Cell surface Gb3 expression is a likely tumour biomarker for acquired cisplatin resistance of NSCLC and MPM cells. Tumour cell resistance to MDR1 inhibitors of cell surface MDR1 and Gb3 could explain the aggressiveness of NSCLC and MPM. Therapy with GCS activity inhibitors or toxin targeting of the Gb3 receptor may substantially reduce acquired cisplatin drug resistance of NSCLC and MPM cells.

Background: A novel link between oncogenic KRAS signalling and WT1 was recently identified. We sought to investigate the role of WT1 and KRAS in proliferation and apoptosis. Methods: KRAS mutations and WT1 (cMyc) expression were detected using Sanger sequencing and real-time PCR in 77 patients with non-small cell lung cancer (NSCLC). Overexpression and knockdown of WT1 were generated with plasmid and siRNA via transient transfection technology in H1299 and H1568 cells. MTT assay for detection of cell proliferation, and TUNEL assay and proteomic profiler assay for apoptosis evaluation were carried out. Dual luciferase reporter assay and ChIP-PCR were performed to validate the effect of WT1 on the cMyc promoter. Results: KRAS mutations showed a negative impact on overall survival (OS). High expressions of WT1 and cMyc were associated with poor OS in KRAS mutant subgroup. The potential mechanisms that WT1 promotes proliferation and impedes apoptosis through affecting multiple apoptosis-related regulators in KRAS mutant NSCLC cells were identified. WT1 could activate cMyc promoter directly in KRAS mutant cells. Conclusion: The results suggest that WT1 and c-MYC expression is important for survival in KRAS mutant tumors as opposed to KRAS wild-type tumors. For treatment of KRAS mutant NSCLC, targeting WT1 and cMyc may provide alternative therapeutic strategies.

A major problem with anti-cancer drug treatment is the development of acquired multidrug resistance (MDR) of the tumor cells. Verotoxin-1 (VT-1) exerts its cytotoxicity by targeting the globotriaosylceramide membrane receptor (Gb3), a glycolipid associated with multidrug resistance. Gb3 is overexpressed in many human tumors and tumor cell lines with inherent or acquired MDR. Gb3 is co-expressed and interplays with the membrane efflux transporter P-gp encoded by the MDR1 gene. P-gp could act as a lipid flippase and stimulate Gb3 induction when tumor cells are exposed to cancer chemotherapy. Recent work has shown that apoptosis and inherent or acquired multidrug resistance in Gb3-expressing tumors could be affected by VT-1 holotoxin, a sub-toxic concentration of the holotoxin concomitant with chemotherapy or its Gb3-binding B-subunit coupled to cytotoxic or immunomodulatory drug, as well as chemical manipulation of Gb3 expression. The interplay between Gb3 and P-gp thus gives a possible physiological approach to augment the chemotherapeutic effect in multidrug resistant tumors.

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9532 Background: Sunitinib malate (SU11248) is an oral multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activities due to inhibition of KIT, VEGFRs, PDGFRs, RET, and FLT3. In previous phase I/II and III trials in pts with imatinib-resistant GIST, sunitinib demonstrated efficacy and favorable clinical tolerability when administered in 6-week treatment cycles consisting of 4 weeks sunitinib (50 mg QD), followed by 2 weeks off treatment. The current study examined continuous sunitinib dosing as a way to avoid potential reactivation of tumor cells during the off-treatment period. Methods: This open-label, multicenter, phase II trial was designed to evaluate the efficacy, safety, and tolerability of sunitinib administered once daily using a continuous-treatment regimen in pts with imatinib-resistant GIST. Treatment is initiated with 37.5 mg sunitinib daily, with the option to titrate dosing on an individual basis depending on tolerability. The primary study endpoint is clinical benefit rate, defined as percent of evaluable pts with confirmed CR, PR, or SD ≥24 weeks using RECIST. Secondary endpoints included ORR, TTP, PFS, OS, and safety/tolerability measures. Results: Of 28 pts who had started treatment at the time of this analysis, early results were available for 17 pts from two centers. The most commonly occurring treatment-related adverse events were stomatitis, hand-foot syndrome, gastroesophageal reflex, and fatigue, which were generally grade 1. Two pts experienced treatment-related grade 3 hypertension, and another exhibited grade 3 asymptomatic neutropenia. Five pts have been evaluated for benefit after 8 weeks of treatment. Stable disease (which is the clinical benefit typically observed in GIST pts treated with sunitinib) was demonstrated in all five pts. Expanded safety/tolerability and efficacy results will be available for presentation. Conclusions: Continuous dosing of sunitinib is feasible and appears to be associated with acceptable tolerability in pts with imatinib-refractory GIST, similar to the extensive experience documented with intermittent sunitinib dosing. It is possible that continuous daily dosing of sunitinib may further improve the outcomes of pts with GIST. [Table: see text]

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