 equivalents was 56%. The AUC(0-168 h) following i.m. injection was 11 226 +/- 1130 ng/ml*h. Therefore, the i.m. bioavailability of CDB-2914 equivalents was 62%. In the second study, the serum concentrations of CDB-2914 and mifepristone equivalents were compared following an oral bolus dose in two different formulations. When administered at 5 mg/kg in aqueous suspending vehicle (ASV), the mean peak serum concentration (C(max)) of CDB-2914 equivalents (192 +/- 64 ng/ml) occurred at 5 +/- 1 h, whereas the C(max) of mifepristone equivalents (82 +/- 25 ng/ml) occurred at 3 +/- 1 h. Following administration in gelatin capsules (35 mg/monkey), the C(max) of CDB-2914 equivalents (129 +/- 24 ng/ml) occurred at 5 +/- 1 h, while the C(max) of mifepristone equivalents (31 +/- 8 ng/ml) occurred at 3 +/- 1 h. The serum concentration (AUC(0-120 h)) of CDB-2914 equivalents was 4.7- or 5. 3-fold greater than that of mifepristone equivalents when administered orally in ASV or gelatin capsules respectively. The serum protein binding characteristics of CDB-2914 were also studied. CDB-2914 bound to human alpha(1)-acid glycoprotein (AAG), but not with as high an affinity as mifepristone. In contrast, neither CDB-2914 nor mifepristone bound with high affinity to AAG, corticosteroid binding globulin or sex hormone binding globulin in monkey serum. Collectively, these results indicated that CDB-2914 was more efficiently absorbed than mifepristone following oral administration to female rhesus monkeys.

The tumor suppressor p53 can reduce stable transfection in the presence of irradiation

The tumor suppressor p53 is believed to play an essential role in maintaining genome stability. Although it is currently unknown how p53 is involved in this important biological safeguard, several previous publications indicate that p53 can help to maintain genome integrity through the recombination-mediated DNA repair process. The integration of linearized plasmid DNA into the host chromosome utilizes the same repair process, and the frequency can be measured by clonogenic assays in which cells that were stably transfected by plasmid integration can be scored by their colony-forming abilities. To gain insight into whether p53 has a direct role in plasmid integration into the host chromosome, we determined the frequency of stable transfection with CHO cells expressing either wild-type or mutant p53 in the presence and absence of irradiation. We found that low-dose irradiation ( approximately 50 to 100 cGy) increased stable transfection frequencies in CHO cells regardless of their p53 status. However, the increase of transfection frequency was significantly lower in CHO cells expressing wild-type p53. Our data thus suggest that wild-type p53 can suppress plasmid DNA integration into the host genome. This p53 function may play a direct and significant role in maintaining genome stability.

Histone H1 dephosphorylation is mediated through a radiation-induced signal transduction pathway dependent on ATM

Ionizing radiation is known to activate multiple signal transduction pathways, but the targets of these pathways are poorly understood. Phosphorylation of histone H1 is thought to have a role in chromatin condensation/decondensation, and we asked whether ionizing radiation (IR) would alter H1 phosphorylation. Our data demonstrate that low doses of IR result in a dramatic, but transient, dephosphorylation of H1 isoforms. The in vivo IR-induced dephosphorylation of H1 is completely blocked by wortmannin and is abrogated in ataxia telangiectasia cells. Furthermore, we measured radiation-induced inhibition of cyclin dependent kinase activity and activation of histone H1 phosphatase activity. Both activities were affected by radiation-induced signals in an ATM-dependent manner. Thus, the rapid IR-induced dephosphorylation of H1 involves a pathway including ATM and a wortmannin-sensitive step leading to both inhibition of cyclin-dependent kinase activities as well as activation of H1 phosphatase(s).

Third ventricular lesion masquerading as suprasellar disease

We discuss the case of a patient who presented with a bitemporal visual field disturbance thought to arise from chiasmatic compression secondary to a suprasellar mass. The patient was ultimately diagnosed with medulloblastoma with diffuse intraventricular disease. Careful review of magnetic resonance (MR) findings in this case demonstrate the apparent suprasellar mass to be within the suprachiasmatic recess of the third ventricle. The role of MR imaging in distinguishing between suprasellar disease involving the third ventricle and primary third ventricular lesions is discussed.

The radiation-induced S-phase checkpoint is independent of CDKN1A

We recently demonstrated that, in response to radiation, replication is down-regulated at the level of individual origins throughout S phase of the cell cycle. Since several in vitro studies demonstrate that CDKN1A (formerly known as p21) down-regulates replication by inhibiting PCNA, and since CDKN1A can retard progression of cells through S phase in vivo, the question arises whether CDKN1A is involved in the S-phase damage-sensing pathway. In the present study we analyzed the effect of ionizing radiation on CDKN1A+/+ and CDKN1A-/- cells derived from the HCT 116 cell line. Neither progression of cells through S phase nor survival after exposure to ionizing radiation is influenced by CDKN1A status in either synchronous or asynchronous cells. These results establish that CDKN1A is not necessary for the acute S-phase damage-sensing pathway that functions to prevent firing of replication origins during S phase.

Radiation down-regulates replication origin activity throughout the S phase in mammalian cells

An asynchronous culture of mammalian cells responds acutely to ionizing radiation by inhibiting the overall rate of DNA replication by approximately 50% for a period of several hours, presumably to allow time to repair DNA damage. At low and moderate doses, this S phase damage-sensing (SDS) pathway appears to function primarily at the level of individual origins of replication, with only a modest inhibition of chain elongation per se. We have shown previously that the majority of the inhibition observed in an asynchronous culture can be accounted for by late G1cells that were within 2-3 h of entering the S period at the time of irradiation and which then fail to do so. A much smaller effect was observed on the overall rate of replication in cells that had already entered the S phase. This raised the question whether origins of replication that are activated within S phase per se are inhibited in response to ionizing radiation. Here we have used a two-dimensional gel replicon mapping strategy to show that cells with an intact SDS pathway completely down-regulate initiation in both early- and late-firing rDNA origins in human cells. We also show that initiation in mid- or late-firing rDNA origins is not inhibited in cells from patients with ataxia telangiectasia, confirming the suggestion that these individuals lack the SDS pathway.

