(550a) Drug Encapsulated Polymeric Microspheres for Temporally-Staged, Localized Brain Tumor Therapy

The American Cancer
Society 2012 estimate is that 22,910 malignant tumors of the brain or spinal
cord will be diagnosed in the United Sates. Approximately 59.8% will be fatal.
Despite current treatments, survival remains low with a median survival of approximately
one year despite maximal therapy. Complete tumor removal cannot always be
achieved because of the potential for brain damage, leading to cancerous
regrowth and ultimately, patient death. In addition, these tumors can develop
drug resistance, rendering chemotherapy ineffectual. We believe that the
development of a topical, slow release, multi-drug delivery system (M-DDS) that
is applied post-surgically directly in the tumor cavity could significantly increase
life expectancy. Our M-DDS consists of multi-drug loaded poly(lactic acid)
(PLA), poly(lactic-co-glycolic acid) (PLGA), and poly(ε-caprolactone)
(PCL) microspheres suspended in an aqueous solution of  a degradable, thermoresponsive
poly(N-isopropylacrylamide) (PNIPAM) synthesized in our laboratory. At
room temperature, PNIPAM suspends drug encapsulated microspheres that can be directly
?sprayed on? the post-surgical site. The 37°C temperature of the brain would
pass PNIPAM through its lower critical solution temperature, causing the
polymer matrix to solidify and form an adherent gel layer with entrapped drug
loaded microspheres on the surface of the brain. This would provide intimate
contact with the remaining tumor cells, conforming to the convoluted morphology
of the brain surface. Over time PNIPAM would degrade along with PLGA, PLA, and
then PCL microspheres, releasing multiple chemotherapeutics at different rates
directly to the tumor remnants to inhibit cancerous re-growth. This work
focuses on microsphere characterization, model drug (rhodamine B (RB)) and
chemotherapeutic encapsulation, and RB release from microspheres and
microspheres entrapped in PNIPAM.

Both double and single
emulsions have been applied to form PLA, PCL, and PLGA microspheres. Smooth,
nonporous microspheres were produced with an adjustable size dependent on impeller
speed during the emulsification process. RB, a hydrophilic dye and the model
drug, was successfully encapsulated within PLA, PCL, and PLGA based
microspheres and microsphere morphology remained unaffected. The encapsulation
efficiency was polymer dependent; PLGA was most efficient at RB incorporation (84.6
± 4.8%) due
to its hydrophilic nature. An in vitro release from PLGA microspheres
alone and PLGA microspheres entrapped in degradable PNIPAM was characterized in
PBS at 37 °C. A biphasic release profile was seen for both conditions, with an
initial, moderate, continuous release (passive diffusion) followed by a significant
increase in the release curve slope (polymer degradation) before plateauing.
Microspheres entrapped in PNIPAM had a two day delay of release compared to
microspheres alone, with the release plateau occurring at day 22 versus day 20.
In both instances, smaller microspheres (22.5 ± 7.8 µm) released faster than
the larger microspheres (42.2 ± 15.4 µm) during the diffusion period due to a
higher surface area to volume ratio, showing release profile tunability.

Our M-DDS has also been
tested to visualize local and topical delivery on brain tissue. RB encapsulated
PLGA microspheres suspended in degradable PNIPAM were ?sprayed on? a rat brain
that was preserved at 37 °C. The PNIPAM solution underwent a phase transition
on the rat brain, showing stable adhesion to the tissue and efficient entrapment
of drug loaded microspheres to a localized site (Figure 1).

The chemotherapeutic
gefitinib has also been successfully encapsulated in PLGA microspheres (Figure
2). These gefitinib loaded PLGA microspheres will be tested against a C6 glioma
cell line to explore drug efficacy along with PCL microspheres encapsulating
the chemotherapeutic temozolomide. A pilot animal study will be conducted to
test the effect of the delivery system on a rat model and the diffusion of the
chemotherapeutics through the brain. Our M-DDS has the potential to provide a localized,
tunable time release of multiple chemotherapeutics that will directly impact
tumor remnants to inhibit cancerous re-growth, overcome tumor drug resistance,
and increase patient life expectancy.

a)                                                                 b)

Figure 1: Sprayed RB
encapsulated PLGA microspheres entrapped in degradable PNIPAM on a rat brain at
37 °C viewed with a) bright field and b) fluorescent microscopy

a)                            
                                b)

Figure 2: Gefitinib
encapsulated PLGA microspheres viewed by a) fluorescent and b) scanning
electron microscopy