Microspheres with ultrahigh holmium content for radioablation of malignancies

PURPOSE

The aim of this study was to develop microspheres with an ultra high holmium content which can be neutron activated for radioablation of malignancies. These microspheres are proposed to be delivered selectively through either intratumoral injections into solid tumors or administered via an intravascularly placed catheter.

METHODS

Microspheres were prepared by solvent evaporation, using holmium acetylacetonate (HoAcAc) crystals as the sole ingredient. Microspheres were characterized using light and scanning electron microscopy, coulter counter, titrimetry, infrared and Raman spectroscopy, differential scanning calorimetry, X-ray powder diffraction, magnetic resonance imaging (MRI), and X-ray computed tomography (CT).

RESULTS

Microspheres, thus prepared displayed a smooth surface. The holmium content of the HoAcAc microspheres (44% (w/w)) was higher than the holmium content of the starting material, HoAcAc crystals (33% (w/w)). This was attributed to the loss of acetylacetonate from the HoAcAc complex, during rearrangement of acetylacetonate around the holmium ion. The increase of the holmium content allows for the detection of (sub)microgram amounts of microspheres using MRI and CT.

CONCLUSIONS

HoAcAc microspheres with an ultra-high holmium content were prepared. These microspheres are suitable for radioablation of tumors by intratumoral injections or treatment of liver tumors through transcatheter administration.

Characterization of holmium loaded alginate microspheres for multimodality imaging and therapeutic applications

In this paper the preparation and characterization of holmium-loaded alginate microspheres is described. The rapid development of medical imaging techniques offers new opportunities for the visualisation of (drug-loaded) microparticles. Therefore, suitable imaging agents have to be incorporated into these particles. For this reason, the element holmium was used in this study in order to utilize its unique imaging characteristics. The paramagnetic behaviour of this element allows visualisation with MRI and holmium can also be neutron-activated resulting in the emission of gamma-radiation, allowing visualisation with gamma cameras, and beta-radiation, suitable for therapeutic applications. Almost monodisperse alginate microspheres were obtained by JetCutter technology where alginate droplets of a uniform size were hardened in an aqueous holmium chloride solution. Ho(3+) binds via electrostatic interactions to the carboxylate groups of the alginate polymer and as a result alginate microspheres loaded with holmium were obtained. The microspheres had a mean size of 159 microm and a holmium loading of 1.3 +/- 0.1% (w/w) (corresponding with a holmium content based on dry alginate of 18.3 +/- 0.3% (w/w)). The binding capacity of the alginate polymer for Ho(3+) (expressed in molar amounts) is equal to that for Ca(2+), which is commonly used for the hardening of alginate. This indicates that Ho(3+) has the same binding affinity as Ca(2+). In line herewith, dynamic mechanical analyses demonstrated that alginate gels hardened with Ca(2+) or Ho(3+) had similar viscoelastic properties. The MRI relaxation properties of the microspheres were determined by a MRI phantom experiment, demonstrating a strong R(2)* effect of the particles. Alginate microspheres could also be labelled with radioactive holmium by adding holmium-166 to alginate microspheres, previously hardened with calcium (labelling efficiency 96%). The labelled microspheres had a high radiochemical stability (94% after 48 h incubation in human serum), allowing therapeutic applications for treatment of cancer. The potential in vivo application of the microspheres for a MR-guided renal embolization procedure was illustrated by selective administration of microspheres to the left kidney of a pig. Anatomic MR-imaging showed the presence of holmium-loaded microspheres in the kidney. In conclusion, this study demonstrates that the incorporation of holmium into alginate microspheres allows their visualisation with a gamma camera and MRI. Holmium-loaded alginate microspheres can be used therapeutically for embolization and, when radioactive, for local radiotherapy of tumours.

