The Combination of Vemurafenib and Procaspase-3 Activation Is Synergistic in Mutant BRAF Melanomas

Abstract

The development of vemurafenib resistance limits the long-term efficacy of this drug for treatment of metastatic melanomas with the V600EBRAF mutation. Inhibition of downstream MAPK signaling with vemurafenib induces apoptotic cell death mediated by caspase-3, suggesting that addition of a procaspase-3 activator could enhance anticancer effects. Here we show that the combination of PAC-1, a procaspase-activating compound, and vemurafenib is highly synergistic in enhancing caspase-3 activity and apoptotic cell death in melanoma cell lines harboring the V600EBRAF mutation. In vivo, the combination displays a favorable safety profile in mice, and exerts significant antitumor effects. We further demonstrate that addition of PAC-1 to the clinically useful combination of vemurafenib and a MEK inhibitor, trametinib, starkly enhances the caspase-3 activity and proapoptotic effect of the combination. Moreover, addition of low concentration PAC-1 also delays the regrowth of cells following treatment with vemurafenib. Finally, PAC-1 remains potent against vemurafenib-resistant A375VR cells in cell culture and synergizes with vemurafenib to exert antitumor effects on A375VR cell growth in vivo. Collectively, our data suggest that inhibition of MAPK signaling combined with concurrent procaspase-3 activation is an effective strategy to enhance the antitumor activity of vemurafenib and mitigate the development of resistance.

Mechanisms of Acquired BRAF Inhibitor Resistance in Melanoma: A Systematic Review

“…A considerable number of preclinical studies are investigating other novel targets for overcoming BRAF inhibitor resistance. These include combining BRAF and/or MEK inhibitors with inhibitors of pre-mRNA splicing (to counteract resistance caused by BRAF splicing) [ 251 ], BH3-mimetics [ 252 , 253 ], BCL2 inhibitors [ 254 ], mitochondrial-targeted agents [ 255 , 256 ], inhibitors of p90 ribosomal S6 kinases [ 257 , 258 ], pro-caspase activating compounds [ 259 ], Rho kinase 1 (ROCK1) inhibitors [ 260 ], protein kinase Cδ inhibitors [ 261 ], tubulin inhibitors [ 262 ], ErbB2 or ErbB3 inhibitors [ 222 , 263 , 264 ], activators of the liver-X nuclear hormone receptor [ 265 ], an antibody conjugate targeting the endothelin B receptor [ 266 ], monoclonal antibodies against chondroitin sulfate proteoglycan 4 [ 267 ], inhibitors of sterol regulator element binding protein I (SREBP-1) [ 268 ], copper chelators [ 269 ], polo-like 3 kinase inhibitors (including in models of BRAF + MEK inhibitor resistance) [ 270 , 271 ], anti-nodal antibodies [ 272 ], PAK1 inhibitors [ 273 ], GLI1/2 inhibitors [ 274 ], inhibitors of IQ motif-containing GTPase activating protein 1 (IQGAP1) [ 275 ], serotonin agonists [ 276 ], CK2 inhibitors [ 277 ], p53 activators [ 278 ], metformin [ 279 ], statins [ 280 ], non-steroidal anti-inflammatory drugs [ 281 ], mibefradil [ 282 ], hydroxychloroquine (an autophagy inhibitor) [ 83 ], and A100 (a reactive oxygen species-activated prodrug) [ 283 ].…”

Procaspase-3 Overexpression in Cancer: A Paradoxical Observation with Therapeutic Potential

“…On the basis of compelling data in mouse models of cancer 64,199,206,209 and m canine cancer patients, 51,199 a phase 1 clinical trial of PAC-1 for late-stage cancer patients was initiated (). Thus far, it has been reported that PAC-1 has excellent pharmacokinetics in human cancer patients (e.g., a half-life of ~20 h 210 ), and PAC-1 has been dosed as high as 750 mg (oral tablet, once-a-day for 21 days) with signs of efficacy in these late-stage cancer patients.…”

Synergistic and targeted therapy with a procaspase-3 activator and temozolomide extends survival in glioma rodent models and is feasible for the treatment of canine malignant glioma patients

“…By relieving the physiologic labile zinc inhibition of procaspase-3, PAC-1 is able to enhance the ability of procaspase-3 to undergo auto-activation, sensitize the cellular procaspase-3 population to upstream apoptotic signaling events, and enhance the activity of caspase-3 generated through the induction of apoptosis [ 22 , 26 ]. In recent reports PAC-1 has demonstrated dramatic synergy with a number of anticancer agents [ 27 ], most notably with doxorubicin for the treatment of metastatic osteosarcoma [ 26 ], and with vemurafenib for the treatment of mutant BRAF melanoma [ 28 ].…”