Homologous recombination is a highly conserved determinant of the synergistic cytotoxicity between cisplatin and DNA topoisomerase I poisons

Spatiotemporal Concurrent Liberation of Cytotoxins from Dual-Prodrug Nanomedicine for Synergistic Antitumor Therapy

Nanomedicine developed to date by means of directly encapsulating cytotoxins suffers from crucial drawbacks, including premature release and detoxification prior to arrival at pharmaceutics targets. To these respects, redox-responsive polymeric prodrugs of platinum (Pt) and camptothecin (CPT), selectively and concomitantly activated in the cytoplasm, were elaborated in manufacture of dual prodrug nanomedicine. Herein, multiple CPTs were conjugated to poly(lysine) (PLys) segments of block copolymeric poly(ethylene glycol) (PEG)-PLys through the redox responsive disulfide linkage [PEG-PLys(ss-CPT)] followed by reversible conversion of amino groups from PLys into carboxyl groups based on their reaction with cis-aconitic anhydride [PEG-PLys(ss-CPT&CAA)]. On the other hand, Pt(IV) in conjugation with dendritic polyamindoamine [(G3-PAMAM-Pt(IV)] was synthesized for electrostatic complexation with PEG-PLys(ss-CPT&CAA) into dual prodrug nanomedicine. Subsequent investigations proved that the elaborated nanomedicine could sequentially respond to intracellular chemical potentials to overcome a string of predefined biological barriers and facilitate intracellular trafficking. Notably, PEG-PLys(ss-CPT&CAA) capable of responding to the acidic endosomal microenvironment for transformation into endosome-disruptive PEG-PLys(ss-CPT), as well as release of G3-PAMAM-Pt(IV) from nanomedicine, prompted transclocation of therapeutic payloads from endosomes into cytosols. Moreover, concurrent activation and liberation of cytotoxic CPT and Pt(II) owing to their facile responsiveness to the cytoplasmic reducing microenvironment have demonstrated overwhelming cytotoxic potencies. Eventually, systemic administration of the dual prodrug construct exerted potent tumor suppression efficacy in treatment of intractable solid breast adenocarcinoma, as well as an appreciable safety profile. The present study illustrated the first example of nanomedicine with a dual prodrug motif, precisely and concomitantly activated by the same subcellular stimuli before approaching pharmaceutic action targets, thus shedding important implication in development of advanced nanomedicine to seek maximized pharmaceutic outcomes.

Combination of baicalein and 10-hydroxy camptothecin exerts remarkable synergetic anti-cancer effects

BACKGROUND

10-Hydroxy camptothecin (HCPT), a naturally occurring alkaloid, is a clinical drug for cancer chemotherapy. Baicalein (BA) is a flavonoid extracted from the root of Scutellaria baicalensis. The synergistic anti-cancer effect of BA and HCPT has not been reported.

PURPOSE

To explore whether and how BA enhances the anti-cancer effect of HCPT in BGC823 cells.

METHODS

Cell viability was measured by MTT assay. Apoptosis and cell cycle were analyzed through flow cytometry and western blotting analysis. DNA damage was determined by a comet assay. The activity of topoisomerase I (Topo I) was detected by the plasmid DNA relaxation assay. The synergistic anti-cancer effect of BA and HCPT in vivo was tested by BGC823 xenografted tumor model.

RESULTS

BA at non-toxic doses prominently enhanced the anti-cancer activities of HCPT in BGC823, MCF7 and SMMC7721 cells. Combination treatment of BA and HCPT induced BGC823 cells apoptosis mainly via intrinsic rather than extrinsic pathways, and preferentially arresting cell cycle in G1 and G2 phases with the aid of p21. Of note, p53, the upstream regulator of cell apoptosis and cycle, was increased by 5 folds in combination group. It helped to further trigger DNA damage and inhibit Topo I catalytic activity after combination treatment of BA and HCPT. Moreover, the BGC823 xenografted tumor growth rate in nude mice was repressed in a greater degree (P< 0.01) in the combinational group than the single-drug group.

CONCLUSION

HCPT and BA, a new and effective combination therapy, synergistically target Topo I and up-regulate p53 to induce cell apoptosis and cell cycle arrest.

Phase I pharmacokinetic and pharmacodynamic study of Carboplatin and topotecan administered intravenously every 28 days to patients with malignant solid tumors

PURPOSE

Preclinical studies have shown that the combination of topotecan and carboplatin is synergistic. To evaluate the schedule dependency of this interaction, the following phase I trial was designed to determine the safety and maximum tolerated dose (MTD), pharmacokinetics, and pharmacodynamics of carboplatin and topotecan in patients with malignant solid tumors.

