SN-38 In Tumors Research Articles

Translational Pharmacokinetic/Pharmacodynamic Modeling and Simulation of Oxaliplatin and Irinotecan in Colorectal Cancer.

Despite the recent advances in this field, there are limited methods for translating organoid-based study results to clinical response. The goal of this study was to develop a pharmacokinetic/pharmacodynamic (PK/PD) model to facilitate the translation, using oxaliplatin and irinotecan treatments with colorectal cancer (CRC) as examples. The PK models were developed using qualified oxaliplatin and irinotecan PK data from the literature. The PD models were developed based on antitumor efficacy data of SN-38 and oxaliplatin evaluated in vitro using tumor organoids. To predict the clinical response, translational scaling of the models was established by incorporating predicted ultrafiltration platinum in plasma or SN-38 in tumors to PD models as the driver of efficacy. The final PK/PD model can predict PK profiles and responses following treatments with oxaliplatin or irinotecan. After generation of virtual patient cohorts, this model simulated their tumor shrinkages following treatments, which were used in analyzing the efficacies of the two treatments. Consistent with the published clinical trials, the model simulation suggested similar patient responses following the treatments of oxaliplatin and irinotecan with regards to the probabilities of progression-free survival (HR = 1.05, 95%CI [0.97;1.15]) and the objective response rate (OR = 1.15, 95%CI [1.00;1.32]). This proposed translational PK/PD modeling approach provides a significant tool for predicting clinical responses of different agents, which may help decision-making in drug development and guide clinical trial design.

Two-Stage SN38 Release from a Core-Shell Nanoparticle Enhances Tumor Deposition and Antitumor Efficacy for Synergistic Combination with Immune Checkpoint Blockade.

Long-circulating nanomedicines efficiently deliver chemotherapies to tumors to reduce general toxicity. However, extended blood circulation of nanomedicines can increase drug exposure to leukocytes and lead to hematological toxicity. Here, we report a two-stage release strategy to enhance the drug deposition and antitumor efficacy of OxPt/SN38 core-shell nanoparticles with a hydrophilic oxaliplatin (OxPt) prodrug coordination polymer core and a lipid shell containing a hydrophobic cholesterol-conjugated SN38 prodrug (Chol-SN38). By conjugating cholesterol to the phenol group of SN38 via an acetal linkage and protecting the 20-hydroxy position with a trimethylsilyl (TMS) group, Chol-SN38 releases SN38 in two stages via esterase-catalyzed cleavage of the acetal linkage in the liver followed by acid-mediated hydrolysis of the TMS group to preferentially release SN38 in tumors. Compared to irinotecan, OxPt/SN38 reduces SN38 blood exposure by 9.0 times and increases SN38 tumor exposure by 4.7 times. As a result, OxPt/SN38 inhibits tumor growth on subcutaneous, spontaneous, and metastatic tumor models by causing apoptotic and immunogenic cell death. OxPt/SN38 exhibits strong synergy with the immune checkpoint blockade to regress subcutaneous colorectal and pancreatic tumors with 33-50% cure rates and greatly inhibits tumor growth and invasion in a spontaneous prostate cancer model and a liver metastasis model of colorectal cancer without causing side effects. Mechanistic studies revealed important roles of enhanced immunogenic cell death and upregulated PD-L1 expression by OxPt/SN38 in activating the tumor immune microenvironment to elicit potent antitumor immunity. This work highlights the potential of combining innovative prodrug design and nanomedicine formulation to address unmet needs in cancer therapy.

