Abstract
We have recently demonstrated that multi-kinase inhibitors such as sorafenib and pazopanib can suppress the detection of chaperones by in situ immuno-fluorescence, which is further enhanced by phosphodiesterase 5 inhibitors. Sorafenib and pazopanib inhibited the HSP90 ATPase activity with IC50 values of ~1.0 μM and ~75 nM, respectively. Pazopanib docked in silico with two possible poses into the HSP90 ATP binding pocket. Pazopanib and sildenafil combined to reduce the total protein levels of HSP1H/p105 and c-MYC and to reduce their co-localization. Sorafenib/pazopanib combined with sildenafil in a [GRP78+HSP27] –dependent fashion to: (i) profoundly activate an eIF2α/Beclin1 pathway; (ii) profoundly inactivate mTOR and increase ATG13 phosphorylation, collectively resulting in the formation of toxic autophagosomes. In a fresh PDX isolate of NSCLC combined knock down of [ERBB1+ERBB3] or use of the ERBB1/2/4 inhibitor afatinib altered cell morphology, enhanced ATG13 phosphorylation, inactivated NFκB, and further enhanced [sorafenib/pazopanib + sildenafil] lethality. Identical data to that with afatinib were obtained knocking down PI3K p110α/β or using buparlisib, copanlisib or the specific p110α inhibitor BYL719. Afatinib adapted NSCLC clones were resistant to buparlisib or copanlisib but were more sensitive than control clones to [sorafenib + sildenafil] or [pazopanib + sildenafil]. Lapatinib significantly enhanced the anti-tumor effect of [regorafenib + sildenafil] in vivo; afatinib and BYL719 enhanced the anti-tumor effects of [sorafenib + sildenafil] and [pazopanib] in vivo, respectively.
Highlights
We have recently published that phosphodiesterase 5 inhibitors can enhance the lethality of traditional cytotoxic chemotherapy agents as well as the lethality of the multi-kinase inhibitors sorafenib, pazopanib and regorafenib, and of celecoxib and a non-COX2 inhibitory analogue of the drug OSU03012
When combined with sildenafil both sorafenib and pazopanib modestly decreased HSP90 expression in 6 h as measured using a COOH terminal antibody but strongly reduced expression of its essential co-chaperone CDC37 that correlated with reduced co-localization as judged by the pure-yellow merged signal becoming more orange in hue (Figure 1D) [9]
From our prior studies in Tavallai et al and Roberts et al we were aware that tumors treated with [sorafenib/regorafenib + sildenafil] re-grow after therapy with higher ERBB1 phosphorylation and that the combination of [sorafenib/ regorafenib + sildenafil] can reduce the detection by in-cell western/immuno-fluorescence of the chaperones HSP90, GRP78 and HSP70 [6, 8]
Summary
We have recently published that phosphodiesterase 5 inhibitors (sildenafil; tadalafil; vardenafil) can enhance the lethality of traditional cytotoxic chemotherapy agents as well as the lethality of the multi-kinase inhibitors sorafenib, pazopanib and regorafenib, and of celecoxib and a non-COX2 inhibitory analogue of the drug OSU03012. The drug OSU-03012 (AR12) was originally thought to act as an anti-cancer agent by inhibiting the enzyme PDK-1 within the PI3K pathway it was subsequently shown that this compound was not primarily acting as a PDK-1 inhibitor, and subsequently it was demonstrated that the primary mechanism by which AR-12 killed tumor cells was via the PKR-like endoplasmic reticulum kinase (PERK) -dependent induction of endoplasmic reticulum stress signaling and a toxic form of autophagy. Other studies linked the effects of AR-12 on tumor cell biology to the regulation of chaperone proteins [4, 5]. We have shown that sorafenib, pazopanib, AR-12 and regorafenib can reduce the apparent expression chaperone proteins HSP90, GRP78 and HSP70 using an in-cell western/ immuno-fluorescence approach [5,6,7,8,9,10,11,12]. As OSU-03012, sorafenib, pazopanib and regorafenib down-regulate the www.impactjournals.com/oncotarget
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