FDA review summary: Mozobil in combination with granulocyte colony-stimulating factor to mobilize hematopoietic stem cells to the peripheral blood for collection and subsequent autologous transplantation.

PURPOSE: On December 15, 2008, the US Food and Drug Administration approved plerixafor (Mozobil; Genzyme Corp.), a new small-molecule inhibitor of the CXCR4 chemokine receptor, for use in combination with granulocyte colony-stimulating factor (G-CSF) to mobilize hematopoietic stem cells (HSC) to the peripheral blood for collection and subsequent autologous transplantation in patients with non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). This summary reviews the database supporting this approval. EXPERIMENTAL DESIGN: The safety and efficacy of plerixafor were demonstrated by 2 multicenter, randomized, placebo-controlled studies in patients with NHL and MM who were eligible for autologous HSC transplantation. The primary efficacy end points were the collection of > or = 5 x 10(6) CD34+ cells/kg from the peripheral blood in 4 or fewer apheresis sessions in patients with NHL or > or = 6 x 10(6) CD34+ cells/kg from the peripheral blood in 2 or fewer apheresis sessions in patients with MM. RESULTS: The 2 randomized studies combined enrolled 600 patients (298 with NHL and 302 with MM). Fifty-nine percent of patients with NHL who were mobilized with G-CSF and plerixafor had peripheral blood HSC collections of > or = 5 x 10(6) CD34+ cells/kg in 4 or fewer apheresis sessions, compared with 20% of patients with NHL who were mobilized with G-CSF and placebo (p < 0.001). Seventy-two percent of patients with MM who were mobilized with Mozobil and G-CSF had peripheral blood HSC collections of > or = 6 x 10(6) CD34+ cells/kg in 2 or fewer apheresis sessions, compared with 34% of patients with MM who were mobilized with placebo and G-CSF (p < 0.001). Common adverse reactions included diarrhea, nausea, vomiting, flatulence, injection site reactions, fatigue, arthralgia, headache, dizziness, and insomnia. CONCLUSIONS: This report describes the Food and Drug Administration review supporting the approval of plerixafor.

(13)C-5-FU breath test current status and future directions: a comprehensive review.

Breath tests (BTs) represent a safe non-invasive alternative strategy that could provide valuable diagnostic information in conditions like fat malabsorption, carbohydrate (lactose and fructose) malabsorption, liver dysfunction, impaired gastric emptying, abnormal small bowel transit time, small intestinal bacterial overgrowth and Helicobacter pylori infection. To date, despite the availability of a number of breath tests, only three have gained approval by the FDA for application in a clinical setting ((13)C-urea breath test for the detection of H. pylori; NO breath test for monitoring asthma and alkane breath test for heart transplant rejection). Unfortunately, none of these tests investigate cancer patients or response to cancer chemotherapy. Several years ago it was realized that the presence of a reliable non-invasive approach could assist in the detection of patients at risk of developing severe life-threatening toxicities prior to the administration of fluoropyrimidines (e.g. 5-FU) or related cancer chemotherapy. 5-FU toxicity results mainly from deficient uracil catabolism. This review discusses the development of a BT that utilizes an orally administered pyrimidine ([2-(13)C]-uracil) which is metabolized via the same catabolic pathway as 5-FU. This ([2-(13)C]-uracil) breath test could provide a valuable addition to the patients' standard of care.

Increased prevalence of dihydropyrimidine dehydrogenase deficiency in African-Americans compared with Caucasians.

PURPOSE: African-American patients with colorectal cancer were observed to have increased 5-fluorouracil (5-FU)-associated toxicity (leukopenia and anemia) and decreased overall survival compared with Caucasian patients. One potential source for this disparity may be differences in 5-FU metabolism. Dihydropyrimidine dehydrogenase (DPD), the initial and rate-limiting enzyme of 5-FU catabolism, has previously been shown to have significant interpatient variability in activity. Several studies have linked reduced DPD activity to the development of 5-FU toxicity. Although the distribution of DPD enzyme activity and the frequency of DPD deficiency have been well characterized in the Caucasian population, the distribution of DPD enzyme activity and the frequency of DPD deficiency in the African-American population are unknown. EXPERIMENTAL DESIGN: Healthy African-American (n=149) and Caucasian (n=109) volunteers were evaluated for DPD deficiency using both the [2-(13)C]uracil breath test and peripheral blood mononuclear cell DPD radioassay. RESULTS: African-Americans showed significantly reduced peripheral blood mononuclear cell DPD enzyme activity compared with Caucasians (0.26+/-0.07 and 0.29+/-0.07 nmol/min/mg, respectively; P=0.002). The prevalence of DPD deficiency was 3-fold higher in African-Americans compared with Caucasians (8.0% and 2.8%, respectively; P=0.07). African-American women showed the highest prevalence of DPD deficiency compared with African-American men, Caucasian women, and Caucasian men (12.3%, 4.0%, 3.5%, and 1.9%, respectively). CONCLUSION: These results indicate that African-Americans, particularly African-American women, have significantly reduced DPD enzyme activity compared with Caucasians, which may predispose this population to more 5-FU toxicity.

