Camptothecin-resistant Cell Lines Research Articles

Phase I study of indenoisoquinolines LMP776 in adults with relapsed solid tumors and lymphomas.

2558 Background: Indenoisoquinolines (ID) are non-camptothecin inhibitors of topoisomerase (TOP1) identified following a COMPARE analysis of the National Cancer Institute’s (NCI) in vitro anticancer drug discovery screen. IDs have improved characteristics over camptothecin top1 inhibitors, with better chemical stability (lacking the labile hydroxylactone E-ring) producing stable DNA breaks that are resistant to reversal of the trapped DNA-TOP1 cleavage complex and at different DNA sequence sites to camptothecins (Kohlhagen et al. Mol Pharmacol. 2005). IDs have shown more activity against camptothecin-resistant cell lines and mouse models, as well as in cells overexpressing the ATP-binding cassette (ABC) transporters, and multidrug resistance (MDR-1/ABCB1) genes. A parallel first-in-human Phase I study conducted at the NCI of LMP400 in patients with refractory solid tumors and lymphomas showed this molecule to be well tolerated (Kummar et al, Cancer Chemother Pharmacol. 2016). A trial of LMP776 (NSC725776), has completed accrual. Primary Objectives: define the maximum tolerated dose (MTD) of LMP776 and the dose-limiting toxicities (DLTs). Methods: Phase I trial using Design 4 of the Simon accelerated titration designs (Simon et al. JNCI, 1997), with doses escalated based on toxicity during cycle 1. LMP776 was administered via central line QD over 1 hour on days 1–5 q 28-days. Response is defined by RECIST 1.1 on CT. Results: 32 of 34 patients (pts) were evaluable for toxicity and response. Enrollment was expanded at dose level (DL) 2 to 6 pts due to a hypocalcemia DLT, with subsequent enrollment on a 3+3 design. MTD was established at DL7 (12mg/m2, DLT myelosuppression). Common Grade 3/4 adverse events by CTCAE v.4 included anemia (5 pts, 15%), thrombocytopenia (5), lymphopenia (5) and neutropenia (3 pts, 9%). 12 (37%) pts experienced stable disease (SD), with a median of 4 cycles of treatment (range 2-9). 10 (30%) pts with SD remained on study for ≥4 months, with 4 pts on study ≥6 months. Conclusions: LMP776 is overall well tolerated. Explorative correlatives and additional trials are being considered. Clinical trial information: NCT01051635.

MicroRNA global expression analysis and genomic profiling of the camptothecin-resistant T-ALL derived cell line CPT-K5

The clinical use of the camptothecin (CPT) derivatives, topotecan and irinotecan, has had a significant impact on cancer therapy. However, acquired clinical resistance to these drugs is common, which greatly hampers their clinical efficacy. MicroRNAs (miRNAs) is an exciting novel class of endogenous non-coding RNAs that negatively regulate gene expression of up to 50% of the protein-coding genes at the post-translational level. Abnormal expression of miRNAs is associated with pathogenesis of cancer and is also implicated in anticancer drug resistance phenotypes. We used global expression analysis to examine for differential miRNA expression between the camptothecin-resistant cell line CPT-K5 and its parental CPT-sensitive RPMI-8402. In the CPT-K5 cell line 18 miRNAs were deregulated. Fifteen of these were down-regulated and three were up-regulated. The miRNA-193a-3p, miR-130a-3p, and miR-29c-3p were the most down-regulated miRNAs at 205.9-fold, 33.9-fold and 5.5-fold, respectively, while the miRNA let-7i-5p was the most up-regulated at 3.9-fold. We used subtraction BAC-based array CGH analysis to examine for genomic copy number changes. Only for the three most down-regulated miRNAs a positive correlation was found with genomic loss of their chromosomal regions in which they are encoded. Potential functional targets of the differentially expressed miRNAs were examined by searching the miRBase and miRTarBase databases. Recurrent KEGG pathways that theoretically could be affected by the deregulated miRNAs are lysine degradation, cell cycle, PI3K-Akt-, ERbB- and p53- signaling pathways. We show that the intracellular levels of several miRNAs are significantly deregulated upon acquisition of CPT resistance in the T-ALL derived cell line CPT-K5, and that genomic copy number changes is not a major cause of deregulation. In addition, the most deregulated miRNAs in our study have previously been described to be involved in various types of chemotherapeutic resistance, including the chemotherapeutics CPT, gefitinib and cisplatin in other cancer and cell types. Our study adds to the current knowledge of the mechanisms of acquired CPT resistance. Specific miRNAs may prove to be future targets to reverse or inhibit development of CPT resistance thereby providing means for a more effective treatment.

