Imaging-Guided Evaluation of the Novel Small-Molecule Benzosuberene Tubulin-Binding Agent KGP265 as a Potential Therapeutic Agent for Cancer Treatment

Abstract

The selective disruption of tumor-associated vasculature represents an attractive therapeutic approach. We have undertaken the first in vivo evaluation of KGP265, a water-soluble prodrug of a benzosuberene-based tubulin-binding agent, and found promising vascular-disrupting activity in three distinct tumor types. Dose escalation in orthotopic MDA-MB-231-luc breast tumor xenografts in mice indicated that higher doses produced more effective vascular shutdown, as revealed by dynamic bioluminescence imaging (BLI). In syngeneic orthotopic 4T1-luc breast and RENCA-luc kidney tumors, dynamic BLI and oxygen enhanced multispectral optoacoustic tomography (OE-MSOT) were used to compare vascular shutdown following the administration of KGP265 (7.5 mg/kg). The BLI signal and vascular oxygenation response (ΔsO2) to a gas breathing challenge were both significantly reduced within 2 h, indicating vascular disruption, which continued over 24 h. A correlative histology confirmed increased necrosis and hemorrhage. Twice-weekly doses of KGP265 caused significant growth delay in both MDA-MB-231 and 4T1 breast tumors, with no obvious systemic toxicity. A combination with carboplatin produced significantly greater tumor growth delay than carboplatin alone, though significant carboplatin-associated toxicity was observed (whole-body weight loss). KGP265 was found to be effective at low concentrations, generating long-term vascular shutdown and tumor growth delay, thus providing strong rationale for further development, particularly in combination therapies.

Demonstrating Tumor Vascular Disrupting Activity of the Small-Molecule Dihydronaphthalene Tubulin-Binding Agent OXi6196 as a Potential Therapeutic for Cancer Treatment

“…We found >90% vascular shutdown within 6 h of administering doses of OXi6197 greater than 35 mg/kg, which appears to be somewhat more active than CA4P, where similar shutdown required 100 mg/kg [ 47 ] or OXi8007, which required about 250 mg/kg [ 31 ]. Meanwhile, the benzosuberene analog KGP265 was effective at 5 mg/kg [ 33 ]. Lower doses are attractive, but ultimately it is the therapeutic window which is most important.…”

“…Lower doses are attractive, but ultimately it is the therapeutic window which is most important. Vascular disrupting agents have also been tested in syngeneic tumors generally examining the extremely aggressive 4T1 breast cancer in the BALB/c mouse [ 33 , 49 , 50 , 51 ].…”

“…Human breast cancer cells MDA-MB-231-luc (kindly provided by Dr. Edward Graves, Stanford University) and mouse kidney cancer cells RENCA-luc were grown as described previously [ 33 ]. Cells were maintained in RPMI-1640 medium supplemented with 10% heat-inactivated FBS, 1% penicillin and streptomycin.…”

“…The Pinney laboratory has spearheaded the development of several small-molecule inhibitors of tubulin polymerization, guided in part by pertinent structure activity relationship (SAR) correlations associated with combretastatin A-4 and related analogs [ 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Three particularly potent molecules ( Figure 1 ) showed inhibition of tubulin polymerization in the low µM range in a cell free assay, cell cycle arrest in the sub-µM range and selective cytotoxicity in the pM to nM range: specifically the benzosuberene KGP18 [ 30 , 33 ], the indole OXi8006 [ 31 , 34 ] and the dihydronaphthalene OXi6196 [ 29 ]. As with the original combretastatins, these molecules are extremely hydrophobic, but derivatization as their corresponding phosphate prodrug salts yields water soluble agents that are readily administered intraperitoneally.…”

“…Although elevated serum AP suggests a poor prognosis for renal cell carcinoma (RCC), the AP level is decreased in the kidney in RCC [ 39 ]. Nonetheless, abundant non-specific phosphatases rapidly release the active drugs in vivo ( Figure 1 ) and we recently reported vascular disrupting activity of the phosphate prodrugs KGP265 (parent agent KGP18) [ 33 ] and OXi8007 (parent agent OXi8006) [ 31 ] in mice.…”