3. NIR materials for MPTT
According to different properties, PTAs used in MPTT can be divided into
organic agents and inorganic agents. Organic PTAs include NIR cyanine
dyes, donor-acceptor (D-A)
structured small molecules, semiconductor polymer NPs (SPNs).[23,
78-80] Inorganic PTAs include
noble
metal materials, metal sulfide materials, metal oxide materials, quantum
dots (QDs), carbon-based nanomaterials (such as graphene and carbon
nanotubes) and other two-dimensional (2D) materials (such as black
phosphorus, boron nitride and graphite carbon nitride, Mxenes),
etc.[81-83] Organic PTAs may have the advantages in biodegradability
and biocompatibility, while inorganic PTAs usually present the higher
PCE and better photothermal stability.
3.1. Organic agents
3.1.1. NIR cyanine dyes
Cyanine dyes, anthocyanin series of fluorescent dyes, are a class of
synthetic fluorescent dyes with polymethyl bridge chain chemical
structure. Cyanine dyes have a very high extinction coefficient, and the
length of the bridge chain and the chromophores at both ends directly
control the absorption peak and emission peak of the dyes.[84-86]
There are many kinds of cyanine dyes, which can be divided into cyanine,
partial cyanine and multinucleated cyanine according to the conjugated
system of chromophore. According to the types of heterocyclic nuclei
they contain, they can be divided into sulfur carbocyanine, oxygen
carbocyanine and indocarbocyanine. According to the length of multiple
methyl chains, it can be divided into first methyl cyanine, second
methyl cyanine (carbon cyanine), fifth methyl cyanine (two carbon
cyanine), seventh methyl cyanine (three carbon cyanine), etc. By
adjusting the length of the conjugated chain, the spectrum of cyanine
can extend from the visible region to the near infrared region.[30,
87-90] Background interference can be effectively eliminated by using
the red region measurement, and more ideal analytical sensitivity and
selectivity can be obtained. Cyanine dye spectrum is very sensitive to
the change of external microenvironment, which is very suitable for the
analysis of biological and environmental samples. Yang et al. developed
a straightforward approach for creating modified one-dimensional
nanoscale coordination polymers (1D-NCPs) using poly(ethylene glycol)
(PEG), which exhibit inherent biodegradability, a substantial surface
area, pH-responsive behaviors, and versatile theranostic capabilities.
Taking the instance of NCPs containing Mn2+ and
indocyanine green (ICG), the researchers demonstrated the fabrication of
Mn-ICG@pHis-PEG as a carrier for Gambogic acid (GA), a natural inhibitor
of
HSP90
that plays a crucial role in cellular resistance to heat-induced damage.
Upon NIR triggered heating, the Mn-ICG@pHis-PEG/GA nanocomplex achieved
MPTT at around 43 °C, demonstrating exceptional efficacy in tumor
ablation.[91] In another study, Wu et al. introduced a versatile and
biodegradable hollow mesoporous organosilica nanocapsule platform
(HMONs), which was ingeniously capped with gemcitabine (Gem) molecules
using a pH-sensitive acetal covalent linkage. HMONs showcased a
favorable release of small molecules specifically at tumor
tissue/cellular sites, thereby mitigating the risk of drug accumulation.
Upon encapsulating ICG and the HSP90 inhibitor 17AAG, the resulting
construct denoted as ICG−17AAG@HMONs−Gem−PEG demonstrated MPTT with an
operating temperature of around 41 °C, accompanied by exceptional
efficacy in tumor ablation.[92] Jiang et al. presented a
groundbreaking study featuring a novel nanoscale coordination polymer
centered around a heptamethine cyanine dye, termed Hf-HI-4COOH. This
compound emerged as an exceptionally potent photosensitizer,
particularly tailored for nucleus-targeted MPTT. Notably, Hf-HI-4COOH
exhibited robust NIR absorption characteristics and boasted an efficient
PCE of 39.51%.[93] The formulation’s prolonged circulation within
the bloodstream, augmented accumulation at tumor sites, and its
nucleus-targeting attributes collectively contribute to a substantial
suppression of breast tumors in murine models subjected to MPTT, all
without apparent toxicity. Shi et al. employed poly(lactic-co-glycolic
acid) (PLGA) as a carrier, loaded with a NIR photothermal agent (IR820),
a fluorescence imaging agent (ZnCdSe/ZnS QDs), and an autophagy
inhibitor (chloroquine, CQ) to form PLGA/IR820/ZnCdSe/ZnS co-loading NPs
(PIFC NPs). The effective intracellular delivery of CQ molecules via
PIFC NPs plays a pivotal role in attenuating the degradation of
autophagic lysosomes within tumor cells (Figure 1).[94] This, in
turn, effectively inhibits the autophagy-mediated repair process of
cells damaged by MPTT. Notably, the modulation of autophagy sensitizes
MPTT, presenting a novel avenue for future cancer treatment research.