Production of GMP-grade radioactive holmium loaded poly(L-lactic acid) microspheres for clinical application

Radioactive holmium-166 loaded poly(L-lactic acid) microspheres are promising systems for the treatment of liver malignancies. The microspheres are loaded with holmium acetylacetonate (HoAcAc) and prepared by a solvent evaporation method. After preparation, the microspheres (Ho-PLLA-MS) are activated by neutron irradiation in a nuclear reactor. In this paper, the aspects of the production of a (relatively) large-scale GMP batch (4 g, suitable for treatment of 5-10 patients) of Ho-PLLA-MS are described. The critical steps of the Ho-PLLA-MS production process (sieving procedure, temperature control during evaporation and raw materials) were considered and the pharmaceutical quality of the microspheres was evaluated. The pharmaceutical characteristics (residual solvents, possible bacterial contaminations and endotoxins) of the produced Ho-PLLA-MS batches were in compliance with the requirements of the European Pharmacopoeia. Moreover, neutron irradiated Ho-PLLA-MS retained their morphological integrity and the holmium remained stably associated with the microspheres; it was observed that after 270h (10 times the half-life of Ho-166) only 0.3+/-0.1% of the loading was released from the microspheres in an aqueous solution. In conclusion, Ho-PLLA-MS which are produced as described in this paper, can be clinically applied, with respect to their pharmaceutical quality.

Lanthanide bearing microparticulate systems for multi-modality imaging and targeted therapy of cancer

The rapid developments of high-resolution imaging techniques are offering unique possibilities for the guidance and follow up of recently developed sophisticated anticancer therapies. Advanced biodegradable drug delivery systems, e.g. based on liposomes and polymeric nanoparticles or microparticles, are very effective tools to carry these anticancer agents to their site of action. Elements from the group of lanthanides have very interesting physical characteristics for imaging applications and are the ideal candidates to be co-loaded either in their non-radioactive or radioactive form into these advanced drug delivery systems because of the following reasons: Firstly, they can be used both as magnetic resonance imaging (MRI) and computed tomography (CT) contrast agents and for single photon emission computed tomography (SPECT). Secondly, they can be used for radionuclide therapies which, importantly, can be monitored with SPECT, CT, and MRI. Thirdly, they have a relatively low toxicity, especially when they are complexed to ligands. This review gives a survey of the currently developed lanthanide-loaded microparticulate systems that are under investigation for cancer imaging and/or cancer therapy.

Surface characteristics of holmium-loaded poly(L-lactic acid) microspheres

Radioactive holmium-166-loaded poly(L-lactic acid) microspheres (Ho-PLLA-MS) are promising systems for the treatment of liver malignancies. The surface characteristics of Ho-PLLA-MS before and after both neutron and gamma irradiation were investigated in order to get insight into their suspending behaviour and to identify suitable surfactants for clinical application of these systems. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used for surface characterization. The residual amounts of poly(vinyl alcohol) (PVA) of the microspheres, which was used as an emulsifier during the solvent evaporation process, were determined using a colorimetric iodine-borate method and the wettability of microspheres and PLLA films with and without holmium (Ho) loading was tested using suspending experiments and contact angle measurements. XPS showed that the surface of Ho-PLLA-MS mainly consisted of PLLA, less than 10% of the surface was covered with PVA after several washing and sieving steps. A colorimetric assay showed that the microspheres contained 0.2-0.3% (w/w) PVA. Combined with XPS data, this assay demonstrates that the PVA is likely dissolved in the core of the microspheres. XPS analysis also showed that after neutron irradiation, some holmium appeared on the surface. Moreover, Ho-loaded PLLA films had a much higher contact angle (85 degrees) than non-loaded films (70 degrees). Therefore, the Ho on the surface of neutron-irradiated Ho-PLLA-MS is probably the reason for their poor suspending behaviour in saline. No surface changes were seen with XPS after gamma irradiation. Based on their surface characteristics, a pharmaceutically acceptable solvent (1% Pluronic F68 or F127 in 10% ethanol) was formulated with which a homogeneous suspension of radioactive Ho-PLLA-MS could be easily obtained, making these systems feasible for further clinical evaluation.

Advances in nuclear oncology: microspheres for internal radionuclide therapy of liver tumours

Liver metastases cause the majority of deaths from colorectal cancer, and response to chemotherapy and external radiotherapy is poor. An alternative is internal radionuclide therapy using (90)Y labeled microspheres. These microspheres are very stable and have a proven efficacy in the field of treatment of primary or metastatic hepatic cancer. Whilst these glass spheres showed encouraging results in patients, their high density is a serious drawback. Currently, other materials with lower densities and other radioisotopes are being investigated in order to optimize this promising new therapy. Three major radiolabeled microsphere materials, viz. glass, resin-based and polymer-based, are now available for therapy or are being tested in animals. In this review the preparation, stability and degradation of these spheres are discussed.