Effects of two progestin-only contraceptives, Depo-Provera and Norplant-II, on the vaginal epithelium of rhesus monkeys

The objective of this study was to determine whether progestin-only contraceptives induce thinning of the vaginal epithelium in nonhuman primates. Eight intact rhesus monkeys (four per group) were treated with either a single intramuscular injection of 30 mg of Depo-Provera or a subcutaneous insertion of Norplant-II (2 x 75 mg rods; day 0). Norplant-II rods were removed 90 days after insertion. Vaginal biopsies were obtained during a pretreatment menstrual cycle and following treatment on days 10, 30, 60, 118, and 146. Formalin-fixed vaginal biopsies were evaluated for epithelial thickness and the degree of keratinization. The circulating levels of estradiol, progesterone, medroxyprogesterone acetate (MPA), or levonorgestrel (LNG) were monitored throughout the study by specific radioimmunoassays. Circulating levels of estradiol and progesterone confirmed the stage of the menstrual cycle in which pretreatment biopsies were obtained. Following treatment with Depo-Provera, serum levels of MPA increased to 2.3 +/- 0.6 ng/ml (x +/- SE, n = 4) within 24 hr. Serum levels of MPA were maximal on day 14 (5.5 +/- 0.9 ng/ml), dropped below 1 ng/ml by day 50, and were nondetectable by day 70. Circulating levels of LNG were elevated 24 hr after insertion of Norplant-II (5.8 +/- 3.0 ng/ml), peaked on day 2 (7.6 +/- 4.2 ng/ml), remained between 1.4 and 6.2 ng/ml from days 14 to 90, and were nondetectable by day 118, the first serum sample after removal of Norplant-II. There were no significant differences (p > 0.05) in the epithelial thickness (microm), number of epithelial cell layers, or type of epithelium present in vaginal biopsies obtained during the follicular or luteal phases of the pretreatment menstrual cycle. Conversely, a pronounced effect of progestin treatment was observed on the vaginal epithelium. There were no significant differences (p > 0.05) between the two progestin treatment groups, but a significant effect (p < 0.05) over time was observed (two-way ANOVA). Compared with pretreatment menstrual cycle controls, the vaginal epithelial thickness was decreased (p < 0.05) by day 30 or 60 following Norplant-II insertion or Depo-Provera injection, respectively. The number of epithelial cell layers was also decreased (p < 0.05) on days 30 and/or 60 in progestin-treated monkeys compared with pretreatment control cycles. Following removal of Norplant-II or metabolic excretion of MPA, the vaginal epithellium regenerated and the thickness was no longer different (p > 0.05) from the pretreatment control cycle. These data demonstrate that progestin-only contraceptives induced thinning of the vaginal epithelium in rhesus monkeys, and this effect was rapidly reversible following physical or metabolic removal of the progestin.

S phase damage sensing checkpoints in mammalian cells

Mammalian cells have evolved multiple responses for dealing with DNA damage. One response is to acutely downregulate DNA synthesis at the initiation step. Essentially nothing is known about the initial signal that activates this SDS pathway or the macromolecules involved in transducing the signal into the final inhibitory step at origins. Determining whether any radiation induced changes in known proteins involved in cell cycle regulation or in other signal transduction pathways are primary or secondary responses to DNA damage constitutes a major challenge to identifying members of the pathway. It may turn out to be easier to identify the final mediator in the pathway, namely the protein(s) whose interaction with origins is ultimately affected by radiation. Hopefully, mutations in SDS genes in genetically tractable systems such as S cerevisiae or Schizosaccharomyces pombe will allow the identification of homologous genes in mammals. Most tumour cells are TP53 negative, and yet it is not clear that TP53 status influences radiation sensitivity. The SDS pathway may therefore represent an important protective mechanism that stands in the way of effective tumour cell killing by radiation therapy. It is hoped that an understanding of this pathway will provide opportunities for developing novel antineoplastic targets and/or radiation sensitizers.

A p53-independent damage-sensing mechanism that functions as a checkpoint at the G1/S transition in Chinese hamster ovary cells

In response to a moderate dose of radiation, asynchronous mammalian cell populations rapidly and transiently down-regulate the rate of DNA synthesis to approximately 50% of preirradiation values. We show here that only half of the reduction in overall replication rate can be accounted for by direct inhibition of initiation at origins in S-phase cells. The other half results from the operation of a newly defined cell cycle checkpoint that functions at the G1/S transition. This checkpoint senses damage incurred at any time during the last 2 hr of G1 and effectively prevents entry into the S period. The G1/S and S-phase checkpoints are both p53-independent and, unlike the p53-mediated G1 checkpoint, respond rapidly to radiation, suggesting that they may represent major damage-sensing mechanisms connecting the replication machinery with DNA repair pathways.

Cloning and characterization of Chinese hamster p53 cDNA

We have cloned and sequenced Chinese hamster p53 cDNA and have compared the p53 sequence in different Chinese hamster cell lines to several relevant phenotypes. Our results indicate that a mutation in CHO cells that changes Thr211 to Lys211 abrogates the ability to arrest in G1 and apparently renders cells capable of amplifying DNA. However, this mutation has no effect on the G2 checkpoint or on acute down-regulation of DNA replication after a radiation challenge.

Desmoplastic fibroma: a role for radiotherapy?

Desmoplastic fibroma is a rare, locally aggressive, benign tumor that is considered the skeletal counterpart of the desmoid tumor of soft tissues. Although the treatment of choice of desmoplastic fibroma is surgical excision, radiation therapy should be considered when surgery is not a viable option.

Extradural failure in glioblastoma multiforme: MRI demonstration

Glioblastoma multiforme is invariably associated with intracranial failure following conventional therapy. Extracranial as well as metastatic failure are rarely seen. Subtle extracranial abnormalities in most patients with glioblastoma multiforme are not indicative of convexity failure. However, in patients with high p53 and Ki67 immunoreactivity and in whom the dura was not closed at the time of craniotomy, the possibility of early extradural failure should be considered.