Targeting the epidermal growth factor receptor in the treatment of colorectal cancer: state of the art.

The epidermal growth factor receptor (EGFR) is an important mediator of normal cellular processes such as growth, survival, differentiation and morphogenesis. Disturbances in the EGFR pathway have been associated with the development and progression of malignancy, including cellular proliferation, angiogenesis, invasion/metastasis and anti-apoptosis, as well as with resistance to chemotherapy and/or radiation therapy. As a result, this is an excellent rationale for treatment with EGFR-specific therapeutic agents. These agents may be EGFR-targeted antibodies or small molecules that inactivate the receptor tyrosine kinase. While only cetuximab has received US FDA approval for the treatment of colorectal cancer, numerous agents are currently in development and in clinical trials and constitute an area of intensive, ongoing research.

The role of Sp1 and Sp3 in the constitutive DPYD gene expression.

Dihydropyrimidine dehydrogenase (DPD), the initial and rate-limiting enzyme in the 5-fluorouracil (5-FU) catabolic pathway, has been implicated as one of the factors determining the efficacy and toxicity of the anticancer agent 5-FU. Studies have attributed variation in DPD activity partially to alterations at the transcriptional level of DPYD gene. We investigated the transcription factors implicated in the constitutive expression of DPYD by utilizing a 174-bp fragment of the DPYD promoter region in which three consensus Sp protein binding sites (SpA, SpB and SpC) were predicted. The binding of Sp1 and Sp3 transcription factors to this region was detected by electrophoretic mobility shift and chromatin immunoprecipitation assays. By ectopically expressing human Sp1 and Sp3 in Sp-deficient Drosophila S2 cells, we demonstrated that Sp1 is a strong activator, while Sp3 by its own is a weak activator of the DPYD promoter. Moreover, Sp3 may serve as a competitor of Sp1, thus decreasing the Sp1 induced promoter activity. SpA, SpB and SpC sites are all Sp1 inducible. In the full activation of the DPYD promoter in human cell lines, the SpB site is essential; the SpC site works cooperatively with SpB, while SpA has minor promoter activity. These studies provide further insight into the molecular mechanisms underlying the heterogeneity of DPD activity, and may facilitate the efficacy and safety of 5-FU-based chemotherapy.

The uracil breath test in the assessment of dihydropyrimidine dehydrogenase activity: pharmacokinetic relationship between expired 13CO2 and plasma [2-13C]dihydrouracil.

PURPOSE: Dihydropyrimidine dehydrogenase (DPD) deficiency is critical in the predisposition to 5-fluorouracil dose-related toxicity. We recently characterized the phenotypic [2-(13)C]uracil breath test (UraBT) with 96% specificity and 100% sensitivity for identification of DPD deficiency. In the present study, we characterize the relationships among UraBT-associated breath (13)CO(2) metabolite formation, plasma [2-(13)C]dihydrouracil formation, [2-(13)C]uracil clearance, and DPD activity. EXPERIMENTAL DESIGN: An aqueous solution of [2-(13)C]uracil (6 mg/kg) was orally administered to 23 healthy volunteers and 8 cancer patients. Subsequently, breath (13)CO(2) concentrations and plasma [2-(13)C]dihydrouracil and [2-(13)C]uracil concentrations were determined over 180 minutes using IR spectroscopy and liquid chromatography-tandem mass spectrometry, respectively. Pharmacokinetic variables were determined using noncompartmental methods. Peripheral blood mononuclear cell (PBMC) DPD activity was measured using the DPD radioassay. RESULTS: The UraBT identified 19 subjects with normal activity, 11 subjects with partial DPD deficiency, and 1 subject with profound DPD deficiency with PBMC DPD activity within the corresponding previously established ranges. UraBT breath (13)CO(2) DOB(50) significantly correlated with PBMC DPD activity (r(p) = 0.78), plasma [2-(13)C]uracil area under the curve (r(p) = -0.73), [2-(13)C]dihydrouracil appearance rate (r(p) = 0.76), and proportion of [2-(13)C]uracil metabolized to [2-(13)C]dihydrouracil (r(p) = 0.77; all Ps < 0.05). CONCLUSIONS: UraBT breath (13)CO(2) pharmacokinetics parallel plasma [2-(13)C]uracil and [2-(13)C]dihydrouracil pharmacokinetics and are an accurate measure of interindividual variation in DPD activity. These pharmacokinetic data further support the future use of the UraBT as a screening test to identify DPD deficiency before 5-fluorouracil-based therapy.