Intra-arterial embolization of head-and-neck cancer with radioactive holmium-166 poly(L-lactic acid) microspheres: an experimental study in rabbits

A total of 22 NZW rabbits with VX2 squamous cell carcinomas transplanted into the auricles were intra-arterially (i.a.) embolized with radioactive or inactive holmium-labelled poly(L-lactic acid) (HoPLA) microspheres with a mean diameter of 38-80 microm. The effects on tumour growth, the efficiency of i.a. infusion, the efficacy of retention of microspheres in the primary tumour and the excretion of free holmium-166 were analyzed. Complete tumour remissions were obtained in 79% and 86% following embolization with radioactive and inactive microspheres, respectively. Over 95% of the microspheres were retained in the tumour and the leaching of holmium-166 in urine and faeces was less than 0.1% in 2 days. The injection efficiency was not optimal, as 40% of the microspheres were retained in the cannulation system. Arterio-arteriolar connections should be detected and closed prior to embolization to prevent stray emboli from entering the brain. It is concluded that 166HoPLA microspheres are promising candidates for further studies on radio-embolization of unresectable head-and-neck cancer.

Holmium-166 poly lactic acid microspheres applicable for intra-arterial radionuclide therapy of hepatic malignancies: effects of preparation and neutron activation techniques

Since one of the most frequent sites of human metastatic cancer is the liver, particularly in colon and rectum carcinoma, there is a special need for the development of an effective therapy. This study describes the parameters for reproducible production of poly lactic acid (PLA) microspheres with an average diameter of 37 microm and labelled with neutron-activated holmium-166 (Emax=1.84 MeV, t1/2=26. 8 h), suitable for use in internal radionuclide therapy of liver metastases. It is demonstrated that holmium-loaded PLA microspheres can be prepared by a relatively simple method, with incorporation of 17.0%+/-0.6% holmium (n=5), and that 20 GBq can be obtained from 400 mg neutron activatable microspheres. In order to produce this high amount of activity, the microspheres must be free of water and irradiation must be performed in a polyethylene vial, with a relatively low neutron flux (5x10(13) cm-2 s-1) within 1 h. Under these well-defined conditions minor surface changes were seen which barely affected total volume and consequently total radioactivity of the microspheres with a diameter of 20-50 microm. Overall structural integrity was maintained in terms of form and size. In vitro analyses showed that >99.3% of 166Ho activity was retained in the microspheres after 192 h incubation in PBS, plasma and leucocytes, while in liver homogenate retention was still 98.4%.

186Re-etidronate in breast cancer patients with metastatic bone pain

The aim of this study was to evaluate the efficacy of 186Re-1,1-hydroxyethylidene diphosphonate (etidronate) in breast cancer patients with painful bone metastases.

METHODS

Thirty patients with advanced breast cancer who had metastatic bone pain were treated with 186Re-etidronate using different dosages in a noncomparative, open-label study. Twenty-four patients were evaluated for efficacy (6 patients had incomplete datasets). Dosages varied from 1295 to 2960 MBq (35 to 80 mCi). Efficacy was evaluated according to the multidimensional pain model using a paper-and-pencil diary. The diary was kept twice daily for 8-10 wk (2 wk before through 6-8 wk after 186Re-etidronate treatment). Response was determined with a strict criteria, in which pain intensity (PI), medication index (MI) and daily activities (DA) were core determinants. Response was defined as: (a) Reduced PI > or = 5% while MI and DA were at least constant; or (b) Reduced PI <25% in combination with improvement of MI or DA > or = 25%, without worsening of either factor. Duration of response should always exceed a minimum of 2 wk.

RESULTS

Fifty-eight percent (n = 14) of all patients reported a response. The maximum follow-up period was 8 wk. Duration of response ranged from 2 to 8 wk (mean 4 wk). Patients (14/24) not only experienced considerable pain reduction, but in 12 patients this was also accompanied by noteworthy reduction in MI (> or = 25%). No clear dose-response relationship was found.

