David J. Adams

Phase I Evaluation of Prolonged-Infusion Gemcitabine With Mitoxantrone for Relapsed or Refractory Acute Leukemia

PURPOSE To ascertain the maximum tolerated duration of infusion of gemcitabine at 10 mg/m(2)/min in combination with mitoxantrone at 12 mg/m(2) daily for 3 days in the treatment of acute leukemia. PATIENTS AND METHODS Thirty-four patients were enrolled. Stratum I consisted of 26 patients, median age 50 years (range, 25 to 71 years), with relapsed or refractory leukemia. Stratum II contained eight patients, median age 62.5 years (range, 38 to 83 years), who had received fewer than three cycles of myelotoxic therapy for chronic myeloid leukemia or myelodysplasia that had evolved into leukemia. Patients received mitoxantrone at 12 mg/m(2) daily for 3 days. After the first mitoxantrone dose, gemcitabine was provided intravenously at 10 mg/m(2)/min with the duration adjusted by following a continuous reassessment model. RESULTS Severe myelosuppression, and stomatitis or esophagitis were the most common hematologic and nonhematologic dose-limiting toxicities. Several patients developed febrile neutropenia, nausea, or vomiting. In both strata, the maximum recommended duration of infusion of gemcitabine was 12 hours (7,200 mg/m(2)). The mean steady-state concentration of gemcitabine was 24.72 micromol/L and varied over a fivefold range among patients. Overall response rates in this phase I trial for strata I and II were 42% and 63%, respectively. CONCLUSION Prolonged-infusion gemcitabine at a fixed dose rate of 10 mg/m(2)/min for 12 hours with 12 mg/m(2)/d mitoxantrone for 3 days is a tolerable induction regimen and achieves plasma concentrations sufficient for maximal intracellular activation. Stomatitis or esophagitis should be anticipated; however, this regimen may induce significant responses in patients with difficult-to-treat leukemias.

Camptothecin analogues with enhanced antitumor activity at acidic pH

Background: Camptothecin (CPT) is a specific inhibitor of the nuclear enzyme topoisomerase I, which is involved in cellular DNA replication and transcription. Topoisomerase I is therefore an attractive target for anticancer drug development, and two analogues of CPT, topotecan (TPT) and irinotecan (CPT-11), have demonstrated significant antitumor activity in the clinic. This activity is limited, however, by lability of the CPT E ring lactone, which forms the inactive hydroxy acid at physiological pH. The reaction is reversible at acidic pH, which provides a rationale for selectivity, because many solid tumors create an acidic extracellular environment while maintaining a normal intracellular pH. Purpose: To exploit the tumor-selective pH gradient to improve the efficacy of CPT-based chemotherapy. Methods: CPT analogues were evaluated by growth inhibition assay in three human breast cancer cell lines that had been adapted to in vitro culture at acidic pH versus the respective cells cultured at physiological pH. The MCF-7, MDA-MB-231, and MCF-7/hc cell lines represent the hormone-dependent and hormone-independent stages of the disease, and a MCF-7 variant that is resistant to the alkylating agent 4-hydroperoxycyclophosphamide (4-HC), respectively. Antiproliferative activity of SN-38 (the active metabolite of CPT-11), and TPT was compared to that of CPT and two CPT analogues, 10,11-methylenedioxy-CPT (MDC), and the alkylating derivative, 7-chloromethyl-10,11-MDC (CMMDC). Results: In general, MDC was the most potent and TPT or CPT the least potent analogue, regardless of pH. However, if the comparison was based on magnitude of potentiation by pH, a different rank order emerged. CPT was modulated 4-fold; MDC, SN-38, and TPT were each modulated 5- to 6-fold, while the activity of CMMDC was increased 10- to 11-fold by acidic pH in MCF-7 lines, and 65-fold in MDA-MB-231 cells. Thus MDC was the superior CPT analogue based on potency, but CMMDC was the best candidate for pH modulation. Drug specificity was also observed. While the alkylating agent, 4-HC, was 2- to 3-fold more active at acidic pH, modulation was not observed for 5-fluorouracil, doxorubicin, or paclitaxel. Preliminary mechanism studies indicated that pH modulation of CPT analogues was directly correlated to intracellular levels of glutathione. In addition, protein-associated DNA strand breaks were more rapidly induced at acidic pH. Conclusion: These results suggest that CPT-based drug development and resulting chemotherapy could benefit from evaluation of differential activity at acidic versus physiological pH. Analogues have been identified that could have improved therapeutic indices based on the pH gradient that selectively exists in human tumors.

