This technology includes a new chemical scaffold (with lead compound XL5) against hRpn13 that induces apoptosis, which may have clinical efficacy against cancer. The structure of XL5-conjugated hRpn13 guided the design of XL5-PROTAC degrader compounds that exhibit greater efficacy than previous hRpn13-targeting compounds, as evaluated by selectivity for hRpn13, induction of apoptosis, and loss of cell viability. In cells, XL5-PROTACs revealed the presence of a truncated hRpn13 product that binds to proteasomes and is selectively degraded by XL5-PROTACs. The presence of this truncated hRpn13 protein correlates with induction of apoptosis by XL5-PROTACs, providing a previously unknown mechanism of action for hRpn13 targeting.