Free SN-38 Research Articles

Targeted delivery of SN38 to breast cancer using amphiphilic diblock copolymers PHPMA-b-PBAEM as micellar carriers with AS1411 aptamer

Breast cancer treatment can be challenging, but a targeted drug delivery system (DDS) has the potential to make it more effective and reduce side effects. This study presents a novel nanotherapeutic targeted DDS developed through the self-assembly of an amphiphilic di-block copolymer to deliver the chemotherapy drug SN38 specifically to breast cancer cells. The vehicle was constructed from the PHPMA-b-PEAMA diblock copolymer synthesized via RAFT polymerization. A single emulsion method was then used to encapsulate SN38 within nanoparticles (NPs) formed from the PHPMA-b-PEAMA copolymer. The AS1411 DNA aptamer was covalently bonded to the surface of the micellar NPs, producing a targeted DDS. Molecular dynamics (MD) simulation studies were also performed on the di block polymeric system, demonstrating that SN38 interacted well with the di block. The in vitro results demonstrated that AS1411- decorated SN38-loaded HPMA NPs were highly toxic to breast cancer cells while having a minimal effect on non-cancerous cells. Remarkably, in vivo studies elucidated the ability of the targeted DDS to enhance the antitumor effect of SN38, suppressing tumor growth and improving survival rates compared to free SN38.

Synergistic Nanomedicine Delivering Topoisomerase I Toxin (SN-38) and Inhibitors of Polynucleotide Kinase 3'-Phosphatase (PNKP) for Enhanced Treatment of Colorectal Cancer.

Inhibitors of a DNA repair enzyme known as polynucleotide kinase 3'-phosphatase (PNKP) are expected to show synergistic cytotoxicity in combination with topoisomerase I (TOP1) inhibitors in cancer. In this study, the synergistic cytotoxicity of a novel inhibitor of PNKP, i.e., A83B4C63, with a potent TOP1 inhibitor, i.e., SN-38, against colorectal cancer cells was investigated. Polymeric micelles (PMs) for preferred tumor delivery of A83B4C63, developed through physical encapsulation of this compound in methoxy poly(ethylene oxide)-poly(α-benzyl carboxylate-ε-caprolactone) (mPEO-b-PBCL) micelles, were combined with SN-38 in free or PM form. The PM form of SN-38 was prepared through chemical conjugation of SN-38 to the functional end group of mPEO-b-PBCL and further assembly of mPEO-b-PBCL-SN-38 in water. Moreover, mixed micelles composed of mPEO-b-PBCL and mPEO-b-PBCL-SN-38 were used to co-load A83B4C63 and SN-38 in the same nanoformulation. The loading content (% w/w) of the SN-38 and A83B4C63 to mPEO-b-PBCL in the co-loaded formulation was 7.91 ± 0.66 and 16.13 ± 0.11% (w/w), respectively, compared to 15.67 ± 0.34 (% w/w) and 23.06 ± 0.63 (% w/w) for mPEO-b-PBCL micelles loading individual drugs. Notably, the average diameter of PMs co-encapsulating both SN-38 and A83B4C63 was larger than that of PMs encapsulating either of these compounds alone but still lower than 60 nm. The release of A83B4C63 from PMs co-encapsulating both drugs was 76.36 ± 1.41% within 24 h, which was significantly higher than that of A83B4C63-encapsulated micelles (42.70 ± 0.72%). In contrast, the release of SN-38 from PMs co-encapsulating both drugs was 44.15 ± 2.61% at 24 h, which was significantly lower than that of SN-38-conjugated PMs (74.16 ± 3.65%). Cytotoxicity evaluations by the MTS assay as analyzed by the Combenefit software suggested a clear synergy between PM/A83B4C63 (at a concentration range of 10-40 μM) and free SN-38 (at a concentration range of 0.001-1 μM). The synergistic cytotoxic concentration range for SN-38 was narrowed down to 0.1-1 or 0.01-1 μM when combined with PM/A83B4C63 at 10 or 20-40 μM, respectively. In general, PMs co-encapsulating A83B4C63 and SN-38 at drug concentrations within the synergistic range (10 μM for A83B4C63 and 0.05-1 μM for SN-38) showed slightly less enhancement of SN-38 anticancer activity than a combination of individual micelles, i.e., A83B4C63 PMs + SN-38 PMs at the same molar concentrations. This was attributed to the slower release of SN-38 from the SN-38 and A83B4C63 co-encapsulated PMs compared to PMs only encapsulating SN-38. Cotreatment of cells with TOP1 inhibitors and A83B4C63 formulation enhanced the expression level of γ-HA2X, cleaved PARP, caspase-3, and caspase-7 in most cases. This trend was more consistent and notable for PMs co-encapsulating both A83B4C63 and SN-38. The overall result from the study shows a synergy between PMs of SN-38 and A83B4C63 as a mixture of two PMs for individual drugs or PMs co-encapsulating both drugs.