Dihydropyrimidine dehydrogenase deficiency: impact of pharmacogenetics on 5-fluorouracil therapy.

Through the use of pharmacogenetic studies, interindividual variability in response (efficacy and toxicity) to 5-fluorouracil (5-FU) chemotherapy has been linked to the rate-limiting enzyme in the drug's catabolic pathway, known as dihydropyrimidine dehydrogenase (DPD). This pharmacogenetic syndrome, known as "DPD deficiency," results in excessive amounts of 5-FU available to be anabolized to its active metabolites and is relatively undetectable by clinical observation prior to 5-FU administration. Extensive studies have associated both profound and partial deficiency in DPD activity with severe, unanticipated toxicity after 5-FU administration, while research on the molecular basis behind DPD deficiency has been linked to various sequence variants of the DPYD gene. Due to the widespread use of 5-FU, the severity of toxicity associated with DPD deficiency, and the prevalence of DPD deficiency in the population, extensive research is continually being performed to develop quick and accurate phenotypic and genotypic assays suitable for clinical settings that would allow clinicians to identify patients susceptible to adverse 5-FU reactions.

Structure-activity study with bioreductive benzoquinone alkylating agents: effects on DT-diaphorase-mediated DNA crosslink and strand break formation in relation to mechanisms of cytotoxicity.

PURPOSE: Structure-activity studies were carried out with the model bioreductive alkylating agent benzoquinone mustard (BM) and its structural analogs. The specific objectives were: (1) to investigate the effects of functional group substitutions to the benzoquinone ring on DNA crosslink and strand break formation subsequent to reduction of the analogs by DT-diaphorase (DTD) in vitro, (2) to correlate DNA crosslink and strand break formation by the analogs with anaerobic reduction of the BM analogs by DTD and their redox cycling in vitro, and (3) to correlate DNA crosslink and strand break formation by the BM analogs with their cytotoxic effects in cancer cells. METHODS: DNA interstrand crosslink and single-strand break formation were assessed using agarose gel assays. To determine DNA interstrand crosslinks or single-strand breaks, linearized or supercoiled plasmid DNA, respectively, were incubated with purified human DTD and increasing concentrations of each BM analog. Subsequently, DNA was electrophoresed on an agarose gel and DNA crosslink and strand break formation were quantified using densitometry. The rates of reduction of the BM analogs by purified human DTD were measured in vitro under hypoxic conditions, and the redox cycling potential was determined under aerobic conditions using HPLC analysis. The cytotoxic activities of these agents in human tumor cell lines were measured by the MTT assay, with and without the DTD inhibitor, dicoumarol. RESULTS: BM analogs with electron-donating groups (MeBM, MBM, m-MeBM), electron-withdrawing groups (CBM, FBM), sterically bulky groups (PBM, m-PBM, m-TBM) and positional isomers (MeBM, m-MeBM, PBM, m-PBM) were synthesized. After reduction by DTD, the BM analogs produced a concentration-dependent increase in DNA crosslink and DNA strand break formation. The E(10) (extent of DNA crosslink formation produced by 10 micro M BM analog) for DNA crosslink formation displayed the rank order MeBM approximately MBM>m-MeBM approximately PBM approximately BM>CBM>FBM>m-PBM approximately m-TBM. For DNA strand break formation, the E(10) values (extent of DNA strand break formation produced by 10 micro M BM analog) displayed the rank order MeBM>MBM>m-MeBM>PBM>BM approximately CBM>FBM>m-PBM approximately m-TBM. Importantly, the cytotoxic activity of the BM analogs in SK-Mel-28 human melanoma cells correlated positively with the E(10) values for DTD-mediated DNA crosslink formation ( r(s)=0.87, P<0.05) and DNA strand break formation ( r(s)=0.95, P<0.05). Similar correlations were observed in NCI-H661 human lung carcinoma cells. Furthermore, the D(10) values (concentration of BM analog that decreased the surviving cell fraction to 0.1) for cytotoxic activity of the BM analogs correlated with the maximum levels of DNA crosslinks formed with each BM analog, with r(s) values of -0.85 ( P<0.05) for the NCI-H661 cell line, and -0.81 ( P<0.05) for the SK-MEL-28 cell line. The half-time of reduction (t(1/2)) of the BM analogs by DTD did not correlate with DNA crosslink formation, DNA strand break formation, or cytotoxic potency of the analogs. CONCLUSIONS: Functional groups on the benzoquinone ring affect the ability of BM to produce DNA crosslinks and strand breaks following reduction by DTD. Electron-donating groups increased DNA damage, whereas electron-withdrawing groups and sterically bulky groups at the C6 position had no effect or decreased the ability of the compounds to produce DNA damage compared to BM. Moreover, both DNA crosslink and strand break formation appear to have an important impact on the cytotoxicity of the BM analogs. These results may have significance for optimal use of BM-based antitumor agents and for rationalization of the development of novel therapeutic compounds that require bioactivation by DTD.