CONCLUSION

With strict pain assessment criteria, 186Re-etidronate showed a response of 58% in the palliative treatment of metastatic bone pain originating from breast cancer.

Efficacy of rhenium-186-etidronate in prostate cancer patients with metastatic bone pain

Rhenium-186-etidronate has been developed for pain relief of bone metastases and has previously been studied with regard to toxicity, pharmacokinetics and dosimetry. Its palliating effect on bone pain has not been studied extensively. To justify further efficacy investigations, patients participating in two toxicity studies were studied using a strict pain assessment methodology.

METHODS

Forty-three patients entered the study, 37 of whom were evaluable for pain assessment. Administered dosages ranged from 1295 MBq (35 mCi) to 3515 MBq (95 mCi) 186Re-etidronate. Pain relief was assessed using a handwritten diary containing questions reflecting the multidimensional character of chronic pain. The diary was marked twice daily for a maximum of 10 wk (2 wk prior to and 6/8 wk after the injection). A response was determined using a specific decision rule, in which pain intensity, medication index and daily activities were core determinants.

RESULTS

A response was reached in 54% (20 of 37) of the patients and varied from 33% (n = 6) in the "35-mCi" group to 78% (n = 7) in the "50/65-mCi" group to 70% (n = 7) in the "80/95-mCi" group.

CONCLUSION

Pain assessment using the multidimensional pain model showed that 186Re-etidronate is an effective agent in the treatment of metastatic bone pain in prostate cancer and warrants further placebo-controlled studies.

Transient cranial neuropathy in prostatic cancer with bone metastases after rhenium-186-HEDP treatment

Rhenium-186 (tin) hydroxyethylidene diphosphonate (186Re-HEDP), a bone-seeking radiopharmaceutical, has been successfully used in the treatment of patients with painful bone metastases. Toxicity is usually limited to reversible thrombocytopenia. An infrequent but clinically significant side effect is the occurrence of transient cranial neuropathy. We report on two prostatic cancer patients with metastatic bone cancer. Both patients developed transient cranial neuropathy shortly after treatment with 186Re-HEDP. Transient neuropathy of cranial nerves needs to be distinguished from neurological abnormalities caused by disease progression.

Phase 1 study of rhenium-186-HEDP in patients with bone metastases originating from breast cancer

Rhenium-186-1,1-hydroxyethylidene diphosphonate (186Re-HEDP) has been used for the palliative treatment of metastatic bone pain. A Phase 1 dosage escalation study was performed using 186Re-HEDP in patients with metastatic breast cancer.

METHODS

Twelve patients with metastatic breast cancer were studied. Each patient had at least four bone metastases and adequate hematological function. Groups of three consecutive patients were treated with dosages starting at 1295 MBq (35 mCi) and increasing to 2960 MBq (80 mCi) (escalated in increments of 555 MBq).

RESULTS

A transient increase in pain ("flare" reaction) was observed in six patients. Two patients who received 2960 MBq 186Re-HEDP showed Grades 3 (platelets 25-50 x 10(9)/l) and 4 (platelets < 25 x 10(9)/l) platelet toxicity, which was defined as unacceptable. Prior to treatment, alkaline phosphatase levels were elevated in seven cases. These patients showed a transient decline in alkaline phosphatase levels during the first 4 wk.

CONCLUSION

The maximum tolerated administered activity of 186Re-HEDP in patients with metastatic breast cancer is 2405 MBq (65 mCi). Thrombocytopenia proved to be the dose-limiting toxicity, which could not be predicted adequately by the administered activity. Changes of alkaline phosphatase levels suggest anti-tumor effects of 186Re-HEDP.

Bone marrow absorbed dose of rhenium-186-HEDP and the relationship with decreased platelet counts

Rhenium-186(Sn)-1,1-hydroxyethylidene diphosphonate (186Re-HEDP) has been used for palliation of metastatic bone pain. The purpose of this study was to find a relationship between the bone marrow absorbed dose and the toxicity, expressed as the percentage decrease in the peripheral blood platelet count.