In vitro evaluation of novel SN-38 prodrug activated by α-rhamnosidase of exogenous enzyme.

This study introduces the α-rhamnose (Rham)-conjugated prodrug of SN-38 (Rham-SN-38) as a promising alternative to irinotecan. α-rhamnosidase, responsible for SN-38 release from Rham-SN-38, does not express in human cells, minimizing individual variability and side effects. The injection of the α-rhamnosidase into the tumor tissues makes it possible, for the first time, to activate the Rham-SN-38. Furthermore, α-rhamnosidase demonstrates significantly higher activity than carboxylesterase, the specific enzyme activating irinotecan. SN-38 release mediated by α-rhamnosidase completes within 2h, with a kcat/Km value approximately 5.0 × 104-fold higher than that of irinotecan. The 50% inhibition concentration (IC50) of Rham-SN-38 against three types of cancer cells and one normal cell exceeds 4.5 × 103nM. The addition of α-rhamnosidase significantly increases cytotoxicity, with IC50 comparable to free SN-38. The QIC50, an index reflecting the difference in cytotoxicity with and without α-rhamnosidase, exceeds approximately 1.0 × 102-fold. Rham-SN-38, synthesized in this study, demonstrates significant potential as a prodrug for cancer therapy.

Abstract PO1-04-06: Exposure-response analyses of sacituzumab govitecan efficacy and safety in patients with metastatic breast cancer

Abstract Background: Sacituzumab govitecan (SG) is an antibody-drug conjugate that is composed of an anti Trop-2 antibody coupled to the cytotoxic SN-38 payload via a proprietary, hydrolysable CL2A linker. SG (10 mg/kg on D1 and D8 of every 21D cycle) is approved for patients (pts) with metastatic triple-negative breast cancer (mTNBC) who received ≥2 prior systemic therapies (≥1 in the metastatic setting). The relationship between exposure of SG, free SN-38, and total antibody (tAB) following SG administration and its efficacy and safety were evaluated in pts with HR+/HER2‒ metastatic breast cancer (mBC) and all pts with mBC (mTNBC or HR+/HER2‒ mBC), respectively. Methods: Available exposure and efficacy outcomes from HR+/HER2‒ mBC pts from phase 3 study TROPiCS-02 (n=260) and safety outcomes from mBC pts in phase 1/2 study IMMU-132-01, phase 3 study ASCENT and TROPiCS-02 (total n=569) were analyzed. Exposure-response (ER) models were developed to characterize the relationship between exposure and efficacy (complete response [CR], overall response rate [ORR], clinical benefit rate [CBR], overall survival [OS] and progression-free survival [PFS]) and safety (adverse events [AEs] of vomiting, diarrhea, hypersensitivity reactions, nausea, neutropenia, febrile neutropenia, time to first dose reduction and first dose delay) endpoints. Exposure metrics of SG, free SN-38, and tAB were evaluated as predictors and effect of clinically relevant covariates was characterized within the modeling framework. Results: Average SG-related serum exposures over the duration of treatment (until the event) were associated with significantly increased efficacy (probability of CR, ORR, CBR and longer OS and PFS) and safety events (probability of any grade AE). Neutropenia was the only AE where the increase in exposure was significantly associated with the increased probability of Grade ≥3 and Grade 4 events. Baseline Trop-2 expression level was not correlated with assessed efficacy and safety endpoints. Conclusions: Within the exposure range achieved with the 10 mg/kg regimen, higher exposure values were associated with a higher probability of achieving better efficacy. The 10 mg/kg SG dose achieved an acceptable balance between efficacy and safety which supports the appropriateness of this regimen in pts with HR+/HER2‒ mBC. Citation Format: Indrajeet Singh, Abhishek Sathe, Paul Diderichsen, Han Witjes, Arne Van Schanke, John Maringwa, Wendy Verret, Sandhya Girish, Ahmed Othman. Exposure-response analyses of sacituzumab govitecan efficacy and safety in patients with metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-04-06.

Supramolecular prodrug of SN38 based on endogenous albumin and SN38 prodrug modified with semaglutide side chain to improve the tumor distribution

