Testing chemotherapeutic combinations in the Human Tumor Colony--Forming Assay

Glycoprotein targeted therapeutics: a new era of anti-herpes simplex virus-1 therapeutics

Herpes simplex virus type-1 (HSV-1) is among the most common human pathogens worldwide. Its entry into host cells is an intricate process that relies heavily on the ability of the viral glycoproteins to bind host cellular proteins and to efficiently mediate fusion of the virus envelope with the cell membrane. Acquisition of HSV-1 results in a lifelong latent infection. Because of the cycles of reactivation from a latent state, much emphasis has been placed on the management of infection through the use of DNA synthesis inhibitors. However, new methods are needed to provide more effective treatment at earlier phases of the viral infection and to prevent the development of drug resistance by the virus. This review outlines the infection process and the common therapeutics currently used against the fundamental stages of HSV-1 replication and fusion. The remainder of this article will focus on a new approach for HSV-1 infection control and management, the concept of glycoprotein-receptor targeting.

Combinatorial approaches to the prevention and treatment of HIV-1 infection

The discovery of the human immunodeficiency virus type 1 (HIV-1) in 1982 soon led to the identification and development of antiviral compounds to be used in treatment strategies for infected patients. Early in the epidemic, drug monotherapies frequently led to treatment failures because the virus quickly developed resistance to the single drug. Following the advent of highly active antiretroviral therapy (HAART) in 1995, dramatic improvements in HIV-1-infected patient health and survival were realized as more refined combination therapies resulted in reductions in viral loads and increases in CD4+ T-cell counts. In the absence of an effective vaccine, prevention of HIV-1 infection has also gained traction as an approach to curbing the pandemic. The development of compounds as safe and effective microbicides has intensified and has focused on blocking the transmission of HIV-1 during all forms of sexual intercourse. Initial preclinical investigations and clinical trials of microbicides focused on single compounds effective against HIV-1. However, the remarkable successes achieved using combination therapy to treat systemic HIV-1 infection have subsequently stimulated the study and development of combination microbicides that will simultaneously inhibit multiple aspects of the HIV-1 transmission process by targeting incoming viral particles, virus-infected cells, and cells susceptible to HIV-1 infection. This review focuses on existing and developing combination therapies, covering preclinical development, in vitro and in vivo efficacy studies, and subsequent clinical trials. The shift in focus within the microbicide development field from single compounds to combination approaches is also explored.

In vitro extreme drug resistance assay to taxanes or platinum compounds for the prediction of clinical outcomes in epithelial ovarian cancer: a prospective cohort study

PURPOSE

We sought to investigate the efficacy of in vitro extreme drug resistance (EDR) assay for the prediction of drug response, platinum-resistance (progression-free survival, PFS <6 months) and survival in patients with epithelial ovarian cancer (EOC) who received taxane- and platinum-based chemotherapy after surgery.

METHODS

Between December 2005 and August 2007, 43 patients were enrolled prospectively. They underwent staging laparotomy followed by six or nine cycles of taxane- and platinum-based chemotherapy, and their tumors were submitted for in vitro EDR assay to taxanes (paclitaxel or docetaxel) and platinum compounds (carboplatin or cisplatin).

RESULTS

The rates of EDR to taxanes and platinum compounds were 20.9% (9/43) and 23.3% (10/43). Patients with EDR to platinum compounds showed a lower rate of overall response (60 vs. 100%), a higher rate of platinum-resistance (50 vs. 18.2%) and poor overall survival (OS) (median OS; 29.2 vs. 33.7 months) than those without EDR to platinum compounds (P < 0.05), whereas patients with EDR to taxanes showed poor PFS than those without EDR to taxanes (12.5 vs. 19 months, P < 0.01). Moreover, suboptimal debulking surgery and EDR to taxanes were poor prognostic factors for PFS (adjusted hazard ratio 3.215 and 3.984; 95% confidence interval 1.845-7.895 and 3.814-11.674, respectively) although there was no independent risk factor for poor OS by the multivariate Cox's proportional hazard analysis.