Evidence for a role of chloroethylaziridine in the cytotoxicity of cyclophosphamide

Abstract A number of investigators have observed that the use of 4-hydroperoxycyclophosphamide (4-HC) in multiwell plate cytotoxicity assays can be associated with toxicity to cells in wells that contain no drug. Previous reports have implicated diffusion of 4-HC decomposition products, and acrolein in particular, as the active species. Purpose: The purpose of this study was to elucidate the species responsible for the airborne cytotoxicity of 4-HC, and to devise ways to minimize such effects in chemosensitivity assays. Methods: To this end, analogues of 4-HC were synthesized to identify the contributions of individual cyclophosphamide metabolites to cytotoxicity. The analogues were then tested for activity against three human breast tumor cell lines (including a line resistant to 4-HC), and one non-small-cell lung carcinoma line. Cytotoxicity was evaluated by assays that quantitate cellular metabolism and nucleic acid content. Results: Didechloro-4-hydroperoxycyclophosphamide, a compound that generates acrolein and a nontoxic analogue of phosphoramide mustard, gave no cross-well toxicity. In contrast, a significant neighboring well effect was observed with phenylketophosphamide, a compound that generates phosphoramide mustard but not acrolein. Addition of authentic chloroethylaziridine reproduced the airborne toxicity patterns generated by 4-HC and phenylketophosphamide. Increasing the buffering capacity of the growth medium and sealing the microtiter plates prevented airborne cytotoxicity. Conclusions: Since it is unlikely that phosphoramide mustard is volatile, these findings implicate chloroethylaziridine rather than acrolein as the volatile metabolite of 4-HC that is responsible for airborne cytotoxicity. The fact that chloroethylaziridine is generated in amounts sufficient to volatilize, diffuse across wells and cause cytotoxicity indicates that it is an important component in the overall cytotoxicity of 4-HC in vitro. Furthermore, these findings suggest that chloroethylaziridine may also contribute to the toxicity of cyclophosphamide in vivo.

Anti proliferative activity of ELACYT™ (CP-4055) in combination with cloretazine (VNP40101M), idarubicin, gemcitabine, irinotecan and topotecan in human leukemia and lymphoma cells

This study evaluated combination drug partners for CP-4055, the C18:1Δ9,trans unsaturated fatty acid ester of cytarabine in HL-60 and U937 cells. Growth inhibition was assessed by ATP assay and drug interaction by the combination index and three dimensional methods. Synergy was observed in HL-60 cells for simultaneous combinations of CP-4055 with gemcitabine, irinotecan and topotecan, while combinations with cloretazine (VNP40101M) and idarubicin were additive. In U937 cells, synergy was observed with gemcitabine and additivity for the other drugs. In HL-60, the IC50 concentration of CP-4055 could be reduced 10-fold and that of gemcitabine 3-fold in combination versus the agents alone, an interaction that was independent of drug sequence, ratio and exposure time. In contrast, interactions of CP-4055 with the topoisomerase inhibitors became antagonistic when the drugs were administered 24 h prior to CP-4055 and at certain drug ratios, particularly in U937 cells. In summary, CP-4055 produced additive to synergistic anti proliferative activity when combined simultaneously with drugs from four mechanistic classes in cell culture models of human leukemia and lymphoma. The impact of drug sequence and ratio on the interactions argues for incorporation of these parameters into the design of combination chemotherapy regimens.

Phase I Evaluation of Prolonged-Infusion Gemcitabine With Irinotecan for Relapsed or Refractory Leukemia or Lymphoma

PURPOSE To estimate the maximum-tolerated duration of infusion of gemcitabine at 10 mg/m(2)/min in combination with irinotecan at 40 mg/m(2) daily for 3 days in the treatment of relapsed or refractory acute leukemia or lymphoma. PATIENTS AND METHODS Patients with leukemia or lymphoma were escalated in separate strata. Stratum I consisted of 11 patients, median age of 47 years (range, 18 to 68 years), with relapsed or refractory leukemia. Stratum II contained nine patients, median age of 48 years (range, 39 to 68 years), who had refractory non-Hodgkins lymphoma. Patients received irinotecan at 40 mg/m(2) daily for 3 days, beginning just before the first dose of gemcitabine. Gemcitabine was given at 10 mg/m(2)/min, with the total duration adjusted following a modified continuous reassessment model. RESULTS Severe myelosuppression and stomatitis/esophagitis were the most serious hematologic and nonhematologic toxicities. Several patients developed febrile neutropenia, nausea, or vomiting. In both strata, the maximum recommended duration of infusion of gemcitabine was 12 hours delivered at 10 mg/m(2)/min (7,200 mg/m(2)). The overall response rate for one cycle of this therapy in this phase I trial for patients with leukemia was 18% (95% confidence interval, 8% to 45%), and for those with lymphoma, 33% (95% confidence interval, 17% to 66%). CONCLUSION A prolonged infusion of gemcitabine at 10 mg/m(2)/min for 12 hours with 3 days of irinotecan at 40 mg/m(2)/d is a tolerable induction regimen for patients with acute leukemia or lymphoma. Stomatitis/esophagitis should be anticipated; however, this regimen may induce responses in patients with difficult-to-treat hematologic malignancies.