To improve the biodistribution of the drug in the tumor, a supramolecular prodrug of SN38 was fabricated in situ between endogenous albumin and SN38 prodrug modified with semaglutide side chain. Firstly, SN38 was conjugated with semaglutide side chain and octadecanedioic acid via glycine linkers to obtain SI-Gly-SN38 and OA-Gly-SN38 prodrugs, respectively. Both SI-Gly-SN38 and OA-Gly-SN38 exhibited excellent stability in PBS for over 24 h. Due to the strong binding affinity of the semaglutide side chain with albumin, the plasma half-life of SI-Gly-SN38 was 2.7 times higher than that of OA-Gly-SN38. Furthermore, with addition of HSA, the fluorescence intensity of SI-Gly-SN38 was 4 times higher than that of OA-Gly-SN38, confirming its strong binding capability with HSA. MTT assay showed that the cytotoxicity of SI-Gly-SN38 and OA-Gly-SN38 was higher than that of Irinotecan. Even incubated with HSA, the SI-Gly-SN38 and OA-Gly-SN38 still maintained high cytotoxicity, indicating minimal influence of HSA on their cytotoxicity. In vivo pharmacokinetic studies demonstrated that the circulation half-life of SI-Gly-SN38 was twice that of OA-Gly-SN38. SI-Gly-SN38 exhibited significantly reduced accumulation in the lungs, being only 0.23 times that of OA-Gly-SN38. The release of free SN38 in the lungs from SI-Gly-SN38 was only 0.4 times that from OA-Gly-SN38 and Irinotecan. The SI-Gly-SN38 showed the highest accumulation in tumors. The tumor inhibition rate of SI-Gly-SN38 was 6.42% higher than that of OA-Gly-SN38, and 8.67% higher than that of Irinotecan, respectively. These results indicate that the supramolecular prodrug delivery system can be constructed between SI-Gly-SN38 and endogenous albumin, which improves drug biodistribution in vivo, enhances tumor accumulation, and plays a crucial role in tumor growth inhibition.

Abstract LB439: Intra-tumoral administration of releasable hydrogel microsphere drug conjugates for long acting therapeutics

Abstract Background. Intra-tumoral (IT) injections of therapeutics hold promise for the treatment of solid tumors. However, drugs administered directly in the tumor have short IT residence times potentially limiting their exposure and therefore efficacy. We are developing a platform of novel hydrogel microsphere (MS) conjugates that enables long-acting tumor residence after a single injection of the conjugate. We demonstrate this approach not only solves the problem of short acting intra-tumoral therapy, but also allows for the safe administration of two therapies with overlapping toxicities such as SN-38 and a PARP inhibitor (PARPi). Methods. Hydrogel microsphere (MS) conjugates were prepared and characterized. Using MS conjugates labeled with rhodamine and fluorescein, we established methods to directly measure the IT concentration and half-life of the released drug after IT administration into CT26 tumor bearing mice. We next measured the tissue pharmacokinetics and efficacy of MSs attached to SN-38, a potent topoisomerase 1 inhibitor and immunomodulator, using NSG mice bearing 22Rv1 ATM-/- xenografts. Finally, we measured the anti-tumor efficacy of MS~SN-38 in combination with an oral PARPi, talazoparib, in 22Rv1 ATM-/- xenografts. Results. We successfully established methods to quantify the concentration of released drug and MS bound drug from tumor biopsies using fluorescent surrogates. When applied to MS~SN-38 conjugates, locally injected tissues showed high levels of SN-38 with a long half-life of about one week. In contrast, the systemic half-life of free SN-38 is ~30 minutes. IT MS~SN-38 was ~10-fold more efficacious as an anti- tumor agent than systemic SN-38 from subcutaneous administration of MS~SN-38. Finally, we show high anti-tumor synergy from the SN-38 localized in a tumor by IT MS~SN-38 in combination with systemic administration of the PARPi talazoparib. Conclusions. This microsphere technology allows for sustained delivery of high local concentrations of drugs administered intratumorally. Here, IT MS~SN-38 resulted in an intra-tumoral half-life of ~1 week and marked anti-tumor efficacy in 22Rv1 ATM-/- xenografts. We also demonstrated that long-acting IT injections enables safe use of drug combinations with well-described overlapping toxicities such as SN-38 and PARPi. The microsphere technology may offer an alternative strategy for localizing and sustaining drugs in tumors and may mitigate toxicities from combination therapy where two agents have a similar toxicological profile. Other combinations, including small molecules and immuno-oncology agents, are being explored. Citation Format: John A. Hangasky, Jeff Henise, Deborah Charych, Christopher W. Carreras, Gary Ashley, Daniel V. Santi. Intra-tumoral administration of releasable hydrogel microsphere drug conjugates for long acting therapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB439.

Development of a Targeted SN-38-Conjugate for the Treatment of Glioblastoma.

