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<p>Mild hyperthermia (39°C-43°C) has numerous therapeutic benefits as an adjuvant
therapy in the treatment of a variety of tumor types. Hyperthermia increases tumor
blood flow and vascular permeability, promoting drug delivery and tumor oxygenation.
Hyperthermia enhances the uptake and efficacy of numerous chemotherapeutic agents,
including cisplatin, resulting in increased cytotoxicity. In addition to these biological
responses, hyperthermia can be used as a drug-release trigger for temperature-sensitive
nanoparticles, resulting in an improved and more targeted drug delivery system. Cisplatin
was chosen because 1) it shows broad spectrum activity against a wide range of heatable
cancers (i.e., those in sites such as the pancreas, colon and rectum, cervix and bladder,
and 2) the same hyperthermic temperatures that enable temperature-sensitive lipsome-drug
release also enhance cisplatin-induced cytotoxicity.</p><p>The role of hyperthermia
in enhancing cisplatin delivery and cytotoxicity was investigated at both the cellular
and tissue levels. While hyperthermia treatment is applicable to a variety of tumor
types, the focus of this work was on bladder cancer. The synergistic effects of hyperthermia
and cisplatin were investigated, along with the role of copper transport protein 1
(Ctr1) in this process. In addition, cisplatin was encapsulated within temperature-sensitive
liposomes, which were used in combination with hyperthermia for targeted drug delivery.
These studies demonstrated that the combination of cisplatin and hyperthermia improved
drug delivery, and potentially anti-tumor efficacy, and that targeted delivery was
enhanced through incorporation of temperature-sensitive liposomes. As many current
methods for administering bladder hyperthermia have drawbacks, such as invasiveness
and regional heating, the final aim of this study was to develop and test a less-invasive
and more focused preclinical bladder heating device in a rat model. </p><p>Hyperthermia
sensitizes cells to the cytotoxic effects of the commonly used chemotherapeutic agent
cisplatin by increasing drug accumulation and subsequent platinum-DNA adduct formation.
However, the molecular mechanisms underlying this enhancement remain unclear. Understanding
the fundamental mechanisms involved in the synergistic interaction is necessary to
increase the therapeutic benefits of this combination in the clinic. The synergism
between the anti-cancer benefits of cisplatin and the drug delivery benefits of hyperthermia
may offer a novel and more effective treatment for many cancer patients. We hypothesized
that hyperthermia increases cisplatin accumulation and efficacy in part by modulating
the function of Ctr1, a major regulator of cellular cisplatin uptake. To test this
hypothesis, we examined the significance of Ctr1 during combined hyperthermia and
cisplatin therapies and assessed the importance of cisplatin- and hyperthermia-induced
Ctr1 multimerization in enhancing cisplatin cytotoxicity. We observed increased Ctr1
multimerization following hyperthermia treatment (41°C) in vitro, compared to normothermic
controls (37°C), suggesting that this may be a mechanism for increased cisplatin uptake
in heat-treated cells. The impact of increased Ctr1 multimerization was evaluated
by measuring platinum accumulation in wild-type (WT) and Ctr1-/- cells. WT cells contained
greater levels of platinum compared to Ctr1-/- cells. A further increase in platinum
was observed following hyperthermia treatment, but only in the WT cells. Hyperthermia
enhanced cisplatin-mediated cytotoxicity in WT cells with a dose-modifying factor
(DMF) of 1.8 compared to 1.4 in Ctr1-/- cells. Our data suggest that heat increases
Ctr1 activity by increasing multimerization, resulting in enhanced drug accumulation.
Although we recognize that the effect of heat on cells is multi-factorial, our results
support the hypothesis that Ctr1 is, in part, involved in the synergistic interaction
observed with cisplatin and hyperthermia treatment. </p><p>In addition to assessing
cisplatin delivery at the cellular level, we evaluated cisplatin delivery at the tissue
level, using novel cisplatin-loaded temperature-sensitive liposomes. We hypothesized
that delivering cisplatin encapsulated in liposomes under hyperthermic conditions
would improve the pharmacokinetic profiles of cisplatin, increase drug delivery to
the tumor, decrease normal tissue toxicity, and enhance the anti-tumor activity of
cisplatin. We successfully prepared temperature-sensitive liposomes loaded with cisplatin
and demonstrated that heat (42°C) sensitizes cisplatin-resistant cells to the cytotoxic
effects of cisplatin in vitro. </p><p>Decreased toxicity was observed in animals treated
with the cisplatin liposome (± heat) compared to the free drug treatments. A pharmacokinetic
study of cisplatin-loaded temperature-sensitive liposomes and free drug was performed
in tumor-bearing mice under normothermic and hyperthermic conditions. Cisplatin half-life
in plasma was increased following liposome treatment compared to free cisplatin, and
cisplatin delivery to the tumors was greatest in mice that received liposomal cisplatin
under hyperthermia. These initial in vivo data demonstrate the potential effectiveness
of this cisplatin-loaded liposome formulation in the treatment of certain types of
cancer. To assess the anti-cancer efficacy of the liposome treatment, a tumor growth
delay study was conducted and demonstrated equivalent efficacy for the cisplatin-loaded
temperature-sensitive liposome compared to free drug. </p><p>In addition to the liposome
work, we developed and evaluated a novel heating device for the bladder. Despite the
evidence that hyperthermia is an effective adjuvant treatment strategy, current clinical
heating devices are inadequate, warranting the development of a new and improved system.
We induced hyperthermia using ferromagnetic nanoparticles and an alternating magnetic
field device developed by Actium Biosystems. Initial preclinical studies in a rat
model demonstrated preferential bladder heating. However, our preliminary studies
show severe toxicity with the direct instillation of the nanoparticles in the bladder,
and further studies are needed to potentially modify the nanoparticle coating, the
catheterization procedure, as well as to develop a different animal model.</p>
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