Etirinotecan pegol in women with recurrent platinum-resistant or refractory ovarian cancer

ABSTRACTIntroduction: A PEGylated form of irinotecan, a topoisomerase I inhibitor, is now available in commerce; its safety and efficacy have been tested in platinum resistant/refractory ovarian cancer (PROC) patients. This novel agent is known as Etirinotecan Pegol (EP). EP, like irinotecan, exerts its action through its principal metabolite SN-38.Areas covered: This drug evaluation article focuses on the most recent investigations and clinical progress regarding EP, a long-acting polymer conjugate of irinotecan for the treatment of PROC.Expert opinion: EP provides prolonged and continuous exposure of SN-38 in tumors, when compared to its parent drug irinotecan. Results from phase II studies are comparable in terms of efficacy to other agents of proven use in PROC. A limitation of the use of EP is the schedule-dependent toxicities (mainly diarrhea and dehydration). In the future, EP could be investigated in association with other agents, even in attempts to restore sensitivity to other treatments. PROC remains a very difficult setting and EP might be a valid agent for patients with good performance status that have exhausted therapeutic options. In such a setting, participation in clinical trials is strongly encouraged.

SN-38-Loaded PLGA microspheres injected intratumorally for cancer: preparation, characterization and evaluation

7-ethyl-10-hydroxycamptothecin (SN-38), an active metabolite with broad spectrum cytotoxic activity produced by 7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxy camptothecin (CPT-11), has been shown to be useful in the treatment of various tumors. The aim of this research was to develop SN-38 loaded PLGA microspheres (SN-38-PLGA-MS) to extend retention time of SN-38 in tumor and reduce its concentrations in plasma, thereby to improve therapeutic efficacy and reduce side effects. The SN-38-PLGA-MS was prepared by emulsion-solvent evaporation method at a molar ratio of 1:10 (SN-38: PLGA). Tumor retention and plasma leakage were assessed by measuring drug concentrations in tumor sites and plasma at different time points. The therapeutic effect of SN-38-PLGA-MS was further evaluated by pharmacodynamic studies and histological analysis. The freeze-dried microspheres can effectively prolong the retention time of SN-38 in tumor site from 144 h to 432 h, which was 3.00 times than SN-38 solution. The in vivo pharmacodynamic results revealed that SN-38-PLGA-MS significantly improved the inhibition of tumor cell growth. In summary, SN-38-PLGA-MS was proved as a promising carrier for inhibiting tumor cell proliferation, and had important clinical value in the treatment of tumors.

In vitro and in vivo evaluation of SN-38 nanocrystals with different particle sizes.

7-Ethyl-10-hydroxycamptothecin (SN-38) is a potent broad-spectrum antitumor drug derived from irinotecan hydrochloride (CPT-11). Due to its poor solubility and instability of the active lactone ring, its clinical use is significantly limited. As one of the most promising formulations for poorly water-soluble drugs, nanocrystals have attracted increasing attention. In order to solve these problems and evaluate the antitumor effect of SN-38 in vitro and in vivo, two nanocrystals with markedly different particle sizes were prepared. Dynamic light scattering and transmission electron microscopy were used to investigate the two nanocrystals. The particle sizes of SN-38 nanocrystals A (SN-38/NCs-A) and SN-38 nanocrystals B (SN-38/NCs-B) were 229.5±1.99 and 799.2±14.44 nm, respectively. X-ray powder diffraction analysis showed that the crystalline state of SN-38 did not change in the size reduction process. An accelerated dissolution velocity of SN-38 was achieved by nanocrystals, and release rate of SN-38/NCs-A was significantly faster than that of SN-38/NCs-B. Cellular uptake, cellular cytotoxicity, pharmacokinetics, animal antitumor efficacy, and tissue distribution were subsequently examined. As a result, enhanced intracellular accumulation in HT1080 cells and cytotoxicity on different tumor cells were observed for SN-38/NCs-A compared to that for SN-38/NCs-B and solution. Besides, compared to the SN-38 solution, SN-38/NCs-A had a higher bioavailability after intravenous injection; while the bioavailability of SN-38/NCs-B was even lower than that of the SN-38 solution. SN-38/NCs-A exhibited a significant inhibition of tumor growth compared to SN-38 solution and SN-38/NCs-B in vivo. The antitumor effect of SN-38/NCs-B was stronger than SN-38 solution. The tissue distribution study in tumor-bearing mice showed that nanocrystals could markedly improve the drug accumulation in tumor tissue by the enhanced permeability and retention effect compared to SN-38 solution, and the amount of SN-38 in tumors of SN-38/NCs-A group was much more than that of SN-38/NCs-B group. In conclusion, nanocrystals dramatically enhanced the anticancer efficacy of SN-38 in vitro and in vivo, and the particle size had a significant influence on the dissolution behavior, pharmacokinetic properties, and tumor inhibition of nanocrystals.

