Phase I study of bortezomib and 153Sm-lexidronam combination for refractory and relapsed multiple myeloma

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Background: Multiple myeloma (MM) is a highly radiosensitive B-cell malignancy and radiation therapy has been an effective treatment for these patients. Recent preclinical studies have demonstrated that the bone-seeking radionuclide, Samarium Sm153 lexidronam (Sam) in combination with the proteasome inhibitor, bortezomib (Vel), can synergistically inhibit proliferation of myeloma cell lines in vitro and reduce MM growth in mice bearing human MM without significant myelotoxicity. These results provide the basis for a new therapeutic approach of combining Vel and Sam to overcome resistance and to minimize nontumor tissue toxicity among refractory and relapsed MM patients. Methods: The primary objective of this Phase I study is to determine the response rate and tolerability of Vel + Sam combination in patients with relapsed or refractory MM. Patients will be enrolled on this Phase I dose-escalation trial which involves six cohorts. Previous treatment with Vel is permissible. Dose escalation in parallel arms is as follows: A complete treatment cycle is 8 weeks. Vel is given on days 1, 4, 8 and 11 followed by a 45-day rest period. Sam is administered on day 4. The cycle is repeated on Day 57 if disease is stable or improved and platelets and neutrophils recover to at least grade 1 toxicity. DLT is defined as cycle 1 grade 4 hematologic or grade ≥3 non-hematologic toxicity. Results: Cohorts 1 and 4 have been enrolled (3 patients per cohort). One cycle of treatment has been completed thus far. No significant toxicity has been observed except a transient fever in one patient. There have been no dose limiting toxicities to date. The first six patients will be evaluated for response within the next two weeks. Conclusions: The trial will continue to enroll patients in cohorts 2 and 5. Updated results from the trial will be presented at the meeting.

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Analysis of urine samples from metastatic bone cancer patients administered 153Sm-EDTMP

153Sm-EDTMP is currently undergoing clinical evaluation as a radiotherapeutic agent for the relief of pain associated with cancer metastatic to bone. These clinical studies have demonstrated biodistributions similar to those seen earlier in animals, namely, rapid clearance from blood, selective uptake in bone and in particular metastatic bone lesions. The radioactivity not deposited in bone is cleared through the kidneys into the urine. In this study, urine samples collected from 9 patients injected with 153Sm-EDTMP underwent complexation analysis via Pharmacia SP-Sephadex C25 cation exchange chromatography. The results showed 96.9 +/- 1.7% of the radioactivity in the urine to be present as a complex of 153Sm. An HPLC method was developed and it was demonstrated that different complexes of 153Sm could be separated. A non-radioactive analytical standard of the Sm-EDTMP chelate was synthesized, characterized and shown to have the same HPLC retention profile as the 153Sm-EDTMP drug product. HPLC analysis was performed on six urine samples and in each case a single radioactivity peak with an elution profile the same as that of a 153Sm-EDTMP standard was observed. These results indicate that the 153Sm-EDTMP chelate is excreted intact in the urine of patients.

Therapeutic radionuclides: production and decay property considerations

The development of effective therapeutic radiopharmaceuticals requires careful consideration in the selection of the radionuclide. The in vivo targeting and clearance properties of the carrier molecule must be balanced with the decay properties of the attached radionuclide. Radionuclides for therapeutic applications fall into three general categories: beta-particle emitters, alpha-particle emitters, and Auger and Coster-Kronig-electron emitters following electron capture. Alpha particles and Auger electrons deposit their energy over short distances with a high LET that limits the ability of cells to repair damage to DNA. Despite their high levels of cytotoxicity, the relatively short range of alpha particles requires binding of the carrier molecule to most cancer cells within a tumor in order to be effective. Because of the extremely short range of Auger electrons, the radionuclide must be carried directly into the nucleus to elicit high radiotoxicity, making it necessary to deliver the radionuclide to every cell within a tumor cell population. These characteristics impose rigid restrictions on the nature of the carrier molecules for these types of particle emitters but successful targeting of these types of radionuclides could result in high therapeutic ratios. Most beta-emitting radionuclides are produced in nuclear rectors via neutron capture reactions; however, a few are produced in charged-particle accelerators. For radionuclides produced by direct neutron activation, the quantities and specific activities that can be produced are determined in large part by the cross-section of the target isotope and the flux of the reactor. Many applications (e.g., therapeutic bone agents, radiolabeled microspheres, radiocolloids) do not require high-specific activities and can therefore utilize the wide range of radionuclides that can be produced in sufficient quantity by direct neutron activation. Other applications (e.g., MAb labeling) require high-specific activity radionuclides in order to deliver a sufficient number of radionuclide atoms to the target site without saturating the target or compromising the integrity of the carrier molecule. Most radionuclides, produced at NCA levels in reactors, are produced via indirect reactions. High-specific activity beta emitters can also be obtained from radionuclide generator systems where the longer-lived parent radionuclide may be obtained from direct neutron activation, as a fission product, or from charged-particle accelerators. It is essential that the half-life of a radionuclide used in RNT be compatible with the rates of localization in target tissues and clearance of the carrier molecule from normal tissues. This consideration is especially important for the various MAbs and their fragments that are currently under investigation as carrier molecules to RIT.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical and clinicopathologic response of canine bone tumor patients to treatment with samarium-153-EDTMP