CONCLUSIONS

In vitro EDR assay to taxanes and platinum compounds may be helpful for predicting drug response, platinum-resistance and survival in patients with EOC who received taxane- and platinum-based chemotherapy after staging laparotomy.

In vitro activity of bortezomib in cultures of patient tumour cells--potential utility in haematological malignancies

Bortezomib represents a new class of anti-cancer drugs, the proteasome inhibitors. We evaluated the in vitro activity of bortezomib with regard to tumour-type specificity and possible mechanisms of drug resistance in 115 samples of tumour cells from patients and in a cell-line panel, using the short-term fluorometric microculture cytotoxicity assay. Bortezomib generally showed dose-response curves with a steep slope. In patient cells, bortezomib was more active in haematological than in solid tumour samples. Myeloma and chronic myeloid leukaemia were the most sensitive tumour types although with great variability in drug response between the individual samples. Colorectal and kidney cancer samples were the least sensitive. In the cell-line panel, only small differences in response were seen between the different cell lines, and the proteasome inhibitors, lactacystin and MG 262, showed an activity pattern similar to that of bortezomib. The cell-line data suggest that resistance to bortezomib was not mediated by MRP-, PgP, GSH-; tubulin and topo II-associated MDR. Combination experiments indicated synergy between bortezomib and arsenic trioxide or irinotecan. The data support the current use of bortezomib but also points to its potential utility in other tumour types and in combination with cytotoxic drugs.

Tumor heterogeneity in ovarian cancer as demonstrated by in vitro chemoresistance assays

OBJECTIVE

Tumor heterogeneity has been demonstrated in solid tumors. In vitro assays were developed in an effort to predict in vivo tumor response to therapy. We compare the in vitro assay results from multiple synchronous tumor samples in primary and recurrent ovarian cancers.

METHODS

38 patients underwent surgery for primary (18) or recurrent (20) ovarian cancer. Two (22) or three (16) samples were obtained per patient and tested using the EDR assay (Oncotech, Inc.). The percentage of Extreme (E), Intermediate (I) and Low (L) drug resistance for each chemotherapy was compared between synchronous specimens.

RESULTS

A total of 92 samples were collected and 787 drug assays were performed. Tumor heterogeneity was seen in 22.4% of all cases, including 18.6% primary and 26.1% recurrent diseases (p=0.01). Two category differences (L vs. E) were seen in 4.1% primary and 11.3% recurrent cases (7.8% of all cases). Overall, an increased frequency in EDR was seen in recurrent disease as compared to primary for all agents tested (22.9% primary vs. 31.6% recurrent, p=0.006). Marked heterogeneity of the drug resistance profiles was seen with paclitaxel as compared with cisplatin/gemcitabine (p=0.03), taxotere (p=0.04) or topotecan (p=0.04). No association was demonstrated between assay results and clinicopathologic parameters collected in this cohort.

CONCLUSIONS

Treatment failure is often attributed to the development of chemoresistance. These results suggest that tumor heterogeneity may play an equally important role in treatment failure. Recurrent lesions exhibit greater heterogeneity and more frequent EDR. These data can influence therapeutic strategy i.e., multiple samples, sequential, or consolidation therapy.

Evaluation of drug interactions in the established FEC regimen in primary cultures of tumour cells from patients

BACKGROUND

Chemotherapy using multi-drug regimens is considered more active than single-agent therapy. This may be due to synergistic interactions or, simply, a higher probability of administering an active agent. We investigated in vitro the type of drug interactions in a recognized regimen in relationship to tumour type and drug sensitivity.

PATIENTS AND METHODS

The possibility of synergistic and additive interactions between individual cytotoxic drugs was investigated for the component drugs of the established FEC regimen, i.e., 5-fluorouracil, epirubicin and cyclophosphamide, in 243 patient tumour samples representing various drug sensitivity using the non-clonogenic fluorometric microculture cytotoxicity assay.

