Exploiting TLK1 and Cisplatin Synergy for Synthetic Lethality in Androgen-Insensitive Prostate Cancer

Abstract

Cellular organisms possess intricate DNA damage repair and tolerance pathways to manage various DNA lesions arising from endogenous or exogenous sources. The dysregulation of these pathways is associated with cancer development and progression. Synthetic lethality (SL), a promising cancer therapy concept, involves exploiting the simultaneous functional loss of two genes for selective cell death. PARP inhibitors (PARPis) have demonstrated success in BRCA-deficient tumors. Cisplatin (CPT), a widely used chemotherapy agent, forms DNA adducts and crosslinks, rendering it effective against various cancers, but less so for prostate cancer (PCa) due to resistance and toxicity. Here, we explore the therapeutic potential of TLK1, a kinase upregulated in androgen-insensitive PCa cells, as a target for enhancing CPT-based therapy. TLK1 phosphorylates key homologous recombination repair (HRR) proteins, RAD54L and RAD54B, which are critical for HRR alongside RAD51. The combination of CPT with TLK1 inhibitor J54 exhibits SL in androgen-insensitive PCa cells. The formation of double-strand break intermediates during inter-strand crosslink processing necessitates HRR for effective repair. Therefore, targeting TLK1 with J54 enhances the SL of CPT by impeding HRR, leading to increased sensitivity in PCa cells. These findings suggest a promising approach for improving CPT-based therapies in PCa, particularly in androgen-insensitive cases. By elucidating the role of TLK1 in CPT resistance, this study provides valuable insights into potential therapeutic targets to overcome PCa resistance to CPT chemotherapy. Further investigations into TLK1 inhibition in combination with other DNA-damaging agents may pave the way for more effective and targeted treatments for PCa and other cancers that exhibit resistance to traditional chemotherapy agents.

Keywords: CPT-based PCa therapy; PCa; TLK1 inhibitor J54; TLK1 signaling; homologous recombination repair; synthetic lethality.

Figure 1

Viability of PC3 and C4-2B cells treated with CPT or in combination with J54. For each CPT dose, the combination with J54 was highly significant for C4-2B (mean p = 0.006, one-tailed paired) but marginal for PC3 cells. * p < 0.005; ** p < 0.001, ns = not significant.

Figure 2

RAD54-T700 phosphorylation is induced by DNA damage (CIPT) w/o the induction of hsp70 expression, but is limited by concomitant J54 treatment.

Figure 3

Time course of tumor progression in PC3-Luc xenografts. The pattern of tumor growth was studied over time with calipers (bottom left) or through one final analysis with the IVIS system one day before sacrifice. Body weights in time lapse were also recorded (bottom right). NI is not inoculated. Also note the important parameter of radiance divided by the full body area (label on top of rectangles) which, in essence, represents the total burden of tumor cells for the animal.

Figure 4

Western blot analysis of PARP and cleaved PARP from three sets of independent tumors from all treatment groups, and a separately probed one for PCNA and tubulin for loading control.

Figure 5

Key elements of statistical analyses for the combination CPT and J54 on tumor volumes and body weight changes vs. control. (A) Survival analysis. (B) Interaction analysis (a measure of synergy) between CPT and J54. (C) Interaction analysis for area under the curve (AUC) of tumor volumes over time and CPT doses.

Figure 5

Key elements of statistical analyses for the combination CPT and J54 on tumor volumes and body weight changes vs. control. (A) Survival analysis. (B) Interaction analysis (a measure of synergy) between CPT and J54. (C) Interaction analysis for area under the curve (AUC) of tumor volumes over time and CPT doses.