Tumor Physiology and Charge Dynamics of Anticancer Drugs: Implications for Camptothecin-based Drug Development

Charge is an important characteristic of drug molecules, since ionization sites determine the pKa at a particular pH. The pKa in turn can affect many parameters, including solubility, dissolution rate, reaction kinetics, formulation, cell permeability, tissue distribution, renal elimination, metabolism, protein binding and receptor interactions. The impact of charge dynamics is amplified in human solid tumors that exhibit the glycolytic phenotype and associated acidic extracellular microenvironment. This phenotype is driven by hypoxia and creates a pH gradient in tumors that favors uptake of weak acids and exclusion of weak bases. Established anticancer drugs exhibit a range of pKas and thus variable ability to exploit the tumor pH gradient. The camptothecins are a prime example as they represent a diverse class of approved anticancer drugs and drug candidates whose charge distribution varies with pH. An in silico method was used to predict charge distribution of camptothecins at physiological versus acidic pH in both the lactone and carboxylate forms. A significant amount of uncharged carboxylate was predicted at acidic pH that could enter tumor cells and accumulate in mitochondria to inhibit mitochondrial topoisomerase I. A model is presented to describe the charge dynamics of a new camptothecin analog and the impact on nuclear and mitochondrial mechanism(s) of action. This example illustrates the importance of integrating tumor physiology and charge dynamics into anticancer drug development.

Dasatinib (BMS-35482) has synergistic activity with paclitaxel and carboplatin in ovarian cancer cells

PURPOSE To explore the activity of dasatinib alone and in combination with paclitaxel and carboplatin in ovarian cancer cells and to determine if dasatinib activity can be predicted based on evaluation of the SRC pathway. EXPERIMENTAL DESIGN Microarray analysis was performed for IGROV1, OVCAR3, A2780 and SKOV3 ovarian cancer cells and the status of the genomic SRC signature pathway was determined. Cells were treated with carboplatin, paclitaxel and dasatinib individually and in combination. Pre- and post-treatment phospho-SRC (pSRC) and SRC protein expression was determined. Dose-response curves were constructed, and drug interaction was assessed by the Combination Index (CI) method. RESULTS SRC protein expression levels reflected the SRC pathway genomic signature in the cell lines with the lowest (SKOV3) and highest (IGROV1) pathway expression, but not in those with intermediate expression (OVCAR3, A2780). Dasatinib treatment caused loss of pSRC in all cell lines, with 50% growth inhibition for IGROV1 at 70 nM, OVCAR3 at 34 nM, A2780 at 4.1 μM and SKOV3 at 530 nM. Dasatinib combined with cytotoxics yielded a synergistic effect (CI=0.46 to 0.79) in all cell lines except SKOV3. CONCLUSION Dasatinib in combination with standard chemotherapeutic agents appears to interact in a synergistic manner in some ovarian cancer cell lines. Further research is needed to evaluate tumor cell characteristics which predict response to dasatinib.

Pre-clinical evaluation of SN-38 and novel camptothecin analogs against human chronic B-cell lymphocytic leukemia lymphocytes

The topoisomerase I inhibitor camptothecin and its analogs have potent activity against a wide range of solid tumors and several hematologic malignancies. Previous studies with these compounds using the MTT metabolic inhibition assay have shown significant cytotoxicity against lymphocytes from patients with chronic B-cell lymphocytic leukemia (B-CLL). Yet the water soluble analogue, topotecan, which was inhibitory at > 1 microM in vitro, had no clinical activity in vivo. In the present study, we evaluated the in vitro cytotoxicities of SN-38, the active form of irinotecan, and two newer water soluble camptothecin derivatives 10,11-methylenedioxy-20(S)-camptothecin glycinate (MDCG) and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin glycinate (CMMDCG). These two glycinate esters are prodrugs for 10,11-methylenedioxy-20(S)-camptothecin (MDC) and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin (CMMDC), respectively. Effects on cellular metabolism, induction of apoptosis, and overall cell survival were used to evaluate chemosensitivity. We report that the relative cytotoxic potency for these compounds is MDC > or = CMMDC > or = SN-38 >> TPT > CPT-11, where MDC, CMMDC, and SN-38 were over an order of magnitude more cytotoxic than TPT and CPT-11. We also investigated potential mechanisms underlying the unexpected cytotoxicity of these camptothecin derivatives in B-CLL cells that are known to be arrested in G0/G1 of the cell cycle, and found that this class of compounds inhibited [3H]uridine incorporation. We therefore postulate that the inhibition of RNA rather than DNA synthesis may be responsible for the observed cytotoxicity in non-cycling B-CLL cells.