Definitive radiotherapy for T1 and T2 squamous cell carcinoma of the tonsil

BACKGROUND

To assess whether survival or local control of early squamous cell carcinoma of the tonsil has been compromised by a moderate-dose approach.

METHODS

Between 1970 and 1989, 185 patients with SCCa of the tonsil were seen at our institution. Fifty-three patients with T1 (30) and T2 (23) lesions treated with definitive radiotherapy were reviewed. Median follow-up was 60 months. The effects of total dose and site of the primary on survival and local regional control were analyzed.

RESULTS

Three-year determinate survival was 77%. Mean total dose was 63.1 Gy. Site of the primary significantly affected survival (86% for fossa, 54% for pillars, p < 0.025). Local control at 2 years was 81% and was independent of dose > or = 63 Gy or site of the primary. Grade 4 complications defined by the RTOG/EORTC Acute Morbidity criteria occurred in three patients.

CONCLUSIONS

Tumor doses on the order of 63 Gy or less result in excellent local control and survival rates for T1 and T2 carcinomas of the tonsil. Local control rates are better for fossa lesions than for pillar lesions.

A phase 1-2 trial of superselective carboplatin, low-dose infusional 5-fluorouracil and concurrent radiation for high-grade gliomas

Recent trials have suggested that low-dose infusional 5-FU is more efficacious when given during radiotherapy than is bolus 5-FU. Additionally, intra-arterial cisplatin for brain tumors has been shown to be associated with both high response rates as well as significant toxicity. A dose escalation study was therefore performed using superselective carboplatin, a cisplatin analogue with a favorable CNS toxicity profile in combination with 6 weeks of infusional 5-FU at 225 mg/m2 and concurrent radiotherapy. Eight patients were treated at the starting dose of 200 mg/m2 carboplatin and 11 patients were treated at 300 mg/m2. No toxicity was observed that was attributable to infusional 5-FU. However, two ischemic events related to the superselective delivery of carboplatin were observed, and one patient was noted to have asymptomatic retinal toxicity from the carboplatin. Of 19 patients, 5 had objective responses with 25% or greater reduction in tumor volumes. Continuous infusional 5-FU can be given in combination with partial brain radiotherapy without significant toxicity. Superselective carboplatin delivery is associated with a low incidence of stroke, but no significant retinal toxicity.

Esthesioneuroblastoma. Long-term outcome and patterns of failure--the University of Virginia experience

BACKGROUND

Esthesioneuroblastoma is a rare tumor arising from olfactory epithelium. This retrospective review analyzed the patterns of failure and long term outcome of patients with esthesioneuroblastoma evaluated at a single institution.

METHODS

Forty patients with esthesioneuroblastoma were evaluated at the University of Virginia, with a median follow-up of 130 months. In most cases, treatment consisted of combined-modality therapy, including radiotherapy and surgery for Stages A and B disease and the addition of chemotherapy for Stage C disease. Fifteen patients received chemotherapy that included cyclophosphamide plus vincristine. Thirty-eight patients received radiotherapy, with a median dose of 50 Gy. Initial surgery for 23 patients included craniofacial resection, whereas the remainder had less extensive surgery (3 had no initial surgery). Five patients were salvaged with high dose chemotherapy and autologous bone marrow transplantation (CTX/BMT).

RESULTS

Actuarial survivals at 5, 10, and 15 years are 78%, 71%, and 65% respectively. Fifty-five percent of patients failed therapy, and 68% of the failures were locoregional. Thirty-nine percent of recurrences occurred later than 5 years from diagnosis. Three of the five patients were successfully salvaged with CTX/BMT compared with four of seventeen patients who underwent conventional salvage therapy.

CONCLUSIONS

Esthesioneuroblastoma is associated with long term survival and late recurrences. Multimodality therapy should be used initially. Durable remissions of failures can be achieved with CTX/BMT:

Radiation effects on DNA synthesis in a defined chromosomal replicon

It has recently been shown that the tumor suppressor p53 mediates a signal transduction pathway that responds to DNA damage by arresting cells in the late G1 period of the cell cycle. However, the operation of this pathway alone cannot explain the 50% reduction in the rate of DNA synthesis that occurs within 30 min of irradiation of an asynchronous cell population. We are using the amplified dihydrofolate reductase (DHFR) domain in the methotrexate-resistant CHO cell line, CHOC 400, as a model replicon in which to study this acute radiation effect. We first show that the CHOC 400 cell line retains the classical acute-phase response but does not display the late G1 arrest that characterizes the p53-mediated checkpoint. Using a two-dimensional gel replicon-mapping method, we then show that when asynchronous cultures are irradiated with 900 cGy, initiation in the DHFR locus is completely inhibited within 30 min and does not resume for 3 to 4 h. Since initiation in this locus occurs throughout the first 2 h of the S period, this result implies the existence of a p53-independent S-phase damage-sensing pathway that functions at the level of individual origins. Results obtained with the replication inhibitor mimosine define a position near the G1/S boundary beyond which cells are unable to prevent initiation at early-firing origins in response to irradiation. This is the first direct demonstration at a defined chromosomal origin that radiation quantitatively down-regulates initiation.