NMDA receptor antagonists to characterize rat renal organic cation transporter function.

We hypothesized that uncompetitive NMDA glutamate receptor antagonists memantine (2,5-dimethyl-1-adamantanamine), and amino-alkyl-cyclohexane compounds: MRZ 2/579 (1-amino-1,3,3,5,5-pentamethylcyclohexane HCl), MRZ 2/600 (1-amino-1-ethyl-3,3,5,5-tetramethylcyclohexane HCl), and MRZ 2/615 (1-amino-1,3,5,5-tetramethyl-3-ethylcyclohexane HCl), all derivatives of amantadine (1-adamantanamine HCl), would inhibit the energy-dependent uptake of amantadine into rat renal tubules. All compounds displayed a concentration-dependent inhibition of amantadine uptake in the proximal and distal renal tubules. MRZ 2/579 showed a novel distal tubule selectivity of inhibition (P < 0.001). At a therapeutic amantadine concentration, bicarbonate-dependent transporter inhibition selectivity was observed with all compounds (P < 0.05) except MRZ 2/600, the only compound with a sterically bulky group next to the amino group of the cyclohexane ring structure. Steric hindrance around the ionized amino group of the cyclohexane ring appears to prevent bicarbonate-mediated organic cation transport. Furthermore, the distal tubule inhibition selectivity with MRZ 2/579 provides a novel tool to study the relative importance of organic cation transporters (OCTs) in proximal vs. distal renal tubules.

Aripiprazole (Otsuka Pharmaceutical Co).

Otsuka Pharmaceuticals in collaboration with Bristol-Myers Squibb is developing aripiprazole, a dual dopamine autoreceptor agonist and postsynaptic D2 receptor antagonist, for the potential treatment of psychoses including schizophrenia [281327], [340364]. A regulatory filing for schizophrenia in the US was submitted at the end of 2001 [340364]. The compound entered phase III trials in Japan in 1995 [192966]. Although presynaptic dopamine autoreceptor agonists may be efficacious in the treatment of schizophrenia, they may also potentially increase the risk for exacerbation of psychosis through stimulation of postsynaptic dopaminergic receptors [245791], [350478], [350479]. However, earlier neuropharmacology studies have shown that aripiprazole can act as a presynaptic D2 agonist while displaying an antagonistic effect at the postsynaptic D2 receptors [281327], [337126], [350479], [424587], [424588]. In animal models, aripiprazole inhibits the apomorphine-induced stereotypy, without causing catalepsy [281327], [337126]. Moreover, in contrast to classical antipsychotics that produce disabling movement disorders, aripiprazole does not cause an upregulation of D2 receptors or an increase in expression of the c-fos mRNA in the striatum, in agreement with the low risk for extrapyramidal side effects (EPS) during aripiprazole treatment [245781], [262096], [350481], [350483]. Collectively, aripiprazole is an important atypical antipsychotic candidate with a favorable safety profile. Moreover, the mechanism of action of aripiprazole differentiates it from both typical and atypical antipsychotics and hence, may provide important leads for pharmacotherapy of schizophrenia and other psychotic disorders. In January 2000, Lehman Brothers predicted peak sales of aripiprazole could reach US $500 million [357788]. In February 2001, Credit Suisse First Boston predicted sales of US $403 million in 2005 [399484].

The effect of functional groups on reduction and activation of quinone bioreductive agents by DT-diaphorase.

