A phase 1 study of gemcitabine combined with dasatinib in patients with advanced solid tumors.

PURPOSE: Dasatinib has been shown preclinically to overcome resistance to gemcitabine. We evaluated the safety and biological activity of the combination of dasatinib and gemcitabine in patients with advanced solid tumors. EXPERIMENTAL DESIGN: In a phase 1 study (3 + 3 design), patients received daily dasatinib with weekly gemcitabine on days 1, 8 and 15 of a 28-day cycle (except cycle 1 which was 8 weeks). Dose escalation began with dasatinib 70 mg orally (PO) daily and gemcitabine 800 mg/m(2) intravenously (IV) weekly. RESULTS: Forty-seven patients (15 men; median age = 55 years; median number of prior systemic treatments = 4) were enrolled. Dose-limiting toxicities were grade 3 fatigue and dehydration, with the maximum tolerated dose being dasatinib 100 mg PO qd and gemcitabine 600 mg/m(2) IV weekly. The most common grade 3-4 toxicities were anemia (21.5 %), thrombocytopenia (26.2 %), leukopenia (26.2 %), and pleural effusion (10.7 %). Six of 47 patients attained stable disease (SD) ≥ 6 months or partial response including 2 of 8 patients with pancreatic cancer (SD ≥ 6 months; both gemcitabine-refractory), 2 of 3 patients with thymoma (SD for 9.8 and 15 months), 1 of 1 patient with anal squamous cancer (SD 15 months) and 1 of 5 patients with inflammatory breast cancer. No significant changes in circulating tumor cells or interleukin-8 levels were observed. CONCLUSIONS: The combination was well tolerated at doses of dasatinib 100 mg PO daily and gemcitabine 600 mg/m(2) IV weekly. SD ≥ 6 months/ PR was observed in gemcitabine-refractory pancreatic cancer, thymoma, anal cancer and inflammatory breast cancer.

A Dictyostelium chalone uses G proteins to regulate proliferation.

BACKGROUND: Several studies have shown that organ size, and the proliferation of tumor metastases, may be regulated by negative feedback loops in which autocrine secreted factors called chalones inhibit proliferation. However, very little is known about chalones, and how cells sense them. We previously identified two secreted proteins, AprA and CfaD, which act as chalones in Dictyostelium. Cells lacking AprA or CfaD proliferate faster than wild-type cells, and adding recombinant AprA or CfaD to cells slows their proliferation. RESULTS: We show here that cells lacking the G protein components Galpha8, Galpha9, and Gbeta proliferate faster than wild-type cells despite secreting normal or high levels of AprA and CfaD. Compared with wild-type cells, the proliferation of galpha8-, galpha9- and gbeta- cells are only weakly inhibited by recombinant AprA (rAprA). Like AprA and CfaD, Galpha8 and Gbeta inhibit cell proliferation but not cell growth (the rate of increase in mass and protein per nucleus), whereas Galpha9 inhibits both proliferation and growth. galpha8- cells show normal cell-surface binding of rAprA, whereas galpha9- and gbeta- cells have fewer cell-surface rAprA binding sites, suggesting that Galpha9 and Gbeta regulate the synthesis or processing of the AprA receptor. Like other ligands that activate G proteins, rAprA induces the binding of [3H]GTP to membranes, and GTPgammaS inhibits the binding of rAprA to membranes. Both AprA-induced [3H]GTP binding and the GTPgammaS inhibition of rAprA binding require Galpha8 and Gbeta but not Galpha9. Like aprA- cells, galpha8- cells have reduced spore viability. CONCLUSION: This study shows that Galpha8 and Gbeta are part of the signal transduction pathway used by AprA to inhibit proliferation but not growth in Dictyostelium, whereas Galpha9 is part of a differealnt pathway that regulates both proliferation and growth, and that a chalone signal transduction pathway uses G proteins.

Dictyostelium cells bind a secreted autocrine factor that represses cell proliferation.

BACKGROUND: Dictyostelium cells secrete the proteins AprA and CfaD. Cells lacking either AprA or CfaD proliferate faster than wild type, while AprA or CfaD overexpressor cells proliferate slowly, indicating that AprA and CfaD are autocrine factors that repress proliferation. CfaD interacts with AprA and requires the presence of AprA to slow proliferation. To determine if CfaD is necessary for the ability of AprA to slow proliferation, whether AprA binds to cells, and if so whether the binding requires the presence of CfaD, we examined the binding and effect on proliferation of recombinant AprA. RESULTS: We find that the extracellular accumulation of AprA increases with cell density and reaches a concentration of 0.3 microg/ml near a stationary cell density. When added to wild-type or aprA- cells, recombinant AprA (rAprA) significantly slows proliferation at 0.1 microg/ml and higher concentrations. From 4 to 64 microg/ml, the effect of rAprA is at a plateau, slowing but not stopping proliferation. The proliferation-inhibiting activity of rAprA is roughly the same as that of native AprA in conditioned growth medium. Proliferating aprA- cells show saturable binding of rAprA to 92,000 +/- 11,000 cell-surface receptors with a KD of 0.03 +/- 0.02 microg/ml. There appears to be one class of binding site, and no apparent cooperativity. Native AprA inhibits the binding of rAprA to aprA- cells with a Ki of 0.03 mug/ml, suggesting that the binding kinetics of rAprA are similar to those of native AprA. The proliferation of cells lacking CrlA, a cAMP receptor-like protein, or cells lacking CfaD are not affected by rAprA. Surprisingly, both cell types still bind rAprA. CONCLUSION: Together, the data suggest that AprA functions as an autocrine proliferation-inhibiting factor by binding to cell surface receptors. Although AprA requires CfaD for activity, it does not require CfaD to bind to cells, suggesting the possibility that cells have an AprA receptor and a CfaD receptor, and activation of both receptors is required to slow proliferation. We previously found that crlA- cells are sensitive to CfaD. Combined with the results presented here, this suggests that CrlA is not the AprA or CfaD receptor, and may be the receptor for an unknown third factor that is required for AprA and CfaD activity.