Antitumor efficacy and intratumoral distribution of SN-38 from polymeric depots in brain tumor model.

We investigate antitumor efficacy and 2D and 3D intratumoral distribution of 7-ethyl-10-hydroxycamptothecin (SN-38) from polymeric depots inside U-87MG xenograft tumor model in nude mice. Results showed that polymeric depots could be used to administer and controlled release of a large amount of SN-38 directly to the brain tumor model. SN-38 released from depots suppressed tumor growth, where the extent of suppression greatly depended on doses and the number of depot injections. Tumor suppression of SN-38 from depots was three-fold higher in animals which received double injections of depots at high dose (9.7 mg of SN-38) compared to single injection (2.2 mg). H&E staining of tumor sections showed that the area of tumor cell death/survival of the former group was two-fold higher than those of the latter group. Fluorescence imaging based on self-fluorescent property of SN-38 was used to evaluate the intratumoral distribution of this drug compared to histological results. The linear correlation between fluorescence intensity and the amount of SN-38 allowed quantitative determination of SN-38 in tumor tissues. Results clearly showed direct correlation between the amount of SN-38 in tumor sections and cancer cell death. Moreover, 3D reconstruction representing the distribution of SN-38 in tumors was obtained. Results from this study suggest the rationale for intratumoral drug administration and release of drugs inside tumor, which is necessary to design drug delivery systems with efficient antitumor activity.

Impediments to enhancement of CPT-11 anticancer activity by E. coli directed beta-glucuronidase therapy.

CPT-11 is a camptothecin analog used for the clinical treatment of colorectal adenocarcinoma. CPT-11 is converted into the therapeutic anti-cancer agent SN-38 by liver enzymes and can be further metabolized to a non-toxic glucuronide SN-38G, resulting in low SN-38 but high SN-38G concentrations in the circulation. We previously demonstrated that adenoviral expression of membrane-anchored beta-glucuronidase could promote conversion of SN-38G to SN-38 in tumors and increase the anticancer activity of CPT-11. Here, we identified impediments to effective tumor therapy with E. coli that were engineered to constitutively express highly active E. coli beta-glucuronidase intracellularly to enhance the anticancer activity of CPT-11. The engineered bacteria, E. coli (lux/βG), could hydrolyze SN-38G to SN-38, increased the sensitivity of cultured tumor cells to SN-38G by about 100 fold and selectively accumulated in tumors. However, E. coli (lux/βG) did not more effectively increase CPT-11 anticancer activity in human tumor xenografts as compared to non-engineered E. coli. SN-38G conversion to SN-38 by E. coli (lux/βG) appeared to be limited by slow uptake into bacteria as well as by segregation of E. coli in necrotic regions of tumors that may be relatively inaccessible to systemically-administered drug molecules. Studies using a fluorescent glucuronide probe showed that significantly greater glucuronide hydrolysis could be achieved in mice pretreated with E. coli (lux/βG) by direct intratumoral injection of the glucuronide probe or by intratumoral lysis of bacteria to release intracellular beta-glucuronidase. Our study suggests that the distribution of beta-glucuronidase, and possibly other therapeutic proteins, in the tumor microenvironment might be an important barrier for effective bacterial-based tumor therapy. Expression of secreted therapeutic proteins or induction of therapeutic protein release from bacteria might therefore be a promising strategy to enhance anti-tumor activity.

Preclinical activity of nanoliposomal irinotecan is governed by tumor deposition and intratumor prodrug conversion.