PURPOSE: Bioreductive antitumor agents are an important class of anticancer drugs that include the clinically used drug, mitomycin C, and new agents such as EO9 and tirapazamine that have recently been tested in clinical trials. These agents require activation by reductive enzymes such as DT-diaphorase or NADPH:cytochrome P450 reductase. A major focus for improving cancer chemotherapy has been to increase the selectivity and targeting of antitumor drugs to tumor cells. Bioreductive antitumor agents are ideally suited to improving tumor selectivity by an enzyme-directed approach to tumor targeting. However, none of the bioreductive agents developed to date has been specific for activation by a single reductive enzyme. This is in part due to a lack of knowledge about structural factors that confer selectivity for activation by reductive enzymes. The purpose of this study was to investigate the ability of specific functional groups to modify reduction and activation of quinone bioreductive agents by DT-diaphorase. METHODS: We used a series of model benzoquinone mustard (BM) bioreductive agents and compared the parent compound BM to MBM, which has a strong electron-donating methoxy group, MeBM, which has a weaker electron-donating methyl group, CBM, which has an electron-withdrawing chloro group, and PBM and its structural isomer, meta-PBM (m-PBM), which both have sterically bulky benzene rings attached to the quinone moiety. We determined the rate of reduction of these agents by purified human DT-diaphorase under hypoxic and aerobic conditions. We also measured the cytotoxic activity of these agents in human tumor cell lines with and without the DT-diaphorase inhibitor, dicoumarol. RESULTS: Under hypoxic conditions in vitro, the t(1/2) values for reduction of the analogs by purified DT-diaphorase were 4, 6, 8, 9, 10 and 21 min for BM, MeBM, CBM, MBM, PBM and m-PBM, respectively. Under aerobic conditions the rank order of redox cycling after two-electron reduction by DT-diaphorase was MBM > MeBM > BM approximately CBM approximately PBM approximately m-PBM. The rate of reduction by DT-diaphorase of HBM, a non-alkylating analog of BM, was similar to that of BM under hypoxic conditions, and the rate of redox cycling under aerobic conditions was comparable to that of BM, suggesting that structural changes to the cytotoxic group of these BMs do not affect DT-diaphorase-mediated reduction and redox cycling potential. MBM, MeBM and PBM were more toxic than BM in the NCI-H661 human non-small-cell lung cancer cells and SK-MEL-28 human melanoma cells, while CBM displayed significantly increased cytotoxic activity compared to BM only in the NCI H661 cells. m-PBM had similar cytotoxic activity compared with BM in both cell lines. These cell lines have moderate to high levels of DT-diaphorase activity. When cells were pretreated with the DT-diaphorase inhibitor, dicoumarol, the cytotoxic activity of BM increased while that of MBM decreased in both cell lines, suggesting that BM was inactivated by DT-diaphorase while MBM was activated by this enzyme. Pretreatment of the SK-MEL-28 melanoma cells with dicoumarol resulted in an increased cytotoxic activity of MeBM, but pretreatment of the NCI-H661 cells did not affect the cytotoxicity of MeBM. This suggests, that similar to the results with BM, DT-diaphorase is an inactivating enzyme for MeBM in the SK-MEL-28 cell line. Dicoumarol had no significant effect on the cytotoxicity of CBM, PBM or m-PBM in both cell lines. CONCLUSIONS: These studies demonstrated that functional groups can significantly affect the reduction and activation of bioreductive agents by DT-diaphorase. All the functional groups decreased the rate of reduction of the quinone group by DT-diaphorase. Since MeBM and MBM, with electron-donating functional groups, and CBM with an electron-withdrawing functional group had similar half-lives of reduction by DT-diaphorase, steric rather than electronic effects of the functional groups appear to be more important for modifying the rate of reduction by DT-diaphorase. Steric effects on reduction by DT-diaphorase were also influenced by the position of the functional group on the quinone ring moiety, as the reduction of m-PBM was much slower than the reduction of PBM. The electron-donating methoxy and methyl functional groups increased the ability of the reduced products of MBM and MeBM to undergo redox cycling. DT-diaphorase appeared to be an activating enzyme for MBM. This may have resulted in part from increased formation of reactive oxygen species resulting from the increased redox cycling by MBM. In contrast, DT-diaphorase was an inactivating enzyme for BM, and for MeBM in the SK-MEL-28 melanoma cells, possibly because the hydroquinone product of BM and MeBM may be less cytotoxic than the semiquinone produced by one-electron reduction by NADPH:cytochrome P450 reductase.