The isolation and characterization of estradiol-fatty acid esters in human ovarian follicular fluid. Identification of an endogenous long-lived and potent family of estrogens

The estradiol-fatty acid esters are highly potent and long-lived estrogens that were first isolated and identified from in vitro biosynthetic experiments (Mellon-Nussbaum S., Ponticorvo, L., Schatz, F., and Hochberg, R. B. (1982) J. Biol. Chem. 257, 5678-5684). Other studies have indicated that these esters exist endogenously, but the evidence is indirect, resting solely on the presence of a nonpolar saponifiable metabolite. Although there are similar reports of other naturally occurring fatty acid esters of biologically active steroid hormones, likewise, none has been isolated and characterized. In this study we have found that follicular fluid from the ovaries of women stimulated with gonadotrophins contains relatively large amounts of a nonpolar saponifiable derivative of estradiol (approximately 10(-7)M), which we presumed to be fatty acid esters. Using a combination of chromatographic techniques we isolated these estradiol metabolites and identified them by mass spectral analysis. They are a mixture of five different estradiol-17 fatty acid esters. The amount of each present was determined by separating the esters by reversed phase high performance liquid chromatography and then quantifying each peak by radioimmunoassay and UV absorption. The esters of estradiol are predominantly unsaturated, with linoleate the most abundant comprising 43% of the total. The other esters are: palmitate (20%), arachidonate (19%), oleate (14%), and stearate (4%). Thus these studies conclusively demonstrate the existence of these unusually powerful estrogens.

Radiotherapy for basaloid squamous cell carcinoma of the head and neck

Basaloid squamous cell carcinoma (BSCC) of the head and neck is a recently described high-grade variant of squamous cell carcinoma. It is a biologically virulent neoplasm with a propensity for nodal, as well as systemic, metastases. Because of the limited number of published reports, we reviewed data from patients of the University of Virginia Health Sciences Center and identified 16 cases of BSCC. The intent of this study was to determine the role of radiotherapy in the treatment of BSCC and better define the clinical features of this entity. Radiotherapy alone, or in combination with surgery, resulted in excellent local control rates. Distant metastases, chiefly pulmonary, occurred in more than half of the patients.

The dosimetric consequences of weighted fields using the same isocenter in radiosurgery

One handicap in achieving ideal dosimetry with the Gamma Knife is the limited number of standard collimator sizes (4, 8, 14 and 18 mm). We report an approach that makes possible the creation of 50% or higher isodose lines, corresponding to collimator sizes from 4 to 18 mm. This technique, which uses the same icocenter, but with different sized and weighted collimators, improves matching for given isodose lines to the diameter of the lesion in a defined plane. However, when combination fields, designed to reproduce the 50% isodose diameter of the 8- and 14-mm collimators, are compared to the standard sizes, there are significant differences in the three-dimensional dosimetry.

Extracranial absorbed doses with Gamma Knife radiosurgery

Radiosurgery is used with increasing frequency, not only for the treatment of cerebral arteriovenous malformations (AVMs), but also for the treatment of other well-defined lesions including acoustic neuromas, meningiomas, pituitary adenomas as well as solitary metastases. Although investigators have addressed dosimetric aspects of stereotactic radiosurgery in terms of target volume, little if any attention has been focused on the absorbed doses received at extracranial sites. Therefore, absorbed doses to the eye, thyroid, sternum and gonads were measured in 111 patients (100 adults and 11 children) using thermoluminescent dosimetry (TLDs). For the 100 adults, the average maximum target absorbed dose was 35 +/- 8 Gy. The measured absorbed dose in selected organs of adults from Gamma Knife radiosurgery using one or more isocenters was 9 +/- 8 cGy for the eye, 15 +/- 7 cGy for the thyroid, 20 +/- 10 cGy for the sternum and 3 +/- 2 cGy for the gonads. The absorbed doses received by the children (13 years and younger) was similar with the exception of a marked increase in gonadal dose. The use of multiple isocenters is associated with higher absorbed doses to extracranial sites.

Aromatase and testosterone fatty acid esters: the search for a cryptic biosynthetic pathway to estradiol esters

The estradiol fatty acid esters (lipoidal derivatives, LE2) are extremely potent estrogens that accumulate in fat, including fat of menopausal women. These steroidal esters are protected from metabolism and are converted to the free, biologically active steroid through the action of esterases. Previous studies have shown that biosynthetic pathways in the adrenal gland exist in which steroid fatty acid esters are substrates. This led us to determine whether a cryptic aromatase pathway exists in which testosterone esters could be converted directly into LE2. We tested a representative fatty acid ester, testosterone stearate, both as an inhibitor and as a substrate for the aromatase enzyme from human placental microsomes. This ester had neither activity. In addition, we tested [1 beta-3H]testosterone acetate as a substrate for this enzyme complex, measuring the production of 3H2O as evidence of aromatization. Although the rate of reaction was considerably slower than that of testosterone, 3H2O was produced. However, when [2, 4, 6, 7-3H]testosterone acetate was incubated and the steroidal products isolated, we found that hydrolysis of the substrate had occurred. Both [3H]-labeled testosterone and estradiol were found, and very little if any [3H]estradiol acetate was formed. Thus, we conclude that an aromatase pathway involving testosterone esters does not exist and that the sole source of LE2 is through direct esterification of estradiol.

Measurement of estradiol-17-fatty acid esters in human tissues

We have developed a gas chromatographic/mass spectral method for the sensitive and reproducible measurement of estradiol-17-fatty acid esters in human tissues and blood. To provide an internal standard for quantification, a trideuterated analog of a representative estradiol ester is added to the tissues. Estradiol (E2) released from the nonpolar ester fraction by alkaline hydrolysis is derivatized to form the ditrimethylsilyl ether and then analyzed by gas chromatographic/mass spectral, monitoring the molecular ions mass per U charge of the ditrimethylsilyl derivative of E2 and [2H3]E2. There are low but detectable levels of E2 ester in the blood of cycling females; there are none in urine. While the E2 ester is present in breast cyst fluid, its concentration, 77-140 pmol/L, is considerably less than E2, 110-2,863 pmol/L. But there is a large amount of E2 ester in fat. In premenopausal women the average E2 ester in fat (sc and omental) is 957 +/- 283 38 fmol/g (SEM); in women who are menopausal less than 12 yr, the E2 ester in fat is 669 +/- 158 fmol/g; in women who are menopausal at least 15 yr, the fat level is 399 +/- 146 fmol/g. Muscle from the same women have lower concentrations of the ester; in 8 out of 12 muscle specimens it was not detectable. The E2 esters are extremely potent estrogens. Although they are hormonally active they require enzymatic hydrolysis to exert their hormonal action. These studies show that these long chain esters of E2 are sequestered in fatty tissues, wherein they represent a protected store of preformed hormone. Under the proper stimulation, adipose tissue can activate the estrogenic signal through the action of hormonally sensitive esterases. Thus, through signaling between estrogen sensitive tissues and neighboring fat cells, a local paracrine loop may exist.