EXPERIMENTAL DESIGN

In part 1, patients received carboplatin on day 1 and topotecan on days 1, 2, and 3 (C-->T schedule). In part 2, topotecan was administered on days 1, 2, and 3, followed by carboplatin on day 3 (T-->C schedule). Pharmacokinetics were determined in plasma and DNA topoisomerase I catalytic activity and Pt-DNA adducts in WBC and tumor tissue.

RESULTS

Forty-one patients were included. Dose-limiting toxicities during the C-->T schedule were grade 4 thrombocytopenia and febrile neutropenia (MTD: carboplatin target area under the free carboplatin plasma concentration versus time curve, 4 min mg/mL; topotecan, 0.5 mg/m(2)/d). Dose-limiting toxicities during the T-->C schedule included grade 4 neutropenia, thrombocytopenia, neutropenic fever, and grade 4 nausea and vomiting (MTD: carboplatin target area under the free carboplatin plasma concentration versus time curve, 6 min mg/mL; topotecan, 0.9 mg/m(2)/d). One complete response and five partial responses were observed. The clearance of and exposure to carboplatin and topotecan did not depend on the sequence of drug administration. No schedule-dependent effects were seen in Pt-DNA levels and DNA topoisomerase I catalytic activity in WBC and tumor tissue. However, myelotoxicity was clearly more evident in the C-->T schedule.

CONCLUSION

The T-->C schedule was better tolerated because both hematologic and nonhematologic toxicities were milder. Other pharmacodynamic factors than the ones investigated must explain the schedule-dependent differences in toxicities.

A novel Rad18 function involved in protection of the vertebrate genome after exposure to camptothecin

In Saccharomyces cerevisiae, Rad18 functions in post-replication repair pathways, such as error-free damage bypass involving Rad30 (Poleta) and error-prone damage bypass involving Rev3/7 (Polzeta). Chicken DT40 RAD18(-/-) cells were found to be hypersensitive to camptothecin (CPT), while RAD30(-/-) and REV3(-/-) cells, which are defective in translesion DNA synthesis, were not. RAD18(-/-) cells also showed higher levels of H2AX phosphorylation and chromosomal aberrations, particularly chromosomal gaps and breaks, upon exposure to CPT. Detailed analysis by alkaline sucrose density gradient centrifugation revealed that RAD18(-/-) and wild type cells exhibited similar rates of elongation of newly synthesized DNA in the presence or absence of low concentrations of CPT but that DNA breaks frequently occurred on both parental and nascent strands within 1h after a brief exposure to an elevated concentration of CPT, with more breaks induced in RAD18(-/-) cells than in wild type cells. These data suggest a previously unanticipated role for Rad18 in dealing with replication forks upon encountering DNA lesions induced by CPT.

Phase I and Pharmacologic Study of Infusional Topotecan and Carboplatin in Relapsed and Refractory Acute Leukemia

PURPOSE

To assess the maximum tolerated dose, toxicities, pharmacokinetics, and antileukemic activity of topotecan and carboplatin in adults with recurrent or refractory acute leukemias.

EXPERIMENTAL DESIGN

Patients received topotecan and carboplatin by 5-day continuous infusion at nine dose levels. Patients achieving a complete remission received up to two additional courses for consolidation. Plasma topotecan and ultrafilterable platinum were assayed on days 1 to 5. In addition, pretreatment levels of various polypeptides in leukemic cells were examined by immunoblotting to assess possible correlations with response.

RESULTS

Fifty-one patients received a total of 69 courses of therapy. Dose-limiting toxicity consisted of grade 4/5 typhlitis and grade 3/4 mucositis after one course of therapy or grade 4 neutropenia and thrombocytopenia lasting >50 days when a second course was administered on day 21. Among 45 evaluable patients, there were 7 complete remissions, 2 partial remissions, 1 incomplete complete remission, and 1 reversion to chronic-phase chronic myelogenous leukemia. Topotecan steady-state plasma concentrations increased with dose. No accumulation of topotecan or ultrafilterable platinum occurred between days 1 and 5 of therapy. Leukemic cell levels of topoisomerase I, checkpoint kinase 1, checkpoint kinase 2, and Mcl-1 correlated with proliferating cell nuclear antigen but not with response. In contrast, low Bcl-2 expression correlated with response (P = 0.014, Mann-Whitney U test).

CONCLUSIONS

The maximum tolerated dose was 1.6 mg/m(2)/d topotecan plus 150 mg/m(2)/d carboplatin. The complete remission rate in a heavily pretreated population was 16% (33% at the highest three dose levels). Responses seem to correlate with low pretreatment blast cell Bcl-2 expression.