An improved synthetic procedure for the preparation of 195mPt labelled anti-tumour complexes

Ultrasound-Triggered Delivery of Iproplatin from Microbubble-Conjugated Liposomes

The PtIV prodrug iproplatin has been actively loaded into liposomes using a calcium acetate gradient, achieving a 3-fold enhancement in drug concentration compared to passive loading strategies. A strain-promoted cycloaddition reaction (azide- dibenzocyclooctyne) was used to attach iproplatin-loaded liposomes L(Pt) to gas-filled microbubbles (M), forming an ultrasound-responsive drug delivery vehicle [M-L(Pt)]. Ultrasound-triggered release of iproplatin from the microbubble-liposome construct was evaluated in cellulo. Breast cancer (MCF-7) cells treated with both free iproplatin and iproplatin-loaded liposome-microbubbles [M-L(Pt)] demonstrated an increase in platinum concentration when exposed to ultrasound. No appreciable platinum uptake was observed in MCF-7 cells following treatment with L(Pt) only or L(Pt)+ultrasound, suggesting that microbubble-mediated ultrasonic release of platinum-based drugs from liposomal carriers enables greater control over drug delivery.

Facile Synthesis of a Pt(IV) Prodrug of Cisplatin and Its Intrinsically 195mPt Labeled Analog: A Step Closer to Cancer Theranostic

Background, Aims and Objectives:

Cisplatin is extensively used in chemotherapy for treatment of a broad range of cancers. But its undesired side reactions with biomolecules that lead to severe side effects especially on kidney and nervous system, are limiting its clinical utility. To reduce its side effects, the kinetically inert Pt(IV) prodrug was recognized as an alternative approach from satisfactory results of preliminary experiments. But, its approval as anticancer drug for clinical use requires detailed investigations of its anticancer action and pharmacological pathways by employing its analogue which can be traced by a suitable technique. As a step closer towards translation of Pt(IV)-based prodrug from research to clinical level, a protocol for efficient synthesis of ^195mPt-radiolabeled Pt(IV) prodrug was devised.

Materials and Methods:

In order to achieve the aim, we started synthesis from elemental platinum avoiding lengthy steps. The synthesis protocol was standardized on its cold analogue, as [PtCl₂(NH₃)₂(OCOCH₂CH₂COOH)₂] which has been characterized with nuclear magnetic resonance (¹H, ¹³C{1H} and ¹⁹⁵Pt{1H}) spectroscopy, microanalyses and cyclic voltammetry. Also, cytotoxicity of [PtCl₂(OCOCH₂CH₂COOH)₂(NH₃)₂] was evaluated against MCF-7 human breast cancer cell lines using cisplatin as test control.

Results:

Intrinsically, ^195mPt-labeled analogue of prodrug was obtained with high radionuclidic and radiochemical purity. It was confirmed by chromatography and γ-ray spectrometry.

Conclusion:

The ^195mPt-radiolabeled prodrug was synthesized in a facile manner. It can be utilized in evaluating the mechanism of anticancer action and pharmacokinetics by enabling synergistic use of molecular imaging and targeted drug delivery.

Microwave-assisted synthesis of the anticancer drug cisplatin, cis-[Pt(NH3)2Cl2]

A rapid one-step microwave-assisted synthesis of cisplatin and two purification methods were developed. The process requires about 80 min and could be used to incorporate short-lived Pt radionuclides into cisplatin.

Noninvasive measurements for studying the tumoral pharmacokinetics of platinum anticancer drugs in solid tumors

An effective methodology to determine the amount of cisplatin or carboplatin at the solid tumor site in a noninvasive manner may enable clinicians to design drug regimens based on an individual's in situ pharmacokinetics. Such noninvasive methods may allow optimization of an individual's drug exposure at the target site, as well as provide a screening measure to determine individual efficacy based on exposure to these platinated drugs. 195mPt appears to be the radionuclide of platinum most suitable for radiolabeling cisplatin or carboplatin, and an analysis is presented of the methods available for preparing such radiolabeled drugs. The use of this methodology is illustrated in detail in studies in animals, as well as some preliminary studies in humans. The animals used were Sprague Dawley rats bearing the Walker 256 carcinoma, and drug biodistribution was studied following administration of cisplatin or carboplatin radiolabeled with 195mPt. This radionuclide permitted noninvasive imaging of the drug and its metabolites at the tumor site and at selected organs. The results obtained show an ability to estimate the amount of platinated drug species in the tumor environment using a noninvasive methodology. Various compartmental models were tested, some of which could be validated experimentally. This noninvasive method is able to provide individual estimates of the active component of the drug at the target site, and is therefore a method that can be implemented in human studies.

The synthesis of 191Pt labelled JM216, an orally active platinum anti-tumour agent

The orally active platinum anti-tumour complex JM216[bis-acetatoamminedichlorocyclohexylamineplatinum(IV)] is at present in stage II clinical trials. A procedure for synthesising the complex labelled with 191Pt or 188Pt at the platinum centre has been developed. The purity (shown by HPLC) is 98% and the specific activity (0.3-0.4 Ci/kg) is enough for in vivo and in vitro studies.

A comparative binding of platinum anti-tumour compounds to plasma proteins in the rat (in vivo) and mouse (in vitro)

Plasma protein binding of 195mPt-labelled cisplatin, carboplatin and iproplatin has been studied in vivo in rat and in vitro in mouse, using both electrophoresis and trichloroacetic acid precipitation. After intravenous injection plasma clearance rates were biphasic for all 3 compounds, (t1/2 alpha, 13-17 min) but cisplatin was retained thereafter longer than the others. By 5 min, gel electrophoresis showed protein labelling with all 3 drugs but none involved low mol.wt. proteins (< 16 kDa). At 2 h a notable proportion of the protein bound platinum was associated with the latter components. There was a general resemblance between the distribution patterns of cisplatin and carboplatin whereas iproplatin showed a persistent retention of the label with time to higher mol. wt. proteins. From in vitro incubation with mouse plasma, rates of interaction respectively were cisplatin t1/2 alpha, 35 min, beta 8 h, carboplatin t1/2, 44 h and iproplatin t1/2, 104 h. By electrophoresis the protein bound fraction pattern (1 h) was again similar for cisplatin and carboplatin with virtually no binding to low mol. wt. proteins. After 24 h these were now involved to a high degree (40%). Iproplatin showed relatively marked binding to proteins of higher mol. wt. but no transfer with time to the low mol. wt. protein zone. A possible explanation is the need for in vivo metabolism for this compound as manifest in the rat. It is suggested that the significance of interaction with low mol. wt. proteins merits further investigation in relation to the antitumour and toxicological actions of these drugs.