RESULTS

Using a cell survival of < or = 50% as a limit for drug activity and sample sensitivity, the overall response rates to the most active single drug (Dmax) and the combination were 56% and 64%, respectively, with a distribution among diagnoses similar to that in the clinic. For 86% of the samples there was concordance with respect to judgement of activity using either Dmax or the combination. For samples being sensitive to at least one single drug, 95% were also sensitive to the combination whereas for samples with insignificant Dmax effect, only 2% were sensitive to the combination. In samples with modest Dmax effects, i.e., cell survival in the range > 50%- < or = 80%, 45% responded to the combination. The effect of the combination was generally well predicted from the Dmax effect.

CONCLUSIONS

The superior antitumour effect of drug combinations compared with single drugs may be due to the higher chance of selecting an active agent. However, for intermediately sensitive tumours, additional interaction effects of a combination may be of clinical significance.

Correlation between extreme drug resistance assay and response to primary paclitaxel and cisplatin in patients with epithelial ovarian cancer

OBJECTIVE

The extreme drug resistance (EDR) assay has been correlated with failure of response to chemotherapy in greater than 99% of patients. The goal of this study is to correlate the results of the EDR assay to response to first-line paclitaxel/cisplatin among patients with epithelial ovarian cancer.

METHODS

Seventy-five of 100 patients with epithelial ovarian cancer for whom EDR assay was performed were treated with weekly induction cisplatin (1 mg/kg body wt) x 4, followed by monthly paclitaxel (135 mg/m2) and cisplatin (75 mg/m2) x 6 and were evaluable for correlation of response to chemotherapy and EDR assay. Specimens for EDR assay were obtained at primary surgery and the EDR assay was performed by Oncotech, Inc. Response to chemotherapy was correlated to EDR assay results regarding paclitaxel and cisplatin.

RESULTS

Among 75 evaluable patients, the prevalence of EDR to paclitaxel was 20.0% (n = 15) and to cisplatin it was 2.7% (n = 2). Only 1 patient (1.3%) exhibited EDR to both paclitaxel and cisplatin. Surgical assessment of response was performed in 42 patients; 33 patients were clinically evaluable. The overall response rate was 85.3%. The overall response rate for patients whose tumors demonstrated no EDR to either paclitaxel or cisplatin did not differ significantly from that for patients whose tumors demonstrated EDR to at least one of these two drugs (86.4% versus 81.3%, respectively, P = 0.692). Similarly, the complete surgical response rate for both groups did not differ significantly (25.4% versus 12.5%, respectively, P = 0. 34). A single patient whose tumor exhibited EDR to both paclitaxel and cisplatin had tumor progression. The sensitivity, specificity, positive predictive value, and negative predictive value of the EDR assay were 79.6, 27.0, 86.0, and 19.0%, respectively.

CONCLUSIONS

EDR to paclitaxel does not preclude response to the combination of paclitaxel and cisplatin as primary therapy for patients with epithelial ovarian cancer. The role of the EDR assay in the primary management of patients with epithelial ovarian cancer remains to be determined.

In vitro testing of chemotherapeutic drug combinations in acute myelocytic leukaemia using the fluorometric microculture cytotoxicity assay (FMCA)

The fluorometric microculture cytotoxicity assay (FMCA) was employed for analysing the effect of different chemotherapeutic drug combinations and their single constituents in 44 cases of acute myelocytic leukaemia (AML). A large heterogeneity with respect to cell kill was observed for all combinations tested, the interactions ranging from antagonistic to synergistic in terms of the multiplicative concept for drug interactions. However, an 'additive' model provided a significantly better fit of the data compared to the effect of the most active single agent of the combination (Dmax) for several common antileukaemic drug combinations. When the two interaction models were related to treatment outcome 38% of the non-responders showed preference for the additive model whereas the corresponding figure for responders was 80%. Overall, in 248 of 290 (85%) tests performed with drug combinations, there was an agreement between the effect of the combination and that of the most active single component. Direct comparison of Dmax and the combination for correlation with clinical outcome demonstrated only minor differences in the ability to predict drug resistance. The results show that FMCA appear to report drug interactions in samples from patients with AML in accordance with clinical experience. Furthermore, testing single agents as a substitute for drug combinations may be adequate for detection of clinical drug resistance to combination therapy in AML.

