Hypothesis

Combining miltefosine (Kennedy pathway inhibitor) with DZNep (SAHH inhibitor, Ki 50 pM) creates a catastrophic S-adenosylmethionine (SAM) depletion in P. falciparum, collapsing H3K9me3 genome-wide. This "SAM crash" is selectively lethal to C580Y K13-mutant parasites, which depend on active SAM metabolism to maintain their heterochromatin-based resistance.

Quantitative Evidence from Public Data

GSE84082 — PfSAMS is HDAC inhibitor-responsive (96 samples)

• PfSAMS (SAM synthetase) downregulated -0.92 log2FC at 2h under TSA (HDAC inhibitor)
• PfSAHH shows transient dip (-0.84 at 2h)
• Demonstrates SAM pathway is drug-stress responsive — not constitutive

GSE278703 — SAM pathway stress-activated under kinase inhibition (12 samples)

• PfSAHH upregulated +0.77 log2FC under PfCLK3 inhibitor
• PfSAMS upregulated +0.49 log2FC
• Parasite upregulates SAM metabolism as a survival response → depleting it during stress = vulnerability window

GSE246115 — C580Y depends on SAM, Y493H does not (123,054 cells)

• C580Y K13 mutant has SAHH +0.63 log2FC vs WT under DHA → actively maintains SAM pathway
• Y493H K13 mutant has SAHH -1.02 log2FC vs WT → bypasses SAM dependency
• Critical implication: SAM crash strategy selectively targets C580Y-type resistance (most prevalent globally, ~6.5% of 112,933 samples)

GSE290639 — SAM crash is orthogonal to sirtuin axis (ChIP-seq)

• Sir2aKO shows SAM pathway genes are NOT Sir2a targets (stable H4K16ac at SAMS/SAHH)
• SAM crash hits HMTs (Axis 1: H3K9me3) while sirtuin inhibition hits H4K16ac (Axis 2)
• Combining both axes = synergistic heterochromatin collapse

GSE317694 — What SAM depletion would look like (HP1 ChIP-seq)

• BIX01294 (models SAM depletion at HMT level) causes 35% HP1 displacement from heterochromatin
• rif region: >99% HP1 loss — this is what catastrophic H3K9me3 loss does

Mechanism

1. Miltefosine blocks Kennedy pathway → forces PfPMT to consume SAM for PC biosynthesis
2. DZNep inhibits PfSAHH (Ki 50 pM) → blocks SAM regeneration from SAH
3. Combined: catastrophic SAM depletion → H3K9me3 cannot be maintained
4. Heterochromatin collapses (as shown by BIX01294 ChIP-seq data)
5. C580Y parasites, which depend on active SAHH to maintain their resistance chromatin state, are selectively killed

Selectivity

• PfSAHH has Cys59 (human has Thr60) → structural basis for selective inhibition
• DZNep Ki = 50 pM vs PfSAHH → extraordinary potency
• Miltefosine is FDA-approved for leishmaniasis (known safety profile)

Proposed Experiment

1. Miltefosine + DZNep checkerboard in C580Y vs Y493H K13-mutant lines + WT 3D7
2. Predict: strong synergy in C580Y, reduced synergy in Y493H
3. Validate SAM depletion by LC-MS/MS of intracellular SAM/SAH ratio
4. Confirm H3K9me3 loss by Western blot at 24h, 48h

References

• Botte CY et al. Nat Microbiol 2023 (SAM competition model validated)
• GSE84082, GSE278703, GSE246115, GSE290639, GSE317694 (this analysis)