Abstract 4461: MPT0B098, a novel microtubule inhibitor, displays potent anti-angiogenic activity via destabilizing hypoxia-inducible factor-1alpha mRNA

Abstract Identification of a single agent that is able to target tumor cells, rapidly destroy tumor vasculature and inhibit angiogenesis could be an ideal approach for targeting solid tumors. We recently discover a novel sulfonamide compound, 7-aryl-indoline-1-benzene-sulfonamide (MPT0B098), as a potent microtubule inhibitor through binding to the colchicine binding site of tubulin. MPT0B098 is active against various human cancer cell growth with IC50 values ranged from 70-300 nM. Notably, HUVEC cells exhibit less susceptibility to the inhibitory effect of MPT0B098 with an IC50 of 510 nM. In addition, MPT0B098 exhibits no cross resistance with vincristine, paclitaxel, etoposide and camptothecin-resistant cell lines. Interestingly, MPT0B098 is still active toward cells (KB L30) with beta1-tubulin mutation. MPT0B098 arrests cells in G2/M phase and subsequently induces cell apoptosis through the caspase-dependent apoptotic pathway. In addition, using sub-lethal dose, MPT0B098 effectively suppressed to the tube formation and migration of HUVECs induced by VEGF. The expression levels of HIF-1alpha and VEGF were significantly inhibited in a concentration-dependent manner by MPT0B098 under hypoxic condition. Furthermore, HIF-1alpha-regulated genes, including cathepsin D, PDGF, VEGF, and VHL, were found to be down-regulated by MPT0B098 in A549 cells. Moreover, the decrease of the amount of HuR, a HIF-1alpha mRNA stability protein, translocated from nuclear to cytoplasm and suppression of AKT activity were coincided with decreased amount of HIF-1alpha mRNA by MPT0B098 treatment under hypoxia condition. MPT0B098 significantly suppressed tumor growth and microvessel density of tumor in H460 and KB-Vin10 xenografted mouse model. Taken together, our results indicate that MPT0B098 is a promising anticancer drug with potential for the treatment of human malignancies. (The study was supported by grants of DOH99-TD-C-111-004 from Department of Health and CA-099-PP-02 from National Health Research Institutes, Taiwan, R.O.C.) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4461. doi:10.1158/1538-7445.AM2011-4461

Sequence‐specific targeting of IGF‐I and IGF‐IR genes by camptothecins

We and others have clearly demonstrated that a topoisomerase I (Top1) inhibitor, such as camptothecin (CPT), coupled to a triplex-forming oligonucleotide (TFO) through a suitable linker can be used to cause site-specific cleavage of the targeted DNA sequence in in vitro models. Here we evaluated whether these molecular tools induce sequence-specific DNA damage in a genome context. We targeted the insulin-like growth factor (IGF)-I axis and in particular promoter 1 of IGF-I and intron 2 of type 1 insulin-like growth factor receptor (IGF-IR) in cancer cells. The IGF axis molecules represent important targets for anticancer strategies, because of their central role in oncogenic maintenance and metastasis processes. We chemically attached 2 CPT derivatives to 2 TFOs. Both conjugates efficiently blocked gene expression in cells, reducing the quantity of mRNA transcribed by 70-80%, as measured by quantitative RT-PCR. We confirmed that the inhibitory mechanism of these TFO conjugates was mediated by Top1-induced cleavage through the use of RNA interference experiments and a camptothecin-resistant cell line. In addition, induction of phospho-H2AX foci supports the DNA-damaging activity of TFO-CPT conjugates at specific sites. The evaluated conjugates induce a specific DNA damage at the target gene mediated by Top1.

DNA Repair Enzyme,O6-Methylguanine DNA Methyltransferase, Modulates Cytotoxicity of Camptothecin-Derived Topoisomerase I Inhibitors