Glomus jugulare tumors. Long-term control by radiation therapy

The records of 49 patients with glomus jugulare tumor seen at the University of Virginia from 1932 to 1985 were retrospectively reviewed with the objective of assessing long-term results of treatment. Follow-up ranged from 5 to 31 years, with a minimum of 10 years in 36 patients (73%). According to McCabe's classification, 17 patients (35%) were Group I, 11 patients (22%) were Group II, and 21 patients (43%) were Group III. Analysis by therapeutic technique revealed that 20 patients received surgery alone (41%), 15 patients received radiation therapy alone (31%), and 14 patients received combined therapy (28%). Only 7 patients (14%) have had clinical or radiologic evidence of disease progression. Three of these patients were treated by surgery alone and three by a combination of surgery and radiation, but the dose was less than 4000 cGy. Only one patient treated by radiation therapy alone or with surgery and radiation to a dose in excess of 4000 cGy demonstrated disease progression. Salvage radiation therapy was given to three of the seven patients when progressive disease was detected. Radiation therapy is an effective treatment for glomus jugulare tumor with minimal late progression of disease in adequately treated patients and no significant long-term complications.

Phase I/II trial of superselective arterial 5-FU infusion with concomitant external beam radiation for patients with either anaplastic astrocytoma or glioblastoma multiforme

From August 1987 through September 1989, 25 patients with either anaplastic astrocytoma (8 patients) or glioblastoma multiforme (17 patients) were entered into a Phase I trial of combined intra-arterial 5-fluorouracil (5-FU) and external beam radiation therapy. The intra-arterial 5-FU was given in a superselective, supraopthalmic fashion, in escalating doses from 200 mg to 600 mg on a weekly basis during the radiotherapy. Each patient received from 1-4 courses of 5-FU. Radiotherapy consisted of 5,000 rads in 25 fractions given to partial brain fields including the mass and surrounding edema plus a 3-cm margin as defined by computed tomography scan. There were a total of 4 significant acute complications out of a total of 70 infusions. These included 3 ischemic events of which 2 were transient. In addition, 1 patient experienced a cerebral bleed. No patients developed ocular complications. Electroencephalograms (EEGs) were performed immediately before and during 21 intra-arterial infusions. Two patients developed significant EEG changes during intra-arterial infusion, and both of these patients experienced untoward reactions. The remaining patients showed no EEG changes during their infusions. The median survival for patients with glioblastoma multiforme was 15 months. We believe the toxicity of superselective intra-arterial 5-FU infusion combined with external beam radiotherapy is acceptable. This type of treatment deserves further study.

Estrogenic action of estriol fatty acid esters

Recent studies suggest that, estriol, like estradiol, is biosynthetically esterified with fatty acids. We have synthesized the stearate estriol, at C-16 alpha, C-17 beta and the diester, C-16 alpha,17 beta and tested these D-ring esters for their estrogenic action both in vivo and in vitro, comparing them to estradiol, estriol and estradiol-17-stearate. None of the estriol esters bind to the estrogen receptor. They are only weakly estrogenic in a microtiter plate estrogen bioassay: stimulation of alkaline phosphatase in the Ishikawa endometrial cells. However, both estriol monoesters are extremely potent estrogens when injected subcutaneously (in aqueous alcohol) into ovariectomized mice. Compared to the free steroids, they produced a dramatically increased uterine weight with a greatly prolonged duration of stimulation. The 16 alpha,17 beta-diester also induced a protracted uterotrophic response, but the stimulation of uterine weight was comparatively low. Since the esters of estradiol and estriol do not bind to the estrogen receptor, their estrogenic signal must be generated through the action of esterase enzymes. These naturally occurring esters have the potential of being extremely useful pharmacological agents for long-lived estrogenic stimulation.

Steroidal fatty acid esters

Several years ago we discovered an unexpected family of steroidal metabolites, steroidal fatty acid esters. We found that fatty acid esters of 5-ene-3 beta-hydroxysteroids, pregnenolone and dehydroisoandrosterone are present in the adrenal. Subsequently, others have shown the existence of these non-polar 5-ene-3 beta-hydroxysteroidal esters in blood, brain and ovaries. Currently, almost every family of steroid hormone is known to occur in esterified form. We have studied the esters of the estrogens and glucocorticoids in some detail, and have found that these two steroidal families are esterified by separate enzymes. In a biosynthetic experiment performed simultaneously with estradiol and corticosterone, we established that the fatty acid composition of the steroidal esters is quite different. The corticoid is composed predominantly of one fatty acid, oleate, while the estradiol esters are extremely heterogeneous. Our studies have demonstrated that the estrogens are extremely long-lived hormones, that they are protected by the fatty acid from metabolism. They are extremely potent estrogens, with prolonged activity. Esterification appears to be the only form of metabolism that does not deactivate the biological effects of estradiol. We have demonstrated the biosynthesis of fatty acid esters of estriol, monoesters at both C-16 alpha and C-17 beta. They too are very potent estrogens. These fatty acid esters of the estrogens are the endogenous analogs of estrogen esters, like benzoate, cypionate, etc., which have been used for decades, pharmacologically because of their prolonged therapeutic potency. We have found that the estradiol esters are located predominantly in hydrophobic tissues, such as fat. Sequestered in these tissues, they are an obvious reservoir of estrogenic reserve, requiring only an esterase for activation. To the contrary the biological activity of the fatty acid esters of the glucocorticoid, corticosterone, is not different from that of its free parent steroid. We have shown that the rapid kinetics of its induction of gluconeogenic responses is caused by its labile C-21 ester which is rapidly hydrolyzed by esterase enzymes. While it appears that the physiological role of the estrogen esters may be related to their long-lived hormonal activity, the role of the other families of steroidal esters is not yet apparent. They, and perhaps the estrogen esters as well, must serve other purposes. Indeed they may serve important biological functions beyond those which we ordinarily associate with steroid hormones.

