Ultra-Long-Term Delivery of Hydrophilic Drugs Using Injectable In Situ Cross-Linked Depots

Achieving ultra-long-term release of hydrophilic drugs over several months remains a significant challenge for existing long-acting injectables (LAIs). Existing platforms, such as in situ forming implants (ISFI), exhibit high burst release due to solvent efflux and microsphere-based approaches lead to rapid drug diffusion due to significant water exchange and large pores. Addressing these challenges, we have developed an injectable platform that, for the first time, achieves ultra-long-term release of hydrophilic drugs for over six months. This system employs a methacrylated ultra-low molecular weight pre-polymer (polycaprolactone) to create in situ cross-linked depots (ISCD). The ISCD’s solvent-free design and dense mesh network, both attributed to the ultra-low molecular weight of the pre-polymer, effectively minimizes burst release and water influx/efflux. In vivo studies in rats demonstrate that ISCD outperforms ISFI by achieving lower burst release and prolonged drug release. We demonstrated the versatility of ISCD by showcasing ultra-long-term delivery of several hydrophilic drugs, including antiretrovirals (tenofovir alafenamide, emtricitabine, abacavir, and lamivudine), antibiotics (vancomycin and amoxicillin) and an opioid antagonist naltrexone. Additionally, ISCD achieved ultra-long-term release of the hydrophobic drug tacrolimus and enabled co-delivery of hydrophilic drug combinations encapsulated in a single depot. We also identified design parameters to tailor the polymer network, tuning drug release kinetics and ISCD degradation. Pharmacokinetic modeling predicted over six months of drug release in humans, significantly surpassing the one-month standard achievable for hydrophilic drugs with existing LAIs. The platform’s biodegradability, retrievability, and biocompatibility further underscore its potential for improving treatment adherence in chronic conditions.

Figure S1.Synthesis and characterization of PCLDMA. A. Schematic showing methacrylation of hydroxylfunctionalized PCL to yield PCLDMA. B. 1 H-NMR spetrcum of of PCLDMA.The chemically equivalent protons are labeled with the same color and their NMR signals are marked with the same colored box for ease of understanding.The NMR integration of each signal corresponds to the expected ratio of each type of hydrogen in the PCLDMA molecule.

Figure S2 .
Figure S2.Schematic illustrating hydrolysis of polycaprolactone domains and subsequent collapse of ISCD.The ISCD consists of a cross-linked network of polymethacrylate chains (red) connected by ester bonds (dark blue).Hydrolysis of these ester bonds (light blue) disconnects the polymethacrylate chains, enabling the depot to degrade.

Figure S3 .Figure S4 .
Figure S3.Infrared thermal imaging confirms that there is no noticeable heat generated during ISCD polymerization.

Figure S5 .
Figure S5.In vitro cumulative release of TAF from ISCD depots formed by injecting pre-polymer mixture into PBS (37 o C) compared with TAF release from pre-formed implants with cylindrical shape.Data are presented as mean ± standard deviation (n=3, experiments performed at least twice).

Figure S6 .
Figure S6.Swelling rate of different ISCD formulations studied in benzyl alcohol aftera week.Data are presented as mean ± standard deviation (n=3, experiments performed at least twice).

Figure S9 .
Figure S9.The scheme of the pharmacokinetic (PK) model for subcutaneous injection of ISCD.The disposition kinetics (referred to as Systems) of analytes is characterized by two compartments (CBlood/Plasma and CTissue), with first-order rate constants for elimination (kel), distribution (k12), and redistribution (k21), and Vc for the central volume of distribution.At the SC implant site (referred to as SC Depot), the release/absorption model assumes three sequential release phases, delineated by first-order release rate constants (ki, km, ks).Initially, a fraction (fi) of the ISCD implant is released (ki), leading to the maximum concentration in the central compartment.Subsequently, drug release continues with an intermediate phase (km) for a fraction of the total released drug mass (fm), followed by a sustained release phase (ks) for the remaining drug amount (1-fi-fm).The time delays associated with the intermediate (Tdm) and sustained-release (Tds) phase are characterized by a gamma distribution function with shape (N) and rate parameter (Td).F represents the bioavailability of ISCD implants.

Figure S10 .
Figure S10.Time profiles of the blood/plasma concentration in rats after a single IV dose of A. TFV (1 & 4 mg/kg) B. TAC (1 & 2 mg/kg), and C. NAL (1 & 2 mg/kg).Time profiles of the blood/plasma concentration in rats after subcutaneous injection of ISCD containing D. TFV, E. TAC, and F. NAL.Data presented as symbols reflect the mean ± standard deviation of three technical repeats (n=3).Lines represent the model-predicted drug concentrations.

Figure S11 A.
Figure S11 A. Pecentage of the initial amount TAF amount remaining in the explanted ISFI following the 2month in vivo study in rats.B. ISFI explanted after the 2-month in vivo study is a fragmented solid.Data are presented as individual values for each animal.

Figure S13 .
Figure S13.Convolution analysis-based prediction of human PK of a single subcutaneous dose of TAC-loaded ISCD (at different dosages) upto 6 months.

Table S2 .
The estimated PK parameters of disposition and release kinetics were obtained from the concentration-time profiles following IV administration and SC implants of ISCDs in rats.

Table S3 .
The disposition PK parameter values obtained from the concentration-time profiles of TAC (0.075 mg/kg/day) and NAL (1 mg) following oral or IV administration in humans.