Dasatinib (BMS-35482) interacts synergistically with docetaxel, gemcitabine, topotecan, and doxorubicin in ovarian cancer cells with high SRC pathway activation and protein expression.

Purpose This study aimed to explore the activity of dasatinib in combination with docetaxel, gemcitabine, topotecan, and doxorubicin in ovarian cancer cells. Methods Cells with previously determined SRC pathway and protein expression (SRC pathway/SRC protein IGROV1, both high; SKOV3, both low) were treated with dasatinib in combination with the cytotoxic agents. SRC and paxillin protein expression were determined pretreatment and posttreatment. Dose-response curves were constructed, and the combination index (CI) for drug interaction was calculated. Results In the IGROV1 cells, dasatinib alone reduced phospho-SRC/total SRC 71% and p-paxillin/t-paxillin ratios 77%. Phospho-SRC (3%–33%; P = 0.002 to 0.04) and p-paxicillin (6%–19%; P = 0.01 to 0.05) levels were significantly reduced with dasatinib in combination with each cytotoxic agent. The combination of dasatinib and docetaxel, gemcitabine, or topotecan had a synergistic antiproliferative effect (CI, 0.49–0.68), whereas dasatinib combined with doxorubicin had an additive effect (CI, 1.08). In SKOV3 cells, dasatinib resulted in less pronounced reductions of phospho-SRC/total SRC (49%) and p-paxillin/t-paxillin (62%). Phospho-SRC (18%; P < 0.001) and p-paxillin levels (18%; P = 0.001; 9%; P = 0.007) were significantly decreased when dasatinib was combined with docetaxel and topotecan (p-paxillin only). Furthermore, dasatinib combined with the cytotoxics in the SKOV3 cells produced an antagonistic interaction on the proliferation of these cells (CI, 1.49–2.27). Conclusions Dasatinib in combination with relapse chemotherapeutic agents seems to interact in a synergistic or additive manner in cells with high SRC pathway activation and protein expression. Further evaluation of dasatinib in combination with chemotherapy in ovarian cancer animal models and exploration of the use of biomarkers to direct therapy are warranted.

Dasatinib (BMS-35482) potentiates the activity of gemcitabine and docetaxel in uterine leiomyosarcoma cell lines

BackgroundTo explore the activity of dasatinib alone and in combination with gemcitabine and docetaxel in uterine leiomyosarcoma (uLMS) cell lines, and determine if dasatinib inhibits the SRC pathway.MethodsSK-UT-1 and SK-UT-1B uLMS cells were treated with gemcitabine, docetaxel and dasatinib individually and in combination. SRC and paxcillin protein expression were determined pre- and post-dasatinib treatment using Meso Scale Discovery (MSD) multi-array immunogenicity assay. Dose-response curves were constructed and the coefficient of drug interaction (CDI) and combination index (CI) for drug interaction calculated.ResultsActivated phosphorylated levels of SRC and paxillin were decreased after treatment with dasatinib in both cell lines (p < 0.001). The addition of a minimally active concentration of dasatinib (IC25) decreased the IC50 of each cytotoxic agent by 2-4 fold. The combination of gemcitabine-docetaxel yielded a synergistic effect in SK-UT-1 (CI = 0.59) and an antagonistic effect in SK-UT-1B (CI = 1.36). Dasatinib combined with gemcitabine or docetaxel revealed a synergistic anti-tumor effect (CDI < 1) in both cell lines. The triple drug combination and sequencing revealed conflicting results with a synergistic effect in SK-UT-1B and antagonistic in SK-UT-1.ConclusionDasatinib inhibits the SRC pathway and yields a synergistic effect with the two-drug combination with either gemcitabine or docetaxel. The value of adding dasatinib to gemcitabine and docetaxel in a triple drug combination is uncertain, but may be beneficial in select uLMS cell lines. Based on our pre-clinical data and known activity of gemcitabine and docetaxel, further evaluation of dasatinib in combination with these agents for the treatment of uLMS is warranted.