Determining the rate of tumor growth and decay in patients with metastatic breast cancer as an early efficacy endpoint: A study assessing ixabepilone efficacy

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Background: Early efficacy assessment in drug development should help find new cancer therapies. We have developed a novel method to analyze tumor response to therapy by quantifying the rate of tumor regression (d) and growth (g). We have shown g is slower when pts are on effective therapy and that g correlates with survival (Stein et al, Oncologist 2008). We utilized this method to evaluate a phase III trial of capecitabine (CAP) ± IXA in second line therapy (Tomas et al, JCO 2007) and a three-cohort phase II trial in second and subsequent lines of therapy in pts with MBC consisting of (1) Daily X 5 IXA given to taxane (TAX)-naïve patients (Denduluri et al, JCO 2007); (2) Daily X 5 IXA in pts previously treated with TAX (Low et al, JCO 2005); and (3) Daily X 3 IXA in pts previously treated with TAX (Denduluri et al, Invest New Drug 2007).

Methods: Using tumor measurements assessed by RECIST and a two-phase mathematical equation we determined d and g.

Results: In the phase III study g was superior to PFS identifying a significant difference between the arms very early—before the 200th pt had enrolled. In an individual patient the g values could be estimated as early as the 3rd evaluation, long before tumor growth was observed clinically. IXA + CAP in second line (g = 0.0018) was more effective than CAP (g = 0.0023) at reducing g, and more effective (p=0.0085) than single agent IXA in the Phase II study (g = 0.0027). Single agent IXA was comparably effective (p=0.814) in reducing the g of tumors previously exposed to a TAX (g = 0.0032) as in reducing the g of TAX-naïve tumors (g = 0.0035), consistent with its development as an agent active in TAX-refractory disease. Unlike differences in g, the d of single agent IXA (0.118) was comparable to that of IXA+CAP (0.0074) suggesting differences were primarily driven by effect on the growth of residual tumor.

Conclusions: Unlike PFS, an incremental measure of efficacy, g is a continuous variable and can more accurately assess differences between treatments. Because calculations of g are indifferent to assessment intervals, estimating a tumor’s g allows comparison of efficacy across trials.

Value of stable disease (SD) in drug development of targeted therapies (TGT)

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It has been widely asserted that the efficacy of TGT cannot be assessed by traditional response measures since they are not expected to cause tumor shrinkage. Despite the lack of substantiating data, this idea has become conventional wisdom, often guiding clinical trial design. Aware the acceptance of SD as a measure of activity led to its being increasingly reported with traditional cytotoxic agents (CTX), we set about to methodically compare the occurrence of SD in phase II trials of TGT and CTX. We systematically catalogued response assessments in 147 phase II studies reported between 10/06 and 3/08 in 5 journals (Cancer, BJC, CCR, JCO, and Lancet Oncology). Eighty used CTX, 59 used TGT and 8 used both “classes” of agents. Thirty-eight properties including CR, PR, SD, PFS, and OS were recorded for each study. CTX and TGT studies were comparable with similar distribution of histologies and similar PFS and OS in these patients with refractory tumors. For CTX vs. TGT, the median numbers of pts/study was 47.1 vs. 51.9; median PFS, 5.55 vs. 4.54 mos; and median OS, 12.55 vs. 12.88 mos. SD was defined by duration in only 31% of studies, a median duration of 9.5 weeks. SD rates were nearly identical for the two therapy groups - 34.6% for CTX and 33.1% for TGT- and their distribution by histology was similar, suggesting properties other than therapy are responsible for SD. Correlations or lack thereof between %SD and PFS or OS were similar for both CTX and TGT. The overall response rate (CR + PR) was higher with CTX than with TGT (29.4% vs. 13.3%) and demonstrated a strong correlation (p<0.0001) of uncertain importance with PFS and OS for all therapies. Examination of 33 NSCLC studies (16 CTX/17 TGT) found similar results. We conclude that SD as currently defined and measured in not a property of TGT but of the phase II patient population and is similarly found with CTX. Responses are observed with TGT as with CTX, and this analysis suggests that even for TGT it is a measure of activity that should be sought. Assertions that SD is a particular characteristic of TGT should be replaced by definitions that seek clinically meaningful SD.

No significant financial relationships to disclose.