The effect of anticancer drug sequence in experimental combination chemotherapy

A series of drug combination sequence studies was conducted in vitro using HEC-1A human endometrial carcinoma cells or 8226 myeloma cells. Four drugs were evaluated for schedule-dependent and sequence-dependent inhibition of human tumor colony formation in soft agar. Six different two-drug combinations were analyzed using the median dose effect method, and three different three-drug combinations were examined using the cumulative surviving fraction method. The results show that the specific sequence and method of drug exposure significantly influenced the production of antagonistic, additive, or synergistic cytotoxicity patterns. Drug combinations that were consistently synergistic included bleomycin or mitomycin C and cisplatin in 8226 cells, and etoposide plus bleomycin in human endometrial cancer (HEC-1A) cells. Most other two-drug combinations of bleomycin, etoposide, cisplatin, and mitomycin C were antagonistic in vitro, irrespective of the sequence of exposure. Among the three-drug combinations tested, consistent synergism was noted with cisplatin, etoposide, and bleomycin when either of the latter two agents was tested as a continuous exposure in vitro. Within individual two- and three-drug combinations, it was possible to observe synergism, additivity, or antagonism based on the particular exposure sequence tested. These results suggest that antitumor agent cytotoxicity in vitro can be radically influenced by the sequence of drug administration, a feature commonly overlooked in many clinical combination drug regimens.

Combination chemotherapy tested in a short-term thymidine incorporation assay in primary cultures of ovarian adenocarcinomas

Fifty-six tumor specimens from patients with ovarian adenocarcinoma were tested for sensitivity to single and combination drug regimens in a short-term antimetabolic assay measuring inhibition of thymidine incorporation. Response in primary cultures to drug combinations was compared with response to each component drug: cisplatinum, chlorambucil, adriamycin, etoposide and activated cyclophosphamide. Using cut-off criteria previously shown to correlate with "sensitive" and "resistant" tumors for single drugs, 11% of tumors showed increased sensitivity to a combination compared with the single drugs, but 10% showed decreased sensitivity to a combination. The majority of tumors remained in the same "sensitive" or "resistant" categories obtained with the single drugs. Analysis by isobolograms demonstrated synergy, addition or antagonism with the same combination on different tumors. No significant difference between combinations and the best single drug used alone was found in 70% of assays. Overall thymidine incorporation inhibition by the combination and by the best single drug was highly correlated. It is suggested that the best single drug predicts the effectiveness of its combination regimens.

In vitro testing of chemotherapeutic combinations in a rapid thymidine incorporation assay

A total of 199 solid human tumors were tested with a rapid thymidine incorporation assay for sensitivity to one of several clinically used multi-drug combinations and to each agent in the combination separately. Melanomas, lung and breast cancers accounted for the majority of specimens. In 120 specimens, at least one single agent exhibited in vitro activity (80% or greater inhibition of thymidine incorporation), and in 116 of these (96.7%) the drug combination was active in vitro. In the 79 specimens where no single agent was active in vitro, the combination was also inactive in 62 (78.5%). Overall, there was concordance of in vitro activity of the most active single agent and the combination of agents in 89.5% of specimens tested. A lack of significant in vitro synergy was noted in all of the drug combinations and tumor types tested. Of note is the fact that in 141 of the 199 tests (70.9%) either no drug (n = 79) or only 1 drug (n = 62) demonstrated in vitro activity. We conclude that the rapid thymidine incorporation assay can be used to test for in vitro sensitivity to drug combinations, and that sensitivity to a drug combination can be inferred if a tumor is sensitive to any component drug of the combination.