METHODS

The bone marrow absorbed dose was calculated according to the MIRD model using data obtained from ten treatments of patients suffering from metastatic prostate cancer; noninvasive and pharmacokinetic methods were used. The bone marrow doses were related to toxicity using the pharmacodynamic sigmoid Emax model.

RESULTS

The mean bone marrow absorbed doses using the noninvasive and pharmacokinetic methods were in a close range to each other (1.07 mGy/MBq and 1.02 mGy/MBq, respectively). There was a good relationship between the toxicity and the bone marrow absorbed dose (r = 0.80). Furthermore, the EDrm50 (i.e., the bone marrow absorbed dose producing a 50% platelet decrease) to bone marrow for 186Re-HEDP was on the order of 2 Gy.

CONCLUSION

Although the function of normal bone marrow is affected by metastases in patients with metastatic bone disease, the MIRD model can be used to relate toxicity to the bone marrow absorbed dose after a therapeutic dosage of 186Re-HEDP.

Dose escalation study of rhenium-186 hydroxyethylidene diphosphonate in patients with metastatic prostate cancer

Rhenium-186 hydroxyethylidene diphosphonate (186Re-HEDP) has been used for the palliative treatment of metastatic bone pain. A phase 1 dose escalation study was performed using 186Re-HEDP. Twenty-four patients with hormone-resistant prostate cancer entered the study. Each patient had at least four bone metastases and adequate haematological function. Groups of at least three consecutive patients were treated with doses starting at 1295 MBq and increasing to 3515 MBq (escalated in increments of 555 MBq). Thrombocytopenia proved to be the dose-limiting toxicity, while leucopenia played a minor role. Early death occurred in one patient (10 days after administration) without clear relationship to the 186Re-HEDP therapy. Transient neurological dysfunction was seen in two cases. Two patients who received 3515 MBq 186Re-HEDP showed grade 3 toxicity (thrombocytes 25-50 x 10(9)/l), defined as unacceptable toxicity. After treatment alkaline phosphatase levels showed a transient decrease in all patients (mean: 26% +/- 10% IU/l; range: 11%-44%). Prostate-specific antigen values showed a decline in eight patients, preceded by a temporary increase in three patients. From this study we conclude that the maximally tolerated dose of 186Re-HEDP is 2960 MBq. A placebo-controlled comparative study on the efficacy of 186Re-HEDP has been initiated.

Evaluation of thrombocytopenia in patients treated with rhenium-186-HEDP: guidelines for individual dosage recommendations

A potential limitation of rhenium-186-1,1-hydroxyethylidene diphosphonate (186Re-HEDP) therapy in patients with painful bone metastases is thrombocytopenia. Given the palliative character of this therapy, it is essential to be able to predict the degree of thrombocytopenia before therapy.

METHODS

Thus far, 39 prostatic cancer patients with multiple painful bone metastases were treated. Twenty-one patients underwent the therapy twice, resulting in 60 therapies. From the pre-therapy 99mTc-HDP scintigram, the bone scan index (BSI) was determined as an index of the extent of bone involvement.

RESULTS

The administered activity ranged from 1104 to 3479 MBq 186Re-HEDP. The platelet count was lowest 4 wk following therapy. From this value and the pretreatment level, the percentage decrease in the platelet count was determined (47% +/- 19%, range 14%-89%). The BSI ranged from 8 to 93. Regression analysis showed a functional relation (R = 0.78; p < 0.001) of the percentage of platelet decrease with BSI and administered activity normalized to standard body surface area.

CONCLUSION

Using this relation, it is possible to predict thrombocytopenia by pretreatment bone scintigraphy and to adjust the dosage to each patient to avoid unacceptable toxicity.