Glioblastoma (GBM) is the most aggressive and fatal brain tumor, with approximately 10,000 people diagnosed every year in the United States alone. The typical survival period for individuals with glioblastoma ranges from 12 to 18 months, with significant recurrence rates. Common therapeutic modalities for brain tumors are chemotherapy and radiotherapy. The main challenges with chemotherapy for the treatment of glioblastoma are high toxicity, poor selectivity, and limited accumulation of therapeutic anticancer agents in brain tumors as a result of the presence of the blood-brain barrier. To overcome these challenges, researchers have explored strategies involving the combination of targeting peptides possessing a specific affinity for overexpressed cell-surface receptors with conventional chemotherapy agents via the prodrug approach. This approach results in the creation of peptide drug conjugates (PDCs), which facilitate traversal across the blood-brain barrier (BBB), enable preferential accumulation of chemotherapy within the neoplastic microenvironment, and selectively target cancerous cells. This approach increases accumulation in tumors, thereby improving therapeutic efficiency and minimizing toxicity. Leveraging the affinity of the HAIYPRH (T7) peptide for the transferrin receptor (TfR) overexpressed on the blood-brain barrier and glioma cells, a novel T7-SN-38 peptide drug conjugate was developed. The T7-SN-38 peptide drug conjugate demonstrates about a 2-fold reduction in glide score (binding affinity) compared to T7 while maintaining a comparable orientation within the TfR target site using Schrödinger-2022-3 Maestro 13.3 for ligand preparation and Glide SP-Peptide docking. Additionally, SN-38 extends into a solvent-accessible region, enhancing its susceptibility to protease hydrolysis at the cathepsin B (Cat B) cleavable site. The SN-38-ether-peptide drug conjugate displayed high stability in buffer at physiological pH, and cleavage of the conjugate to release free cytotoxic SN-38 was observed in the presence of exogenous cathepsin B. The synthesized peptide drug conjugate exhibited potent cytotoxic activities in cellular models of glioblastoma in vitro. In addition, blocking transferrin receptors using the free T7 peptide resulted in a notable inhibition of cytotoxicity of the conjugate, which was reversed when exogenous cathepsin B was added to cells. This work demonstrates the potential for targeted drug delivery to the brain in the treatment of glioblastoma using the transferrin receptor-targeted T7-SN-38 conjugate.

Design, Synthesis, and Evaluation of Glucose Transporter Inhibitor-SN38 Conjugates for Targeting Colorectal Cancer.

Irinotecan (1), a prodrug of SN38 (2) approved by the US Food and Drug Administration for treating colorectal cancer, lacks specificity and causes many side effects. To increase the selectivity and therapeutic efficacy of this drug, we designed and synthesized conjugates of SN38 and glucose transporter inhibitors (phlorizin (5) or phloretin (6)), which could be hydrolyzed by glutathione or cathepsin to release SN38 in the tumor microenvironment, as a proof of concept. These conjugates (8, 9, and 10) displayed better antitumor efficacy with lower systemic exposure to SN38 in an orthotopic colorectal cancer mouse model compared with irinotecan at the same dosage. Further, no major adverse effects of the conjugates were observed during treatment. Biodistribution studies showed that conjugate 10 could induce higher concentrations of free SN38 in tumor tissues than irinotecan at the same dosage. Thus, the developed conjugates exhibit potential for treating colorectal cancer.

Abstract P1-14-04: A Phase 0 Clinical trial of Sacituzumab Govitecan in Patients with Breast Cancer Brain Metastases and Recurrent Glioblastoma

Abstract Purpose: Sacituzumab govitecan has shown efficacy and acceptable tolerability in a multicenter phase I/II clinical trial (NCT01631552) in patients with advanced epithelial cancers. Our study was initiated to determine the bioavailability of Sacituzumab govitecan (SG) in breast brain metastasis and glioblastoma. The goals were to evaluate the extent by which SG can penetrate the blood brain barrier and access tumor tissues by testing free SN-38, SN-38G and total SN-38 concentrations in tumor tissue, serum, and CSF. Patients and methods: Patients diagnosed with brain metastatic breast cancer and recurrent glioblastoma were enrolled in a single-center clinical phase 0 study to receive a single intravenous dose of SG at 10 mg/kg one day before surgical resection. Tumor and corresponding serum were collected during surgery to measure their levels of SN-38 and its metabolites. Following recovery, patients resumed SG treatment at 10 mg/kg on days 1 and 8 of 21-day cycles and were assessed for responses by MRI every third cycle using response assessment in neuro-oncology (RANO) criteria. Total Sn-38 levels were quantified in tumor tissue and corresponding serum from the patients. Trop-2 and carbonic anhydrase IX (CAIX) expression was investigated by IHC. SG activity was tested in a breast cancer intracranial mouse model. Results: An average of 2365 ng/ml in serum and 132 ng/g in tissue of total SN-38 was quantified in our patient samples. Trop-2 expression was observed in 90% of patient tumors. 40% of the samples showed high expression of CAIX. SG significantly inhibited tumor growth in vivo and increased overall survival. 20% of patients in the breast cancer arm of the trial demonstrated a complete response by RANO criteria and the remaining 80% of patients demonstrated a partial response. Ultimately, 80% of the patients in the breast cancer metastasis arm survived. Conclusion: Sacituzumab govitecan is an effective drug that crosses the blood brain barrier to inhibit the growth of metastatic breast cancer to the brain after tumor resection surgery. Citation Format: Pegah Ghamasaee, Henriette Balinda, Andrew Brenner, John Floyd. A Phase 0 Clinical trial of Sacituzumab Govitecan in Patients with Breast Cancer Brain Metastases and Recurrent Glioblastoma [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-14-04.