Biological activity of the fatty acid ester metabolites of corticoids

Fatty acid esters of all families of steroid hormones are known to exist naturally. While their physiological roles are not clear, the C-17-fatty acid esters of estradiol are extremely potent and unusually long-lived estrogens. Thus, it appeared that increased potency would be a logical consequence of the esterification of all of the active steroid hormones. To test this hypothesis we measured the effect of an ester of corticosterone, corticosterone-21-stearate, on the induction of tyrosine aminotransferase in adrenalectomized rats. Surprisingly, while the ester is active compared to the unesterified corticoid corticosterone, there was no difference in either the magnitude or the duration of the induction of this enzyme. To determine whether the C-21-steroidal ester could itself induce this gluconeogenic response, we tested corticosterone-21-oleate and corticosterone-21-stearate as competitors for the binding of [3H] dexamethasone to the glucocorticoid receptor in rat liver cytosol. Both were poor ligands, with binding affinities of about 4% and more than 1%, respectively, compared to corticosterone. From these results, it is doubtful that the esters could act directly in vivo without prior cleavage of the fatty acid. We measured the rate of hydrolysis of corticosterone-21-stearate and estradiol-17-stearate by rat liver esterases. Corticosterone-21-stearate is hydrolyzed at a much greater rate (10- to 25-fold) than estradiol-17-stearate. Consequently, the difference in both potency and duration of response between the ester of the corticoid and that of the estrogen can be explained by the very rapid rate of conversion of the former into the unesterified form. Since the esterification of the corticoids appears not to be related to an increased biological half-life, as it is in the estrogens, the question remains as to the physiological role that they might play.

The synthesis of 11 beta-methoxy-[16 alpha-123I] iodoestradiol and its interaction with the estrogen receptor in vivo and in vitro

In order to produce an estrogen receptor mediated imaging agent, we have synthesized 11 beta-methoxy-16 alpha-iodoestradiol labeled with 123I, and have studied its interaction with the estrogen receptor and its distribution in rats and rabbits. This 123I-labeled steroid, 11 beta-methoxy-16 alpha-[123I]iodoestradiol, binds with high affinity, Ka = 6 x 10(9) M-1, and specificity to the estrogen receptor in uterine cytosol. When tested in vivo, this radiolabeled steroid concentrates by a receptor mediated mechanism, in the estrogen target tissue, the uterus, producing very high target to nontarget tissue ratios. The results of these experiments indicate that 11 beta-methoxy-16 alpha-[123I]iodoestradiol may be a useful imaging agent for clinically monitoring and detecting estrogen receptor containing tumors.

Actions of an estradiol-17-fatty acid ester in estrogen target tissues of the rat: comparison with other C-17 metabolites and a pharmacological C-17 ester

The C-17 fatty acid esters of estradiol (E2) are a unique family of nonpolar estradiol metabolites. They are potent long-acting estrogens that represent the natural analog of the synthetic esters used for estrogen therapy. We measured the uterotropic response and the formation of uterine nuclear estrogen receptors (ERn) produced by iv administration of a representative ester, E2-17-stearate, in comparison to E2, other natural C-17 conjugates of E2, E2-17-glucuronide, and E2-17-sulfate, and the pharmacological ester E2-17-cyclopentylpropionate. While E2-17-stearate produced a sustained and greater uterotropic response compared to E2, the maximal induction of ERn by the ester was only about one third of that induced by a similar dose of E2. However, the induction of ERn by E2-17-stearate was markedly sustained compared to that by E2. Furthermore, the initiation of the ERn response to E2-17-stearate was delayed. Since E2-17-esters do not bind to the ER, this delay is consistent with the requirement for hydrolysis of the esters before interaction with the ER. Neither of the ionic conjugates of E2 (sulfate and glucuronide) produced an increase in ERn concentrations or a uterotropic response. The synthetic ester cyclopentylpropionate, like E2, produced a rapid ERn response and a significantly shorter uterotropic response than the stearate ester. When the induction of ERn by E2-17-stearate was investigated in other target tissues there were no marked differences in the brain, pituitary, and liver. No blood-brain barrier was apparent for the formation of ERn, despite the fact that this steroidal ester circulates in the blood bound to lipoproteins. These findings suggest that this unusual family of steroidal esters has biological properties that differentiate them from other known estrogens, natural and synthetic, in terms of their ability to produce a slow-onset sustained estrogenic stimulus in a variety of different estrogen target tissues.

Binding of estradiol-17-fatty acid esters to plasma proteins

The C-17 fatty acid esters of estradiol are a unique family of long-acting estrogens that circulate in blood. The unusual duration of the estrogenic action of these esters has been shown previously to correlate with their very slow rate of metabolism. However, in striking contrast to their slow rate of metabolism, the clearance of these esters from blood is relatively rapid, not very different from that of estradiol (E2). Studies on the effect of the size of the carboxylic acid moiety on the rates of both metabolism and clearance have suggested that an active process might be involved in the cellular uptake of these circulating esters, and this, in turn, raised the question of how E2-fatty acid esters are transported in blood. The binding of representative E2-17-fatty acid esters to both human and rat plasma proteins known to bind either E2 or fatty acids was investigated. As expected, both E2 and 5 alpha-dihydrotestosterone bound to human sex hormone-binding globulin, whereas none of the E2 esters bound to this human plasma protein. Similarly, E2 bound to rat alpha-fetoprotein (AFP) and unsaturated fatty acids bound to both human and rat AFP, but none of the E2 esters bound to AFP of either species. These steroid esters bind to lipoproteins. Over 85% of a representative ester, E2-17-stearate, partitioned in the lipoprotein fractions of both human and rat serum, while the synthetic short chain ester, E2-17 beta-acetate, like E2 itself, partitioned predominantly in the nonlipoprotein fraction of blood. These results demonstrate the unusual binding of a family of steroid hormones to plasma lipoproteins and open the possibility that they are transported into target cells through the mediation of lipoprotein receptors.