Two camptothecin-resistant cell lines, CPT30 and KB100, were established and characterized previously in our laboratory. Because enhanced sensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and decreased expression of O(6)-methylguanine-DNA methyltransferase (MGMT) protein were observed in these lines, we hypothesized that MGMT may be a determinant of cytotoxicity associated with camptothecin-derived DNA topoisomerase I inhibitors (CPTs). We used the Tet-On system to induce expression of MGMT in Chinese hamster ovary (CHO) cells and RNA interference to knock down MGMT expression in human nasopharyngeal carcinoma HONE-1 cells in order to identify any correlations between MGMT expression and CPTs cytotoxicity. CHO-derived Tet-On-inducible cells (S12+) showed MGMT overexpression and statistically significant more resistance to BCNU, camptothecin, 7-ethyl-10-hydrocamptothecin (SN38), and topotecan than parental CHO cells (p < 0.05), but there was less resistance to CPTs than to BCNU. Knockdown of MGMT expression with small interfering RNA in HONE-1 cells conferred increased sensitivity to BCNU and CPTs compared with mock control. Furthermore, alteration of MGMT expression coincides with CPT-induced cell death and poly(ADP-ribose) polymerase cleavage. There were no differences in protein levels and catalytic activity of topoisomerase I between MGMT-proficient and MGMT-deficient cells from the Tet-On-inducible and small interfering RNA (siRNA) systems. Resistance to CPTs coincided with decreased amounts of protein-linked DNA breaks generated by CPTs in MGMT-proficient cells and vice versa in MGMT-deficient cells. Our data indicate that MGMT can modulate cytotoxicity of CPT-derived topoisomerase I inhibitors.

Cellular Topoisomerase I Inhibition and Antiproliferative Activity by MJ-III-65 (NSC 706744), an Indenoisoquinoline Topoisomerase I Poison

To overcome camptothecin's (CPT) lactone instability, reversibility of the drug-target interaction, and drug resistance, attempts to synthesize compounds that are CPT-like in their specificity and potency yet display a unique profile have been underway. In this pursuit, we have identified one of the idenoisoquinoline derivatives, MJ-III-65 (NSC 706744; 6-[3-(2-hydroxyethyl)amino-1-propyl]-5,6-dihydro-2,3-dimethoxy-8,9-methylenedioxy-5,11-dioxo-11H-indeno[1,2-c]isoquinoline) with both similarities and differences from CPT. MJ-III-65 traps topoisomerase I (Top1) reversibly like CPT but with different DNA sequence preferences. Consistent with Top1 poisoning, protein-linked DNA breaks were detected in cells treated with MJ-III-65 at nanomolar concentrations. These MJ-III-65-induced protein-linked DNA breaks were resistant to reversal after an hour of drug removal, compared with CPT, which completely reversed. Studies in human cells in culture found MJ-III-65 to be cytotoxic. Furthermore, limited cross-resistance was observed in camptothecin-resistant cell lines. MJ-III-65 also exhibits antitumor activity in mouse tumor xenografts.

Topoisomerase I-mediated inhibition of hypoxia-inducible factor 1: mechanism and therapeutic implications.

We have shown previously that the camptothecin analogue topotecan (TPT), a topoisomerase I (Top 1) poison, inhibits hypoxia-inducible factor 1 (HIF-1) transcriptional activity and HIF-1alpha protein accumulation in hypoxia-treated U251 human glioma cells. In this article, we demonstrate that TPT does not affect HIF-1alpha protein accumulation but inhibits its translation. In addition, we demonstrate that Top 1 is required for the inhibition of HIF-1alpha protein accumulation by TPT as shown by experiments performed using camptothecin-resistant cell lines with known Top 1 alterations. Experiments performed with aphidicolin indicated that TPT inhibited HIF-1alpha protein accumulation in the absence of DNA replication. DNA-damaging agents, such as ionizing radiation and doxorubicin, did not affect HIF-1alpha protein accumulation. Ongoing transcription was essential for the inhibition of HIF-1alpha protein accumulation by TPT. Our results demonstrate the existence of a novel pathway connecting Top 1-dependent signaling events and the regulation of HIF-1alpha protein expression and function. In addition, our findings dissociate the cytotoxic activity of TPT from the inhibition of the HIF-1 pathway and raise the possibility of novel clinical applications of TPT aimed at targeting HIF-1-dependent responses.