Novel disulfide bond bridged 7-ethyl-10-hydroxyl camptothecin-undecanoic acid conjugate/human serum albumin nanoparticles for breast cancer therapy.

7-Ethyl-10-hydroxyl camptothecin (SN38), a semisynthetic derivative of camptothecin, exhibited extreme pharmacological activities in treating a range of cancers. However, its poor aqueous solubility and low stability hinder its clinical applications. Hence, a redox-responsive SN38 prodrug encapsulated human serum albumin (HSA) nanoparticle is developed to realize its potential in the clinic. First, a disulfide bond bridged 7-ethyl-10-hydroxyl camptothecin-undecanoic acid conjugate (SN38-SS-COOH) was synthesized and characterized structurally. After that, SN38-SS-COOH/HSA nanoparticles (SNH NPs) were prepared by the desolvation method. The SNH NPs with a feed molar ratio of 9 : 1 of SN38-SS-COOH : HSA showed a spherical structure with a diameter range of approximately 120-150 nm revealed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Fluorescence quenching confirmed the formation of SNH NP complexes by dual hydrophobic force and electrostatic interaction. The SNH NPs have a high drug loading of 10.44% and an encapsulation efficiency of 89.59% with good stability. Moreover, the redox responsiveness was validated by glutathione (GSH)-triggered accelerated release of parent drug SN38. In an in vivo pharmacokinetic study, the SNH NPs exhibited a significantly prolonged circulation time (t1/2, 3.77-fold) compared with free SN38. Finally, the in vivo antitumor efficacy and systemic toxicity of SNH NPs in a breast xenograft model were thoroughly evaluated. The inhibition rate of tumor growth induced by the SNH NPs reached 70.1%, while only 50.1% was achieved for irinotecan at an equivalent SN38 dosage of 10 mg kg-1. More importantly, the SNH NPs achieved a higher level of tumor growth inhibition (85.3%) by increasing the dosage to 60 mg kg-1 SN38 without obvious adverse effects. Taken together, the use of redox-responsive SN38 prodrug/HSA NPs could be a promising strategy to deliver highly active SN38 for breast cancer chemotherapy.

Targeted Ultrafine Iron Oxide Nanoparticles for Delivery of the Topoisomerase Inhibitor SN38 and Ovarian Cancer Treatment

Ovarian cancer remains a challenge to decrease mortality and improve diagnostic efficiency in gynecological cancers. To develop a delivery system capable of efficient cancer cell targeting and delivering novel efficacious therapeutics, we assembled folic acid (FA) conjugated ultrafine iron oxide nanoparticles (uIONP) with encapsulation of DNA topoisomerase inhibitor SN38, which target ovarian cancer cells with over-expression of folate receptor alpha (FRα) and deliver SN38 to induce apoptosis. The assembled FA-uIONP-SN38 exhibited higher drug loading efficiency than the larger counterparts with core diameters more than 10 nm. The targeting specificity of FA-uIONP-SN38 for SKOV-3 cancer cells was validated, with HEK293 kidney cells and Raw264.7 macrophages as non-targeted cell line control. It was found that more SKOV-3 cancer cells were killed due to apoptosis by FA-uIONP-SN38 at the same SN38 dosages compared with uIONP-SN38 and free SN38, respectively. The delivery of this inhibitor to SKOV-3 cancer cells by FRα-targeted FA-uIONP carrier was enhanced by about 10-folds with less cytotoxicity comparing to the free drug SN38. The developed FA-uIONP-SN38 holds a great potential as a theranostic approach in treating ovarian cancer.

Exposure-response analyses of sacituzumab govitecan (SG) efficacy and safety in patients (pts) with metastatic triple-negative breast cancer (mTNBC).