A phase II trial of gefitinib monotherapy in patients with unresectable adrenocortical carcinoma (ACC)

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Background: ACC is a rare malignancy with a very poor prognosis. Surgery is the only potential curative option. Gefitinib is an oral EGFR inhibitor that may have activity in solid tumors that express EGFR. ACC over expresses EGFR in a high proportion of cases. Methods: From April 2004 through December 2006, the ACC Working Group conducted a phase II trial of Gefitinib as second line, monotherapy in patients with pathologically confirmed unresectable ACC who had progressed on mitotane or chemotherapy. All prior systemic therapy was discontinued 28 days prior to starting gefitinib. Patients were ineligible if: had received prior therapy with any EGFR inhibitor, pregnant or breast feeding, had other co-existing malignancies (other than basal cell carcinoma or cervical cancer in situ), had an ECOG PS > 2, absolute neutrophil counts < 1,500, or platelets < 20,000. Patients were not allowed concomitant use of phenytoin, carbamazepine, rifampicin, barbiturates, or St John’s Wort. Patients took gefitinib 250 mg orally once a day. Each cycle was 21 days with radiological assessment every 6 weeks.Response rate as determined by RECIST criteria was the primary endpoint. Results: 19 patients accrued to the study (18 with measurable disease and 1 without). Pt Characteristics: Female 79% (15/19); Median age 48 (range 26–74); 84% (12 female and 4 male =15/19) of the patients had steroid secreting tumors. Grade 3 toxicity was noted in 2 patients and included, hypertension and lower extremity edema and elevated liver transaminases. No grade 4 toxicities occurred. Of 19 patients evaluable, there were no complete responders, partial responders or patients with stable disease (0% response rate; 95% CI: 0%-18%). Conclusions: Gefitinib demonstrated no activity in patients with unresectable ACC. This study is now closed. This study demonstrated the ability to successfully accrue to a trial of novel agents in rare tumors in a multicenter setting.

[Table: see text]

The efficacy of combination chemotherapy with cisplatin and gemcitabine in patients with advanced adrenal cortical carcinoma (ACC)

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Background: ACC is a rare, but highly lethal disease for which more effective systemic therapies are needed. Prior studies have concluded that cisplatin and doxorubicin have single agent activity and that combinations of these and other agents, most notably etoposide, may have additive or synergistic effects. However, the majority of responses are neither complete nor durable. Anecdotal evidence of activity by gemcitabine in patients with ACC motivated the present analysis, designed to assess the efficacy of cisplatin and gemcitabine in combination in patients with metastatic ACC. Methods: 18 patients with metastatic disease were evaluated. Patient’s ages ranged from 19 to 63 years with a median age of 46 years. 5 patients were treated at initial presentation, while 13 were treated after disease progression on or following a previous chemotherapy regimen. Among the latter, the median number of prior regimens was 1, with a median of 4 prior drugs. Sites of metastases included lung (10/18), liver (12/18), retroperitoneum/adrenal bed (5/18) and bone (2/20). The starting dosages were 100 mg/m2 of cisplatin and 1250 mg/m2 of gemcitabine. A total of 56 cycles were administered to 18 patients, with a range of 2 to 12 cycles and a median of 3. Results: The toxicity of this regimen in this patient population was similar to that reported with this regimen in other tumor types. The partial response rate was 11% with an additional 16% of patients demonstrating cytoreduction that did not meet the criteria for a partial response. Conclusions: We conclude that the combination of cisplatin and gemcitabine has activity in ACC. While the superiority of this combination over single agent platinum is not established, the combination does not appear to be superior enough to warrant its routine use, especially in patients with more indolent disease, where single agent platinum can be followed by single agent gemcitabine. An attribute this combination has over other regimens used in patients with ACC, notably those incorporating doxorubicin and/or etoposide, is that it can be given at full doses without excessive toxicity to patients with hormone producing tumors in combination with ketoconazole.

No significant financial relationships to disclose.

Modulation of P-glycoprotein phosphorylation and drug transport by sodium butyrate

P-Glycoprotein (Pgp) expression in cell lines derived from tumors arising from cells which normally express Pgp can be increased by sodium butyrate and other differentiating agents. Although the Pgp level increased 25-fold after sodium butyrate treatment in SW620 human colon carcinoma cells, the intracellular accumulation of vinblastine, adriamycin, and actinomycin D increased rather than decreased. In contrast, colchicine showed the expected decrease in accumulation, as a result of increased efflux. Likewise, treatment of a Pgp-expressing multidrug-resistant SW620 subline with sodium butyrate resulted in active interference with Pgp function. This effect was partially reversed by phorbol esters with a resulting decrease in the accumulation of vinblastine, adriamycin, and actinomycin D. Sodium butyrate, while increasing Pgp levels, inhibited the phosphorylation of Pgp. Time course studies revealed a tight relationship between decreased Pgp phosphorylation and increased vinblastine accumulation after sodium butyrate treatment. Either treatment with phorbol esters or withdrawal of sodium butyrate increased Pgp phosphorylation while decreasing vinblastine accumulation. These studies suggest that the specificity of Pgp transport can be modulated by phosphorylation and that vinblastine, adriamycin, or actinomycin D transport, but not that of colchicine, is diminished after dephosphorylation by sodium butyrate.