16 Alpha-[125I]iodo-11 beta-methoxy-17 beta-estradiol: a radiochemical probe for estrogen-sensitive tissues

We have synthesized an analog of 16 alpha-iodoestradiol, 11 beta-methoxy-16 alpha-iodo-estra-1,3,5-(10)triene-3,17 beta-diol (16 alpha-iodo-11 beta-methoxyestradiol), as a potential radiopharmaceutical for the in vivo imaging of estrogen-sensitive tissues. This steroid was synthesized labeled with 125I by halogen exchange of the stable intermediate 11 beta-methoxy-16 beta-bromo-17 beta-estradiol with Na125I. The halogen exchange reaction produces the radioiodinated steroid with a 65-80% yield in 3 h. This rapid synthesis and purification of the 125I-labeled estrogen permits a similar synthesis with 123I, a radioisotope with excellent properties for imaging. The 11-methoxy analog is a highly potent estrogen that binds to the estrogen receptor with an affinity equal to that of estradiol. In vivo, 11 beta-methoxy-16 alpha-[125I]iodoestradiol concentrates in an estrogen receptor-dependent manner in the uterus, producing remarkably sustained and much higher uterus to blood ratios than 16 alpha-[125I]iodoestradiol. Thus, this radiosteroid shows great promise, both as a research probe of the estrogen receptor and as a clinical tool for the imaging of estrogen-responsive tumors.

Metabolism of estradiol fatty acid esters in man

Fatty acid esters of estradiol coupled at the C-17 position are naturally occurring metabolites of estradiol (E2). They have been recovered after incubation of E2 with human tissue and identified in human plasma. We investigated the primary metabolic transformation of E2, namely C-17 oxidation, of two representative fatty acid esters, in five normal subjects (four men and one woman), aged 25-55 yr, using a radiometric method. The transfer of tritium from the C-17 alpha position to tritium water after iv injection of free E2 was compared to that of E2-17 beta-stearate and E2-17 beta-arachidonate. Both esters were oxidized at the C-17 position to a greater extent than was free E2. In addition, the oxidation of the E2 fatty acid esters proceeded more slowly. Thus, the time necessary to reach half the maximal extent of reaction ranged from 30-45 min for the three E2-17 beta-arachidonate studies and from 2.5-4 h for the five E2-17 beta-stearate studies, while that for free E2 was less than 15 min in each instance. The disappearance of intact E2-17 beta-stearate from plasma after bolus injection was studied in two subjects (one of the five above and one additional subject). The t1/2 values calculated for the 0-60 min period were 24 and 16 min. The rate of disappearance E2-17 beta-stearate was slower than that of E2. The biological activity of E2 esters is thought to reside in their ability to be converted, by hydrolysis, to free E2. The E2 esters must undergo hydrolysis before the oxidation of free E2 to estrone can proceed. Since the oxidation reaction is extremely rapid, studying the rate of oxidation after injection of the E2 fatty acid esters provides an index of their in vivo hydrolysis and, thus, a measure of their subsequent biological activity as the free hormone. The unsaturated arachidonate ester of E2 was oxidized at a faster rate than the saturated stearate ester; this implies that the hydrolysis of the arachidonate ester was faster. Evidence of continuing oxidation of E2-17 beta-stearate at times well after its level in plasma markedly decreased indicates that the ester is removed from the circulation before its subsequent hydrolysis and oxidation. We conclude that in man, the C-17 oxidation of both E2-17 beta-arachidonate and E2-17 beta-stearate proceeds more slowly but to a greater extent than that of the free steroid.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis of estradiol fatty acid esters by human breast tumors: fatty acid composition and comparison to estrogen and progesterone receptor content

The estradiol-17 beta-fatty acid esters are non-polar metabolites of estradiol, formed in many tissues, including human breast tumors. It has been shown in the rat that the synthesis of these esters is greatest in those tissues that respond to estrogen stimulation. Thus the possibility was explored that the biosynthesis of the estradiol esters in human breast tumors occurs mainly in those tumors that are estrogen sensitive; and thus that the synthesis of this family of non-polar metabolites of estradiol could be used as an additional marker for the identification of hormonally dependent tumors. However, the conversion of estradiol to the esters did not correlate with other indicators of estrogen responsiveness, the progesterone or estrogen receptors. Interestingly, the composition of the fatty acids in the estradiol-17-esters synthesized in the human tumors was markedly different from those originally identified in the bovine uterus. In the bovine uterus, the esters were predominantly unsaturated, 85%, while in this study the saturated esters were the major component. Since after systemic administration the saturated estradiol-17-esters have been found to be much longer-lived than the unsaturated esters, the biosynthesis of the relatively high proportion of saturated esters by human breast tumors may indicate a significantly prolonged duration for the estrogenic signal produced by endogenously formed estradiol esters. These esters formed and sequestered within the tumor cell, may serve as a preformed store of estradiol, which after enzymatic hydrolysis, can locally stimulate growth of tumors that are estrogen responsive.

The clearance and metabolism of estradiol and estradiol-17-esters in the rat

The C-17 fatty acid esters of estradiol are naturally occurring estrogens which have been shown to circulate in blood. They are long-acting estrogens, analogous to the synthetic alkyl and aryl esters of estrogens which have been used pharmacologically for decades. To determine the mechanisms involved in the prolonged stimulation evoked by these nonpolar estrogens, several C-17 alkyl esters were synthesized and labeled with 3H at C-17 alpha, and their metabolism and clearance were studied and compared to those of estradiol in rats. The conversion of the C-17-3H to 3H2O was used as a marker of metabolism. While the clearance of the long chain esters from blood is somewhat slower than that of estradiol (t 1/2 = approximately 16 vs. 2 min, respectively), the rates of metabolism are dramatically different. For example, the t 1/2 of metabolism for two representative esters, estradiol-17-stearate and arachidonate, are 580 and 365 min, respectively, while the t 1/2 of metabolism for estradiol is about as fast as its clearance from blood (approximately 2 min). When the effect of chain length was studied, it was found that for the smaller esters, there was an inverse relationship between the size of the acyl group and the clearance from blood, i.e. the longer carboxylic acids were cleared more slowly. However, when the acyl group was lengthened from C12 to C14, the rate of clearance increased and was even faster with C18. Nevertheless, with all of the esters tested, the rate of metabolism steadily decreased as the chain length increased. These results are interpreted as indicating that the control point or rate-limiting step in the metabolism of the estradiol esters is the esterase that hydrolyzes the ester to estradiol. Thus, the prolonged estrogenic action of the C-17-alkyl esters is due to the slow release of estradiol from this hydrophobic reservoir.