A major challenge in the clinical use of cytotoxic chemotherapeutics is maximizing efficacy in tumors while sparing normal tissue. Irinotecan is used for colorectal cancer treatment but the extent of its use is limited by toxic side effects. Liposomal delivery systems offer tools to modify pharmacokinetic and safety profiles of cytotoxic drugs. In this study, we defined parameters that maximize the antitumor activity of a nanoliposomal formulation of irinotecan (nal-IRI). In a mouse xenograft model of human colon carcinoma, nal-IRI dosing could achieve higher intratumoral levels of the prodrug irinotecan and its active metabolite SN-38 compared with free irinotecan. For example, nal-IRI administered at doses 5-fold lower than free irinotecan achieved similar intratumoral exposure of SN-38 but with superior antitumor activity. Tumor response and pharmacokinetic modeling identified the duration for which concentrations of SN-38 persisted above a critical intratumoral threshold of 120 nmol/L as determinant for antitumor activity. We identified tumor permeability and carboxylesterase activity needed for prodrug activation as critical factors in achieving longer duration of SN-38 in tumors. Simulations varying tumor permeability and carboxylesterase activity predicted a concave increase in tumor SN-38 duration, which was confirmed experimentally in 13 tumor xenograft models. Tumors in which higher SN-38 duration was achieved displayed more robust growth inhibition compared with tumors with lower SN-38 duration, confirming the importance of this factor in drug response. Overall, our work shows how liposomal encapsulation of irinotecan can safely improve its antitumor activity in preclinical models by enhancing accumulation of its active metabolite within the tumor microenvironment.

Abstract 2509: Hsp90-inhibitor drug conjugates (HDC): Novel tumor-selective drug delivery platform with unprecedented anticancer activity

Abstract Background: Various strategies have been used to make chemotherapeutic compounds more tumor selective in order to increase their safety and efficacy, but they were met with only limited success. Antibody Drug Conjugates (ADCs) and folate receptor mediated drug delivery (FRDC) are the emerging concepts in the drug delivery field, but they are limited to high potent toxins and narrow sets of indications. We established a novel tumor-directed drug delivery platform technology based on the unique property of Hsp90 inhibitors. One prominent feature of Hsp90 inhibitors is their ability to be retained selectively in tumor cells for a prolonged period of time. The difference in residency time in tumor against plasma and normal tissues is 10-25 fold. Moreover, the chaperone protein Hsp90 is overexpressed 2-3 fold in tumor compared to normal tissues. Combining the overexpression Hsp90 and longer residency of its inhibitors in tumor, a strategy to link anticancer drugs to an Hsp90 inhibitor, where the attached “payload” is released in the tumor selectively for prolonged periods, was conceived. Results: Though the HDC concept is applicable to most small molecule anticancer drugs, we chose a common topoisomerase-1 inhibitor (SN-38) for proof-of-concept studies. More than 100 Hsp90 inhibitor/SN38 conjugates were synthesized; we chose STA-12-8666 as our lead molecule based on its in vitro and in vivo pharmacokinetic properties. The conjugate binds strongly to Hsp90 as determined by client protein degradation assays and has good stability in plasma of several species (human>rat>mouse). In xenograft tumor tissue distribution studies, we demonstrate that mice dosed once weekly with 50 mg/kg STA-12-8666 clear the parental HDC and its cleavage products, SN-38 and the Hsp90 inhibitor, from plasma and normal tissue within 24 hr. However, we detected 0.6 µM and 0.3 µM SN-38 in tumor at 24h and 48h, respectively. SN-38 was not detected in tumor at 24h or 48h with an equivalent dose of the SN-38 prodrug, irinotecan. Xenograft studies using multiple cell lines demonstrated superior efficacy for STA-12-8666 compared to irinotecan. For example, in MCF-7 breast cancer xenografts, STA-12-8666 produced 70% regression in tumor volume compared to moderate tumor growth inhibition by irinotecan with no regression. Similar results were observed in in colon, SCLC, ovarian, bladder, NSCLC, melanoma models. Preliminary toxicological evaluation of STA-12-8666 resulted in better or comparable toxicities to that of irinotecan. Conclusion: We designed a novel tumor-directed drug delivery platform by conjugating previously validated small molecule chemotherapeutics to HSP90 inhibitors. Our lead candidate STA-12-8666, has great tissue distribution profile, superior in vivo antitumor activity and better safety profile than the active control irinotecan, warranting its clinical evaluation. Citation Format: Dinesh Chimmanamada, David Proia, Takayo Inoue, Luisa Shin Ogawa, Suqin He, Manuel Sequeira, Donald Smith, John-Paul Jimenez, Chaohua Zhang, Jim Sang, Jaime Acquaviva, Masazumi Nagai, Yuan Liu, Josephine Ye, Dan Zhou, Andrew Sonderfan, Ritu Singh, Noriaki Tatsuta, Teresa Przewloka, Jun Jiang, Junyi Zhang, Weiwen Ying. Hsp90-inhibitor drug conjugates (HDC): Novel tumor-selective drug delivery platform with unprecedented anticancer activity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2509. doi:10.1158/1538-7445.AM2014-2509