Substituted dibenzo[c,h]cinnolines: topoisomerase I-targeting anticancer agents

Several substituted dibenzo[c,h]cinnolines were synthesized and evaluated for their potential to target topoisomerase I and for their relative cytotoxic activity. Select benzo[i]phenanthridines are capable of stabilizing the cleavable complex formed with topoisomerase I and DNA. This study was initiated to examine whether dibenzo[c,h]cinnolines, which are in essence aza analogues of benzo[i]phenanthridines, possess similar pharmacological properties. 2,3-Dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine is one of the more potent benzo[i]phenanthridine derivatives in regard to topoisomerase I-targeting activity and cytotoxicity. The structure–activity relationship observed with these substituted dibenzo[c,h]cinnolines parallels that observed for benzo[i]phenanthridine derivatives. Compared to similarly substituted benzo[i]phenanthridines, the dibenzo[c,h]cinnoline analogues exhibit more potent topoisomerase I-targeting activity and cytotoxicity. The relative IC50 values obtained in assessing the cytotoxicity of 2,3-dimethoxy-8,9-methylenedioxydibenzo[c,h]cinnoline and 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine in the human lymphoblastma cell line, RPMI8402, are 70 and 400 nM, respectively. In tumor cell lines selected for resistance to camptothecin and known to express mutant topoisomerase I, benzo[i]phenanthridine derivatives were not cross-resistant. In contrast, similarly substituted dibenzo[c,h]cinnolines with significant topoisomerase I-targeting activity did exhibit cross-resistance in these camptothecin-resistant cell lines. The cytotoxicity of these dibenzo[c,h]cinnolines was not diminished in cells overexpressing the efflux transporter, MDR1. These data indicate that substituted dibenzo[c,h]cinnolines can exhibit potent topoisomerase I-targeting activity and are capable of overcoming the multi-drug resistance associated with this efflux transporter.

2″-Substituted 5-phenylterbenzimidazoles as topoisomerase I poisons

5-Phenylterbenzimidazole (1) is active as a topoisomerase I poison (topo I) and is cytotoxic to human tumor cells. No cross-resistance was observed for 1 when it was evaluated against the camptothecin-resistant cell line, CPT-K5. Derivatives of 1 substituted at the 2″-position, however, did exhibit cross-resistance to this cell line. The basis for the resistance of this cell line towards CPT is that it possesses a mutant form of topo I. These results suggest that substituents at the 2″-position may be in proximity to the wild-type enzyme. Therefore, we hypothesized that terbenzimidazoles with 2″-substituents could be capable of interacting with the enzyme and thereby influence activity within this class of topo I poisons. 5-Phenylterbenzimidazoles with a hydroxy, hydroxymethyl, mercapto, amino, N-benzoylaminomethyl, chloro, and trifluoromethyl group at the 2″-position were synthesized. In addition, several 2″-ethyl-5-phenylterbenzimidazoles were prepared containing either a methoxy, hydroxy, amino, or N-acetylamino group at the 2-position of the ethyl side-chain. These 2″-substituted 5-phenylterbenzimidazoles were evaluated as topo I poisons and for cytotoxic activity. The presence of a strong electron-withdrawing group at the 2″-position, such as a chloro or trifluoromethyl group, did enhance both topo I poisoning activity and cytotoxicity. Studies on the relative DNA binding affinity of 1 to its 2″-amino and 2″-trifluoromethyl derivatives did exhibit a correlation with their relative differences in biological activity.

Mechanism of action of the dual topoisomerase-I and -II inhibitor TAS-103 and activity against (multi)drug resistant cells

TAS-103 is a recently developed dual inhibitor of topoisomerase-I (topo-I) and topoisomerase-II (topoII). TAS-103 has documented cytotoxicity in vitro and antitumor activity against a variety of mouse, rat, and human xenografts in vivo. To determine TAS-103 activity against (multi)drug resistant cells in vitro and to delineate its mechanism of action. TAS-103 was evaluated for activity against three human multidrug-resistant cell lines representing resistance mediated by P-glycoprotein (Pgp)-, multidrug resistance protein (MRP), and lung resistance protein (LRP) as well as one camptothecin-resistant cell line associated with a mutated topo-I enzyme. Drug sensitivity following short (2 h), intermediate (6-8 h) and long term (24 h) exposures were compared. The mechanism of action was studied by evaluating inhibition of topoisomerase-I and -II specific DNA relaxation assays, drug-induced DNA/protein cross-link formation, and competitive DNA intercalation with ethidium bromide. Increasing the exposure time only modestly potentiated TAS-103 cytotoxicity (3-5 fold) demonstrating a lack of strong exposure duration dependency. TAS-103 cytotoxicity was not affected by the presence of any of the drug resistance mechanisms studied. TAS-103 inhibits topo-I and -II activity in DNA relaxation assays, but in our assay system TAS-103 was found to have only a weak ability to induce DNA-protein crosslinks. DNA migration patterns in agarose gel electrophoresis indicate that TAS-103 can interact directly with DNA. Also its ability to displace ethidium bromide which has intercalated into the DNA provides an indication on the nature of drug-DNA interaction. TAS-103 cytotoxicity is not affected by the presence of Pgp, MRP, LRP or mutations in the CAM binding region of the topo-I enzyme and its growth-inhibitory effect appears to be weakly dependent on exposure duration. The presented evidence suggest that the inhibitory effects of TAS-103 on topo-I and -II may in part be related to its DNA binding rather than primarily through stabilization of topo-I or -II intermediates with DNA through specific binding to the enzymes.