1076 Background: SG is an antibody-drug conjugate composed of an anti–Trop-2 antibody coupled to the cytotoxic SN-38 payload via a proprietary, hydrolyzable linker. SG is approved for pts with mTNBC who received ≥2 prior chemotherapies (> 1 in the metastatic setting). The relationships between exposure of SG, free SN-38, and total antibody (tAB) following SG administration and its efficacy and safety outcomes were evaluated in pts with mTNBC. Methods: Available exposure efficacy and safety outcomes from the mTNBC cohort of the phase 1/2 IMMU-132-01 study (relapsed/refractory pts; n = 24) and mTNBC pts from the phase 3 ASCENT study who had received ≥2 prior therapies (> 1 in the metastatic setting; n = 253) were analyzed. Pts in IMMU-132-01 received 8 or 10 mg/kg SG and pts in ASCENT received 10 mg/kg SG on d1 and d8, of every 21d cycle. Effect of exposure on CR, ORR and the evaluated adverse events (AEs) of vomiting, diarrhea, hypersensitivity reactions, nausea, and neutropenia were analyzed using logistic (CR, ORR) or ordinal logistic (AE) regression models while OS, PFS, time to first dose reduction and time to first dose delay were analyzed using Cox PH models. Several exposure metrics related to the PK of SG, free SN-38, and tAB were evaluated as predictors of SG efficacy and safety and the most statistically significant exposure metric was retained in the model; effect of other covariates was characterized within the modeling framework. Results: Higher values of the average exposure over the treatment duration (CAVG) for SG (CAVGSG) were significantly associated with an increase in the probability of CR and ORR and higher CAVG values for tAB (CAVGtAB) were significantly associated with longer OS and PFS. The probability of Grade ≥1 evaluated AEs, the risk of dose reductions and dose delays were found to increase significantly with increasing CAVGSG. Neutropenia was the only AE where the effect of exposure was significantly associated with the probability of Grade ≥3 evaluated AEs. No statistically significant associations between exposure and the probability of Grade 4 AEs were observed for any of the evaluated endpoints. The developed models were used to estimate the efficacy and safety outcomes for the 8 mg/kg vs 10 mg/kg SG dose levels and the results indicated a more favorable risk/benefit profile for the 10 mg/kg dose level driven by the higher estimated efficacy. Baseline Trop-2 expression level was not statistically correlated with magnitude of clinical response based on the limited available Trop-2 data. Conclusions: Exposure-response relationships were observed for all evaluated efficacy and safety endpoints for SG in patients with mTNBC, and the higher efficacy (as assessed by CR, ORR, OS and PFS) achieved with the exposures associated with the 10 mg/kg SG dose regimen and its manageable safety profile support the appropriateness of the approved regimen of SG. Clinical trial information: NCT02574455, NCT01631552.

Improvements in Drug-Delivery Properties by Co-Encapsulating Curcumin in SN-38-Loaded Anticancer Polymeric Nanoparticles.

SN-38 is an immensely potent anticancer agent although its use necessitates encapsulation to overcome issues of poor solubility and stability. Since SN-38 is a notoriously challenging drug to encapsulate, new avenues to increase encapsulation efficiency in polymer nanoparticles (PNPs) are needed. In this paper, we show that nanoprecipitation with curcumin (CUR) increases SN-38 encapsulation efficiencies in coloaded SN-38/CUR-PNPs based on poly(ε-caprolactone)-block-poly(ethylene glycol) (PCL-b-PEG) by up to a factor of 10. In addition, we find a dramatic decrease in PNP polydispersities, from 0.34 to 0.07, as the initial CUR-to-polymer ratio increases from 0 to 10, with only a modest increase in PNP size (from 40 to 55 nm). Compared to coloaded PNP formation using nanoprecipitation in the bulk or in a gas-liquid, a two-phase microfluidic reactor shows similar trends with respect to CUR content, although improvements in SN-38 encapsulation efficiencies both with and without CUR are found using the microfluidic method. Additional precipitation studies without copolymer suggest that CUR increases the dispersion of SN-38 in the solvent medium of micelle formation, which may contribute to the observed encapsulation enhancement. Cytotoxicity studies of unencapsulated SN-38/CUR mixtures show that addition of CUR does not significantly affect SN-38 potency against either U87 (glioblastoma) or A204 (rhabdomyosarcoma) cell lines. However, we find significant differences in the potencies of SN-38/CUR-PNP formulations depending on initial CUR amounts, with an optimized formulation showing subnanomolar cytotoxicity against A204 cells, significantly more potent than either free SN-38 or PNPs containing only SN-38.

189P Pharmacokinetics (PK) of sacituzumab govitecan (SG) in patients (Pts) with metastatic triple-negative breast cancer (mTNBC) and other solid tumors