Pharmacokinetics of rhenium-186 after administration of rhenium-186-HEDP to patients with bone metastases

The pharmacokinetics of 186Re-HEDP, a radiopharmaceutical for palliative treatment of metastatic bone pain, was investigated in 11 patients (17 studies) who suffered from metastatic breast or prostate cancer. Half-life times of 186Re in three blood fractions (whole blood, plasma and plasma water) were 40.1 +/- 5.0, 41.0 +/- 6.0 and 29.5 +/- 6.4 hr, respectively. Time-dependent increase in plasma-protein binding was observed, probably caused by in vivo decomposition of 186Re-HEDP. Total urinary 186Re excretion was 69% +/- 15%, of which 71% +/- 6% was excreted in the first 24 hr after injection. The BSI (i.e., fraction of the skeleton showing scintigraphic evidence of metastatic disease) closely correlated with the fraction of dose non-renally cleared (r = 0.98). This implies that the amount of radioactivity taken up by the skeleton and hence the bone marrow absorbed dose can be predicted from a diagnostic pre-therapy 99mTc-HDP scintigram. The pharmacokinetic behavior indicates that 186Re-HEDP has suitable properties to justify its application.

In vitro binding characteristics for cesium of two qualities of prussian blue, activated charcoal and Resonium-A

The in vitro binding characteristics of radioactive 137Cs to two forms of Prussian blue [colloidally (soluble) K3Fe[Fe(CN)6] and insoluble Fe4[Fe(CN)6]3] and to activated charcoal and sodium polystyrene sulfonate (Resonium-A) were investigated by constructing Langmuir isotherms at pH = 1.0, 6.5 and 7.5 at 37 degrees C. At the three pHs investigated, 137Cs binding to activated charcoal and sodium polystyrene sulfonate was negligible. Binding of 137Cs to insoluble Prussian blue exceeded that for the soluble form and was pH dependent for both formulations. Maximum binding capacities were 87 mg/g (pH = 1.0), 194 mg/g (pH = 6.5) and 238 mg/g (pH = 7.5) for the insoluble form and 48 (pH = 1.0), 73 (pH = 6.5) and 78 (pH = 7.5) for the soluble form. As activated charcoal did not bind 137Cs, charcoal hemoperfusion is of no value. This has been confirmed by an in vitro experiment, using a Gambro Adsorbs 300 C cartridge.

Technetium-99m-MAG3 versus iodine-123-OIH: renal clearance and distribution volume as measured by a constant infusion technique

The renal clearance and distribution volume of 99Tc-mercaptoacetyltriglycine (MAG3) and 123I-o-iodohippurate (OIH) were determined separately in six normal male volunteers using the constant infusion clearance technique in order to validate single injection clearance techniques and subsequently the normal values for these parameters. MAG3 renal clearance was 257 +/- 24 ml/min/1.73 m2, compared to the OIH clearance of 556 +/- 46 ml/min/1.73 m2 resulting in a MAG3/OIH clearance ratio of 0.47 +/- 0.06. The MAG3 and OIH apparent distribution volumes at steady-state were 14.8 +/- 3.7 and 19.4 +/- 5.3 liters, respectively, the latter value approximating the extra cellular fluid volume. Urinary excretion in the 0-30-min period after intravenous administration was 64.4 and 70.2% for MAG3 and OIH, respectively. This investigation revealed some significant differences in the normal values of the renal clearance and distribution volume of MAG3 compared with other studies.

Can technetium 99m bisdiethylphosphinoethanebis-t butylisocyanide (99mTc-DEPIC) be used for routine radionuclide ventriculography?

Radionuclide ventriculography is a useful investigation in the evaluation of cardiac function. Generally, in vivo technetium 99m-labelled red blood cells (RBC) yield good quality images in ventriculography. However, it is widely believed that some drugs have an adverse effect on RBC labelling. Zanelli et al. (1987) developed a radiopharmaceutical (technetium 99m bis-diethylphosphinoethanebis-t-butylisocyanide, 99mTc-DEPIC) to obtain better results in patients using such drugs. We undertook a prospective study of 6 patients with cardiovascular and/or pulmonary disease using several kinds of drugs to evaluate imaging of the cardiac blood pool with 99mTc-DEPIC and in vivo labelled 99mTc-RBC. After injection, blood samples were taken, and gated equilibrium blood pool studies were performed. The radiochemical purity of the injected 99mTc-DEPIC varied from 76.4 to 93.6% (mean 86.4%, SD 5.7%). The protein (pre-albumin) binding was 100%. Biological half-life in blood varied from 3.3 to 4.7 h (mean 4.1 h, SD 0.5 h). For 99mTc-RBC no significant blood disappearance was seen for 8 h. The percentage of RBC-bound 99mTc varied from 96.9% to 98.3% (mean 97.0%, SD 0.5%) and was stable for at least 8 h. The heart-to-lung, heart-to-spleen, and heart-to-liver ratios were higher for 99mTc-RBC than for 99mTc-DEPIC. Furthermore, 99mTc-DEPIC showed a significant decline of the ejection fraction with time. Visually, the images with 99mTc-RBC were superior to those with 99mTc-DEPIC, especially a few hours after injection. According to our findings, in vivo labelling of 99mTc-RBC is still the method of choice for routine radionuclide ventriculography.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acid sequence of phosvitin derived from the nucleotide sequence of part of the chicken vitellogenin gene

