Cucurbitacin I

Food and Chemical Toxicology, 2007, 44(12):2033-2039.

Inhibition of P-glycoprotein-mediated transport by terpenoids contained in herbal medicines and natural products[Reference: WebLink]

Terpenoids form a large and structurally diverse family of natural products and are ingredients of various herbal medicines. We have investigated possible interactions between herbal medicines and conventional medicines, and recently reported that monoterpenoids contained in Zanthoxyli Fructus can be potent inhibitors of P-glycoprotein (P-gp).
METHODS AND RESULTS:
In the present study, the influence of 70 kinds of terpenoids present in natural products on P-gp-mediated efflux transport was investigated. LLC-GA5-COL150 cells transfected with human MDR1 cDNA encoding P-gp were used to screen the terpenoids. Large increases in the intracellular accumulation of [(3)H]digoxin were observed in the presence of (R)-(+)-citronellal, (S)-(-)-beta-citronellol, alpha-terpinene, terpinolene, (-)-beta-pinene, abietic acid, ophiobolin A, Cucurbitacin I, and glycyrrhetic acid. A study of the concentration-dependency revealed that the IC(50) of ophiobolin A, glycyrrhetic acid, (R)-(+)-citronellal, abietic acid, and Cucurbitacin I was smaller than that of verapamil. The transcellular transport of [(3)H]digoxin across Caco-2 cell monolayers was then examined in the presence of (R)-(+)-citronellal, abietic acid, and glycyrrhetic acid. Significant increases in the apical-to-basolateral transport and decreases in the basolateral-to-apical transport and efflux ratio were demonstrated.
CONCLUSIONS:
These findings suggest that some natural products containing these terpenoids may inhibit P-gp-mediated transport and interact with P-gp substrates in the intestinal absorption process.

Biochemical Pharmacology, 18 Dec 2015, 102:45-63.

Cucurbitacin I elicits the formation of actin/phospho-myosin II co-aggregates by stimulation of the RhoA/ROCK pathway and inhibition of LIM-kinase.[Reference: WebLink]

Cucurbitacins are cytotoxic triterpenoid sterols isolated from plants. One of their earliest cellular effect is the aggregation of actin associated with blockage of cell migration and division that eventually lead to apoptosis.
METHODS AND RESULTS:
We unravel here that Cucurbitacin I actually induces the co-aggregation of actin with phospho-myosin II. This co-aggregation most probably results from the stimulation of the Rho/ROCK pathway and the direct inhibition of the LIMKinase. We further provide data that suggest that the formation of these co-aggregates is independent of a putative pro-oxidant status of Cucurbitacin I.
CONCLUSIONS:
The results help to understand the impact of cucurbitacins on signal transduction and actin dynamics and open novel perspectives to use it as drug candidates for cancer research.

Cancer Biology & Therapy, 01 Jan 2015, 16(2):233-243.

Cucurbitacin-I inhibits Aurora kinase A, Aurora kinase B and survivin, induces defects in cell cycle progression and promotes ABT-737-induced cell death in a caspase-independent manner in malignant human glioma cells.[Reference: WebLink]

Because STAT signaling is commonly activated in malignant gliomas as a result of constitutive EGFR activation, strategies for inhibiting the EGFR/JAK/STAT cascade are of significant interest.
METHODS AND RESULTS:
We, therefore, treated a panel of established glioma cell lines, including EGFR overexpressors, and primary cultures derived from patients diagnosed with glioblastoma with the JAK/STAT inhibitor Cucurbitacin I. Treatment with cucurbitacin-I depleted p-STAT3, p-STAT5, p-JAK1 and p-JAK2 levels, inhibited cell proliferation, and induced G2/M accumulation, DNA endoreduplication, and multipolar mitotic spindles. Longer exposure to Cucurbitacin I significantly reduced the number of viable cells and this decrease in viability was associated with cell death, as confirmed by an increase in the subG1 fraction.
CONCLUSIONS:
Our data also demonstrated that cucurbitacin-I strikingly downregulated Aurora kinase A, Aurora kinase B and survivin. We then searched for agents that exhibited a synergistic effect on cell death in combination with cucurbitacin-I. We found that cotreatment with cucurbitacin-I significantly increased Bcl(-)2/Bcl(-)xL family member antagonist ABT-737-induced cell death regardless of EGFR/PTEN/p53 status of malignant human glioma cell lines. Although >50% of the cucurbitacin-I plus ABT-737 treated cells were annexin V and propidium iodide positive, PARP cleavage or caspase activation was not observed. Pretreatment of z-VAD-fmk, a pan caspase inhibitor did not inhibit cell death, suggesting a caspase-independent mechanism of cell death. Genetic inhibition of Aurora kinase A or Aurora kinase B or survivin by RNA interference also sensitized glioma cells to ABT-737, suggesting a link between STAT activation and Aurora kinases in malignant gliomas.

Cytotherapy, 2015, 17(5):647-664.

Combined immunotherapy with whole tumor lysate-pulsed interleukin-15-activated dendritic cells and cucurbitacin I promotes strong CD8(+) T-cell responses and cures highly aggressive lymphoma.[Reference: WebLink]

Dendritic cell (DC)-based therapies could be important strategies for lymphoma treatment.
METHODS AND RESULTS:
AKR/J mice with Dalton's lymphoma were treated with recombinant interleukin-15 (rIL-15)-activated autologous DCs and pulsed with whole tumor cell lysates in the presence or absence of suboptimal doses of the STAT3 inhibitor Cucurbitacin I. One group of treated mice received an additional dose of rIL-15 to boost the DC-based adoptive cell therapy (ACT). Kaplan-Meier survival analysis and multiple immunologic and enzymatic parameters were assessed to demonstrate the efficacy of the vaccination protocol. Therapy with tumor lysate-pulsed, rIL-15-activated DCs plus Cucurbitacin I significantly prolongs the survival of tumor-bearing mice but fails to provide a complete cure. Additional treatment of vaccinated mice with rIL-15 dramatically improves the therapeutic efficacy and provides a lifelong cure with no relapse. DCs derived from the surviving vaccinated mice regained their anti-tumor potential against the lymphoma cells with respect to growth inhibition and cytotoxicity. Both cluster of differentiation (CD)4(+) and CD8(+) T cells were mobilized in metastatic organs of successfully vaccinated mice in large numbers and demonstrated antigen-specific proliferation and tumor cell cytotoxicity. ACT also augments DC function by upregulating tumor necrosis factor-related apoptosis-inducing ligand and tumor necrosis factor-α expression. In addition, combinatorial immunotherapy restores the levels of antioxidant enzymes and liver function enzyme activities that are severely repressed in untreated tumor-bearing mice.
CONCLUSIONS:
Effective vaccination for a complete cure against aggressive lymphoma requires DC-based ACT in combination with chemotherapy and cytokine therapy.