HPLC analysis and extraction method of SN-38 in brain tumor model after injected by polymeric drug delivery system.

SN-38 is a highly potent anticancer drug but its poor solubility in aqueous solvent and adverse side effects limit clinical applications. To overcome these limitations, SN-38-loaded-injectable drug delivery depots have been intratumorally administered in xenograft tumor model in nude mice. The extraction and high performance liquid chromatography (HPLC) were performed in order to determine the amount of SN-38 inside tumors. SN-38 was extracted from tumors using DMSO. HPLC analysis was validated and resulted in linearity over the concentration range from 0.03 to 150 µg/mL (r(2) ≥ 0.998). Lower limit of detection (LLOD) and lower limit of quantitation (LLOQ) were 0.308 µg/mL and 1.02 µg/mL, respectively. The extraction efficiency (% recovery) of SN-38 in porcine tissues was similar to that of tumors which provided more than 90% recovery in all concentrations. Moreover, the variability of precision and accuracy within and between-day were less than 15%. Therefore, this extraction and HPLC protocol was applied to determine the amount of SN-38 in tumors. Results show higher remaining amount of SN-38 in tumor from SN-38-loaded polymeric depots than that of SN-38 solution. These results reveal that SN-38-loaded polymeric depots can prevent the leakage of free-drug out of tumors and can sustain higher level of SN-38 inside tumor. Thus, the therapeutic efficacy can be elevated by SN-38-loaded polymeric depots.

Local enzymatic hydrolysis of an endogenously generated metabolite can enhance CPT-11 anticancer efficacy

Irinotecan (CPT-11) is a clinically important anticancer prodrug that requires enzymatic hydrolysis by carboxyesterase to generate the active metabolite SN-38. However, SN-38 is further metabolized to inactive SN-38 glucuronide (SN-38G), thus diminishing the levels of active SN-38. Although exogenously administered glucuronide drugs are being investigated for cancer therapy, it is unknown if endogenously generated camptothecin glucuronide metabolites can be used for tumor therapy. Here, we tested the hypothesis that tumor-located hydrolysis of endogenously generated SN-38G can enhance the antitumor efficacy of CPT-11 therapy. EJ human bladder carcinoma cells expressing membrane-tethered beta-glucuronidase (EJ/mbetaG cells) were used to selectively hydrolyze SN-38G to SN-38. Parental EJ and EJ/mbetaG cells displayed similar in vitro and in vivo growth rates and sensitivities to CPT-11 and SN-38. By contrast, EJ/mbetaG cells were more than 30 times more sensitive than EJ cells to SN-38G, showing that SN-38 could be generated from SN-38G in vitro. Systemic administration of CPT-11 resulted in tumor-located hydrolysis of SN-38G and accumulation of SN-38 in EJ/mbetaG subcutaneous tumors. Importantly, systemic administration of CPT-11, which itself is not a substrate for beta-glucuronidase, dramatically delayed the growth of EJ/mbetaG xenografts without increased systemic toxicity. Thus, the anticancer activity of CPT-11 can be significantly enhanced by converting the relatively high levels of endogenously generated SN-38G to SN-38 in tumors. The high concentrations of SN-38G found in the serum of patients treated with CPT-11 suggest that clinical response to CPT-11 may be improved by elevating beta-glucuronidase activity in tumors.