Sensitization to Radiation from an Implanted125I Source by Sustained Intratumoral Release of Chemotherapeutic Drugs

Targeting of radio-enhancing drugs

OBJECTIVE

Toxicity to normal tissue is frequently the dose-limiting factor in the chemotherapy and mixed modality treatments of cancer. If the radio-enhancing drug could be localized at the disease site and released slowly over time, then systemic drug toxicities could be decreased while simultaneously maintaining high drug concentrations in the tumor. These considerations support a role for a sustained release intra-tumoral delivery systems for the delivery of radio-enhancing drugs.

METHODS

Two approaches aimed at achieving the end of localizing the radio-enhancing drug to the tumor are described. First, nanoparticles, which have a prolonged circulation time and facility for enhanced tumor targeting. Structural defects in the walls of the tumor vasculature allow the passage of particles too large to pass through the walls of normal blood vessels. This characteristic of tumor blood vessels, referred to as the enhanced permeability and retention (EPR) effect, allows relatively large entities (typically liposomes, nanoparticles, and macromolecular drugs) to pass from the blood vessels to tumor tissue and as a result nanoparticles accumulate in the tumor while being excluded from normal tissue. Second, biodegradable implanted polymers. In these devices, the radio-enhancing drug is physically trapped within the polymer matrix which is implanted in the tumor. The drug is released as the polymer degrades in response to its local environment. The degradation rate of the polymer device can be adjusted to control the rate of drug release. By this means, the level of radio-enhancing drug can be maintained at the tumor site for the duration of radiation treatment.

RESULTS AND CONCLUSIONS

Results of experiments indicate that for both methods tumor control could be optimized by maintaining the radio-enhancing drug at a useful concentration in the tumor over a period of time compatible with the duration of fractionated radiation treatment. These studies have provided proof of principle support for the further development of this approach. To date, while some of the methods and devices for drug delivery described in this paper have been involved in clinical trials, none have so far been developed for routine clinical application.

New combination chemotherapy of cisplatin with an electron-donating compound for treatment of multiple cancers

Cisplatin is the first and most widely used platinum-based chemotherapy drug and is the cornerstone agent in treating a broad spectrum of cancers. However, its clinical application is often limited by severe toxic side effects and drug resistance. Based on the discovered dissociative electron transfer mechanism of cisplatin, a novel combination of cisplatin with [9-(2-carboxyphenyl)-6-diethylamino-3-xanthenylidene]-diethylammonium chloride (basic violet 10, BV10) is proposed to potentiate the chemotherapeutic effect of cisplatin. Here, we show that this combination enhances the anti-cancer effect of cisplatin in both in vitro cell lines and in vivo xenograft mouse models of cisplatin-sensitive and -resistant lung, ovarian and cervical cancers while introducing minimal additional toxic side effects. Furthermore, femtosecond time-resolved laser spectroscopic measurements demonstrate that cisplatin reacts with BV10 via an electron transfer mechanism. These results indicate that the combination of cisplatin with BV10 is promising for improving the chemotherapy of cancers with various extents of cisplatin resistance.

Synthesis and Characterization of Lyophilized Chitosan-Based Hydrogels Cross-Linked with Benzaldehyde for Controlled Drug Release

In this study, chitosan-based hydrogels were produced by incorporating three drugs with a different solubility into a polymer matrix. The lyophilized chitosan salt was prepared using an innovative and less-expensive synthetic process by the freeze-drying technique. Firstly, the three drugs (caffeine, ascorbic acid, and 5-fluorouracil (5-FU)) were selected as model drugs to test the in vitro release behavior of the hydrogel. The drugs were solubilized in chitosan salt, lyophilized, and cross-linked with benzaldehyde involving the formation of a Schiff base with (–C=N-) linkage to produce a physical hydrogel. Subsequently, the physicochemical properties of N-benzyl chitosan and lyophilized chitosan salt were evaluated by Fourier-transform infrared (FTIR) spectra, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The intrinsic viscosity of the conventional chitosan was determined by the Mark–Houwink–Sakurada equation. Moreover, the kinetics of hydrogel swelling and drug release were studied by the UV-visible method at physiological conditions (pH = 7.4 at 37°C). The results show that lyophilized N-benzyl chitosan had a maximum swelling ratio of 720 ± 2% by immersion in phosphate-buffered saline solutions (PBS) (pH = 7.4 at 37°C). In vitro drug releases were evaluated in PBS, and the obtained results show that the maximum drug release after 24 h was 42% for caffeine, 99% for 5-FU, and 94% for ascorbic acid. Then, to optimize the cumulative release of caffeine, Tween 20 was added and 98% as a release percentage was obtained. The drug-loading results were investigated with the Korsmeyer–Peppas kinetic model and applied to determine the drug release mechanism.