Forty dogs with spontaneous skeletal neoplasia were treated with 153Sm-EDTMP (ethylenediaminetetramethylene phosphonic acid). Both primary and metastatic lesions were treated. Two treatment regimes, a single (37 MBq (1.0 mCi)/kg dose or two 37 MBq (1.0 mCi)/kg doses separated by 1 wk) were tested. Response to treatment was varied. Large lesions with minimal tumor bone formation responded poorly, while primary lesions with substantial ossification usually exhibited a transient response. Small lesions with minimal lysis, metastatic lesions, and axial skeleton lesions generally responded well. The major adverse side effects of treatment were platelet and white blood cell count depression below baseline values for up to 4 wk (p less than 0.05). Minor depression of packed cell volume and transient elevation of serum alkaline phosphatase were also noted (p less than 0.05). No significant differences (p greater than 0.05) between the two treatment groups, either in treatment effect or undesirable side effects, were detected.

Clinical and clinicopathologic effects of samarium-153-EDTMP administered intravenously to normal beagle dogs

A study was undertaken to determine the degree of acute bone marrow and vital organs injury sustained when dogs were administered doses of 153Sm-EDTMP calculated to irradiate an acute bone lesion arising from cancer metastasis to a dose considered palliative or even therapeutic (20-160 Gy). The study revealed significant (p less than 0.05) temporary depression of the bone marrow in all doses in the therapeutic (greater than 40 Gy) range. Palliative (20 Gy) doses caused significant leukocyte depression but insignificant (p greater than 0.05) depression of platelet and packed cell volumes when compared to control animals. A mild transient rise in the levels of serum alkaline phosphatase occurred immediately following radioisotope administration. All hematologic parameters had returned to normal by six weeks after the last injection of radioisotope. The study indicates potential for this compound as a safe, therapeutic radiopharmaceutical for treatment of cancer bone metastasis.

Skeletal localization of samarium-153 chelates: potential therapeutic bone agents

A series of stable complexes of 153Sm has been produced using multidentate acetate and phosphonate ligands. Biodistribution studies in unanesthetized rats showed varying degrees of bone and soft-tissue uptake for these complexes. Of the complexes studied, [153Sm] ethylenediaminetetramethylenephosphonate (EDTMP) showed the best combination of high bone uptake, low nonosseous uptake, and rapid blood clearance which warranted its further investigation in rabbits. Rabbit studies confirmed the [153Sm]EDTMP results obtained in rats. Blood clearance in rabbits was found to be more rapid than [99mTc] methylene diphosphonate (MDP). Scintigraphic images were virtually indistinguishable from [99mTc]MDP images. Lesion/normal bone ratios were determined from digitized images obtained using a drill hole model and found to be approximately 17:1. Based on these excellent biodistribution characteristics, [153Sm] EDTMP could be therapeutically useful in treating metastatic bone cancer.

153Sm radiotherapeutic bone agents

Samarium-153 is a radionuclide which can be produced in high yield by neutron irradiation and which has nuclear properties that make it attractive for use as a radiotherapeutic agent. Several phosphonate complexes of 153Sm were synthesized and characterized by electrophoresis and HPLC. A procedure based on cation exchange chromatography was developed for measuring complex yields. The complexes could be produced in yields greater than 99%, were anionic, and most exhibited a single HPLC peak.

A new Cd-115 leads to In-115m radionuclide generator

A new column-type Cd-115 leads to In- 115m generator has been developed by adsorbing CdI4(-2) on an anion-exchange resin and eluting the In-115m with 0.05 M HCl. The In-115m yield of the prototype column is 90% in a volume of 3 ml, with Cd-115 breakthrough of less than 3 X 10(-4)%. Over thirty generators with up to 40 mCi of activity have been produced using components of a commercial Mo-99 leads to Tc-99m generator system; they behaved like the prototype. In-115m oxine prepared from these generators has been used to label canine platelets and to image an induced canine thrombus in vivo.