Expression of the multidrug resistance-associated protein gene in refractory lymphoma: quantitation by a validated polymerase chain reaction assay

Previous work investigating the role of MDR-1 overexpression in relapsed and refractory lymphoma led us to investigate a possible role for multidrug resistance-associated protein (MRP) as a cause of resistance in patients who did not overexpress MDR-1. A quantitative polymerase chain reaction (PCR) method for measuring MRP expression was validated. Immunoblot analysis suggested that no major discrepancy was present between mRNA expression and protein levels. MRP levels were found to be independent of sample tumor content by immunophenotyping, suggesting that the presence of normal cells had no significant impact on measurements of MRP expression. We evaluated MRP in 55 biopsy samples from 40 patients with refractory lymphoma enrolled on a trial of infusional chemotherapy (EPOCH). Pre- and post-EPOCH samples were available from 15 patients. MRP levels were also evaluated in 16 newly diagnosed, untreated lymphoma patient samples. No significant difference in MRP mRNA expression was noted between pre- and post-EPOCH groups. Also, MRP levels in the newly diagnosed patient samples were not significantly different from either pre- or post-EPOCH groups. Two of 15 paired pre- and post-EPOCH patient samples exhibited overexpression of MRP after EPOCH chemotherapy, with measured increases of 10-fold and 18-fold. We conclude that MRP overexpression is not responsible for non-P-glycoprotein (Pgp)-mediated drug resistance in the majority of these patients, although it may be important in a subset of patients. Defining this subset prospectively could aid in the development of clinical trials of MRP modulation in drug-resistant lymphoma.

Identification of mutations at DNA topoisomerase I responsible for camptothecin resistance

A camptothecin-resistant cell line that exhibits more than 600-fold resistance to camptothecin, designated CPT(R)-2000, was established from mutagen-treated A2780 ovarian cancer cells. CPT(R)-2000 cells also exhibit 3-fold resistance to a DNA minor groove-binding ligand Ho33342, a different class of mammalian DNA topoisomerase I inhibitors. However, CPT(R)-2000 cells exhibit no cross-resistance toward drugs such as Adriamycin, amsacrine, vinblastine, and 4'-dimethyl-epipodophyllotoxin. The mRNA, protein levels, and enzyme-specific activity of DNA topoisomerase I are relatively the same in parental and CPT(R)-2000 cells. However, unlike the DNA topoisomerase I activity of parental cells, which can be inhibited by camptothecin, that of CPT(R)-2000 cells cannot. In addition, parental cells after camptothecin treatment results in a decrease in the level of DNA topoisomerase I, whereas CPT(R)-2000 cells are insensitive to camptothecin treatment. These results suggested that the mechanism of camptothecin resistance is most likely due to a DNA topoisomerase I structural mutation. This notion is supported by DNA sequencing results confirming that DNA topoisomerase I of CPT(R)-2000 is mutated at amino acid residues Gly717 to Val and Thr729 to Ile. We also used the yeast system to examine the mutation(s) responsible for camptothecin resistance. Our results show that each single amino acid change results in partial resistance, and the double mutation gives a synergetic effect on camptothecin resistance. Because both mutation sites are near the catalytic active center, this observation raises the possibility that camptothecin may act at the vicinity of the catalytic active site of the enzyme-camptothecin-DNA complex.