SG is a novel antibody-drug conjugate (ADC) composed of an anti–Trop-2 antibody coupled to SN-38 via a proprietary, hydrolyzable linker. SG is approved for pts with mTNBC who received ≥2 prior chemotherapies (>1 in the metastatic setting) and has accelerated approval for pts with metastatic urothelial cancer who received prior platinum-containing chemotherapy and a PD-1/PD-L1 inhibitor. These analyses evaluated the PK of SG, Free SN-38, and Total Antibody (tAB) with SG administration. Population PK (PopPK) models were developed using data from 529 pts across 2 clinical studies, IMMU-132-01 (phase 1/2 in pts with advanced epithelial cancers including TNBC, UC, and lung cancer; PK n=276) and ASCENT (phase 3 in pts with mTNBC who received ≥2 prior therapies (>1 in the metastatic setting); PK n=253). Pts received SG at 8 to 18 mg/kg IV (IMMU-132-01) or 10 mg/kg IV (ASCENT) on d1 and d8, of every 21d cycle. Clinically relevant covariates were evaluated to assess their impact on exposure. The PopPK models of SG and tAB were developed independently. The model of Free SN-38 was developed in a sequential manner with a first-order release of Free SN-38 (payload) from SG (the ADC). The typical parameter estimates for clearance and steady-state volume of distribution were 0.133 L/hr and 3.68 L for SG and 0.0164 L/hr and 4.26 L for tAB. Bodyweight correlated with the clearance and volume parameters of all 3 analytes, but with limited impact on the exposure with the clinical regimen. There was no model-predicted accumulation of either SG or Free SN-38 with repeated dosing. Overall, mild to moderate renal impairment, mild hepatic impairment, age, sex, baseline albumin level, race, ECOG status, tumor type, UGT1A1 genotype or Trop-2 expression did not have a clinically relevant impact on exposure of any of the evaluated analytes. The PK of SG, Free SN-38, and Total Antibody were well characterized based on a robust dataset across two large trials. The analyses supported the approved 10 mg/kg clinical regimen and did not identify a need for dose-adjustment based on any of the evaluated patient demographics or disease characteristics.

A Single Short 'Tone Burst' Results in Optimal Drug Delivery to Tumours Using Ultrasound-Triggered Therapeutic Microbubbles.

Advanced drug delivery systems, such as ultrasound-mediated drug delivery, show great promise for increasing the therapeutic index. Improvements in delivery by altering the ultrasound parameters have been studied heavily in vitro but relatively little in vivo. Here, the same therapeutic microbubble and tumour type are used to determine whether altering ultrasound parameters can improve drug delivery. Liposomes were loaded with SN38 and attached via avidin: biotin linkages to microbubbles. The whole structure was targeted to the tumour vasculature by the addition of anti-vascular endothelial growth factor receptor 2 antibodies. Tumour drug delivery and metabolism were quantified in SW480 xenografts after application of an ultrasound trigger to the tumour region. Increasing the trigger duration from 5 s to 2 min or increasing the number of 5 s triggers did not improve drug delivery, nor did changing to a chirp trigger designed to stimulate a greater proportion of the microbubble population, although this did show that the short tone trigger resulted in greater release of free SN38. Examination of ultrasound triggers in vivo to improve drug delivery is justified as there are multiple mechanisms at play that may not allow direct translation from in vitro findings. In this setting, a short tone burst gives the best ultrasound parameters for tumoural drug delivery.

SN38-based albumin-binding prodrug for efficient targeted cancer chemotherapy

Developing new therapeutic strategies that damage tumour cells without harming normal tissues is among the primary obstacles in chemotherapy. In this study, a novel β-glucuronidase-sensitive albumin-binding prodrug was designed and synthesized to selectively deliver the drug SN38 to tumour sites and maximize its efficacy. After intravenous administration, the prodrug Mal-glu-SN38 covalently bound to plasma albumin through the Michael addition, enabling it to accumulate in the tumour and release SN38 when triggered by extracellular β-glucuronidase. Compared to irinotecan, Mal-glu-SN38 displayed a slower plasma clearance and increased drug exposure over time. Moreover, Mal-glu-SN38 caused an increase in tumour-site accumulation of both the albumin-prodrug conjugate and free SN38 released from albumin conjugate when compared with irinotecan. After administration of multiple doses, Mal-glu-SN38 also significantly delayed the tumour growth, resulting in an impressive reduction or even disappearance of tumours (67% of mice cured) without causing any observable side effects.

Fabrication of supramolecular nano-assembly irinotecan prodrug into polymeric nanomaterials for delivery in cervical carcinoma therapy

GLOBOCAN estimates in 2020 on the basis of occurrence, mortality, and development for 36 distinct types of tumor cells worldwide. Chemotherapy is the most preferred treatment for carcinoma, and also for hormonal, radiation, autoimmune, and genetic disorders. We propose a straightforward and cost-effective way to overcome the myriad barriers to the therapeutic potential of irinotecan (SN-38), including the rebuilding of medicines, targeting of supramolecular nanoassemblies, and therapeutic treatments. The drug SN-38 was capable by covalent combination of lipophilic linoleic acid by the end of carboxyl group action to provide an impulsive nanoassembly to extremely stable nanomaterials (NMs). The morphology of the recently synthesized SN-38-NM was tested by electron microscopy. The anticarcinoma properties of both HeLa and CaSki (cervical carcinoma lines) of SN-38 and SN-38-NMs were evaluated after successful synthesis. Further research on mechanistic cell death pathways showed that proliferation of cervical carcinoma cell lines was correlated with cells subjected to apoptosis, including AO/EB staining, nuclear staining, and flow cytometric studies. SN-38-NMs have higher biocompatibility in conjunction with free SN-38. This report describes SN-38-NMs as a positive and secure treatment device for cervical carcinoma, which requires further clinical assessment.