Induction of cleavage in topoisomerase I c-DNA by topoisomerase I enzymes from calf thymus and wheat germ in the presence and absence of camptothecin.

In this study, we further examined the sequence selectivity of camptothecin in mammalian topoisomerase I cDNA from human and Chinese hamster. In the absence of camptothecin, almost all the bases at the 3'-terminus of cleavage sites are T for calf thymus and wheat germ topoisomerase I. In addition, wheat germ topoisomerase I exhibits preference for C (or not T) at -3 and for T at -2 position. As for camptothecin-stimulated cleavage with topoisomerase I, G (or not T) at +1 is an additional strong preference. This sequence selectivity of camptothecin is similar to that previously found in SV40 DNA, suggesting that camptothecin preferentially interacts with topoisomerase I-mediated cleavage sites where G is the base at the 5'-terminus. These results support the stacking model of camptothecin (Jaxel et al. (1991) J. Biol. Chem. 266, 20418-20423). Comparison of calf thymus and wheat germ topoisomerase I-mediated cleavage sites in the presence of camptothecin shows that many major cleavage sites are similar. However, the relative intensities are often different. One of the differences was attributable to a bias at position -3 where calf thymus topoisomerase I prefers G and wheat germ topoisomerase I prefers C. This difference may explain the unique patterns of cleavage sites induced by the two enzymes. Sequencing analysis of camptothecin-stimulated cleavage sites in the surrounding regions of point mutations in topoisomerase I cDNA, which were found in camptothecin-resistant cell lines, reveals no direct relationship between DNA cleavage sites in vitro and mutation sites.

Sequential modifications of topoisomerase I activity in a camptothecin-resistant cell line established by progressive adaptation

The DNA-topoisomerase I (Topo I) inhibitor, camptothecin (CPT), is a plant alkaloid with an important antitumor activity. In order to investigate the cellular mechanism leading to the development of the resistance to this agent, we have established by progressive adaptation a P388 subline resistant to CPT. After 5 months of continuous drug exposure, the resistance index reached a value of 20 and the resistant cell line, P388CPT0.3, was maintained in the presence of CPT. CPT-induced single strand breaks measured by alkaline elution were found drastically reduced in the resistant cell line. Topo I activity and CPT-induced DNA cleavage were measured on cells at different steps of resistance. We first observed that the Topo I activity was strongly decreased. In addition, the resistant cells recovered the ATP-independent relaxation activity after 3 months of exposure to CPT, but still kept a reduced CPT-induced DNA cleavage. Further evaluations at the final stage of the resistance induction have indicated that cells presented a CPT-resistant form of Topo I. Rearranged Topo I gene on one allele and a reduced Topo I transcription were also observed in resistant cells. The putative role of the rearrangement was discussed. These data show that the resistance mechanism has evolved from a decreased Topo I activity to an altered form of the enzyme, and suggest that multiple mechanisms of Topo I modifications could contribute to CPT resistance.

Radiation sensitivities in various anticancer-drug-resistant human lung cancer cell lines and mechanism of radiation cross-resistance in a cisplatin-resistant cell line.

To determine whether there exists cross-resistance between anticancer drugs and radiation, six drug-resistant human lung cancer cell lines and their parental cell lines were examined for radiosensitivity using a growth-inhibition assay. Only one cisplatin-resistant cell line, PC-9/CDDP, showed cross-resistance to radiation. The other three cisplatin-resistant cell lines (PC-7/CDDP, PC-4/CDDP, and H69/CDDP), an etoposide-resistant cell line (H69/VP) and a camptothecin-resistant cell line (PC-7/CPT) did not show cross-resistance to radiation. To analyze the mechanism of radiation resistance in PC-9/CDDP cells, the formation and repair of radiation-induced DNA single-strand breaks (ssb) and double-strand breaks (dsb) were examined by alkaline elution and neutral elution respectively. Although the formation of DNA ssb and repair of both DNA ssb and DNA dsb were the same for both cell lines, the formation of DNA dsb in PC-9/CDDP cells was significantly less than those in PC-9 cells. Measurement of intracellular glutathione content in all of the cell lines revealed that only PC-9/CDDP cells had a significant increase of glutathione content compared to the parental cells. Buthionine sulfoximine treatment of PC-9/CDDP cells caused an increase of DNA dsb to the same levels as in PC-9 cells after irradiation and caused a complete radiosensitization. These results indicate that cross-resistance to radiation in drug-resistant cells in a rare phenomenon, and increased glutathione content may play a crucial role in the emergence of cross-resistance to radiation in the drug-resistant cells.