Development of Second-Generation CDK2 Inhibitors for the Prevention of Cisplatin-Induced Hearing Loss

Abstract

There are currently no FDA-approved therapies to prevent the hearing loss associated with the usage of cisplatin in chemotherapeutic regimens. We recently demonstrated that the pharmacologic inhibition with kenpaullone or genetic deletion of CDK2 preserved hearing function in animal models treated with cisplatin, which suggests that CDK2 is a promising therapeutic target to prevent cisplatin-induced ototoxicity. In this study, we identified two lead compounds, AT7519 and AZD5438, from a focused library screen of 187 CDK2 inhibitors, performed in an immortalized cell line derived from neonatal mouse cochleae treated with cisplatin. Moreover, we screened 36 analogues of AT7519 and identified analogue 7, which exhibited an improved therapeutic index. When delivered locally, analogue 7 and AZD5438 both provided significant protection against cisplatin-induced ototoxicity in mice. Thus, we have identified two additional compounds that prevent cisplatin-induced ototoxicity in vivo and provided further evidence that CDK2 is a druggable target for treating cisplatin-induced ototoxicity.

BRAF inhibition protects against hearing loss in mice

“…Mice treated with carrier or dabrafenib alone showed no significant threshold shift or change in body weight. Cisplatin-treated animals had significantly elevated threshold shifts at 8-, 16-, and 32-kHz frequencies, consistent with previous studies ( 13 , 34 ). Animals cotreated with dabrafenib and cisplatin had significantly reduced threshold shifts, with average reduction of 14.9 dB at 16 and 32 kHz.…”

“…In contrast, in cochlear postmitotic cells, inhibition of the BRAF pathway by dabrafenib reduces cell death and enhances cell survival as shown here. CDK2 inhibitors that we previously identified in similar screens also showed protection in postmitotic cochlear cells whereas both BRAF inhibitors and CDK2 inhibitors are two known groups of anti-proliferative compounds in tumor cells ( 13 , 34 ). Cellular roles for ARAF (Raf-1), a family member of BRAF, in protection from apoptotic stimuli have been shown previously in endothelial and cardiomyocyte postmitotic cells, although these pathways were independent of MEK kinase ( 71 , 72 ).…”

“…Recently, we identified several CDK2 inhibitors that protect against cisplatin- and noise-induced hearing loss ( 13 , 34 ). AZD5438 is a second-generation CDK2 inhibitor that is orally bioavailable; thus, we sought to determine whether the compound could be combined with dabrafenib to provide enhanced protection from cisplatin- and noise-induced hearing loss (fig.…”

“…For noise posttreatment protocol, compound treatments were administered twice daily at dabrafenib (60 mg/kg) and AZD5438 (35 mg/kg) 8 hours apart at 24-, 48-, and 72-hour time intervals after noise insult. ABR threshold and wave 1 amplitude measurements ABR in mice was measured for left ears as described previously with minor modifications (13,34). In brief, ABR waveforms were recorded in a sound booth (Industrial Acoustic Company) by using subdermal needles positioned in the skull, below the pinna, and at the base of the tail, and the responses were fed into a low-impedance Medusa digital biological amplifier system (RA4L; TDT; 20-dB gain).…”

“…Dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor) combination therapy is used currently for melanoma and non–small lung carcinoma treatment and is more efficient than dabrafenib alone in inhibiting the pathway ( 18 , 33 ). Previously, we have identified CDK2 inhibitors as candidate therapeutics for hearing loss ( 13 , 34 ). Thus, the combination of dabrafenib and AZD5438 (a CDK2 inhibitor) may offer better efficacy against ototoxicity and lower general toxicity.…”