Synthesis of novel polymeric nanoparticles (methoxy-polyethylene glycol-chitosan/hyaluronic acid) containing 7-ethyl-10-hydroxycamptothecin for colon cancer therapy: in vitro, ex vivo and in vivo investigation

The goal of the current study was to target 7-ethyl-10-hydroxycamptothecin (SN38) orally to colon tumours by synthesizing a targeting polymer. To achieve the optimum delivery for SN38, initially methoxy-polyethylene glycol (mPEG)-chitosan was synthesized and then nanoparticles were developed through ionic gelation between mPEG-chitosan and hyaluronic acid as a ligand for cell-surface glycoprotein CD44 receptor. The SN38 was loaded in nanoparticles (SN38-NPs) using the non-covalent physical adsorption method. The size of the optimized SN38-NPs was 226.7 nm, encapsulation efficiency was 89.23% and drug content was 7.98 ± 0.54% in the optimum formulation. The attachment of mPEG to chitosan was confirmed by proton nuclear magnetic resonance. The results of differential scanning calorimetry and Fourier transforms infra-red analysis indicated that SN38 existed in amorphous form and functional groups of SN38 protected in the formulations which could be a sign of suitable encapsulation of SN38 in SN38-NPs. In vitro study indicated that SN38-NPs were more potent against the cancer cells than free SN38. The cellular uptake of SN38-NPs improved up to 1.6-fold against human colorectal adenocarcinoma (Caco-2) cells. Moreover, SN38-NPs remarkably demonstrated superior anti-tumor efficacy in contrary to pure SN38. This suggests the advantage of SN38-NPs as a potent oral drug carrier which could be further explored for clinical investigations.

In situ activation of STING pathway with polymeric SN38 for cancer chemoimmunotherapy

STING (stimulator of interferon genes) signaling pathway has attracted considerable attention in cancer immunotherapy due to its capacity to boost vigorous antitumor immunity. However, the shortage of effective STING agonists limits the promotion of STING pathway in cancer treatment. Herein, we present an approach for in situ activation of STING pathway with nanoparticles delivered DNA-targeting chemo agents, based on the understanding that cytosol DNA is a pre-requisite for STING pathway activation. Through in vitro screening among several DNA-targeting chemo agents, we identified 7-ethyl-10-hydroxycamptothecin (SN38) as the most potent drug for stimulating interferon (IFN)-β secretion and proved that this process is mediated by the passage of DNA-containing exosomes from treated tumor cells to bone marrow-derived dendritic cells (BMDCs) and subsequent activation of the STING pathway. Furthermore, we designed a polymeric-SN38 conjugate that could self-assemble into nanoparticles (SN38-NPs) for in vivo application. The SN38-NPs formulation reduced toxicity of free SN38, effectively stimulated the activation of STING pathway in E0771 tumors, and resulted in a tumor suppression rate (TSR%) of 82.6%. Our results revealed a new mechanism of SN38 in cancer treatment and should inspire using more DNA-targeting agents, especially in nanoformulation, for activating STING pathway and cancer chemoimmunotherapy.

Injectable Reactive Oxygen Species-Responsive SN38 Prodrug Scaffold with Checkpoint Inhibitors for Combined Chemoimmunotherapy.

Chemotherapeutic agents have been widely used for cancer treatment in clinics. Aside from their direct cytotoxicity to cancer cells, some of them could activate the immune system of the host, contributing to the enhanced antitumor activity. Here, the reactive oxygen species (ROS)-responsive hydrogel, covalently cross-linked by phenylboronic acid-modified 7-ethyl-10-hydroxycamptothecin (SN38-SA-BA) with poly(vinyl alcohol) (PVA), is fabricated for topical delivery of anti-programmed cell death protein ligand 1 antibodies (aPDL1). In the presence of endogenous ROS, SN38-SA-BA will be oxidized and hydrolyzed, leading to the degradation of hydrogel and the release of initial free SN38 and encapsulated aPDL1. It is demonstrated that SN38 could elicit specific immune responses by triggering immunogenic cell death (ICD) of cancer cells, a distinct cell death pathway featured with the release of immunostimulatory damage-associated molecular patterns (DAMPs). Meanwhile, the released aPDL1 could bind to programmed cell death protein ligand 1 (PDL1) expressed on cancer cells to augment antitumor T cell responses. Thus, the ROS-responsive prodrug hydrogel loaded with aPDL1 could induce effective innate and adaptive antitumor immune responses after local injection, significantly inhibiting or even eliminating those tumors.