Controlling injectability and in vivo stability of thermogelling copolymers for delivery of yttrium-90 through intra-tumoral injection for potential brachytherapy

Intra-tumoral injection of radiopharmaceuticals such as yttrium-90 (⁹⁰Y) or phosphorus-32 (³²P) is an important route for brachytherapy in unresectable solid tumors such as locally advanced hepatocellular carcinoma. However, the injected radiopharmaceuticals can potentially leak out from the tumor site due to high intra-tumoral pressure. In this study, we demonstrated the use of thermogelling copolymers that can be injected into tumor and subsequently solidify as hydrogels within the tumor that can potentially overcome the above problem. To this end, a series of thermogelling polyurethane copolymers with varying compositions were designed and synthesized from Pluronic F127, poly(3-hydroxylbutyrate), and poly(propylene glycol), which were characterized in terms of their molecular structures, compositions, phase diagrams, rheological properties, and injectability and body temperature stability in vitro and in vivo. The analyses of our data elucidated the injectability of the copolymer solutions at low temperatures, and the stability of the hydrogels at the body temperature. This provided the basis on which we could identify one copolymer with balanced composition as the most suitable candidate for intra-tumoral injection and for prevention of the leakage. Finally, the injectability and in vivo stability of the copolymer solution and hydrogel loaded with ⁹⁰Y were further demonstrated in a mouse tumor model, and the in vivo biodistribution of ⁹⁰Y showed that the radionuclide could be retained at the tumor site, indicating that the ⁹⁰Y-loaded copolymer has a great potential for tumor radio-brachytherapy.

Electron transfer-based combination therapy of cisplatin with tetramethyl-p-phenylenediamine for ovarian, cervical, and lung cancers

The platinum-based chemotherapy is the standard treatment for several types of cancer. However, cancer cells often become refractory with time and most patients with serious cancers die of drug resistance. Recently, we have discovered a unique dissociative electron-transfer mechanism of action of cisplatin, the first and most widely used platinum-based anticancer drug. Here, we show that the combination of cisplatin with an exemplary biological electron donor, N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), may overcome the resistance of cancer cells to cisplatin. Our steady-state absorption and fluorescence spectroscopic measurements confirm the effective dissociative electron-transfer reaction between TMPD and cisplatin. More significantly, we found that the combination of 100 μM TMPD with cisplatin enhances double-strand breaks of plasmid DNA by a factor of approximately 3.5 and dramatically reduces the viability of cisplatin-sensitive human cervical (HeLa) cancer cells and highly cisplatin-resistant human ovarian (NIH:OVCAR-3) and lung (A549) cancer cells. Furthermore, this combination enhances apoptosis and DNA fragmentation by factors of 2-5 compared with cisplatin alone. These results demonstrate that this combination treatment not only results in a strong synergetic effect, but also makes resistant cancer cells sensitive to cisplatin. Because cisplatin is the cornerstone agent for the treatment of a variety of human cancers (including testicular, ovarian, cervical, bladder, head/neck, and lung cancers), our results show both the potential to improve platinum-based chemotherapy of various human cancers and the promise of femtomedicine as an emerging frontier in advancing cancer therapy.

Relative biologic effectiveness in terms of tumor response of 125I implants compared with 60Co gamma rays

PURPOSE

To measure the relative biologic effectiveness (RBE) for 125I seeds compared with external beam radiotherapy using a clinically relevant in vivo system.

METHODS AND MATERIALS

Photon emission from a detailed source model was simulated using the Monte Carlo code MCNP4C, sampling from a 125I spectrum. The mouse RIF-1 tumor was treated with either temporary implant of an 125I seed or with 60Co gamma rays. The tumors were always the same size at the initiation of treatment, and the endpoint was growth inhibition.

RESULTS

The dose-response curve for both modalities was close to linear and was independent of the initial 125I activity (dose rate) for the range investigated. Calculation of the RBE for tumor response requires assigning a unique value for the tumor dose that is not homogenous but depends on the distance from the 125I source. Because tumor regrowth will depend on the subpopulation of cells that have the greatest probability of survival (i.e., those at the greatest distance from the 125I source), one approach is to use the dose to this population. On this basis, the RBE for 125I compared with 60Co gamma rays is 1.5. If the 125I dose is computed as the average dose to the tumor, corrected for the dose that is wasted as overkill in the cell population closest to the center of the 125I seed, the RBE is 1.4.

CONCLUSION

The result, an RBE of 1.4-1.5 is similar to findings obtained by other methods, supporting the validity of this approach to derive an RBE with validity in a clinical context.