The naturally occurring C-17 fatty acid esters of estradiol are long-acting estrogens

C-17 fatty acid esters of estradiol are naturally occurring biosynthetic metabolites of estradiol. A representative component of this family of esters, estradiol-17-stearate, was studied in order to determine the estrogenic properties of these unusual hydrophobic steroids. Following the classical estrogen bioassay, a solution of this ester in oil was injected subcutaneously into immature rats once a day for 3 days. There was little effect on the uterus on the first day after the third injection. However, on subsequent days a large stimulation of uterine growth occurred. The course of this estrogenic effect was exactly opposite to that obtained with estradiol. In order to eliminate the possibility that this effect on the time course of estrogenic stimulation was caused by increased solubility of the hydrophobic esters in the carrier oil, the steroids were administered to adult ovariectomized animals in aqueous medium via a single intravenous injection. The uterotrophic response to estradiol was maximal at 12 h and was completely dissipated in 48-60 h. Estradiol-17-stearate produced a uterotrophic effect of twice the duration of estradiol. In the immature rat, aqueous intravenous injections of estradiol-17-stearate produced a greater uterotrophic effect than estradiol and this effect was still maximal 96 h later. In addition, this single injection of estradiol-17-stearate advanced the time of vaginal opening, a marker for puberty in the female rat. The mechanism of the prolonged estrogenic stimulation was investigated by studying the steroidal content of the uterus after injecting [3H]estradiol and [3H]estradiol-17 -stearate i.v. into immature rats. At 1 and 4 h there was significantly more radioactivity in the uteri of the [3H]estradiol treated animals. At later times (8 h and onwards) the total radioactivity in the uterus did not differ appreciably between the two groups. However at these later times, the amount of [3H]estradiol was far greater in the uteri of animals receiving [3H]estradiol-17-stearate. Consequently, the prolonged estrogenic effects of the endogenous C-17 fatty acid esters of estradiol are caused by the increased duration of the estrogenic signal. It is hypothesized that one of the roles of the fatty acid is to protect the steroid nucleus from metabolism and thereby prolong the life of the parent C18 steroid. Thus, the results of these experiments are consistent with the family of endogenous alkyl esters of estradiol having a physiological role as long-acting estrogens.

The interaction of C-17 esters of estradiol with the estrogen receptor

Various C-17 alkyl esters of estradiol (E2) were tested as ligands for the estrogen receptor. The naturally occurring fatty acid esters, represented by E2-17-stearate, E2-17-palmitate, and E2-17-arachidonate, did not compete with [3H]E2 for receptor-binding sites. [3H]E2-17-stearate did not bind in a specific or saturable manner to uterine cytosol. On the other hand, the long-acting pharmacological esters of E2, E2-17-acetate, -propionate, -valerate, etc., were highly effective in competing for the binding of [3H]E2 to the uterine receptor. However, it was found that these short chain esters were hydrolyzed to E2 when incubated with uterine cytosol under the conditions used for the binding assay. Consequently, [3H]E2-17-acetate and [3H] E2-17-valerate were tested as ligands in an assay in which the hydrolytic activity was minimized by partially purifying the receptor with (NH4)2SO4 precipitation and by limiting the duration of the incubation. In this assay there was no specific binding of the C-17-valerate ester. There was a relatively small amount of specifically bound radioactivity in the incubation of the acetate ester, but upon high performance liquid chromatographic analysis, the specifically bound steroid was found to be E2 and not the ester. These results indicate that the C-17 esters of E2, from C2 to the long chain fatty acids, all of which are potent long-acting estrogens, exert their estrogenic effects only after hydrolysis to the free C18 steroid.

Microsomal 5-ane-3 beta-hydroxysteroid oxidoreductase from pubertal rat Leydig cells: partial purification and characterization

A 3 beta-hydroxysteroid oxidoreductase which acts on 5 alpha (beta)-reduced C19 and C21 steroids (5-ane-3 beta-hydroxysteroid oxidoreductase; 5-ane-3 beta-HSO) has been solubilized from pubertal rat Leydig cell microsomes and purified 300-fold by ion exchange and gel filtration chromatography. The partially purified enzyme is stable only in the presence of 0.4 M NaCl and appears to exist as a molecule having a molecular weight of 35,000 or as aggregates with a molecular weight in excess of 150,000. NAD+ and NADH+ are used exclusively as cofactors. The velocity of the steroid oxidation reaction was unaffected by either Ca2+ or Mg2+. The steroid oxidation reaction has a pH optimum between 8.0 and 8.5, a temperature optimum at 35 degrees C and an activation energy of 12,850 cal/mol. The pH optimum of the steroid reduction reaction is 6.6. A variety of 5 alpha-reduced C19 and C21 steroids can be utilized as substrates. Treatment of microsomes with phospholipase A2 resulted in a 26 to 90% loss of enzyme activity, paralleling decreased microsomal phospholipid content, and suggesting a role for phospholipids in 5-ane-3 beta-HSO activity. Assays with combined substrates indicate that one enzyme is responsible for activities observed with 5 alpha- and 5 beta-reduced C19- and 5 alpha-reduced C21-3 beta-hydroxysteroids. Purification data indicate that the 5-ane-3 beta-HSO and the 5-ene-3 beta-hydroxysteroid oxidoreductase:isomerase are distinct enzymes.