The amino acid sequence of the egg yolk storage protein phosvitin has been deduced from the nucleotide sequence of part of the chicken vitellogenin gene. Of the phosvitin sequence, 210 amino acids including the N-terminal residue are contained on one large exon, whereas the remaining six amino acids are encoded on the next exon. Phosvitin contains a core region of 99 amino acids, consisting of 80 serines, grouped in runs of maximally 14 residues interspersed by arginines, lysines, and asparagines. The serines of the core region are encoded by AGC and AGT codons exclusively and the arginines by AGA and AGG, which results in a continuous stretch of 99 codons with adenine in the first position. The N-terminal quarter of the phosvitin sequence contains 16 serines grouped in a cluster with alanines and threonines and coded mainly by TCX triplets. The C-terminal part includes 27 serines, preferentially coded by AGC and AGT, 13 histidine residues, and the sequence ...Asn-Gly-Ser... at which the carbohydrate moiety of phosvitin is attached. Heteroduplex formation between cloned DNAs from chicken and Xenopus vitellogenin genes shows that the phosvitin sequence contains a stretch of highly conserved sequence.

Sequence homologies within the 5′ end region of the estrogen-controlled vitellogenin gene in Xenopus and chicken

In oviparous vertebrates vitellogenin, the precursor of the major yolk proteins, is synthesized in the liver of mature females under the control of estrogen. We have established the organization and primary structure of the 5' end region of the Xenopus laevis vitellogenin A2 gene and of the major chicken vitellogenin gene. The first three homologous exons have exactly the same length in both species, namely 53, 21 and 152 nucleotides, and present an overall sequence homology of 60%. In both species, the 5'-non-coding region of the vitellogenin mRNA measures only 13 nucleotides, nine of which are conserved. In contrast, the corresponding introns of the Xenopus and the chicken vitellogenin gene show no significant sequence homology. Within the 500 nucleotides preceding the 5' end of the genes, at least six blocks with sequence homologies of greater than 70% were detected. It remains to be demonstrated which of these conserved sequences, if any, are involved in the hormone-regulated expression of the vitellogenin genes.

The nucleotide sequence of the chicken apo very low density lipoprotein II gene

The nucleotide sequence of the chicken apo Very Low Density Lipoprotein II (apoVLDL II) gene and the regions immediately flanking the gene was determined. Nuclease S1 mapping showed that transcription is initiated at two sites, about 11 bp apart, of which the one lying downstream is used preferentially. Comparison of the 2918-base pair gene sequence with the earlier determined cDNA sequence [Wieringa et al. (1981) Nucleic Acids Research 9, 489-501] enabled us to identify the four exons which are 38 (or 49), 100, 160 and 358 bp long. One of the intron-exon junctions has an unusual sequence. In the 5' flanking region several palindromic sequences are observed. Sequences near the 5' and 3' ends show homologies with the ovalbumin gene.

Structure of the chicken apo very low density lipoprotein II gene

We describe two cloned genomic DNA fragments, both bearing the entire apo very low density lipoprotein II gene. Electron microscopy and restriction enzyme mapping showed that this gene is split into at least four coding sequences by three or more intervening sequences. A very short exon at the 5'-end of the gene is separated by a 1.5-kilobase intron from the second exon, which codes for the AUG initiation codon of the mRNA.