A phase II clinical trial of ixabepilone (Ixempra; BMS-247550; NSC 710428), an epothilone B analog, in patients with metastatic renal cell carcinoma.

PURPOSE: Ixabepilone (Ixempra; BMS-247550) is an epothilone B analog and nontaxane microtubule-stabilizing compound with clinical activity in a range of solid tumors. This phase II study was conducted to assess the efficacy and safety of ixabepilone in patients with metastatic renal cell carcinoma. EXPERIMENTAL DESIGN: Patients with metastatic renal cell carcinoma who had measurable disease and had not received previous cytotoxic or targeted therapy were treated with 6 mg/m(2) ixabepilone i.v. daily for 5 days every 3 weeks. Levels of Glu-terminated and acetylated tubulin, markers of microtubule stabilization, were assessed by Western blot. VHL gene mutation status was determined by sequencing. RESULTS: Eighty-seven patients received a total of 590 cycles, with a median of 5 cycles (range, 1-29). The overall response rate was 13% (Response Evaluation Criteria in Solid Tumor). One patient had a complete response, 10 patients had partial responses, and 59 patients had stable disease. The median duration of response was 5.5 months. The median overall survival of renal cell carcinoma Motzer grade 0 and 1 patients with clear cell histology was 19.25 months. Treatment-related adverse events were primarily alopecia, gastrointestinal toxicity, neuropathy, and fatigue. Biopsies were done at baseline and after five doses of ixabepilone. Microtubule target engagement was achieved in 84.6% to 92.3% of patients evaluated. No correlation was identified between the target engagement, VHL gene mutation status, and clinical response. CONCLUSION: Ixabepilone can cause tumor regression in some patients with metastatic renal cell carcinoma and could be considered in combination regimens with other therapies.

Relationship of EGFR mutations, expression, amplification, and polymorphisms to epidermal growth factor receptor inhibitors in the NCI60 cell lines.

PURPOSE: The mechanism of sensitivity and resistance to epidermal growth factor receptor (EGFR) inhibitors is incompletely understood, particularly in cancers other than non-small-cell lung cancer (NSCLC). To understand the variable response to this class of drugs, we used the NCI60 cancer cell lines. We aimed to determine if there are interactions between EGFR expression, mutations, polymorphisms, and gene amplification, and whether these factors are associated with variability in response to EGFR inhibitors. EXPERIMENTAL DESIGN: The EGFRVIII and tyrosine kinase (TK) domain mutations were examined in the NCI60 cancer cell lines. Five polymorphisms, -216G/T, -191C/A, intron 1 (CA)n, R497K, and 2607A/G, were genotyped. EGFR amplification was also assessed with high-density single-nucleotide polymorphism chip and real-time PCR, respectively. The results were correlated with cytotoxicity data for erlotinib and other 11 EGFR inhibitors, as well as other publicly available data for these lines. RESULTS: All 12 inhibitors behaved similarly. No EGFRVIII but putative TK mutations in two cell lines were found. Both mutant cell lines were insensitive to all inhibitors. Meanwhile, response did not correlate with EGFR amplification but with EGFR gene expression, especially in the cell lines with relatively normal gene status. In addition, EGFR expression was associated with the -216G/T polymorphism but not with the intron 1 (CA)n polymorphism. A combination of -216G/T and R497K polymorphisms was weakly associated with drug response. CONCLUSIONS: These observations suggest that in addition to TK mutations, germ-line variability may also contribute to the pharmacodynamics of EGFR inhibitors, particularly when EGFR is genetically normal.

Aberrant transcription from an unrelated promoter can result in MDR-1 expression following drug selection in vitro and in relapsed lymphoma samples.

The development of drug resistance in the treatment of cancer remains a major problem. The hallmark of multidrug resistance is cross-resistance to multiple structurally unrelated compounds. The MDR-1 gene encoding P-glycoprotein mediates one of the most extensively studied mechanisms of drug resistance. Previous studies led to the proposal that two promoters control expression of the MDR-1 gene, and these were designated the upstream and downstream promoters. In the present article, we provide evidence that transcripts originating from the putative upstream promoter of MDR-1 are in fact aberrant transcripts whose expression is regulated by nearby genomic sequences that include a human endogenous retroviral long terminal repeat (LTR). Expression of this LTR occurs in all cells. We show that following drug selection, especially in cases where gene amplification has occurred, MDR-1 transcripts can begin near this retroviral LTR with transcription proceeding in the direction opposite of the usual LTR transcription. Because expression of these aberrant MDR-1 transcripts (AMT) is found primarily in drug-resistant cell lines, we conclude that the development of drug resistance or the attendant drug exposure might have a role in the activation of this phenomenon or the selection of cells expressing AMTs. Demonstration of similar aberrant transcripts in tumor samples obtained from patients with relapsed lymphoma suggests that this phenomenon may also occur clinically.

Single-nucleotide polymorphism (SNP) analysis in the ABC half-transporter ABCG2 (MXR/BCRP/ABCP1).

Variations in the amino acid sequence of ABC transporters have been shown to impact substrate specificity. We identified two acquired mutations in ABCG2, the ABC half-transporter overexpressed in mitoxantrone-resistant cell lines. These mutations confer differences in substrate specificity and suggest that naturally occurring variants could also affect substrate specificity. To search for the existence of single nucleotide polymorphisms (SNPs) in ABCG2, we sequenced 90 ethnically diverse DNAs from the Single Nucleotide Polymorphism Discovery Resource representing the spectrum of human genotypes. We identified 3 noncoding SNPs in the untranslated regions, 3 nonsynonymous and 2 synonymous SNPs in the coding region and 7 SNPs in the intron sequences adjacent to the sixteen ABCG2 exons. Nonsynonymous SNPs at nucleotide 238 (V12M; exon 2) and nucleotide 625 (Q141K; exon 5) showed a greater frequency of heterozygosity (22.2% and 10%) than the SNP at 2062 (D620N; exon 16). Heterozygous changes at nucleotide 238 are in linkage disequilibrium with an SNP observed 36 bases downstream from the end of exon 2. No polymorphism at amino acid 482 was identified to correspond to the R to G or R to T mutations previously found in two drug resistant cell lines. Among 23 drug resistant sublines for which sequence at position 482 was determined, no additional mutations were found. Heterozygosity at amino acid 12 allowed us to identify overexpression of a single allele in a subset of drug resistant cell lines, a feature that could be exploited clinically in evaluating the significance of ABCG2 expression in malignancy. We conclude that ABCG2 is well conserved and that described amino acid polymorphisms seem unlikely to alter transporter stability or function.