Initial pharmacokinetics and bioavailability of PSC 833, a P-glycoprotein antagonist

Resistant cancer cells have been shown to overexpress a 170-kd membrane glycoprotein called P-glycoprotein. P-glycoprotein, a product of the multidrug resistance 1 gene, functions as an energy-dependent efflux pump that decreases intracellular drug concentrations. A variety of nonchemotherapeutic agents have been shown to inhibit P-glycoprotein-dependent drug efflux including cyclosporin. PSC 833 is a nonimmunosuppressive derivative of cyclosporin D with the ability to reverse multidrug resistance because of P-glycoprotein overexpression in vitro. As part of early clinical development of PSC 833, the authors investigated the bioavailability of an oral formulation of PSC 833. PSC 833 (3 mg/kg) was administered as a 2-hour intravenous infusion on day 1 of the treatment cycle. Serial blood samples for the determination of PSC 833 whole blood concentrations were obtained after both the intravenous and oral doses. On day 5 of the study, patients received a single oral dose (9 mg/kg) of PSC 833. A total of 14 patients were treated. The intravenous data were best described by a two-compartment open model. The oral data also were described using a two-compartment model, with oral absorption incorporating a lag time to account for possible delays in absorption. There was large intra- and interpatient variability in the pharmacokinetics of PSC 833 in these patients. The absolute bioavailability of PSC 833 was 34% but ranged from 3% to 58% of the administered dose. The clearance (CI) of PSC 833, in general, was consistent between the two dose forms administered. The pharmacokinetic behavior of PSC 833 appears to be similar to that of cyclosporine.

Methods to detect P-glycoprotein-associated multidrug resistance in patients' tumors: consensus recommendations

Multidrug resistance (MDR), especially that associated with overexpression of MDR1 and its product, P-glycoprotein (Pgp), is thought to play a role in the outcome of therapy for some human tumors; however, a consensus conclusion has been difficult to reach, owing to the variable results published by different laboratories. Many factors appear to influence the detection of Pgp in clinical specimens, including its low and heterogeneous expression; conflicting definitions of detection end points; differences in methods of sample preparation, fixation, and analysis; use of immunological reagents with variable Pgp specificity and avidity and with different recognition epitopes; use of secondary reagents and chromogens; and differences in clinical end points. Also, mechanisms other than Pgp overexpression may contribute to clinical MDR. The combined effect of these factors is clearly important, especially among tumors with low expression of Pgp. Thus, a workshop was organized in Memphis, Tennessee, to promote the standardization of approaches to MDR1 and Pgp detection in clinical specimens. The 15 North American and European institutions that agreed to participate conducted three preworkshop trials with well-characterized MDR myeloma and carcinoma cell lines that expressed increasing amounts of Pgp. The intent was to establish standard materials and methods for a fourth trial, assays of Pgp and MDR1 in clinical specimens. The general conclusions emerging from these efforts led to a number of recommendations for future studies: (a) although detection of Pgp and MDR1 is at present likely to be more reliable in leukemias and lymphomas than in solid tumors, accurate measurement of low levels of Pgp expression under most conditions remains an elusive goal; (b) tissue-specific controls, antibody controls, and standardized MDR cell lines are essential for calibrating any detection method and for subsequent analyses of clinical samples; (c) use of two or more vendor-standardized anti-Pgp antibody reagents that recognize different epitopes improves the reliability of immunological detection of Pgp; (d) sample fixation and antigen preservation must be carefully controlled; (e) multiparameter analysis is useful in clinical assays of MDR1/Pgp expression; (f) immunostaining data are best reported as staining intensity and the percentage of positive cells; and (g) arbitrary minimal cutoff points for analysis compromise the reliability of conclusions. The recommendations made by workshop participants should enhance the quality of research on the role of Pgp in clinical MDR development and provide a paradigm for investigations of other drug resistance-associated proteins.

Clinical reversal of multidrug resistance

Reversal of drug resistance offers the hope of increasing the efficacy of conventional chemotherapy. We tested dexverapamil as a P-glycoprotein antagonist in combination with EPOCH chemotherapy in refractory non-Hodgkin's lymphoma. In a cross-over design, dexverapamil was added to EPOCH after disease stabilization or progression occurred. Objective responses were observed in 10 of 41 assessable patients. Biopsies for mdr-1 were obtained before EPOCH treatment and at the time of cross-over to dexverapamil. Levels of mdr-1 were low before EPOCH, but increased four-fold or more in 42% of patients in whom serial samples were obtained. Pharmacokinetic analysis revealed median peak concentrations of dexverapamil and its metabolite, nor-dexverapamil, of 1.66 mumol/l and 1.58 mumol/l, respectively. Since both are comparable antagonists, a median peak total reversing concentration of 3.24 mumol/l was achieved. Pharmacokinetic analysis of doxorubicin and etoposide levels confirmed a delay in the clearance of doxorubicin ranging from 5% to 24%; no change in the pharmacokinetics of etoposide was observed. This study provides sufficient rationale for testing dexverapamil in a randomized clinical trial.